G E O C H E M I S T R Y A N D G E N E S I S OF M U S S O O R I E P H O S P H O R I T E S

D I S T R I C T D E H R A D U N , U.P.

ABSTRACT

THESIS SUBMITTED FOR THE DEGREE OF

Bottor of ^Ijttosiopljp IN

G E O L O G Y

KR. FARAHIM KHAN M. Sc., M. Phil. (Allg.)

DEPARTMENT OF GEOLOGY FACULTY OF SCIENCE

ALIGARH MUSLIM UNIVERSITY ALIGARH (INDIA)

19 9 1

ABSTRACT

Mussoorie, which occupies an elongated E-W Hil l , is situated

about 31 km. north of Dehradun town and is located betv/e en 1600 m.

and 2600 m. above m .s . l . in the Doon va l l ey of the Uttar Pradesh state.

The study area in Mussoorie l i es between north lat i tudes 30°25' N : 30°30'

and east longitudes, 78°0'A8" : 78®10'57" E. The phosphorite deposits of

Muaaoorla at® the only •well known and old phosphorite deposits of U.P.

The deposits are quarried from severa l open cast mines on the top as

well as on the slopes ^ of the Mussoorie hill - a popular summer h i l l

resort of Uttar Pradesh.

The commercially exp lo i tab le phosphorite deposits of Mussoorie

are restr icted to the Mussoorie sync l ine . The deposits are intimately

associated with a group of sedimentary shale-chert-carbonate-phosphate

'rocks with some foss i l remains and pyr i te that constitute a part of the

lowermost sequence of the Ta l Formation of Lower Cambrian age of the

Lesser Himalayan region of North-western Ind i a . The phosphate horizon,

that is l a r g e l y restr icted to the upper part of the chert member, va r i e s

in thickness from a few mm to about 10 metres. The main phosphate

horizon occurs between the chert and black shales but thin phosphatic

bands are also found intercalated with the under ly ing chert as we l l as

the ove r l y ing black shales. The ind iv idua l phosphorite bands are not

continuous, though the phosphorite horizon extends for about a total

s tr ike length of over 120 kms. pa ra l l e l to both the limbs of the

Mussoorie sync l ine .

The Krol and Ta l formations, which have a thrust contact with

the Jaunsars, form a syncline that appears to have been t i l ted to the

south. The syncl ine, made up of the Bla in i , In f ra Krol, Krol and Tal

rocks is in direct contact with Nagthat Formation on the north-east .

The genera l str ike of these formations swings from N10°W to N55°W. At

certain places a few reversa ls indicate re fo ld ing of the formations

result ing in the generation of local synforms and antiforms. The

pr inc ipa l streams in the area genera l l y fol low old fault al ignments.

Faul ts , which resulted in the development of steep scarps, often d isp lay

shearing, shattering and drag folds of the formations.

- 2 -

Spectrochemical analysis of the Mussoorie phosphorites

revea l the presence of major elements l ike SiO„, A1 0 , Fe 0 . , FeO,

TiO^, MnO, CaO, MgO, P205» ^2° trace

elements l ike Cu, Pb, Ni, Co, Zn, Cr, Sr, Ba, Rb, V, Li and Cd.

The dispersion pattern and mutual relationship of

s igni f icant major oxides indicate that 5102^ CaO and MgO are

antipathetical ly related with ^^^ relationship suggests a

gradual replacement of these oxides by P2'^5 diagenesis. Since

majority of samples have CaO/P20g rat io greater than 1.31, the most

common substitution is that of PO^"^ by CO^^" . The presence of

considerable amount of OH and sympathetic relationship of H^O^ with

CaO/P^Og ratio suggests the possibi l i ty of reversible substitution

between PC. ^ "^(OH),. 4 4

The variat ion trends in the chemical composition of the

phosphorites and the host rocks may perhaps be due to certain marked

changes in the supply of the material, var iat ion in composition of

waters and physico-cheijiical condition of the basin of deposition. The

low manganese content coupled with low FeO/MnO rat io , enrichment of

P20g in the younger sediments, low content of al lcal ies as well as

their inter-relationship and distribution pattern in the petrochemical

f i e lds indicate that most probably these phosphatic rocks v/ere

1 deposited in a shallow water geosyncl inal basin favoured by s l ight ly

al lkal ine medium - often approaching a very weakly acidic medium in

. euxinic milieu.

The concentration trends of the trace elements reveal that

the phosphorites are more enriched in Ba, Cu, V, Cr, Pb, Ni and Sr

than in L i , Cd, Co and Rb. Similarly, the black shales are re lat ive ly

richer in Ba, V, Cr, Sr and Ni than in L i , Cd, Rb and Co. The

pattern of trace element distribution in the phosphorites and the

geochemical behaviour of indiv idual elements suggest that most of the

trace elements, that found their way into the ancient sediments,

appear to have invaded the latt ices of the phosphates, carbonates,

s i l icates and clay minerals and combined with them structural ly . The

- 3 -

va r i ab l e concentration of trace elements in the phosphorites have been

inf luenced by var ious physico-chemical processes involved during

weathering and leaching of the pre -ex is t ing rocks, and subsequently

many of them were assimilated to the sediments. The adsorption of

some trace elements was mainly influenced by the pr inc ipa l absorbants

l ike the phosphate minerals, some organic matter in addition to c l a y ,

i ron oxides and s i l i ca te minerals.

Correlation coef f ic ient and plotted diagrams of s ign i f i cant

trace elements also indicate that the presence of these elements may

be due to their inter elemental a f f i n i t i e s . However, adsorption on

the surface of the apat i te , substitution in the apatite la t l i ce and

biogenic ac t i v i ty are supposed to be ch ie f ly responsible for the

distr ibut ion, abundance and f i xa t ion of s igni f icant trace elements.

The higher concentration of certain trace elements in thee phosphate

r ich ores is mainly due to certain favourab le physico-chemical

conditions such as low Eh-pH; moderate sa l in i ty and shallow water

reducing condit ions, etc . at the time of their deposit ion.

In the l i gh t of present inves t iga t ion , it is suggested that

the deposition of phosphate might have occurred in an euxinic shallow

marine environment aided by s l i ght l y a lka l ine to very weakly ac id ic

medium with restr icted c irculat ion in warm and dry palaeocl imatic

condit ions. Addi t ional ly , the deposition is controlled by some

geo log ica l and biogenic factors such as excess charge of phosphate in

certain zones of phosphogenic basin, l i tho log ica l fac ies var ia t ions ,

sub-basinal topographic restr ic t ions, some structural disturbances and

concentration of dissolved phosphorus by certain micro-organisms.

Chemical factors such as negat i ve Eh, pH with around 7.8, inf luences

of pressure and temperature, r e la t i ve proportions of Cao/MgO and

Cao/P^Dg/ the chain of replacement among CaO-MgO-P^O^ as well as

easy ionic substitution of certain elements are the other factors

favourab le for the deposition of the ores. Penecontemporaneous and

post deposit ion also p layed some role in control l ing the concentration

of the deposits .

- 4 -

From the study of l i tholog ica l , chemical and mineralogical

assemblages, it is inferred that the precipitation of the phosphorites

of Mussoorie was dependent essential ly upon changes in Eh-pH

conditions, fluctuations and shift ing of micro-environmental conditions

leading to mutual replacement of the chemical components and regular

supply of phosphorus. A genetic model of the phosphorite deposits of

Mussoorie has also been proposed suggesting that the phosphorus

seems to have been derived from various sources l ike vo lcanic ,

phytoplanktone and other marine micro-organisms and also r i ver

water. Marine upwelling was responsible for the concentration of

phosphatic ingredients over the shelf area of a more or less restricted

basin probably occupying an arm of the pre-exist ing sea. The role of

geochemical environment in the deposition of phosphorites as well as

the dccompanying act iv i ty of micro-organisms mutually interacted

under a set of shallow intert idal and subtidal environmental

conditions leads one to bel ieve that the precipitation of phosphate was

essential ly dependent upon pK and Eh condtions, part ia l pressure of

CO^/ temperature, replacement processes and ionic substitution.

The presence of appreciable quantity of organic matter,

higher concentration o f vanadium, association of carbonates, black

shales and pyr i te suggest deposition of phosphorite in a more or less

reducing environment. The various forms in which phosphorite occurs

appear to be related to some environmental vicissitudes at the time of

deposition followed by some later structural disturbances related to

the' upl i f t of Himalays. Later enrichment of phosphates may have

taken place during the period of diagenetic processes as also a l i t t l e

supergene enrichment through later i t i zat ion.

G E O C H E M I S T R Y A N D G E N E S I S OF M U S S O O R I E P H O S P H O R I T E S

D I S T R I C T D E H R A D U N , U.P.

THESIS SUBMITTED FOR THE DEGREE OF

Hottor of IN

G E O L O G Y

KR. FARAHIM KHAN M. Sc., M. Phil. (Alig.)

DEPARTMENT OF GEOLOGY FACULTY OF SCIENCE

ALIGARH MUSLIM UNIVERSITY ALIGARH (INDIA)

1 9 9 1

T4370

DEDICATED TO

IVIV PARENTS

Dr. Syjad Husain Israili M.Sc Ph.D., D.Sc

/.Ab 'Ac;, jr.J/ L M i. J Ptdha) P R O F E S S O R & C H A I R M A N

DEPARTMENT OF GEOLOGY ALIQARH M U S L I M UNIVERSITY A L I G A R H - 2 0 2 002 ( INDIA) Phone ( 0571 ) 2 5 6 1 5 Telex . 5 6 4 - 2 3 0 - A M U - I N

Ref.No.. Dated

The thesis entitled, "Geochemistry and Genesis of Mussoorie phosphorites.

District Dehradun, U.P." and is being submitted for the award of degree of Doctor

of Philosophy at the Aligarh Muslim University, Aligarh, by Mr. Kr. Farahim Khan,

is his original contribution.

The work has been carried out under my supervision. It has not been pub-

lished or submitted for any degree of this or any other university. He is therefore,

allowed to submit the thesis for the award of Ph.D. degree of this university.

RT'^-CE-CE. 2 43 , L A X M I B A I R O A D , N E A R M A R R I S R O A D C R O S S I N G , A L I G A R H - 2 0 2 0 0 1

ACKNOWLEDGEMENTS

I wish to express my heartful gratitude to my dear

parents who lighted the academic lamp of my l i fe .

I wish to record here my deep sense of gratitude to

Professor S.H. Israi l i , Chairman, Department of Geology, Allgarh

Muslim University, Aligarh, under whose able and inspirlnw

supervision this work has been brought to a successful completion.

I am grateful to my supervisor for the trouble he took to guide me

in adverse circumstances and for providing the research faci l i t ies

available in the department.

I am deeply indebted to Professor S.N. Bhalla, Department

of Geology, Aligarh Muslim University, Aligarh, for his advice and

encouragement from time to time.

I am extremely grateful to Dr. Zafar Husain, Sciontlfft

Off icer, A.M.D., Department of Atomic Energy and Dr. L.A.K. Rao Reader, Department of Geology, Aligarh Muslim University, Aligarh,

for providing literature, their kind assistance and keen Interest that

greatly helped me to present this investigation In its final form.

Sincere thanks are also due to Dr. R.J. Azmi, Scientist,

Wadia Institute of Himalayan Geology, Dehradun, for carrying out the

f ie ld work under his proper guidance. I am also thankful to

Dr. Shadab Khurshld, Reader, Department of Geology and Dr. M. Arif Siddlqui and Mr. Ralsuddin Ansarl, Lecturers, Department of

Mechanical Engineering and Dr. Masroor Khan, Pool Officer, Department

of Botany, Aligarh Muslim University, Allgarh, for their co-operation

and encouragement during the completion of this work. I am also

thankful to Mr. Badee Asghar and Mr. Ashfaq Ahmad, Instructor,

Computer Centre, Allgarh Muslim University, Aligarh, for extending

help in the factor-vector analyses.

- 2 -

I am sincerely thankful to my colleagues, Mr. Akram All, Mr. Noorul Hasan and Mr. M. Arif for their help and many fruitful

discussions during the preparation of the thesis.

I am also thankful to Dr. Nizamuddin Khan, Mr. Mohammad Toyyab, Mr. All Imran Usmani, Mr. Mohammad Ahmad, Mr. Mohammad Mobin, Mr. Ghulam Haider, Mr. All Husain and Mr. Abdul Musawwir

for their co-operation and encouragement.

I am very much thankful to Mr. S.M. Hasan for typing

the thesis whereas Mr. Feroz Ahmad, Mr. Habeeb Ahmad and

Mr, Saleemuddin Ahmad are gratefully acknowledged for their kind

assistance in different aspects of the thesis.

In the last, I gratefully acknowledge my brothers,

Mr. Mohammad Taiyab Khan, Advocate, Supreme Court of India,

Mr. Zeeshan AH, Aircraft man, Indian Air Force, my other family

members, in-laws and my wife, for their patience, financial support,

moral encouragement and ful co-operation at a l l stages of the present

investigation.

( KR. FARAHIM KHAN )

CONTENTS

LIST OF FIGURES LIST OF TABLES LIST OF PLATES

i V

X

CHAPTER-I INTRODUCTION

General Statement Location and Accessibility Indian Phosphate Deposits Climate physiography Drainage and Vegetation Status of Mussoorie Phosphorites Fossil Assemblages and Age Scope and Purpose of Investigation Previous Work Methods and Techniques

1 1 2 4 4 5 6 7 11 12 16

CHAPTER-II GEOLOGICAL SET-UP General Statement Regional Geology Geology of the Area Classification of Tal Rocks Age

24

24 24 27 31 34

CHAPTER-III NATURE AND MODE OF OCCURRENCE ... 35 Nature of Mussoorie phosphorites ... 35 Platy and Laminated ... 36 Granular ... 37 Veriegated Lenticular ... 37 Nodular ... 38 Pelletal ... 38

Mode of Occurrence of Mussoorie Phosphorites 39 Maldeota Block ... 39 Masrana Block ... 41 Durmala Block ... 42 Upper Krol phosphorites ... 43 Radioactivity in Phosphorites and ... 43

associated horizons

CHAPTER-IV PETROGRAPHY Phosphorites

Cellophane Texture Dahlite Gangue Minerals

45 45 45 47 48 48

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Calcite Dolomite Quartz

Ferrous Minerals Accessory Minerals Replacement

Host Rocks Cherty Limestone Dolomite Limestone Black Shale with Slltstone

CHAPTER-V GEOCHEMISTRY OF THE MAJOR ELEMENTS General Statement Major Oxides

Silicon Oxide Alumina Ferric and Ferrous Oxides Titanium Oxide Manganese Oxide Lime and Magnesia Phosphorus Pentaoxide Soda and Potash Loss on Ignition Carbon dioxide

Mutual Relationship of Significant Oxides Relationship of Major Oxides with . P^Oc and CaO

IntSr-relationship of Various Oxides . Petrochemical Fields and Trends

Conclusion

CHAPTER-VI GEOCHEMISTRY OF THE TRACE ELEMENTS General Statement

Copper Lead Nickel Cobalt Zinc Chromium Strontium Barium Rubidium Vanadium Lithium Cadmium

Interpretation and Conclusion

-iii-

CHAPTER-VII FACTOR-VECTOR ANALYSIS OF PHOSPHORITE ... 164 GEOCHEMISTRY

Introduction ... 164 Results ... 165

Means, Standard Deviation and ... 165 Coefficient of Variance

Correlation Coefficient ... 166 Correlation Matrix ... 166 Eigen Vectors and Eigen Values ... 167 Rotated Factor Matrix ... 167

Interpretation of Factors ... 169 Silica Precipitation Factor ... 170 Phosphate Precipitation Factor ... 171 Carbonate Precipitation Factor ... 172 Oxidizing to Reducing Conditions ... 172 Residual Pore Water ... 173 Detrital Clay ... 173 Organic Activity ... 174

CHAPTER-VIII GENESIS OF PHOSPHORITE ... 176 Introduction ... 176 Geologic Contrdls ... 184 Chemical Controls ... 193 Biogenic Controls ... 204

A Proposed Genetic Model of the Phos- ... 2 07 phorite Deposits of Mussoorie

CHAPTER-IX SUMMARY AND CONCLUSION ... 211

REFERENCES ... ... 219

TABLES ... ... 2 37

PLATES ...

LIST OF FIGURES

Figure-1 Location map of the area. ... Figure-2 Rock phosphate deposits. ... 3

Pigure-3 Geological map of part of the Mussoorie ... 30

syncline showing the locations of the sections examined.

Pigujre-4 Sketch map of the Mussoorie syncline show- 40 ing various blocks.

Figure-5 Graph showing relative abundance of certain... 58 major oxides (SiOg^ AI2O3/ FCjO^+FeO, MgO, CaO, P2®5 Maldeota phosphorites.

Figure-6 Graph showing the concentration trends of ... 61 certain major oxides (AI2O3/ Pe202+Fe0, MgO, limestone, chert, and shale of Maldeota and Durmala phosphorite deposits.

Figure-7 Bar diagram showing variation of major ... 55 oxides and their frequency per cent distri-bution in Maldeota and Durmala phosphorite deposits.

Pigure-8 Bar diagram showing relative distribution ... 66 of major oxides in the host rocks of Maldeota and Durmala phosphorite deposits.

Figure-9 Bar diagram showing relative distribution ... 67 of major oxides in the host rocks of Maldeota and Durmala phosphorite deposits.

-li-

Figure-10 Graphicalrepresentation of P2O5 in ••• 88 relation to SiOj, Al203# Ti02 and MnO in Maldeota and Durmala phosphorites.

Pigure-11 Graphical representation of P2°5 *•* 89 relation to CaO, MgO, NajO, KgO, H2O and CO2 in Maldeota and Durmala phosphorites,

Pigure-12 Graphical representation of CaO in 90

relation to SiOj* AlgOg* Fe2®3' Ti02/ MnO, MgO, NajO, K2O, H2O and COj in Maldeota and Durmala phosphorites.

Pigure-13 Graphicalrepresentation of SiOj-AlgOg, ... m Si02-Pe202, SiOg-MgO, MgO-MnO, Mg0-C02, Pe202+Pe0-Al203, Pe202+Pe0-Mn0, Fe202+ PeO-MgO, P20^-Si02/Al203, P205-Ca0/si02 and PjOg-CaO/MgO in Maldeota and Durmala phosphorites.

Pigure-14 Graph showing the relationship of CaO ... 114 and P2O5 in limestone and shale of Maldeota and Durmala phosphorite deposits.

Figure-15 Triangular diagrams showing chemical ... 117 relationship of important major consti-tuents of Maldeota and Durmala phosphorites.

Pigure-.16 Triangular diagrams showing chemical ... lis relationship of important major consti-tuents of Maldeota and Durmala phosphorites.

-lii-

Pigure-17 Triangular diagrams showing chemical ... 120 relationship of important major consti-tuents of Maldeota and Durmala phosphorites.

Figure-18 Graph showing relative abundance of certain... 131 trace elements (Cu-Zn, Ni-Co, Cr-V and Ba-Sr) of Maldeota phosphorites.

Pigui:«-19 Graph showing the concentration trends ... 132 of certain trace elements (Cr, Sr, V, Ba, CU/ Ni, Co, Zn) in limestone, chert and shale of Maldeota and Durmala phosphorite deposits.

Pigure-20 Graph showing the average concentration ... 135 trends of certain trace elements (Cu, Zn, Ni, Co, Cr, V, Ba, Sr) in different rock types of Maldeota and Durmala.

Figure-21 Point diagrams indicating geochemical 139 relationship among certain trace elements (Pb-Zn, Pb-Cd, Zn-Cd, Sr-Ba, Ni-Co) in Maldeota and Durmala phosphorites.

Pigure-22 Point diagrams showing mutual relation- ... 143 ship between Cu, Ni, Co, Zn, Ba, V, Cr and Sr and ^^ phosphoric ore.

Figure-23 Point diagrams indicating the geochemical ... 144 relation between certain major oxides and trace elements(PjOg-Cu, MgO-Cu, AIjO^-Ni, CaO-Zn, AljOg-Cr, CaO-sr, AljOg-V and K20-Ba) in Maldeota and Durmala phosphorites.

-iv-

Figure-24 Cu/P, Cu/Mg-Mg, Ni/Al-Al, Ni/Pe-Pe, ... 1 4 5

Ni/Mg-Mg, Zn/Ca-Ca and Zn-Pe plots for Maldeota and Ourmala phosphorites.

Pigure-25 Cr/Ai-Al, Sr/Ca-Ca, V/Ai-Al, Ba/K-K and ... 1 5 7

V/P-P plots for Maldeota and Durmala phosphorites.

-xix-

LIST OF TABLES

I. Generalised geological succession of the area. ... 25

II. Lithostratigraphy of Tal Formation in parts of ... 29 Mussoorie syncline.

III. Minimum, maximum and average values of major ... 237 elements for various lithological units.

IV. Major element con^osition of Maldeota phospho- ... 2 38 rites, Dehradun district, Uttar Pradesh (in wt %),

V. Chemical composition of Durmala phosphorites, ... 241 Dehradun district, Uttar Pradesh (in wt %),

VI. Major element conposition of various rocks ... 242 associated with phosphorites of Maldeota and Durmala.

VII. Correlation coefficient of Maldeota phosphorite ... 244 samples.

VIII. Correlation coefficient of Durmala phosphorite ... 245 samples.

IX. Si02/Al203# Mg0/Al203, MgO/MnO, ... 246 AljOj/TiOg and Fe202/Fe0 ratios for Maldeota phosphorites.

X. Na20/K2®' FeO/MnO ratios ... 249 for Maldeota phosphorites.

XI. Ca0/P20g, CO2/P2O5, CaO/MgO and Ca0/Si02 ratios ... 251 for Maldeota phosphorites.

-vi-

XII. Sl02/Al203# MgO/Al203# Fe202/Al203, MgO/MnO, ... 253 Al203/Ti02, Pe203/PeO, Na20/K20/, CO^/H^O'*',

H^O/CO^, FeO/HnO, CaO/P^O^, CO^/P^O^, CaO/MgO

and Ca0/si02 ratios for Durmala phosphorites. XIII. Recalculated to 100 wt % of the bulk compo- ... 254

nents of CaO, MgO and P2^5 ii Maldeota phosphorites.

XIV. Recalculated to 100 wt % of the bulk compon- ... 256 ents of CaO, MgO and CO2 in Maldeota phosphorites.

XV. Recaulated to 100 wt % of the bulk components ... 258 of CaO, MgO and SiOg in Maldeota phosphorites.

XVI. Recalculated to 100 wt % of the bulk compo- ... 260 nents of NagO, CaO and P2O5 in Maldeota phosphorites.

XVII. Recalculated to 100 wt % of the bulk components... 262 of Si©2/ AI2O3 and KgO in Maldeota phosphorites.

XVIII. Recalculated to 100 wt % of the bulk components... 264 of NajO, KgO and CaO in Maldeota phosphorites.

XIX. Recalculated to 100 wt% of the bulk components ... 265 of P2^5' ^2° ^^2 Maldeota phosphorites.

XX Recalculated to 100 wt % of the bulk components... 268 of CaO, MgO and Pe202+Fe0 in Maldeota phosphorites,

XXI. Recalculated to 100 wt % of the bulk components... 270 of CaO, PejOj+PeO and NajO+KjO in Maldeota phosphorites.

-vli-

XXII. Recalculated to 100 wt % of the bulk components ... 272 of MgO, Fe202+Pe0 and AI2O2 in Maldeota phos-phorites.

XXIII. Recalculated to 100 wt % of the bulk components ... 274 of (A) CaO, MgO and P2O5 ; (B) CaO, MgO and CO2 (C) CaO, MgO and Si©2 in Durmala phosphorites.

XXIV. Recalculated to 100 wt % of the bulk components ... 275 of (A) NagO, CaO and PjOg (B) SIO2, AlgO^ and K2O (C) Na20, KgO and CaO in Durmala phosphorites.

XXV. Recalculated to 100 wt % of the bulk components ... 276

of (A) P2°5'

+ PeO in Durmala phosphorites. XXVI. Recalculated to lOO wt % of the bulk components... 277

of (A) CaO, Fe203+Pe0 and Na20-»-K20 (B) MgO, PejO^+FeO and AlgO^ in Durmala phosphorites.

XXVII Trace element composition of Maldeota phos-phorite samples (in ppm).

XXVIII. Trace element composition of Durmala phos-phorite samples (in ppm).

XXIX, Trace element analysis of limestone, chert and shale associated with Mussoorie phosphorites (in ppm). Comparison of the abundance of trace elements

278

281

282

XXX.

XXXI. in phosphorites.

Cu/Al X 10"^, Cu/Mg X 10"^, Cu/P x 10"^ and Ni/Al X 10"^ ratios for Maldeota phosphorites.

284

285

-viii-

XXXII. Ni/Pe X 10"^, Ni/Mg x 10"^, Zn/Pb 287 and Zn/Ca x 10' phosphorites.

,-4 ratios for Maldeota

Cr/Pe X 10 -2

XXXIII.

XXXIV.

XXXV.

XXXVI.

XXXVII.

XXXVIII.

XXXIX.

XL.

XLI. XLII. XLIII.

Zn/Fe X 10 , Cr/Al x 10'^^ and Sr/Ca x 10"^

ratios for Maldeota phosphorites, o V/Pe X 10" '

Ba/Na X lO"-", V/Al X 10~^,/V/Mg x i C ' and V/P X 10"^ ratios for Maldeota phosphorites.

Cu/Al X Cu/Mg X 10"^, Cu/P x 10"^, Ni/Al x Ni/Fe x 10"^, Ni/Mg x 10"^, Zn/Pb and Zn/Ca x 10"^ ratios for

Durmala phosphorites. Zn/Fe X 10 , cr/Al x 10'^, Cr/Fe x 10"^, Sr/Ca x 10-^, Ba/Na x V/Al x lO"^, V/Fe x 10"^, V/Mg X 10"^ and V/P x lO"^ ratios for Durmala phosphorites. Mean, standard deviation and coefficients of variation of Maldeota phosphorite analyses. Mean, standard deviation and coefficients of variation of Durmala phosphorite samples. Correlation Matrix of Maldeota phosphorite samples for 24 variables. Correlation matrix of Durmala phosphorite samples for 24 variables. Vector model of Maldeota phosphorite analyses. Vector model of Durmala phosphorite analyses. Rotated factor matrix (R-mode) data for Maldeota phosphorite analyses.

289

291

293

294

295

296

297

298

299

301

302

-ix-

XLIV. Rotated factor matrix (R-mode) data for ... 304 Durmala phosphorite analyses.

Tables-I and ir are in the text.

-xxiv-

LIST OF PLATES

(Hand Specimen Photographs)

Plate^I Figure-1 Platy and laminated phosphorite made up of

alternating bands of carbonate (light) and phosphate minerals (dark) (Maldeota west).

Figure-2 Granular phosphorite (dark) constituted mostly of coarse grains and minute granules (Maldeota west).

Plate~II Figure-1 Lenticular phosphorite made up of dark lenti-

cles of phosphatic material alternating with light coloured bands of calcareous and or/ siliceous material.

Figure-2 The phosphate nodule associated with black

shales that occur in contact with phosphorite horizon at Maldeota west block.

Plate-Ill Figure-l Pelletal phosphorite made up of hard, black

coloured, elliptical and disc like pellets embedded in matrix of cherty carbonate (Maldeota west).

Figuxre-2 A hand specimen of phosphorite showing alter-nating bands of pyrite (light) and phosphatic material (dark) (Durmala block).

-xl-

(Photomicrographs of thin Sections)

Plate~iv Pigure-1 Mlcrocrystalllne collophane (dark) containing

dot like inclusions of ferruginous material and occurring in the form of pellets embedded in a carbonate matrix (light) (X 55).

Plgure-2 Dahllite (light) surrounding the oolitic collophane (dark) (crossed nicols, X 55).

Pigure~3 A phosphatic pellet (dark) enclosed in a carbonate matrix (light) (X 55)

Pigure-4 Interstitial collophane (dark) occurring in the voids between calcite and quartz grains (light) (X 55).

Plate-V Pigure-1 Oolites of collophane (dark) having nucleus

of carbonate (light) (X 55), Pigure-2 Phosphatic ovules (dark and light) embedded

in a carbonate matrix (light)(X 55). Pigure-3 Nodules of collophane (dark) embedded in a

cementing material consisting of dolomite (light) (crossed nicols, X55).

Figure-4 Mlcrocrystalllne to cryptocrystalline silica (light) associated with collophane (dark) (X 55).

-xii-

Plate-VI Figure-1 Mlcroaphanitic mass of amorphous looking

collophane (dark) showing a vein of quartz (light) (X 55).

Figure-2 A calcite vein (light) cutting across the collophane (dark) (X 55).

Figure-3 A calcite vein (light) in phosphate matrix (dark) (X 55).

Figure-4 A vein of collophane (dark) in a ground mass composed of calcite (light) (crossed nicols, X 55) .

Plate-VII Figure-1 Amorphous collophane (dark) showing a vein

of quartz (light) (X 55). Figure-2 Pellets and ovules of collophane (dark)

showing complete and partial replacement of phosphate material by carbonate material (light) (X 55).

Figure-3 Stromatolitic phosphorite of Durmala showing concentric structure consisting of thin alter-nating bands of phosphate and carbonate material (X 55).

Figure-4 Stromatolitic phosphorite of Durmala showing a typical structure composed of phosphate and carbonate materials (X 55).

-xili-

Plate-viii Pigure-1 Dolomitic limestone showing anhedral coarse

grains of calcite and dolomite (X 55). Pigure-2 Carbonaceous shale composed of fine grained

calcite, illite feldspars and sericite etc. (X 55).

Figure-3 Carbonaceous shale showing cubes of pyrite (X 55).

Figure-4 Limestone showing con?)act and fine texture, with mostly fine to coarse anhedral grains of calcite and cryptocrystalline variety of silica in the form of chert (X 55).

CHAPTER - I INTRODUCTION

F I G . l LOCATION MAP OF T H E A R E A

CHAPTER - I

INTRODUCTION

GENERAL STATEMENT :

The phosphorite deposits around Mussoorie (Pig, 2) in Dehradun district of Uttar Pradesh were first reported by King (1885) from the Tal Formation in the form of phosphatic nodules. These deposits have been investigated by many earlier workers from point of view of their geology and economic importance. The present investigation, however, may be considered as a first serious attempt to study the geochemistry of the phos-phorite deposits and the associated sediments in order to present a conceptual genetic model not only for these deposits but also to apply the same in areas of similar geologic and environmental setting.

LOCATION AND ACCESSIBILITY

Mussoorie, whxch forms a part of the outer hill ranges of the Himalaya in Uttar Pradesh, is situated about 31 kms. north of Dehradun town. It is located between 1600 m and 2600 m. above m.s.l. in the Doon valley of the Uttar Pradesh state. The study area in Mussoorie lies between north latitudes 30°25• t 30°30« and east longitudes, 78°00'48" i 78°10«57" (Fig. 1). Most of the economic phosphorite deposits of Mussoorie are presently mined from the Maldeota and Durmala open cast mine blocks . The Maldeota phosphorite mining block, which is located about 12 km, away from Dehradun is approachable from the town by a metalled

road. The Durmala mining block, which is about 18 kms. S70°E from Mussoorie,is connected by a good tarred road, knovm as the Mussoorie-Tehri road.

INDIAN PHOSPHATE DEPOSITS S

During the last two decades, India achieved a major breakthrough in the discovery of large reserves of sedimentary phosphorites through an intensive exploration programme. The discovery of large sedimentary phosphate deposits in association with stromatolitic structures in the Precambrian rocks around Udaipur at Jhamarkotra (reserves 17 m.t. and 3600 m.t.), Matoon (reserves 9.20 m.t.), Kanpur and other localities (reserves 4,0 m.t, and 4,75 m.t,) in Rajasthan; Curobum in Andhra Pradesh; Hirapur-Mardeora (reserves 1.44 m.t.) and Jhabua (reserves 5.67 m.t. and 2.04 m.t.) in Madhya Pradesh; Pithoragarh and Lalitpur (reserves 5.0 m.t.) in Uttar Pradesh, is no doubt the most out-standing attainments of the systematics of prospecting and exploration (Fig. 2). Other important promising phosphate deposits of India occur in the Hazaribagh and Singhbhum districts of Bihar; Purulia in West Bengal; Jammu and Kashmir state; Chamba, Mandi, Bilaspur, Mahasu and Sirmur in Himachal Pradesh; Paritibba, Garhwal, Nainital, Mussoorie (reserves 18.0 m.t.) gnfl the Vindhyan tract in Uttar Pradesh; Jaisalmer and possibly in some parts of Jodhpur in Rajasthan; Khammam, Warangal, Karimnagar, Adilabad, Kasipatnam, Mehboobnagar, Kurnool in Andhra Pradesh;

Territory of Trichirapalli, S. Arcot in Tamil Nadu state and in the Union ^

r N

Reserves 4.90m.tonnes Grade 10-15'/.P205 — r • f Mussoone

ySrinagar / I M U S S O O R I E D E P O S I T • ./'/Reserves 18.00 m ton nes ^ t /^Grode 2 0 •/. P2O5 BIRMANIA O E P O S I T S I KANPUR DEPOSIT Reserves 4.00m tonnes Grade IO-I2V.P2O5 OTHER DEPOSIT Reser ves-4.75m tonnes Grade 5-25 •/. P2O5

c ; X Shillong j

HIRAPUR DEPOSIT Reserves 1.44mtonnes Grade J7-33V. P2O5 LALITPUR DEPOSIT I Reser ves-5.00 m.f onnes Grade-1S-2S •/.P20s|

JHAMARKOTRA DEPOSIT Reserves 17.00 m tonnes 36.00 m.tonnes Grade- 30'/. and 12.29 V. P2O5 t ATON DEPOSIT Reserves-9.20 m.toones Grade 26.16 •/. P2O5

{ After; A.Pant, 1979 )

FIG.2 ROCK PHOSPHATE D E P O S I T S

Pondicherry; Lacadive Islands (Arabian Sea) (Dar, 1970; Kapur, 1980; and Lodha, et al., 1984).

A moderate forecast shows consumption of rock phosphate rising to 4 million tonnes in 2000 A.D, Based on known reserves, production is expected to rise 2,50 million tonnes in 2000 A.D. (Dhoundial, 1984).

CLIMATE S

The climate of Mussoorie is highly variable as compared to Dehradun. In the valleys of the Jamuna and Tons rivers and their feeders, the heat is generally excessive from March to the end of the October except during or shortly after heavy monsoon showers. During the winter months from November to March, the climate is somewhat pleasant in the valleys. In open situations above the valleys the climate is more equable though the heat is always excessive. In winter the higher peaks remain snow-bound and thermometer sometimes records over 20 degrees of frosts.

The heaviest rainfall, recorded in Mussoorie, is 87 inches. This is due to their position with regard to the outer intercep-ting range of hilLs.

PHYSIOGRAPHY :

Geographically, the Dehradun-Mussoorie sector of Uttar Pradesh is a part of Lesser and sub-Himalayan range lying between

the Yamuna valley on the west and the Ganga valley on the east. Physiographically, the lesser Himalayan zone being 64,000 to 80,000 metres wide and having an average altitude of about 3030 metres forms parallel and intricate system of hill ranges. The sub-Himalayan zone is 8,000 to 48,000 metres wide whose altitude rarely exceeds 909 metres. Mussoorie lies between 1600 metres and 2600 metres altitude. Towards the north of Dehradun the Mussoorie-Narendra Nagar range (Nagitibba range) runs in Northwest direction. To the north of this range there are a number of parallel and sub-parallel hill ranges, highly dissected by tributaries of the Yamuna and the Ganga rivers.

DRAINAGE & VEGETATION :

The Himalayan system of drainage is not a consequent drainage but due to some peculiarities, it is spoken as an antecedent drainage, meaning thereby a system of drainage in which the main channels of flow were in existence before the present physiographic features of the region were impressed on it. The drainage of the slopes follows for a time in longitudinal valleys, in structural troughs parallel to the mountains but sooner or later the rivers invariably takes an acute bend and descend to the plains by cutting across the mountainous country.

The vegetation of the lesser and sub-Himalayas Include mostly evergreen and oak and conlfereous forests. In the lower slopes, the magnificient forests of Chir (Pinus longifolia),

deodar (cedrus deodara) the blue pine (Plnus excelsa)* oaks and magnolias are conunon whereas Birch, Spruse, Silver fir and other species are also found on higher slopes.

STATUS OF MUSSOORIE PHOSPHORITES :

Till 1965, the Mussoorie phsophorite occurrences were the only known sedimentary phosphorite deposits in the country. In the year 1966, they were thoroughly investigated by the Geological Survey of India under the guidance of Sheldon. These phosphorites are found to occur associated with carbonaceous shale-chert-limestone succession which has been recognised as an ideal phosphatic suit of rocks of marine origin. They occur both on the northern and southern flanks of the Mussoorie Syncline. The synclinal axis extends about 20 kms. towards NW-SE. The phosphorite horizon that occurs as a transition zone between the underlying Krol limestone and the overlying Tal shales has many intercalations of chert and shales. To evaluate the possibility of locating the economically exploitable deposits of phosphorite in parts of Mussoorie Syncline, a phased programme of exploration was chalked out by the Geological Survey of India and USAID in late sixties. On the basis of previous pioneering work of King (1885) as well as the later investigation of Srivastava (1952), Singh (1961) and srivastava and Ali (1966). A detailed exploration work led to the mining and commercial exploitation of phosphorite in few selected blocks by the Pyritesphosphates and Chemicals Limited. In the Maldeota mine block the thickness of the phosphorite horizon varies from 0.45 metre to 7.8 metres with 15% to 30.9% ^2^5 content. The

phosphatic horizon is traceable over a strike length of about 1,35 km. The reserves estimated is in the order of 10.64 m. tonnes.

In the Durmala mine block most prominent phosphorite zone occurs over a strike length of about 1.52 km. The thickness of the phosphatic horizon varies between 3.0 and 9 metre and Pj^s content ranges from 23.6% to 32.6%. The total estimated reserve is about 9,14 m, tonnes (IGCP Project - 156; Phosphorite, 1981; Ed. G.S.I, & P.P.C.L.).

Significant concentration of uranium has also been reported from the phosphorites of the Mussoorie Syncline by Saraswat,et al, (1970) and sharma (1974).

FOSSIL ASSEMBLAGES & AGE :

Though the present investigation does not seriously demand age determination, yet an attempt has been made to review precisely the subject on the basis of previous worker^ view on the various lithounits of the Mussoorie area in Lesser Himalayas as summarised below s-

Krol Formation :

The Krol and Infra-Krol Formations do not yield good fossil record and provide very conflicting evidence of fauna* Ghosh and Srivastava (1963) recovered monolete and trilete spores of Triassic affinity in the Lower Krol and Gundu Rao (1970) reported Upper Precambrian oncolites from the Upper

8

Krol of the Mussoorie Hills. Tewari (1969) and Sinha (1975) noticed Upper Jurassic to Upper Cretaceous non-planktons in the middle Krol of the Solan area in Himachal Pradesh. Likewise in the underlying Infra-Krol, Ghosh and srivastava (1963) unearthed triletes in Mussoorie area suggesting Permian age.

Azmi and Pancholi (1983) have reported occurrence of conodontophorid elements (Protohertizina) and other shelly microfauna mainly belonging to hypolithic (Cirotheca and Anabarites sp) and rarely bryozoa (Escharophora sp) - from the Upper Krol Phosphorite(Krol D) of Durmala in the northern limb of the Mussoorie syncline. The assemblage is quite diagnostic of the earliest Cambrian (Tommotian) age. In the light of the above, the Tommotian microfaunal assemblage from the Upper Krol phosphorite is quite significant because it clearly demonstrates the presence of the earliest Cambrian (Tommotian) strata in the Krol beds specially, in the Durmala area of Mussoorie. Therefore, Krol succession appears to be quite promising for delineation of the Precambrian-Cambrian boundary in the Himalayan region (Azmi and Pancholi, 1983).

The Krol assemblage as a whole cannot be con^^ared to any other stromatolitic assemblage known neither in the Lesser Himalaya nor in the Vindhyan or the Riphean (Azmi and Joshi, 1983).

Tal Formation s

Unconformably overlain by the Eocene Subathu, the Tal happens to be the only formation that has revealed a rich assemblage of datable fossil fauna (Valdiya, 1975).

Chert-phosphorite Member :

The chert phosphorite member of the Lower Tal Formation in the Lesser Himalaya has yielded a few fossil records of varied nature. While Patwardhan (1978), reporting Moravamminids from the Lower Tals, advocated Permian age of phosphorite Member, while Bhatia (1980) described them as dasycladacean cylindroporella algae of Middle Jurassic to Upper Cretaceous age. Ahluwalia (1978) recorded Upper Palaeozoic foraminifera or Porifera (7) from this horizon which too according to Bhatia (1980) are distorted sections through discs of primary branches of Clypeina, a Jurassic Palaeocene dasycladacean algae. Srivastava (1974) mentioned about the presence of conodont like forms resembling fragmentary reminiscent of Gondolella indicating Triassic age of Chert-Phosphorite Member.

Azmi, et al. (1980-81) discovered simple cone conodonts indicating precisely Cambro-Ordovician age to this Chert-Phosphorite Member exposed around Maldeota Phosphorite mine, Dehradun. Tempted with this discovery, Singh and Shukla (1981), Kalia (1982), and Jain, et al. (1982) have claimed for the discovery of Upper Cretaceous annelids, Permian endothried Foraminifera and Lower Jurassic micro foraminifera respectively from the phosphorites of Maldeota.

Black Shales s

From the succeedxng black shales of Chert-Phosphorite

10

Member, Srivastava (1972) reported the presence of a small-sized lamelllbranch, viz., Posldonla et Ornati of Middle Jurassic age, but Singh (1981) has rightly refuted its validity and Bhatia (1980] has reserved its age significance. Later He (1973) recorded 'Estherids * from the carbonaceous shale Member of Lower Tal Formation and compared them with Triassic Estherids of Venezuela and Columbia, but surprisingly extended the range of his assemblage to Lower Cretaceous.

Shell Limestone :

The only other horizon hitherto considered as the top member of the Tal Formation is the sheillimestone (singtali or Nilkanth Formation) which contains definite body fossils of Upper Cretaceous to Lower palaeocene age (Mathur, 1977); Saklani, et al. (1977), Bhatia (1980). Kalia on the other hand seems to be confident in her deduction of assigning Permian age for the Tal Formation based on the discovery of fusulinids (1972) and algae (1976) from the upper Tal Shell Limestone; followed by the discovery of Thyrid Foraminifera from the Maldeota phosphorite (1982). It is, therefore, evident that the palaeontological data from the Krol-Tal succession is not only significant in resolving the long prevailing age controversy of the Blaini-Krol-Tal succession but also demands further investigation for delineating precisely the Precambrian-Cambrian boundary in the Krol beds of the Lesser Himalaya.

11

SCOPE & PURPOSE OF INVESTIGATION :

The aim of present Investigation is to make a detailed study of the Mussoorie phosphorites and other associa-ted sediments with special reference to their geochemistry and genesis. Much work has been carried out on these phosphorites by the earlier workers in the past and various views regarding the geology, stratigraphy, structure, genesis, etc., have been expressed from time to time. The present investigation has been thus undertaken with a view t-

1. To bring out clearly the factors involved during the process of formation of these phosphorites.

2. To investigate the various chemical and biochemical processes involved in the deposition of phosphorites.

3. To determine the geochemical behaviour^inter-elemental relation and dispersion pattern of the major and trace elements of the phosphorites and their associated syn-

' sedimentary rocks. 4. To study the geochemical behaviour of the alkali elements

like Na and K in relation to their pH and trace element contents.

5. To study the mineralogy and chemistry of various rock units in order to understand the genesis of the various minerals present in the phosphorites and to assess the quality of the deposit.

6. The classification of phosphorites and its application in exploration and ejqjloitation of other phosphorite deposit similar in their mode of origin and age.

12

The present study would therefore envisage to study and critically investigate the geochemistry of the phosphorite deposits of Mussoorie in an attempt to throw more light on the genesis of the phosphorites and also their physical and chemical conditions of deposition. The author made use of a large number available published work, old and new, which greatly aided his present investigation and helped him to arrive at a reasonable conclusion. Nonetheless, with limited time as well as restricted resources available in our country for such an Investigation of world-wide importance, the author tried to present his best under the existing circumstances,

As a part of this investigation a detailed petrographlc and geochemlcal studies have been envisaged in order to evolve a conceptual model for the origin of the Mussoorie phosphorites primarily on the basis of their geochemistry in relation to the various contemporary physical and chemical environment of deposition.

PREVIOUS WORK :

The phosphorite deposit of Mussoorie constitutes a part of the lowermost sequence of the Tal Formation which was first identified by Medlicott (1864) around Bidasini. King (1885) was the first to report phosphorites in the form of phosphatic nodules around Mussoorie hills followed by Sheldon in 1966.

The geology and stratigraphy of Krol and Tal Formations of Lesser Himalaya has been subjected to gradual refinement through many workers. According to Valdiya (1975), the Tal

13

Formation, containing datable fossil assemblages in the lawns down hills in Garhwal occupies a crucial position at the top of the 6100 metre thick succession of predominantly unfossiliferous sediments constituting the Krol Nappe,

Ravishankar (1971, 1975) studied the Tal Formation of Mussoorie syncline, and established a stratigraphic succession and outlined the depositional conditions of various lithounits in which these phosphate deposits are known to occur.

Valdiya (1980 b) has presented a detailed synthesis as an outcome of the workshop on the stratigraphy and correlations of the Lesser Himalayan formations.

Singh (X979) has also discussed the stratigraphy. The fossil assemblages and age of Tal Formation, discussed by many earlier workers, has already been given in foregoing pages.

petrography of Mussoorie phosphorites was discussed by Pareek (1972) and Patwardhan and Panchal (1984). On the basis of petrographical studies they proposed trapping mechanism for the accumulation of the phosphorus.

Mlneralogical studies carried out by Rao, et al. (1974) reveals that the Mussoorie phosphorites are conposed essentially of fluoro-carbonate apatites particularly collophane (amorphous and colloidaDand francolite (a crystalline carbonate apatite).

Dubey and Parthasarthy (1975) presented a brief account on mineralogical nature of the Mussoorie phosphorites based on X-ray and infra-red studies. Raha (1970-72) studied the minera-logy and crystal chemistry of Mussoorie phosphorites based on microscopic studies and cell parameters.

14

Geochemical studies carried out by Saraswat, et al. (1970) indicate that the Mussoorie phosphorites contain low to medium PjOg content and the significant values of uranium and rare metals such as Mo, Ni# V, etc. also occur associated with them, enhance their in^jortance as it may perhaps be possible at a later date to recover these metals as a bye-product of a phosphate based industry. Study of radioactive phosphorites of Mussoorie, carried out by Sharma (1974)^ indicates that concentration of uranium is significant in granular phosphorites than in other types. Uranium and rare metal mineralisation is syngenetic and is due to adsorp-tion on the surfaces of fine grained carbonaceous, clayey and collophane matrix.

In recent years, Banerjee and McArthur (1991) have given a note on the mineralogy and geochemistry of Mussoorie phosphorites They suggested that the analytical data is consistent with the older age and tectonic setting of the deposit reflecting deep burial diagenesis and prolonged weathering. Intimate association of stromatolitic chert and pyrite with phosphorite and the absence of non-pyritic chert suggest pyrite formation was iron limited and sulphate reduction was pronounced.

PatwaJTdhan and Ahluwalia (1973, 1975) discussed the origin of Mussoorie phosphorites and its palaeogeographic inplications on the basis of the lithological gradation and textural variation of these sediments and suggested an indirect role of organisms whose productivity was supported during the oceanic upwelling. It is recognised for the deposition of Mussoorie phosphorites which are associated with black-shale-chert-carbonate-pyrite facies in the lower Himalayas.

15

Chaudhrl (1978) discussed the origin, transportation and accumulation/precipitation of phosphate deposits in Mussoorie and other areas invoking almost all types of mechanism postulated for phosphorite genesis.

Redcliffe, et al. (1984) described tidal environment deposition in the Lower Tal Formation on the basis of the occurrence of sedimentary structures obtained from the massive limestone and dolomitic limestones of Durmala phosphate deposit. These structures were considered as good indicators of tidal sedimentation processes. Their view is further corroborated by the presence of algal remains* pyrite and carbonaceous matter which is indicative of deposition in restricted, shallow water basins where euxinic conditions prevailed. Two idealised facies can be recognised in the Lower Tal Formation - interdial and shallow sub-tidal.

Recently, Ahluwalia (1989) discussed the genesis of Tal phosphorite. According to him, the precipitation of primary phosphatic mud could be inorganic or organic. The inorganic mode could operate above the sediment water interface or below it, the interstitial pores of the loose sediments. The organic or biochemical mode could have operated with the aid of bacteria, algae, phytoplankton, and their mass mortality. The Tal phos-phate of Himalaya and many other phosphorites of the world cannot be exclusively categorized as organic or inorganic in origin and more often than not, result from a suitable combi-nation of these two factors.

Ravishankar (1976) described Maldeota phosphorite prospects discussing in detail the exploration, grade, tonnage

16

and beneflclation techniques applied with recommendation for future mining. Role of 'Mussoorie Phos' as a direct phosphatlc fertilizer in acidic soils, was discussed by Jaggi/ et al. (1976). According to them the low grade Mussoorie rock phosphate cannot be directly utilised in the manufacture of chemical ferti-lizer. However, due to increased chemical reactivity of the phosphorus bearing mineral, the Mussoorie phosphate can be utilized as a direct phosphatlc fertilizer in acidic soils and for long duration crops. The presence of CaO content in these phosphorites makes it to act as a liming material in soils which are highly acidic and helps the cultivators in lowering cost of Inputs as no additional liming material is required.

In 1981, various aspects as geology, mineralogy, petrology, petrography, chemistry, genesis, reserves and grade, palaeo-tectonics, palaeogeography and depositional history of the basin of the phosphorite deposits occurring in the Mussoorie syncline were discussed in the fourth International field workshop and seminar organised under the aegis of IGCP Project -156 in India by UNESCO-IUGS, Indian National Committee for IGCP and the G.S.I.

METHODS & TECHNIQUES s

In order to achieve the required objectives, the following scheme of investigation was adopted in the present study.

17

Field Studies :

During the field studies, with the help of geological map of the investigated area, 150 fresh unweathered representa-tive samples were collected from outcrops, adits, quarry and different underground levels of PPCL mine. Regular spacing of sampling was not always possible. The sampling was done from three major lithologlcal units viz., phosphorite, shales, chert and underlying Krol limestone where it was found to be phospha-tlsed. However, more attention was paid to the phosphorite unit.

Laboratory Techniques $

Thin sections of about 100 representative samples of different lithologlcal units were examined under the petrological microscope to study the petromineralogy. Based on the results obtained from petromineralogical studies, a total of 59 samples were selected for chemical analysis. The samples were crushed and finally powdered in centrifugal ball mill. The powder was sieved by standard sieve of -200 and was utilised for the preparation of solution 'A' and ' B ' .

The chemical analysis of these samples were carried out for the quantitative determination of major elements following the method outlined by Shapiro and Brannock (1962).

Preparation of Solution 'A* S

Solution 'A' was prepared by fusing 0,2 gm of rock powder with 5 ml of dried 30% NaOH for five minutes in a nickel

18

crucible. Some water was added after the melt cooled down and allowed to stand over night till the melt disintegrated to a one-litre volumetric flask and solutions were acidified with 20 ml of 1 s 1 HCl and made up to the volume.

Preparation of Solution 'B* :

For the preparation of solution 'B', 0,5 gm, of rock powder was mixed with 15 ml add mixture of HP s H2S0^ : HNO^ in the ratio of 12 j 4 : was kept on steam bath furnace for 4-6 hours to digest completely. Then the content was transferred into 400 ml beaker using minimum of water, and kept on a hot plate till the SO^ fumes came off, removed and a few drops of 1 » 1 HNO^ and HClO^ mixture was added, again the beaker was placed on hot plate, for any organic matter to remove, and the solution became clear. For removing the brown precipitate of MnOj/ if present, 1 ml, hydrazinsulphate solution (0.2%) was added and again boiled. The solution then was cooled to room temperature and transferred into 250 ml volumetric flasks, marked the volume and transferred the same into plastic bottle. The standard solutions of known concentration were also prepared for each element and were run through instrument as reference with which the per cent of unknown sample was calculated.

Laboratory Techniques for Major Elements s

Solution *a' was used for the quantitative determination of silica (SiOj) and alumina (AljO^) whereas for other major

19

oxides viz., Solution 'B' was utilized. Al203# SiOj, p2°5 ^^^ determined by Lambda 3 B UVMS Spectrophotometer while CaO, MgO, MnO, Na20# were determined by Atomic Absorption Spectro-photometer, H2O and CO2 were determined by loss on ignition and volumetric method respectively.

Lambda SB Spectrophotometer s

Application : The Lambda 3 Double-Beam UV-Visible spectrophoto-meter is versatile general purpose instrument usable in a wide range of applications as indicated by the performance specifi-cations. It is available in 190 to 750 nra, or 190 to 900 nm wavelength ranges and accepts a full complement of accessories. This spectrophotometer combines an optoit»chanical system with micro-corrqputer electronics to achieve precision. Records operation outputs further extend the versatility of this spectrophotmeter.

Pt±aciple of Operation : The Lambda 3 is an electro-optical mechanical instrument utilizing a reflecting littow mono-chromator^, control functions such as wavelength driver, filter and source changes, recorder control and enhanced manual wave-length setting are performed by the microcomputer. Self baseline/ background correction, atuomatic response time, transmittance to absorbance conversion, scale expansion, zero-suppression, and self-diagnostics are typical of microcomputer data handling functions. The instrument produces control signals which are available at the back panel.

20

Methods : Solution *A' and solution 'B' were used for deter-mining various oxides as P2S' eliminating errors due to possible reagent contamination, a reagent blank was prepared with distilled water for each set of determination.

The standard solution of known strength and blanks were also prepared. They were run through the instrument and with their reference, the percentage of unknown solution was calcula-ted. These oxides were determined by spectrophotometer at wave-lengths noted against each.

Elements Wavelength Si 650 mu A1 775 mu Tl. 430 mu P 430 mu

Loss on Ignition s HgO was determined by Ignition of the sample powder in an oven up to 1000®C and loss in weight due to water vapours and other gases was calculated.

Volumetric Method s Volumetric method unlike gravimetric methods which were mainly confined to precipitation reactions, are applicable to almost every type of chemical reactions, neutrali-zations, complex iron formation and oxidation reduction reactions, Carbon dioxide (COj) was determined volumetrically. In a series of 250 ml beaker, 0.5 gm. of calcium carbonate as standard and 0.5 gm. of the powdered sart$>le were placed. 25 ml of hydro-chloric acid {0.5 N) was added to each beaker and allowed to

21

remain overnight. The remaining acid in beaker was titrated with sodium hydroxide (0,35 N) and bromophenol blue was used as an indicator, which ©ave yellow to blue end point. The calculation for CO2 P®^ cent was made as stated below

1, Calculated the acid alkali ratio = 25/Volume of NaOH for blank. 2, Multiplied each of the NaOH titration value by acid alkali

ratio. 3, Subtracted each figure obtained in step 2 from 25 ml, HCl.

This gave the HCl in millilitres consumed by the carbonates. 4, A factor was obtained on the basis of titration of the

standard CaCO^ (This standard contains 44 per cent CO2) ss 44/HCl consumed by standard = Factor

5, Multiplied each sample value for HCl consumed as obtained in step 3 by the factor to obtain CO2 in per cent.

6, Where P2O5 is greater than few tenths of a per cent, corrections were made by multiplying its value by 0.67 and subtracting this from the value obtained in step 5.

Laboratory Techniques for Trace Elements :

Analysis of about 59 samples for the quantitative determination of trace elements were carried out on a GBC 902 Atomic Absorption Spectrophotometer (AAS). The trace elements determined include Cu, Ni, Co, Cd, Pb, Zn, Rb, Sr, Li, V and Ba.

22

Principle of Atomic Absorption Spectrophotometer : The principle of AAS Is based primarily when energy Is applied to a population of atoms produced In an 'atom cell', some of the atoms are excited to higher energy levels. The energy can be applied In the form of heat In a flame or electrically heated furnace. The excited atoms eventually return to their lower energy levels. In the process, the energy required from the thermal source is released and this released energy which appears as radiation is the emission spectrum of the atom and is cha racterlstic of the particular atomic species. Depending on the method of supplying energy and the nature of the signal detected, the technique is known as either absorption, emission or fluorescence spectro-metry. Any species which is excited to emit radiation at a particular wavelength will also absorb radiation at that wave-length. This particular property is the basis of AAS which allows the measurement of the concentration of species in an atomic vapour capable of absorption of radiation at a particular wavelength.

Technique : In general, after choosing the proper hollow cathode lamp for the analysis, the lamp should be allowed to warm up for a minimum of 15 minutes. During the period, align the Instrument, position the monochromator slit width and adjust the hollow cathode current. Subsequently, light the flame and regulate the flow of fuel and oxidant, adjust the burner and nebulizer flow rate for maximum per cent absorption and stability and balance the photometer. Run a series of standard of the elements render analysis. Set the curve corrector to read out

23

the proper concentration. For best results^ standards are run each time a sample or series of sanple are run.

The wavelengths of the elements determined by AAS are as follows i"

Elements Wavelength ( nm) Slit width

Ca 422.7 0.5 Mg 285.2 0.5 Mn 279.5 0.2

Na 589.0 0.5

K 766.5 0.5 Cu 324.7 0.5 Ni 341.5 0.2 Co 346.6 0.2 Cd 228.8 0.5 Pb 283.3 0.5

zn 307.6 0.5 Rb 794.8 0.2 Sr 460.7 0.2

Li 670.8 0.5 Cr 357.9 0.2

V 306.0 0.2 Ba 305.1 0.2

CHAPTER - II GEOLOGICAL SET-UP

CHAPTER - II

GEOLOGICAL SET-UP

GENERAL STATEMENT s

The only exploitable phosphorite deposit of Uttar Pradesh th«t

state^occurs at Mussoorie, being intimately associated with a variety of shale-chert-carbonate rocks of sedimentary origin with some pyrites, constitutes a part of the lower roost sequence of the Tal Formation of the Lesser Himalayan region of north-western India. Due attention has been given to describe the more inportant stratigraphies lithologic and sedimentary features of the rock formations as well as those of the phosphorites asso-ciated with them. Briefly, the important contributions made by some of the previous workers on the regional stratigraphy, structure and lithology of the formations in the Lesser Himalaya of the NW Himalaya have been reviewed for an appraisal of their general geological set-up.

In course of geological survey of the phosphorites from the opencast and underground mine workings of Maldeota and Durmale, Mussoorie, a wealth of local information pertaining to these features besides sampling of specimens for geochemical analysis were systematically collected,

regional GEOLOGY :

The Dehradun-Mussoorie sector of Uttar Pradesh state forms a part of Lesser Himalaya between the Yamuna valley on

25

the west and the Ganga valley on the east (Lat. 30°25' to 30°30' and Long. 78°00'48" to 78°10'57").

Valdiya (1980 b) presented a detailed synthesis of the stratigraphy and correlations of the Lesser Himalayan formations. Ravi Shankar (1971, 1975) classified the Tal Formation of the Mussoorie syncline and touched upon the depositional conditions of the various lithounits including the phosphate deposits. The age of the lower Tal Formation was critically studied by many previous workers like Patwardhan (1978), Bhatia (1980), Ahluwalia (1978), Srivastava (1974) and Azmi, et al. (1980, 1981), based primarily on fossil evidences.

The generalised geological succession of the region as recognised by the G.S.I. (1981) is given as follows

Table-I

Group/Formation Age

Alluvium Dun gravel/old Terraces Siwalik Group Subathu Group Tal Formation Krol Formation Infra Krol Blaini Formation Nagthat Formation Chandpur Formation Simla Formation

Recent Pleistocene to sub-recent Middle Miocene Upper Palaeocene to Upper Eocene Jurassic to Cretaceous Permian to Jurassic* Permian Permo-Carboni ferous Devonian-Silurian* Devonian-Silurian* Early Palaeozoic to Precambrian

•Tentative age

26

This great and unbroken 6100 metre thick succession of predominantly unfossiliferous sedimentary rocks, that constitute mainly the Krol Nappe and extend as an imposing southern rampart of the Lesser Himalaya/ has been divided into six distinct forma-tions viz., Mandhali, Chandpur, Nagthat, Blaini, Krol and Tal in the ascending order (see Valdiya, 1975).

The Blaini boulder bed divides the composite stratigraphic column of the Lesser Himalayas into (i) Pre-Blaini formations and (ii) Post-Blaini formations. The pre-Blaini formations are considered to be extending from Proterozoic to Devonian in age whereas the age of the post-Blaini formations is permo-carboni-ferous to sub-recent (see Ahmad, 1976).

Around the Mussoorie syncline, the pre-Blaini sequences are referred to as Simla Formation, Chandpur Formation and Nagthat Formation whereas the post-Blaini formations are known as Infra Krol, Krol and Tal formations, the Subathu Group and the Siwalik Group.

The Lesser Himalayan formations lying between the Main Boundary Fault (MBF) and the Main Central Thrust (MCT), that occur mainly in Himachal Pradesh,and Garhwal and Kumaon regions in Uttar Pradesh, constitute a structurally complicated and tectonically disturbed sequence consisting of a number of high to low grade metamorphic and sedimentary rocks. Prom time to time many contrasting views have been expressed to explain their structural complexity and also to determine their strati-graphic correlations based on generation of more and more new data for about a decade and it ultimately led to a progressive refinement of the understanding of their complex problems of stratigraphy, structure and tectonics.

27

The Sub-Himalaya is largely composed of the Siwallk Group (Neogene) which is separated from the older tertiaries by the northerly dipping Main Boundary Fault/Thrust. The Siwaliks generally show open to isoclinal Jura-type folds and reverse faults. At Kalsi, northwest of Dehradun, the Siwalik rocks are tectonically juxtaposed against the upthrusted Palaeogene rocks along the Main Boundary Fault. But south-eastwards, in Dehradun area, due to overlapping of the Main Boundary Fault by the Krol thrust, the Siwalik rocks are brought directly in contact with the pre-tertiary rocks of the 'Krol Nappe',

As a consequence of last phase of tertiary folding the Blaini-Infra Krol-Krol-Tal and Subathu sequence are co-axially folded along with their basement in the form of a doubly plunging syncline which is popularly known as the 'Mussoorie syncline*.

GEOLOGY OF THE AREA :

It was H.B. Medlicott (1864) first introduced the Tal Formation from the type area in the Tal valley in south-western Pauri-Garhwal of U.P» About a century later Tewari and Kumar (1967) found some sandy, oolitic and shelly limestone In the vicinity of Nilkanth, immediately to the northwest of the type area in the Tal valley.

The Tal Formation which associates the potential phospho-rite horizon and overlies the Krol Formation, constitutes the uppermost lithostratigraphic unit of the thick sedimentary sequence of the Krol Nappe. The Krol and Tal Formations, which have a thrust contact with the Jaunsars, form a syncline that

28

appear to have been tilted to the south. In the Mussoorie area, the syncline made up of Blaini, Infra Krol, Krol and Tal rocks is in direct contact with Nagthat Formation on the north-east. The strike of these formations varies from NlO^W to N55°W. At certain places a few reversals indicate refolding of the forma-tions resulting in the generation of local synforms and anti-forms, e.g., in the Pari Tibba-Chamansari area, southeast of Mussoorie, where folding has also caused thinning and thcikening of the formations. Their outcrops are located at various eleva-tions depending upon the degree of erosion at any given place. The principal streams in the area generally follow old fault alignments. Faulting, which resulted in the development of steep scarps, often display shearing, shattering and drag folds of the formations.

The evidences of the Pharat and Bidhalna 'windows' through which Simla Formation with Nummulitic cover rocks peep on the frontal side of the Krol belt, provide support in favour of the horizontal movement of Krol-Tal sequences along the Krol Thrust. The northern counter part of the Krol-Tal sequences along the Krol thrust according to Auden, is the Tons Thrust, which also overrides the autochthonus Simla siate-Nummulitic zone.

The stratigraphy of the Tal Formation has been worked out in greater detail, particularly in view of the fact that the economic deposits of phosphorite are restricted to its base. Details of the lithostratigraphy of the formation are given below.

29

TABLE-II S LITHOSTRATIGRAPHY OF TAL FORMATION IN PARTS OF MUSSOORIE SYNCLINE.

Subathu Group

Olive shale, shell marl and limestone

UNCONFORMITY

Upper Tal Formation

(ii) Limestone member (Shelly calcareous grits)

Upper Palaeocene to Upper Eocene

20 m Lower and/or Middle

(i) Quartzite member 1300 m Cretaceous (Sequence of quartzite, arkoses, grits and thin grey-to green shales, red silt stone, often mudcracked).

DISCONFORMITY

Lower Tal Formation

Transition

(iv) Calcareous member 5 m (iii) Arenaceous member 300-500 m (massive banded siltstone/ subgraywacke) (ii) Argillaceous member 150 m

(a) Silty shale/ siltstone

(b) Splintery shale (c) Finely cleaved,bended

shale often calcareous buff on weathering.

(d) Black micaceous shale, pyritic, often carbona-ceous and sandy.

(i) Chert member (a) Main phosphorite unit 10 m (b) Chert Unit 200 m DISCONFORMITY (Submarine diastem)

overlap-Transition at places

Argillceous limestone (often phosphatic) inter-layered with thin streaks of phosphate rock and chert, brecciated at places.

Upper Krol Formation

Light grey, argillaceous limestone, purple and grey shale/slate. Grey to bluish grey dolomitic limestone and dolomites and associated shales (with phosphorite horizon near Durmala village)

31

CLASSIFICATION OF TAL ROCKS !

The Tal Formation has been divided into a Lower and an Upper sequences by Auden (1934) and into Lower, Middle and Upper sequences by Bhargava (1975). Valdiya (1975) also proposed a three-fold classification of Tal into Jogira, Mashat and Bansi members. Bhatia (1980) has reviewed and presented in detail various lithounits of the Tal Formation as proposed by different workers.

However, on the basis of distinctive lithology, mappability, sharpness and easy recognition of the stratigraphic contacts, the Tal rocks have been classified into two Formations, viz.. Lower Tal Formation and Upper Tal Formation. A break in sedimen-tation is also represented in some parts of the area as a result of sharply changing environment of deposition from essentially marine in Lower Tal to sub-aqueous or subaerial (non-marine) in the upper Tal Formation. The boundaries between the Lower Tal and the Upper Tal formations are thus natural and distinct (G.S.I., 1981).

Lower Tal Formation s

The thickness of the Lower Tals vary in different sections from 75 m to 880 m. The formation is further divisible into four members on the basis of their difference in lithology and depen-ding upon the dominance of one type of sediments over others, viz., cherty, pelitic, psammitic and calcareous. The boundaries of the Various members are more or less gradational.

32

Chert Member :

The mineralisation of rock-phosphate is largely localised

in the chert member which is divisible into (a) chert horizon

and (b) phosphate horizon on the basis of their lithological

changes. A detailed description of these horizons is presented

as follows s

(a) The Chert Horizon s

The Chert horizon comprises of a thick sequence of bedded black cherts with thin intercalations of light to dark grey shales. The chert is often thickly bedded and generally gets nodular upwards. The nodules are phosphatic. The phosphate content of these nodules seems to vary considerably. But it was generally found to be inversely proportional to the size of the nodules. The inter-nodular portions of the chert is generally devoid of any phosphatic contamination. Associated with the chert, there are also some bands of limestone and disseminations of small pyritiferous nodules.

The Mussoorie syncline at Toneta-Kaphulti attains a thickness of about 2 00 m. The thickness, however, decreases south-eastwards. Southeast of Durmala on the northern limb of Mussoorie syncline, the occurrence of chert is rather rare. The poor development or total absence of chert in the south-eastern part of the syncline could be explained partly due to stratigraphic overlap and partly because of their tectonic elimination.

33

(b) The Phosphate Horizon s

The phosphate horizon being largely restricted to the upper part of chert member varies in thickness from a few mm to about 10 metres. The main phosphorite horizon occurs between the chert and black shales but thin phosphatic bands are also found intercalated with the underlying chert as well as the overlying black shales. The Individual phosphorite bands are not continuous though the phosphorite horizon extends for about a total strike length of over 120 kms. along both the limbs of the Mussoorie syncline.

At places, the phosphorite horizon rests directly over the Krol limestone without any sign of unconformity. In such situa-tions, the Krol limestone is also known to contain in its upper parts, bands of phosphorite (Ghosh, 1968; Patwardhan and Ahlu-walia, 1973; Raha, 1973).

The phosphorite also becomes stromatolitic, showing mega-

scopically discernible stromatolitic inclusions and columns

mostly towards the top of the succession.

Upper Tal Formation :

The Upper Tal Formation is less thicker than the Lower Tal and it varies from 70 m to 160 m in thickness. This Formation is sub-divided into a lower quartzite member and an upper lime-stone member. The white to purplish white coloured sandstone/ quari:zite of the upper Tal are occasionally current-bedded and ripple-marked. The sandstone is often pebbly and the pebbles

34

are being predominantly composed of vein-quartz, green slate and abundant pink feldspars. The topmost horizon of the upper Tal Is constituted of a dark grey limestone containing abundant fragment of lamelie-branch and brachlopod shells.

AGE 1

The age of Blainl-Krol-Tal sequence has been assigned to be of Late Precambrlan by Singh (1979 a, b, 1981) and Late Precambrian to Early Palaeozoic by Azmi, et al. (1981) and Azml and joshi(1983) on the basis of late palaeontological evidence and they refuted the accepted view of Late Palaeozoic to Mesozoic age of the sequerce by the previous earlier workers.

was Singh's contention was regarding the age of the sequence^mainly based on some sedimentological observations and the apparently unfossiliferous nature of these Lesser Himalayan rocks.

Azml and his associates (1980, 1981, 1983) deductions are essentially based on their discovery of Cambro-Ordovician boundary conodonts from the chert-phosphorite member of the Tal Formation of the Mussoorle syncllne.

Thus, presently, the age of the Mussoorle phosphorite belonging to the Tal Formation which was hitherto believed to have been formed eitter in the Permian or in the Jurassic Cretaceous period, has been refixed to be Late Precambrian to Cambrian.

CHAPTER - III NATURE AND MODE OF OCCURRENCE

CHAPTER ~ III

NATURE AND MODE OF OCCURRENCE

The phosphorite deposits of Mussoorle In Dehradun district, U.P» show a great variation in their mode of occurr-ence. They are found interbedded with the chert and black shale sequence which conformably overlies the Krol Formation/ which is predominantly made up of impure limestone and dolomite.

Nature of Mussoorie Phosphorites :

The phosphorite deposits of Mussoorie are generally dull grey to brownish black when fresh but turn brittle and friable on weathering. These are occasionally bedded, white and orange incrustations are seen at places, on the surface of the phos-phorites. The phosphorites from different parts of the Mussoorie syncline have been classified into various types by earlier workers (Ghosh, 1968; Saraswat, et al., 1970 and 1971; Rao and Rao, 1971; Patwardhan and Ahluwalia, 1973; Sharma, 1974; Mehrotra, et al., 1981 and Banerjee and McArthur, 1991). Broadly speaking five distinct varieties of phosphorites are classified in the field based on their physico-morphological features and are described below »-

1. Platy and laminated 2. Granular 3. Veriegated lenticular 4. Nodular 5. Pelletal

36

1. Platy and Laminated j

It is made up of alternating bands of carbonate and phosphate minerals ranging from less than a millimetre to a few millimetres in thickness (Plate- I ? Pig. 1 ). It is dull black to dark brownish in colour, thinly bedded and very fine grained. The phosphatic layer consists of small pellets of collophane arranged in rows parallel to the bedding plane and are embedded in a fine collophane matrix. This variety has the highest concentration of phosphate and was found to be intimately associated with pyrite, limonite and goethite. On weathering a large portion of calcareous material is usually leached out from the ore.

Microscopically, these platy and laminated phosphorites fall into two well defined textural and mineralogical varieites viz., 1) completely aphanitic and the other, 2) fine grained with little granularity.

The first variety is a completely aphanitic crypto-crystalline assemblage of collophane showing colloform structure under higher magnification, and mostly isotropic though some-times it shows anisotropism. The second variety is very fine grained, thinly laminated and occasionally with wavy and curved laminations consisting of aggregates of dark grey to black isotropic collophane. Joints and fractures filled with secondary quartz in the form of veins are occasionally seen.

37

2, Granular s

This variety of phosphate is generally black but occa-sionally the colour changes to light green or dark brown. The grains are coarser than that of the former one and constituted mostly of minute granules and pellets of phosphatic material (collophane and dahllite) set in a carbonate and/or siliceous matrix (Plate- I ; Figure- 2 ), in other variety francolite is seen embedded in a groundmass of carbonate of lime alongwith collophane, which when thoroughly weathered, gives rise to a powdery material. This type of phosphorite is also of good grade.

3. Variegated Lenticular s

In this variety, dark lenticles of cherty or phosphatic material, composed of dahllite and collophane were found alternating with lighter coloured bands which are occasionally feebly phosphatic and generally composed of calcareous and/or siliceous material. The longer axes of the lenticles vary in length from 2 mm. and the shorter are from 1 mm, to 2 cm. At places the lenticles are aligned oblique to the bedding plane. (Plate- II i Figure- 1 ).

A thin section study shows that the variety consists of elongated pellets, composed of dark grey to brownish grey isotropic collophane embedded in a carbonate or cherty matrix. The boundary between these pellets and the groundmass is generally irregular though sharp with no visible replacement

38

relation. However, recrYstallised calcite veins are seen

occasionally along the fracture planes traversing these

pellets.

4. Nodular :

Most of the nodules are spheroidal, flattened, plano-convex and ellipsoidal (Plate- II ; Figure- 2 ). The colour of the nodules is usually light to dark grey and black. The nddules vary in size from 4.5 cm x 2.5 cm x 1.5 cm to 27 cm x 18 cm X 9 cm as long x intermediate x shorter axes. In general, this type of -phosphorite is associated with black shales that occur in contact with phosphorite horizon. At places this variety also occurs in the lower most part of the chert member just overlying the Krol limestone. The phosphate content of nodules is more or less inversely proportional to their size, the smaller the nodules the higher is the content of phosphates.

Thin section study shows that the nodular phosphate rock consists of smaller ovoid or aggregate of ovulites composed of dark grey to greyish brown anisotropic collophane embedded in a cementing material consisting of calcite. These ovulites are sometimes concentrically arranged with fibrous anisotropic dahllite forming the outer rims of collophane.

5. Pelletal t

The pellets,composed of collophane, are black in colour, hard, elliptical to disclike in shape and measure 1 mm. to few cms. in length. They are eitdDedded in a matrix of cherty carbonate

39

They are found to occur parallel or subparallel to the bedding

plane. This variety could be seen within the chert bands

(Plate- III; Figure- 1 ).

Mode of occurrence of Mussoorie Phosphorites :

Associated with carbonaceous shales, chert and limestone, the phosphorites occupy parts of northern and southern flanks of Mussoorie syncline. The outcrop of the phosphorite horizon is somewhat oval shaped with the perimeter of 120 kms. striking NW-SE, So far about ten phosphorite deposits have been reported from around Mussoorie though the deposits located at Maldeota, Masrana and Durraala blocks (Pigure-4) found to be economic. An attenpt has been made to describe the mode of occurrence of the phosphorite deposits of Maldeota (East and West Blocks), Masrana and Durmala in some details. The geological set up, structure and distribution of phosphorite deposits are presented in Figure-3.

1. Maldeota Block s

The phosphorite deposits in Maldeota area which is traceable for over a strike length of about 1350 m are being mined from the following two workings

a) Maldeota (East) and b) Maldeota (West) The eastern part of Maldeota is composed of three blocks

from east to west namely, i) Chiphaldi, ii) Dubra and iii) Mathet (Fig. 4). The phosphorite, which is usually associated

40

Toneto-Kaphulf .Block

Kimoi |(^*Kaphult i ^ .

\ X , I Block DhobighatBlockN^«% XKoltN

\ Kimoi

M M c c n n n ! ? ^ ' ^ " ' " ^ ^ ^ •MasranQ MasranaBlock MUSSOORIE M i d l a n j b ^ ^ D h o b l q h ^ r

S E C T O R I ^ - - ^ ^ r i t i b b ^ v M a i k h ^ ^ . Durmala V ^ v - - ^ * N Block

Pan'tibbaBlock

I

Silgaon- Bhusti Block

P a r l l l b b o Chomasari Block y *

|~l-~| Tectonic Outliers | 3 | Uupper Tal 2 I Lower Tal

I I I Krol Limestone | — | Road

S C A L E 0 2 4 1 I L 6 Kms. J

F I G . A S K E T C H M A P OF T H E M U S S O O R I E S Y N C L I N E

SHOWING VARIOUS B L O C K S

41

with shales and with or without chert, directly overlies the Krol limestones, occasionally having intercalations of phosphatic materials (up to 2 cm thick) in some of the adjoining carbonates along their bedding planes, replacing some of the carbonate materials, and thus rendering the limestone slightly phosphatic.

Maldeota (West) block lies to the west of the Bandal river and covers a distance of about 1.5 km. of the Krol-Tal contact between Tomotwala and Timli villages. The block forms a part of the southern limb of Mussoorie syncline. The maximum thickness of massive chert noticed near Surkhet is 25 m. \i«rtiich gradually decreases on either side. The phosphorite unit occurs towards the upper part of the chert member overlying bedded chert and associated shales. Wherever the black chert bed is not developed, phosphatic horizon directly overlies the Krol limestone and dolomite. The average thickness of the phosphate unit in the workings varies from 0,45 m. to 7.8 m. Phosphate rock, generally bedded and granular type with carbonate matrix, is dominant in the area and extends for a strike length of 1.4 km.

2. Masrana Block t

Masrana block is located at a distance of 11 kms. from Mussoorie on Mussoorie-Tehri road. It is eastward continuation of Kimoi block (Fig. 4). The Krol-Tal contact runs for a distance of 3 kms. The chert-shale-phosphorite sequence (chert member) of Lower Tal Formation ranges up to a thickness of

42

60 m, with rock phosphate and associated with 0,20 m. to 8,5 m. thick chert-shale bands. Phosphorite is commonly concentrated towards upper part of the chert-shale phosphorite sequence. Chert or black shale are poor in phosphate content. The phos-phate is seen over 1.5 km, strike length.

3, Durmala Block :

Durmala phosphate deposit is situated on the northern limb of the Mussoorie syncline between Masrana and Bhusti blocks. It is about 18 kms, from Mussoorie in S70°E direction. Massive limestone/dolomitic limestone and calcareous shale of Krol and the overlying member of Lower Tal Formation are the main rock types met within the area. The presence of prominent phosphorite zone over a strike length of 1,52 km, was indicated by the officers of Geological Survey of India, The thickness of the zone varies from 3 m , to 9 m. Apart from the main band of phosphorite, the presence of another small band with thickness varying from 0,5 m, to 1,5 m, has been indicated. The two bands are separated by chert and/or shale, often phosphatic, varying in thickness from 2 m, to 5.7 m. The smaller band contains granular type of phosphorite, whereas the major band is dominantly of bedded^platy type of phosphorite with occasional laminae of granular and lenticular varieties.

43

Upper Krol Phosphorite t

The Upper Krol Phosphorite that occurs approximately 450-500 m. below from the main phosphorite deposit of the Lower Tal in the eastern proximity of village Durraala in a normal stratigraphic order, is a bed of 14,25 - 15.0 m. thickness with its exposed lateral continuity for about 100 m. The general strike and dip of the phosphorite bed conform the attitudes of the Upper Krol limestone. The phosphorite is characterised by mostly banded nature with a few thin cherty bands in the lower part. Unlike the Lower Tal phosphorite this Krol phosphorite is underlain and overlain by calcareous shales only.

Radioactivity in Phosphorite and Associated Horizons J

Although the phosphorite horizon is traceable over a larger part of the perimeter of the Mussoorie syncline, signi-ficant concentrations of uranium are confined to the area bet-ween Mussoorie and Sahastisdhara in its southern limb. Radio-activity is confined here to the phosphorite, chert and carbonaceous shale horizons, which carry phosphorite lenses. The phosphorite horizon varies in thickness from about 1 m. to 5 m. but radioactivity is restricted to the bottom most part of the formation measuring 0.3 m. to 1.5 m. in thickness. The chert, however, is not everywhere radioactive but radio-activity is confined to about 1/2 metre from the bottom of the

44

rock. The overlying black shales are feebly radioactive through-out the bed but carry higher radioactivity in portions in which phosphorite lenses occur. This is particularly true of the basal first one metre thick portion of the horizon which immediately lies above the main phosphorite bed.

OHAPTER ~ IV PETROGRAPHV

CHAPTER - IV

PETROGRAPHY

An attempt has been made to examine closely the petro-mineralogical characteristics of the phosphorites and their host rocks. A detailed thin section study of about 59 representa-tive sannples collected from mine workings as well as from their sections of the exposed outcrops at Maldeota and Durmala, was made, llie study has been useful not only for understanding the stages involved in mineralization but also for the collection of samples for geochemical studies.

(1) PHOSPHORITES t

Phosphorite usually contains a number of apatite like

phosphate minerals whxch have been reported in literature and

are designated by subspecies; pedolite, dahlite, francolite,

staffeiite, kurskite, grodnolite, wilkeite, ellestadite and

morinite. Due to such a wide mineralogical variations collo-

phane, a generic name of phosphorite, is often used in litera-

ture. The mineral composition of composite phosphorite samples

from Maldeota is given below j-

Mineral Wt.% Cellophane 45.50 Calcite 28.30 Quartz 7.9 Pyrite 5.6 Sericite-muscovite clay 3.4 Dolomite 1.2 Limonite 1.2

46

Collophane :

Cellophane happens to be the dominant mineral of phos-phorite of all varieties in this area having a composition 3Ca3(P04)2/ Ca(C03F20)H20 (see Kerr, 1959) i.e. carbonate hydroxyl fluorapatite, The colour of collophane ranges from greyish yellow to greenish black. It contains dot like inclusions without any preferred orientation; This may be due to dark coloured ferruginous material. It is microcrystalline in nature and isotropic to weakly anistrppic under crossed nicols (Plate-IV / Pig. 1 & 2).

Collophane occurs in the form of ovules, pellets, lenti-

cles, aggregated ovules, micro-aphanitic mass, superficial

ovulite, nodules and oolites.

The ovules are isolated bodies that are circular, ovoidal to elongated and widely scattered in the matrix. They range in diameter size from 4 microns to 89 microns but the average is 30 microns. The ovules consist of two distinct parts - the nucleus, and the envelope. The nucleus comprises of detrital silica and occasionally detrital carbonate. The envelope is essentially a structureless body. The margins of the ovules are regular,uniform and complete but often crenulated, which may be due to the replacement phenomenon (Plate- V , Fig. 2 ).

The pellets made up of dark grey to brownish grey iso-tropic collophane are enclosed in a carbonate matrix. The boundaries between these pellets and the groundmass are generally irregular though sharp with no visible replacement

47

(Plate-IV, relation^Pig.1 & 3). Inclusions of angular small elastic quartz grains are seen in these pellets.

The lenticles are elongated and continuous bodies. These

may be formed due to 1) elongated nature of ovular bodies and

ii) diagenetic stretching of collophane.

The ovular bodies usually coalesce together and give rise to aggregate ovules. The dark coloured varieties appear to be cemented by the light coloured ones (Plate- V, Pig, 2 ). Mlcroaphanitic mass is an amorphous looking collophane of matrix (Plate- VI, Pig. 1 ). Superficial ovulite has only one concentric layer around the carbonate nucleus. At places the concentric layer is discontinuous as a result of incomplete oolitization.

Nodules are in the shape of smaller ovoids which are conqposed of dark grey to greyish-brown anisotropic collophane embedded in a cementing material consisting of calcite (Plate-V, Fig. 2 ). Oolites have numerous concentric layers on the envelope having nucleus of carbonate (Plate- V, Pig, 1 ),

Texture t

The different textures encountered In the phosphatlc

material are described as ovulite, microaphanite, interstitial

collophane and massive collophane. Ovulite is composed of well

sorted ovoidal to spheroidal and elongated aggregate masses

possessing a modal diameter of 0.0002 m. to 2 mm, (Plate- v

Pig, 2 ), Mlcroaphanlte is composed of interlocking grains

48

having sutured arrangement and the modal diameter is less than

0.0002 mm. (Plate- VI, Fig. 1 ). The interstitial collophane is seen to occur in the

voids between calcite, quartz and feldspar grains. The collo-phane is isotropic and greenish in colour under crossed nicols (Plate- IV, Fig, 4 ). Massive collophane is dark greyish in colour and at places replaces the calcite. This variety is intensely intersected by numerous calcite veins (Plate- VI, Fig. 3 ).

Pahlite J

Dahlite (intermediate composition between hydroxyl-apatite) 3Ca3P205 Ca(0H)2 and Podolite BCaPjOs CaCO^ -Winchell) is anisotropic mineral and occurs in fibrous sub-radiating form surrounding the collophane (Plate- iv. Fig. 2 ) in nodular and oolitic varieites of phosphorites. Dahlite is colourless to pale-brown and has moderate relief, Hie birefrin-gence is weak and interference colours are bluish grey to white of first order. Dahlite is secondary mineral much like apatite having parallel extinction. Dahlite on the outer margins of collophane seems to have developed due to recrystallization and alteration of collophane,

Gangue Minerals s

The predominant gangue minerals, associated with phos-

phate minerals, include calcite, dolomite and quartz.

49

Calcite t

Calcite is a carbonate gangue mineral of Mussoorie phosphorites. It has the composition CaCO^. It is usually colourless to light grey in colour and occurs as coarse particles in the form of rhombohedral crystals v^ich are usually subhedral, occasionally anhedral and rarely euhedral. The are equidimensional and the polysynthetic twinning is parallel to the long as well as short diagonal of rhombs. TSie cirystals are tightly packed with slight sutured margins that could be the effect of solution pressure. It is recogn-ised by its light birefringence, perfect rhombohedral cleavage and marked change in relief on rotation of stage in plane polarised light. Calcite also occurs as micrite v^ich is a lime<rmud or its indurated equivalent either in crystalline or fine grained forms with diameter not exceeding 0.005 mm. in size. This interference colour is pearly grey to white of the high orders. The extinction is symmetrical to the cleavage traces. Calcite veins cutting across the phosphate matrix are seen in some of the thin sections (Plate- VI, Pig. 2 & 3).

Dolomite t

Dolomite is also a gangue mineral having the composition CaMg(C02)2« Dolomite also shows almost the same optical charac-teristics as that of calcite and varies in size from 0,38 to

50

1.76 mm. The crystals are usually subhedral to euhedral and twin lamellae parallel to short diagonal. It has rhombohedral cleavage, high birefringence (light white) and marked change, in relief on rotation of the stage in plane polarized light (Plate- V Fig.l & 3).

Quartz :

Quartz is the dominant gangue mineral of the phosphorite and is distributed in the entire rock mass with the major part in the matrix. The grains are angular to subrounded and range in size from 4 to 45 microns. Quartz vein is seen in phosphate matrix (Plate- VI, Pig. 1 ). It occurs in different forms associated with collophane, viz., i> as micro-crystalline silica showing a mosaic pattern with tortuous contact, secondary overgrowth of silica is also observed (Plate- V, Pig. 4 ); ii) as cryptocrystalline silica which is fine grained with wavy extinction? iii) as fibrous silica occurring in the form of microphanitic mass and is found usually in the matrix; and iv) as detrital quartz which occurs as inclusions in the matrix and secondary overgrowth is also noticed.

Ferrous Minerals :

Pyrite being Intimately associated with phosphate, is the most common iron mineral present in the unweathered rock phosphate. It occurs as subhexagonal lumps and tortuous streaks and ranges in size frcwi 10 microns to 89 microns, the

51

average being 25 microns. In polarized light, the colour is steel grey having high relief and is isotropic under crossed nicols. In reflected light, it is brass-yellow in colour, v

Limonite is another ferrous mineral which is present in minor amount. The colour of limonite in polarized light is light brown to orange and is isotropic in crossed nicols. Limonite is generally the alteration product of pyrite and is thus found more in the weathered san^les. Pyrite/limonite ratio could serve as an index of weathering.

Accessory Minerals :

The mosaic is constituted mainly of carbonate minerals together with minor amounts of feldspar, muscovite and sericite. These minerals occur as shapeless plates and elongated laths, sericite and muscovite are generally colourless to yellowish in colour (Plate- IV, Fig. 4 ).

Replacement s The mutual replacement of phosphate, carbonate

and silica has been noticed in these sediments. However, car-

bonate replacement is very common and discussed depending upon

the minerals involved.

The carbonate material penetrates into ovules of collo-phane and as the intensity of replacement increases it becomes thicker replacing the phosphate material completely (Plate- VII, Pig. 2 ). When intensity of replacement is low the phosphate material is partially replaced (Plate- VII, pig, 2 ).

52

In weathered rock phosphate feeble carbonate replacement of silica is observed possibly due to leaching out of carbonate by chemical weathering, thus a ratio of carbonate and silica in such rocks along with pyrite/limonite ratio could illustrate the extent of weathering.

The replacement is also observed in matrix. At places the phosphate pellets are embedded in a carbonate matrix which indi-cates a replacement of original phosphate by carbonate or intra-basinal transport of earlier formed phosphate pellets and their redeposition contemporaneous with the precipitation of chiefly carbonate mud (Plate- IV, Pig. 1 & 3).

(2) HOST ROCKS $

The associated rocks of Mussoorie phosphorites were also studied for detailed petromineralogical characters. The thin sections of all the lithological units belonging to the different blocks were investigated with a view to note the variations in the nature of the rocks belonging to these blocks.

Cherty Limestone :

It is dark grey in colour. The rock is close grained, compact and fine textured in nature. The fine grained and compact calcareous material is associated with chert. The detrital grains of quartz varying between medium to fine in size exhibit the considerable rounding. The textural features of this rock type remain almost the same in all the blocks.

53

Calcite is colourless. The grains of calcite vary between fine to coarse aggregates. The grains are mostly anheclral(Plate-VlI Fig.4).The cryptocrystalline variety of silica occurs in the form of chert. The fine grains of quartz are interlocked in the calcareous material. The quartz grains are anhedral. Quartz also occurs as secondary veins and appears to traverse the rock.

Limonite occurs as a brown colour cement around the detrital grains of quartz.

Dolomitic Limestone :

It is grey to bluish grey^ massive, compacted rock with coarse grains of calcite and dolomite, which are anhedral in shape and constitute the bulk of these rocks (Plate-VIII,Fig.1).

Black Shale with Siltstone Bands t

Shale is black in colour. It is indurated and banded sediment composed of finely divided mineral matter of clay grade and with varied composition. It is very close textured rock. The shale is alternated with siltstone bands which are also fine grained.

Quartz is fine grained colourless mineral. It constitutes both shale and siltstone. The opaque cubes of pyrite constitute the bulk of heavy residual material, which is the characteristic feature of this rock (Plate-vm,PIG.2 S 3). LOW calcite, illite and other clay minerals, feldspar and sericite have been identi-fied in these carbonaceous shales. Phosphatic nodules occur in the carbonaceous shales at places.

OMAPTEK - V V

GEOCHEMISTRV OF

TME IVIAJOR EEEIVIENTS

CHAPTER - V

GECX:HEMISTRY OF THE MAJOR ELEMENTS

GENER/OI STATEMENT S

According to Subramanian (1980), the geochemistry of sedimentary phosphates centres around the geochemical behaviour of apatite in marine environment. Geochemistry controls various mechanisms that could account for the composition and variability of phosphate minerals. These mechanisms are selective precipita-tion, dissolution, exchange reaction with animal shells, sorption by organic and inorganic compounds in the marine environment and isomorphous substitution of a number of cations and anions.

Goldschmidt and his co-workers (1958) demonstrated that a knowledge of ionic radii and of ionic charges could be used for predicting not only into which minerals any element could enter but also allowed the prediction of the sequence of crystallization in isomorphous mixtures containing particles of different size and valency. The understanding of the distribution of elements in the sedimentary sequence was greatly facilitated by the introduction of the 'ionic potential' into geochemical discussions as this quotient of ionic charge and radius gave a general clue to the distribution of elements in the process of weathering and of sediment foirmation.

The variation in major and trace elements abundance was attributed to a change in environmental condition of deposition (see Mahadevan, 1985). The concentration and the kind of element adsorbed or entering into a crystal structure depend on a number of factors such as pH, Eh, nature and structure of the adsorbant.

55

availability and concentration of ions (see Krauskopf, 1967), rate of nodular growth, nature and rate of sedimentation and various other parameters (see Cronan, 1969; Ghosh, 1975; Glasly, 1977 and Roy, 1981).

According to Salgal and Banerjee (1987), the factors which might be held responsible for the marked qualitative and quanti-tative differences in the major and trace elements in different types of proterozolc phosphorite deposits under study are -1. The basic chemistry of basinal waters.

2. The role of biological activity Influencing the distri-bution, fixation and sequence of precipitation.

3. Capability of individual element to enter into apatite lattice.

4. Behaviour of elements during post-deposltional alterations. 5. Changes due to secondary processes like weathering and

leaching.

The study carried out by the authors (1987) indicates that within the interpreted and Inferred basinal conditions, as stated above, the chemistry of basinal waters and subsequently, post-deposltional alterations played significant roles in producing different kinds of phosphorite in different proterozolc basins. Biological activities influenced the distribution of elements in the basinal waters and also controlled the sequence of their precipitation. The original conposition of sedimentational water was of prime Importance. Conceding the facts that some of the trace elements and some of the major mobile elements were either Introduced into the apatltlc mud or left the Indurated apatite, the concentration or depletion of major and trace elements depended primarily on such factors like their mobility with

56

respect to apatite, associated assemblages, types and amount of weathering and effects of secondary process. Various major and trace elements, which combined to form phosphorite of a particular compositions, changed their characters in due course of geological history. In spite of such addition and substractions of primary elements, they left some traces of their presence in the original sediments. They have been used for interpreting various palaeo-environmental conditions (see Saigal and Banerjee, 1987).

About fifty-nine carefully selected samples representing

the phosphorites including nineteen samples of the host rocks

viz., limestone, chert and shale were collected from the study

area. The rock and ore samples were analysed for the quantitative

determination of their major oxides, viz.,

FeO, Ti02, MnO, CaO, MgO, K2O, H20''' and CO2 in weight per cent. The analytical data, so obtained, are presented in Tables-IV, V and VI.

For each lithological unit, minimum, maximum and average content were determined and the data are presented in Table-III. The relative abundance and concentration trends of certain major oxides in Maldeota phosphorites and associated host rocks were plotted in Figures 5 and 6 respectively. The statistical treat-ment of the geochemical data of Maldeota and Durmala phosphorites has been carried out in order to determine the range of variation and frequency per cent distribution of major oxides which is given in Figure-7. The mode, unimodal positively skewed, unimodal negatively skewed and bimodal nature of distribution has been identified and described. The relative distribution of the major oxides in limestone, chert and shale is shown by bar graphs in Pigure-8.

57

MAJOR OXIDES :

The abundance and distribution of the major oxides in the different rocks and their frequency per cent distribution in Maldeota and Durmala phosphorite deposits around Hussoorie is given as follows

Silicon Oxide (SiO^) :

SiOj being a lithophile element has an affinity for the silicate phase (see Mason, 1966). A comparison of the chemical composition of the average central California phosphorites with that of the global average phosphorites reveals that the former are highly enriched in SiO^ (see Kolodony, 1981). The highest P2O5 content (21.47%) in S. Africa is found in a few samples, which significantly contains the lowest SiOg and K2O (i.e. quartz and glauconite) values (see Parker, 1975 and Birch, 1980).

Silica is largely present in the form of chert that was precipitated as a coherent gel. The average content of Si02 in sea water is 3 ppm. The quantitative variation trends of Si02 in Maldeota and Durmala phosphorites are from 8.04% to 14.8% and 7.02% to 9.83% respectively. The abundance of SIO2 in limestone, chert and shale ranges from 12.30% to 16.58%, 63.75% to 70.73% and 32.17% to 52.19% respectively.

The bar graphs (Fig. 7) that represent frequency per cent distribution, show bimodal nature of SiOg in the phosphorite deposits of the two localities. The maxima are at 5% to 15% classes in Maldeota and at 5% to 10% in Maldeota phosphorite, the crude mode is between 7.5% and 12.5% whereas in Durmala the typical mode varies between 7.5% and 17.5%.

o CM Q. O

7

i

/ f

OD f I

>

\ [ o «D

J-10 -a-ro -3 -

m

fA IR

CM CNJ <N

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UD CNJ CD

•/

irt O

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J-IT) J-

cn U3 m J-rr)

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C7>

CO

10 cn

& 2 aj I

o (d O o tn 2 o OJ fa

CO O IN 0) fa

CM

<N O •H tn

58

U) CJ •a •H X 0 !-i 0 io E C •H (d i-i 0) 0 • in 0) 0 •w •w VH (U 0 u x; c a (d m •d c 0 X! a, X) (0 (0 (0 (0 -M 0 0) Q) > -d •H tH -u (0 (0 rH Q) 1-1 c •H O) C •H 0 & u 0 x: in V c (B j:: a in (0 0 M CM 0 Oi in

a M fa

59

According to Krumbein and Garrels (1952) the solubility of silica depends on the pH of the solution. The higher the pH, the more the silica goes Into solution. If the pH decreases, for instance by the addition of carbon dioxide, silica precipitates. This process may sometimes lead to a notable concentration of silica.

Some veins and the cementing materials of these phospho-rites are made of silica. The low concentration of silica in the phosphorites may be due to continuous leaching of the oi^s by ground water. The presence of carbonate in fluor-carbonate apatite phase may be responsible for the precipitation of silica in the very fine grained quartz and the siliceous cement. The associa-tion of silica in these phosphorites may be partly due to the presence of detrltal quartz and partly to secondary silica as chemical precipitates.

Alumina (AI2O3) s

According to Goldschmidt (1937), aluminium is a litho-phlle element and during weathering it is liberated from the pre-existing minerals and transported as hydrolysates and only very little is found as precipitates (see Mason, 1966). Oxidates, evaporates and sea water carbonate rocks constitute about 2.5% AI2O2 (see Green, 1959). Aluminium generally occurs as suspensates as well as in sediments. It mostly occurs in low temperature to humid areas (see Mason, 1966 and Birch, 1980).

Mason (1958) on the other hand opined that the accumula-tion of the products of chemical break down of alumino-sllicates gives rise to a mud consisting essentially of the clay minerals.

60

that are rich In alumina and also potassium by absorption. The abundance of clay size materials in the non-pelletal phosphorites, particularly in the collophane mudstones, results in Ai202 content and much steeper regression line (see Cook, 1972),

Major element analysis of the Central California continen-tal margin phosphorites indicates that they are grossly similar to the average phosphorite (Kolodny, 1981). Samples collected from the offshore region of Pescadero contain highest percentage of P2O5 and CaO and the lowest amounts of SiOj and AI2O3. These results support mineralogical and petrographic data v^ich suggest that the Pescadero phosphorites are the purest of all Central Californian margin sanples, this may be result of concentrations via reworking. The relatively high Si02 and AI2O2 values for point Sur and Twin Knoll phosphorite suggests that they have been more diluted by detrital quartz and alumino silicates as well as skeletal opal (see Mullins and Resch, 1985) .

The quantitative variation trends observed in AljO^ from the Maldeota and Durmala phosphorites are from 0,89% to 1.8%, 0.03% to 1.62% respectively. The abundance of alumina recorded from limestone, chert and shale varies from 2.10% to 2.35%, 1.58% to 2.0% and 1.15% to 1.83% respectively.

The frequency per cent distribution shows bimodal nature of AI2O2 in both the phosphorite deposits. The maxima are at 0.5% to 1.5% classes in Maldeota, whereas at 0% to 0,5% and 1.5% to 2.0% classes in Durmala. The crude mode of AI2O2 in Maldeota is between 0.75% and 1.25% while in Durmala it is between 0.25% and 1.75%.

The ionic potential of aluminium being about 6, it makes the metal an important constituent of hydrolysates. Aluminium

in o cx^ d-

T

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cf

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61

OC LU X o

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to K (A 0 01 L U Q

62

remains In solution in both acid and alkaline conditions, the precipitation of A K O H ) ^ on the other hand is favoured by the neutral solution.

The low concentration of alumina may be due to lesser quantity of clay minerals and high association of ferru-ginous minerals like magnetite and liraonite that constitute the cementing material of the phosphatic rocks.

The presence of AlgO^ in the phosphatic rocks indicates the humid to low temperate climatic conditions in the study area at the time of precipitation and phosphatization of these sediments

Ferric and Ferrous Oxides (Fe^O^ and FeO) :

Goldschmidt (1937) placed iron into the siderophile group, but it also resembles to the elements of chalcophile group.

According to Banerjee, et al. (1982), the primary associa-tion of iron with phosphate in Hirapur phosphorites is not established with certainty. The ferruginous content of the rocks, which gives them colouring, is probably due to the oxidation of iron content of the detritus mainly at the time of transportation and sedimentation, but the fine grained hematite rich pockets may be chemogenic in origin.

Among all the Proterozoic deposits of India, the Bijawar (M.P.) and Cumbum (A.P.) deposits contain the highest quantities of Fe202. The Jhabua (M.P.) and Matoon, Jhamarkotra (Rajasthan) and Pithoragarh (U.P.) phosphorite contain comparatively low percentages of Pe202. Although the phosphorites of Bijawar and Cumbum are markedly ferruginous, the primary association of iron with phosphorites could not be established with certainty because no Iron phosphate mineral Is associated with these rocks.

63

The baslnal Iron formations suggest that the environment of phosphate and Ironstone deposition have many factors in common. Each displays two contrasting fades - a cratonic or platform fades (Nodular phosphorite with glauconite and the oolitic ironstone fades) and a geosynclinal or basinal fades (the bedded phosphates and the bedded or non-ooUtic ironstones). The basinal fades, that seem to require a somewhat anaerobic milieu are with slightly lower than normal pH in which clastic sedimen-

A.

tation is exceedingly show or inhibited. The platform fades is aerobic,and somewhat more turbulent and is apt to be arenaceous although clastic accumulation is small. If these conditions are maintained for long, circulation of oceanic waters may supply all the needed phosphorus or iron. It would also supply the needed silica to produce the bedded cherts which are characteristic of both the Precambrian iorn formation and the bone-phosphorites.

According to Parker (1975) and Mullins and Rasch (1985), inspection of analysis shows that generally KjO, Fe^O^, FeO and MgO follow each other and these trends lie in well with glauco-nite trends observed in thin section. The marginally higher iron content in the pellets may be of residual origin vrtiereby Fes was oxidised.

Experimental work by Casteno and Garrels (1950) and Parker (1975) and their observations show that stability of the iron bearing minerals is determined by the oxidation-reduction potential. At the lowest potential iron sulphide will form, and at a slightly higher potential ferrous carbonate is preci-pitated, Under fully oxidizing conditions the ferric hydroxides are found. The immediate causes of precipitation in the basin

64

are not clear (Mahabaleshwar, 1985). According to Trendell (1983), precipitation is caused by the oxidation of the ferrous iron in the basin water by oxygen (Mason, 1966),

The variation trends of Maldeota phos-phorites are from 2,19% to 4,6% and 0.44% to 1.43% respectively whereas in Durmala phosphorites F®2®3 range from 3,12% to 5.0% and 1.14% to 2,19% respectively. The abundance of P®2®3 and FeO in limestone ranges from 3,84% to 4,32% and 0,2 3% to 0.96% respectively. In chert, ^6202 varies from 3,68% to 4,11% and FeO ranges from 0,35% to 1.72%, The abundance of FeO in shale range from 6.02% to 8.03% and 1.11% to 2.59% respectively.

The study of frequency per cent histograms indicate unimoda] positively skewed distribution of Maldeota phosphorites and bimodal nature of ^^2^3 unimodal negatively skewed distribution of FeO in Durmala phosphorites. The maxima are at 2% to 4% classes of Fe2°3 ^^^ ® classes of FeO in Maldeota phosphorites while 2% to 6% classes of ^©2^3 ^ 3% classes of FeO in Durmala phosphorites. The crude modes of

case of Maldeota phosphorites varies from 3% to 9% and 1% to 3% respectively. The typical modes of FeO in Durmala phosphorites are at 3% to 5% and 1.5% to 2.5% respec-tively.

Generally, iron is precipitated as ferric hydroxide alongwith the formation of argillaceous sediments. The higher concentration of ^62^3 some samples may be due to secondary iron oxide coatings.

65

50 1-z Ul 40 u 0: UJ a. 30

(5 z UJ 20

i UJ oe u. 10

10 15 2025 Si02V.

50

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20

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50 "T" 50

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30 ] -• 30

20 • 20

1 0 :: 10

7 1 n

05 10 16 20 2.5 AI2O3V.

55 50

3 0

20

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0

JI!I Mgo%

0 12 16 20 2428 32

P2 05%

0 2 t 6 8 10 FejOaV. 100

80

60

ttO 20

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100

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MB 0 020J<060e 10 Na2 0v.

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100

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50

40

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50

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0 Pea 03% 0 1 2 3

Fe 0 %

100

80

60

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50

40

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0 0 005 01045 MnoVo

50

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40 40

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NOjO % K2 0% HaOv. 8 10 12 1416 C02%

FIG.7. BAROIAGRAM SHOWING VARIATION OF MAJOR OXIDES AND THEIR FREQUENCY PERCENT DISTRIBUTION IN MALDEOTA ( §) AND DURMALACOJ PHOSPHORITE DEPOSITS

100

BO

60 CM

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66

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SAMPLE NOS. LIMESTONP-CHERTJ > SHALE '

20

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8

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8

6

in O cC

2

0

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0 7 5

z 0 2 5

0

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.SAMPLE NOS. LIMESTONE^CHERT-" '—SHALE

RG-8. BAR DIAGRAM SHOWING R E U T I V E DISTRIBUTION OF MAJOR OXIDES IN THE HOST ROCKS OF MALDEQTA A N D D U R M A U PHOSPHORITE D E P O S I T S .

67

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ur

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68

Titanium Oxide (TIO3) :

Being a strongly lithophile element Ti02 is less mobile and possesses strong resistance to chemical weathering as compared to the others (see Mason, 1966). Hawkes and Webb (1962) also categorized titanium as a very immobile element just like Fe and A1,

The depleted elements in phosphorites {B, Co, Ga, Hg, Li, Sn, Ti and Zr) fall mainly in two categories. Some occur in a relatively stably and the insoluble minerals like Ga in clays, Zr in Ziroon, Ti in ilmenite and rutile are therefore richer in highly detrital shales and largely in chemogenic phosphates (see Altschuler, 1980). The elements Al, K, Ti and Zr are consistantly of clay groups and may be due to substitution and adsorbed into the clay surfaces (see Howard and Hough, 1979; Rasmy and Easily, 1983). The constituents such as SiO^, Al203» Ti02, NajO and K2O are associated with silicates and other detrital minerals. Some magnesium, alkalies as well as silica, sulphur (SO^) are known to be incorporated in phosphate lattices (see McConnell, 1973).

The quantitative variation trends of Ti02 in Maldeota and Durmala phosphorites are from 0.33% to 0.87% and 0.80% to 0,92% respectively. The abundance of TIO2 in limestone, chert and shale ranges from 0.53% to 1.24%, 1.41% to 2.37% and 0.38% to 0.68% respectively.

The frequency per cent distribution shows unimodal positive and unimodal symmetrically skewed nature of Ti02 in Maldeota and Durmala phosphorites respectively. The maxima are at 0.5% to 1.0% in Maldeota and Durmala phosphorites. The crude mode

69

varies from 0.25% to 0,75% in Maldeota and Durmala phosphorites. Much of the titanium is found in the clay fractions of

the hydrolysate sediments. Practically/ no titanium enters ocean water as a solute, owing to the prohibitive ionic potential. Titanium is thus not found in evaporate sediments. The low content of Ti02 In phosphori tes of the study area Indicates its lesser mobility and adsorption on the surface of clay, iron and phosphate bearxng minerals. The low concentration may also be due to leaching of ores and a minor content might have been adsorbed in the crystal lattices of apatite.

Manganese Oxide (MnO) s

Manganese oxide being highly mobile unlike titanium and aluminium (Mason, 1966). The low MnO values in the phosphorites of Hirapur phosphorites (M.P.) was due to leaching and secondary nature of the deposits (Banerjee, et al.# 1982; Saigal and Banerjee 1987). It is possible that Mn is either present as adsorbed ion on the surface of apatite or present in some other discrete mineral species of similar paragenesis not identified in the present investigation (Banerjee and Saigal, 1988).

MnO in Maldeota and Durmala phosphorites is very low and varies from 0.02% to 0.06% and 0.03% to 0.06% respectively. The abundance of MnO in limestone, chert and shale ranges from 0.05% to 1.29%, 0.02% to 0.05% and 0.01% to 0.06% respectively.

The frequency per cent distribution of MnO in Maldeota and Durmala phosphorites show unimodal positively skewed nature. The maxima are at 0 to 0.1% class in the case of Maldeota and at 0 to 0.5% class in Durmala. The crude mode in Maldeota and Durmala varies from 0.05% to 0.15% and 0.02% to 0.07% respectively.

70

Manganese, like iron is enriched in hydrolyzate residue formed by lateritic weathering and is concentrated mostly in the oxidate sediments. It is generally absent in sediments formed as a result of solution or reprecipitation.

The low concentration of manganese in Mussoorie phospho-rites indicates shallow marine conditions of the sedimentary basin. The MnO may partly be emplaced in the apatite structure and/as adsorbed on the mineral surfaces of clay* phosphate and iron bearing minerals.

Lime and Magnesia (CaO and MgO) :

Calcium and magnesium fall in the lithophile group (Goldschmidt, 1923). They have high mobility like Na and K (Mason, 1966) .

Phosphate of divalent metals with additional anions (OH, P, 0 and sometimes Co) or in the form of acid phosphates are most stable, also when the compounds contain relatively large cations (Ca, Sr and sometimes Pb)(see Batekhtin, 1959). Calcium is the only one of the common metals in geologic environments that forms such structures, calcium phosphate in its many varieties is by far the most abundant inorganic compounds of phosphorus. The inorganic geochemistry of phosphorus is largely a study of calcium-phosphate, just as inorganic geochemistry of carbon is largely a study of calcium carbonate (see Krauskopf, 1967).

The solubility of Ca-phosphate is highly dependent on pH, the mineral and dissolved chemical species involved and surface effects. Chemical analysis of phosphorite shows the

71

material to be mainly hydrous tricalcium-phosphate with varying amounts of calcium carbonates and fluorides. Because of admixture of non-phosphatic materials, such as calcite* dolomite and chalcedony as cement and also of detrital contaminates such as quartz and clay, the content are highly variable (see Pettijohn, 1984).

It has been reported from almost all phosphorite deposits of the world that calcium is a well known and most significant element found in the crystal lattices of apatite and its chemical composition,

+ 2

The uptake of Mg by clay minerals is proposed to explain Mg"*" depletions in marine interstitial waters (see Sholkovitz, 1973). According to Martin and Harris (1970) and Birch (1980), Mullins and Risch (1985), the higher concentration of MgO in sea waters, however, may inhibit the precipitation. However, Burnett (1977) found on the Peru-Chile shelf that only the sediments which contained dolomite, chlorite or sepiolite contained detectable apatite. He believes that the diagenetic reactions +2

that take up Mg ions would be favourable for the precipitation of apatite. MgO shows moderate enrichment possibly owing to goethite scavenger activity in these samples (see Parker and Siesar, 1972).

Magnesium in recent CaCO^ sediments varies between 3 and 5 times that of MgCO^ by weight percentage (see Chav, 1954). The magnesium content increases with the increase of age ( see Chillingar, 1956 and Ronov, 1959 ). MgO is is iithophile and this is borne out by its presence in ferro-magnesium silicates in all the stony and stony-iron meteorites (Mason, 1966). Bremner (1975) pointed out that direct precipitatio

72

of apatite is inhibited in the muds by their relatively high MgO content and low temperature (11°C).

It is well known that magnesium has a close chemical affinity with calcium in the geological environment. The apatite being a calcium-phosphate mineral with additional anions like F, COj* OH, CI and sometimes 0 indicates the association of magnesium with this mineral.

The variation trends of CaO and MgO in Maldeota phos-phorites are from 40.28% to 43.57% and 2.19% to 4.27% respec-tively, whereas in Durmala phosphorites they vary from 39.17% to 44.00% and 2.34% to 6.24% respectively. CaO in limestone, chert and shale ranges from 37.27% to 41.87%, 11.96% to 13.48%, and 12.62% to 42.30% whereas MgO in the same rocks ranges from 4.61% to 7.29%, 0.38% to 2.08% and 2.48% to 8.12% respectively.

The frequency per cent distribution of CaO and MgO in Maldeota phosphorites show unimodal symmetrically skewed nature, whereas CaO and MgO in Durmala phosphorites show unimodal negative and unimodal positive nature of distribution respec-tively. The maxima are at 40% to 45% class of CaO and 2% to 4% class of MgO in the case of Maldeota and at 40% to 45% class of CaO and 0 to 4% class of MgO in the case of Durmala. The crude mode of CaO and MgO in Maldeota varies from 42.5% to 47.5% and 3% to 5% respectively, v/hereas in Durmala the mode of CaO is 37.5% to 42.5% and that of MgO is 2% to 6%.

Calcium is precipitated as calcium carbonate either by purely inorganic process or by the action of organisms. Lime-stone can be partly or wholly converted to dolomite by the metasomatic action of magnesium rich solutions and magnesium is thereby precipitated and concentrated together with calcium (pettijoha,1984).

73

The magnesium content is a function of both the magnesium content of skeletal debris in the limestone and of post-depositional additions. Normally magnesium is added through the dolomitization process, although some ancient rocks contain less magnesium than that demanded by organic debris, suggesting that the magnesium released by the break down of high magnesium calcite has been lost (see Chav, 1954 b).

The occurrence of magnesium may be due to ionic substi-+ 2 +2

tution of Mg by Ca in the apatite during marine conditions of the basin. The low concentration of Mg may be due to adsorp-tion by fine grained quartz and clay minerals and in the huge masses of iron.

Phosphorus Penta Oxide •

Goldschmidt (1937) classified phosphorus as a sidero-

phile element. The original source of phosphorus that takes

part in the exogenic processes is the content of phosphate

minerals in igneous rocks of which fluorapatite is the principal

mineral. To some extent phosphorus is also derived from other

phosphates, for example monazite and xenotime. Owing to the

low solubility of fluorapatite some phosphorus remains

insoluble and becomes re-deposited in the residual sediments.

Another part of the phosphorus passes into solution as alkali

phosphates and dissolved or colloidal calcium phosphate in

waters containing carbon dioxide and in swamp water rich in

organic matter. Some of this phosphorus is reprecipitated as

calcium phosphate, and the bulk of it is carried to the sea.

74

Thus the primary source of phosphorus in sea water is the continental run-off. The inorganic extraction of phosphorus from sea water is derived from the precipitation of carbonate fluorapatite (McClellan and Lehr, 1969; McConnell, 1965, 1973 a) and probably by adsorption processes (Gulbrandsen and Roberson, 1973). The inorganic extraction is mainly controlled by the solubility of CO^-P apatite in sea water. According to Roberson (1966), sea water is generally supersaturated with respect to phosphate. Sillen (1961) deduced from thermodynamic considera-tion that the deep sea water with an average of 10"^ to IC^'^M phosphate is in equilibrium with OH-apatite. Kramer (1964) has computed that deep ocean water is probably near equilibrium with respect to OH and CO^-F apatite, whereas shallower coastal waters are probably supersaturated.

Brooks, et al. (1968) investigated that there is a distinct increase of PO^ with depth. This is attributed by McConnell (1965), Gulbrandsen and Cremer (1970) mainly to bacterial activity and partly to release of phosphorus from metal phosphates.

If bottom water from the ocean, saturated with phosphate, is transported by the bottom currents and for one reason

or other ascends to a higher level with increasing pH and decreasing CO2 - pressure precipitation of phosphate may occur in restricted basins.

According to Sheldon (1980), increase of temperature and decrease of pressure tend to change the sea water chemistry towards saturation with respect to apatite.

75

According to Jitts (1959), it is quite likely that

major portion of the phosphate associated with the acid

soluble fractions is tied up with the sedimentation in the

adsorbed state. The fact that i) the waters are characterised

by high concentration of phosphate, ii) large quantities of

finer minerals are kept in suspension as evidenced by the

turbidity of the waters and iii) silts are capable of adsorbing

lesser quantities of phosphate and that in natural state they

seldom approach saturation with phosphate.

Phosphate associated with the acid soluble fraction of

the sediments in association with the carbonate phasa and in

adsorbed state can occur in at least with two kinds of asso-

ciations, i) in areas of high organic productivity associated

with reducing conditions during their formations and ii) in

areas which do not have a high organic productivity and

associated with oxidizing conditions in the environment

(see Paropkari, et al., 1981).

According to McArthur, 1978 and Reedman, 1984, the

phosphate content varies with particle size and there is a

gradual increase in phosphate grade with depth. This is

partly due to lateritlzation processes near the surface which

have increased the iron content at the expanse of the phosphate

content but it is mainly due to partial solution of apatite

in the shallower zone and reprecipitation as secondary apatite

(Staffelite) at deeper levels.

The P2O5 content of Matoon phosphorite deposits,

district Udaipur (Rajasthan) is as high as 36% (Banerjee,

1982), In the Jaiselmer phosphorite deposits (Rajasthan)

76

of Mesozoic age the Pg^S content varies from 5 to 15% (Viqar, 1981). Along the continental margins phosphorites contain P2O5 several to 33%.

With progressive leaching/weathering of the carbonate fraction, the grade of ore in terms of increases (Chaudhuri, et al., 1980; Sant and Sharma, 1984),

In several regions of the world, massive sediments are reported to contain more than 1000 ppm phosphorus (Subramanian, 1984). Riggs (1980) reported that sediments of S.E. coast of U.S.A. contains as high as 40% P2O5 (about 17000 ppm) but these are, as stated by him, likely to be detrital continental apatitic grains derived from the earlier phosphate deposits (see Hashmi, et al., 1978 and Subramanian, 1984).

The quantitative variation trends of PjO^in Maldeota and Durmala phosphorites are from 15.43% to 30.34% and 25.68% to 32.45%. The abundance of P2O5 found in limestone, chert and shale is from 0.60% to 2.52%, 0.14% to 1.85% and 1.47% to 4.64% respectively.

The frequency per cent distribution of P2O5 in Maldeota and Durmala phosphorites shows unimodal symmetrical nature of distribution. The maxima are at 16% to 2 0% class in the case of Maldeota and at 20% to 30% class in the case of Durmala. The crude mode of P2O5 ^^ Maldeota and Durmala phosphorites varies from 18% to 26% and 25% to 35% respectively.

soda and Potash (Na^O and K^O) :

Sodium and potassium are strongly lithophile elements (see Goldschmidt, 1937). Wedepohl (1970) discussed their

77

chemical characters and mentioned that^^ftey^ctl^ffer from many other groups of elements especially in their mobility.

Sodium content is fairly high in Hirapur phosphorites (M.P.) compared to any known phosphorite types from India (see Banerjee, et al.# 1982). Sodium and sulphate concentrations in the pelletal phosphorite indicate high palaeosalinity (see Smirnov, et al., 1962). Each elemental association reflects a grouping of elements, viz., structurally substituted in major mineral apatite, adsorbed on the mineral surface or existing as discrete mineral derived from apatite during weathering. Most elements actually exist in more than one association (see McArthur, 1978; Banerjee, 1982; Banerjee, et al., 1984 and Saigal and Banerjee, 1987).

The alkalinity may have been locally raised due to the deconposition of organic matter and formation of ammonia in semi restricted environment (Murray and Irvin, 1889).

Low Na and K content in Jhamarkotra, Matoon, Karwaria deposits, in contrast to higher values of these elements in Neemach Mata deposits, indicate differences in the salinity conditions during the time of their formation which, in turn, gives scope to infer a more restricted lagoonal to supra-tidal conditions in the Neemach Mata area than the cortpara-tively open lagoons and shoals in other phosphorite beaing areas of Udaipur (see Saigal and Banerjee, 1987).

Heterogenous but higher than normal contents of alkalies observed In many Proterozoic phosphorites could be explained by involving one or more of the following postulates, i) higher salinity conditions during the formations of these phosphorites

78

indicating supratidal concentrations, ii) high carbonate substitution for phosphate in apatite lattice, iii) likely contamination by clay, mica and feldspar, iv> occurrence of alkalies in some discrete phase independent of apatite and (v) insignificant weathering effects (see Saigal and Banerjee, 1987).

The presence of high amounts of alkalies in the Proterozoic phosphorites of India, seems to have been contributed by clay minerals which are common in the phos-phorites (Saigal and Banerjee, 1987). The Na, Sr, CO3 and SO^ contents of carbonate-fluorapatite may be used as a crude •weathering index* for phosphates. Unweathered Moroccan carbonate fluorapatite contains about 1.6% NajO; 2.6% SO^; 8.3% COj and 0.23% Sr. Concentrations may be characteristic of the original composition of apatite in other deposits (Gulbrandsen, 1960, 1970; Bliskovski, et al., 1967; Lehr, et al., 1967; Tooms, et al., 1969 and McArthur, 1978 b). The constituents such as Si02, Al203# ^iOjr Na20 and K2O are associated with silicate and other detrital minerals (see McConnell, 1973).

The higher concentrations of lithophile elements (Al, Mg, K) in the rocks is due to the presence of terrigenous minerals (feldspars and clay minerals) in the sediments prior to lithification (McConnell, 1973; Birch, 1980 and Mullins and Rasch, 1985).

The variation trends of Na20 and K2O in Maldeota and Durmala phosphorites are from 0.22% to 0.31%, 0.01% to 0.06% and 0.31% to 0.41% respectively. The abundance of Na20 and

79

K2O in limestone, chert and shale ranges from 0.16% to 0,71%, 0.05% to 0.11% , 0.16% to 0.22%, 0.02% to 0.08% and 0.30% to 0.88%, 0.01% to 0.09% respectively.

The frequency per cent distribution of NajO and K2O in Maldeota shows unimodal positively skewed nature whereas in Durmala it shows unimodal symmetrical and unimodal positively skewed nature respectively. The maxima of NajO and K2O in Maldeota are at 0.2% to 0.4% and 0 to 0.05% class and the same in Durmala are at 0.2% to 0.4% and 0.01% to 0.03% respectively. The curde mode of Na20 in Maldeota and Durmala varies from 0.3% to 0.5% and that of K2O in both the deposits varies from 0,02% to 0.07% and 0.02% to 0.04% respectively.

The low content of alkalies in these phosphorites may be due to poor association of detrital constituents and high Fe202 concentration.

Loss on Ignition (H O"*") :

Water content of the samples of phosphorites is determined as ignition loss.

The variation trends of £ 20* in Maldeota and Durmala phosphorites are from 1.0% to 2.28%, and 1.05% to 1.13% respectively. The abundance of HgO" in limestone, chert and shale ranges from 0.69% to 0.86%, 0,41% to 0.64% and 1,06% to 2,32% respectively.

The frequency per cent distribution of H2O'*" in Maldeota and Durmala shows unimodal positively skewed nature. The maxima are from 1% to 2% in Maldeota and 1% to 1.3% class in Durmala.

80

The crude mode of H2O"'" varies from 1.5% to 2.5% and 1.15% to 1.45% in Maldeota and Durmala phosphorites respectively.

The low content of HjO" in these sediments indicated contenporary phosphatization of the Tal sediments during warm and arid climatic conditions.

Carbon dioxide (CO^) s

The average 'apatite* CO2 content of phosphatised limestone was 5.7% which is high relative to the 'apatite* COg content (1.8%) determined for the Phosphoria Formation of the Western United States (see Gulbrandsen, 1970). The influence of CO2 is so often mentioned in the leaching of limestone and phosphate rocks. The CO2 has very little effect on the amount of phosphorus taken into solution, whether from lean phosphatic limestones or from apatite. On the other hand, the amount of lime leached is greatly increased by the passage of CO2 through liquid. This means that the concentration of phosphate is more likely to be in the residual surface bed in case CQ^ is abundant than in case it is sparing by present (see Grahm, 1926).

In carbonate fluorapatites, 4% CO2 is considered to be the normal concentration. Consequently the low CO2 values of the Hirapur-Bassia apatites (M.P.) is due to the process of decarbonation caused by the dissolution and reprecipitation There is a general tendency for the depletion of CO2 in these apatites leading to formation of fluorapatite. This COj is an indicator of hidden weathering in the rocks (see Banerjee, et al., 1982).

81

Authigenically derived phosphatlc rock from Seldana Bay and the S. African shelf contain an average of 2.6% and 1.8% CO2 respectively. These values are markedly different from the CO2 content of the apatite phase in phosphorite rocks of the replacement type which has been determined by both Parker (1971) and Birch (1975) to be 5.5% (range 4.8 - 5 . 1 % ) .

It would appear that the highest COj values are associated with phosphorites fomed by replacement of calcareous sediments, whereas low CO2 values are related to authigenic varieties which originated in carbonate poor sediments of Auglhas bank of S. Africa and west coast of S. Africa.

CO2 in Maldeota and Durmala phosphorites varies from 9.98% to 12.87% and 8.83% to 12.76% respectively.

CO2 in limestone, chert and shale ranges from 21.02% to 25.04%, 4.10% to 5.46% and 8.17% to 9.77% respectively.

The frequency per cent distribution of CO2 shows bimodal nature both in Maldeota and Durmala. The maxima are at 12% to 16% class in Maldeota and 10% to 14% in Durmala. The crude mode of CO2 varies from 13% to 15% in Maldeota and 9% to 13% in Durmala phosphorites.

MUTUAL RELATIONSHIP OF SIGNIFICANT OXIDES :

In order to ascertain the physico-chemical nature of the basin of deposition, it is desirable to find out the relationship between the various elements. In the present study, an attempt has been made to determine the correlation coefficient (Tables-VII & VLLI) and to plot the concentration

82

among the significant major oxides {Figs. 10, 11, 12, 13 and 14) in an attempt to find out the relationship of P2®5 with other major constituents and also inter-relationship among the major constituents.

Relationship of Major Oxides with ^^^ ^^^ '

The author has tried to find out the behaviour of various chemical components in relation to P2®5 CaO. The results so obtained are discussed below j-

Si02 vs. '

The (PO^)"^ trivalent anions may be replaced by similarly 2

built and equidimensional anions such as divalent (SO^)" and tetra-valent (SiO^)"^ (Krishnan, 1942; Batekhtin, 1959; Manheim, et al., 1980; Axelford, et al., 1984). The substi-4+ 5+ tution of small Si ions for P in apatite is well substan-tiated. If appreciable Si "*" substitutes for P"*" it is apparently necessary to have a corresponding substitution of balance charges. The coupled replacement Si " + S®"*" ^ is well documented throughout in literature on the different phosphorites of the world (see Heinrich, 1954; Cruft, 1966; Gevasimovskiy, et al., 1973). Silica shows gradual decrease +2

with the increase of P2O5/ while Ca increases simultaneously (see Cook, 1972; Khan, et al., 1981).

A plausible substitution that could help to balance the decrease in charges due to carbonate and sulphate substitution

83

is the substitution of silicate (SiO^)"^ for (PO^)""^. This

would increase the negative charges (see Khudolozhkin, et al.,

1972; Altschuler, 1980; Banerjee, et al./ 1980; Maheim and

Gulbrandsen, 1983). Examination of chemical data of phosphorite presented

by Bushinsky (1935), Dietz, et al. (1942), Gulbrandsen (1966) and Summerhayes (1970) shows that generally there is an inverse relationship between Si02 and P2O5 contents in the phosphorites of U.S.S.R. and Southern California.

This relationship has primarily been explained in terms of diluent allogenic minerals such as quartz, calcite, feldspar and glauconite in the phosphorites from the S. Africa, continen-tal margin (see Parker, 1975).

Si02 content of the phosphorites of Maldeota and Durmala blocks of Mussoorie area plotted against respective

shows strong negative relationship (Pigs. 10A, Tables-VII & VIII). Such an inverse relationship indicates -1. A gradual removal of Si02 by P2^5 because ionic radii

of Si " (0.39 %) and p" ^ (0.35 are very similar hence, a diadochic relationship exists between the two.

2. The (PO^)"^ has been mutually substituted by (SiO^)"'^ before the final precipitation of phosphorites in the basinal environment.

3. The precipitation took place in marine, shallower conditions of the basin which is a well known fact for all older phosphorites.

4. This relationship may be due to the presence of detrital minerals like quartz, feldspars, micas and clay bearing minerals.

84

The present study further indicates that much of Si02 content is not related to apatite. Between SIO2 and CaO there is no significant correlation and it is observed that CaO remains almost constant with the variation of SiOj (Fig. 12A ) .

The relationship of AljO^ with random in Maldeota block while in Durmala, seems to be weakly-negative (Figs. lOB & 12B). There is a progressive increase in A1202 indicating the precipitation of phosphorites under controlled physico-chemical condition at low to moderate Eh i.e. slightly reducing to fairly oxidizing conditions and at neutural to moderate pH 7.1 to 7.8 (Israili, 1978).

The ability of Alumina, which is closely associated with silica, to substitute Ca as well as P In significant amounts Is in conformity to the recent extension of the possibilities of their isomorphic substituion as proposed by Fisher and McConnell (1969). The negative relationship of

AI2O3 with CaO in Durmala phosphorite may be due to ionic + 2 +3

substitution of Ca by A1 in the carbonate fluorapatite phase due to weathering of the ores.

Fe203/Al203 ratio (Tables-IX & X) indicates that iron is exclusively contained in the alumino-sllicate mineral phase. The variable MgO/Al203 (Tables-IX & x) ratio indicates that Mg is a terrigenous impurity and related to the carbonate fluorapatite.

85

Fe202 and FeO vs. P2°5 *

In phosphate deposits of N.W. Queensland, an inverse relationship of FejO^ with P2O5 is primarily a reflection of the tendency of phosphate to be associated with lateritic weathering profiles. It is also apparent from the analysis that there is a considerable concentration of total iron in the non-pelletal phosphorites conpared to the pelletal material. The FeO content and the FeO/PegOj ratios both suggest that the non-pelletal phosphorites have been subjected to more oxidising conditions than have the pelletal phospho-rites (see Cook, 1972).

Subramanian (1976) has shown that Pe and P are oogenetic in fresh water as well as in estuarine environment; and Nariagu (1972) has experimentally verified the role of Fe in P mass transfer in the aquatic environment.

Bortleson and Free Lee (1974) have shown that Fe and P are positively correlated in lake sediments and that the oxidation condition will control the rate of Fe in either mobilising or releasing P to the water. In a very highly oxidising environment, Fe"*" removes P"*" from water by the formation of sorbed complex on Pe (OH)^ thereby making

— 3 +2 available only a small amount of PO^ for Ca to form apatite in the marine environment (see Banerjee and Saigal, 1988). Hence for the continentally derived P to reach the ocean for apatite precipitation the milieu should

86

have positive but not extreme oxidising and acidic conditions and any change in these parameters may trap the dissolved PO^^ in the estuarine regions where the phosphorus could be sorbed by FeCOH)^ or clay minerals (see Olsen and Fredrikson, 1966; Kajitani, 1968 and Shangqing, 1984) . The ionic radii of

Fe "*", Fe "*" and Al^^ are apparently too small to enable them to +2

substitute readily for Ca in most natural environment (see Cruft, 1972) .

During the early proterozoic, at least, the disposal and concentration of P in marine sediments was controlled largely by the distribution of iron and the periodic upwellings of reducing iron rich ocean waters of the type envisaged by Holland (1973).

show negative relationship with both ferric and ferrous oxides (Figs, lOC, D and 12C, D). The antipathetic relationship of the above constituents in Mussoorie phosphorites indicates that iron oxides are not

related to apatite. The existence of iron oxides as coating

around the pellets of collophane may be traced as due to oxidation of some admixed pyrite in the sediments.

These FejOj content may be due to occurrences of

ferruginous minerals like pyrite, limonite, etc. Their negative relationship may be due to the mutual ionic substi-+2

tution of divalent cations of Ca by trivalent cations of Fe"*" in the depositional basin. + 2

According to Subramanian (1980), Fe is an effective ion to remove the phosphates fran water in reducing environ-ments. The Pe202/Al203 ratio in Maldeota phosphorite falls between 1,38 to 10,10 which is lower than that of Durmala

87

phosphorites, where it ranges from 0,20 to 2 0.0 indicating

the association of alumino-silicate minerals. The

dominance of F®2®3 over FeO and variable FejO^/PeO ratio in

Mussoorie phosphorites is due to association of pyrite with

these sediments which can be interpreted as an indication of

reducing conditions at the site of deposition. of

The presence^higher content of phosphorites

indicates the geochemical affinity of both the elements. The

negative relationship also indicates the precipitation was in

the sea basin not in the lake.

TiOj vs. PjOg and CaO j

The antipathetic relationship shown by 'detrital trace

elements* is clearly exhibited by P2O5 and TiO^ which is

located predominately in detrital, rutile, ilmenite and

leucoxene (see Cook, 1972). Goldschmidt (1954) reports that

under some conditions it is absorbed by clay minerals. The

Ti02 data marked a trend of increasing titanium oxide with

decreasing P2®5 content is quite apparent in all phosphorite

types. The Ti02 content of the non-pelletal phosphorites is,

however, higher than that of the pelletal phosphorites. The

Ti02 content of the phoscretes is low due to the titaniferous during

minerals remaining relatively insoluble/the solution, mobili-

zation and reprecipitation of apatite as phoscrete (see Cook,

1972).

Titanium has random correlation with P2®5 Maldeota

phosphorites while in Durmala phosphorites it is antipathetically

30

^ 20 In

10

0

10

u. u

0 M 1-0 0-8

2 0-6

02 0

oys-O-Qtt

• •©•

u

0 • •

• o , *

%

• • ••

-H

m % ' < 5?

• o • Om * O

J 1 1 0

10

o O)

• /r 0.03 oy-a-O'iffi

• . • O • O 0

10 20 30 P205

UO

0

0-5 O-i* 0-3 0 - 2

0 - 1

0

88 •v,008 o»'--0-13 B

• «

o

V

• vk — 0'20 0-17 0

« _i

• o

_i 1 1

orz-0-U3

10 20 30 70P2O5

Fig. 10. Graphical represaitation of PgO^ in relation to Si02, Al20g. Fe-0», FeO, TiO„ and MnO in Maldeota(») and Durmala(o)

Z o Z phosphorites.

89 •r=-0-35 or = _o-38

> 1 * O • • o •

• o o

_1 1

12

10

B

O 6 CT) s , cN

30 •r=r -a05 or- -07 9

.M • • o • • •

or= 0'ti6

0 • . a

-I ' - '

0-5 0-5

o 0.3

0.2

O'l

0

D .r=-o-17 oi: 0-61

• • .

•r= -0.29 or=-o-55

o > .

o . •• . o a 0 I* I

10 20 %P2 05

-J 1_ 1 30 kO

17.5

15

c\l

5H

- 1 L.

•r= -O-i+O or = -0-i3

»o

o o

_1 1 I 1 I

10 2 0

VoPaOs 30 UO

Fig. 11. Graphical representation of P20g in relation to CaO, MgO,

Na20. n^O and CO2 in Maldeota(«) and Durmala(o) phosphorites.

90 30

20

f\i O •C-io

? 3 u-

o cn

2

1

0

12

10 8

6 t*

2

0

•r=001 or=0l5 A

'"Vi"

.r= 0-12 or= -0 1+9

f

. o

.r = -0 25 0-19

«

_i 1 I S-J 1_ J 10 20 30 itO 50 60

•/• CoO

6

5 h

CO O 3 < 5? 2

1

0

1-2

1 -0

0 - 6 <M

2 0.6

O-i* 0-2

0

12 VO

O 0-0

0-1*

0-2

0

• r : of:

0-10 -Oil B

' o • • -vy:. e •

:0.0e :0-96

•S9' *

'f'

--0 02 H = 026

• V

10 20 30 I+O 50 60 7o CoO

12 10

«M ^ 6

2

0

0 - 6

0-5 oO-t c 0-3

0-2

0.1 0

06

0-5 OU 0-3 0 2 0 1

0

o

•r=-0-32 or = -0-07

• r=:0-26 p or=-0-1 7

or=-0-08

•'"•••K't-'. J 10 20 30 t+O 50 60 %CoO

CM X

.r= 002 »r=-0.1(»

10 20 30 itO 50 60 Vo CoO

1 5

ro O O 10

K oM • o .

"lO 20 30 ito 50 60 % CaO

Fig. 12. Graphical representation of CaO in relation to Si02, Al^O^,

Na^O, K2O. H^O and CO2 in Maldeota ( « ) and Durmala ( o ) phosphorites.

91

related to P2O5 (Fig. lOE). Ti02 and CaO show sympathetic correlation both in Maldeota and Dujrmala phosphorites (Fig. 12E). There is a little variation in Al203/Ti02 ratio (Tables-IX & XII) which suggests a closer association of Ti with A1 in a general way, though geochemical coherence is not so strong. The sedimentation intensity of titanium appears to vary with total sedimentation intensity at the site of deposition as indicated by almost constant Al202/Ti02 ratios in Maldeota and Durmala phosphorite deposits.

The random correlation of Ti02 with P2O5 may be possible due to leaching remobilization and reprecipitation. Their negative relationship indicates the location of minor amount of Ti02 outside the crystal lattice of apatite by mutual ionic substitution and adsorption on the mineral surface of apatite, iron and clay bearing minerals.

MnO vs. P2°5 •

Manganese content of the phosphatic stromatolites from Jhamarkotra (Rajasthan) and other areas plotted against respective P2O5 values shows antipathetic relationship. Such a relationship indicates that Mn has no direct affinity for the phosphate nor it occurs in apatite structure (see Banerjee, et al., 1984; Banerjee and Saigal, 1988). The Mn is present dominantly as Mn02, although a limited amount of Mn substitution in the apatite lattice could conceivably occur in the more manganiferous phosphorites either as Mn "*

2 + — substituting for Ca or alternatively by (MnO.)" substituting

92

f o rCPO^ ) " ^ ( s e e V a s i l i e v a , 1958; C r u f t , 1966; Rao, e t a l . ,

1987) .

The d i s t r i b u t i o n of phosphorus i n the unconso l ida ted

sediments i s mainly c o n t r o l l e d by -

1. The phosphorus content of the minera l source m a t e r i a l .

2. The concen t r a t i on and s t a t e o f d i s p e r s i o n of MnO and

i r o n compounds on the sediment s u r f a c e s .

3. D i s t r i b u t i o n of b iogenous matter .

4 . Chemical p r e c i p i t a t i o n or replacement of s o l i d phases .

P wi th Mn and i r o n o x i d e s in t roduced in to the ocean

water i n a d i s s o l v e d as w e l l as i n suspended s t a t e

are l a r g e l y depos i t ed t oge the r i n an o x i d i z i n g e n v i r o n -

ment (Rao, e t a l . , 1987 ) .

The concent ra t ion of manganese in Mussoor ie phospho r i t e s

i s found to be low and they have an a n t i p a t h e t i c r e l a t i o n s h i p

( P i g , l O F ) . Such a r e l a t i o n s h i p i n d i c a t e s -

1. N o n - a f f i n i t y with minor occurrences of MnO

o u t s i d e a p a t i t e l a t t i c e s .

2. The MnO may be a s s o c i a t e d with d e t r i t a l g r a i n s and i t

may be introduced in the system dur ing weather ing

p r o c e s s .

Calcium may be r ep l a ced in p a r t by Mn, Cr , S r , Or in

smal l p a r t by Na, K, Mg, Fe o r even carbon ( s e e Winchel l and

Winche l l , 1968 ) .

Isomorphic subst i tut ion of Ca"*" c a t i o n s by Mn"*" i ons 4+ 2+

and V # (V0^) were observed in the anc ient phosphor i tes ( s e e

Kr ishnan, 1942; He in r i ch , 1954; e r u f t , 1966; Khudolozhkin,

e t a l . , 1972; G i l i n s k a y a , e t a l . , 1984 and P e t t i j o h n , 1984 ) .

93

Mn and CaO show sympathetic relationship in Maldeota

phosphorites and weakly antipathetic correlation in Durmala

phosphor i t e s ( P i g . 12 P) which may be a t t r i b u t e d p a r t l y t o 2+ 2+

the s u b s t i t u t i o n o f Ca by Mn and j u s t a d d i t i o n o r adsorp-

t i o n of MnO i n the a p a t i t e c r y s t a l l a t t i c e du r ing and or

a f t e r the fo rmat ion of phospho r i t e s i n the b a s i n .

CaO v s . P jOg i

The p l o t t i n g of CaO content a g a in s t r e s p e c t i v e P j ^ S

v a l ue s a l s o shows an a n t i p a t h e t i c r e l a t i o n s h i p between the

two in the phosphor i t e s of the study area ( F i g . 11 A ) . This

i n v e r s e r e l a t i o n s h i p i n d i c a t e s a g radua l removal of one by

the o t h e r . According t o Ames (1959) ca rbonate f l u o r a p a t i t e

i s the end p roduct of d i a g e n e t i c replacement i n which

d i s s o l v e d phosphate i ons s u b s t i t u t e f o r ca rbonate i n

c a l c a r eous m a t e r i a l s . 4-2 —3 2 Since Ca , PO^ , CO^ have s i n g l e va l ence s t a t e s ,

changes i n Eh cannot produce s e p a r a t i o n i n t o carbonate r i c h

and phosphate r i c h l a y e r s ; hence the i n d i v i d u a l enrichment

w i l l have t o take p l a c e w i t h i n a narrow pH r ange . R e l a t i v e

t o CO^ / the Ca2(PO^)2 i s l e s s s o l u b l e . Hence^ in the pH

range 7 to 7 .5 , Ca3(PO^)2 can p r e c i p i t a t e f i r s t wh i l e CO^"^

remains in s o l u t i o n so l ong as the pH i s b u f f e r e d i n t h a t

r ange . When the pH i n c r e a s e s to 8, CaCO^ w i l l p r e c i p i t a t e

( s e e G a r r e l s and C h r i s t , 1965 ) .

94

The a p a t i t e d i s t r i b u t i o n p a t t e r n i n d i c a t e s a p o s i t i v e

c o r r e l a t i o n of CaO and P2°5* Comparison of f e a b l y weathered

with the h i g h l y weathered phosphor i t e s and the v a r i a t i o n s i n

the compos i t ions of carbonate a p a t i t e as r e f l e c t e d by the

normal ised s t r u c t u r a l concent r a t i on v a l u e s can be taken as

a measure of the chemical i n g r e d i e n t of the d e p o s i t i o n a l wate rs

at the t ime of the phosphor i t e fo rmat ion ( s e e Bane r j ee , e t a l . ,

1982) ,

Calcium i s the ch i e f c o n s t i t u e n t p r e c i p i t a t i n g with

phosphate under a l k a l i n e cond i t i on forming c a l c - p h o s p h a t e .

P e t r o l o g i c a l l y co l l ophane has been i d e n t i f i e d which i s a

group of m ine ra l s o f which f l u o r a p a t i t e Ca2(PO^)2P i s the

ch ie f m i n e r a l . Add i t ion of f l u o r i n e to the l a t t i c e of c a l c -

phosphate i n c r e a s e s i t s s t a b i l i t y dur ing f l u c t u a t i o n s i n the

p r e c i p i t a t i n g system. Accord ing t o s o l u b i l i t y product c a l c u l a -

t i o n s , phosphate i n a system of high s o l u b l e ca l carbonate

s t a r t s p r e c i p i t a t i n g at somewhat lower pH than CaCO^ and the

p r e c i p i t a t i o n of phosphate i n the form of c a l c phosphate would

continue t i l l t h i s c r i t i c a l of pH i s not d i s t u r b e d . CaO i n the

analysed samples of the study area shows sympathetic r e l a t i o n -

sh ips w i th phosphate i o n s . I t i s found that the ( PO^ ) " ^ i ons

+ 2

have been almost comparat ive ly used up by Ca ions to

p r e c i p i t a t e ca l c -phosphate in h igh grade o r e s . In low and

medium grade o res some of the ca lc ium l e f t under r e a c t i n g with

phosphate i ons might have p r e c i p i t a t e d as CaCO^* Such in cases

the va lue of l o s s on i g n i t i o n (LOI ) have gone up. Fu r the r ,

r e s i d u a l ca lc ium i s supposed to have been inco rpo ra ted i n the

format ion of i n s i g n i f i c a n t s i l i c a t e s ( s e e Cook, 1972; Khan,

e t a l . , 1981) .

95

The v a l u e s from geochemical data of phospho-

r i t e s ( T a b l e s - X I I & X I l ) a r e v i r t u a l l y i n c o n s i s t e n t . The average

CaO/p20^ r a t i o s in Maldeota and Durmala a re 2.16 and 2.17

r e s p e c t i v e l y . These va lue s are g r e a t e r than 1,31 which i n d i c a t e

that the phosphor i t e s are composed of ca rbonate a p a t i t e and

sugges t s u b s t i t u t i o n of PO^ by CO^ in the a p a t i t e .

Prom the above d i s c u s s i o n , i t i s e v i d en t tha t a sediment

high i n ca lc ium phosphate and low in ca l c ium carbonate could be

formed when there are c o n d i t i o n s f o r cont inuous removal of

ca lc ium as the phosphate and the a c t i v i t y p roduct of carbonate

i s not exceeded , t h i s can occur i n a r e s t r i c t e d b a s in with low

pH i . e . 7 .0 t o 7 . 5 .

I t i s , t h e r e f o r e , i n f e r r e d that du r ing the phospha t i z a -

t i o n the sea became enr iched i n phosphate content by l owe r ing

of pH due to r e l e a s e of CO2 i n s h a l l o w marine environment which

i s s u b j e c t e d t o continuous chemical changes with mixing of

v a r i o u s types of mate r i a l b rought by r i v e r s , e t c .

MgO v s . P2O5 and CaO :

The i n h i b i t i n g e f f e c t of Mg on the c r y s t a l l i z a t i o n o f

a p a t i t e i s ev iden t whether i t i s in s o l u t i o n o r i n the o r i g i n a l

c a r bona te . These exper imenta l r e s u l t s suggest a pathway f o r the

g enes i s of a p a t i t e and i n d i c a t e cond i t i ons f o r i t s f o rmat i on ,

which could p r e v a i l w i th in the sediment i n v e r y sha l l ow water

dur ing a ve ry e a r l y d i a g e n e t i c s t age ( s ee Wa l te r and Hanov,

1978; Morse, 1979; Nathan and Lucas, 1981 and Lucas , 1984 ) .

Mg i s n e g a t i v e l y c o r r e l a t e d with P, the h igh P peak i s

c l e a r l y f o l l o w e d by h igh Mg peak a long the t r a v e r s e in the

96

phosphor i tes of Jhamarkotra. This r e f l e c t s rhythmic a l t e r a t i o n s

o f ' M g - p o o r P - r i c h * l a y e r s w i th 'magnes ia r i c h p - poo r * l a y e r s .

This p e r i o d i c rhythmic i ty o f the elements i n the Precambrian

laminated phosphat ic s t r o m a t o l i t e s c l e a r l y i n d i c a t e s the w i t h

a f f i n i t y of do lomite ^ the c a r b o n a t e - f l u o r a p a t i t e du r ing the

sed imentat ion and p r e c i p i t a t i o n i n the s h a l l o w e r water b a s i n s

( s e e B a n e r j e e , 1978) .

The r e l a t i o n s h i p o f MgO with PgO^ and CaO i s i l l u s t r a t e d

i n F i gu r e s 11 B and 12G, An i nve r s e r e l a t i o n s h i p e x i s t i n g between

MgO and a continuous replacement o f MgO by P2O5

dur ing d i a g e n e s i s . The phosphate rocks of Maldeota show a n t i -

p a t h e t i c r e l a t i o n s h i p between CaO and MgO whereas i n Durmala 2+

they have weakly sympathetic r e l a t i o n s h i p . The presence of Mg

r a t h e r i n h i b i t e d the growth of a p a t i t e c r y s t a l l i t e s , formed

dur ing r e g i o n a l metamorphism and r e c o n s t i t u t i o n o f phosphate

m i n e r a l s .

C r u f t , e t a l . (1965) and McConnell (1973) r epor ted tha t

Mg"*" could be s u b s t i t u t e d f o r Ca^^ in the a p a t i t e s t r u c t u r e .

I t i s q u i t e p o s s i b l e that both CaO and MgO were competing du r ing

d i a g e n e s i s f o r t h e i r s u r v i v a l i n the p resence of ^2^5*

p h o s p h a t i z a t i o n there i s a cha in of replacement between CaO-

Mg0-P20^ and tha t MgO acted as a c a t a l y s t in the p rocess of

replacement of CaO by P2®5 ( s e e Bachra/ e t a l . , 1965; G u l -

brandsen, 1969; Martens and H a r r i s , 1970; A t l a s , 1975 and

Burnett , 1977 ) .

Amorphous calc-phosphate can readily convert to apatite

in Mg-free sea water by exchanging Mg"*" for Ca"'" ions from the

water (see Krishnan, 1942; Martens and Harris, 1970; Banerjee,

et al.# 1980), Because Mg ion is much smaller in size than Ca,

97

+ 2 i t s s u b s t i t u t i o n in l a r g e amount i s not f a v o u r e d , Mg i s

+2 d i v a l e n t l i k e Ca and, t h e r e f o r e , imposes no change in the

ba l ance of cha rges , and i t i s inc luded as a component of a p a t i t e

chemical f o rmu la ^^ (CO3) ^3(003?) ^^F^

( see Simpson, 1966; McC l e l l an and Lehr , 1969; Manheim and

Gulbrandsen, 1983; P e t t i j o h n , 1984) .

In reducing environment, f e r r i c - o x i - h y d r o x i d e coa t i ng s

on c l a y p a r t i c l e s are reduced to p y r i t e , making new exchange + 2 + 2 s i t e s f o r Mg ions a v a i l a b l e ( e . g . H o n t m o r i l l o n i t e ) . Mg

f u r t h e r might be l o s t by s u r f a c e a b s o r p t i o n on c a l c i t e (Ca-Mg

overgrowth ) ( s e e Khudolozhkin, e t a l . , 1972 and Sho lkowitz ,

1973) or on b i o g e n i c opa l ( s e e Donne l ly , e t a l w 1977) or by

d o l o m i t i z a t i o n .

In sea water amorphous ca l c - phospha te p r e c i p i t a t e s +2 r a p i d l y conver t s t o a p a t i t e in Mg f r e e sea water through

+2 exchanging f o r Ca ( H e i n r i c h , 1954; Winche l l and W inche l l ,

1968; Marten and H a r r i s , 1970 ) . I t i s e s t a b l i s h e d that r educ t i on

in pH of sea wate r t o 7 .0 a l l o w s p r e c i p i t a t i o n of a p a t i t e wi th

a CaO/MgO r a t i o of 1 .2 . The f a v o u r a b l e environment f o r the

set t lement of na tu ra l a p a t i t e must then be e i t h e r neu t r a l o r

acxdic ( s e e Nathan and Lucas , 1976 ) . 4.3 +2 +2

L ike Al and a l k a l i e s , Ca can be r ep l aced by Mg

in the a p a t i t e c r y s t a l l a t t i c e s i n s h a l l o w e r marine c o n d i t i o n s .

The i nve r se r e l a t i o n s h i p of CaO and MgO suppor t s the above

ob se r va t i ons i n the phosphor i t e samples of the study a r e a .

Furthermore, the i n v e r s e r e l a t i o n s h i p i s supported by

the exper iments c a r r i e d out by Martens and H a r r i s (1970) who

concluded tha t Mg^^ ions i n h i b i t the p r e c i p i t a t i o n of a p a t i t e

98

s t r u c t u r e due to which a dec r ea se i n MgO content occurs du r ing

p20g enr ichment . However, t he work of Martens and H a r r i s (1970)

a l s o sugges t s that the r e was p robab l y a t h r e s h o l d of Ca/Mg

above which a p a t i t e could p r e c i p i t a t e . The replacement of

magnesian c a l c i t e by ca rbonate a p a t i t e might be r e s p o n s i b l e

f o r the f o rmat i on of do lomi te ( dec rease i n Ca/Mg r a t i o s ) . 2+

However, Ca ions are r e a d i l y taken in ca rbonate a p a t i t e

s t r u c t u r e with the r e j e c t i o n of Mg^"^ i o n s .

The geochemical behav iour of these o x i d e s may be due to -

1 . I o n i c s u b s t i t u t i o n of Ca"*" in the a p a t i t e c r y s t a l

l a t t i c e i n the a l k a l i n e environment of the b a s i n .

2 . P r e c i p i t a t i o n i n s h a l l o w marine b a s i n . +2 +2

3. S u b s t i t u t i o n of Mg by Ca i n a p a t i t e may dec r ea se

the c r y s t a l l i t e s i z e of the a p a t i t e by the i n c r e a s e

of Mg i o n s .

4 . The minor amounts of Mg may be due t o poor supply

of Mg from source rock .

The h igher CaO/MgO r a t i o ( T a b l e s - X I & X I l ) i n Mussoor ie 2+

phosphor i t e s i n d i c a t e s ent rance of Ca ion in carbonate a p a t i t e

s t r u c t u r e .

Na20 v s . P2O5 and CaO :

Gu lbrandsen (1966 and 1969) has shown that there i s

an approx imate ly 1 : 1 r e l a t i o n s h i p between the atomic r a t i o s

of S and Na i n the Phosphor ia phospho r i t e s , U . S . A . and he has

i n t e r p r e t e d t h i s r e l a t i o n as r e f l e c t i n g a coupled s u b s t i t u t i o n

i n the phosphate mineral o f Na"*" and s"*" f o r Ca"*" and P"*"^.

Apart f rom t r ace amounts of p y r i t e and f e l d s p a r , there a re no

99

S or Na m ine ra l s in the Agulhas phosphor i t e and i t i s t h e r e f o r e

suggested t h a t the S and Na va lues f o r these rocks r e f l e c t

s u b s t i t u t i o n e f f e c t s i n the f r a n c o l i t e ( s e e Pa rke r , 1975 ) .

Both the a l k a l i e s (sodium and potass ium) i n the phos -

pho r i t e d e p o s i t s of Geo rg i a b a s i n . North A u s t r a l i a and most of

the Ind ian phosphor i t e s have been repor ted to have random

c o r r e l a t i o n between NajO and p2®5* random behaviour of

both the a l k a l i e s i n phosphor i t e s may be due to g l a c i a l and

a r i d t o humid cond i t i ons a t the time of d e p o s i t i o n which

enhanced the r a t e of weather ing p r i o r t o d e p o s i t i o n ( s e e

Simpson, 1964; Ronov, e t a l . , 1965; Howard and Hough, 1979 ) .

Lehr , e t a l . (1968) have shown tha t the s i z e of the

c r y s t a l a p a t i t e dec reases wi th i n c r e a s i n g ca rbonate , sodium

and magnesium s u b s t i t u t i o n . I t seems p r o b a b l e tha t the concen-

t r a t i o n e f f e c t s of Na, Mg, and CO^ r e s p o n s i b l e f o r the highly-

s u b s t i t u t e d a p a t i t e s t r u c t u r e s , may i n h i b i t c r y s t a l g rowth .

Jacob (1933) noted tha t s e a - f l o o r phosphor i t e g e n e r a l l y

have l a r g e r s u b s t i t u t i o n s than those on onshore d e p o s i t s .

Russel and Trueman (1971 ) ; Smirnov, e t a l . (1962) suggested

that the Na and SO^ contents of phosphor i t e s f rom Queensland,

A u s t r a l i a i n d i c a t e d f o rma t i ona l environment of high s a l i n i t y .

In con t r a s t to above. Cook (1972) suggested tha t the chemical

v a r i a t i o n s between o f f - s h o r e and onshore phospho r i t e s may be

due to s u b - a e r i a l weather ing of the onshore d e p o s i t s o p e r a t i n g

dur ing the f o rmat i on . An i n v e r s e r e l a t i o n s h i p e x i s t s between

Na and P c o n c e n t r a t i o n s . s i m i l a r trend was noted by Cook (1972)

f o r some elements in the Queensland p h o s p h o r i t e s .

1 0 0

Most of the p l o t s of Na20 with r e s p e c t to CaO sugges t

that only ve ry smal l p a r t of Na20 has s u b s t i t u t e d in the a p a t i t e

s t r u c t u r e , w h i l e the r e s t of i t occurs i n a s s o c i a t i o n of o the r

m ine r a l s . This random d i s t r i b u t i o n p a t t e r n a l s o r e f l e c t s v a r y ing

degrees of weather ing at d i f f e r e n t l o c a t i o n s ( s e e B a n e r j e e , e t a l .

1982) .

The phosphor i t e s of Durmala show p o s i t i v e c o r r e l a t i o n of

Na20 with p2°5 whereas i n Maldeota phospho r i t e s , Na20

has random p o s i t i v e and nega t i v e c o r r e l a t i o n with P2O5 and CaO

r e s p e c t i v e l y ( F i g . I IC and 12H) .

The random p o s i t i v e c o r r e l a t i o n between

i n the study area may be due t o minor s u b s t i t u t i o n of Ca^ by

Na"*" i n a p a t i t e l a t t i c e du r ing phospha t i z a t i on and i t was

r e s p o n s i b l e f o r ba l anc ing the chemical composit ion of a p a t i t e .

Na20 content in the rocks i s ve ry low which may be due t o

decrease i n the c l i m a t i c v i c i s s i t u d e s which enhanced the r a t e

of weather ing p r i o r to d e p o s i t i o n ( s ee Ronov, e t a l . , 1963 ) .

The presence of ^32© in the phospho r i t e s f u r t h e r supported the

s u b s t i t u t i o n of v a r i o u s e lements dur ing a l k a l i n e marine

cond i t i ons i n which the s i z e of the c r y s t a l l i t e d ec r ea s ed .

This r e l a t i o n s h i p i n d i c a t e s d e p o s i t i o n near the sea shore w i th

high s a l i n i t y .

The r e l a t i o n s h i p of Na20 between P2^5 sugges t s

that bu lk of sodium p re sen t i n these phospho r i t e s happens to

be compensatory ca t i ons i n a coupled s u b s t i t u t i o n p a i r of 2+ +2

Na f o r the Ca and SO^ f o r PO^ to p r e s e r v e e l e c t r o n e u t r a l i t y ,

( s e e Gu lbrandsen , 1966) .

1 0 1

The presence of Na20 and its relation to CaO in

Mussoorie phosphorites indicates rapid phosphatization and

also palaeosalinity of the basinal sea water during phosphati-

zation -

KjO vs. P2O5 and CaO :

I t i s a n t i c i p a t e s tha t a nega t i v e c o r r e l a t i o n e x i s t s

between P2®5 e lements which are l o c a t e d ou t s i de the

l a t t i c e i n mine ra l s of d e t r i t a l o r i g i n ( S i 02 , AI2O3/ K2O, T i 0 2 ) .

( s ee Cook, 1972) . The pH of the b a s i c s o l u t i o n , the NajCO^/

a p a t i t e conta ins approx imate ly f i v e times as much a l k a l i e s as

potassium c a r b o n a t e - a p a t i t e ( s e e Simpson, 1964) ,

The concent ra t ion o f potass ium i n the Mussoor ie phospho-

r i t e s appears to be too l ow . The p l o t s of K2O aga in s t r e s p e c t i v e

va lues of p2®5 and CaO ( F i g s . I I D and 1 2 l ) and c o r r e l a t i o n

c o e f f i c i e n t v a lue s ( T a b l e s - V I I and V I I I ) i n d i c a t e a weak

nega t i ve r e l a t i o n s h i p between K2O and the two other ox ides i n

Maldeota phosphor i t e s v/hereas in Durmala phosphor i t e s K2O shows

p o s i t i v e r e l a t i o n s h i p wi th P2O5 content .

The negative relationship between K2O and the two

oxides indicates presence of minor amounts of KjO outside

the apatite crystal lattice and a positive correlation between

K2O and ^ ^^^ remobillzation, reprecipitation

leaching/weathering of ore in the alkaline shallow marine

conditions.

102

H2O v s . P2O5 and CaO :

According to Simpson (1964), of the 11% volatlles in

the a p a t i t e , l e s s than h a l f can be accounted f o r by CO2 i n the

samples . Water forms the o the r v o l a t i l e r e l e a s e d when the

a p a t i t e i s heated . Th is wate r p robab l y i s p r e sen t i n the c r y s t a l s + 2 —3

as hydrogeneous (H^O^) s u b s t i t u t i n g f o r Ca and ( PO^ ) " r e s p e c -

t i v e l y . The wide v a r i a t i o n s i n a p a t i t e obse rved in nature i s

r e l a t e d t o the f o l l o w i n g s u b s t i t u t i o n ( H e i n r i c h , 1954) f o r

PO^ - SO^, ASO^, VO^, CrO^, SiO^, AlO^, COj and OH,

The p r e c i p i t a t i o n of a p a t i t e i s f a vou red w i th in the

sediments by the h igh phosphate concent ra t i on i n the i n t e r -

s t i t i a l wate rs by the a v a i l a b i l i t y of s u i t a b l e nuc l ea t i on s i t e s + 2

and by d i a g e n e t i c r e a c t i o n tha t removes i n t e r f e r i n g Mg i ons

f rom the po r e s o l u t i o n s . Concentra t ion of a p a t i t e i n t o indura ted

phosphate nodules i s brought about by winnowing and reworking

p r o c e s s e s , p o s s i b l y i n response to a change i n the sedimentary

environment caused by e u s t a t i c sea l e v e l f l u c t u a t i o n s o r

tectonism ( s e e Ba t i kh t i n , 1959 and Burnet t , 1977).

Water forms the o the r v o l a t i l e r e l e a s e d when a p a t i t e i s

heated . Th i s water p r o b a b l y i s p re sent i n th?' c r y s t a l s as 2 + —3

hydrogen i ons (H^04) s u b s t i t u t i n g f o r Ca and (PO^) r e s p e c -

t i v e l y ( s ee Simpson, 1964).

The concent ra t ion p l o t s and c o r r e l a t i o n c o e f f i c i e n t

v a lue s of H2O''' with P2'^5 A"^ CaO ( F i g s , l l E and 12J) show an

a n t i p a t h e t i c r e l a t i o n s h i p among these c o n s t i t u e n t s sugge s t ing

thereby s u b s t i t u t i o n of (OH)^ f o r PO^. The excess water s u b s t i -

tu te s both Ca and P i n the form of H^O and H^O^. The high

103

CO2/H2O r a t i o ( Tab l e s -X and X I I ) i n d i c a t e s carbonate bea r ing

hydroxyl a p a t i t e composit ion of these p h o s p h o r i t e s .

CO2 v s . P2O5 and CaO :

The r e s u l t s of the ana lyses of these phosphor i t e s show

that the p resence of CO2 i s too h igh to be exp l a ined as an

obvious ca rbonate impur i ty . However, the e x p l a n a t i o n f o r h i g h e r

CO2 content may be found i n one or more of the f o l l o w i n g

s i t u a t i o n s

1 . In carbonate a p a t i t e , up t o 15 p e r cent carbonate i s

p r e s en t i n the l a t t i c e and the t o t a l carbonate depends

on the r a p i d i t y of metasomatic replacement of c a l c i t e

by the phosphat ic a l k a l i n e s o l u t i o n s .

2 . P a r t i c l e s of 'amorphous ' c a l c i t e i s t oo small t o have a

coherent or o rdered atomic s t r u c t u r e ( s e e Thewl i s , e t a l . ,

1939; Car l s t rom, 1955 ) .

3. Carbonates o r b i c a r b o n a t e ions are l i m i t e d t o the s u r f a c e

of a p a t i t e c r y s t a l l i t e s or exchanged w i th s u r f a c e phos -

phate ions ( see Neuman, 1953) and t rapped in i n t e r s t i t i a l

s i t e s . - 2 2+ - 3

4 . COj s u b s t i t u t i o n of Ca or PO^ in the a p a t i t e

s t r u c t u r e (Deans and V incent , 1938; S a n d e l l , 1939;

McConnell and Gruner , 1940; McConnel l , 1952 and 1960 ) . _ 2

5. Funct ion of CO^ r a d i c a l in the a p a t i t e s t r u c t u r e may

be p re sent as an i n t e g r a l p a r t of the a p a t i t e l a t t i c e

( A l t s c h u l e r , e t a l . , 1958; Rooney and Ker r , 1967;

M c C l l e l l a n and Lehr , 1969) .

104

P h y s i o l o g i c a l chemists f a vou r the hypothes i s ( 2 ) and/or

( 3 ) f o r bone a p a t i t e , wh i l e the m i n e r a l o g i s t s g e n e r a l l y p r e f e r

( 4 ) and ( 5 ) . In an attempt t o e x p l a i n the s u b s t i t u t i o n of CO^

group f o r PO^ group^ McConnell (1973) suggested that the s u b s -

t i t u t i o n might have taken p l a c e i n the f o l l o w i n g manner t-

( a ) PO^ — COjOH or CO^P

( b ) H20^ — Ca^"^ j,i 2

The p r i n c i p a l ions s u b s t i t u t i o n s a r e Na , CO^ # SO^"

+ 2

and p o s s i b l y Mg and i t i s t o be noted tha t these ions a re

a l s o abundant ions in sea w a t e r . Thus the composit ion of marine

a p a t i t e r e f l e c t s s a l i n i t y and p o s s i b l y may a l s o be used as an

i n d i c a t o r of p a l a e o s a l i n i t y ( s e e Krauskopf , 1967 and Gu lbrandsen ,

1969 ) . Carbonate s u b s t i t u t i o n s of phosphate i n smal l amounts

that commonly ranges from a f ew tenths of p e r cent e q u i v a l e n t

COj t o s e v e r a l p e r cent have r e c e i v ed most a t t e n t i o n ( s e e

A l t s c h u l e r , e t a l . , 1952, 1958; S i lverman, e t a l . # 1952;

Winard, 1963; Smith and Leh r , 1966 and Rooney and Ker r , 1967 ) .

The p r o c e s s of phosphate p r e c i p i t a t i o n i s pu r e l y a t t r i -

buted to chemical f a c t o r s , such as l o s s of COj and i n c r e a s e i n

pH r e s u l t i n g from warming of phosphate r i c h w a t e r s . I t i s o b s e r -

ved that phosphor i t e would predominant ly p r e c i p i t a t e i n the pH

range of 7 ,1 t o 7 .8 ( s e e Kazakov, 1937; Krumbein and G a r r e l s ,

1952; Compbel l , 1952) . S imul taneous ly , c a l c ium-ca rbona te would

a l s o p r e c i p i t a t e t o some ex t en t i n the same pH range but p r e -

dominant p r e c i p i t a t i o n of CaCOj would on ly take p l a c e when the

pH i s above 7 . 8 . C a l c u l a t i o n s o f s o l u b i l i t y products i n d i c a t e

p r e c i p i t a t i o n of c a l c - phospha te around pH - 8.1^would be c l o s e l y

f o l l o w e d by p r e c i p i t a t i o n of carbonates i n s l i g h t l y h igh ph

reg ime.

105

A s u b s t a n t i a l p a r t of phosphate and carbonate a l s o

shows ev idences of c o - p r e c i p i t a t i o n which l a t t e r d i f f e r e n t i a t e d

dur ing the d i a g e n e s i s . F l u o r i n e must have been f i x e d in the

phosphate l a t t i c e a t about t h i s time r e s u l t i n g in an i n c r e a s e

of the s o l u b i l i t y of phosphate phase . When speedy removal of

PO^, Ca, Mg and CO^ ions from the s h a l l o w e r s u r f i c i a l marine

waters takes p l a c e dur ing the pro longed day l i g h t hours and

changes i n the b a s i n wate r chemistry dur ing the r e s p i r a t i o n

p r o c e s s e s at n i gh t , pH o f t h e sha l l ower zones must have f l u c -

tuated p e r i o d i c a l l y l e ad ing to a l t e r n a t i n g CaPO^ and s i l i c o n

s a t u r a t i o n c y c l e s . The n a t u r a l c yc l e s must have r e l e a s e d CO2

tha t a c i d i f i e d the w a t e r . Th is a c c e l e r a t e d the d e p o s i t i o n of

s i l i c a g r a i n s i n the s t r o m a t o l i t i c l a y e r s ( K l o t z , 1968; Schmatz

and Swanson, 1969; Earner , 1971; B a n e r j e e , 1979; Baner j ee and

Basu, 1980 ) .

Gu lbrandsen (1970 ) , proposed that a r e g i o n a l i n c r e a s e

of CO2 i n a p a t i t e of Phosphor ia Formation of U . S . A . with a

r e g i o n a l i n c r e a s e in the wate r temperature of the o r i g i n a l

environment and hence the h igh CO2 va lue s f o r the Agulhas Bank

phosphor i t e s may imply that the a p a t i t e s formed in waters tha t

were c o n s i d e r a b l y warmer than those i n which Phosphor ia a p a t i t e s

were formed.

CO2 shows a weak and crude l i n e a r r e l a t i o n s h i p with

P20^ i n most a p a t i t e s , but i n more weathered rocks , the CO2

content i s h i g h e r , p o s s i b l y due to secondary vein f i l l i n g

c a l c i t e s and i n t h i s , the p l o t d e v i a t e s s i g n i f i c a n t l y from

l i n e a r i t y . This l i n e a r random c o r r e l a t i o n a l s o i n d i c a t e s

v a r i a b l e l e ach ing (Roger , 1922 ) .

The g r a p h i c a l r e p r e s e n t a t i o n o f CO2 a g a i n s t P2O5

CaO as i l l u s t r a t e d in f i g u r e s I I F and 12K shows that a

o

106

negat ive c o r r e l a t i o n e x i s t s between these c o n s t i t u e n t s i n d i -

ca t ing s u b s t i t u t i o n of both Ca and P by C.

In comparison to the composit ion and CO^/P^O^ r a t i o of

an i d e a l f l u o r a p a t i t e ( S a n d e l l , e t a l . , 1939) , the CO2/P2O5

r a t i o s ( T a b l e s - X I and X I I ) of these phospho r i t e s are g e n e r a l l y

h i ghe r . This r a t i o i n Durraala phosphor i t e s approaches v e ry

near to that of carbonate f l u o r a p a t i t e , whereas i n Maldeota

phosphor i t e s t h e i r h i ghe r CO2/P2O5 r a t i o i s i n d i c a t i v e of

carbonate hydroxy l f l u o r a p a t i t e and carbonate hydroxy l a p a t i t e .

Furthermore, the h i g h e r CO2/P2O5 r a t i o i n d i c a t e s the

p o s s i b i l i t e s of PO^"^ s u b s t i t u t i o n by CO^^. Lehr , e t a l . (1968)

have shown tha t the c r y s t a l l i t e s i z e of the a p a t i t e d ec r ea se s

with i n c r e a s i n g ca rbonate , sodium and magnesium s u b s t i t u t i o n s .

The r e l a t i o n s h i p o f these two e lements

supported the f o l l o w i n g authors o b s e r va t i on s r ega rd ing the

phosphogenes is of these sediments

1. During phospha t i z a t i on CO^ might have r ep l a ced

PO^ w i t h i n the b a s i n and t h i s r e a c t i o n i s p a r t l y

ba l anced by Ca^^ by Na^^ and c o n t r o l l e d by c r y s t a l l o -

g raph ic cont ro l on the deg ree of ca rbonate s u b s t i t u t i o n .

2. The presence of f l u o r i n e as carbonate f l u o r a p a t i t e may

be ba lanced by the c r y s t a l l o g r a p h i c s t r u c t u r e of the

a p a t i t e .

3. The r e l a t i o n s h i p may be due to speedy removal of PO^,

Ca, Mg and CO^ ions from the s h a l l o w e r s u r f i c i a l marine

wate rs dur ing the p ro longed day l i g h t hours and changing

of b a s i n a l water chemist ry dur ing the n i g h t . This

supported the pH f l u c t u a t i o n s p e r i o d i c a l l y l e ad ing to

1 0 7

CaPO^ and s i l i c o n s a t u r a t i o n c y c l e .

4. This r e l a t i o n s h i p shows the p s u e d o i s o t r o p i c / i s o t r o p i c

nature of a p a t i t e which i s g e n e r a l l y formed dur ing low

temperature c o n d i t i o n s in which very f i n e g r a ined ,

minute, equ id imens iona l s p h e r u l i t i c a gg r ega t i ons were

formed,

5. I t a l s o supported the hypothes i s of d i r e c t i n o r g a n i c

p r e c i p i t a t i o n of phosphor i t e s by means of upwe l l ing

c u r r e n t s .

6 . The mutual i o n i c s u b s t i t u t i o n of PO^ by CO^ i n d i c a t e d

the presence of these ions i n abundance i n sea water

and p r o b a b l y used as an i n d i c a t o r of p a l a e o s a l i n i t y .

INTER^RELATIONSHIP OF VARIOUS OXIDES :

S iO j v s . AI2O3 '

P e t t i j o h n (1957) noted t h a t the abundance of Si02 and

AI2O3 r e f l e c t s the m i n e r a l o g i c a l matur i ty of sandstone and

s h a l e .

Alumina c o n s t i t u t e s a s i g n i f i c a n t pe rcentage 3 t o 8%

in the phosphate r i c h rocks ( s e e James, 1966 ) . The h igh S iO^/

AI2O3 r a t i o s could be e xp l a ined as due t o l o s s of aluminium

which has a h i ghe r s o l u b i l i t y than s i l i c a i n a very a c i d i c

cond i t i ons ( s e e Krauskopf , 1956; Wey and S i f f e r t , 1961 ) .

When Si02 and AI2O3 are p l o t t e d on a graph ( F i g . 13A) ,

they show v e r y weak n e g a t i v e c o r r e l a t i o n i n Maldeota phospho-

r i t e s whereas i n Durmala phospho r i t e s they show weakly sympa-

t h e t i c r e l a t i o n s h i p sugge s t ing the CO-ex i s tence of qua r t z and

1 0 8

the a l u m l n o - s i l i c a t e minera l s in the phosphor i t e s . On the o the r

hand poor concentrat ion and i n s i g n i f i c a n t r e l a t i o n s h i p of these

const i tuents a l s o r e f l e c t s the complex m ine r a l o g i c a l v a r i a t i o n s

and immature nature of these sediments v/hich may be due to

t h e i r d e p o s i t i o n immediately a f t e r e r o s i o n .

Si02 v s . '

Prom the m u l t i v a r i a t e a n a l y s i s of i r on ores ( see Sahu

and Raikar , 1983) , Si02 has a negat ive c o r r e l a t i o n with

and s t rong ly loaded to the f i r s t f a c t o r which i s i n t e rp r e t ed

as g r o s s - l i t h o l o g y together with FegO^. The model of Si02

d i s t r i b u t i o n l a t e r a l l y and v e r t i c a l l y may be in te rp re ted as

mic ro -bas ins of sedimentation f o r the i r o n - o r e s and p h y l l i t e s

a longwith s i l i c a content . The non-homogeneity of l a t e r a l and

v e r t i c a l s e c t i on f o r the m u l t i v a r i a t e f o r e c a s t i n g may be due

to the secondary enrichment of Fe^O^ o r due to leaching o f Si02

along the v e r t i c a l d i r e c t i o n ( see Ra ikar , 1987 ) .

The Si02 and cons t i tuents show weakly negat ive

and p o s i t i v e c o r r e l a t i o n i n Maldeota and Durmala phosphor i tes

( F i g . 13B) . The concentrat ion of ^620^ v a r i e s with the v a r i a t i o n

of S iO j content .

I ron , during weather ing , i s converted in to f e r r i c ox ide

and Car r ied as s t a b i l i z e d c o l l o i d s or as adsorbed coat ings on

d e t r i t a l p a r t i c l e s . The i ron content which i s adsorbed on

these c o l l o i d a l p a r t i c l e s i s separated according to t h e i r

s e t t l i n g v e l o c i t i e s ( see Wedepohl, 1970) .

109

This r e l a t i o n s h i p may be due t o s m a l l - s c a l e l each ing

of Si02 both l a t e r a l l y and v e r t i c a l l y by the c i r c u l a t i n g

groundwater and secondary enrichment of on

the surface of phospho r i t e .

Si02 v s . MgO i

in the Mussoorie p h o s p h o r i t e s , Si02 and MgO have a

sympathetic r e l a t i o n s h i p ( P i g . 13C) . The concent ra t ion of

magnesium i s d i r e c t l y r e l a t e d to the i n c r e a s e o r dec rease of

matr ix i n a r ock . I t i s t h e r e f o r e , i n f e r r e d tha t the concen-

t r a t i o n o f MgO in these sediments might be due to the amount

of matr ix p r e sen t i n these rock types .

MgO v s . MnO :

The r e l a t i o n s h i p between MgO and MnO i s shown in

f i g u r e 13 D f o r Mussoorie p h o s p h o r i t e s . A sympathetic c o r r e l a -

t i on e x i s t s between the two o x i d e s . The m o b i l i z a t i o n of MgQ

and MnO dur ing the metamorphism of the phosphogenic sediments

of Mussoor ie and t h e i r concent r a t i on due to g r a v i t y might be

the p o s s i b l e causes f o r such a r e l a t i o n s h i p .

MgO v s . CO2 s

CO2 p l o t s a g a in s t MgO va lues show a w ide l y s c a t t e r e d

d i s t r i b u t i o n p a t t e r n { P i g . 13E) i n the Mussoor ie p h o s p h o r i t e s .

This i n d i c a t e s a c l o s e a s s o c i a t i o n of CO2 wi th MgO tha t l ed to

1 1 0

the fo rmat ion of magnesian carbonate t o a c e r t a i n e x t e n t .

Pe202 + FeO vs^ *

Warington (1866) found tha t i r on and aluminium

hydrox ides cause the p r e c i p i t a t i o n of phosphorus from s o l u t i o n s .

The r e s u l t s obta ined by Cook (1972) i n d i c a t e tha t dur ing

vfeathering the r e i s an o v e r a l l * though somewhat i r r e g u l a r ,

i n c r e a s e i n most major e lements l o ca ted o u t s i d e the a p a t i t e

l a t t i c e ( S iOg , A l jO j^ " 2 ® ' * The i r

i n c r ea se in concent ra t i on , i n some i n s t a n c e s , may r e s u l t from

the i n s o l u b i l e nature o f the host m ine ra l s , but in g e n e r a l ,

i t i s p r o b a b l y the r e s u l t of i n t r o d u c t i o n the cons t i t uen t s

dur ing the course of wea the r ing .

Alumina p l o t t e d a g a i n s t pe rcentage of t o t a l i ron on a

graph i s shown i n F i gu re 13F.

AI2O3 shows weakly a n t i p a t h e t i c c o r r e l a t i o n wi th t o t a l

i r o n i n these sediments . In m a j o r i t y of the samples, A l jO^

remains constant and the t o t a l i r o n i s found to be v a r y i n g .

The r e l a t i o n s h i p between the two ox ides s u g g e s t s that alumina

i s a p a r t i t i o n e d element between a l u m i n o - s i l i c a t e and ca rbonate

f l u o r a p a t i t e m i n e r a l s . I t i s a l s o i nd i c a t ed tha t both t o t a l

i r o n and alumina behave almost s i m i l a r l y i n a sha l l ow marine

environment which i s s u b j e c t e d to rap id phys i co - chemica l

changes even at a shor t d i s t a n c e due to the mixing of the land

de r i v ed m a t e r i a l . Their concent ra t i on i s a f f e c t e d only by

hydroxyphosphates of Mg and o ther c a t i ons in s l i g h t l y a l k a l i n e

I l l

lOh

CD B]

5 '

2

0

0 ' 6

0-5

S js:o-3

0-2

0-1

0

0 - 6

0-5 Oi»

O cO-3 X

0-1

0 -

•r= -015 orrr 018

J • . '

»P 20 Vo Si 02 • r= 016 or=0-10

30

2 1 + 6 8 % MgO

•r= - 0 - 2 9 or= 0-5,

10 12

12

10

<08 0 rJ -01 6 UL

2

0

25

cmIO O o

2 6 8 10 12 13 V.Fea O + FeO

12

10

8

0 01 6 z

U

7

0

•r = - 0 0 2 or= 0-18

• •

30

•r = 005 or= 0-76

0 .. t

• <» <

h 6 8 10 12 v.Mgo

H •r = -0-37 or= 0-25

12

10

8 0 0 1 S. 6 s?

It

2

0

12

10

8 n O , N 6 <

2

0

30

(75

20

10

J J u. ._J 1 6 6 10 12 13

V . F e a O + F e O

.r= o-iu c <>r= 0-83

. ' f '

• r = - 0 - 1 0

3 0

« • • •

2 6 8 % F e 2 03+ FeO

10 12 II*

4 0 0

10 20 30 V . P 2 O 5

7

6

10 o c5 .V

• . *

10 20 30 1*0 V, P2O5

70

60

O 50 F

o o 1*0

30

20

10

0

• • • • • •

K

% '

10 20 V.PaOj

30 ifO

Fig. 13. Graphical representation of Si02-Al20g, Si02-Fe202

MgO-MnO, Mg0-C02, Fe20 FeO-MgO, P20g-Si02/Al20g, P20g-Ca0/Si02 and

Si02-Mg0,

Fe20g+FeO-MnO, P20g-CaO/MgO

in Maldeota ( • ) and Durmala ( 0 ) phosphorites.

1 1 2

( c a l c a r e o u s ) medium (Wedepohl, 1970 ) . The Fe202/Al202 r a t i o

i n Maldeota phosphor i te f a l l s between 1.38 to 10.10 ( T a b l e - I X )

which i s l ower than that of Durmala phospho r i t e s where i t

ranges f rom 0.20 to 20.0 ( T a b l e - X I l ) i n d i c a t i n g c l o s e a s s o -

c i a t i o n of a l u m i n o - s i l i c a t e m i n e r a l s .

Pe203 + PeO v s . MnO :

I t i s l o g i c a l t o b e l i e v e that both Mn and Fe a re

int roduced i n t o the phospho r i t e i n course of weather ing and

both of them are l oca ted o u t s i d e the a p a t i t e l a t t i c e - an

ab so rp t i on supported by the s t u d i e s of Cook ( 1 9 7 2 ) . Murty,

e t a l . (1973 and 1980) . Rao, e t a l . (1976) have c l e a r l y

e s t a b l i s h e d the presence of non - l i thogenous i r o n and Mn i n

the form of hydrox ides in the s h e l f sediments , p a r t i c u l a r l y

i n the s h e l f r e g i o n . In v i ew of t h i s f a c t , and i t s nega t i v e

c o r r e l a t i o n with Mn i n the nor thern r eg i on and the l ack of any

c o r r e l a t i o n in the south, i t seems p o s s i b l e that a p a r t of

phosphate in these sediments was f i x e d in a s s o c i a t i o n with

i r o n ( a s f e r r i c - p h o s p h a t e ^ ) .

I ron ox ide p r e c i p i t a t e s at a lower pH than MnO, thus

i r on and MnO may be separa ted but i t i s not s o . Neut ra l

p r e c i p i t a t i o n in a s l i g h t l y reduc ing environment g i v e s s i m u l -

taneous p r e c i p i t a t i o n of both ca rbona te s . Separa t ion of i r o n

and Mn i s a l s o p o s s i b l e under o x i d i z i n g c o n d i t i o n s because

i r o n ox ides o r hyrox ides p r e c i p i t a t e s at a l owe r o x i d a t i o n

p o t e n t i a l Eh than the comparable Mn compounds at a g iven pH

( see Mason, 1966) .

113

G r a p h i c a l r e p r e s e n t a t i o n of ^^^ r e l a t i o n

to MnO ( F i g . 13G) shows that an a n t i p a t h e t i c c o r r e l a t i o n

e x i s t s between these ox ides i n Maldeota phosphor i t e s whereas

in Dunnala they have p o s i t i v e r e l a t i o n s h i p .

T a b l e s - I X , X and X I I r e v e a l that phosphor i t e s of the

study a rea have a high and v a r i a b l e MgO/MnO and FeO/MnO r a t i o s .

The v a r i a b l e PeO/MnO r a t i o i n d i c a t e s that i r o n and manganese

were d e l i v e r e d a t the s i t e of d e p o s i t i o n i n d i f f e r e n t p r o p o r -2+ 2+ t i o n s . Fe i n s o l u t i o n i s more e a s i l y o x i d i z e d than Mn and

2+

i t i s s t a b i l i z e d as ^©2^3 FeCOH)^/ whereas Mn o x i d i z e s

to MnCOH)^ o r Mn(OH)^ or Mn02.

I t i s presumed tha t the pH of the medium might have

s l i g h t l y i nc r ea sed due to the mixing of v a r i o u s t e r r e s t r i a l

m a t e r i a l s g i v i n g r i s e t o s e v e r a l chemical changes that r e s u l t e d

in enrichment of Fe and Mg as ox ides and d e p l e t i o n in the

concent ra t i on of MnO.

Fe203 + FeO v s . MgO :

The a n t i p a t h e t i c r e l a t i o n s h i p between ^62^3

in the phosphat ic rock samples o f P i t h o r a g a r h area ( U . P . ) ,

has been exp la ined as due to the s i m i l a r i t y of Mg"*" wi th

Fe"*" i ons tha t caused mutual s u b s t i t u t i o n of each o ther under

s i m i l a r phys ico -chemica l c o n d i t i o n s f o r t h e i r enrichment ( s e e

Khan, 1978 ) .

The r e l a t i o n s h i p between t o t a l i r o n and MgO i s shown

i n f i g u r e 13H f o r Mussoorie phospho r i t e s . The Maldeota phos -

p h o r i t e s i n d i c a t e an i n v e r s e r e l a t i o n s h i p whereas the Durmala

1 1 4

h-5

O ^ 3

1.5

+ LrME STONE oSHALE

10 20 30 40 50 60

Vo CaO

Fig. 14. Graph showing the relationship of CaO and in limestone and shale of Maldeota and Durmala phosphorite deposits.

115

phosphor i t e s r e f l e c t a sympathet ic r e l a t i o n s h i p between the

two c o n s t i t u t e n t s .

An a n t i p a t h e t i c r e l a t i o n s h i p between these rocks 2+ 2+ may be due t o the s i m i l a r i t y of Mg ion with Fe which

caused mutual s u b s t i t u t i o n of one f o r the other under s i m i l a r

phys i co - chemica l cond i t i ons f o r t h e i r enr ichment .

Si02/Al203 v s . P2O5 s

When Si02/Al203 r a t i o ( T a b l e s - I X and X I l ) was p l o t t e d

a ga in s t r e s p e c t i v e P2O5 v a l u e s ( F i g . 131 ) , i t was observed

that P2O5 i n c r e a s e s with the dec rease of Si02/Al203 r a t i o .

The author i s of the op in i on tha t P2^5 a l s o be taken as

a matur i ty index and i t s abundance in rocks should be an

i n d i c a t o r of t h e i r m i n e r a l o g i c a l ma tu r i t y . C lose a f f i n i t y

of ^2^5 l imestones , do lomi tes and q u a r t z i t e s a l s o f a v o u r s

the above o b s e r v a t i o n .

CaO/siOj v s . P2O5 :

G r a p h i c a l r e p r e s e n t a t i o n of P2O5 in r e l a t i o n to CaO/si02

r a t i o ( T a b l e s - X I and X I I ) i s shown in F i gu re 13J. I t i s

observed tha t with the i n c r e a s e of Ca0/si02 r a t i o there i s

an i n c r e a s e in P2O5 content .

CaO/MgO v s . P2°5 '

The CaO/MgO r a t i o ( T a b l e - X I and X I I ) p l o t t e d a g a i n s t

P2O5 i n d i c a t e s an inve r se r e l a t i o n s h i p ( P i g . 13K) . I t has

116

a l r e a d y been s t a t e d tha t i n the p roce s s e s of p2®5 enrichment

the re i s a g r a d u a l removal of CaO and MgO up t o a c e r t a i n

l i m i t (up t o 30-35% of whereas MgO remains s t a t i o n a r y

and on ly CaO i s removed a t t h e expense of MgO,

Accord ing to Martens and H a r r i s (1970) the magnesium

i ons seem to r e t a r d the r e a c t i o n ( s a l i n i t y ) when Ca/Mg r a t i o

approaches 4 ,5 to 5 . 2 . The d i a g e n e t i c r e a c t i o n o c c u r r i n g w i t h i n

anox ic sediment cou ld a r i s e the Ca/Mg r a t i o t o the p o i n t where

a p a t i t e may p r e c i p i t a t e .

PETROCHEMICAL FIELDS AND TRENDS :

The i d e a of t h i s s tudy was taken f rom Green and

P o l d e r v a a r t ( 1 9 5 8 ) . Though i t i s d i f f i c u l t t o d e r i v e a g e n e r a l

t rend f o r sedimentary rocks due t o t h e i r complex p h y s i c o -

chemical c o n d i t i o n s which b rough t out t h e s e r o c k s . An attempt

i s made he re t o d i s c u s s the geochemica l c h a r a c t e r i s t i c s of

the v a r i o u s c o n s t i t u ^ e n t s of the p h o s p h o r i t e s i n the l i g h t of

a p p r o p r i a t e t r i a n g u l a r d i ag r ams based on the a n a l y t i c a l

de te i rminat ions . The bu lk components are r e c a l c u l a t e d t o

pe r cent we ight ( T a b l e s - X I I I t o XXVI ) .

F i g u r e - 1 5 A i l l u s t r a t e s Ca0-Mg0-P20^ d iag ram showing the

v a r i a t i o n t r end of CaO and P2O5 with r e s p e c t t o MgO i n the

system. Th i s t r end r e v e a l s t h a t most of the p o i n t s l i e a long

Ca0-P20^ l i n e and MgO does not i n c r e a s e beyond 15 per c e n t . I t

demonst rates t h a t with the a d d i t i o n of P2^5 g e n e r a l l y

a pronounced d e c r e a s e of MgO and CaO f rom Maldeota t o Durmala

p h o s p h o r i t e s .

117

+ 3 O

U K --s •H ^ CM 2 0 a

u

•H O

1 •H 4-> s (U 1-H • s •H a u X3 u

-a

o (A (0 a

C8 4-1 O CD a to S

03

2 1

CO

tl

CO

H

m

.2? b

t- D< o m 'I-* o 2 ^ a a

1 1 8

t o a s CM o a •H

M g

CO

00 •H

119

The CaO-MgO-CO^ ( F i g , 15B) d iagram shows the concen t r a -

t i o n of p o i n t s near Ca co rner a long CaO-C02 s i d e . The system

I n d i c a t e s that MgO i s s y m p a t h e t i c a l l y r e l a t e d to CO^ vdil le

CaO i s I n v e r s e l y r e l a t e d to CO2. The r e l a t i v e l y h i ghe r va lues

of CO2 wi th the inc rease of MgO may be a r e l a t i v e phenomenon

i n d i c a t i n g a p o s i t i v e ev idence f o r a d d i t i o n of these c o n s t i -

tuents in these d e p o s i t s .

The Ca0-Mg0_Si02 d iagram ( F i g . 15C) which a l s o r e p r e s e n t s

almost the same p a t t e r n i n d i c a t e s a composit ion i n which s i l i c a

i n c r e a s e s wi th the i nc r ea se of magnesia a t the expense of l i m e .

However, the lower concen t r a t i on of Si02 in these phosphor i t e s

p robab l y i n d i c a t e s tha t MgO i s r e l a t e d t o carbonate h y d r o x y l -

a p a t i t e r a t h e r than the t e r r i g e n o u s i m p u r i t i e s .

In P igure -15D, the Na20-Ca0-P20g d iagram r e v e a l s tha t

the p o i n t s that l i e a long Ca0-P20^ s i d e have meagre concent ra -

t i on of Na20, The system a l s o i n d i c a t e s that the c o n s t i t u e n t s

are r e l a t e d t o carbonate a p a t i t e . The s i m i l a r t rend of Na20

with r e s p e c t to CaO as w e l l a s ^2^5 i n t e r p r e t e d as due + 2+

to coupled s u b s t i t u t i o n of Na f o r Ca and PO^ to p r e s e r ve

e l e c t r o n e u t r a l i t y . From the d iagram Si02-AI2O3-K2O ( F i g . l 6 E )

i t i s e v i d en t that the p o i n t s are concentrated along S i02 -

AI2O3 s i de i n d i c a t i n g the presence of i n s i g n i f i c a n t amounts

of admixed a l u m i n o - s i l i c a t e mine ra l s in these rocks .

The Ca0-Na20-K20 d iagram ( F i g , 16F) r e v e a l s that most

of the p o i n t s are concent ra ted at CaO c o r n e r .

The d iagram of P20g-H2 0-CO2 ( F i g . 16G) i n d i c a t e s the

v a r i a t i o n t rend of P2°5 ^^^^ r e s p e c t to COj + system

1 2 0

Ftj 0,+ F«0 V. ^ rlOO

100

MgOVo vlOO

CQO %

100 —r-—I 1 1 1 1 1 1 1-10 20 30 40 50 60 70 50 90 100

Fe203»F»0V. AI2O3V.

Fig. 17- Triangular diagrams showing chemical relationship of important major constituents of Maldeota ( • ) and Durmala { o ) phosphorites.

121

demonstrates p o s i t i v e c o r r e l a t i o n between CO2 and H2O. The

inc rease of CO2 and H^O in the system tends t o decrease the

p^Oj content and v i c e - v e r s a . This trend i n d i c a t e s the s u b s t i -

tu t ions of PO^ by CO^OH as w e l l as the p o s s i b i l i t y of PO^ by

(OH)^ both at Maldeota and Durmala p h o s p h o r i t e s .

The t e r n a r y diagram of Ca0-Mg0-Pe202+Fe0 ( F i g . 16H)

shows s c a t t e r of po in t s at CaO corner/ i n d i c a t i n g a weakly

p o s i t i v e c o r r e l a t i o n between MgO and Fe202+Pe0, CaO i n c r e a s e s

at the expense of MgO and the t o t a l i ron content in carbonate

rocks .

In Ca0-Fe202+Pe0-Na20+K20 diagram ( F i g . 171) most of

the p l o t s l i e on CaO-FejOj+FeO s i d e and s l i g h t l y sp read ing

towards Fe202+Fe0 corner showing- v a r i a t i o n i n t o t a l i r on

though the t o t a l a l k a l i e s remain almost cons t an t . I t i s

observed tha t behav iour of t o t a l a l k a l i e s i s not much a f f e c t e d

with the v a r i a t i o n of l ime and the t o t a l i r o n i n d i c a t i n g

d e p o s i t i o n o f these rocks i n a s l i g h t l y a l k a l i n e medium.

F i g . 17J shows v a r i a t i o n o f Mg0-Fe202+Pe0-Al202 in

the t e rna ry diagram with s t r ong s c a t t e r of po in t s widening

towards the MgO-Al202 s i d e . I t i n d i c a t e s h i g h e r percentage

of t o t a l i r o n and MgO. I t might be due t o the presence of

p y r i t e and f e r romagnes ian minera l s i n these sediments .

CONCLUSION :

Mussoorie phosphorites of Tal sedimentation basin are

a s soc i a t ed with l i m e s t o n e - c h e r t - s h a l e s u c c e s s i o n . The g e o -

chemical study of these sediments r e v e a l s tha t i n the l i m e -CaO i s 43.84%,

stone,^C02 - 23.05%, Si02 - 15.51% and MgO - 5.77%. The rock

1 2 2

i s poor i n alumina (2.16%)/ i r o n (4.08%) and a l k a l i e s (Na20

and K2O - 0.57% and 0,08% r e s p e c t i v e l y ) . The cher t i s made

up of 70.14% of Si02 and 12.20% of CaO^ and i t i s poor i n

o ther c o n s t i t u e n t s . B lack s h a l e s have h i g h e r concent ra t i on

of S iO j (45 .05%) , CaO (2 3.13%) and CO^ (9 .39%) and l ower

concent r a t i on of other ma jo r o x i d e s . The most common type o f

phosphor i t e s i n the Mussoorie area conta ins PgO^ (10% t o 33%),

CaO (43 .17%) , Si02 (11 .30%) , MgO (3.64%) and CO2 (11 .30%) .

The d i s t r i b u t i o n o f v a r i o u s chemical c o n s t i t u e n t s , as

mentioned above, show a wide v a r i a t i o n from rock to rock i n

the d i f f e r e n t l i t h o l o g i c a l u n i t s of the a r e a . This v a r i a t i o n

in chemical composit ion may {nerhaps be due t o changes i n the

supply of the ma te r i a l or a v a r i a t i o n i n phys i co - chemica l

cond i t i on o f the b a s in of d e p o s i t i o n .

On p l o t t i n g Si02, CaO and MgO contents of the Mussoor ie

phosphor i t e s a ga in s t the r e s p e c t i v e va lue s o f ^2^5'

3 c o n s t i t u t e n t s have i n v e r s e r e l a t i o n s h i p among themselves

that may i n d i c a t e a g r adua l replacement of these ox ides by

P20^ dur ing d i a g e n e s i s . S ince m a j o r i t y of the samples have

Ca0/P20g r a t i o g r e a t e r than 1 .31, the most common s u b s t i t u t i o n — 3 2—

i s that of PO^ by CO^ (Maur ice S lansky, 1986 ) . The sympathet ic

r e l a t i o n s h i p o f H2O''" with Ca0/P20^ r a t i o sugges t s the p o s s i -

b i l i t y of r e v e r s i b l e s u b s t i t u t i o n between PO^:;;iii:i(OH)^.

This v iew i s supported by Bane r j ee , e t a l . (1984)

that a p a r t i c u l a r pe rcentage of an element in a rock and

i t s d i s t r i b u t i o n w i th in v a r i o u s rock c o n s t i t u e n t s i s p r i m a r i l y

c o n t r o l l e d by the a v e d l a b i l i t y of these e lements i n the fo rma-

t i o n a l environment and t h e i r i o n i c r a d i i which determine the

p o s s i b i l i t i e s of i n t e r e l ement l a t t i c e accommodation.

1 2 3

The low manganese content and enrichment of P2O5 in

younger sediments i n d i c a t e s a sha l lowing in the b a s i n of

d e p o s i t i o n i n the l a t e r s t a g e s of phosphate f o m a t i o n which

l ed in the l ower ing of pH, mixing of land d e r i v e d m a t e r i a l s

and f l u o r i s h i n g of a l gae and other b ioherms.

The p r e c i p i t a t i o n of CaCO^ i n d i c a t e s a warm and a r i d

c l imate due t o which on ly few r i v e r s f l owed in to the b a s i n

b r i n g i n g very little detrital m a t e r i a l . Pet rochemica l f i e l d s

and t rends a l s o i n d i c a t e t h a t these rocks were depos i t ed in

g e o s y n c l i n a l b a s i n under s h a l l o w water reducing cond i t i ons

supported by low FeO/MnO r a t i o . The low concent ra t i on of

a l k a l i e s and t h e i r i n t e r r e l a t i o n s h i p , r ep r e sen ted by t e r n a r y

d iagrams, sugges t tha t the d e p o s i t i o n of phosphate might have

been f avou red by a s l i g h t l y a l k a l i n e medium o f t e n approaching

a ve ry weakly a c i d i c medium in an e u x i n i c m i l i e u .

CHAPTER - VI

GEOCHEMISTRV OF

THE TRACE ELEMENTS

CHAPTER ~ V I

GEOCHEMISTRY OF THE TRACE ELEMENTS

GENERAL STATEMENT J

I n r e c e n t y e a r s the chemical compos i t i on of r o c k s ,

more p a r t i c u l a r l y the d i s t r i b u t i o n of t r a c e e lements I n

sediments has been used f o r d i s t i n g u i s h i n g and I d e n t i f y i n g

p r e c i s e l y t h e i r d e p o s l t l o n a l env i ronment , some of the e a r l i e r

workers , p a r t i c u l a r l y i n the e a r l i e r y e a r s o f t h i s c en tu ry ,

have emphasized the d i s t r i b u t i o n and s i g n i f i c a n c e o f t r a c e

e lements i n g e o l o g i c a l m a t e r i a l s . Washington ( 1 9 3 1 ) , w h i l e

d i s c u s s i n g t h e d i s t r i b u t i o n o f chemical e l ements i n the e a r t h ' s

c r u s t found t h a t the minor e lements a re r e l a t e d not on l y t o

the rock types but a l s o t o the m a j o r e l ements c o n s t i t u t i n g

the r o c k s .

Accord ing t o the concept of t r a c e e lement geochemxstry by

Goldschmldt ( 1 9 5 4 ) , c e r t a i n minor e lements have a tendency t o

f o l l o w the c o n c e n t r a t i o n t r e n d s of major e lements t h a t a re

s i m i l a r t o t h e i r i o n i c r a d i i and bond t y p e s . He found t h a t

the d i s t r i b u t i o n o f e lements xn d i f f e r e n t phases depends upon

the e l e c t r o n i c c o n f i g u r a t i o n of t h e i r atoms. G ra f (1960) n o t i c e d

the f o l l o w i n g forms In which minor and t r a c e e lements occu r xn

some c a r b o n a t e rocks - i ) s o l i d s o l u b i l i t y i n the i n d i v i d u a l

m i n e r a l s , 11) i n d e t r l t a l m i n e r a l s , i l l ) as a u t h l g e n l c p r e c i -

p i t a t e s , i v ) as b y - p r o d u c t s of r e c r y s t a l l i z a t l o n and v ) as

i n d i v i d u a l e l ements , o r t h e i r compounds adsorbed on the

v a r i o u s m i n e r a l s .

125

Strakhov and h i s co -worke r s (1956) found tha t Pe, Mn,

P and a number of minor e lements such as V, Cr , N i , Co, Cu,

Pb, Zn, Ga and some o the r s a r e t r an spo r t ed by r i v e r wa te r s

mainly i n suspens ion and t o a minor ex tent on ly i n t rue

s o l u t i o n . Among the suspended m a t e r i a l s , the re are some c o a r s e r

f r a c t i o n s whose t r a n s p o r t a t i o n i s s l ower than tha t o f the f i n e r

ones . These d i f f e r e n c e s i n mode of element m ig r a t i on i n streams

a r e p a r t l y r e s p o n s i b l e f o r the d i f f e r e n t i a t i o n of e lements du r ing

sed imenta t ion .

Elements adsorbed i n c o l l o i d a l matter tend t o accumulate

i n the c l a y zone, whereas t h e d e t r i t a l m i n e r a l s and elements

p r e sen t i n t h e i r l a t t i c e s a r e depos i t ed both i n s i l t s and sands .

In tense chemical weather ing of the source r ock breaks down the

complex s i l i c a t e s , a l u m i n o s i l i c a t e s and s u l p h i d e s of i gneous

and metamorphic r o c k s . The t r a c e e lements thus r e l e a s e d a r e

u s u a l l y Pe, Mn, P , V, Cr , Co, Cu, Pb, Zn, Be, e t c . that mig ra te

p a r t l y i n suspens ion as c l a y mine ra l s * consequent ly there w i l l

be a h i ghe r concent ra t ion o f the elements i n the f i n e g r a i ned

a r g i l l a c e o u s and ca l c a r eous deep water sed iments .

A p a t i t e s a re capab l e of concent ra t ing c o n s i d e r a b l e

amounts of v a r i o u s t r a c e e lements ( s e e Gu lb randsen , 1966;

Kholodov, 1973; C a l v e r t , 1976; A l t s c h u l e r , 1980; P revot and

Lucas , 1980 and McArthur, 1980 ) . As po in ted out by Tooms, e t a l .

( 1969 ) , the t r a c e element p a t t e r n i s a f u n c t i o n of two f a c t o r s -

a c r y s t a l chemica l , the c a p a b i l i t y of the a p a t i t e l a t t i c e t o

accept f o r e i g n t r a c e i ons and a geochemical one, the a v a i l a b i l i t y

of these e l a n e n t s i n the environment of the a p a t i t e f o r m a t i o n .

126

The t r a c e elements tha t tend t o show a s i m i l a r g e o -

chemlcal t rend i nc lude , Ba, Co, Cu, L i ( ? ) , N i , Pb ( ? ) , Rb,

and Zn. A l l o f them are b e l i e v e d t o be l o c a t e d ou t s i de the

a p a t i t e l a t t i c e . The i r i n c r e a s e in c o n c e n t r a t i o n in some

ins tances may r e s u l t from the i n s o l u b i l i t y o f the host m i n e r a l s ,

but i n g e n e r a l , i t i s p r o b a b l y , the r e s u l t o f i n t r o d u c t i o n

dur ing the course of weather ing ( s ee Cook, 1972) ,

Accord ing t o K r e j c i - G r a f ( 1972 ) , T i and Th are the

c h a r a c t e r i s t i c t r a c e e lements a s soc i a t ed w i t h i n sediments and

t h e i r s u r f a c e s tha t undergo a long pe r iod by s u b a e r i a l weath -

e r i n g , They a re known as a t y p i c a l cont inent e lements . T h e i r

contents d ec r ea s e with i n c r e a s i n g d i s t a n c e o f the d e p o s i t i o n a l

s i t e s from the l a n d . The t r a c e e lements v i z , , B, Cr , Cu, Ga,

Ni and V a re more concentrated i n marine than i n c o n t i n e n t a l

sediments, C r concent ra tes i n the sediments of g y t t j a f a c i e s

( s l i g h t l y a n a e r o b i c ) , w h i l e V concent ra tes i n sediments of

saprope l f a c i e s ( h i g h l y a n a e r o b i c ) , Concent ra t ion of Pb , N i

and Co a lways takes p l a c e w i t h i nc r ea s ing reduc ing c o n d i t i o n s ,

N i and Cu sometines become enr iched in o r g a n i c matter i n the

d e p o s i t s formed i n a r educ ing environment.

D i s t r i b u t i o n and concen t r a t i on of some other t r a ce

e lements , l i k e Mg, S r , Mn i n the ca rbonate r o c k s , are o f t e n

used as environmenta l i n d i c a t o r s . However, the d i s t r i b u t i o n

of these e lements i s a l s o s t r o n g l y i n f l u e n c e d by d i a g e n e t i c

p r o c e s s e s , S r has o f t e n been used as f a c i e s i n d i c a t o r , and

i t s concen t r a t i on i n c r e a s e s f rom b a c k - r e e f f a c i e s t o f o r e - r e e f

f a c i e s . Accord ing V e i z e r and Demovic (1974) Sr i s environment

s e n s i t i v e , a l though d i a g e n e s i s and the nature of carbonate

minera l s p r e s e n t a l s o a f f e c t i t s d i s t r i b u t i o n .

127

According to B a n e r j e e , e t a l . ( 1984 ) , the g e o l o g i c a l

l i t e r a t u r e has abundant documentation t o show tha t the

environment p l ayed s i g n i f i c a n t r o l e s and o f t e n assumed

pr imary importance f o r the compos i t iona l changes in the

marine p h o s p h o r i t e s , c a rbona tes and some a s s o c i a t e d sed iments .

O f t en , the d i s t r i b u t i o n and concen t r a t i on of some t r a c e e lements

i n carbonate rocks , a r e used as environmenta l i n d i c a t o r s .

However, d i s t r i b u t i o n of e lements i s i n f l u e n c e d by geog raph ic

f a c t o r s of element a v a i l a b i l i t y , type and i n t e n s i t y of wea the r -

ing i n the source a r ea , deg ree of s o r t i n g d u r i n g t r a n s p o r t a t i o n ,

i n t e r s t i t i a l pore wate r , e a r l y d i a g e n e t i c changes, hydrodynamic

behav iour of c l a s t i c s t o the cu r r en t s , waves, provenance and

d i s p e r s a l p a t t e r n , r e a c t i o n s t a k i n g p l a c e a t the sediment

w a t e r - i n t e r f a c e and a l s o r e a c t i o n s w i th in and amongst the

p r oduc t s .

An attempt has been made to p r e s en t and d i s c u s s the

geochemical abuwiance and d i s t r i b u t i o n of c e r t a i n s i g n i f i c a n t

t r a c e e lements l i k e Cu, Pb, N i , Co, Zn, Cr , s r , Ba, Rb, V, L i ,

and Cd i n the Mussoor ie phospho r i t e s and a s s o c i a t e d rocks

i n d i v i d u a l l y i n the l i g h t o f the work done as c i t e d above .

The concen t r a t i on t rend of the v a r i o u s t r a c e elements o c c u r r i n g

i n the phospho r i t e s of the s tudy a rea have been compared wi th

the average va lue s of t r a c e e lements in phospho r i t e s g i v en by

Krauskopf (1955) and t r a c e e lement th r e sho ld v a l u e s f o r Phos -

pho r i a Formation o f U . S . A . g i v e n by Gu lbrandsen (1966) and

t r a c e e lements i n Moroccan phosphor i t e s f rom Prevot and Lucas

(1979) ( T ab l e -XXX ) .

1 2 8

The abundance and concen t r a t i on t r e n d s of twe lve t r a c e

elements i n phosphor i t e s and the a s s o c i a t e d rocks of the

Maldeota and D u m a l a mining b l o c k s o f Mussoor ie are p r e s en ted

i n Tab les -XXVI I# XXVI I I and XXIX. The r e l a t i v e abundance,

concent r a t i on t rends and ave rage concen t r a t i on of c e r t a i n

t r a c e eieinents (Cu, Zn, N i , Co, Cr , V, Ba and S r ) i n the p h o s -

p h o r i t e s and a s s o c i a t e d hos t rocks have been shown i n P i g u r e s -

18, 19 and 20.

The geochemistry and d i s t r i b u t i o n of i n d i v i d u a l t r a c e

elements have been d i s c u s s e d i n the f o r e g o i n g p a g e s .

copper :

Copper i s a s t rong c h a l c o p h i l e e lement i n i t s geochemical

b e h a v i o u r . I t shows h igh a f f i n i t y wi th su lphur but smal l amounts

of copper have a l s o been r epo r t ed from s i l i c a t e and ca rbonate

phases . Due to s i m i l a r i t y of r a d i i o f Cu "** ( 0 .69 X) and Pe^"*"

( 0 .76 8 ) . Carobb i and P i e r u c c i n i (1947) have suggested t h a t 2+ 2+

Cu r e p l a c e s Pe and Mg f o r i n s t ance , i n t ou rma l ine .

Copper has s i m i l a r mean concent ra t i on i n a l l the rock

types bu t wi th a maximum v a l u e i n the c h e r t s , though the l e v e l

of c oncen t r a t i on be ing a p p r e c i a b l y be low the C la rke va lue f o r

sedimentary r o c k s . They i n d i c a t e tha t most of the copper i s

a s s o c i a t e d w i th c l a y m i n e r a l s , copper i n the weather ing c r u s t

i s thus a s s o c i a t e d with c l a y minera l s and su l ph ide o x i d a t i o n

p r o d u c t s . Cu tends t o be l o s t from the ca rbonate p h o s p h o r i t i c

rocks whose minera l compos i t ions are g r e a t l y a l t e r e d by wea the r -

ing ( s e e p rosh l ayakova , e t a l . , 1987 ) .

129

The e l ementa l m o b i l i t y i n secondary o x i d i z i n g and

a c i d i c environments can be h igh f o r the t r a c e elements l i k e

Cu, isn, N i and Co. Vflien the r e l a t i v e m o b i l i t y f o r an element

i s low# the observed concen t r a t i on of tha t element i s bound

to be h i gh ( s e e Roonwall and Kumar, 1987 and Ghosh* 1988 ) . Ba,

Cu, Mn, Ni and V have normal abundance i n phosphor i t e s and

sha l e s ( s e e Tooms, e t a l . , 1969 and Mohammad, e t a l » , 1981 ) .

Copper and uranium are ca rbonate hosted and conf ined t o the

marg ina l s h e l f sequence ( s e e Singh, 1988 ) .

Krauskopf (1956) has shown tha t Cu i s e f f e c t i v e l y

absorbed by Pe (OH)^, Mn(0H)2 and c l a y m i n e r a l s . The Cu

content i n phosphor i t e s as r epo r t ed by Krauskopf (1956) and

i n phospho r i t e s o f Phosphor ia Formation of U . S . A . r epo r t ed by

Gulbrandsen (1966) i s 4 t o 40 and 100 ppm r e s p e c t i v e l y . The

concen t r a t i on of Cu i n Ma ldeota phosphor i t e s v a r i e s f rom 12 ppm

to 99 ppm whereas i n Durmala phospho r i t e s i t ranges from 21 ppm

to 72 ppm. The host rocks , a s s o c i a t e d wi th phospho r i t e s , show

v a r i a t i o n i n the concent ra t i on range of copper from 9 ppm t o

172 ppm, 10 ppm to 140 ppm and 10 ppm t o 204 ppm i n l imes tone ,

cher t and s h a l e r e s p e c t i v e l y . R e l a t i v e abundance o f Cu i n

phosphor i t e s anp l e s of Maldeota i s r ep re sented i n P i g u r e - I S A .

The c o n c e n t r a t i o n t rends and average concen t r a t i on i n the

d i f f e r e n t rock types of the study a rea have a l s o been shown

i n P i g u r e s - 1 9 B and 20. The concent ra t i on r anges o f Cu i n th r ee

d i f f e r e n t rocks c l e a r l y i n d i c a t e p r e f e r e n t i a l abundance of

copper i n b l a c k s h a l e . I t has been observed by s e v e r a l workers

tha t the o r g a n i c f r a c t i o n of b l a c k sha le i s o f t e n l o c a l l y

1 3 0

enr iched i n coppe r . High concent r a t i on o f i r o n i n b l a ck

sha l e s a l s o supports i t s enrichment i n these sediments .

Copper does not show any c o r r e l a t i o n w i th P2®5

i n bu lk o re but shows s i g n i f i c a n t c o r r e l a t i o n with

phosphate concen t r a t e . The i r p resence can be exp l a ined as due

to ad so rp t i on of Cu on the a p a t i t e c r y s t a l s u r f a c e du r ing d i a -

genes i s o r by v i r t u e of t h e i r a f f i n i t y f o r c e r t a i n a s s o c i a t e d

elements ( S a i g a l and Bane r j e e , 1987 ) . Cu and Ca show a l i n e a r

r e l a t i o n s h i p i n a l l the i n t e r - co lumnar ca rbonates but the Cu

p l o t s a g a i n s t "^al^ss show a w ide ly s c a t t e r e d d i s t r i b u t i o n

p a t t e r n i B a n e r j e e , e t a l . , 1984 ) . The p l o t of Cu, Cr and e x t r a c -

t a b l e P i n the sediments w i th the e x t r a c t a b l e P that show a

p o s i t i v e r e l a t i o n s h i p and i n d i c a t e tha t a l l these e l e n « n t s have

a common source , namely, the phosphate minera l phase i n the a l l u -

v i a l sediment s ink in the Doon v a l l e y (S ingh and Subramanian,1988) ,

A sympathetic c o r r e l a t i o n of ^2^5 w i th Cu i s r epo r t ed

i n which Cu can e a s i l y be s u b s t i t u t e d by Ca i n the a p a t i t e

l a t t i c e (BaCtekht in , 1959; C r u f t , 1966; Saraswat , e t a l . , 1987

and I s r a i l i and Khan, 1980 ) .

Phosphorus and copper have s i g n i f i c a n t p o s i t i v e c o r r e l a -

t i o n wi th o r gan i c matter , p o i n t i n g towards c e r t a i n c o n t r i b u t i o n

to the enrichment of these e l e n « n t s in the d e p o s i t i o n a l e n v i r o n -

ment (A l -Bassam, e t a l . , 1983 ) . Cu might have r e p l a c e d on a minor

s c a l e t o Ca i n the a p a t i t e l a t t i c e or i t may be p re sent as an

a d s o r p t i v e e lement .

In the study a rea , a weak sympathetic c o r r e l a t i o n i s

obta ined between Cu and P jO^ ( F i g . 22 A ) . Th i s i n d i c a t e s the

s u b s t i t u t i o n o f Cu by Ca i n the a p a t i t e l a t t i c e or i t may a l s o

131

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trace elements (Cr, Sr, V, Ba, Cu, Ni, Co. Zn) in limestone, chert and shale of Maldeota and Durmala phosphorites.

133

be due t o the adso rp t i on of Cu on the a p a t i t e s u r f a c e du r ing

d i a gene s i s / Cu p l o t s a g a i n s t Mg show a w i d e l y s c a t t e r e d

d i s t r i b u t i o n p a t t e r n i P i g . 23B ) .

The h i g h l y v a r i a b l e Cu/Al and Cu/Mg r a t i o s iTab les -XXXI

and XXXV) i n phosphor i t e s sugge s t a noncoherence of Cu wxth

the two e l ements . The graph showing Cu/P r a t i o p l o t t e d agaxnst

pe rcentage phosphorus ( P i g . 24A) i n d i c a t e s a w ide l y s c a t t e r e d

c o r r e l a t i o n . This sugges t s i o n i c s u b s t i t u t i o n of copper i n

phosphate l a t t i c e o r i t has been adsorbed by the gangue c o n s t i -

tuents of phospho r i t e s a t the s i t e o f d e p o s i t i o n .

An i n v e r s e r e l a t i o n s h i p i s ob ta ined when pe rcentage of

magnesium i s p l o t t e d a g a i n s t Cu/Mg r a t i o ( F i g . 24B ) . This a l s o

supports the above mentioned v i ew that copper r e p l a c e s magnesium.

According to Krauskopf , the concen t r a t i on of Cu i n phosphate i s

due to a l g a l mat t e r . Th is p o s s i b i l i t y has a l s o been r epor ted

by Verraa (1978) and Raha (1978) but other workers b e l i e v e tha t

the concen t r a t i on of copper i n sediments a s s o c i a t e d with b l u e

green a l g a e p o s s i b l y be due t o s i m i l a r phys i co - chemica l c o n d i -

t i o n s at the time of t h e i r c o n c e n t r a t i o n .

Lead 8

Lead occurs in the upper l i t h o s p h e r e both as a c h a l c o -

p h i l e and l i t h o p h i l e e l ement . I t i s p r e sen t i n s i l i c a t e and

phosphate mine ra l s as Pb^"*" i ons and p a r t i c u l a r l y r e p l a c e s Ca

(1 .06 %) d i a d o c h i c a l l y . I t i s a l s o found i n such ca lc ium

minera l s as a p a t i t e (up to 50 g/ton Pb; Goldschmidt , 1937 b ) .

1 3 4

The i o n i c r a d i u s of Pb (1 .32 X) makes i t p o s s i b l e t o r e p l a c e

Sr (1 .27 X ) . Accordingly^ d i v a l e n t l ead commonly occurs i n the 2+

s t r u c t u r e of potass ium f e l d s p a r s . I t may r e p l a c e Ca i n mine ra l s

formed a t l ower te r rperature .

High contents of Pb a r e a t t r i b u t e d t o su lph ides by

B l i s s k o v s k i y (1969 a ) who proposed that the normative l e ad

i s f i x e d by adso rp t i on on the marine a p a t i t e . The C la rke l e v e l

f o r the Pb charged sedimentary rocks i s 20 ppm. The Pb l e v e l

i n the Karatau i n Kurumsak-Chulakta phospho r i t e s i n i s o l a t e d

cases a t t a i n 0.3% ( see Kholodov, 1973) . There i s a Pb peak

i n the supergene zone in the phosphate r i c h rocks , whereas

the u n a l t e r e d rocks have the maximum Pb i n the c l a y e y -

p h o s p h a t i c - s i l i c e o u s s h a l e s ( c h e r t s ) ( s e e Ramsay and E a s i l y ,

1983; and P rosh layakova , e t a l . # 1987) . Because of the e f f i -

c i ency of su l ph ide p r e c i p i t a t i o n of l e a d , i t i s sometimes

found i n f a i r l y h igh concen t r a t i on i n sediments formed under

reducing c o n d i t i o n s ( s e e Encyc l . of Geochem. and Env. S c . , 1972 ) .

L imestone and do lomi tes a re g e n e r a l l y low in l e a d . In

these rocks i t s concent ra t i on i s h i g h l y v a r i a b l e as ev idenced

by 5 -10 ppm (Rankama and Sahama, 1950 and Krauskopf , 1955) ,

16 ppm (Runnels and Sch leecher , 19b6) , 26 ppm (Ostrom, 1957)

and 7.2 ppm (Graphs , 1960 ) . The concent r a t i on of Pb i n the

l imestone o f Mussoorie v a r i e s f rom 34 ppm t o 50 ppm, whereas

i n the phospho r i t e s and b l a c k sha l e i t goes up to 148 ppm and

92 ppm r e s p e c t i v e l y .

Lead p l o t s a g a in s t z i nc show s c a t t e r e d d i s t r i b u t i o n

p a t t e r n ( P i g . 21A) whereas a weak p o s i t i v e r e l a t i o n s h i p i s

obta ined between l ead and cadmium in the Mussoor ie phosphor i t e s

135

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( F i g . 21B) v^ l ch i n d i c a t e s c l o s e a s s o c i a t i o n of l ead with

cadmium i n these sediments .

C a l c i t e and do lomite cannot i n c o r p o r a t e s i g n i f i c a n t

amount of l e a d because sea water and i n t e r s t i t i a l waters

u s u a l l y c o n t a i n ve ry l i t t l e l e a d . +2 I t may be suggested t h a t the minor content of Pb

+2

might have been r ep l aced by Ca i n o x i d i z i n g cond i t i ons of

the marine environment. Th is Pb may a l s o be adsorbed i n the

gangue c o n s t i t u e n t s of the phosphor i t e r o c k s . Some mob i l i s ed

l ead i s adsorbed on newly formed c l a y m i n e r a l s as k a o l i n i t e

( s e e Wedepohl, 1974 ) .

In the study a rea , s l i g h t l y h igh c o n c e n t r a t i o n of l e a d

i n phospho r i t e s and b lack s h a l e s i n d i c a t e s i t s p r e c i p i t a t i o n

wi th p y r i t e which i s an i n d i c a t o r o f r educ ing cond i t i ons of

the d e p o s i t i o n a l b a s i n .

N icke l :

Geochemica l l y , n i c k e l i s a s i d e r o p h i l e element and i t s

bu lk i s found i n nreta l l i c i r o n . I n ac id i gneous rocks Ni i s

l e s s en r i ched than in b a s i c and u l t r a b a s i c r o c k s .

Dur ing weather ing of u l t r a b a s i c rocks the element forms

a number of h y d r o s i l i e a t e s w i th compl icated chemical compos i t i on .

According t o Go ldschmidt ( 1 9 4 4 ) , n i cke l i s l i k e l y t o be enr iched

i n magnesium bea r ing mine ra l s because N i - 0 bond i s s t r o n g e r than

Mg-0 bond and more cova l en t i n na tu re .

1 3 7

The Ni l e v e l s In the phosphor i t e b e a r i n g beds of

Dzhanatas depos i t/ Malyy, Karatan b a s i n a r e l e s s than

the C lark v a l u e , a l though i t i s l e s s than f o r Cu, the maximum

be ing 100 ppm i n a s i l i c e o u s p h o s p h o r i t e s . N i d i s t r i b u t i o n i s

biraodal and i s s i m i l a r t o t h a t of Cr ( s e e Prosh layakova* e t a l . #

1987 ) . N i cke l i n s p i t e of i t s low concen t r a t i on i n phospho r i t e s

behaves a lmost l i k e vanadium. I t i s , however , a l e s s e v i d en t

s u b s t i t u t e i n a p a t i t e which may e x p l a i n i t s lower c o n c e n t r a t i o n .

I t s c o n c e n t r a t i o n i n c r e a s e s when phospho r i t e s conta in g l a u c o n i t e s

and i r o n o x i d e s ( s ee Debrabant and Paquet , 1975 and Lucas , e t a l . /

1978 and S a i g a l and Bane r j e e , 1987 ) . C r u f t (1966) suggested tha t

( i ) the f o rmat i on of a p a t i t e was c o - g e n e t i c with su l ph ide s and

some Ni was i nco rpo ra t ed i n the s t r u c t u r e or ( i i ) l a t e r a l t e r a -

t i on pe rmi t ted Ni t o be r e l e a s e d from the su l ph ide s and i n c o r -

porated i n the a p a t i t e or ( i i i ) Ni i s p r e s e n t i n a very f i n e

g ra ined s t a t e i n su lph ide i n c l u s i o n .

The concent ra t i on of Ni i n carbonate rocks has been

r epor ted by many e a r l i e r workers as 3-10 ppm by Krauskopf

(1955 ) , 10 ppm by Runnels and Sch l e i che r (1956) and 15 ppm

by Graf ( 1 9 6 0 ) . The s t u d i e s c a r r i e d out by Krauskopf (1955)

and Gulbrandsen (1966) i n d i c a t e that in p h o s p h o r i t e s , the Ni

content r anges from 4 to 200 ppm and 100 ppm r e s p e c t i v e l y . The

p re sent s tudy i n d i c a t e s tha t Ni ranges i n abundance f rom 45

ppm t o 342 ppm i n Maldeota phosphor i t e s whereas i t v a r i e s

bet%*een 45 ppm and 140 ppm i n Durmala p h o s p h o r i t e s . The concen-

t r a t i o n of Ni (46 - 250 ppm) i n b l ack sha l e i s h i g h e r than i n

l imestone o r cher t in which i t i s 31 ppm t o 94 ppm and 50 ppm

1 3 8

t o 215 ppm r e s p e c t i v e l y . The r e l a t i v e abundance, concen t r a t i on

and average concent ra t i on t r ends of N i i n phospho r i t e s and

a s s o c i a t e d rocks have been shown i n P i gu r e s - 18B , 19B and 20

r e s p e c t i v e l y .

I n the study a r ea , the s c a t t e r ed r e l a t i o n s h i p between

Ni and Co ( F i g . 21E) i n d i c a t e s that the Co i o n i c r a d i i d i f f e r

from that of phosphorus and i t i s not so easy to accommodate

Co i n the a p a t i t e s t r u c t u r e , i t a l s o i n d i c a t e s adso rp t i on by

means of h i g h e r content of i r o n and c l a y and e lementa l group

a s s o c i a t i o n s i n these p h o s p h o r i t e s . N i - C r p l o t s f o r Maldeota

and Durmala phosphor i t e s show a weak sympathet ic c o r r e l a t i o n

( F i g . 21F) i n d i c a t i n g an i n c r e a s e of Cr c o n c e n t r a t i o n w i th the

i n c r e a s e of N i . I n Maldeota phosphor i t e s N i - P j O g p l o t s show

a wide s c a t t e r w i t h i n themselves without showing any tendency

f o r l i n e a r i t y whereas i n Durmala phospho r i t e s they show a weak

p o s i t i v e r e l a t i o n s h i p ( P i g . 22B) which i n d i c a t e s ad so rp t i on of

Ni i n the phosphat i c g e l s . N i - A l j O ^ p l o t s do not show any

s i g n i f i c a n t r e } . a t i onsh ip i n these phospho r i t e s ( P i g . 23C ) ,

The N i /A l , Ni/Pe and Ni/Mg r a t i o s a r e found to be

v a r i a b l e i n these phospho r i t e s (Tab l e s -XXXI , XXXII and XXXV).

When N i/A l , Ni/Pe and Ni/Mg r a t i o s are p l o t t e d a g a i n s t the

r e s p e c t i v e v a l u e s of A l , Pe and Mg ( P i g . 24 C, D and E ) , they

show a s t r ong negat ive r e l a t i o n s h i p . This i n v e r s e r e l a t i o n s h i p

sugges t s the replacement o f A l , Pe and Mg by N i . This s u b s t i -

t u t i on i s due t o the i d e n t i c a l i o n i c r a d i i o f Ni^"*" (0 .72 8 ) ,

Mg^"^ (0 .65 %) and Fe^"^ (0 .76 X ) .

139

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Mutua l ly p o s i t i v e c o r r e l a t i o n amongst Cd, Co and Cu

and a l s o w i th r e s p e c t t o Ni and Zn sugges t s t h a t these e lements

p r obab l y form a d i s t i n c t i v e group cons ide red t o be t y p i c a l o f

o r gan i c matter (Krauskop f , 1955 and Gulbrandsen , 1966 ) . N i and

Co may se rve as i n d i c a t o r s o f genera l m i n e r a l i z a t i o n i n ' r e d

bed* environments ( s e e ( B o y l e , 1984 ) .

H igher concen t r a t i on of Ni i n Mussoor ie phosphor i t e s and

b l a c k s h a l e s and p r o g r e s s i v e p o s i t i v e r e l a t i o n s h i p with P2^5

has been r epo r t ed by Sa raswat , e t a l . ( 1 9 7 0 ) . i t may be p o s s i b l e

tha t l i k e vanadium, n i c k e l was a l s o adsorbed i n the f e r r u g i n o u s

m ine r a l s , c l a y e y masses and phosphat ic and s i l i c e o u s g e l s . I t

may a l s o be int roduced d u r i n g the sed imentat ion p roce s s e s which

made the geochemistry of the sediments .

Coba l t t

Geochemica l ly , c o b a l t be ing a s i d e r o p h i l e element and a

member of i r o n f a m i l y (Go ldschmidt , 1929) i s c l o s e l y r e l a t e d to

n i c k e l . I f i n the p roces s of weather ing and sed imentat ion ,

c o b a l t shows no marked d i f f e r e n t i a t i o n , the l o s s of Co in the

weathered p roduc t of igneous rocks i s g r e a t e r than tha t of N i .

The i o n i c r a d i u s of Co "*" ( 0 . 74 X) i s more o r l e s s i d e n t i c a l t o

those o f Ni^"^ (0 .72 X ) , and Fe^"^ (0 .76 % ) .

Krauskopf (1955) r epo r t ed Co from 2 t o 50 ppm and

Gulbrandsen (1966) up t o 50 ppm in the phosphor i a Formation,

U . S . A . and Saraswat , e t a l . (1967) from 10-15 ppm i n the phos -

p h o r i t e s of Mussoor ie a r e a , U . P . ( I n d i a ) .

1 4 1

D e s p i t e the f a c t that p e l l e t a l phospho r i t e s are r i c h

i n Ba# Co, Mn* V, Y, La and Pb i n comparison t o s t r o m a t o l i t i c

phospho r i t e s , they do not show any d e f i n i t e r e l a t i o n s h i p w i th

P2O5, i n d i c a t i n g t h e i r a s s o c i a t i o n e i t h e r wi th other minor

minera l phases which a re abundant i n these phosphor i t e s o r

they are adsorbed on the a p a t i t i c s u r f a c e s ( s e e Bane r j e e , e t a l . ,

1984; S a i g a l and Bane r j ee , 1987; Baner j ee and S a i g a l , 1 9 8 8 ) .

The concen t r a t i on of c o b a l t i n Maldeota phosphor i t e s

ranges from 2 ppm to 28 ppm ( F i g , 18B) whereas i n Durmala

p h o s p h o r i t e s , i t v a r i e s between 5 ppm and 8 ppm. The a s s o c i a t e d

sediments have e q u a l l y low concent ra t i on of t h i s element

( F i g . 19B ) . The a n a l y t i c a l d a t a and t h e i r p l o t t i n g i n d i c a t e s

that c o b a l t does not show any s i g n i f i c a n t r e l a t i o n with P20g

( F i g . 2 2 c ) . However, i t shows c l o s e coherence with Ni and Fe .

The occurrence of Co i n these sediments may be due to i t s s l i g h t

adso rp t i on by the f i n e l y c r y s t a l l i n e masses o f phosphate , c l a y

and i r o n b e a r i n g m i n e r a l s .

Zinc J

Zinc i s predominant ly a c h a l c o p h i l e e l ement . I t i s

consequent ly very mob i l e . Accord ing t o Wickman (1944) the

element i s v e r y mobi le and l i e s on the b o r d e r between the

s o l u b l e c a t i o n s and the e lements of h y d r o l y z a t e s . During

weather ing Zn goes r e a d i l y i n t o s o l u t i o n as su lphate o r

c h l o r i d e , which i s l a t e r on t r anspo r t ed by s u r f a c e o r ground

wa te r s . The i o n i c r a d i i of Zn^"*" (0 .74 and Fe^"^ (0 .76 X) a r e

142

c l o s e l y s i m i l a r . The c l o s e l y i d e n t i c a l i o n i c r a d i i o f these 2+ 2+ two ions sugges t tha t Zn should be camouf laged i n Fe

f o l l o w i n g the c l a s s i f i c a l p r i n c p a l ( s ee Goldschmidt , 1937 ) .

The accumulation of z i nc in sedimentary environment

o r i g i n a t e s p r i m a r i l y from chemical weather ing of magmatic and

metamorphic rocks and p r o b a b l y a d d i t i o n a l l y f rom the d e g a s s i n g

of the upper l a y e r s of the e a r t h ( s e e Wedephol, 1973 ) .

The e lementa l m o b i l i t y i n secondary o x i d i z i n g and a c i d i c

environments i s h igh f o r the t r a c e e lements l i k e Cu, Zn, Ni and

Co (Roonwal l and Kumar, 1987 ) . Most t r a c e e lements (Co, N i , Cu,

Pb and Zn) i n the nodules a re p r e s en t i n the manganese and f e r r i c

ox ides ( s e e Ghosh, 1988 ) . These elements a re carbonate hos ted

and a re con f ined to the marg ina l s h e l f sequence showing a d i v e r s e

l i t h o f a c i e s a s s o c i a t i o n I s e e Singh, 1988 ) .

The p l o t Zn-PjOg i s a t y p i c a l example o f the lack of any

c l e a r t r end i n t h i s group o f e lements . There i s a tendency f o r

the p e i l e t a l phosphor i t e s of N.W. Queensland, A u s t r a l i a t o have

a lower concent r a t i on of Co, Cu, Mo, N i , Pb and Zn than the non-

p e l l e t a l phosphor i t e s ( s e e Cook, 1972 ) .

The concent ra t i on of Zn i n Maideota phosphor i t e s ranges

from 23 ppm to 105 ppm ( F i g . 18 A ) whereas i n Durmala, i t ranges

f rom 30 ppm t o 58 ppm. The concent ra t i on of Zn i n a s s o c i a t e d

l imestone i s f r a n 24 ppm t o 59 ppm whereas i n cher t and s h a l e ,

i t ranges froutn 5 ppm to 39 ppm and 8 ppm to 102 ppm r e s p e c t i v e l y

( P i g . 19 B and 2 0 ) .

I n Maideota phospho r i t e s Zn shows a synpa the t i c r e l a t i o n -

sh ip w i th cadmium whereas i n Durmala phospho r i t e s they have a

nega t i v e r e l a t i o n s h i p ( P i g . 21 C ) . Zn does not show any

1 4 3

120

80 3 O

"•0

20 % P2O5

ij eI)

3001

-2001 a a.

lOOi < .0 »

_L W

•/. P2O5 To

12

a. "o o

• «)• • 0

• • 00

M M • • •

-alr •/. P205

- 0

i20r

80

"to

600

E Q. a.

UOO

200

P2O5

o f/v • r • ° • I 0 Q

20 10 V.P2O5

-5*0

12001

teooi re CD

400

d 1200

600

•lOO

~ gig - ---jjjy

" 800 G

"•00

60

•/» P2O5 Vo

5 •• 0 i''-.

20 %P205

60

200

. ' f ' . " ' 0 8 • • f * o 0 • • • 'o . : •

2t MO V.P2O5

60

Fig. 22. Point diagrams showing mutual relationship between Cu, Ni, Co, Zn, Ba, V, Cr and Sr and P20g in the phosphoric ore.

144

i20r

- 8 0 -E tx a.

S ifO-

•g o. o. "c Nl

1 0 0 -

8 0 -

uo-

6oor

20 ifO 60 V.P2O5

..O

20 MO V. CaO

0/ t

"tOO-B a 5

200

10 20 % AI2O3

fiO

120

1 0

I •

't •/. MgO

600

hoo

2 0 0 . ys'y a •

I '/. AI2O3

1000

•peoo

S

(too

' • • •

. 5 ° • • •

30 7. KjO

.12

300

= 200

100

1200

•=000

<(00

1 2 V.AlgOj

V ^ • —

t 20

o o o

itO 60 V. CaO

Fig. 23. Point diagrams indicating the geochemical relation between certain major oxides and trace elements (P^Og-Cu, MgO-Cu, Al20g-Ni, CaO-Zn, Al20g-Cr, CaO-Sr, AI^O^-V and K20-Ba) in Maldeota ( • ) and Durmala ( o ) phosphorites.

1 4 5

i-it

1-2

° o-a *

o 0-4

0

2.it

1 6

X OP

2 O.g

0

0-0 2

00)6

0-008

2-8

2.'«

x 1.6 cr

0-8

8 V, p 12

•» o • • . « . o . V„ . ••••• -1-2 'I

% 8 7

S

2 4 V. Fe

16

J 1 6 7

••J 2 V.Mq

1-8

' o 1.2

X cr

'z 0-6

• t

I ••

2 't V. Mg

1 4 12

0 X 1 z

J-Ir-

• « o • . • ** • '-a J

o.'t 0-8 V. A I

. ' fa -

20 ifO % Ca

V2

60

Fig. 24. Cu/P. Cu/Mg-Mg, Ni/Al-Al, Ni/Fe-Fe, Ni/Mg-Mg, Zn/Ca-Ca and Zn-Fe plots for Maldeota ( • ) and Durmala ( o ) phosphorites.

1 4 6

s i g n i f i c a n t r e l a t i o n s h i p w i th P2®5 study a r e a .

However, i n Durmala phospho r i t e s Zn has a weak p o s i t i v e r e l a t i o n -

sh ip with CaO ( F i g . 18 D and 19 D ) . When Zn i s p l o t t e d a g a i n s t

Pe, an i n v e r s e r e l a t i o n s h i p i s obta ined ( P i g . 20 G ) , i n d i c a t i n g

replacement of i r o n by Z i n c . In the p l o t of Zn/Ca r a t i o a g a i n s t

Ca ( F i g . 24 F ) , i t i s obse rved t h a t no s i g n i f i c a n t c o r r e l a t i o n

e x i s t s between the former two and ca lc ium remains almost constant

The v a r i a b i l i t y of Zn/Pb r a t i o I n d i c a t e s non-coherence of Zn

with r e s p e c t t o l e ad ( T a b l e - X X X I l and XXXV). Zn may be adsorbed

by c l a y p a r t i c l e o r a p a t i t e c r y s t a l l i t e s and other e lements

p o s s i b l y en te red in the a p a t i t e l a t t i c e s . Th is element may a l s o

be a s s o c i a t e d with h i ghe r f e r r u g i n o u s content and con f ined t o

sha l l owe r p a r t s of the b a s i n .

Chromium s

Chromium occurs i n nature p r i n c i p a l l y as the t r i v a l e n t

i on Cr^"*" w i th a r a d i u s of 0,64 X. Because of the i d e n t i c a l

chemical p r o p o r t i o n s , i o n i c s i z e and i o n i c charge , i t can

r e a d i l y s u b s t i t u t e Pe^"*" ( 0 . 67 X) and Al^"*" ( 0 . 58 X ) . Cr i s

u s u a l l y concentrated i n r e s l s t a t e s and h y d r o l y s a t e s . The

chromium b e a r i n g s i l i c a t e s r e l e a s e chromium vrtiich i s i n c o r -

pora ted i n t o s h a l e s and s c h i s t s . L i t t l e chromium goest i n t o

s o l u t i o n , and thus p r e c i p i t a t e s and evapo r a t e s have a low

chromium content ( s ee Ecy l , 1972 ) .

Mason (1966) suggested tha t Cr u s u a l l y behaves as a

h i g h l y l l t h o p h i l e e lement . Dur ing d i s i n t e g r a t i o n and weather ing

of rocks , Cr"^^ has l i t t l e m o b i l i t y and i t s behav iour i s s i m i l a r

1 4 7

to that of Fe"*"^. Cr , Pb , Se, Y and a l l l a n t h a n o i d s , though

r e l a t i v e l y d e p l e t e d i n sea wate r , are en r i ched in phospho r i t e s

( s e e Tooms, e t a l . # 1969) and enr iched in s o i l s a l s o ( s e e

Reedraan, 1984 ) .

Concent ra t ion of Cr^ i n phosphate d e p o s i t s has been

repor ted in v a r i o u s p a r t s of the g l obe ( s e e Roonwall and Kumar,

1987) .

P r o h l i c k (1960) proposed that Cr i n the modern sediments

i s concentrated in the c l a y minera l s and raicas/ wh i l e P r e v o t

and Lucas (1980) proposed tha t Cr i s p r i m a r i l y c a r r i e d away

by the a p a t i t e s and i s f i x e d i n c l a y s .

The concent r a t i on o f chromium in ca rbona te r ocks , as

r epo r ted by Rankama and Sahama (1950) i s 2 ppm; Krauskopf ( 1955 ) ,

5 ppm; Runnels and S c h l e i c h e r (1956) 2 ppm; Ostrom (1957 ) ,

118 ppm; Gra f ( 1960 ) , 13 ppm. In p h o s p h o r i t e s , the c o n c e n t r a t i o n

of chromium has been r e p o r t e d to be q u i t e h i g h . Krauskopf (1955)

has r epo r t ed 30^400 ppm and Gulbrandsen (1966) up t o 1000 ppm

of chromium i n Phosphor ia Formation.

Chromium content i n Maldeota phospho r i t e ranges from

61 ppm t o 569 ppm whereas i n Durmala p h o s p h o r i t e s , i t v a r i e s

from 70-260 ppm. The r e l a t i v e abundance of Cr i s shown i n

F i gu r e -18 C.

In a s s o c i a t e d s h a l e , i t ranges f rom 102 ppm t o 500 ppm

which i s q u i t e h igh as compared to the l imes tone and che r t

where i t v a r i e s from 61-71 ppm and 66-245 ppm r e s p e c t i v e l y

( F i g . 19 A ) . The average concent r a t i on t r ends of Cr are shown

i n F i g u r e - 2 0 .

148

Cr shows p o s i t i v e c o r r e l a t i o n wxth 22 G )

which i n d i c a t e s that Cr i s p r e f e r e n t i a l l y con f ined t o a p a t i t e s .

This v i ew has a l s o been suppor ted by the p resence of h i g h e r «

concent ra t i on of Cr i n these phospho r i t e s , which might be due

t o the p resence of o r g an i c mat te r ^Vinogradov, 1953 ) . L a t e r

s t u d i e s by Krauskopf (1956) a l s o con f i rm V i n o g r a d o v ' s o b s e r -

v a t i o n s . Cr does not show any s i g n i f i c a n t r e l a t i o n s h i p w i th

AI2O3 ( P i g . 23 E ) . Higher concent r a t i on of Cr a l s o supports

the o b s e r v a t i o n s of Mason (1966) and Roonwal and Kumar ( 1 9 8 7 ) .

He r s t (1962 ) , and N i c h o l l s and L o r i n g (1962) have d e t e r -

mined the r e l a t i o n s h i p between chromium and aluminium contents

i n sed iments . The author , i n the p re sent s tudy , has a l s o ana lysed

the da ta and c a l c u l a t e d Cr/Al and Cr/Al r a t i o s ( T a b l e - X X X I I I and

XXXVI) which Vary from 0.94 t o 10.14 x 10"^ and 0.12 to 3.99 x

10"^ r e s p e c t i v e l y . The v a r i a b l e Cr/Al r a t i o s p l o t t e d a g a i n s t

r e s p e c t i v e v a l u e s of Al ( F i g . 25 B) shows an i n v e r s e r e l a t i o n s h i p

sugges t ing s u b s t i t u t i o n o f Cr^"^ f o r Al^"*" as mentioned e a r l i e r .

Strontium s

Stront ium i s a l i t h o p h i l e element and occurs as o x y s a l t s

i n i res idua l sediments . The d i s t r i b u t i o n of s t ront ium i n m i n e r a l s ,

r ocks , sediments and water i s a f f e c t e d to a c e r t a i n ex tent by

the p resence o f ca lc ium, which has an i o n i c r a d i u s of 0.99 X,

ve ry c l o s e t o that of s t ront ium, 1.12 X. Stront ium i s u s u a l l y

found i n l a r g e amounts i n c a l c i u m - r i c h m i n e r a l s , and t o a

l e s s e r e x t en t i n p o t a s s i u m - r i c h m i n e r a l s . This phenomenon i s

e xp l a ined by Goldschmidt•s •admittance* theo ry , which says tha t

1 4 9

Sr^"*" i s ' admit tance* i n t o the sma l l e r ca l c ium l a t t i c e bu t i s

•entrapped* i n the potass ium l a t t i c e v^ i ch has a l a r g e r r a d i u s

(1 .33 %) .

The evapo ra te sediments a re compara t i ve ly r i c h i n

stront ium and the ent rance of s t ront ium i n t o the minera l s

of marine s a l t sediments seems t o be r e g u l a t e d by the ca l c ium

content of these m ine r a l s , Sr i n the c r y s t a l l i z i a t i o n from these

aqueous s o l u t i o n s r e p l a c i n g e x c l u s i v e l y the ca lc ium ions , not

potassium (Goldschmidt , 1958 ) . The d i s t r i b u t i o n of s t ront ium

i n m ine ra l s , r ocks , sediments and water i s a f f e c t e d to a c e r t a i n

ex tent by the presence of c a l c ium. Sr i s found i n g r e a t e s t

aniounts i n ca lc ium r i c h m i n e r a l s ( s e e Encyc l , 1972 ) .

I n c a rbona te s , the s t ront ium content v a r i e s w ide l y as

r epo r ted by Rankama and Sahama (1952 ) , 425-675 ppm; Krauskopf

(1955 ) , 400-800 ppm; Runnels and S c h l e i c h e r ( 1956 ) , 470 ppm;

Ostrom (1957 ) , 490 ppm and Graf ( I 9 6 0 ) , 420 ppm. Strontium i n

phosphor i t e s ranges from 50 ppm to 1000 ppm, as r epo r ted by

Krauskopf ( 1955 ) ; 1000 ppm, by Gulbrandsen (1966) and 974 ppm,

by Prevot and Lucas (1979) ( Tab l e -XXX ) .

oai -yert and P r i c e (1983) have r e p o r t e d Sr concen t r a t i on

i s as h igh as 2,410 ppm i n Namibian s h e l f sediments ; the h i gh

va lues are a t t r i b u t e d to f o r a m i n i f e r a l c a l c i t e and/or s u b s t i -

t u t i o n of Sr by Ca i n the carbonate f l u o r a p a t i t e l a t t i c e .

I n the p r e s en t c a s e , s t ront ium ranges from 645 ppm t o

1049 ppm i n Maldeota phospho r i t e s ( P i g . 18 D ) and 388-877 ppm

in Durmala p h o s p h o r i t e s . I n l imestone i t s concent r a t i on v a r i e s

from 345-870 ppm; 238-843 ppm in che r t and 351-780 ppm i n s h a l e

( P i g . 19 A ) .

1 5 0

I t i s no t i ced tha t phosphorus r i c h s anp l e s have h i g h e r

Sr c o n c e n t r a t i o n . I t i s , r h e r e f o r e , i n f e r r e d tha t the concen-

t r a t i o n of s t ront ium i n c r e a s e s wi th the i n c r e a s e of tha t o f

PgOg. The i n c r e a s i n g content of Sr could be due t o the isomor->

phous rep lacement o f Ca by Sr i n the phosphate minera l s and

a l s o p o s s i b l y due t o the f o rmat ion of supergene s t ront ium

phosphates . The tendency of S r t o r e p l a c e Ca i n minera l

s t r u c t u r e s i s fuxrthermore shown by i t s p resence i n a p a t i t e

and i n ca lc ium b e a r i n g amphiboles and py roxenes .

Most o f the data p r e sen ted here , show tha t S r v a lue s

remain e i t h e r constant or show only minor v a r i a t i o n s ( P i g . 18 D)

I t , t h e r e f o r e , negates the p o s s i b i l i t y of Sr content b e i n g

con t r i bu ted by the a s s o c i a t e d ca rbona te s . In Maldeota phospho-

r i t e s S r shows random r e l a t i o n s h i p with P2®5 ^^ ^^ which

i s s u g g e s t i v e of uneven and i r r e g u l a r domains of weather ing ,

l each ing and secondary enrichment i n the study a r e a . In

Durmala, a weak nega t i ve r e l a t i o n s h i p i s o b t a i n e d . Sr -CaO

p l o t s ( P i g . 23 P) show weak sympathetic r e l a t i o n s h i p i n d i c a t i n g

c l o se coherence of Sr w i th Ca . This a l s o i n d i c a t e s enrichment

of Sr due t o the p resence of Ca i n a p a t i t e l a t t i c e .

Sr/Ca r a t i o i n phospho r i t e s i s h igh and v a r i e s f rom

2.18 - 3.70 X 10"^ ( T a b l e - X X X I I l ) . The r e l a t i o n s h i p between

Sr/Ca and pe rcentage of Ca as r ep resented by P i gu re -25 C,

r e v e a l s a s l i g h t l y a n t i p a t h e t i c c o r r e l a t i o n r e f l e c t i n g the reby

the a s s o c i a t i o n of a c o n s i d e r a b l e p o r t i o n of Sr with Ca and

s u b s t i t u t i o n of one by the o t h e r .

151

Kulp, e t a l . (1952) and Tuireklan (1956) s t a ted tha t

Sr/Ca r a t i o I n carbonate s h e l l s and c a r b o n a t e - b e a r i n g sediments

i s a f u n c t i o n of (1 ) the Sr/Ca r a t i o i n the l i q u i d phase f rom

which the s o l i d phase i s d e r i v e d ; ( 2 ) the v i t a l e f f e c t o f

organism; ( 3 ) the p a r t i c u l a r polymorph, c l a c i t e o r a r a g o n i t e ,

i n t o which the s t ront ium i s i n c o r p o r a t e d ; ( 4 ) t enpe ra tu re and

( 5 ) the s a l i n i t y of l i q u i d phase .

Sha l e s , i n the p r e s en t study a r ea , seem to have a

g r e a t e r a b i l i t y to concent ra te s t ront ium (612 ppm) due t o

ion -exchange p r o p e r t i e s o f the c l a y m i n e r a l s .

Barium :

Geochemistry of bar ium i n igneous and metamorphic r o cks ,

i s c h a r a c t e r i s e d t o a l a r g e e x t e n t by i t s a b i l i t y to s u b s t i t u t e

f o r k"*" i o n . A s i m i l a r d i a d o c h i c r e l a t i o n s h i p commonly e x i s t s

between l e ad and bar ium. Barium does not s u b s t i t u t e f o r ca lc ium

i n s i g n i f i c a n t q u a n t i t i e s because the s i z e d i f f e r e n c e i n t h e i r

i o n i c r a d i i i s t oo g r e a t . Barium a l s o resembles s t ront ium.

The barium content i n carbonates as determined by v a r i o u s

i n v e s t i g a t o r s i s r epo r ted t o be 120 ppm (Rankama and Sahama,

1950) ; 20-200 ppm (Krauskop f , 1955) ; 390 ppm (Runnels and

Sch l e i che r , 1956) ; 260 ppm (Ostrom, 1957) and 220 ppm ( G r a f ,

1960) . On the o ther hand. Von Enge lhardt (1936) has r e p o r t e d

2 70-900 ppm of Ba i n phospho r i t e s , whereas i n Phosphor ia

Formation i t s content i s r e l a t i v e l y low i . e . 100 ppm

(Gu lbrandsen , 1966) .

152

In the p re sent area of i n v e s t i g a t i o n ^ Ba v a r i e s f rom

320 ppm t o 796 ppm in Maldeota phosphor i t e s whereas i n Durmala

phosphor i t e s ranges h i ghe r f rom 614 ppm t o 980 ppm. The

r e l a t i v e abundance of Ba and S r p resented i n P i g u r e - l S D,

i n d i c a t e s a lmost a s i m i l a r p a t t e r n of v a r i a t i o n i n Maldeota

phosphor i te samples . I t i s s u g g e s t i v e o f resemblance of Ba

with Sr f rom p o i n t of v i ew of t h e i r d i s t r i b u t i o n and geochemical

b ehav iou r . In a s soc i a t ed r o c k s , l imestone and cher t have low

concent ra t i on of Ba as compaired t o phospho r i t e s wh i l e s h a l e

show h i ghe r concen t r a t i on of Ba i . e . 205 ppm to 617 ppm

( P i g . 19 A and 2 0 ) .

Barium and st ront ium show a weak sympathet ic c o r r e l a t i o n

( P i g . 21 D ) whereas an a n t i p a t h e t i c r e l a t i o n s h i p between Ba

and K2O i s ob ta ined ( P i g . 23 H ) . The sympathet ic r e l a t i o n s h i p

i n d i c a t e s a f f i n i t y of Ba f o r S r .

The e lement i s found t o be i n c r e a s i n g with the i n c r e a s e

of P2O5 content as demonstrated i n P i g u r e - 22 E where Ba shows

weak sympathet ic r e l a t i o n s h i p wi th P2®5* ^ ^ ^ Ba/K r a t i o s

(Tab les -XXXIV and XXXVI) a re p l o t t e d a g a i n s t r e s p e c t i v e

percentage K ( P i g . 25 E ) , an i n v e r s e r e l a t i o n s h i p e x i s t s

i rKi icat ing s u b s t i t u t i o n of Ba^"*" by k" . The h i gh v a r i a t i o n

range i n Ba/K r a t i o s sugges t tha t barium was t r anspo r t ed i n t o

the b a s i n independent ly .

Rubidium :

I t i s a l i t h o p h i l e element and i t s geochemistry i s

dominated by i t s e x t en s i v e d i adoch i c r e l a t i o n w i th potass ium.

153

The behaviour of rubidium in sedimentary processes is controlled largely by adsorption on clay minerals. Of all alkali metals, rubidium has the highest tendency to interstitial capture and is adsorbed more readily than potassium (Goldschmidt, 1937). As a result of this tendency of quick adsorption and particle inclusion of rubidium in the crystal lattices of clays, the bulk of this element is released during the weathering of igneous and metamorphic rocks.

According to Wedepohl (1970), the abundance of Rb in silty limestone varies from 6-167 ppm and in shales, 20-663 ppm, etc. In Maldeota phosphorites, Rb content ranges from 1 ppm to 78 ppm whereas in Durmala it ranges from 1-13 ppm. Associated rocks show variable concentration of Rb, 3-22 ppm in limestone 4-71 ppm in chert and 4-97 ppm in shale.

K/Rb (Table-XXXII and XXXVI) ratios were determined for these phosphorites. This variable ratio of K/Rb (Tables-XXXIII and XXXVI) indicates a close coherence of Rb with potassium. Illites and montmorillonites are the most common clays with large cation exchange capacities and both absorb rubidium more strongly than potassium. This behaviour leads to a temporary decrease in K/Rb during the weathering processes.

Rubidium has a very low concentration in phosphorites which indicates noncoherence of Rb with the elements related to apatite whereas a moderately high concentration in shale may be due to the adsorption of Rb clay minerals.

154

Vanadium :

Vanadium is a lithophile element. In igneous rocks, it occurs in three stable oxidation states, viz., trivalent, quadrivalent and quinquevalent states. In sedimentary rocks* vanadium occurs in quinquevalent state. Vanadium seems to have been released in course of weathering of igneous rocks and subsequently incorporated in clay minerals due to the low solubility and immobility of VCOH)^. In apatite v"*" may replace P "*", which explains the concentration of vanadium in the apatite-rich iron ores as observed by Landergren (1948). Like phosphorus and arsenic the quinquevalent vanadium has a pronounced tendency to form (VO^) tetrahedra in mineral structures.

Vanadium is highly variable in carbonate rocks. It is found to be varying from traces (Ostrom, 1952) to 3000 ppm (Runnels and Schleicher, 1956). Graf has given a range of 10-150 ppm with 1 2 + 3 ppm as an average. Jacob, et al. (1933) have reported 1300 ppm of vanadium in marine phosphorites of Idaho. Krauskopf (1955) quoted a range of 20 to 200 ppm of V in phosphorites. The threshold value of vanadium in Phosphoria Formation of Montana/ Wyoming and Utah (U»S.A») was found to be 300 ppm (Gulbrandsen, 1966). The concentration of vanadium in Maldeota phosphorite ranges from 200 ppm to 605 ppm (Pig. 18 C and 2 0) whereas in Durmala phosphorite it ranges from 440 ppm to 575 ppm. Vanadium in associated limestone, chert and shale ranges from 210-250 ppm, 200-325 ppm and 415-600 ppm respectively (Fig. 19 A and 20).

155

Higher concentration of vanadium is partly explained by the abundance of clay and organic matter in the pelletal phosphorites that may also have acted as the sink for vanadium (Banerjee, and Saigal, 1988). V, Cr and Cu are positively asso-ciated with the clay minerals which determine the stability of the primary assemblages in the supergene enrichment. The elements that are mobile in the supergene zone viz., Cu, Ni, Zn and AS

are partially lost from the phosphorite bearing beds because they are taken up by iron-hydroxides, clay minerals and carbo-nates (see Proshlayakova, et al., 1987),

According to Israili and Khan (1980), the plotting of against PgO^^, shows two trends. The phosphate

poor samples have a negative correlation whereas the phosphate rich samples show a constant V/PgOg ratio. Hence, it is assumed that Vanadium, that was supplied to the basin alongwith the phosphorus was concentrated in sediments with the high phos-phorus content, implying thereby that the physico-chemical conditions for the enrichment of both these elements are similar or nearby so in the phosphorites of Pithoragarh area (U.P.).

According to Mason and Moore (1982), the black shales were deposited slowly in a strongly reducing marine environment rich in organic matter. Some phosphatic shales such as those of the Phosphoria Formation xn wyomxng, Idaho and Montana in U.S.A. show similar geochemical features especially in the enrichment in vanadium and uranium. They seem to have been deposited under similar conditions, that is oxygen deficient marine environment

156

vrtiere organic material was accumulating and the rate of sedi-mentation was very slow. Enrichment of vanadium in the black shales of the Mussoorie area, in the light of above mentioned view* may be due to the presence of organic matter in these shales, and indicates a reducing marine environment of depo-sition. The enrichment of V with P is supported by Nicholls and Loring (1962) who found high vanadium content in coal cyclo-thems in the Great Britain was due to absorption of V by clay and organic matter.

Saraswat, et al. (1970) also reported enrichment of V in the Mussoorie phosphorites. No significant relationship of PjOg with V indicated the adsorption on the apatite surfaces (see Banerjee, et al., 1984; Banerjee and Saigal, 1988). The close relationship between phosphates and vanadates is well known. The behaviour of V is indeed much different in the phosphorite and carbonates; it is enriched in the fomer, where it substitutes easily for P reaching sometimes commercial concentrations. V attraction for apatite is as clear as its affinity with clay minerals (see Krauskopf, 1955; Gulbrandsen, 1966 and Cook, 1972). The presence of V in the phosphorites may be due to chemical affinity with P2®5* ^^ possible that the vanadium accumulation in bituminous sediments is effectively controlled not only by the primary vanadium content of organic matter but also by the reducing character of the environment (see wedepohl, 1974). Vanadium is produced from phosphates as a by-product in the western U,S.

In the study area, vanadium shows an antipathetic rela-tionship with P2O5 of the Maldeota phosphorites whereas the

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metal has a weak sympathetic relationship with P2O5 Durmala phosphorites (Fig. 22 F). V-AI2O3 plots do not show any signi-ficant relationship (Fig. 23 G). Table -XXXIV shows the V/P ratio. The plotting of this ratio against P content (Fig. 25 F)

Indicates an Inverse relationship which possibly suggests replacement of by V "*".

The plotting V/A1 ratio against A1 shows a negative relationship (Fig. 25 D) which way be due to the replacement of Al "*" by V^. The V/Fe and V/Mg ratios (Tables-XXXIV and XXXVI) are highly variable.

Lithium f

Lithium is an alkali metal and strongly lithophile in its geochemical character. Chemically, it is very reactive and tends to enter the silicate minerals where it replaces iron and magnesium rather than other alkalies, like sodium and potassium. During weathering and sedimentation, lithium is evidently readily adsorbed by clay minerals. Hence, shales normally contain a relatively higher proportion of Li.

The average abundance of lithium in the earth's crust has been variously estimated to be 25-40 ppm. The concentration of Li in various rocks were reported by many earlier workers. Rankama and Sahama (1950) reported 46 ppm of Li in shale, whereas Strock (19 36) reported 26 g/ton of Li in limestone, Solov (1961) quoted up to 0.015 per cent of Li in apatite.

159

The concentration of lithium in Maldeota phosphorites ranges from 1 pptn to 15 ppm, whereas in Durmala phosphorites it ranges from 2 ppm to 5 ppm. Associated limestone, chert and shale have a concentration ranging from 1-2 ppm, 2-6 ppm and 2-14 ppm respectively.

Lithium in phosphorites of both the areas seems to be not related with apatite. A relatively high concentration of Li in black shales suggests that Li may be adsorbed by some clay minerals.

Cadmium :

Cadmium is predominantly a chalcophile element in its geochemical character and behaves very much like zinc, both favouring a combination with sulphur. The close similarities of the ionic radii of Cd "*" (0.97 X ) and Ca " (0.99 X ) suggest that these elements are closely associated with each other in nature (see Sandell and Goldich, 1943 and Rankama and Saharaa, 1950).

According to Saigal and Banerjee (1987), in no situation Cd shows positive relation with p2®5' radius of Cd is significantly similar to that of Ca and hence, a partial subs-titution for calcium in apatite structure is possible.

In average phosphorite (Altschuler, 1980) both Zn and Cd form a pair which shows considerable enrichment while Cd is often differentially enriched over zinc.

Association of Cd with ferruginous minerals and organic matter is well known. Insignificant correlation of Cd, Co and

160

Cu with both suggests that these elements are not

genetically related to apatite. Their presence can be explained as due to absorption on the apatite surface during diagenesis or by virtue of their affinity for certain associated elements. Mutually positive correlation amongst Cd, Co and Cu and also with respect to Ni and Zn suggests that these elements probably form a distinctive group, considered to be typical of organic matter (see Krauskopf, 1955; Gulbrandsen, 1966).

The concentration of Cd in Maldeota phosphorite ranges from 5 ppm to 21 ppm while in Durmala it is less than 10 ppm. In the associated sediments it is very low and ranges from 2-11 ppm in limestone, 2-10 ppm in chert and 5-13 ppm in shale.

In the study area, cadmium shows positive relationship with lead and zinc (Pig. 21 B and C). The low concentration of Cd in the phosphorites indicates that it is not genetically related with apatite. The positive relationship of Cd with Zn suggests that this element is associated with some organic matter.

The presence of Cd may also be due to occurrences of other trace elements within and outside the crystal lattices of the collophane bearing minerals ®r due to adsojrption on the apatite surface during diagenesis.

INTERPRETATION & CONCLUSION :

Geochemical methods have received increasing emphasis in recent years as a means of reconstructing the ancient envi-ronment. An attenqpt has been made here to identify the

1 6 1

provenance and determine the environmental condition of the phosphorite deposits of the study area based essentially on •Che geochemical affinity, concentration trends, behaviour and distribution pattern of various trace elements studied*

The trace element distribution pattern shown by the Mussoorie phosphorites and the behaviourcf the individual elements suggest that most of the trace elements that found their way into the ancient sediments appear to have invaded the lattices of the phosphates, carbonates, silicates and clay minerals and combined with them structurally. The variable concentration of trace elements in Mussoorie phosphorites have been influenced by various physico-chemical processes involved during weathering and leaching of the pre-existing rocks, and subsequently they were added to the sediments in traces. The adsorption of some trace elements was mainly influenced by the principal absorbants like phosphate mineral, some organic matters, in addition to clay, iron and silicate minerals.

The concentration trends reveal that the phosphorites are more enriched in Ba, Cu, V, Cr, Pb, Ni and Sr, Li, Cd, Co, and Rb. Similarly, the black shales are richer in Ba, V, Cr, Sr and Ni than Li, Cd, Rb and Co. Thus sr, Pb, are the elements which are suceptible to adsorption by phosphate minerals and the elen^nts which were possibly adsorbed by organic matter include Ni, V, Zn, Cr, Cu and Cd. Elements adsorbed by clay minerals include Li and Rb. The metals as Ni, V, Zn and Cr are commonly reported to be associated with organic matter and Sr and Pb with the phosphate matter (see

162

Heinrich, 1958; Krauskopf, 1955; Gulbrandsen, 1966). Many earlier workers like Van Ingen (1915), Van Ingen and Philips (1915), Bowen and Sutton (1951), Tourtelot (1964), Verma (1978) and Raha (1978) are of the opinion that V, Cr, Ni, Cu and Zn can be accumulated in sediments by organic metabolism. Correla-tion coefficient and plotted diagrams of the significant trace elements also indicate that the presence of such elements may be due to their inter-elemental affinities.

The concentration of Cr and V in these sediments suggests slightly anaerobic to highly anaerobic conditions as Keith and Degens (1959) have applied chromium as an indicator of environ-mental conditions. Enrichment of V inblack shales indicates association with organic matter.

Distribution and concentration of Sr in these rocks is strongly influenced by diagenetic processes. Sr is an environ-mentally sensitive element as it is sometimes used as facies indicator.

The concentration of Pb, Ni also takes place with increasing reducing conditions and Ni and Cu become enriched in organic matter in the deposit.

The Ba concentration indicates that these sediments were deposited under shallow marine conditions.

The author is of the opinion that the higher concentration of V, Cr, Ni, Ba and Sr in the phosphate rich samples is mainly due to certain favourable physico-chemical conditions such as low Eh-pH moderate salinity and shallow water reducing conditions at the time of their deposition.

163

It is, therefore, inferred that the distribution and concentration trends of the trace elements within the phos-phatic sediments were exclusively a function of their chemistry. This phase was apparently followed by subsequent weathering and leaching phase involving largely the chemical influence of circulating underground waters and precipitation of certain mineral phases from ambient solutions and thereby modifying several elemental arrangements. Fixation of most trace elements on the apatite was either through the adsorption on the surface of the apatite or by the substitution in the apatite lattice.

CHAPTER - VII

F/\CTOK-VECTOR ANALVSIS OF

PHOSPHORITE GEOCHEMISTRV

CHAPTER - VII

FACTOR-VECTOR ANALYSIS OP PHOSPHORITE GEOCFCEMISTRY

INTRODUCTION :

Factor-vector analysis is a branch of multivarite stat-tistics that has been used and developed largely by the Psycho-logists. The principal aim of this analysis is to reduce the complex pattern of the correlation amongst many variables to simpler sets of relationship amongst fewer variables. Among the principal contributors to the theory of Factor Analysis mention may be made of Pearson (1901), Spearman (1904), Thurstone (1931) and Holzinger (1944), while a comprehensive modern account can be found in Harman (1960), There are two types of factor analyses viz., R-mode and 0-mode. Q-mode factor analysis consists of a comparison of the sample in terms of variables while R-mode factor analysis comprises a comparison of the relationship between the variables. Furthermore, it should be mentioned that this analysis in no way replaces interpretation, it merely assembles the data in a more readily interpreted form.

In recent years, the factor analysis is often used as an aid to the interpretation of complicated problems. Imbrie and Purdy (1952) and Krumbein and Imbrie (1963) have applied the technique to sedimentary problems, while Reeves and Saadi (1971) have used it for deposition of phosphate bearing strata. Saagar and Esselaar (1969) used factor analysis for the geochemical data of the basal Reef Orange Free gold field^S. Africa and a detailed mathematics of factor-vector analysis was presented by Krumbein and Graybill (1965) and Harman (1967).

165

In many respects Q-mode analysis is more advantageous than R-mode analysis for many geological problems (see Imbrie and Vanadel, 1964; Dawson and Sinclair, 1974). However, the Q-mode analysis encounters problems that arise from a large number of samples and limited computer memory capacity. For these reasons, Varimax-R-mode analysis with computed scores is employed in the present investigation.

Factor-vector analysis involving a large number of variables is only valid with the aid of a high speed electronic computer. For this study the programme used was an l.B.M. package programme, provided by the Computer Centre of Aligarh Muslim University, Aligarh.

RESULTS :

Means, Standard Deviation and Coefficient of Variance s

- ^i Means were calculated in the usual way by X = — and

standard deviations were obtained using the formula s <5 - X x - X)^ ^ ~ J N - 1

The coefficient of variance is a measure of the relative dispersion of a variable. It enables direct comparisons to be made between distributions having different units of measurement, It was computed using the formula s

V == S

166

The values of means, standard deviations and coefficient of variance for the variables of the Maldeota and Durmala phospho-rites are given in Table-XXXVlI & XXXVIII.

Correlation Coefficient ;

The correlation coefficient is a measure of the linear relationship between two variables and its value lies between +1 and -1, depending on whether the variables are related sympa-thetically or antipathetically. As a first step of factor-vector analysis (after means, standard deviation and coefficient of variance) correlation coefficient between the variables (R-mode) are calculated and new variables (i.e. factor and vector) are established consequently based upon the order of magnitude of eigen values of the correlation coefficient matrix. The values of correlation coefficient are given in Tables-XX3SX & XL and computed by using the formula s

r = nsxy - x) ( X y)

/ n T x ^ - x)^ (nSy^ - (Sy)^

Correlation Matrix :

The correlation matrices for Maldeota and Durmala phosphorite samples are given in Tables-XXXlX & X$» respectively. The values are product-moment correlation coefficients.

167

Eigen Vectors and Elgen Values :

The major and trace elemental variability of all the

samples was computed in terms of various admixtures of the eigen

vectors (Tables-XLI and X L U ) . In the eigen vector model there is

a general tendency for the samples classified on geological

evidence, as draining elements related to the composition of

phosphate minerals having high positive loadings of vectors-I,

IV and VII in case of Maldeota and vector-II in the case of

Durroala. In contrast the elements not related to the composition

of phosphate minerals tend to have loadings of vectors-ll, III^

V, VI and VIII for Maldeota and vectors-I, III and IV loadings

for Durmala samples. A given eigen value is proportional to the

per cent of variance in the data which is explained by the given

factor.

Rotated Factor Matrix :

rhe rotated factor matrix is shown in Tables-XLXII & XliCV.

Eight and four factors explaining approximately 99.89 and 99.99

per cent of total variation in the data of Maldeota and Durmala

respectively, have been extracted from the correlation matrix

and the system has been rotated so that the independent factor

axes that correspond with the groupings present in the data.

The group variable that correspond more clsoely to any particular

factor axis may be obtained by scanning each column of the matrix

for the highest values. It can be seen from the Maldeota data

168

that Factor-I may be represented by Si02, MnO, CaO, K2O, H2O"'", CO2, Pb, Sr, and V; Factor II by Si02, CaO, MgO, P2O5' Zn, Cr, Sr, Ba, Rb, Li and Cd; Factor-III by TiO^, MnO, MgO, Na20, K2O and Cr; Factor-IV by MnO, MgO, NfajO* CO2, Zn and Li; Pactor-V by AI2O3/ ^^^ Factor-Vl by Ti02, CaO, Na20, Pb and V; Factor-VII by AI2O2, MgO , ^^ Factor-VIII by Ti02/ MgO, Na20, H2O"'", CO2, Ni, Zn and V; while in the case of Durmala Factor-I is characterised by high positive loadings of Si02, AI2O3, Fe203, MnO, CaO, MgO, NajO, K2O, Cu, Pb, Ba and Li; Factor-II by AI2O3, Ti02, MgO, PjOg, Na20, Cu, Pb, Co, Zn, Sr, and Rb; Factor-III by Ti02, CaO, P2O5. Ni, Cr and Ba and Factor-IV by Si02, Fe203, Ti02, MgO, KjO, H20''", Zn, Li and Cd.

The column headed by communality indicates what proportion of the variability of any particular variable has been explained by the factors shown. It is a measure of the fraction of the variance of each ion that is explained by the factors, the communality of which vary from zero to unity. The high communa-lities indicate that most of the variants of the variables explained by eight and four factors extracted which account for nearly 99.89 and 99.99 per cent of the total variance. The low communalities suggest that the variables would probably be better contained in a space of higher dimensionality. The communality is obtained by squaring the absolute values of each row e.g. a communality of 0.82716 for Si02 is obtained by adding (0.88291)^ + (0.13820)^ + (0.16902)^.

169

Interpretation of Factors i

AS can be seen from the means (Tables-XXXVII & XXXVIII), the constituents Si02# MgO, determined in significant amounts, while AI2O3, Fe2°3'

are also present but they are less significant. The signi-ficance of the former five oxides is due to the fact that the host rocks in which phosphatization took place are dolomitic limestones.

The coefficient of variation clearly indicates a wide dispersion of MnO, Na20, KjO and V and relatively much narrow dispersion of Si02, AI2O3, Ti02, V, and Cd, in the Maldeota samples. Similarly, the Durmala phosphate samples show a wide dispersion of MnO, MgO, KjO, and Rb and a narrow dispersion of Ti02, Na20, H20''', CO^, Pb, Co, Zn, Sr, V and Cd. This demonstrates that samples of the narrow dispersion are likely to be better approximation than those of the wider dispersion. Pe202, MgO, Cu, Ni, Co, Zn, Cr, V and Li in Maldeota and Si02, AI2O3, ^6203, Ni, Cr, Ba, and Li, in Durmala phosphorites show sanewhat intermediate dispersion position.

The correlation coefficient matrix (Tables-XXXIX & XL) shows medium to low positive correlations of P2®5 ^^^^ traces such as Cu, Co, Zn, Cr, Ba, and Li while CaO shows negative relationship with the same elements in Maldeota phosphorites. In Durmala phosphorites there is a slightly positive correlation between P2O5 and CaO with the traces.

1 7 0

In Maldeota phosphorites Si02 has strong negative rela-tionship with weakly negative correlation with traces such as Cu, Co, Zn, Cr, Ba and cd. MgO has a positive correla-tion with NajO/ K2O, Zn, Rb, V, and Li and with K2O, cOj/ Co, Sr, V and Cd in Maldeota and Durmala phosphorites respectively. Higher correlation that exists between Ni-Pb, Ni-Cr, Zn-Rb and Rb-Li (Table-XXXIX) and Cu-Sr, Cu-Rb, Cu-Co, Zn-Co, Cr-V (Table-XL) indicates an association of all these elements with each other.

The results of the factor-vector analyses are now inter-preted in terms of the following factors that are supposed to control the chemical composition and formation of these phos-phorites.

Silica Precipitation Factor :

Factor-I (Table-XLIII) shows high positive loading for Si02 (0.88291) and moderate to low positive loadings for MnO, CaO, K2O, H2O''", CO2, Pb, Sr and V. This factor has high to medium loadings for Ti02, this factor has been interpreted as silica precipitation factor. This factor is found very similar to the factor-I (Table-XLIV), where Si02, MgO, NajO^ K2O, Pb and Ba show high positive loadings while AI2O2, Fe202/ MnO, CaO and Li indicate low positive loadings.

It is indicated that silica was supplied in solution and precipitated authigenically as it is revealed in thin section study. The low Si02 loadings in detrital clay supply

171

factor indicates that silica seems to be partly detrital and was removed from clay minerals under the influence of pH.

The high positive loading and excess of Si02 in Maldeota and Durmala phosphorites are also indicated by the presence of chert that cemented the phosphorites.

The positive loading of AI2O3 (Factor-I, Table-XLIV) indicates the presence of ilmenite and alumino-silicate minerals which a c c u m u l a t e preferentially to Cu, Ni/ Cr and V.

On the basis of authigenic silica distribution of major and minor elements, it could be inferred that these rocks have been deposited in shallow marine environment.

Phosphate precipitation Factor ;

The factor-II shows moderate to high positive loadings for CaO, MgO, P2O5' Zn, Cr, Sr, Ba and Rb (Table-XLIIl) and is interpreted as phosphate precipitation factor or supply of phosphate in solution. This factor in the case of Maldeota phosphorites shows low positive loadings for Si02, Cu, Co and Cd and negative loadings for TiO^, MnO and V. The factor-Ii is more or less similar to the factor-II in Durmala samples (Table-XLIV).

The analysis indicates co-precipitation of carbonate and phosphate forming calcium phosphate and calcium carbonate and Cr, Sr, Ba, etc., loadings are suggested as an indicator of replacement of Ca by these traces in the phosphate lattice. For such a high concentration of phosphate a fell in pH in the basin with adequate supply of phosphatic material is necessary.

1 7 2

This factor is indicative of slightly oxidizing to reducing phosphatic shallow water marine conditions.

Carbonate Precipitation :

Factor four is a bipolar factor having positive loading for MgO and negative loading for CaO and may be considered as a carbonate precipitation factor. This factor is thought to represent normal shelf sea water of slightly oxidizing and alkaline character in which deposition of limestone may occur, further negative loading for MgO is suggestive of a penecontem-poraneous dolomitization. Such an environment is not only conclusive to phosphate deposition but also carbonate deposition.

Oxidizing to Reducing Conditions :

This factor has high positive loading for positive loadings for AI2O2* ^^ (Factor~V, Table-XLIII) while MnO and Cd show negative loading. Factor-IV (Table-XLIV) shows low positive loading for Fe^O^. On the basis of Fe202 loading this factor is, therefore, named for oxidizing to reducing conditions of the basin. It is presumed that with the rise of pH of the system accretion of nodular as well as deposition of disseminated phosphates might be possible.

1 7 3

Residual Pore Water J

This factor has a high to low positive loadings for Na20» Pb, and V and moderate positive loading for Cd (Factor-VI^ Table-XLIIl), as well as moderate to low positive loadings for Al^O^, PjOj, Na20» Cu, Pb, Co, Zn, Sr and Rb (Factor-II, Table-XLIV). The level of loadings in the case of above constituents may, therefore, be taken as the residual pore water factor. The correlation of pore water factor with phosphate and carbonate precipitation factors indicate an increase in porosity or inter-cellu;Lar spaces to accommodate the dissolved carbonate and phosphate.

According to Banerji, et al. (1984), the original compo-sition of the phosphorites of Udaipur as well as the associated carbonates which formed in a highly complex milieu has certainly not formed out of the marine waters of uniform composition, but from the waters of variable composition, such variability in the composition was apparently controlled and governed by the nature of the interstitial waters and the pore-waters which in their turn, affected the fundamental factor, i.e. the grain size* And it is a common knowledge that the original grain size is a function of several factors viz., current and wave intensity, sorting, density of the fluid and the provenance.

Detrital Clay Supply :

Factor-VII (Table-XLIII) has high positive loading for AI2O3 and low positive loadings for MgO, Ni, Co, Cr, Sr, Ba

174

and Li. On the basis of high positive loading for AI2O3 this factor may be inferred as clay supply factor. The low positive loadings for traces can be explained by their adsorption by clay.

The product of clay minerals are likely to be controlled by the activities of Al"*"/ k"*" and Mg"*" in aqueous phase. This association in this factor also suggests a low Eh (anaerobic) condition. The rates of detrital depositions, chemical and bio-chemical precipitation controls are the effect of wave and current action indicated by the presence or absence of clay mineral constituents.

Organic Activity s

The relative importance of organic activity for the fixation of various major and trace elements is indicated by factor-VIII. This factor has a moderate positive loading for Ni and Zn, and a high positive loading for V. Zinc has been found associated with organisms (see Canon, 1955; Van Ingen, 1915; Black and Mitchel, 1952; etc.). Also, Willey (1976) recorded their association with organic carbon in the Placentia Bay. The low positive loading for Ni indicates epigenetic-diagenetic replacement whereas high positive loading for V indicates association of organic matter with vanadium.

Since this factor has a negative correlation with the factor one and two, it is inferred that phosphate precipitation is partially independent of organic activity. The observations made on the formation of phosphorites based on factor-vector analysis may be summarised as followss-

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1. The phosphatic material supplied in a soluble state, was originally rich in calcium and strontium,

2. The precipitation of phosphorite was accompanied by the co-precipitation of calcium carbonate and calcium phosphate,

3. The pH condition of the system was highly variable as demonstrated by the phosphate, carbonate and silica precipitation factors.

4. Due to variation of Eh conditions from reducing to oxidizing condition, carbonate sediment was deposited in deeper water while limestone and calcareous-phosphate in shallow water.

5. The original composition of phosphorite as well as the associated carbonates has formed out of the waters of variable composition which was controlled and governed by the nature of interstitial waters or pore waters which in their turn affected the fundamental factor^ the grain size.

6. Detrital supply must be very low to prevent arenaceous and argillaceous sediments from diluting the phosphates.

7. The presence of trace elements viz., Cu, Co, Cr, Pb, Zn, and V in phosphorite is sporadic and they are probably connected mainly with organic matter.

CHAPTER - VIII GFNESIS OF PHOSPHORITE

CHji^TER - VIII

GENESIS OF PHOSPHORITE

INTRODUCTION :

The genesis or origin of phosphorites is a controversial problem. The complexity of the processes involved in the fotroa-tion of marine phosphorite deposits has been the subject of study by a large number of investigators for a fairly long time, several divergent views regarding the deposition and accumulation of phosphorites have earlier been put forward. However, from a general review of the work on the iirportant phosphorite deposits of the world, it may be said that the formation of phosphorites was essentially controlled by certain interrelated geologic, biogenic and chemical factors.

As regrds to their sources, the phosphorites were earlier supposed to have been derived frcwn coprolites (see Sollas, 1873 and Penrose, 1888), Plentons (see Murray and Renward, 1891), fish remains following their catastrophic deaths (see Blackwelder, 1915, 1916) and residual accumulation at unconformities (see Grabau, 1919).

A departure from earlier thinking on the source and formation of phosphorites was first made by Mansfield (1920), who postulated that the phosphate of Phosphoria Formation of North America owed its origin to the progressive replacement of originally calcareous oolitic deposits by the phosphates present in sea water in a soluble state.

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Mansfield (1940) made an attenqpt to correlate the periods of phosphate deposition within the geologic record with periods of widespread volcanism. He thought that unusual addition of fluorine to the ocean from hydrofluoric vapour emanated from volcanoes, might have lowered the solubility of apatite resulting in its chemical precipitation.

The modern theories of phosphorite formation are more or less modelled after Kazakov (1937, 1938 a), who first suggested a model of direct inorganic precipitation of marine phosphorites. He proposed that phosphate facies are encountered mainly in the border zone between shallow water platform sediments and the deep water geosynclinal accumulation. He also envisaged two types of phosphate deposits. The platform type phosphorites having low to moderate content and being usually nodular are associated with glauconite and arenaceous materials. The geosynclinal phosphorites are usually bedded, platy, flagstone type, high in associated with limestones, blackshales and cherts.

According to Kazakov (1937, 1950) the P^O^ content of marine waters increases with depth from a minimum in the zone of photosynthesis to a maximum at about 500 metres depth as the pH and tenperature decreases and the partial pressure of CO2 increases. At greater depths, the P2®5 content decreases as slightly as the CO2 content drops. The sea water at first gets saturated with calcium carbonate which is immediately precipitated, and later, with calcium phosphate.

According to Sant (1979), by and large the Kazakov-McKelvey concept of the role of the 'oceanic upwelling* in

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the formation of marine phosphorite (which contributes a major share to the phosphate resources of the world) has been accepted, though there is considerable disagreement on the actual process of depsoition, precipitation and fixation of phosphate in sea water. It has, however, been established that the formation of sedimentary phosphate is controlled by certain specific factors such as palaeogeography, palaeotectonics, sedimentary environment and lithoassociation. The right type of environment should also necessarily be prevalent for a long period to facilitate better and large scale deposition and formation of the phosphate. Existence of such environments in various parts of the world at different periods in its histroy is evidenced by the occurrence of several major marine phosphate deposits in geological formations ranging in age from Cambrian to Tertiary.

As evidenced by the known phosphate occurrence in India, such conditions prevailed, at least in past, during the Precambrian, Aravalll, Bijawar, Cuddapah times and also during the Jurassic and Cretaceous- Eocene Periods.

Ocean circulation gyres driven by the trade winds and westerly winds have strong divergent upwelling in the trade wind belt on the eastern sides of the oceans; these gyres have been suggested as the mechanism for marine phosphogenesis (see Kazakov, 1937 and 1950; McKelvey and others, 1953; McKelvey, 1967). However, the most effective circulation systems in so

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far as phosphogenesis is concerned are equitorial upwelUng during episodes of transition from high level, warm oceans to low land cold oceans. The effectiveness of the upwelling of either type depends on the interplay between deep-ocean richness of phosphorus and the intensity of upwelling (see Kazakov, 1937; Klemme, 1958; Kelvey, et al./ 1959; Strakhov, 1962; Sheldon, 1964; Legeros, et al.# 1967; Saffir and Rabin, 1970; Sheldon, 1980).

According to some authors, phosphorites may be formed by replacement of CaCX) by phosphate solutions. This assumption is based on the fact that the conversion of calcite into

-3 +2 carbonate apatite may take place at PO^ and Ca concentra-tions considerably below those required for apatite precipi-tation. The formation of carbonate apatite by calcite replace-ment has been investigated in detail by Ames (1959) and followed by Pevear (1966, 1967).

Most economic phosphate sediments of marine origin, occurring typically as stratified deposits, constitute highly anomalous sediments deposited under very specific conditions, resulting in P2®5 concentrations which may be up to 100-125 times that of the crystal average of 0.2 3% ^^ the formation of sedimentary phosphate deposits have been concerned chiefly with establishing how phosphate in solution in sea water could be concentrated sufficiently to produce very large quantities known to exist as phosphate deposits, some of which may extend over hundred or thousand of square kilometers. Most of the theories fall into one of 3 groups, according to whether emphasis is placed on physico-chemical.

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biological or diagenetic processes as the controlling factors in concentrating phosphate in the sediments (see Gulbrandsen, 1969; Riley, 1968; Warin, 1968; Cook, 1976 a and Trudinger, 1979).

Studies of recent phosphate formation in the off-shore areas of peru-Chile (see Baturin, et al.« 1972; Veeh, et al., 1973; Manheim, et alw 1975; Burnett, 1977; Burnett and Veeh, 1977) and S.W. Africa (see Baturin, 1969, 1971; Senin, 1970; Calvert and Price, 1971; Roman Kevid and Baturin, 1972; Sumraerhayes, 1973; Price and Calvert, 1978), Indicate that there are three main requirements for the formation of contem~ porary phosphorites^ i) an oxygen minimum layer impinging on the sea floor; ii) a limited supply of terrigenous and carbonate detritus and iii) strong persistent upwelling. The oxygen minimum layer is usually between 100 and 500 metres of depth in the present oceans, and thereby encroach into shallower water during periods of slowed oceanic circulation (see Emdyanov and senin, 1969 and Piper and Codispooti, 1975 and Pishcher and McArthur, 1977).

Bachra, et al. (1965) and Martensand Harris (1970), on the basis of their experimental studies, proposed that the presence of Mg ion in solution resembling sea water inhibit the precipitation of apatite. However, they suggested that there

was probably a threshold of Ca/Mg ratio above which apatite could precipitate. The diagenetic mobilization of phosphorus and the formation of apatite concentration from interstitial waters in the model proposed by Bushinskii (1966) and favoured by Kolodny (1978) in a recent view of the genesis

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Of phosphorites. This is also the opinion of the Price and Calvert (1978) based on a geochemical study of phosphorites from the Namibian shelf. They concluded 'the origin of the phosphorites is believed to be the result of the diagenetic precipitation of the phosphorus within sediments*.

The central California margin phosphorites are the result of direct interstitial precipitation. This is supported by recent experimental data which have demonstrated for the first time. They precipitate from marine waters si«5)ly by increasing the phsophorus and fluoride content via degradation of organic material (see Gulbrandsen, 1966; Cristopher and others, 1970 and Gulbrandsen, et al., 1984).

Al-Bassam, et al. (1983) reported that most of the phosphate in the Carrpanian-Masstrichtian depositional basin in the part of Iraq was syngenetically precipitated as phos-phate mud at the sediment water interface, mixed with fine quartz, clay minerals and carbonaceous matter. Further, they added that the intensity of phosphate precipitation was greatly increased in certain periods only giving rise to the phosphate bearing horizon, when physico-chemical condition favourable for apatite precipitation and preservation occurred.

According to Mauricce slansky (1986) phosphate deposits are mainly supplied with phosphorus from deep oceanic reserves by means of upwelling currents. Phosphate minerals precipitate from the interstitial water near the water sediment interface and the margins, particularly the upper boundary of Og minimum layer. Oxidizing encourages stability of the humic compounds formed from planktonic organic matter; the humic acids seem to

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play a direct role in the phosphate precipitation and in the formation of phosphatic particles.

According to Baturin (1989), sedimentation, diagenesis and subsequent transformation control the compositions of marine phosphorites. The role of the first two factors can be judged from the cocnpositions of the phosphorites and the enclosing sediments. However, phosphorites are often redeposited, so the effects on their compositions from the original sediments must remain an open question. One of the few reliable ways of considering this is to examine recent (Holocene) phosphorites in the coastal part of the Namibia shelf, which were formed in recent diatom muds by diagenesis.

Hence, there are three main schools of thought regarding the genesis of phosphorites. Some propose an organic origin based on their association with true coprolites and skeletal materials (see Penrose, 1888). Others proposed a replacement fran shells and sponges (see Fisher, 1873; Traask, 1939; Waggaman, 1952; Graham, et al.# 1954; Gulick, 1955; Ames, 1959; LeGeros, 1965; Degens, 1965; Gulbrandsen, 1960, 1966; Kraus-kopf, 1967; Valdiya, 1972; Patwardhan and others, 1975; Verma, et al., 1975 and Srivastava, et al., 1978).

Another school of thought proposed an inorganic origin of phosphorites (see Kazakov, 1937; McKelvey, 1959, 1967; McKelvey and others, 195 3; Cheney, 1955; Chenny, et al., 1959; Sheldon, 1964; Maughan, 1966; Yochelson, 1968; and Israili# 1976 a, b and 1978).

The area under study has also been investigated by several workers and various views regarding the origin have

183

been put forward. According Ravishankar (1955) the chert member of Nigalidhar, Korai» Mussoorie and part of Garhwal synclines which now occupy separate areas represent part of the same depositional basin. This basin might have been either a sealed, inland extension of a sea gulf or embairment from north or a sheltered depression in the shallow marine restric-ted circulation with undulatory floor topography. The cycles of deposition were presumably controlled by alternate marine transgression and regression, possibly due to an oscillating movement of the basin floor. The phosphate rock might have been formed by the biochemical process with the phosphate derived from decay of phy top lank ton, algae ,, river and sea water,

Rao and Rao (1971) proposed that the chemical composi-tion of the Mussoorie phosphorites falls within the range of carbonate hydroxyl-fluorapatite which usually occurs in the form of marine phosphorites. The composition is also in conformity with the carbonate, phosphorite gradation. Patwardhan and Ahluwalia (l973, 1974) suggested a biochemical mode of origin for the Mussoorie phosphorite deposit on the basis of some geological and petrographical criteria. They believed in an indirect role of organism whose productivity was supported during the oceanic upwelling for the deposition of Mussoorie phosphorites.

On the basis of rare metal studies, Sharma (1974) suggested that the Mussoorie phosphorites appear to be the direct chemical precipitates from phosphate rich upwelling currents.

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Chaudhari (1978) discussed the origin, transportation and accumulation/precipitation of phosphate deposits in Mussoorie and other areas, invoking almost all types of mechanism postulated for phosphorite genesis. According to Patwardhan and Panchal (1984), it is felt by more and more previous workers that some kind of a trapping mechanism for the accumulation of the phosphorus carried up the continental margin by the upwelling currents of oceanic water is necessary for the formation of sedimentary phosphorite deposits. The mechanism should obviously be related to the regional basin topography and palaeogeographic and palaeotectonic conditions.

Recently, Ahluwalia (Abstract volume, 1989) proposed that the Tal phosphate of the Himalaya and many other phos-phorites of the world cannot be exclusively categorized as organic or inorganic in origin and more often than not, result from a suitable combination of these two factors.

In the light of the foregoing views of phospho-genesis, an attenpt has been made to discuss the geologic, biogenic and chemical controls on the formation of phosphorites of the study area.

Geologic Controls :

Cook and McElhinny (1979) suggested that the Cambrian phosphate deposits of Australia were laid down generally in the east-west sea way extending from Australia into Asia and perhaps into Europe, They proposed that the way these deposits were laid down on the southern side of the sea w«y was

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analogous to the Mesozoic Tethyan situation. They believe that probably there would have been strong currents flowing through the sea way 'producing high productivity as a result of coastal entrainment and upwelling, and particularly as a result of intense dynamic upweiling associated with topographic hxghs'.

Riggs (1979) in a paper entitled 'phosphorite sedimenta-tion in Florida-A model Phosphogenic system* described that the formation and subsequent accumulation of phosphorite sediments sufficient to comprise a major stratigraphic unit with the potential of becoming an economic deposit requires a very highly specialized set of environmental conditions in a very special-ized geologic setting. Only if all of a complex set of tectonic and environmental variables are just right will there be a significant precipitation and major accumulation of sedimentary phosphorites. Such stratigraphic occurrences represent sediment systems which are geologically quite abnormal.

Riggs (1979) pointed out that the structural framework which controlled the formation and deposition of phosphorites in Florida was a series of topographic highs. Extensive coastal* shallow near shore shelf, and platform environments occurring around the highs were the sites of major phosphorite sedimenta-tion. Phosphorite precipitation took place as upweiling sea water moved across the shallow platforms and into coastal environments. Further, Riggs argued that phosphorite was deposited wherever phosphorus sources were adequate, the current and geochemical systems were appropriate, and shallow marine environments had the proper geometry.

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The ultimate magnitude of phosphorite deposition depends on the size and extent of the structural system, the duration of the phosphogenlc system through geologic time, and, of course, the volume of phosphorus provided from the sea or from other sources.

The experimental data available on inorganic precipi-tation of phosphorites (see Krumbein and Garrels, 1952 and Gulbrandsen, 1969), pertains in reality to the mineral apatite which is seldom the form in which marine phosphorites occur. However, presuming that an abiotic precipitation of phospho-rites (apatite) should be possible under some geological control.

Most of the older phosphorites deposits show pronounced laminations on a time scale of probably a few years to a few hundred years with thin laminae of shale, mudstone, carbonate or chert. These alternations result from local changes, e.g. shifting of river mouths or of morphological features on the shallow sea-bottom, slight changes in the direction and strength of currents, small scale temporary oscillation, variations in the amount of rainfall on the nearby land and a variety of similar causes (Kazakov, 1937; McKelvey, 1963; Sheldon, 1964; Bentor, 1980 and Boyle, 1984), In the study area, the association of three rock types namely, limestone, chert and shale and preservation of primary bedding and lamina-tions in the bedded phosphorites indicate a change of flow of direction of ancient rivers, shallow sea bottom and strength of low sea basinal currents during and after the deposition of the phosphorites.

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According to Liang and Chang (1984), there are two models of deposition of phosphorite and its host rock in an appropriate medium, viz., 1) if the medium is slightly acidic to alkaline, the depositional order will be (from bottom to top); dolomite, phosphorite, limestone (calcite); and silica (quartzite and chert, etc.); and 2) if the medium happens to be alkaline to acidic, the depositional order will be (from bottom to otop); silica, limestone, phosphorite and dolomite. The stratigraphic sequence of deposition (from bottom to top) in the study area is limestone, chert, phosphorite and shale. This sequence is somewhat similar to the second model of deposition proposed by Liang and Change (1984) and indicates slightly alkaline to weakly acidic medium of the basin.

Some workers assumed that some pelletal and oolitic phosphorite deposits must have been rolled out by currents to give them their typical rounded/oval shape (see Folk, 1959; Sheldon, 1980; Bagti and Mundepi, 1984). The laminations indicated that the environment of phosphorite deposition had much less energy, leading to the inference that the size distribution of phosphorites is not due to mechanical sorting by currents but due to certain processes of accretionary growth (see Gebelien, 1960; Basu, 1984).

Feas and Riggs (1965, 1968), Baturin (1971) and Riggs (1979 a) proposed that the pellets of the Flordia phosphorite deposits (USA) were formed by erosion of an apatite-mud or microsphorite and subsequent rounding and abrasion as the sediment was being reworked.

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Tooms/ et al. U969); Reeves and Saadi (1971) and Calvert (1977) proposed that well developed apatite pellets are formed diagenetically in the muds.

In the study area the occurrence of ovulitic to oolitic shaped collophane indicates poor transportation, rounding and accretions of phosphatic minerals. The pelletal shape of collophane may be due to reworking, and diagenetic origin.

According to Bremner (l979), pelletal phosphorites show evidence of having originated by direct precipitation of apatite. He concluded that precipitation occurred in shallow warm lagoons which were periodically disturbed by storm generated waves. Pellets resulted from the disruption of semi-lithified collophane in upwelled water circulating into the lagoons.

Slightly deformed and semispherical shape of the pellets suggest that the excreted pellets remained soft during subsequent transport and became indurated only prior to their burial by subsequent sediment a ticSn.

The presence of amorphous, crypto- to microcrystalline apatite phase in a few of the samples may be on account of direct inorganic precipitation of apatite. The thin lamina-tions observed in the bedded phosphorites indicates their precipitation in a low energy shallow marine water basin.

At places some lenticles in lenticular phosphorites are aligned oblique to the bedding plane indicating that either some penecontemporaneous deformation occurred before compaction possibly due to agitation of the basin floor when the sediments were in plastic »t,age, or it may also be

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due to effects of current action, Sheldon (1964 a) was first to point out that the

palaeolatitudinal distribution of ancient phosphorites matches the latitudinal distribution of young phosphorites, with both falling within 40° of the equator. Subsequently, Sheldon (1964 b) and later Freas and Eckstrom (1968), applied palaeolatitudes and palaeogeographic reconstructions to the search for new phosphate deposits. The palaeolatitudes of all deposits show a spread from about 0° to 70° but with a clear maximum within 20° of the palaeoequator. When only the major deposits are taken, the two latitude peaks are more clearly defined with peaks between 10° to 20° from the equator. This supports the view that phosphate deposition is most abundant at low latitude locations with a preference towards a sub-equatorial (I0°to 20°) location rather than an equatorial one (0° to 10°) site (see Cook and McElhinny, 1979; Birch, 1980; Al-Bassam, et al., 1983).

According to Long Kang and Zhendong (1988), warm and dry palaeoclimate suggests a low latitude epicontinental sea along the ancient continental margins. Before the overlapping of the Liuping Formation on the Daxing Formation, there had been an uplift in the region. After that the crust became more stable, completing the transformation of geosyncline to plat-form and favouring the deposition of phosphorite (see Long Kang and Chendony, 1988).

The phosphorite deposits of Mussoorie lie between latitudes 30°25'Nand 30°30'Hwhich indicates warm and dry palaeoclimatic conditions with low latitudes, epicontinental

1 9 0

sea basin along the ancient continental margin. It may also be suggested that the basinal uplifting might have caused the initiation of the geosynclinal condition followed by platform structure on which the phosphatization processes took place. This is corroborated by the occurrence of bedded (geosyncliiMtl type) and nodular (platform type) phosphorites in the study area.

The open shelf in turn faced deep water euxinic basin on which pyrite carbonaceous shales were deposited both under acidic and strongly reducing conditions, (see Gulbrandsen, and Pettijohn, 1957; Mason, 1966; Pettijohn, 1969; Beaelkes, 1984). There is a close link between phosphate occurrence and the complex clay minerals, both tending to occur at horizons of reduced sedimentation (see Puller, 1979). A horizon of black shale associated with phosphorites suggests a gradual change in the basinal conditions from euxinic (black shale) to aerated intertidal environment at the time of deposition (see Kanwar and Ahluwalia, 1980; Liang and Chang, 1984; and Verma, 1984).

In the outer Lesser Himalayan region a long narrow linear basin was formed which accommodated Blaini-infra Krol-Krol-Tal sequence of the Krol Belt, Restricted nature of this basin with initial deposition of Boulder Bed suggests faster rate of erosion of the provenance on the north. As a consequence the terrigenous influx became minimum, allowing precipitation of Carbonates of the Krol Formation followed by phosphate accumulation and deposition in Lower Tal times.

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However, the nature of cover rocks of phosphorite beds/ bands and the arenaceous upper Tal sequence suggests the uplift-ment of the provenance again to such heights that it became capable of supplying terrigenous material to the Krol-Tal basin due to faster rate of erosion and denudation. This process perhaps continued till the fossiliferous shell lime-stone of upper most Tais was deposited at the Subathu sea (Eocene) that invaded the entire the outer Lesser Himalaya and considerable parts of the Inner Lesser Himalaya depsoiting the Nummulitic rocks suggesting that this transgressive phase did not last long and the Krol Belt rocks were also uplifted due to early Tertiary orogenic impulse and a fore deep was formed in whxch molassic Siwaliks were laid down (see IGCP Project -156, phosphorite; ed, G.S.I* and P.P.C. Ltd.),

According to Radcliffe, et al. (1984), on the basis of lithology and the occurrence of primary sedimentary structures it is suggested that the sediments of the Lower Tal Formation were deposited in tidal flat environment. Two idealised facies viz., intertidal and shallow subtidal can be chiefly recognised in the Lower Tal Formation, wheireas subtidal conditions pre-vailed during the deposition of Krol beds.

They further added that during Lower Tal sedimentation, some parts of the basin were deeper due to their restricted or sealed nature and this resulted in the deposition of chert and phosphate rock associated with carbonaceous and pyriti-ferous black shale.

The Mussoorie phosphorites are associated with a carbonaceous shale-chert-limestone succession v^ich is

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recognised as an ideal phosphatic suit of rocks or litholo-gical setting for the deposition of marine phosphorites. From the nature of these associated rocks and their superposition it is evident that they are typically geosynclinal type of deposits. A detailed study of lithology and aerial distribu-tion of the rock types of the chert member indicates that the surrouhding ancient land masses, that were probably low lying areas, had very little drainage thus restricting the supply of detrital material which included fine quartz and mud during the deposition of the chert members. The general paucity of the terrigenous sediments also suggests that the depositional basin was bordered by tectonically stable, low land area with mature topography. This presumption leads to believe that climate was warm but arid and therefore, only few rivers flowed into the basin from the bordering land, bringing very little detrital material.

It appears plausible that due to marine upwelling the terrigenous phosphatic material, that had accumulated in marine environment got concentrated in a more or less restricted basin of deposition occupying the arms of a pre-existing sea that also probably extended over the shelf areas. Certain favourable physico-chemical conditions supported the growth of colonies of algae in this part of the ancient sea to maintain their metabolic activities. The various submarine highs divided the Tal phosphorite basin into sub-basins, and the sub-basinal topography further restricted the circulation of the bottom waters leading locally to stronger euxinic conditions even in an otherwise shallow marine basin.

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The variable trend of concentration of phosphates in these deposits may be partly due to the removal of excess soluble silica and lime with subsequent minor structural disturbances, viz., brecciation, pulverization and fragmenta-tion aided by collapsing action by meteoric water, which sub-sequently brought out natural upgradation of the phosphorites.

The granular and pelietal phosphorites might have been formed at the high energy region near the shoreline areas by the continuous working of soft heterogenous (dirty) mud by waves and currents. Local transportation and redeposition of the granular phosphate ingredients were probably responsible for the roundness of these grains, their sharp and definite contact with cementing materials and the presence of broken pellets. On the other hand, the fine-grained phosphate mud settled out and accumulated as cementing material away from the shore in the deeper parts of the basin where wave action was less effective. Remnants of the original phosphate mud is retained in the host rocks as phosphate cement.

Chemical Controls;

According to Subramanian (1980), most of the world's phosphate production comes from marine phosphates. Hence any treatment to explain the mechanism of phosphate formation should take into account the physical chemistry of the sea water. Association with the carbonate minerals and the presence of black shale and pyrite can easily be explained in the light

- 2 of various mineral equilibria in the system containing CO^ ,

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PO^^ and The effect of P and T conditions on such equili-bria can explain the occurrence of various deposits in the deeper part of the marine environment.

Selective precipitation, dissolution, exchange reaction with animal shells, sorption by organic and inorganic compounds in the marine environment, isomorphous substitution of a number of Cations and also of some anions are the various mechanisms that can account for the compositional variability of the

+2

phosphate minerals. Fe is an effective ion to remove the phosphates from water in reducing environments (see Subramanian, 1980).

According to him, some important features of phosphorites of interest to its chemistry of formation are 1. Association with carbonate minerals. 2. Presence of black-shale, pyrite and other features

of reducing environment. 3. The role of organic and inorganic processes in influencing

the concentration and precipitation of phosphates. 4. Occurrence of sedimentary apatite involving extensive

isomorphous substitution of both cations and anions. 5. The vast areal extent of phosphorites considering the

low P content of thepresent and past sea water. According to McArthur (1978) the fact that different

types of phosphate, deposited in the same basin at the same time may show large differences in their chemistry, argues against the formational environment being important in producing the variations in the contents of Na, CO^ and SO^ in marine carbonate-fluorite. Furthermore, phosphorite genesis appears

195

to have taken place on an open shelf environments In contact with sea water (see Baturin, 1969, 1971; Manheim, et al., 1975), Fluctuations in the chemical composition of sea water did not occur either to a sufficient degree or with sufficient rapidity to account for the variations.

Thus, the chemical factors triggering the formation of phosphorites are reviewed and discussed. The following chemical factors are supposed to be effective in controlling the formation and deposition of the phosphorites of the study area s-

1. Effect of pH 2. Effect of Eh 3. Effect of pressure and temperature 4. Effect of geochemical behaviour of significant

major and trace elements.

1. Effect of pH 8

The acidity or alkalinity of an environment is an important factor in determining whether or not certain minerals will precipitate (see Pettijohn, 1984), Krumbein and Garrels (1952) had a pH of 7.8 (about that of sea water) as 'limestone fence', Calcite is freely precipitated at this or higher pH values. According to Kazakov (1937), the preci-pitation of phosphorite takes place at pH value of about 7.1 and that of calcium carbonate at pH values between 7,1 and 7.8. Simultaneous precipitation may also take place when pH is about 7.8, but the ratio of calcium carbonate would be

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much higher in this case due to its high absolute solubility (see Krumbein and Garrels, 1952). According to Campbell (1962), phosphorite precipitates predominantly in the pH range 7.1 to 7,8 and calcium carbonate, when pH is above 7.8. McKelvey,et al., (1953) while discussing the genesis of phosphorites of the Phosphoria Formation of North America remarked that when cold phosphate-rich water upwelled into the larger shelving embay-ment from the ocean, phsophorite was deposited from these ascending waters as their pH increased along with the increase in temperature and decrease in partial pressure of CO2. The carbonates were deposited from these waters when they reached more shallow depth at somewhat higher pH. Thus, it is reasonable to derive that chemical environment of phosphate precipitation is principally dependent upon pH conditions and controlled by variation in the partial pressure of CO2.

Matten and Harris (1969) showed experimentally that Mg ions tend to inhibit apatite precipitation in the sea, and that at pH values of 7.5 - 8.0 this precipitation could take place with a Ca/Mg ionic ratio ijreater than or equal to 5.2, which is well above the value generally found in sea water, usually around 0.20.

Nathan and Lucas (1976) confirmed this lower limit of 5.2 for the Ca/Mg ratio for sea water with a pH value of 7.8-8,1.

Increase of pH causes coprecipitation of both calcite and apatite; the calcite/apatite ratio will be higher; since +2 -3 -2 Ca , PO^ and CO^ all have single valence states, changes

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In Eh cannot prcxiuce separation into carbonate rich and phosphate rich layers; hence the individual enrichment would

—2 have to talce place within a narrow pH range. Relative to CO^ / the Ca3(PO^)2 is less soluble (the solubility product of CaCO^

Q 30 is 4 X 10 ' as against 1.3 x lO""' for Ca3(PO^)2. Hence, in the pH range 7 - 7.5 Ca3(PO^)2 can first precipitate vrtiile CO "" remains in solution so long as the pH is buffered in that range. When pH increases to 8, CaCO^ will precipitate (see Garrels and Christ, 1965).

In the study area, it has been observed that the phos-phate, carbonate and silica have been occasionally found mutually replacing each other. This could be explained possibly by the physico-chemical conditions of the precipitation of the phos-phate, carbonate and silica controlled by the pH of the marine environment. A little change in the pH of 7.8 might facilitate the formation of one or the other of these three sediments. Thus, pH in the study area presumably fluctuated around 7.8 as phos-phate rock indicates pH values less than 7.8 but the associated dolomite and calcite indicate pH values greater than 7.8. The same pH range has also been reported by Sharma (1974).

2. Effect of Eh t

In a general way sediments are deposited under either oxidizing (aerobic) or reducing (anaerobic) conditions. The measure of the oxidizing capacity of an environment is the Eh or oxidation-reduction potential (see Mason, 1949; Zobell, 1946). According to Krumbein and Garrels (1952) and Teodorovich

198

(1955), the oxidation reduction surface, that is the plane separating the oxidizing from the reducing environment, may be above or coincide or below the sediment water interface. In more strongly reducing environments it is above the mud-water interface.

The primary precipitation or replacement Ca3(PO^)2 need not be influenced by Eh, the state of oxygenation in a given environment indirectly plays a role by controlling the rate, extent and nature of release of P from other sinks in the oceans. For exan^jle, it is observed that P has a strong tendency to be associated with Fe in many equatic environment. Bortleson and Fred Lee (1974) have indicated that Fe and P are positively correlated in lake sediments and that the oxidation conditions will control the rate of Fe in either mobilizing or releasing P to the water. Subramanian (1976) has suggested that Fe and P are oogenetic in fresh water as well as in estuarine environment,,, while Nariagu (1972) has experimentally verified the role of Fe in P mass transfer in the aquatic environment. In a very highly oxidising environment, Fe"*" removes P from water by the formation of sorbed complex on Fe(0H)2 thereby making available only a small amount of PO^^ for Ca"*" to form apatite in the marine environment. Hence, for the continent-derived P to reach the ocean for apatite precipitation the river should have positive but not extreme oxidising and acidic conditions. Changes in these parameters may trap the dissolved PO^^ in the estuarine region where the P could be sorbed by Fe(0H)2 or clay minerals.

1 9 9

The narrow pH buffering required for the carbonate and phosphate separation can be generated by the tidal cycles where-by the continent derived fresh water (pH - 6.15, Livingstone, 1983) and the open ocean water (pH - 8.1/ Turekian, 1968) can mix in changing ratios, first to give a more alkaline water to precipitate carbonate, and then to give a less alkaline water to precipitate the phosphate minerals. This perhaps is the geochemical process underlined by the term intertidal.

Usually conodonts, occasional fish remains, and spores and pollen are the fauna or flora of those shales formed in a highly reducing environment. A further indication of oxygen deficiency is an abnormally high (over 2 or 3 per cent) content of organic matter. Normal lalcroblologlcal and scavenger action tend to destroy the organic residues which settle to the bottom. Inhibition of such action because of oxygen deficiency leads to an Increase in these materials in the black shales and related deposits. Iron sulphides (pyrite or marcasite) signify a reducing and wholly oxygen deficient medium (see Kjnambein and Garrels, 1952).

In the study area, the presence of conodonts (as reported by Azml and his associates, 1980, 1981 and 1983),organic matter, low content of Iron and association of pyrite and black shales with phosphorites suggest a reducing environment with negative Eh (see IGCP, Project - 156, Phosphorite, 1981) possibly due to restricted circulation.

200

3. Effect of pressure and teir^jerature :

Since temperature affects the solubility of many minerals and gases, it has therfore, an important effect on chemical precipitation. At lower temperature the solubility of COg is greatly enhanced. Hence the solution of calcium carbonate is promoted in cold waters and conversely precipita-tion of the same material is brought about by a rise in tempera-ture. Temperature also affects the composition of mixed crystals or solid solutions. Shell carbonate is richer in MgO at the lower tenperature (see Chave, 1954).

that The data given by Berner (1971) indicates^the temperature

ranges from 20°C at the surface to 2®C at the bottom of the oceans corresponding to a pressure change from 1 atmosphere to 500 atmospheres. Pressure and temperature have opposing effects on the phosphate solubility but the constant values for dissol-ved phosphate below 100 metres indicate that the pressure effect on the phosphate equilibria is negligible. On the other hand, because of the involvement of the gaseous phase of CO2 in the carbonate equilibria, there may be quantitative changes in the carbonates that are associated with phosphate deposits formed at various depths; similar to the carbonates, phosphates dissolved at greater depth will be reprecipitated at the surface. The effect of temperature on these equilibria can be calculated from the standard chemical thermodynamic concepts (see Koltz, 1988), whereby solubility at any given tenperature can be evaluated from known values at standard conditions.

2 01

Kramer (1964) calculated solubility prcsducts for carbonate fluorapatite, which shows small decrease in solubility of phosphate with increase in temperature over representative of natural conditions. The indirect effect of temperature is possibly due to the antipathetic relation-ship between temperature and CO2 solubility, pH and temperature are naturally related. An increase in temperature is likely to cause an increase of pH and a decrease in solubility of phos-phorite and vice-versa.

4. Effect of geochemical behaviour of significant major and trace elements i

According to Banerjee, et al. ^1984), the availability of the elements in the formational environment and their ionic radii which determine the possibilities of inter element lattice accommodation control the percentage of an element in a rock and its distribution within various rock constituents. According to McConnell (1938), apatite represents a group of minerals

+2 -3 containing Ca and PO^ as essential constituents v/ith associated trace elements among which Mg, Mn, Sr, K, Na, Ba, Cr, Fe, Al, ASO~^, VO^^, Sio^^, COg^, F"^, Cl"^ and OH"^ are important.

It has been experimentally shown (see Bachra, et al., 1965; Marten and Harris, 1970) that Mg "*" ions inhibit the 2+ precipitation of apatite probably because Mg compete with

2+

Ca in the apatite structure. Marten and Harris (1970) deduced some threshold values for the Ca/Mg ratio necessary

2 02

for apatite to precipitate from solution. The magnesium Ions seem to retard the reaction (salinity) when Ca/Mg ratio approaches to 4.5 to 5,2, This ratio remains almost constant in normal sea water. Pore water is* however, known to vary greatly from the sea water values. Thus, it seems that dia-genetic reaction occurring with anoxic sediment could raise the Ca/Mg ratio to the point 5,2) when phosphate may precipitate,

The experimental results suggest a path way for the genesis of apatite and indicate conditions for its formation, which could prevail within the sediments in very shallow water during the very early diagenetic stage (see Walter and Honov, 1978; Morse, 1979; Nathan and Lucas, 1981 and Lucas, 1984),

In the study area, the high Ca/Mg ratio may be due to + 2 preferential entrance of Ca ions in carbonate apatite. The

+ 2 antipathetic relationship of MgO with CaO suggest that Mg + 2

could be substituted by Ca in the apatite structure and may also decrease the crystallite si2e of apatite by - increasing the Mg ions as reported by Cruft, et al. (1965) and McConnell (1973). MgO has negative relationship with P2°5* chain of replacement between CaO-MgO-p^Og during phosphatization indicates that MgO acted as a catalyst in the process of replacement of CaO by PjO^ (see Bachra, et al., 1965; Gul-brandsen, 1969; Marten and Harris, 1970, Atlas, 1975; and Burnett, 1977), The antipathetic relationship among these three oxides also indicates that surficial leaching had a leading role in increasing the content, predominantly

203

at the expanse of MgO, It, therefore, seems plausible that the replacement involving carbonates may be responsible for the increase of Ca/Mg ratio.

According to Slansky (1986) if the CaO/PgO^ ratio is greater than 1.31, the increase may be either due to the substitution of PO^ by CO^ in the apatite, or to the presence of calcite or dolomite in the phosphorite. In the study area, most of the samples of phosphorites have Ca0/P20^ ratio greater than 1.31, the most common substitution is that of

3 2— PO^" by COg . Banerjee and McArthur (1991) have reported CaO/PjOg ratio in one sample of Mussoorie phosphorite as 1.20 well below the 1.32 for end member fluorite showing that there is a CaO deficiency in the sample which could be balanced by AI2O3.

The sycnpathetic relationship of HjO"*" with Ca0/P20g ratio suggests the possibility of reversible substitution in between PO^ (OH)^.

According to Subramanian (1980), the chemical affinity between apatite and fluoride is so considerable that apatite is often used as filters to remove fluoride from drinking +2 water. Thus fluoride, in association with Ca fixes phosphorus from sea water into the sediment. The source of fluoride may be submarine volcanism, spring water or even ground water. Mansfield (1940) speculated that unconformities associated with phosphorite deposits may locally represent periods of active volcanism, causing the fixation of both P and P into fluorapatite.

2 04

— 2 The COj" and orf"are considered to be the principal substitution ions, and Si, Na and Mg are less but significant substitution ions for (PO^)"^.

Biogenic Controls s

Banerjee ( 1970 ) has suggested that the algal stromato-

lites might have played an inportant role in trapping and

precipitating the dissolved inorganic phosphorus from the sea

water. According to him the algal stromatolites in the phos-

phorites of Udaipur was responsible for the coprecipitation of

carbonate and phosphate due to change in environmental condition,

The phosphorite limestone of Lower Tal at Chaiwapakumali in Tehri and near Mussoorie are found to be stromatolitic (Raha and Gururaj, 1979, and Raha, 1977). The Mussoorie stromatolites include what looks like. Mala costroma econcertricum of Missi-ssipian age (Raha, 1977), forms resembling diminutive collenia parva and small branching cylindrical columns.

According to Banerjee (1987), pyrite is intimately associated with the stromatolitic phosphorites of Mussoorie* particularly those of Maldeota and Durmala. Pyrite layers are generally concordant with the laminae of domal and stratified stromatolites, Pyrite is finely disseminated in the phosphatic matrix between strcwnatolite bands and also it is found in larger peloids in peloidal phosphorite. This intimate associa-tion of pyrite and apatite suggests that both were formed within anoxic muds possibly in embayments where water circulation was

2 05

restricted. The absence of non-pyritic ions suggests that pyrite formation was iron-limited (see Raiswell and Berner, 1985) and sulphate reduction was pronounced. According to Banerjee, et al. U984), the variability in the concentration of the trapped trace elements was possibly a function of the quantity and nature of the organic matter present at the time of initial development of the Precambrian phosphatic stromato-lites. Original concentration of the trace elements in biolo-gically/ controlled basinal waters, was possibly the prime controlling factor. The final redistribution of the trace elements within the sediments was eKdusively a function of their chemistry.

In the central Wyoming, the organic matter associated with the phosphorites are so extensive that oil is commercially exploited there. McConnell (1965) has suggested that in the presence of carbonic aitiydrose enzymes precipitation of phosphates takes place under low HCO^/PO^^ ratio whereas this ratio needs to be high as was shown by Ames (1959), for inorga-nic phosphate precipitation. In addition to extraction of phosphorus from sea water for their metabolism, certain organisms have a particular type of cells v^ich may act as porous membranes. These membranes selectively diffuse phosphorus into the body which subsequently combine with the bones. After the death of the organisms Ca2(PO^)2 in the form of bone, teeth, etc. accumulate which on reworking yield substantial amounts of Ca3(PO^)2 in the form of francolite minerals.

206

H2S and NH^ are products of organic decay and may cause certain equilibrium reactions to proceed. For example, Berner (1971) experimentally decomposed fish in sea water and observed the presence of NH-a and other species in the decay products. In Reference to phosphatisation, NH^ can be utilised as -NH3 + 2CX)2 ® ^HCOj^ + H ... (i) HCOj^ + Ca" ^ = CaCOj + H^ ... (ii) and

+ 3CaC03 = 033 (PO^) 2 + SCO"^ ... (Hi) Also H2S = + 2H^ ... (iv) PePO^ = PO^^ + ... (v) Pe" ^ e = Pe" ^ ... (vi)

= PeSj (pyrite) ... (vii)

The above chemical reactions can account for the association of organic matter, carbonates, black shales and pyrite with the phosphate deposits. Reacrion (vi) and (Vii) would suggest a reducing and hence an Eh negative environment for pyrite associated phosphate deposits.

According to Ahluwalia (Abstract volume, 1989), the organisms being an inportant source of phosphate in the oceans where phosphate content is known to increase with phytoplankton and high organic productivity, a biogenic factor does seem to be relevant in Tal where evidences of organic activity are in plenty besides the ubiquitous presence of organic matter in the entire suit of sediments.

2 0 7

Thus, in the study area, the presence of organic matter/ association of pyrite and black shales with the phosphorites/ enrichment of vanadium and the presence of stromatolites as reported by some of the earlier workers, conclusively suggest that the formation of Mussoorie phospho-rites was partially controlled by biogenic factor in shallow water under reducing conditions.

A PROPOSED GENETIC MODEL OF THE PHOSPHORITE DEPOSITS OP MUSSOORIE s

In the light of foregoing statements of facts and discussions, an attempt has been made to present cautiously a modest model for the formation of the phosphorites of Mussoorie, as stated below s-

(1) Tal sediments were deposited in shallow marine conditions as evidenced by the presence of phosphorite associated with limestone - chert - shale succession, which is recognised as an ideal phosphatic suit of rocks for the deposition of phos-phorite. The low manganese content in the analysed san!?>les of these sediments can also be cited as one of the evidences of shallow water conditions of deposition.

(2) The phosphate deposits of Mussoorie were formed in warm and dry palaeoclimatic conditions as indicated by the low latitudes (30®25' N : 30°30'N)of the area. A high concentration of CaO and CO2 in these phosphorites, which is due to the precipitation of CaCO^ at pH greater than 7.8, also indicates

2 0 8

a warro and arid climate and therefore, only few rivers flowed into the basin bringing very little detrital materials.

(3) The basinal uplifting was probably initiated the develop-ment of a geosyhdins followed by evolution of a platform structure on which the phosphatization process commenced. The occurrence of bedded phosphorites with thin laminations and association of chert and shale support their geosynclinal origin.

(4) The ingredients of phosphate are probably derived from three different sources viz, a) volcanic, b) phytoplankton and other micro-organisms and c) rivers. The phosphate-charged upwelling ocean currents coming from deep oceanic reservoirs of the pre-existing sea or an arm of it were the major contri-butors of phosphorite in the area. These upwelling currents, which were due to localized disturbances during deposition brought phosphatic material to the shallower parts of the basin where the increasing pH mostly due to the escape of CO^ gave rise to the enrichment of

(5) Assimilation of the dissolved phosphorus by certain marine organisms and their decay and concentration after their final burial on the sea bottom. The decay of organisms produces ammonia and ammonium salts, which are converted into phosphates and nitrates as follows

NH3 + 2CO2 + HjO = NH^ + 2HC03^.+ H" ... (i) HCO^^ + Ca"*" = CaCXJj + h" ... (ii) and

2P0]J + SCaCOg = Ca3(PO^)2 + 3 CO^^ ... (iii)

2 09

The cycle continues for long till the amount of soluble phosphates in mud increases at the sea bottom. The restricted sea bottom circulations preserve the phosphate rich solutions.

(6) The precipitation of phosphorite is controlled by the pH changes. When cold phosphate-rich water upwelled from the ocean bottom^phosphorite is deposited from these ascending waters as their pH increased along with the increase in tennperature and decrease in partial pressure of COj. The carbonates were deposited from these waters when they reached more shallow depth at a somewhat higher pH. Hence in the pH range 7 - 7.5, Ca3(PO^)2 can first precipitate while CO^^ remains in solution so long as the pH is buffered in that range. When pH increases to 8, CaCO^ will precipitate.

(7) Apatite is the primary mineral which represents a group 2+ - 2

of minerals containing Ca and PO^ as the essential consti-tuents. The crystal structure of apatite favours a number of

— 3 —3 —2 —1 minor substitutions. For exainple, VO^ , SO^ , CO^ and OH are usually substituted by equivalent amounts of PO^^ and minor amounts of Mg, Mn, Sr. Abundance of V and Sr indicates such type of substitution which was influenced by the environ-ment of phosphate mineralisation. The most common substitution

—3 —2 in Mussoorie phosphorite is that of PO^ by COj which is corroborated a higher (1.31) by CaO/PjO^ ratio. (8) The compositional variations with higher CaO/p^Og, CaO/MgO ratio indicate the formation of phosphorite by replacement processes. The antipathetic behaviour of MgO with respect to CaO and PgOg indicates a chain ireplacement between

2 1 0

CaO-MgO-PgOg during phosphatization which further supports that MgO acted as a catalyst in the process of replacement of CaO by antipathetic relationship among the three oxides also indicates that surficial leaching had a leading role in increasing the P2O5 content.

(9) The dispersion pattern and behaviour of trace elements detected in phosphate and other associated rocks suggest that the fixation of these elements was more or less geochemically controlled by adsorption on the surface of apatite or by the substitution in the apatite lattice or by some biogenic activity.

(10) The presence of organic matter, higher concentration of vanadium and also of Ni and Cu, and association of carbonates, blacksshales and pyrite with phosphorite suggest that the phosphorites were deposited in a reducing environment. The enrichment of Cr and V in the phosphorites suggest a slightly anaerobic to highly anaerobic facies.

(11) A greater concentration of the phosphates in the mud possibly led to the formation of phosphate pellets, lenticles, the ovules, etc. under some environmental vicissitudes.

(12) Later concentration of phosphates may have taken place during diagenetic processes and also a little supergene enrich-ment through lateritization as evidenced by some textural complexities in the phosphorites.

CHAPTER - IX

SUIVIMARV AND CONCLUSION

CHAPTER - IX

SUMMARY AND CONCLUSION

Mussoorle, which occupies an elongated E-W Hill is situated about 31 kms. north of Dehradun town and is located between 1600 m. and 2600 m. above m.s.l. in the Doon valley of the Uttar Pradesh state. The study area in Massoorie lies between north latitudes, 30®25' N t 30®30* and east longitudes, TS^OOMS" s 78®10'57". The phosphorite deposits of Mussoorie are the only well known and old phosphorite deposits of U.P. The deposits are quarried from several opencast mines on the top as well as on the slopes of the Mussoorie hill - a popular summer hill resort of Uttar Pradesh.

The only exploitable phosphorite deposit of Mussoorie, being intimately associated with a variety of shale-chert-carbonate rocks of sedimentary origin with some pyrites, constitutes a part of the lowermost sequence of the Tal Forma-tion of the Lesser Himalayan region of north-western India.

In Mussoorie area, the syncline made up of Blaini, Infra-Krol and Tal rocks, is in direct contact with Nagthat Formation on the northeast. The Tal Formation, which conformably overlies the Krol Formation, constitutes the upper most litho-stratigraphic unit of the thick sedimentary sequence of the Krol Nappe and is divided into two formations, viz.. Lower Tal Formation and Upper Tal Formation. The Lower Tal Formation, that varies in thickness from 75 m. to 880 m., is divisible

212

into four members viz., chert, pelltic, psamltic and calcareous

on the basis of their difference in lithology and the dominance

of one type of sediments over the others. The Upper Tal Forma-

tion, which is less in thickness than the Lower Tal (70 m. to

160 m, in thiclcness) is sub-divided into a lower quartzite

member and an upper limestone member.

The phosphorite horizon being largely restricted to the

upper part of chert member, varies in thickness from a few mm.

to about 10 metres. The main phosphorite horizon occurs between

the chert and black shales but thin phesphatic bands are also

found intercalated with the underlying chert as well as the

overlying black shales. The phosphorite horizon extends for

about a total strike length of over 120 kms. along both the

limbs of the Mussoorie syncline.

The Krol and Tal Formations, which have a thrust contact

with Jaunsars, form a syncline that appears to have been tilted

to the south. The strike of these formations varies from NlO®w

to N55®W. At certain places a few reversals indicate refolding

of the formations resulting in the generation of local synforms

and antiforms. The principal streams in the area generally

follow old fault alignments. Faulting, which resulted in the

development of steep scarps, often display shearing, shattering

and drag folds of the formations.

Presently, the age of the Mussoorie phosphorite belonging

to the Tal Formation which was hitherto believed to have been

formed either in the Permian or in the Jurassic-Cretaceous

period has been redefined to be Late Precambrian to Cambrian.

213

The phosphorites of Mussoorie may be classified into

five distinct varieties on the basis of their megascopic

characters as - platy and laminated, granular, lenticular,

nodular and pelletal. The phosphorite deposits located at

Maldeota and Durmala blocks are of economic values.

petromineralogic«l studies have revealed that carbonate

hydroxyl fluorapatite (collophane) is a dominant phosphate

mineral and some dahlite at places. Calcite, dolomite and minor

and variable amounts of quartz are the dominant gangue consti-

tuents. Quartz occurs as microcrystalline silica, cryptocrysta-

lline, fibrous and detrital quartz. Ferruginous minerals like

pyrite and limonite occur sporadically. The other associated

gangue constituents are feldspars, muscovite, sericite, carbo-

naceous matter and opaques of iron oxides. Phosphate minerals

are found in the form of pellets, nodules, ovules and oolites

mutually replaced by carbonate and silica.

Representative samples of phosphorites from Maldeota

and Durmala were chemically analysed in order to determine

quantitatively their major oxides viz., SiOg/ Al203# 'Pe^O^,

PeO, TiOj, MnO, CaO, MgO, ^ 2

terms of weight per cent. The distribution of various chemical

constitutents show a wide variation from rock to rock, in

various lithological units of the area. The concentration

trends of certain major oxides indicate that limestone, is

more enriched in CaO, COj and SiOg than alumina* iron and

alkalies. The chert is having higher concentration of SiOg

and CaO than the other constituents. Black shales are relatively

214

richer In SlOj* CaO, and COg than other major oxides. Most

common types of phosphorite in the study area contain higher

concentration of ^ ^

The dispersion pattern, correlation coefficient and

mutual relationship of significant major oxides represented

by plotted diagrams, indicate that 8102* CaO and MgO are antl-

pathetlcally related with p2®5* I'slationship suggests a

gradual replacement among these oxides during diagenesis. The

presence of magnesium inhibits the growth of apatite crystallites.

The sympathetic relationship of HjO"*" with CaO/PjOg ratio and

presence of considerable amount of water suggest the possibility

of reversible substitution in between PO. — — ^ (OH).. The CO^ 4 NJ 4 2 exhibits sympathetic relationship with MgO in Durmala phospho-

rites while CaO and T?2^5 antipathetically related wxth CO2.

It is, therefore, suggested that with the entry of CO2 m the

apatite lattice Ca and P were partially replaced.

Since majority of the samples have Ca0/P20g ratio greater than 1.31, the most common substitution is that of PO^^ by

2—

COj . The higher CaO/PjOg, COg/PgOg ratios in the phosphorites

are also primarily Indicative of the presence of carbonate

fluorapatite and the formation of phosphorite by replacement

processes of these constituents. The principal oxides like

Si02, AI2O3, Ti02/ K2O, etc., which are not related to apatite

may have association with the silicate group.

The variation trends in the chemical conqposltion of the

phosphorites and the host rocks may perhaps be due to certain

marked changes in the supply of the material, variation in

215

cm^osltlon of waters and physico-chemical conditions of the

basin of deposition. The low manganese content confined with

low FeO/MnO ratio, enrichment of P2®5 younger sediments,

low content of alkalies as well as their inter-relationship and

distribution pattern in the petrochemical fields indicate that

most probably these phosphatic rocks were deposited in a shallow

water geosynclinal basin favoured by slightly alkaline medium

often approaching a very weakly acidic medium in an euxinic

milieu.

The trace elements such as Cu, Pb, Ni, Co, 2n, Cr, Sr,

Ba, Rb, V, Li and Cd have been determined quantitatively in

the phosphorites and country rocks during the present investi-

gation. The concentration trends of trace elements reveal that

the phosphorites are more enriched in Ba, V, Sr, Cr, Ni, Cu and

Pb than in Li, Cd, Co and Rb. Similarly, the black shales are

relatively richer in Ba, V, Sr, Cr and Ni than in Li, Cd, Co

and Rb.

Sr and Pb are the elements which are susceptible to

adsorption by phosphate minerals and the elements %^ich are

possibly adsorbed by organic matter Include Ni, Zn, Cr, V, Cu

and Cd. Elements adsorbed by clay minerals include Li and Rb.

The pattern of trace element distribution in the phospho-

rites and the geochemical behaviour of individual elements

suggests that most of the trace elements, that found their way

into the ancient sediments, appear to have invaded the lattices

of the phosphates, carbonates, silicates and clay minerals and

combined with them structurally.

216

Variable concentration of trace elements in the phosphates

have been influenced by various physico-chemical processes

involved during weathering and leaching of the pre-existing

rocks, and subsequently many of them were assimilated to the

sediments. The adsorption of sane trace elements was mainly

influenced by the principal absorbants like the phosphate

minerals, some organic matter in addition to clay, iron and

silicate minerals.

Correlation coefficient and plotted diagrams of signi-

ficant trace elements indicate that the presence of these

elements may be due to their inter-elemental affinities.

However, adsorption on the surface of the apatite, substitution

in the apatite lattice and biogenic activity are supposed to be

chiefly responsible for the distribution, abundance and fixation

of significant trace elements. Thus higher concentration of

certain trace elements in the phosphate rich ores is mainly due

to certain favourable physico-chemical conditions such as low

Eh-pH, moderate salinity, slightly anaerobic to highly anaerobic

shallow water reducing environmental conditions, etc, at the

time of their deposition.

A statistical method (Factor-Vector analysis) was followed

to explain the complex relations among several geochemldal varia-

bles in terms of simpler and more meaningful relations with the

help of varimax-R-mode factor analysis. The major and trace

elements variability of Maldeota and Durmala phosphorites were

computed in terms of various admixture of factor and vector

scores. Based on the nature of loadings the factors have been

specified as follows

217

1. Silica precipitation

2. phosphate precipitation

3. Carbonate precipitation

4. Organic activity

5. Detrital clay supply

6. Residual poire water

7. Oxidising to reducing condition

The results of the factor-vector analyses indicate that

phosphatic material* supplied in a soluble state, was originally

rich in calcium and strontium and the precipitation of phospho-

rite was accompanied by the co-precipitation of calcium carbonate

and calcium phosphate* The formation of these sediments suggests

variation in pH conditions. The variation of Eh conditions

suggest reducing to slightly oxidizing shallow marine environment,

The concentration of trace elements viz., Cu, Co, Cr, Pb, Zn

and V in phosphorite may be attributed to their association

with organic matter.

The ingredients of phosphates are probably derived from

three different sources, viz., a) volcanic, b) phytoplankton and

other micro-organisms and c) some pre-existing rivers. The phos-

phate charged upwelllng ocean currents coming from the deep

oceanic reservoirs of the pre-existing sea or an arm of it

were the major contributors of phosphorites in the basin. It

is suggested that the deposition of phosphate might have occurred

in an euxinic shallow marine environment aided by slightly

alkaline to very weakly acidic medium with restricted circulation

in warm and dry palaeocllmatic conditions. Additionally, the

deposition is controlled by some geological andbiogenic factors

2 1 8

such as excess charge of phosphate in certain zones of phos-

phogenic basin, lithological facies variations, sab-basinal

topographic restriction's, some structural disturbances and

concentration of dissolved phosphorus by certain micro-organisms.

Negative Eh, pH with around 7.8, influence of the pressure and

temperature, relative proportions of CaO/MgO and CaO/PjOg, the

chain of replacement among Ca0-Mg0-P20g as well as easy ionic

substitution of certain elements are the other factors favoura-

ble for the deposition of the ores. Penecontemporaneous and post-

deposition also played some role in controlling the concentration

of the deposits.

A genetic model of the phosphorite deposits of Mussoorie

has also been proposed. It suggests that the role of geochemical

environment in the deposition of phosphorites as well as the

accompanying activity of mxcro-organisms mutually Interacted

under a set of shallow intertidal and subtidal environmental

conditions, leads one to believe that precipitation of phosphate

was essentially dependent upon pH and Eh conditions, partial

pressure of COg, temperature, replacement processes and ionic

substitution. The presence of appreciable quantity of organic

matter, higher concentration of vanadium and chromium, associa-

tion of carbonates, black shales and pyrite, suggest deposition

of phosphorite in a more or less reducing environment. The various

forms in which phosphorite occurs appear to be related to some

environmental vicissitudes at the time of deposition followed by

some later structural disturbances related to the uplift of

Himalaya. Later enrichment of phosphates may have taken place

during the period of diagenetic processes as also a little

supergene enrichment through lateritization.

RKFER-KMOES

REFERENCES

Al-Bassam, K.S. et al., 1983 - Companian-Mastrichtian phos-phorites of Iraq. Petrology, Geochemistry and Genesis. Min. Deposita, 18, pp. 215-233.

Altschuler, Z.S., Clarke, R,S. and Young, E.J., 1958 - Geoche-mistry of uranium in apatite phosphorus. U.S.G.S. Bull. Prof. Paper 314 D, pp. 45-90.

Altschuler, Z.S./ 1980 - The geochemistry of trace elements in marine phosphorites - part-I characteristic abundance and enrichment. In : Y.K. Bentor (Edition). S.E.P.M. Spl. Pub. no. 29, pp. 19-30.

Ames, L.L., 1959 - The genesis of carbonate apatites. Eco. Geol. vol. 54, no. 5, pp. 829-841.

Atlas,E.L., 1975 - Phosphate equilibria in sea water and inter-stitial waters. Ph.D. thesis. Orego State Univ., Corvallis, Oreg., pp. 154.

Azmi, R.J., Joshi, M.N. and Juyal« K.P., 1980 - Discovery of the Cambro-Ordovician conodonts from the Mussoorie Tal phos-phorites and its significance in correlation of the Lesser Himalaya, 11th Him. Geol. Sem. (Abstract), pp. 5-6.

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2 4 9

TABLE-OC t Na20/K^ , » "2° •

ratios for Maldeota Phosphorites.

S.No . N a ^ / K ^ OO2 / H ^ HjO /C02 PeO/MiK)

3. 5.6 6.95 0.14 ND

4. 1.29 5.29 0.19 34.00

5. 6.00 9.38 0.11 45.00

6. 25.5C 6.57 0.15 36.00

7. 13.67 6.43 0.16 ND

8. 3.83 5.00 0.20 117.50

9. 2.15 6.62 0.15 48.37

11. 8.33 8.04 0.12 ND

18. 6.20 7.79 0.13 37.25 19. 3.50 5.01 0.20 56.51

20. 1.25 13.00 0.08 28.57 21. 3.40 5.23 0.19 66.25 22. 12.50 4.12 0.24 ND

23. 7.00 6.47 0.15 41

24. 3.75 6.76 0.15 17.50

25. 2.38 4.59 0.22 2.06

26. 12.00 10.07 0.10 17.63 27. 12.33 5.82 0.17 10.08 28. 18.50 8.58 0.12 59.50

29. 24.00 5.95 0.17 15 .8 30. 28.00 53.00 0.02 43.00

31. 29.00 10,20 O.lO 22.75 32. 29.00 5.07 fi.20 22.83 33. 8.00 4.86 0.21 ND

2 5 0

S.No. Na20/K20 CO 2 /HgO H^/002 FeO/MnO

3 4* 25.00 6.46 0.16 81.00

35, 26.00 8.74 0.12 40.33

36, 20.00 11.09 0.09 63.00

37. 20.00 9.10 0.11 58.00

38. 10.44 12.52 0.08 45.33

43. 19.00 11.79 0.08 295.00

45. 90.00 6.42 0.16 24.71

46. 28.00 8.22 0.12 121.80

47. 26.00 6.52 0.15 63.33

251

TABLB-XI t CaO/PjOg, co^p^o^, CaoAgo, Ca0/Si02 rat;

Maldeota Phosphorites.

S.No« CaO/P^5 °°2 CaO/MgO CaO/SiOj

3* 1.41 0.40 37.96 6.03

4. 1.35 0.30 28.28 4.97

5. 1.30 0.33 13.44 6.76

6. 1.88 0.43 14.45 5.28

7. 2.8 4 0.8 3 14.25 3.69

8. 1.64 0.35 52.82 4.34

9. 2.01 0.61 9.29 2.77

11. 1.38 0.33 16.92 4.41

18. 1.57 0.48 8.55 5.93

19. 2.82 0.93 11.75 4.01

20. 2.41 0.52 9.95 5.33

21. 0.71 0.49 20.15 1.73

22. 2.62 0.84 33.48 3.69

23. 2.72 0.85 9.63 1.94

24. 1.79 0.70 11.51 2.70

25. 2.85 0.83 10.93 3.57

26. 2.54 0.89 14.81 3.76

27. 3.06 0.82 18.51 2.99

28. 1.51 0.38 9.80 3.28

29. 3.21 0.41 11.38 2.94

30. 1.65 0.53 31.52 3.56

31. 2.17 0.48 21.33 4.15 32. 1.39 0.25 19.11 4.71

33. 2.45 0.58 20.42 3.97

252

S.No. CaO/PjOg CO2 /P2O5 CaO/Hgo CaO/SlOj

34. 2.27 0.81 8.69 2,55

35» 2.14 0.51 13.43 4.02

36. 2.98 0.85 20.01 2.66

37. 1.33 0.30 10.10 5.80

38, 1.91 0.70 5.15 2.26

43* 2.22 0.71 20.64 6.25 45. 2.97 0.93 13.86 3.98

46. 5.19 1.21 691.43 2.72

47. 1.31 0.26 9.45 4.78

(N s w

8 in

a<

o a

Ms

8

s 8

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to

ro

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• • • • • • • in in >* (N (N rg

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8

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0* r-•H fM PJ 10 • • • «

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• • • i • o o •H o o

n <M r - <N 0» r-l CO r )

• • • • • • • f H f«i r-l

Oi o CM in o • • •

r o T-t TC O CM •-I

§ • • •

o O O

a o «N o • • •

o 0\ CO

in o 00 CM

o • • Q g CM Tf

1-1 m <-4 flO f t

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f l •

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2 «

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8 § rO O O rsl • • • C O g O

G in ** «« • • •

g m in

ro in in

m m

o m • m

a 9

o f t m

« o

Q f l vo CM f l

m

o o

LI p) CO in n r; r- (N t-• • « • • o CM H CM fl

cn m

u* 0\ 00 M r - CO « • •

CM

tM 0\ r- »£> • • in

f l \o

r o tn t o

r -

« • * • • « • CN f - \o o n CM f l f t

CO in

253

254

TABLE-JCIIItRegalculated to 100 wt% of the bulk components of CaO, MgC and -" aldecifca Phosphorites.

Sample No. CaO MgO

3. 57.56 1.52 40.92

4. 56.32 1.99 41.69

5. 54.17 4.03 41.79

6. 62.41 4.32 33.27

7. 70.48 4.91 24.61

8. 61.33 1.16 37.51

9 . 62.29 6.70 31.01

11. 56.12 3.32 40.56

18. 57.01 6.67 36.3 3

19. 69.44 5.91 24.64

20. 66.02 6.64 27.3 4

21. 58.60 2.91 38.49

22. 70.85 2.12 27.03

23. 67.98 7.06 24.96

24. 60.88 5.29 3 3.83

25. 69.34 6.34 74.32

26. 68.47 4.62 26.91

27. 72.44 3.92 23.64

28. 56.70 5.78 37.52

29. 71.44 6.28 2 2.28

30. 61.09 1.94 36.97

31. 66.29 3.11 30.60

32. 56.46 2.95 40.59

C o n t i n u e d ,

255

Sample No» CaO MgO P2O3

33. 68.60 3.40 28.0 4

34. 64.32 7.40 28.28

35. 6 4.83 4.8 3 30.34

36. 72.20 3.61 24.19

37. 54.04 5.35 40.61 38. 58.23 11.30 30.47

43. 66.74 3.23 30.03

45. 7 0,98 5.12 23.90

46. S3.75 0.12 16.13

47. 53.42 5.65 40.93

256 TA3LS-XIV : Recalculated to 100 wt% of the bulk ccmponents

of CaO, Mgo and C ^ in Haldeota Phosphorites.

Sample Wo« CaO MgC CO2

3. 76.20 2.01 21.79

4. 79.54 2.81 17.65

5. 75.30 5.60 19.10

6. 77.09 5.33 17.58

7. 73.34 5.15 21.46

8. 81.26 1.54 17.21

9, 70.82 7.62 21.56

11. 76.92 4.55 18.53

18. 70.31 8.22 21.47

19. 70.62 6.01 23.37

20. 75.91 7.63 16.46

21. 72.79 3.61 23.60

22. 7 4.16 2.22 23.63

23. 70.61 7.33 22.05

24. 67.76 5.88 26.36

25. 72.32 6.62 21.06

26. 70.59 4.76 24.65

27. 75 .64 4.09 20.27

28. 73.70 7.51 18 .78

29. 8 2.18 7.22 10.60

30. 7 4.07 2.35 23.58

31. 78.98 3.70 17.32

32. 81.35 4.26 14.39

Continued,

2 5 7

Sample No. CaO MgO

33. 77.71 3.81 18 .48

34. 67.89 7.81 24.30

35. 76.18 5.67 18.15

36. 74.92 3.74 21.34

37. 75.68 7.49 16 .8 3

38. 64.01 12.42 23.57

43. 73.14 3.54 23.32

45. 73.30 5.29 21.41

46. 81.03 0.12 18.85

47. 76.58 8.10 15.32

258

TABLE^Xy : Recalculated to 100 wt% of the bulk components of CaO* I^gO and -'3102 in Maldeota Phosphorites,

Sample No. CaO MgO 310 2

3. 83.88 2.21 13.91

4. 80.88 2.86 16.26

5. 81.81 6.09 12.10

6, 7 9.45 5.50 15.05

7. 74.57 5.23 20.

8. 80.03 1.52 18.45

9. 68.12 7.33 24.55

11. 77.78 •4.60 17.6 2

18 • 77.78 9.09 13.13

19. 74.94 6.38 18.67

20. 77.63 7.81 14.57

21. 75.8 3 3.76 20.41

22. 76.88 2.30 20.8 3

23. 61.73 6.41 31.85

24. 68.65 5.96 25 .39

25. 7 2.90 6.67 20.43

26. 74.99 5.06 19.95

27. 7 2.06 3.89 24.05

28. 71.08 7.25 21.67

29. 7 0.00 6.15 23.84 30. 76.17 2.42 21.42

31. 77.66 3.64 18.70

32. 93.85 4.91 1.24

Continued,

2 5 9

Sample No* CaO Mgo 3102

33. 76.87 3.76 19.36

34. 66.37 7.64 25.99

35. 75.56 5.63 18.81

36. 70.13 3.50 26.36

37. 78.66 7.79 13.55

38. 61.11 11.86 27.03

43. 82.75 4.01 13.24

45. 75.56 5.45 18.99

46. 73.03 0.11 26.86

47. 76.04 8.04 15.92

2 6 0

TABLE-XVI t Recalcu}ated to 100 wt% of the bulk components Na20/CaO and Maldeota Phosphorites.

Sample No. CaO ^2^5

3. 0.38 58.22 41.40

4. 0.42 57.22 42.36

5. 0.33 56.27 43.40

6. 0.72 64.76 34.52

7. 0.65 73.48 25.87

8. 0.35 61.83 37.8 2

9. 0.71 66.29 3 3.00

11. 0.38 57.83 41.79

18. 0.45 60.80 38.75

19. 0.36 73.54 26.10

20. 0.37 70.45 29.18

21. 0.48 60.07 39.45

22. 0.42 72.08 27.50

23. 0.39 72,85 26.75

24. 0.53 63.93 35.54

25. 0.30 73.80 25.88

26. 0.39 71.49 28.10

27. 0.60 74.93 24.45

28. 0.34 59.84 39.60

29. 0.37 75.94 23.67

30. 0.41 62.03 37.54

31. 0.42 68.12 31.43

32. 0.41 57.93 41.64

Continued,

2 6 1

Sample No. CaO P2O5

33. 0.39 70.70 28.90

3 4. C.46 69.13 30.40

35. 0.42 67.83 31.74

36. 0.35 74.64 25.01

37. 0.28 56.94 42.78

38. 1.69 64.53 33.77

43. 0.29 68.76 30.94

45. 1.47 73.71 24.82

46. 0.96 8 3.05 15.99

47. 0.36 56.42 43.22

262

TA3LE--XVII s Recalculated to ICO wt% of the bulk components of ^2° Maldeota Fhosphorites

Sample No* 3x0 2 AI2O3 K^O

3. 84.94 14.45 0.60

4. 84.71 12.91 2.38

• t5.47 13.96 0.56

6. 83.78 16.42 0.19

7. 92.38 7.39 0,22

8. 8 9.98 9.43 0.58

9. 93.b4 5.16 1.29

11. 81.08 18.6 4 0.28

18. 85.03 14.37 0.59

19. 91.45 8.04 0.51

20. 82.57 15.59 1.8 3

21. 93.72 5.46 0.81

22. 93.82 6.01 0.16

23. 94.29 5.56 0.14

24. 91.96 7.49 0.54

25. 92.55 6.G6 0.58

26. 89.35 10.49 0.16

27. 91.95 7.86 0.18

28. 92.56 7.28 0.15

29. 91.10 8.8 3 0.05

30. 89.93 1G.14 0.07

31. 84.14 15.77 0.07

32. 86.68 13.21 O.lO

Continued,

263

Sample No. 340 2 AI2O3 K2O

33. 91.52 8.22 0.25

34. 93.60 6.32 0.06

35. 90.43 9.47 0.08

36. 94.37 5.56 0.05

37. 84.33 15.5 0.11

38. 88.31 11.18 0.50

43. 77.09 22.8 0.11

45. 99.07 8.85 0.80

46. 93.58 6.31 0.11

47. 86.68 13.20 0.10

2 6 4

TABLE--X:ngIi:Recalculated to ICC wt% of the bulk components of Na20, K^O and CaO in Maldeota Phosphorites.

Sample No- NajO CaO

3. 0 .65 0.12 99.23

4. 0.72 0.56 98.72

5. 0.58 0.09 99.33

6. 1.11 0.04 98.85

7» 0.88 0.06 99.06

8. 0 .57 0.15 99. ?8

9. 1.05 0.49 98.46

11. 0.65 0.08 99.28

18. 0.73 0.12 99.15

19. 0.48 0.14 99.38

20. 0.52 0.41 99.07 21. 0.79 0.23 98.98

22. 0.58 0.04 99.38

23. 0.53 0.08 99.39

24. 0.81 0.22 98.97

25. 0.41 0.17 99.41

26. 0.55 0.05 99.40

27. 0.80 0.07 99.13

28. 0.91 C.05 99.C7

29. 0.49 0.02 9 9.49

30. 0.67 0.03 99.31

31. 0.62 C,02 99.36 32. 0.72 0.03 99.26

Continued,

265

Sample No* Na20 CaO

33. 0.56 0.07 99.37

34. 0.67 0.03 99.30

35. 0.61 0.02 99.36

36. 0.46 0.02 99.52

37. 0.49 0.02 99.49

38. 2.56 0.25 97.20

43. 0.43 0.02 99.55

45. 1.96 0.02 98.02

46. 1.14 0.04 98.8 2

47. 0.63 0.02 99.34

266

TABLE-XJ3C Recalculated to lOC wt% of the bulk components of ^'2 ^^ Maldeota Phosphorites.

Sample No* P2°5

3. 68.49 3.96 27.55

4. 73.73 4.18 22.09

5. 73.32 2.57 24.11

6. 66.99 4.36 28.65

7. 51.02 6.59 42.39

8. 70.65 4.89 2 4.46

9. 7 4.05 3.41 22.54

11. 78.69 2.36 18.95

18. 74.37 2.92 22.72

19, 71.59 4.72 23.69

20. 81.06 1.35 17.59

21. 72.14 4.47 23.39

22. 49,07 9.95 40.98

23. 50.45 6.63 42.92

24. 55.45 5,74 38 .81

25. 49.72 9.00 41.28

26. 50.59 4.46 44.94

27. 50.96 7,20 41.8 4

28. 69.93 3.14 26.93

29, 67.7 4 4.69 27 .88

30. 65.09 0.65 3 4.26

31, 65.72 3.06 31.22

32. 77.24 3.75 19.01

Continued,

2 6 7

Sample No. ^2^5 H^O GO 2

33. 58.77 7.04 34.19

34. 51.55 6.49 41.96

35. 63.80 3.72 32.48

36. 51.89 3.98 44.12

37. 75.27 2.45 22.28

38. 56.8 3 3.19 39.98

43. 56.54 3.39 40.06

45. 49.93 6.75 43.31

46. 42.46 6.24 51.30

47. 76.85 3.08 20.06

2 6 8

TABLB-XX t Recalculated to lOC wt% of the bulk componei of CaO, MgO and Pe202i-Pe0 in Maldeota ^-hcsp]

Sample No* CaO MgO Fe20 3 FeO

3. 91.99 2.42 5.58

4. 89.72 3.17 7.11

5. 06.46 6.43 7.10

6. 87.02 6.02 6.96

7. 87.69 6.16 6.16

8. 75.66 1.43 22.90

9. 79.51 8.56 11.93

11. 77.02 4.55 18.43

18. 83.08 9.72 C7.21

19. 78.89 6.72 14.39

20. 83.96 8.44 07.60

21. 83.75 4.16 12.10

22. 8 3.07 2.48 14.45

23. 81.28 8.44 10.28

24. 80.65 7.00 12.35

25. 86.88 7.93 05.17

26. 85.95 5.80 08.25

27. 85.18 4.85 09.97

28. 83.39 8.50 08.11

29. 83.24 7.32 09.44

30. 89 .72 2.85 07.43

31. 86.76 4.07 09.18

Continued,

269

Sample No. CaO MgO Fe^O^

PeO

32. 76.30 3.99 19.70

33. 76.75 3.76 19.49

34. 72.82 8.58 18 .80

35. 76.23 5.68 18.09

36. 77.49 3.87 18.6 4

37. 82.33 8.15 9.52

38. 76.16 14.78 9.06

43. 81.16 3.93 14.91

45. 78.90 5.69 15.40

46. 84.53 0.12 15.35

47. 82.81 8.76 8.43

2 7 0

TABLE-XXI t Recalculated to 100 wt% of the bulk components o£ CaO, PeO, in Maldeota

Phosphorites.

Sample No- CaO 3 PeO KjO

3. 93.60 5.68 0.73

4. 91.66 7.25 1.19

5. 91.83 7.55 0.62

6, 91.61 7.32 1.07

7. 92.62 6.50 0.88

8. 76.34 23.11 0.55

9. 85.78 12.88 1.34

11. 80,22 19.20 0.58

18. 91.30 7.92 0.78

19. 84.12 15.35 0.53

20. 90.92 8.23 0.85

21. 86.60 12.51 0.8 9

22. 84.74 14.73 0.53

2-. 86.36 13.11 0.53

24. 85.94 13.16 0.89

25. 93.86 5.59 0.55

26. 90.75 8.71 0.55

27. 09.29 9.92 0.78

28, 90.34 8.79 0.87

29. 89.39 10.15 0.46

30. 91.75 7.61 0.64

C o n t i n - u e d .

2 71

Sample No- CaO Na20 4 + PeO K^O

31* 89.91 9.51 0.58

32. 79.01 20.40 0.59

33. 7 9.35 20.15 0.50

34. 79.04 20.41 0.56

35. 80.40 19.08 0.52

36. 80.30 19.31 0.40

37. 89.23 10.31 0.46

38. 87.12 10.36 2.51

43. 84.16 15.44 0.40

45. 85.33 12.94 1.7 2

46. 83.78 15.22 1.00

47. 90.21 9.19 0.60

272

TABLE-XXII : Recalculatefi to ICO wt% of the bullc cornp< of Mg<e, + PeO^and AI2O 2 in Kaldeota Pho sp ho rites.

Sample Nq. MgO

PeO

AI2O3

3. 22.86 52.65 24.49

4. 2 4.35 54.54 21.10

5. 41.18 45.45 13.37

G. 37.10 42.87 20.02

7. 43.32 43.32 13.36

8. 5.47 87.54 6.99

9. 38.76 54.07 7.16

11. 16.86 68.28 14.86

18. 50.36 37.46 12.28

19. 29.40 63.03 7.57 20. 44.38 39.96 15 .65

21. 23.66 68 .86 7.48

22. 13.51 78.6 4 7.85

23. 36.29 53.06 10.65

2 4. 32.15 56.69 11.16

25. 53.25 34.65 12.10

26. 34.68 49.29 16.03

27. 27.8 9 57.37 14.74

28. 45.68 43.57 10.75

29. 37.50 48.41 14.08

30. 21.75 56.8 4 21.42

C o n t i n u e d ,

273

Sample No- KgO

FeO Al^O^

31. 23.69 53.48 22.83

32. 15.26 75.29 9.45

33. 15 .C4 78.01 6.^5

34. 28.78 64.59 6.62

35. 22.03 70.24 7.72

36. 15.98 76.92 7.09

37. 40.18 46.92 12.89

38. 5 2.58 32.25 15.17

43. 17.34 65.72 16.93

45. 29,06 61.09 9.84

46. 0.72 90.25 12.32

47. 44.10 42.56 13.35

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TABL&JC3CV t Recalculated to 100 wt % of the bulk ccmponents of (A) P^g, H ^ and 002* CaO, MgO and + PeO in Durmala Phosphorites.

P2O5 H2O4 OO2 CaO MgO Pe202 + P«0

49 70.56 2.63 26.81 87.59 5.16 7.25

52 76 •88 2.27 20.85 89.88 4.92 5.19

53 69.12 3.13 27.60 80.94 6.47 12.59

54 71.70 2.75 25 .55 89.65 0.64 9.71

55 36 .80 7.61 55.59 76.48 10.49 13.04

56 67.12 2.57 30.31 71.73 13.57 14.70

58 52.49 5.80 41.71 77.16 16.51 6.33

277

TABLE-OOCyi : Recalculated to 100 wt% of the bulk components of (A) CaO, + Na20,K20 (B) Mgo,Pe20 3 + 3?eD and AljO^ in Durmala Pho^horites

S.No* (A) (B) CaO

+ PflO K2O

MgO + P0O

AI2O3

49 91,16 7.54 1.30 32.80 46.03 21.16

52 93.82 5.41 0.77 36.59 38.58 24.83

53 5 3.95 13.36 0.69 33.03 64.21 2.76

54 89.28 9.88 0.83 5.78 87.79 6.42

55 85.11 14.50 0.39 41.24 51.26 7.50

56 83.15 16.03 0.82 42.51 46.07 11.42

58 91.80 7.53 0.67 64.17 24.55 11.28

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TABLE-JOCX : Comparision of the abundance of trace elements in Phosphorites

2 8 4

Massoorie Phosphorites Phosphorites of Moroccan Phosphorites Krau^cpf Phosphoria formc»^ Phosphorites

(1955) tion (Gulbrandsen-(frctn Prevot 1966)Threshold and Lxacas 1979) values.

Cu 40 4-40 100 39

Pb 72 — — —

Ni 100 4-200 100 43

Co 5 — — —

Zn 50 10*200 3 00 213

Cr 185 30*400 1000 220

Sr 877 50-1000 1000 97 4

Ba 567 30-300 100 104

Rb 5 — — —

V 443 30*200 300 98

Li 3 1— 11 — —

Cd 11 mmmm

285

TA3LE~XXX.I t CVAijclO"^ , Cu/MgjeiO*"^, C^PxlO"^ and __________ ^^ Ni/AlxlO ratios for Maldeata phosphorites

S.No. Cu/AlxlO"^ Cij/MgxlO"^ Cu/pxlO"^ Ni/AlxlO~^

3. 1.01 0.95 0.48 1.48

4. 0.02 0.22 0.15 0.90

5. 1.23 0.34 0.46 1.58

6. 0.34 0.33 0.29 0.63

7. 0.23 0.06 0.17 0.87

8. 0.64 0.73 0.31 1.45

9. 1.50 0.24 0.72 1.38

11. 0.32 0.25 0.28 0.81

18. 1.09 0.?3 0.59 1.03 19. 0.46 O.lO 0.34 2.20

20. 0.39 0.12 0.40 1.64 21. 0.94 0.25 0.27 4.85 22. 1.25 0.63 0.68 1.94

23. 0.48 0.12 0.49 1.25

24. 0.77 0.24 0.51 0.93 25 0.54 0.11 0.39 1.74 26. 0.73 0.29 0,70 0.54 27. 0.24 0.11 0.25 0.80

28. 1.94 0.40 0.85 1.54 29. 0.14 0.05 0.18 0.98

30. 0.40 0.34 0.25 1.35

31. 0.51 0.43 0.61 1.51

32. 0.72 0.39 0.39 2.47

Continued,

286

S.No. Cv/AlxlO"^ Cu/MgxlO~^ CVPXIO'^ Nl/Alxl0~^

33 0.12 0.45 0.75 1.92

34 0.8 4 0.17 0.60 1.42

35 0.46 0,23 0.50 0.81

36 0.48 0.18 0.38 0.22

37 0.78 0.22 0.88 1.39

38 0.12 0.03 0.16 0.60

43 0.78 0.67 0.99 0.99

45 0.1 0.29 0.88 2.05

46 0.46 7.25 0.71 5.42

41 0.26 0.07 0.13 3.66

2 8 7

TABLE-XXXII : Ni/PexlO"^, Nl/^gxlO*"^, Zn/Ph and Zn/CaxlO"^

ratios for Maldeota phosphorites

S.No. Ni/PexlO"^ Nl/MgxlO"^ Za/Ph Zn/CaxlO"'^

3 0.62 1.39 0.64 1.58

4 0.37 0.68 0.72 1.42

5 0.40 0.44 0.55 1.52

6 0.31 0.30 0.70 1.59

7 0.23 0.23 0.50 0.94

8 0.11 1.64 0.80 1.73

9 0.18 0.22 1.61 3.65

11 0.14 0.63 0.86 1.89

18 0.43 0.22 0.79 1.83

19 0.35 0.50 0.68 1.65

20 0.89 0.50 0.74 1.43

21 0.69 1.33 0.93 2.59

22 0.26 0.98 0.53 1.97

23 0.26 0.32 0.64 1.60

24 0.18 0.28 0.78 1.80

25 0.63 0.34 1.32 2.27

26 0.20 0.22 1.30 2.65

27 0.21 0.37 0.53 0.95

28 0.41 0.31 0.35 0.79

29 0.25 0.32 0.44 0.95

30 0.54 1.05 0.97 1.21

31 0.42 0.70 1.33 2.55

32. 0.26 1.33 0.38 1.15

988

S.No. Ni/Pe xlO"^ Ni/Mg xlO"^ Zn/Pb Zn/Ca xlO"*^

33 0.15 0.77 0.34 1.17

34 0.12 0.28 1.23 2.46

35 0.07 0.24 0.4C 0.96

36 0.15 0.65 0.42 0.85

37 0.38 0.39 0.63 1.23

38 0.31 0.15 0.58 1.02

42 0,39 0.85 0.81 2.14

45 0.33 0.60 0.57 1.58

46 1.81 85.5 0.17 0.75

41 1.58 0.96 1.16 3.40

289

TA3LE-.XXXIII t Zn/Pe xlO, Cr/Al xlO"^, Cr/Pe xlO"^ and 3r/Ca xlO"^ ratios for Maldeota Phosphorites.

S.No. Zn/Pe xlO Cr/Al xlO'^ Cr/Pe xlO~2 Sr/CaxlO"^ K/Rb

3 3.2 2.87 1.21 3.17 57. 14

4 2.64 1.95 0.81 2.70 271. 42

5 2.18 10.94 2.76 2.70 75.00

6 2.90 2.17 1.08 2.76 50,00

7 1.59 1.17 0.31 2.18 N.D.

8 0.7 3 2.76 0.21 3.21 100.00

9 3.27 5.42 0.71 3.15 20.51

11 8.28 0.94 0.15 3.26 66.66 '

18 3.64 2.18 0.88 3.34 57.14

19 1.61 2.28 0.36 3.28 133. 33 20 3.00 1.55 0.86 2.45 33.33

21 3.21 4.14 0.58 2.84 400 „ 00

22 2.10 2.76 0.37 2.46 25.00 23 1.48 2.04 0.42 3.22 40.00

24 1.60 2.18 0.43 3.70 300.00 25. 5.36 1.42 0.51 2.70 200.00 26 4.29 1.64 0.61 2.86 11.11 27 1.18 1.30 0.33 3.0 3 50.00

28 1.61 5.82 1.55 3.63 50.00

29 0.94 1.13 0.28 2.58 N.-D.

30 2.05 1.13 0.28 2.58 17.55

31. 3.93 1.47 0.66 2.93 17.55

290

S.No. Zn/PexlO Ci/AlxlO"^ Cr/PexlO~^ Si/CaxlO'^ K/Rb

32 0.53 1.57 0.17 3.25 8.77

33 0.56 1.88 0.14 2.81 100.00

34 1.06 2.92 0.24 2.74 17.55

35 0.47 4.18 0.39 3.14 17.55 36 0.48 2.16 0.12 2.93 8.77 37 1.44 1.83 0.43 2.39 17.55 38 1.29 5.04 0.61 3.11 116,66 43 1.87 1.17 1.46 3.06 17,55

45 1.43 8.84 0.36 2.28 5.85

46 1.38 9.95 2.72 2.57 20.00

4n 6.30 1.02 3.99 2.24 2o 92

291

TABLE -XXXIV * Ba/l^xlO~\ V/AlxlO"^ V/PexlO"^, V/MgxlO"^ and V/PxlO"^ ratios for Maldeota phosphorites

S.No. Bo/K V/AlxlO"^ V/PexlO"^ V/MgxlO"^ V/PxlO~^

3 1.17 3.96 1.67 3.73 1.88

4 0.281 2.94 1.22 2.22 1.45

5 2.383 5.76 1.45 1.62 2.15

6 6.48 36.51 1.81 1.71 3.06

7 2.815 36.51 2.56 2.56 7.05 8 1.48 107.8 0.80 12.22 6.28

9 0.445 83.33 1.07 1.34 4.00

11 3.98 42.85 0.71 3.3 3.71

18 1.59 34.30 3.43 1.75 4.42

19 7.185 67.2 1.06 1.51 5.0

20 3.2 46.74 2.55 1.43 4.8 0

21 0.712 135.7 1.93 3.74 4.80

22 6.6 143.5 1.93 7.27 7.78

23 2.35 78.57 1.63 2.01 7.84

24 0 .663 87.24 1.72 2.64 5.71

25 1.00 90.0 3.26 1.78 6.43 26 7.17 71.83 2.67 2.89 7.14 27 2.55 73.52 1.9 3.37 7.71 28 7.01 56.86 1.51 1.16 2.48

29 7.41"^ 36.9 0.94 1.21 4.70

30 8.7 4"^ 58.08 2.61 5.0 3.59 31 5.066"^ 50.45 2.59 4.27 5.97

Continued,

292

S.No. Ba/K V/AlxlO"-^ V/PexlO" vAgxiO-2 V/PxlO"^

32 4.58~^ 82.35 0.89 4.44 4.44

33 2.1 107.8 4 0.85 4.36 7.18

34 6.51"^ 38.03 0.81 1.95 7.0 4

35 7.23"^ 88.79 0.83 2.72 5.98

36 7.23"^ 70 0.56 2.36 4.87

37 7.29""^ 95.5 2.42 2.47 lO.O

38 0.821 45.76 2.8 4 1.37 7.05

43 7.45"^ 36.21 l.lO 3.11 4.61

45 4.4-3 70.34 1.14 2.08 6.17

46 6.4 88.57 2.96 139.5 13.74

47 6 . 45"^ 70 3.03 1.83 3.49

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Table-XXXVlI : Mean/ Standard deviation and Coefficients of variation of the values of major and trace elements from Maldeota phosphorite samples.

Elements Mean (X)

Standard Deviation

(S)

Coefficients of Variation

= S/X

Si02 11.46 3.46 0.30 AI2O3 1.25 0.38 0.30

4.48 2.51 0.56 Ti02 0.61 0.24 0.39 MnO 0.04 0.06 1.28 CaO 42.53 3.24 0.07 MgO 3.01 1.42 0.47

21.39 6.21 0.29 0.54 5.34 9.89

KjO 0.13 0.51 3.72 H2O- 1.63 0.66 0.40 CO2 11.51 2.24 0.19 Cu 41.00 21.54 0.52 Pb 72.18 20.84 0.28 Ni 100.21 62.06 0.61 Co 5.78 4.30 0.74 Zn 50.66 21.41 0.42 Cr 185.09 150.41 0.81 Sr 877.21 97.08 0.11 Ba 561.63 120.06 0.21 Rb 5.48 13.21 2.40 V 445.45 107.78 0.24 Li 3.09 2.68 0.86 Cd 11.06 3.78 0.34

296

Table-XXXVIII t Mean* Standard deviation and Coefficients of variation of : the values of major and trace elements from Durmala phosphorte samples.

Standard Coefficients Mean Deviation of Variation

Elements (X) (S) = S/X

SiOj 11.20 4.54 0.40 A1203 1.15 0.63 0.54 Pe^Oj 3.41 1.83 0,53 TIO2 0.82 0.18 0,21 MnO 0.04 0.04 1.16 CaO 40.72 4.09 0.10 MgO 4.27 3.12 0.73

24.03 10.19 0.42 0,33 0.11 0.33

K^O 0.02 0.01 0,68 1.24 0.38 0,31

CO2 11.07 2.48 0,22 Cu 47.85 21.09 0,44 Pb 75.57 18.61 0,24 Ni 97.57 41.26 0.42 Co 6.71 1.38 0.20 Zn 38.85 9.97 0.25 Cr 140.57 66,18 0,47 Sr 589.57 80.62 0.13 Ba 754.85 147.54 0.19 Rb 5.85 4.45 0.75 V 510.00 47.60 0.09 Li 3.00 1.41 0.47 Cd 8.42 0,53 0.06

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Table-XLII j Vector Model of Durmala Phosphorite Analyses

Variables Vector I Vector II Vector III Vector IV

SIO2 0.53734 0.24250 — _

AI2O3 0.17074 0.54610 -0.47444 -

0.17297 -0.63900 - -

TIO2 0.10114 0.57570 - -

MnO 0.25504 -0.46113 -0.37123 -

CaO 0.15132 0.13484 0.78106 0.52222 MgO 0.50856 0.24547 mm -

-0.55283 mm -0.15164 -0.42491

NagO 0.50077 -0.76662 - -

KgO 0.38446 -O.295SO - -

-0.50481 - - -

-0.42177 -0.32430 - -

Cu 0.31060 0.35527 - -

Pb 0.31685 0.39783 -0.34230 -

Ni 0.11087 0.55430 0.68271 -0.43636 Co -0.06926 0.30910 0.82413 -

Zn - 0.41269 - -

Cr -0.39261 0.46401 0.21585 -0.24606 Sr -0.45451 -0.31927 -0.10077 0.54273

Ba 0.52155 - -0.15461 -0.23567

Rb -0.52448 - -0.21681 -

V -0.50154 0.27441 - 0.14433

Li 0.44603 0.25973 -0.14294 -

Cd 0.14067 0.65561 -0.14016

H

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304

Table-XLIV : Rotated Factor Matrix (R-mode) Data for Durmala Phosphorite Analyses

Varia- Factor Factor Factor Factor Coramuna-bles I II III IV lltles

SiOj 0.92644 -0.17661 0.24309 0.94857

AI2O3 0.47821 0.64107 -0.48274 - 0.87269

0.11473 -0.88095 - 0.10595 0.80044

TIO2 -0.20140 0.93313 0.29924 0.16991 0,98914

MnO 0.32925 -0.67749 -0.405 05 - 0.62305

CaO 0.24763 - 0.87897 -0.23377 0.88855

MgO 0.94486 0.11814 - 0.13409 0.92469

-0.92501 0.27060 0.21554 - 0.97549

NajO 0.84518 0.21836 -0.26338 -0.16387 0.85823

K^O 0.79787 -0.18828 - 0.78818 0.65667

HjO'^ -0.82384 -0.28741 M 0.10624 0.77260

-0.46705 -0.76878 -0.53506 - 0.87731

Cu 0.23029 0.72087 -0.75408 - 1.14132

Pb 0.82849 0.19963 - - 0.72624

N1 -0.15067 - 0.95836 - 0.94299

Co - 0.12787 -0.21265 - 0.06157

Zn -0.15442 0.62679 - 0.11452 0.42982

Cr -0.91600 mm 0,29372 - 0.92532

Sr -0.36660 0.62727 -0.61078 - 0.9 0091

Ba 0.80502 -0.47383 0.17117 -0.61472 1.27975

Rb -0.59009 0.72894 - - 0.87995

V -0.97362 - - - 0.94793

LI 0.84852 -0.15200 - 0.13715 0.76190

Cd -0.26937 -0.70792 -0.13256 0.38679 0.74088

PI-/\XES

PLATE-I

Pigure-1 Platy and laminated phosphorite made up of alternating bands of carbonate (light) and phosphate minerals (dark) (Maldeota west).

Pigure-2 Granular phosphorite (dark) constituted mostly of coarse grains and minute granules (Maldeota west).

P L . A T E - I

Fig. 1

Fig.2

PLATE-II

Pigure-1 Lenticular phosphorite made up of dark lentlcles of phosphatlc material alternating with light coloured bands of calcareous and or/siliceous material.

Figure-2 The phosphate nodule associated with black shales that occur in contact with phosphorite horizon at Maldeota west block.

PL/\TE~II

Fig.l

F i g - 2

PLATE-III

Pigure-1 Pelletal phosphorite made up of hard, blacK coiourea, elliptical and disc like pellets embedded in matrix of cherty carbonate (Maldeota west).

Figure-2 A hand specimen of phosphorite showing alternating bands of pyrite (light) and phosphatic material (dark) (Durmala block).

PI^/XTE-III

Fig.l

Fig. 2

PLATE-IV

Figure-1 Mlcrocrystalline collophane (dark) containing dot like inclusions of ferruginous material and occurring in the form of pellets embedded in a carbonate matrix (light) (X 55).

Figure-2 Dahllite (light) surrounding the oolitic collophane (dark) (crossed nicols, X 55).

Figure-3 A phosphatic pellet (dark) enclosed in a carbonate matrix (light) (X 55).

Flgure-4 Interstitial collophane (dark) occurring in the voids between calcite and quartz grain (light) (X 55).

PLATE~IV

Fig.l (X 55) Fig.2 (Cr. nic.,x 55)

Fig-3 (X 55) Fig-4 (X 55)

PLATE-V

Figure-1 Oolites of collophane (dark) having nucleus of carbonate (light) (X 55).

Pigure-2 Phosphatic ovules (dark and light) embedded in a carbonate matrix (light) (X 55).

Pigure-3 Nodules of collophane (dark) embedded in a cementing material consisting of dolomite (light) (crossed nicols, X 55).

Pigure-4 Microcrystalline to cryptocrystalline silica (light) associated with collophane (dark) (X 55).

PL.ATE-V

Fig.l (X 55) Fig.2 (X 55)

Fig.3 (Cr. nic.,X 55) Fig.4 (X 55)

\ i

PLATE-VI

Figure-1 Microaphanitic mass of amorphous looking collophane (dark) showing a vein of quartz (light) (X 55).

Figure-2 A calcite vein (light) cutting across the collophane (dark) (X 55).

Pigure-3 A calcite vein (light) in phosphate matrix (dark) (X 55).

Figure-4 A vein of collophane (dark) in a ground mass composed of calcite (light) (crossed nicols, X 55).

PI^ATE-VI

Fig.l (X 55) Fig.2 (X 55)

Fig.3 (X 55) Fig. 4 (Cr.nic. ,X .55)

PLATE-VII

Figure-1 Amorphous collophane (dark) showing a vein of quartz (light) (X 55).

Figure-2 Pellets and ovules of collophane (dark) showing complete and partial replacement of phosphate material by carbo-nate material (light) (X 55).

Figure-3 StromatolltIc phosphorite of Durmala showing concentric structure consisting of thin alternating bands of phosphate and carbonate material (X 55).

Figure-4 Stromatolltic phosphorite of Durmala showing a typical structure composed of phosphate and carbonate materials (X 55).

P L / \ T E - V I I

Fig.l (X 55) Fig.2 CX 55)

-.fiOv > . .

Fig-3 (X 55) Fig-4 (X 55)

PLATE-VIII

Figure-1 Dolomitic limestone showing anhedral coarse grains of calcite and dolomite <X 55).

Pigure-2 Carbonaceous shale composed of fine grained calcite, illite feldspars and sericite etc. (X 55).

Pigure-3 Carbonaceous shale showing cubes of pyrite (X 55).

Figure-4 Limestone showing compact and fine texture, with mostly fine to coarse anhedral grains of calcite and cryptocrystalline variety of silica in the form of chert (X 55).

V I I T

(X 55) Fig.2 (X 55)

Fig-3 (X 55) Fig-4 (X 55)