biogeochemical evaluation ofnannorrhops ritchiana: a mg-flora from khuzdar, balochistan, pakistan

Vol. 24 No. 4 CHINESE JOURNAL OF GEOCHEMISTRY 2005

Biogeochemical evaluation of Nannorrhops ritchiana: A Mg-flora from Khuzdar,

Balochistan, Pakistan

Sadaf Naseem I , Shahid Naseem 1. , Erum Bashir I , Khaula Shirin 2 , and Shamim A. Sheikh 1

1 Department of Geology, University of Karachi, Karachi 75270, Pakistan 2 PCSIR Laboratories Complex, off University Road, Karachi, Pakistan

Abstract Nannorrhops ritchiana ( Mazari Palm) is a distinctive flora growing in the Saharo-Sindian region. It is well distributed on the uhramafic soil, derived from the Bela Ophiolite in the Khuzdar District, Balochistan, Pakistan. Quantitative estimation of Ca, Mg, Fe and Ni in soil and plant ash has been car- ded out. The constituents of plant ash have been discussed in relation to soil chemistry, pH, climate, mobility, average abundance in plant ash and exclusion mechanism of the flora. Relationship among Ca, Mg, Fe and Ni has been established using scattergrams to evaluate the biogeoehemistry of the plant. High contents of Mg and high coefficient of biological absorption allow it to be classed as Mg-flora. Both Ca and Fe appeared to be antagonistic to Mg. The metal assemblage of N. ritchiana nicely reflected the nature of the bed rock as being serpentinized uhramafic, and its corresponding soils. Good exclusion mechanism of N. ritchiana did not allow it to absorb high Ni from the soil. Relatively high concentrations of Ni in N. ritchiana from the Baran Lak area can be used to localize Ni-mineralization in the study area.

Statistical analyses, such as minimum, maximum, mean, mode, median, standard deviations, and coefficient of correlation, were also made to improve raw geochemical data and interpretations.

Key words Balochistan; biogeochemistry; Khuzdar; Mg-flora; Nannorrhops ritchiana; Pakistan

1 Introduction

Nannorrhops ri tchiana belongs to the family Are-

caceae, commonly known as Mazari Palm. It is a small gregarious perennial palm. It is native of desert of the Saharo-Sindian region, mainly India, Pakistan, Af- ghanistan, Iran and Arabia. It is one of the most versa- tile palms that survive in blazing heat and snowy cold, intense winds, and almost water-free environment. In a favourable environment it can grow as high as + 5 m with blue-gray costapalmate leaves. In the study area it is widely distributed in the Khuzdar region. It is important to note that it is mainly associated with the ultramafic rocks of the Bela Ophiolite. Soils derived from the weathering of ophiolite have high amounts of Cr, Ni, Fe, Co, etc. as well as Mg (Brooks, 1987) . Many species found on ultramafic soil can accumulate and tolerate high concentrations of these elements (Jaf- fre et al. , 1976; Reeves, 1992).

The Jurassic-Cretaceous sedimentary rocks of the Mor Range are bound up with the Bela Ophiolite on the eastern side. Its western contact is concealed under the

ISSN-9426 • Corresponding author: sngeo@ sat. net. pk

Quaternary deposits of the Bela embayment; however it

is overlain by the Nal limestone of Oligocene-Miocene age in the north (Allemann, 1979). The Bela Ophio-

lite has developed as a typical ophiolite (Ahmed , 1993, including: lherzolite, harzburgite, wehrlite, du-

nite, layered gabbro, gabbro, sheeted diabase dyke,

plagiogranite, keratophyre, basaltic pillow lava, chert and limestone ( Kazmi and Jan, 1997 ).

Metallic ion composition of vegetation reflects the

availability of elements in the vicinity of the root system, and the ability of the plant to absorb and accumu-

late these elements (Lintern et al. , 1997; Cohen et

al. , 1999). All heavy metals are toxic to higher plants in excess (Berry and Wallace, 1981 ) and the exclu-

sion mechanism of the plant restricts the uptake of these elements. In contrast, some plants (Indicator

flora) have high tolerance to the metals and thus they

can easily inhabit in the areas of high metal accumulation ( Anthonovics et al. , 1971 ; Macnair, 1987 ).

Some of the hyper accumulator plants are capable of accumulating certain elements, 100 times than normal

species (Baker and Brooks, 1989 ). In recent years there has been ever increasing interest in the study of

metal-tolerant plants for phytoremediation and phytomining (Dunn et al. , 1996; Robinson et al. , 1997a,

b ) .

328 Sadaf Naseem et al. Vol. 24

27 ° 45'

27 ° 30'

27 ° 15 '

27 ° 0 0 '

26 ° 45 '

I [ Recent/Sub recent

l ~ i i ] Hinglaj Group

Nal Limestone

[!ii!!!!ii!!!ii[ Nari Formation

~ l [ l Jumburo Group

. . . . . . Bda Opl~olite ?,?,?,?,>>?

~ Wad L~estone

Thar Formation

~ Pab sandstone

. . . . . . . . . . . . . Parh Group

I- I Shirinab Group I- I

• Town

• Sample location f Drainage

Road

66 ° 15 ' 66 ° 30 '

Fig. 1. Geological sketch map of the study area showing sample localities.

The present study is a reconnaissance biogeochemical survey in the Khuzdar region. The aim of this study is to assess Nannorrhops ritchiana as a Mg-flora. The relationship among Ca, Mg, Fe and Ni in soils and plants is also discussed in light of the coefficient of biological absorption. The present study also focuses on the application of Nannorrhops ritchiana in the exploration of mineral deposits, associated with the Bela Ophi- olite in the Khuzdar area.

2 Description of the area

2.1 Location and access

The area under investigation lies between the towns of Sonaro and Pir Umer in the Khuzdar area (Fig. 1 ). The area is accessible from Karachi by the RCD Highway (Fig. 1 ). The samples of Nannorrhops ritchiana and soils were collected from twenty-four dif-

No. 4 Biogeochemical evaluation of Nannorrhops ritchiana 329

ferent localities along the RCD Highway. The locations of these deposits have been shown in the geological sketch map of the area (Fig. 1 ) .

2.2 Physiography

The area under study is the northern part of the Bela Ophiolite. The whole study area contains undulat- ing hills and mounds due to intense deformation, uplift and erosion. The average altitude of these sampling sites is about 1143 m (3772 ft) . The eastern rock belt (Mor) consists of the complexly folded, hard and re- sistant Ferozahad Group Jurassic rocks, while the western belt (Ham) is composed of cliff-forming Miocene (Nal limestone) and other younger rocks.

2 .3 Drainage

The Porali River is the main stream in the area. It flows from north to south with its numerous tributaries draining through the Bela Ophiolite and adjoining sedimentary rocks. Populations of Nannorrhops ritchiana are mainly confined in the stream beds of the Kanoji, Pat, Turkabar, Dauro, Pai, Dudki and Tur streams. These streams are sub-parallel to dendritic in pattern and are ephemeral.

2.4 Climate

The overall climate of the region is arid and characterized by high temperature and low precipitation. The average summer and winter temperatures are 30 ° and 15°C, respectively. During May to July, the heat is oppressive and temperature may approach to 45~C. Winter is also severe and the minimum temperature may reach 4°C (Raza and Bender, 1995 ). The annual rainfall is less than 243 mm, which is capricious and uncertain during the monsoon (Chaudhary, 1999).

3 Sampling and analytical method

Samples of Nannorrhops ritchiana and related soils were collected from 24 different sites along the RCD Highway. The vegetative samples were first washed with distilled water to remove external impurities such as dust, fungus and automobile exhaust. Then they were dried in a well-ventilated covered place for about 3 weeks. Mixed chopped leaves and petioles were ashed as recommended by Brooks (1972) and Martin et al. (1996) . One gram of air-free ash was treated with concentrated perehloric and nitric acids at a ratio of 7 : 3 . After heated till dryness, the residue was leached with 6 m nitric acid and diluted to 100 mL ( Siegel et al. , 1991 ). The solutions were analyzed for

Fe, and Ni using an Atomic Absorption Spectrophotom- eter ( Hitachi, Model Z5000), at the laboratory of PC- SIR, Karachi. Calcium and Mg were measured by ED- TA titration.

Soils were sieved through 200 mesh and 2 .5 mL of water was added in 1 g of sieved soil and the mixture was left overnight (Robinson et a l . , 1997b). The measurement of pH was carried out with the help of Denver Instrument Model 50. The extractable fraction of soil was determined by adding 10 mL HNO3 in 1 g of soil. The extracts were used to determine different elements as mentioned above.

4 Phytogeography

Phytogeographically, southern Baloehistan and adjoining areas are part of the Saharo-Sindian region. Climatically, this area has mild winters with scanty rainfall and long scorching summers (Ali and Qaiser, 1986). It occupies the largest territory among the other three phytogeographical regions of Pakistan. The Saha- ro-Sindian region extends from the Atlantic coast of North Africa through the entire Sahara, Sinai Peninsu- la, most of Arabia, part of Palestine, Syria, Iraq, I- ran, most of Baloehistan, Sindh and Punjab in Paki- stan and Rajisthan of India. The analysis of phanero- gams of Pakistan indicates the presence of 9 .1% unire- gional and 1.5% biregional flora in the Saharo-Sindian region (Ali and Qaiser, 1986). This region has the lowest species density (0.0009/sq. km) in contrast to the other regions. The number of species per genus is estimated at 3 .86, which is much lower than the global average ( 18 species per genus). The floras of Pakistan do not include a single endemic family, nor is a single genus known to be endemic to southern Balochistan.

The region is a high-altitude mountainous area (av. 1140 m ) , nearly barren, and has very meagre vegetation. However, some wild, native and perennial floras are present near streambeds. Nannorrhops ritchiana and Dodonaea viscosa coexist in the study area (Fig. 2) along with Tecomella undulate. Nerium odo- rum, Prospis cineraria, P. Juliflora, Zizyphus nummu- laria, Z. jujube, Acacia nilotica, Salvadoru oleoides, S. persica, Tamarix aphyIla, T. indica occur widely in this region.

The floristic composition and phytoecology of the above vegetation confirm the arid climate of the area. These species do not have pronounced xerophytic adap- tation, although they receive very little rainfall, and the soil is over drained due to the high relief.


Fig. 2. Young and adult Nannorrhops ritchiana grown over harzburgite (First author for scale).

4.1 Nannorrhops ritchiana

Nannorrhops ritchiana is a small gregarious peren-

nial palm. It is the native of Afghanistan, Pakistan, I- ran, Arabian Peninsula and other surrounding coun-

tries. It is a high-altitude plant. It requires full sunny exposure and can tolerate extreme climatic conditions ( - 10 to 50~C ) as well as drought.

Phylogenically, palms are monocotyledons angio- sperms. They are further divided into Arecida (Sub-

class) , Arecifora ( Super Order) , Arecales (Order) and Arecaceae/Palmae (Family). Nannorrhops ritchiana is the only wild genus and species of Arecaceae family found in Pakistan (Malik, 1984). Physiognom- ieally, they belong to class Phanerophyte and subclass Microphanerophytes (trees and shrubs between 8 - 2

m) . Stem is solitarily unbranched and glabrous. Leav-

es are simple, eostapalmate, stiff and alternate or crowded at the trunk apex. Leaflets have central mid-

veins and are folded. Leaf blade is 60 - 90 cm long, cariaceous, glabrous and fan-shaped. Leaves are di-

vided into 8 to 15 segments with thread like interposed fiber; segments induplieate and deeply (30 - 3 8 era)

bipartite (Malik, 1984). This is a very attractive palm having silvery blue or blue-green leaves. Hastula is ab- sent, petiole is 20 cm x 4 cm from the base and base is

covered with a mass of rust-coloured wool. In the first few years, it has branches above the ground and devel- ops to be a shrub-like appearance (Fig. 2 ) . The stem

of adult plant may attain a height of 6 m with - 30 cm diameter and resemble with other palm trees. Flowers are jointed with > 1 m long branched stalk ( Fig. 2 ). Usually there are 3 white flowers, one sessile and the other two are pedicelled. Fruits are rounded and have a diameter of - 1.5 cm with a single seed. Fruits are brownish-red when ripe and are edible.

4.2 Edaphic characters

Edaphic factors play an imperative role in the bio-

geochemical studies (Robinson et al. , 1997c; Knight et al. , 1997). Description, texture, colour and pH of the collected soils are given in Table 1. In the study area, soils are light gray to light yellowish-brown,

mainly derived from the weathering of ultrabasic rocks, nearly similar to serpentine soil. The serpentine soils are characterized by high Cr, Co, Ni, Mg and Fe and deficient N, P and K (Brooks, 1972, 1987). Textur- ally they are medium- to fine-grained and have low water-holding capacity (Nabais et a l . , 1996; Robinson et al. , 1997b). However, in the northern extremity,

calcareous soils are developed due to the influence of dominant carbonate rocks such as Parh, Wad and Nal limestones (Fig. 1) .


Lower pH will favour the release of bioavailable metal ions from soil (Dong et al. , 1995 ) and it ranges from 6.6 to 7 .4 for serpentine soil ( Robinson et al. , 1997b). The collected soils from the study area have a pH range of 7.3 - 8.8 ( Table 1 ). Possibly the alka-

line nature of soil is due to scarcity of rainfall, which causes retention of Ca and Mg salts. The arid climate of the area also does not favour the development of hu- mus in the soil profile.

Table 1. Location and description of soil samples from the study area

Location Sample No. pH Texture Colour* Description

Mammal Jhal MJ 7.3 Coarse Pale yellowish-brown

Gidan Dan GD 7 .6 Fine Moderate brown

Jauri Jhal JJ 8 .2 Fine Pale brown

Ghermas GM 8.4 Medium Dark yellowish-brown

Petari Jhal PJ 8 .0 Medium Mdi yellowish-brown

Hinar Trik HT 7 .5 Medium Pale yellowish-brewn

Baran Lak LB 8.8 V. Coarse Light gray

Khushal Ghar KG 8.0 Fine Dark yellowish-brewn

Khushal West KW nd Solid rock Pale brown

Pahar Khan East PE nd Solid rock Dark yellowish-brown

Shaban SE nd Solid rock Grayish black

Pahar Khan South PS nd Solid rock Greenish gray

Pahar Khan PK nd Solid rock Olive black

Pahar Khan North PN nd Solid reck Olive black

Bakhalo BK 7.8 Coarse Dark yellowish-brown

Mamir MR nd Solid rock Olive black

Kosano Ust West KS 8 .4 Medium Yellowish gray

Laya Garr LG 8.3 Medium Dark yellowish-brown

Wadh WD 8.1 Fine Dark yellowish-brown

Mehandar MD 7.5 Medium Md. yellowish-brown

Zareen Waher ZW 7.8 Fine Pale yellowish-brown

Garaki Dusht GK nd Solid reck Light olive gray

Pit Umer PU nd Solid rock Yellowish gray

Joi Jhal JI 8.1 Medium Pale yellowish-brown

Note: nd. not determined. * Goddar et a l . , 1970, GSAB, Colorado, USA.

Soil with pelagic sediments

Pelagic sediment with hematite

Pelagic sediment

Soil with pelagic sediments

Calcareous soil with some sand

Clayey soil

Ultrabasic rock with magnesite

Serpentine soil

Weathered dunite

Weathered dunite

Weathered harzburgite

Weathered ultrabasic rock

Ultrabasic with magnesite

Cumulate gabbro

Calcareous soil with sand

Karatophyre

Loam

Loam

Clayey soil

Calcareous sell with sand

Loam

Parh limestone

Parh limestone

Calcareous soil

5 General geology

The study area lies in the southern part of the Axi- al Belt of Pakistan. The Bela Ophiolite is exposed as a sandwiched wedge, enveloped within the sedimentary rocks of Jurassic to Miocene age. The Jurassic-Creta- ceous-Tertiary sedimentary rocks of the Mor-Pab ranges bound the Bela Ophiolite on the eastern side. Its western contact is concealed under the Quaternary deposits of Bela embayment; however it is overlain by the Nal limestone of Oligocene-Miocene age in the north (Atle- mann, 1979).

The Bela Ophiolite is exposed as a 450 km-long and 12 km-wide elongated belt striking north-south, a 5000 km-long southernmost remnant of volcanic rocks and sediments of the former Tethys Ocean (Gansser, 1980). This belt is the largest ophiolite in Pakistan and extends along the western boundary of the Indian Plate from the Khuzdar to the Arabian Sea, west of Ka- rachi (Fig. 1 ) and marked by the Ornach-Nal fault

( Nakata et al. , 1990). Gnos et al. (1998) divided the Bela Ophiolite in-

to two distinct units on the basis of age and tectonic setup. The upper unit (ophiolite) is exposed in the northern part while the lower unit (ophiolite accretion- ary wedge and trench sediments) is well exposed in the southern part. The entire study area is located within the upper unit and it consists of the following se- quences: a metamorphic sole of amphibolite and green schist, about 2 km of serpentinized harzburgite, 1.5 km of peridotite and varieties of gabbro, 0.5 - 1 km of sheeted dyke and 0.1 km of an extrusive. According to Nicolas ( 1 9 8 9 ) , it is a harzburgite type-ophiolite. Ahmed (1992, 1993 ) , on the basis of geochemical studies of basalt and acid igneous rocks, suggested a supra-subduction origin for the Bela Ophiolite. Arif et al. (1997) , on the basis of chromite composition of the Wadh arc, suggested that the Bela Ophiolite may have formed in a tectonic setting, which is transitional between those of island arc and MORB.

The obduction of the Bela Ophiolite onto the Indi-


an passive margin occurred in the Paleocene ( ~ 66 Ma) and final thrusting ended in the Early Eo- cene ( ~50 Ma). The emplacement occurred during the counter clockwise separation of Madagascar and In- dia-Seychelles, which caused shortening and consump- tion of oceanic lithosphere between the Mrica-Arabian and the Indian-Seychells plates (Gnos et al. , 1998). The inner ophiolitic belt contains a pelagic faunal assemblage in sedimentary rocks ranging from Maastrich- tian to Early Eocene ( Hempton, 1987 ). Sarwar (1992) , on the basis of paleontological studies, suggested that the Bela Ophiolite was formed during Ap- tian-Maastrichtian times, while recent paleontological studies by Gnos et al. (1997) indicate it is Albian in age.

6 Biogeochemistry

6. 1 Calcium and magnesium

Calcium and Mg both are classed as essential trace elements (Brooks, 1972 ). Calcium is a cross- linking agent in cell wall, acid-base regulator during metabolism and as an enzyme activator. High amounts of Ca may also be accumulated in mesophyll as Ca ox- alate. Magnesium is an essential part of chlorophyll,

an activator for ATP/ADP metabolism and necessary for DNA/RNA. The concentrations of these elements vary from species to species and are affected by other factors such as climate, soil, etc.

The average abundances of Ca and Mg in native plants are 0 .5% and 0 . 0 7 % , respectively (Brooks, 1972). In the study area, the ash of Nannorrhops r/tch/ana contains as much Ca as 1.5% and 15% and Mg0.21% to 15.7% (Table 2 ) . N. ritchiana can hold high amounts of Mg so it is classified as character- istic Mg-flora ( Brooks, 1972). The high coefficient of biological absorption "A" of N. ritchiana also supports the above statement. It varies from 0.22 to 9.06 ( Fig. 4A) , which is much higher than the average (0.034) of native flora ( Brooks, 1972). Similarly, coefficient "A" is also high (0.13 to 7.47) for Ca in contrast to the world average of 0.14. It is relevant to mention that if Mg is not available in soil, N. ritchiana may accumulate Ca instead of Mg. High amounts of Ca lead to the increase of the effective cation exchange capacity in soils and the enhancement of the selectivity for Ca rela- tive to Mg (Knight et al. , 1997). The diagram of Ca + Fe vs. Mg (Fig. 5A) reflects the antagonism a-

gainst Mg. Plants having Mg > 5%, generally restrict the uptake of Ca + Fe (Fig. 5A).

Table 2. Impor tant statistical parameters of elemental data for soils and plants of the Khuzdar area

Soil Plant

C a ( % ) Mg(%) F e ( % ) N i (x l 0 -6) C a ( % ) Mg(%) F e ( % ) N i ( x l 0 -6)

Min.

Max.

Mean

Mode

Median

S.D.

0.71 0.30 0.72 20

28.05 20.26 5,78 2260

6.35 5.90 2.70 506

6.01 0.60 1.73 50

4.76 1.21 2.86 65

6.14 7.58 1.19 770

1.50 0.21 0.21 5

15.03 15.73 O. 71 75

6.07 4.61 0.40 25

3.00 2.42 0.44 15

4.75 3.02 0.36 15

3.91 3.84 0.14 19

Mutual relationship between Ca and Mg in various forms is demonstrated in Fig. 4. The plots of N. ritchiana (Ca vs. Mg) do not have any typical correspondence (Fig. 3A) ; in contrast, some of the soil samples from the study area show an inverse relation (Fig. 3B). Ca/Mg ratio vs. Ca plots ofN. ritchiana show a gradual increase in Ca/Mg ratio ( Fig. 3C ) , except samples M J, GK, LG and KS. It is a good reflection of availability of Ca and Mg ions in soils and rocks (Fig. 3D) . The diagram (Ca/Mg vs. Mg) shows that Mg-deficient plants have variable Ca/Mg ratios but plants having Mg > 4% have consistent low values (Fig. 3E). The above trend is more precise in the soil samples (Fig. 3F).

Mg/Ca ratios (0.21 to 28.97 ; av. 3 .78) in the soils of the study area signify affinity with black soil of ophiolitic origin (Robinson et al. , 1997c) rather than alluvial soil. In some of the samples the Mg/Ca ratios are low, probably due to assimilation of Ca-bearing water, which was brought in the area from adjacent carbonate rocks (Girdhar and Yadav, 1982).

6.2 Iron

Iron is a micronutrient required in smaller quantity. It is mainly required in chlorophyll production, protein synthesis and respiration. In the study area iron contents vary between 0.21% and 0.71% in the ash of N. ritchiana, with low spread (Table 2) . The Mg


Nannorrhops ritchiana

2O o~ 1 5 ~

10 • 5 0

0 5 10 15 20 Ca %


15

• 0 • • _ t . , • •

0 5 10 15 20 Ca %

Nannorrhops ritchiana [-~

o 1570 o1•

0 5 10 15 20 Mg %


[ ~ Soils and rocks

3O o~ 2 0 ~

10 # o

0 10 20 30 Ca %

Soils and rocks

o • 40 or,n" 30 • = • • o~ lo

0 10 20 30 Ca %

Soils and rocks

o 6 0 ~ 40 ~' 20

0 10 20

~. 30 20 10

0 . t

o 5 i i

10 15 Mg %

25

o 20 L 10

20 0

Mg %

Soils and rocks

i i i

5 10 15 Mg %

1

30

i

2O

Fig. 3. Degree of correspondence among various elements in plant and soil

vs. Mg/Fe plot exhibits a positive linear relationship (Fig. 3G) except in one sample, which contains high Mg. This diagram (Fig. 3G) is a good reflection of bedrock chemistry in which iron is enriched in the ash of N. ritchiana, where Mg is low. In the presence of high Mg, iron is substituted. In spite of high concentrations of iron (5.78 max. ) in the soil, N. ritchiana absorbs a very little quantity of iron, which is evi-

denced from its low coefficient of biological absorption (Fig. 4B).

6 .3 Nickel

Biogeochemically, nickel is classified as a very toxic element, which is harmful to plants at the concentration of less than 1 x 10 -6 ( L ' Huillier and Edig- hoffer, 1996). The average abundance of Ni in the n-


10

8

6

4

2

0

Coefficient of biological absorption Nannorrhps ritchiana

1 2 3 4 5 6 7 8 9 101112131415161718192021222324

Sample No.

F~ Coefficient of biological absorption

0 .8 Nannorrhps ritchiana

0.6

0.2

0 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 9 2 0 2 1 2 2 2 3 2 4

Sample No.

Fig. 4. Coefficient of biological absorption of Nannorrhops ritchiana.

ative plants is about 65 x 10 -6 (Brooks, 1972). On the other hand, some plants may absorb high amounts of Ni ( > 1000 × 10 -6) , such plants are termed as hyperaccumulator (Baker and Brooks, 1989; Robinson et a l . , 1997b; Tilstone and Macnair, 1997; Roosens et a l . , 2003 ). Alyssum bertolonii may accumulate 100000 × 10 -6 Ni in Florence, Italy. Nickel in the leaves of Hbanthsus floribundus may reach up to 23%. L' Huillier and Edighoffer (1996) , on the basis of ex- periments, showed that Ni bioavailability in the ultramafic soil is very variable.

Plants grown over the serpentine soil accumulate high amounts of Ni. It is strange to note that N. ritchiana absorbs a very little quantity of nickel ( 12 x 10 -6 - 7 5 × 10 -6 ) from the soils, which have relatively

high concentrations of Ni (20 x 10 -6 _ 2260 x 10 -6 ). The coefficient of biological absorption (Fig. 4B) also signifies very low values (0 .015 to 0.666; mean 0 . 2 1 5 0 ) , which is less than the world average

(1 .54 ) . The low absorption of Ni is also indicated from its low SD (19) as compared to soil (770) (Ta- ble 2) . Probably this species has good exclusion mechanism that restricts the high intake of toxic nickel. All- away (1968) proposed that the soil-plant system pro- vides an effective barrier against toxicity of Ni. The uptake of Ni by N. ritchiana is illustrated (Fig. 5C) . The deficiency zone (up to 20 × 10 -6) shows a propor- tional concentration of Ni in plant from soil. The higher concentrations of Ni in soil are not reflected in plant ash. Beyond 2000 × 10-6 Ni, plant shows some toxic effect, which is not seen in the form of mutational changes, even minor chlorosis.

The plot of Mg vs. Ni in the ash of N. ritchiana shows slightly positive linear relationship (Fig. 5 B ) , indicating genetic affiliation with Mg-bearing rocks. The coefficient of correlation "R" between Ni and Mg is 0 .43 , which is highest for any other elements (Fig. 6 ) . Nickel has also been shown to occur in association



2° t ; 15 *

~1o $ *

c) 5

O ! 0 5 10

Mg %

[ ]

15 20

Nannorrhops ritchiana [ ~ 80 -] • .

60 ° o 40 •

20 * ¢' ¢' *

o •

0 5 10 15 20 Mg %

'~" Deficiency Uptake of Ni in Nannorrhops ritchiana

- = 8ol * ° " % 80

~ 40 ~-x 41,@ .-~ ~ 20 • z 0

0 500 1000 1500 2000 2500 Ni in soil (xl0 ~)

and the concentrations beyond 65 x 10 -6 in the normal plants, so it is considered anomalous for mineralization. In the study area the concentrations of Ni are high in the Baran Lak (samples LB and SE) area, the rest have nickel concentrations < 65 x 10-6. Proba- bly, the Ni-sulphide deposits are associated with chromite deposits which are common in the Baran Lak are- a. Ahmed (1992) also mentioned the presence of Ni- mineralization in the study area.

Coefficient of correlation o o4o I 0.4 0.344

0.3

0.2 !

0.1 0.065 0.078

o J il i i i

Ca-Mg Mg-Fe Ca-Fe Ca-Ni

0.43 0.365

il i

Fe-Ni Mg-Ni

Fig. 6. Diagram showing correlation coefficient between

Ca-Mg-Fe-Ni of Nannorrhops ritchiana.

Fig. 5. Degree of correspondence between (A) Ca + Fe/ Mg; (B) Ni/Mg and (C) soil-plant relationship for Ni in the ash of Nannorrhops ritchiana.

with Fe in mafic soils (Singh and Gilkes, 1992 ) , which is also obvious from their mutual relations (R , 0.385). Possibly, the low concentrations of nickel in the ash of N. ritchiana are due to high pI-I (Knight et al. , 1997) and a high amount of calcium carbonate, which restrict the mobility of Ni. The other possible cause for low nickel is the sandy soil, which has low sorption and fixation of Ni (Martin et al. , 1996). The absence of organic matter and the arid climate of the area also hinder the accumulation of Ni. One of the in- teresting issues related to the plants grown on the serpentine soil (Mg-Ni rich) is the decrease in the size of the plant (L ' Huillier and Edighoffer, 1996), which is not exactly true in the case of N. ritchiana (Fig, 2). Possibly, N. ritchiana can tolerate high Mg (Mg-flora) but restrict the uptake of Ni.

Biogeochemical techniques are widely used for the exploration of mineral deposits in the world, but they have not been applied in Pakistan, only a few examples can be cited (Naseem et al . , 1995; Naseem and Sheikh, 2002 ). The average abundance of nickel in the plant ash is 18 x 10-6(Rose et al. , 1979), 20 x 10-6( Levinson, 1980) and 65 x 10-6( Brooks 1972),

7 C o n c l u s i o n s

(1) Nannorrhops ritchiana, commonly known as Mazari Palm, is a distinctive flora of the Saharo-Sindi- an Region. In the Khuzdar District of Balochistan, it is of restricted distribution on the ultramafic rocks and their related soils. In the study area, the lower part of the Bela Ophiolite is well exposed, which includes partly to completely serpentinized equivalents of harzburgite, dunite, wehrlite and pyroxenite.

(2) In light of the high contents of Mg and high coefficient of biological absorption the plant was classed as Mg-flora. Both Ca and Fe appeared to be antagonistic to Mg. In some part of the study area, the soils are deficient in Mg. The plant may uptake Ca and Fe instead ofMg, i fMgis < 5%.

(3) The soils originated from the weathering of uhrabasic rocks usually have high contents of Mg-Fe- Ni. The soil-plant relationship indicates that N. ritchiana does not have high amounts of Fe and Ni, reflec- ting its good exclusion mechanism. It also gets support from the large size N. ritchiana. High Mg and Ni generally shunt the growth of the plant. Possibly, it can tolerate high Mg but restrict the uptake of Ni.

(4) The diagram (Ca/Mg vs. Mg) shows that Mg-deficient plants have variable Ca/Mg ratios but those having Mg >4% have consistent low values.

(5) Plant ash of N. ritchiana shows positive cor-


relations among Ni and Mg-Fe-Ca, indicating genetic association with some rocks having these elements, commonly olivines and pyroxenes.

( 6 ) Several deposits and showings of chromite and magnesite are known in the study area. The present study revealed possible zones of Ni mineralization in the Baran ~ area. By using the biogeochemical exploration technique, it is possible to identify new loci for undiscovered Cr and Ni deposits and further de- tailed investigations are needed.

(7) The bed rock chemistry, type of soil, pH, mobility of elements, dispersion mechanism, climate, nature of weathering, average abundance in plant ash, and exclusion mechanism of N. ritchiana have played an important role in the concentration of Ca-Mg-Fe-Ni. Some elements show lower concentrations than the ex- pected values due to basic pH and abundant Ca.

Acknowledgements We are highly indebted to Mr. Shabbir Ahmed Baloch, proprietor, Industrial Mineral Syndicate, Karachi, for his enthusiasm and encouragements during the field work and providing lo- gistic support. We also sincerely thank the inhabitants and tribe chief of the area for their great hospitality and allowing us to work in the area.

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biogeochemical evaluation ofnannorrhops ritchiana: a mg-flora from khuzdar, balochistan, pakistan

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