THE GEOLOGY AND GEOCHEMISTRY OF THE MANGANESE

OCCURRENCE AT OLULILWA, NW NAMIBIA

BY:

THERESIA R. MALOBELA

(201152568)

A THESIS SUBMITTED IN PARTIAL FULLFILMENT OF THE REQUIREMENTS FOR

THE BSC HONOURS DEGREE IN GEOLOGY OF THE UNIVERSITY OF NAMIBIA

University of Namibia

November 2014

SUPERVISORS: Prof. Benjamin S. Mapani (UNAM)

Dr. Rainer Ellmies (Kunene Resources Pty Ltd.)

i

DECLARATION I, the undersigned Theresia R. Malobela, hereby submit this thesis in the partial fulfilment for

requirements for the Bachelor of Science (Honours) in Geology at the University of Namibia and it has

not been previously submitted by me or any other person for a degree at this or any other institution. I,

hereby state that the work presented in this thesis is mine, except where authors are cited.

…………………………….. ………………………..

Signature Date

ii

ACKNOWLEDGMENT First and foremost, I would like to praise and thank the Almighty God for leading me through all aspects

of my undergraduate study, Geology. I would like to extend my heartfelt appreciation for Kunene

Resources Pty Ltd for sponsoring this research project. The financing for my accommodation and

geochemical analyses made everything possible for me. I owe particular gratitude to my supervisors and

mentors, Prof Benjamin S. Mapani and Dr Rainer Ellmies, thank you so much for tipping my inner geo and

shaping me to the geologist I am today. In saying this I dare not forget Prof Fred A. Kamona, because of

you I am now passionate about exploration and economic geology.

I have not forgotten the Kunene Resources crew (my second family), Karina Ndalulilwa, Tobias Mwandingi,

Peter Shikongo, Matjua Kauapirura, Brandon Munro, Peter Schreck and Halleluya Ekandjo. I appreciate

the help you have given me directly or indirectly.

Special thanks goes to Mr Gerard Tripp, Paul Hoskin, Ester Shalimba, Josia Shilunga and Mr Gabes

Nghikongelwa for everything you have done for me and helped me out with all the stress I had to go

through during this final year, SHOTZ ON ME (grapetizer for Mr Nghikongelwa).

I thank the Geology Department for their support and motivation throughout my four years. This

department has become my second home. My classmates, thank you for all the help and discussions we

had. Much appreciation goes to my colleague Petrina Amoomo for the shared ideas and helping hand.

Lastly, I would like to thank my siblings and extended family for their support, love and motivation. Many

more thanks goes to my parents for you two are the people that know how I struggled through this last

year especially with the project. Thank you for so much for your unconditional love.

iii

I DEDICATE THIS THESIS TO

MY PARENTS, Raphael and

Margret Malobela

iv

ABSTRACT The manganese occurrence at Olulilwa is located to the north of the prominent Steilrandberg

Mountain in the Nosib Group siltstones of the Eastern Kaoko Zone (EKZ), Kaoko Belt. The belt is

made up of a sequence of metasedimentary rocks and metabasites on top of pre-Neoproterozoic

basement gneiss. The eastern section of the belt (EZK), is a sequence of shallow-marine and fluvial

meta-conglomerates, meta-arenites and metapelites. Meta-pelites and carbonates were deposited

on top of the gneissic basement (Miller, 2008). The manganese occurrence predominately contains

braunite, jacobsite, hausmanite, rhodonite, spessartine and minor malachite. The Olulilwa

manganese occurrence is 700 m long (east-west) and 200 m wide. The deformation in the area has

folded manganese layers in a series of antiforms and synforms. There are sedimentary structures

such as cross bedding, ripple marks and sand volcanoes present in the siltstones that are in

between some of the manganese layers. The manganese layers are banded although in some parts

of the layers we see hydrothermal overprints suggesting that this occurrence may have been

reworked. The banded Mn samples show syn deposition textures. The duplex structures seen in the

siltstone samples show an indication of shearing where the lithologies are thrusted to the south in

a dextral movement thus allowing some Mn mineralisation along fault and bedding planes

suggesting fluid flow and late Mn mineralisation indicating that an epigenetic character is present

as well. There are four manganese layers all showing similar geochemical characteristics,

although the second layer from the north, is more enriched with Mn (up to 42 wt. % Mn). The Mn

samples show a high concentration of barium. The evidence of syn depositional textures and the

presence of barite suggests that the manganese occurrence at Olulilwa is of both SEDEX and

hydrothermal origin.

Table of Contents DECLARATION .................................................................................................................................. i

ACKNOWLEDGMENT ........................................................................................................................ii

ABSTRACT ........................................................................................................................................ iv

CHAPTER 1: INTRODUCTION ........................................................................................................... 1

1.1 Introduction ........................................................................................................................... 1

1.2 Location of study area ........................................................................................................... 1

1.3 Statement of the problem..................................................................................................... 2

1.4 Objectives of the study ......................................................................................................... 2

1.5 Hypothesis of the study ........................................................................................................ 3

1.6 Significance of the study ....................................................................................................... 3

CHAPTER 2: GEOLOGICAL SETTING ................................................................................................. 4

2.1 Regional Geology ................................................................................................................... 4

2.2 Local Geology ........................................................................................................................ 6

CHAPTER 3: LITERATURE REVIEW ................................................................................................... 9

3.1 Manganese deposits ............................................................................................................. 9

3.2 SEDEX Deposit Type ............................................................................................................ 12

CHAPTER 4: RESEARCH METHODOLOGY ...................................................................................... 15

4.1 Introduction ......................................................................................................................... 15

4.2 Research instruments.......................................................................................................... 15

4.3 Procedures .......................................................................................................................... 16

4.3.1 Desktop study ................................................................................................................... 16

4.3.2 Geological Mapping .......................................................................................................... 16

4.3.3 Rock sampling ................................................................................................................... 16

4.3.4 Soil Sampling ..................................................................................................................... 17

4.3.5 Geochemical analysis ........................................................................................................ 17

CHAPTER 5: RESULTS..................................................................................................................... 20

5.1 Introduction ......................................................................................................................... 20

5.2 Geology................................................................................................................................ 20

5.2.1 Geological Map ................................................................................................................. 20

5.3 Petrography ......................................................................................................................... 27

5.3.1 Description of the lithological units .................................................................................. 27

5.4 Structural Analysis ............................................................................................................... 35

5.5 Geochemistry ...................................................................................................................... 38

CHAPTER 6: DISCUSSION ............................................................................................................... 44

6.1 Introduction: ....................................................................................................................... 44

6.2 Geology................................................................................................................................ 44

6.3 Geochemistry ...................................................................................................................... 44

CHAPTER7: CONCLUSION .............................................................................................................. 48

Recommendations .................................................................................................................... 48

REFRENCE LIST .............................................................................................................................. 49

APPENDIX ...................................................................................................................................... 53

List of Figures Figure 1: The locality map of the Olulilwa Prospect modified after Kunene Resources Annual Report

(2013) ............................................................................................................................................................ 2

Figure 2: The Pan-African Damara Orogen during the early Phanerozoic plate configuration of Gondwana

from Jennings and Bell (2010) ...................................................................................................................... 5

Figure 3: The four structural zones of the Kaoko belt from Goscombe (2003a) .......................................... 6

Figure 4: The generalized stratigraphy of Neoproterozoic cover on the Congo craton in northern Namibia

from http://www.geol.umd.edu/~kaufman/iceages.html ........................................................................... 7

Figure 5: The Local stratigraphic column in Olulilwa (modified After Dr. Ellmies Personal communication

December 2013). Sst- sandstone, slt- siltstone, dol- dolomite, sh- shale, ls- limestone .............................. 8

Figure 6: Showing the strong anastomosing foliation and the C-S fabric ..................................................... 8

Figure 7: The Mn deposit distribution through time from

http://www.sedimentaryores.net/Index_Mn.html .................................................................................... 10

Figure 8: The countries of interest producing Mn ferroalloys from International Mn Institution (2010) .. 10

Figure 9: The characteristics features of a SEDEX deposit from

http://www.unalmed.edu.co/rrodriguez/Earth%20Resources/SEDEX%20Pb%20+%20Zn.htm ............... 14

Figure 10: The basic instruments used for soil sieving ............................................................................... 17

Figure 11: The crushing machine at MME .................................................................................................. 18

Figure 12: The milling machine at MME ..................................................................................................... 18

Figure 13: The geological map of the manganese occurrence area. .......................................................... 21

Figure 14: Cross section of the area along line AB...................................................................................... 22

Figure 15: Cross Section of the area along line CD ..................................................................................... 22

Figure 16: The sand volcano within the manganese layer.......................................................................... 23

Figure 17: Thin bands with a massive layer on the southern side .............................................................. 24

Figure 18: The high grade massive Mn ....................................................................................................... 25

Figure 19: The quartz vein cross cutting the manganese layer .................................................................. 26

Figure 20: The Mn bands with hydrothermal overprint ............................................................................. 27

Figure 21: The strong foliation anastomosing around the granitoid clasts ................................................ 28

Figure 22: The different clasts found in the breccia ................................................................................... 28

Figure 23: The breccia in thin section under XPL showing Carlsbad twinning in feldspars and calcite

matrix .......................................................................................................................................................... 29

Figure 24: The sandstone with the oxidized pyrite cubes and quartz veins ............................................... 30

Figure 25: the sandstone under thin section with different sizes of grains ............................................... 31

Figure 26: Classification of the sandstones ................................................................................................. 31

Figure 27: Sigmodal veins and mylonitic texture observed in the siltstone ............................................... 32

Figure 28: Mn clasts that form due to the hydrothermal fluid that infiltrates the unit ............................. 33

Figure 29: The replacement texture between the Fe minerals .................................................................. 34

Figure 30: The brittle micas with fractures along the cleavage .................................................................. 34

Figure 31: Pyrolusite vein showing the dendritic texture ........................................................................... 35

Figure 32: Slump folds found within the manganese layers ....................................................................... 36

Figure 33: A sketch of the mylonitic texture and the sigmodal Mn hydrothermal veins ........................... 36

Figure 34: Flinn diagram of the breccia clasts falling in the stretch region ................................................ 37

Figure 35: The orientation of the structural readings (see Appendix) taken near the manganese layers . 37

Figure 36: The variogram for the Mn showing two possible geological processes .................................... 38

Figure 37: Variogram for barium showing two possible source ................................................................. 39

Figure 38: Plot showing the metal concentrations in selected samples .................................................... 39

Figure 39: Mn concentration in soil of two extensive traverses. The oval marks the manganese

occurrence area .......................................................................................................................................... 40

Figure 40: Plot of Fe/Mn vs Ba, the Mn nodules put for comparison (Cabral et al, 2011) ......................... 41

Figure 41: Plot of Fe vs. Mn vs. (Co+Cu+Ni)*10 from Bonatti et al. (1972). Purple-BMF 1, Red-BMF 2,

Green-BMF 3 and Blue-BMF 4 .................................................................................................................... 42

Figure 42: Plot of Si vs Al from Peter (1988) ............................................................................................... 42

Figure 43: Plot showing the REE patterns. Red-Massive Mn. Blue-Fault Mn and Green-Banded Mn ....... 43

Figure 44: Depositional environment of Rosh Pinah from Mouton (2006). ............................................... 46

Figure 45: Eh-pH diagram showing the stability fields of Fe and Mn minerals from Evans (1993) 47

List of Table Table 1: The instruments used throughout this research project .............................................................. 15

Table 2: XRF detection limits of selected elements .................................................................................... 53

Table 3: The structural readings taking in the field .................................................................................... 54

Table 4: The sub-round granite clasts measurements from the breccia .................................................... 55

Table 5: Coordinates of 40 selected samples for geochemical analysis ..................................................... 56

Table 6: The XRF analysis of 10 selected samples from MME .................................................................... 57

Table 7: Soil analysis ................................................................................................................................... 57

Table 8: The ICP-MS data analysis from Actlabs ......................................................................................... 61

List of abbreviations SEDEX - Sedimentary Exhalative

DOF - Dolomite Ore Formation

NOT - Nosib Ombombo Transition

EPL - Exploration Prospect License

NP - Northern Platform

EKZ - Eastern Kaoko Zone

CKZ - Central Kaoko Zone

WKZ - Western Kaoko Zone

SKZ - Southern Kaoko Zone

MME - Ministry of Mines and Energy

br - braunite

pyro - pyrolusite

sph - sphalerite

qrtz - quartz

hm - hematite

goe - goethite

haus - hausmannite

gn - galena

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CHAPTER 1: INTRODUCTION

1.1 Introduction Manganese (Mn) is among the world's most widely used metals, ranking fourth after iron,

aluminium and copper (International Manganese Institution, 2014). Most of Mn industrial use

is in steel making with a much lesser amount going into the production of batteries

(International Manganese Institution, 2014). While the ore deposits of other metals have often

been discussed at considerable length in terms of metallogenic evolution, those of Mn did not

receive adequate attention until the 1960s. Besides the Mn nodules found on the ocean floor,

there are Manganese deposits that occur on land (e.g., Otjozondu deposit in Namibia, Kalahari

Mn Field in South Africa, and Woodie Woodie deposit in Australia). Mn total production is

about 22 Million tonnes (International Mn Institution, 2014) and 95 % is consumed by steel

industry and the rest for multitude of purpose (Evans, 1993; Corathers, 2014). The manganese

occurrence which is the subject of this project is found in the Nosib Group of the Northern

Platform, Namibia (Miller, 2008). The occurrence is found some 51 km NW of Opuwo, north

of the Steilrandberg Mountain (Figure 1). The prospect occurs within the Nosib Group

siltstones, above the Mesoproterozoic to Neoproterozoic basement of the Epupa Complex. The

Nosib Group consists of subarkose arenites and shale intercalated siltstones. The Mn is about

700 m long and 300 m in height, the layers vary in thickness pinching out on either sides. The

manganese occurrence was found in June 2013 by Kunene Resources geologists (R. Ellmies

and K. Ndalulilwa, internal report Kunene Resources Pty Ltd., 2013) and no extensive

geological work has been done since discovery.

1.2 Location of study area The study are is located in the Olulilwa village, approximately 51 km from Opuwo town and about

14 km north of the Opuwo-Etanga gravel road (D3703). The area is within the Exploration

Prospecting License (EPL) 4347 (Figure 1) which is owned by Kunene Resources Namibia Pty

Ltd. Opuwo is the capital district of the Kunene Region which is in the north-western part of

Namibia. The town is located about 720 km north-northwest of the city of Windhoek.

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Figure 1: The locality map of the Olulilwa Prospect modified after Kunene Resources Annual Report (2013)

1.3 Statement of the problem Genetic ore-deposit models may aid exploration and lead to the discovery of new deposits. Since

the manganese occurrence at Olulilwa has only recently been found and no extensive geological

work has been done and descriptions are lacking. The prospect has not been mapped nor an

economic appraisal been made.

1.4 Objectives of the study

To produce a geological map of the study area.

To describe the characteristics (lithologies, structures, mineralogy, mineral

textures) of Mn mineralization at Olulilwa.

To produce a genetic model for the manganese occurrence.

EPL 4347

Olulilwa

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1.5 Hypothesis of the study Little is known of the nature of the manganese occurrence at Olulilwa. From a regional

perspective, however, it is known to occur on the platform to a thick sedimentary basin, the Damara

basin. The hypothesis is then, that the manganese occurrence is a SEDEX deposit that has

characteristics typical of other SEDEX occurrences on platforms elsewhere. If correct, this

recognition of the deposit type will form a key ‘cornerstone’ to the generation of an ore-deposit

model that can be used for ongoing exploration.

1.6 Significance of the study Little is known about this terrestrial Mn deposit, therefore this research will contribute to the

knowledge base of these deposits. Locally, the research will provide information on the Kaoko

Belt which is even until today under-studied.

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CHAPTER 2: GEOLOGICAL SETTING

2.1 Regional Geology The Damara Orogeny is part of the Pan-African Orogeny. The orogeny is divided into three belts,

namely: the Damara Belt, the Kaoko Belt and the Gariep Belt (Figure 2). The Damara Belt shows

a well-preserved bivergent symmetry typical for collisional belts and based on the lithological,

structural and metamorphic characteristics, the belt has been subdivided into a number of distinct

tectonostratigraphic zones (from N to S) (Miller, 2008). The Northern Platform which is one of

the tectonostratigraphic zones consists of a thick succession of shelf-type carbonates of the Otavi

Group overlain by mainly siliclastic molasse-type deposits of the Mulden Group (Miller, 2008).

Deformation is characterized by open folding that decreases in intensity towards the north and east

(Kisters, 2008).

According to the simplified geological map of Namibia (Geological Survey of Namibia, 2005)

Olulilwa is located on the Kaoko Belt just 2-3 kilometres north of the Steilrandberg Mountain.

Steilrandberg Mountain is on the boundary between Kunene Zone and Eastern Kaoko Zone

(Goscombe et al, 2003b), which is in cooperated into the Northern Platform (NP) as it is underlain

by shallow water, platform facies of the Otavi Group (Miller, 2008). The Kaoko Belt consists of

four structural zones (Figure 3). They are the Eastern Kaoko Zone (EKZ), the Central Kaoko Zone

(CKZ), the Western Kaoko Zone (WKZ) and the Southern Kaoko Zone (SKZ) (Goscombe et al,

2003a).

EKZ is the foreland of the Kaoko Belt, comprising sub-greenschist facies Damara Sequence

platform carbonates resting on the western margin of the Congo Craton, the Palaeoproterozoic

Kamanjab Inlier in the south and the Epupa Metamorphic Complex in the north (Goscombe, et al,

2003b)). Deformation involved early schistose foliation development overprint by the dominant

late-stage E-W shortening and upright folds (Goscombe et al., 2003a). The EKZ comprises

predominantly Nosib and Otavi Group meta-sediments and minor metamorphic basement rocks

which are progressively less deformed as the platform margin in the east is approached (Dürr et

al, 1995). The Nosib Group developed thick sequences throughout the EZK that pinches out in the

eastern CKZ, indicating a transition from shelf to slope facies at the margin between the zones

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(Miller, 2008). The western margin of the EKZ is marked by the shallow west-dipping Sesfontein

thrust which formed under brittle conditions late in the Damara orogenic cycle (Goscombe et al,

2003b). The Sesfontein Thrust marks the margin between the carbonate shelf and the slope

(Goscombe et al, 2003a). These shear zones may present reactivated growth faults in the passive

margin (Dürr et al, 1995).

Figure 2: The Pan-African Damara Orogen during the early Phanerozoic plate configuration of Gondwana from Jennings and Bell (2010)

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Figure 3: The four structural zones of the Kaoko belt from Goscombe (2003a)

2.2 Local Geology Locally the basement which is the Epupa Metamorphic complex contains granitic ortho- and

paragneisses with minor basic rocks. The basement is be highly deformed, with isoclinal folds and

C-S fabrics that mark a brittle ductile episode (Figure 6). The observable pre-Nosib deformation

occurs as breccia zones that likely formed on the rift shoulders of the Neoproterozoic basin. The

basement is sheared, which most possibly gave way to the hydrothermal fluids which later

precipitated in the shallow marine to form the manganese occurrence.

The area consists of two groups, the Nosib Group and the Otavi Group (Figure 5). The Nosib

Group developed as a result of intracontinental rifting of the Congo craton at about 756 Ma

(Kamona and Günzel, 2007). The manganese occurrence is found within the Nosib Group. The

Nosib age sediments were deposited in half-grabens on the basin margins. According to Kröner

and Correia (1980) the deposition may have started between 1.0 and 0.9 Ga. The Otavi Group in

this area consists of two subgroups namely the Ombombo and the Abenab Subgroup. The

Ombombo Subgroup consists of interbedded clastic and carbonate rocks with thicknesses of up to

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1660 m (Miller, 2008) (Figure 4). It is comprised of a lower ‘Omivero’ shale and mixed, fine

clastic unit overlain by a carbonate-dominated ‘Upper and Lower Omao’ succession. Within the

Upper Omao dolomite there occurs some Cu-Co mineralization which is termed Dolomite Ore

Formation (DOF). Above the Ombombo Subgroup, occurs the Abenab Subgroup. This subgroup

commences with the glaciogenic diamictite units of the Chuos Formation. The upper part of the

Nosib Group terminates in a formation that has been termed the Nosib-Ombombo- (NOT) and

marks the beginning of Otavi Group. The Nosib-Ombombo Transition (NOT) is mineralized with

lead and copper in the Okondaurie area, which is located some 30-40 km east of Olulilwa.

Figure 4: The generalized stratigraphy of Neoproterozoic cover on the Congo craton in northern Namibia from http://www.geol.umd.edu/~kaufman/iceages.html

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Figure 6: Showing the strong anastomosing foliation and the C-S fabric

DOF (Cu-Co)

BIF Chuos Diamictite

Otavi Group (slt,

sst, dol, ls)

Thrust fault

SEDEX Mn

Epupa Basement

Pre-Nosib breccia

Nosib Group (slt, sst,

sh)

NOT Pb-Cu Mineralization

Figure 5: The Local stratigraphic column in Olulilwa (modified After Dr. Ellmies Personal communication December 2013). Sst- sandstone, slt- siltstone, dol- dolomite, sh- shale, ls- limestone

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CHAPTER 3: LITERATURE REVIEW

3.1 Manganese Deposits Manganese oxides are deposited in a variety of terrestrial and marine environments as a

consequence of erosional, supergene and hydrothermal processes. Manganese deposits can also

act as markers of major events in the dynamic evolution of the Earth's surface (Nicholson, 1992).

Depositional textures observed in these Manganese deposits reflect differences in the processes of

formation and depositional environments, which in turn are a response to change in the land–

ocean–atmosphere system over geological time (Nicholson, 1992).

Bühn et al (1992) suggested that manganese (Mn) and iron (Fe) formations form in pelagic shelf

environments during interglacial transgressions with the ultimate source of the metals from

hydrothermal activity. Holland (2005) supports this theory and states that Fe²⁺ and Mn²⁺ were

dissolved in reduced ocean water and precipitated as Fe-Mn formations in intermediate post glacial

periods as the ice cover melted and oceans became oxidized. There were two major (Sturtian and

Marinoan) and one minor (Ediacaran) period of glaciation (Holland, 2005). The large glaciation

periods were ca. 710 Ma and ca. 635 Ma Marinoan which were followed by the smaller glaciation

period at ca. 580 Ma. The association of Mn ores with Banded Iron Formation (BIF) is similar to

their association during the Paleoproterozoic which relates to changes in sea level and the presence

of widespread anoxia in the deep ocean (Frakes and Bolton, 1984; Cabral et al, 2011). Most

Manganese deposits are terrigenous–sedimentary or are deposited in shallow water in shelf

conditions and some formed during transgression.

Mn ores occur in rock units of nearly all ages (Figure 7), however the middle Proterozoic (ca. 1.8–

0.8 Ga) is practically barren of Manganese deposits, except for a very few, small occurrences

developed locally (Roy, 1996). The onset of the Proterozoic was marked by the development of

large shallow sagging basins that acted as repositories of thick sediment piles interlaced with

volcanics (Roy, 1988). Most of the volcanogenic/hydrothermal massive sulphide deposits of

Proterozoic and Phanerozoic age demonstrate a prominent Mn halo (Stumpfl, 1979; Roy, 1981)

indicating significant presence of Mn in the exhalations.

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Figure 7: The Mn deposit distribution through time from http://www.sedimentaryores.net/Index_Mn.html

Figure 8: The countries of interest producing Mn ferroalloys from International Mn Institution (2010)

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There are three classification of Mn ore bodies (Roy, 1968):

1. Hydrothermal Deposits

Hypogene veins are formed by ascending solutions mainly made up of alabandite associated with

Cu, Au, and Ag ores in near proximity. The source of the ascending solution comes from

crystalized igneous rock. The minerals associated with this type of deposit are mostly Mn

carbonates and oxides alongside hydrothermal minerals such as barite and sulphides.

2. Sedimentary Deposits

There are two favoured sources of these type of deposits

(i) Volcanogenic

The direct volcanic activity whereby hydrotherms rich in Mn deposit the metal or barren

hydrotherms leach and collect Mn from volcanics and deposit them later.

SEDEX deposits formed by contemporaneous submarine eruptions may be characterized by iron-

Mn association. The concept of volcanogenic derivation of Mn for sedimentary deposits is based

on four features; one being the high content of minor elements in Mn nodules where the enrichment

in cobalt which is considered to be due to immediate volcanic origin. These are not accepted and

now the Mn nodules are considered to be of both terrigenous and volcanic origin.

(ii) Non volcanogenic

This type is not related to any volcanic source but are derived from weathering of a continental

land mass, transported by a stream and then deposited in standing water adjacent to the land mass.

The minerals associated with this type of deposit are the oxides e.g. pyrolusite

• Diagenesis of Mn sediments

Strakhov (1996) suggested that the sediments originally slightly enriched in iron and Mn, are

redistributed and concentrated during diagenesis to from ore bodies. In Lacustrine deposits, iron

and Mn precipitate and settle to the deepest reaches. Once in the deepest horizons, they are reduced

and taken into solution and pulled up to the silt water zone. Here they re-oxidize and re-deposited

enriching the upper parts of the deep water salts. Thus the enrichment Mn formed in silts are

sedimentary diagenetic products. Mn upward mobility is greater than iron, hence effecting a

separation between the two elements. Hewett (1996) pointed out the absence of large accumulation

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of iron near the sedimentary deposits of Mn derived from supposedly non volcanogenic source.

This observation cannot be explained as the Fe: Mn ratio in normal continental rocks may be as

high as 60:1. Even if iron is separated from Mn in sedimentary processes it should form large

accumulations and accompany Manganese deposits in space and time.

• Metamorphosed Manganese deposits

Braunite, jacobsite, hausmannite are high temperature lower oxides. Mn carbonates subjected to

high temperature are dissociated and the Mn released and reacts with silica to form rhodonite. At

all grades of metamorphism, braunite is the earliest mineral to form. Formation of braunite with

pyrolusite is due to lack of silica. Bixbyite forms after the crystallization of braunite thou they can

occur together during contemporaneous formation.

3. Superficial Mn deposit

Supergene agencies form at or near the surface, leaching and residual enrichment, at low

temperature and high oxide Mn minerals. Colloform pyrolusite accompanied by goethite and chert.

3.2 SEDEX Deposit Type The term SEDEX evolved from the original term proposed by Carne and Cathro (1982) that

included laminated, exhalative sulphides in fine-grained clastic rocks to a diverse group of deposits

containing laminated ores in clastic, carbonate, and metasedimentary rocks (Leach et al., 2005).

SEDEX deposits are the major source of base metals and the age range is from 150 Ma – 1800

Ma, the largest are those of the Proterozoic age (Goodfellow, 1993). SEDEX ores are traditionally

formed by fluids rich in Pb, Zn and Ba that ascends along bounding faults to exhale at higher levels

(Goodfellow, 2007) (Figure 9). This ore is characterized as synsedimentary to early diagenetic

based primarily on the presence of laminated ore textures and tabular morphology of the deposits.

This deposit type is typically Cu poor and some contain economically important amount of Ag and

Ge, whilst the non-sulphide gangue minerals are mainly dolomite, siderite, ankerite, calcite, barite,

and quartz (including chert and ore-related silicification) (Leach et al., 2005). SEDEX deposit

type formed by hydrothermal systems that vented fluids onto the sea floor from sedimentary brines

at similar temperatures and ore depositional paths (Goodfellow, 2007; Galley et al, 1995; Taylor

et al, 2009). SEDEX systems tend to be sited in upper parts of the sedimentary succession in

reduced sedimentary units such as shale, siltstone or mudstone (Goodfellow, 1993).

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Cooke et al. (2000) proposed a two-fold subdivision of SEDEX deposits based on fundamental

differences in the chemistry of mineralised brines from which the ores precipitated. Based on a

number of geological features, SEDEX deposits have been classified into two subdivisions:

- McArthur type deposits which precipitated from oxidised (SO42- predominant), acidic to near-

neutral brines that evolve from sedimentary basins dominated by carbonates, evaporates and

hematitic sandstones and shales (e.g. McArthur River “HYC”, Mount Isa, Hilton).

- Selwyn type deposits which precipitated from acidic, reduced (H2S-predominant) connate brines

that evolved in reduced siliclastic and shale basins (e.g. Sullivan, Rosh Pinah-type deposit,

Rammelsberg, Century and SEDEX deposits of the Selwyn Basin).

SEDEX deposits in Namibia are related to the Chuos Formation and similar to the Gariep- Kaigas

Formation (Frimmel, 1996). In Namibia, the well-known SEDEX deposit type is Rosh Pinah

deposit which is classified to be a Selwyn type deposit due to high concentrations of barium in the

ore which required the fluids to be reduced (H2S-predominant) (Flavianu, 2010). The physico-

chemical properties of the fluids resulted in rapid precipitation of the metal load in response to a

variety of processes such as cooling, dilution or addition of H2S (Rozendaal et al., 2005).

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Figure 9: The characteristics features of a SEDEX deposit from http://www.unalmed.edu.co/rrodriguez/Earth%20Resources/SEDEX%20Pb%20+%20Zn.htm

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CHAPTER 4: RESEARCH METHODOLOGY

4.1 Introduction In this section a full description of the methods used is given to obtain the required results which

are shown in the next chapter. The study is predominantly qualitative and quantitative. Qualitative

observations and measurements (which are quantitative by definition) are done in such a way that

other researchers will be able to reproduce the author’s work.

4.2 Research instruments

Table 1: The instruments used throughout this research project

Instrument Purpose

Compass Measuring strike, dip, foliation and

joints

Note book (A5) To record everything that is observed in

the field during mapping

GPS Used for finding coordinates at rock

units contacts and direct to transverse

points

Marker pen Marking rock samples and the sample

bags

Measuring tape Measuring the thickness of the Mn bands

Clipboard Used to hold notebook and baseline map

XRF To determine the bulk-rock major

element composition of rock samples

(and selected minor and trace elements)

ICP-MS Used for trace element determination of

rock and mineral samples

Polarizing microscope To view thin-sections and polished

sections

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4.3 Procedures Several methods are used to achieve the objectives of this study. The methods include desktop

study (e.g., literature review), geological mapping and analytical techniques (including

geochemical and petrographic studies)

4.3.1 Desktop study

No studies were done in this geographically remote area of Namibia so literature review is done

to relate and understand what is observed locally in the field with terrestrial Manganese deposits

around the world. Books, journals and ‘Gray literature’ reports were obtained from the Ministry

of Mines and Energy (MME) library, Prof. B.S. Mapani (Supervisor) and from Mr. G. Tripp1 .

4.3.2 Geological Mapping

Geological mapping was done and its aim was to study, observe and analyse the structure,

stratigraphy and metamorphism of the lithologies occurring in the study area. The mapping area is

1 km in length by 0.5 km in width, with traverses within this rectangular area being spaced 100 m

apart. A transect was done to be able to draw up a stratigraphic column. The geological map and

cross section were digitized using Quantum GIS Lisboa 1.8.0 Lisboa.

4.3.3 Rock sampling

Systematic sampling of rocks close to the manganese occurrence was done during the field trip

which took place on 14 January- 29 January 2014, the second field trip took place 26 June – 11

July 2014. The texture, grain size and mineral distribution within the rock samples were noted. A

total of 70 samples were collected from the field and 11 samples were cut and made into thin

sections and polished sections. The thin sections and polished sections analysis was to observe the

minerals, microstructures and internal textures which can give an indication of what tectonic

processes that took place during the deposition of the minerals.

1 Gerard Tripp Consultant gerardtripp@gmail.com

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4.3.4 Soil Sampling

Soil sampling was done along a traverse that passes through the study area, this was done to

compare the concentrations with the rock samples. The soil was then sieved using basic

instruments (Figure 8) to 0.18 mm in size which was then taken for XRF analysis.

Figure 10: The basic instruments used for soil sieving

4.3.5 Geochemical analysis

Samples selected for thin-sectioning were also crushed with a jaw crusher and milled at the

laboratory of the Namibian Geological Survey. The crushed samples (Figure 9) were then

pulverised in a vibratory disc mill (Figure 10). Powders was prepared further for XRF analysis.

Another 20 samples were taken for ICP-MS analysis for element identification.

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Figure 11: The crushing machine at MME

Figure 12: The milling machine at MME

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XRF

XRF analysis stands for x-ray fluorescence analysis. XRF as an analytical method used to

determine the chemical composition of all kinds of material, which can be solid, liquid or

powdered. At the Ministry of Mines and Energy the geochemist used a portable XRF Niton

machine to shoot x-rays to the samples and extract the digital data on the computer once assay is

complete. Major elements (Al2O3, CaO, Fe2O3, K2O, MgO, MnO, P2O5, SiO2, TiO2, and Na2O)

were analysed using this technique (see detection limits in table).

ICP-MS

The Inductively Coupled Plasma Mass Spectrometry (ICP-MS) is an analytical method used for

elemental determinations; it has a superior detection capabilities compared to other techniques

especially for rare-earth elements (REE).

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CHAPTER 5: RESULTS

5.1 Introduction This chapter outlines the researcher’s findings based on the field and analytical observations that

were done in the study area. Mineralogical, petrographic and geochemical studies were done to

give more support on the hypothesis that was made.

5.2 Geology

5.2.1 Geological Map

The mapped area (Figure 13) is made up of the Pre-Nosib breccia which overlies the Epupa gneiss-

amphibolite basement, the Nosib Group sedimentary rocks and the Post-Cretaceous sediments.

The oldest unit in the study are is the Pre-Nosib breccia unit. The contact between the Nosib Group

lithologies (siltstone and sandstone) is not very visible although there are some primary contacts

seen between the siltstone and the breccia unit. The Nosib Group consists of the sandstone and the

siltstone-shale intercalations. The manganese layers are found within the siltstone unit. The

youngest unit in the mapped area is the Post-Cretaceous sediments.

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Figure 13: The geological map of the manganese occurrence area.

B

A C

D

22 | P a g e

Figure 14: Cross section of the area along line AB

Figure 15: Cross Section of the area along line CD

BMF 1: Some parts of this layer is banded while others are highly siliceous with Mn staining over

the bands. There occurs lamination and bedding as structures in these siltstones and some

A B

900

1200

Elev

atio

n [

m]

C D 900

1200

Elev

atio

n [

m]

23 | P a g e

manganiferous siltstone, that grades into banded Mn units. Some structures seen are sand volcanos

(Figure 16). The bands are up to 1 cm thick (Figure 17). This layer contains braunite, hausmannite,

goethite and galena.

Figure 16: The sand volcano within the manganese layer

24 | P a g e

Figure 17: Thin bands with a massive layer on the southern side

BMF 2: This layer is massive and contains high Mn content (up to 45% Mn) (Figure 18). This

layer consists of jacobsite, braunite, hausmannite and iron oxides such as hematite, it also contains

minor galena found within the hausmannite matrix. Primary structures have been observed such

as cross bedding and trough bedding, all showing the younging direction to the south.

25 | P a g e

Figure 18: The high grade massive manganese layer

BMF 3: The third manganese layer is banded with some hydrothermal overprint. These

hydrothermal prints have a higher content of Mn and it causes chemical embedment on the grains

that were emplaced during the syngenetic episode. The layer is veined and fractured. The veins are

mostly quartz veins cross cutting the layer (Figure 19) and the fractures are filled with Mn minerals

such as braunite and hausmannite. The veins are mostly located on the eastern side of the

manganese layer, close to the major fault that cuts across the second and third manganese layer.

On the eastern side of the layer it is broken up and at the edges of these island layers we see the

quartz veins. Primary structures such as cross bedding and trough bedding were observed showing

the younging direction to the north. The minerals contained in this rock are: galena, hausmannite,

jacobsite, hematite and goethite.

26 | P a g e

Figure 19: The quartz vein cross cutting the manganese layer

BMF 4: The last layer to the south which has “two arms” on the western side (see Figure 13,

geological map). On one of the arms the younging direction is to the north. The layer is banded

with the same high Mn hydrothermal overprint (Figure 20). Like the third layer, this fourth layer

is fractured and the fractures are filled with crystallized braunite, hausmannite, hematite and

quartz. There are some quartz veins seen mostly on the eastern side of the manganese layer. The

veins are about 20 cm wide and cross cuts the layer in a NNW-SSE direction.

27 | P a g e

Figure 20: The Mn bands with hydrothermal overprint

5.3 Petrography

5.3.1 Description of the lithological units

Pre-Nosib Breccia

The oldest unit in the study area is the Pre-Nosib breccia unit. The breccia contains angular and

sub-rounded clasts of the fractured gneiss-amphibolite basement (Epupa Complex), granitoids and

mafic unit (e.g. pyroxenites, gabbros) (Figure 22). The breccia is not well sorted so the clasts vary

in size, on average the x-axis is 13 cm, the y-axis is 6 cm and the z-axis is 6 cm. The breccia is

clasts supported. This breccia is a sedimentary breccia that has been faulted and deformed, possibly

during the tectonic period before the deposition of the Nosib group. Strong anastomosing foliation

is observe on this unit with C-S fabrics which are an indication of shearing (Figure 21). The

roundness of the clasts increases to the east and was possibly formed during a fanning process, so

it is probably a fanglomerate. The little matrix found in between the clasts is K⁺ and Ca²⁺ rich

(Figure 23).

28 | P a g e

Figure 21: The strong foliation anastomosing around the granitoid clasts

Figure 22: The different clasts found in the breccia

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Figure 23: The breccia in thin section under XPL showing Carlsbad twinning in feldspars and calcite matrix

Sandstones

The sandstone is light grey-brown in color. The minerals found are; quartz, biotite, few spessitine

crystals, braunite and hematite. Oxidized pyrite cubes are sometimes observed in the sandstones

(Figure 24). The grain size of this unit range between 0.2 mm to 2.4 mm (Figure 25), this range is

classified as medium grained to very coarse grained using the Wentworth (1922) classification.

The sandstone is massive with quartz veins that are about 4 cm wide. The Mn mineralization is

found within the open spaces between the mineral grains.

A classification of the sandstones that were collected was done using the Dott (1964)

classification system. The sandstones are classified as subarkose arenites (Figure 26).

30 | P a g e

Figure 24: The sandstone with the oxidized pyrite cubes and quartz veins

31 | P a g e

Figure 25: the sandstone under thin section with different sizes of grains

Figure 26: Classification of the sandstones

Quartz

Lithic FragmentsFeldspar

Arkose Lithic Arenite

Subarkose Sublithic Arenite

32 | P a g e

Siltstones

The siltstone is dark brown in color and contains minerals such as biotite, chlorite and quartz. The

texture observed is fine grained and foliated. The manganese layers end in this siltstones i.e.

manganiferous siltstone. The siltstone is found mostly between the manganese layers, dipping

steeply (50˚- 88˚) with the manganese layers. Sigmoidal shaped Mn vein are observed in the

siltstone. The unit appears to have gone under high strain event which is a later event after the

hydrothermal brecciation. There are two breccia episodes seen, one is tectonic that cross cuts the

brecciation caused by the hydrothermal fluid. Syngenetic textures are observed that have been

disturbed by the hydrothermal fluid that came in and caused the manganese layer to form clasts.

Figure 27: Sigmoidal veins and mylonitic texture observed in the siltstone

33 | P a g e

Figure 28: Mn clasts that form due to the hydrothermal fluid that infiltrates the unit

The polished sections were used to identify the Mn ore minerals, which are; hausmannite,

jacobsite, braunite and pyrolusite. Iron ore minerals were also identified such as goethite and

hematite. Minor sulphide minerals (galena, pyrite and sphalerite) were also observed. Textures

such as replacement textures were seen where magnetite has been replaced by hematite and

hematite replaced by goethite (Figure 29). In some polished sections there seems to be what looks

like a brittle mica (Figure 30). The pyrolusite is found in a vein showing its dendritic texture

(Figure 31). The formation of the pyrolusite is formed from the breaking down of the braunite

mineral as seen from in the polished sections.

The paragenesis obtained for the Mn ores is as follows: galena+ sphalerite+ pyrite > magnetite

>Braunite + jacobsite + hausmannite > hematite > pyrolusite> goethite

34 | P a g e

Figure 29: The replacement texture between the Fe minerals. (haus- hausmannite, goe- goethite, hm- hematite, qrtz- quartz)

Figure 30: The brittle micas with fractures along the cleavage (hm- hematite, qrtz- quartz)

hm

qrtz

goe

mica hm

haus

qrtz

35 | P a g e

Figure 31: Pyrolusite vein showing the dendritic texture (pyro- pyrolusite, br- braunite, sph- sphalerite, gn- galena)

5.4 Structural Analysis

The structures seen in the mapping area are mostly primary structures such as cross bedding, trough

bedding, ripples and sand volcanoes. These structures were used to determine the younging

direction of the units in the study area. Slump folds (Figure 32) were observed in the manganese

layers which indicated that these are slope facies.

The banded Mn samples show syn deposition texture. The duplex structures seen in the siltstone

samples (Figure 33) show an indication of shearing, where the lithologies are thrusted to the north

in a dextral movement thus allowing some Mn mineralisation along fault and bedding planes

suggesting an epigenetic character present as well.

A Flinn diagram is drawn up to visualize the strain that the breccia enjoyed in 3-D (Figure 34).

The clasts have gone under extensional strain.

pyro

br

gn

sph

36 | P a g e

The manganese layers strike in the east-west direction at 270˚ to 290˚ and dip steeply ranging from

50˚ to 88˚ in the northern direction (Figure 35). Using the primary structures found in the bands,

the layers form a syncline that plunges to the west.

Figure 32: Slump folds found within the manganese layers

Figure 33: A sketch of the mylonitic texture and the sigmoidal Mn hydrothermal veins

37 | P a g e

Figure 34: Flinn diagram of the breccia clasts falling in the stretch region

Figure 35: The orientation of the structural readings (see Appendix) taken near the manganese layers

0

0.5

1

1.5

2

2.5

3

0 0.5 1 1.5 2

x/y

y/z

Flinn Diagram

Stretch

Flattening

38 | P a g e

5.5 Geochemistry The mineralogy and geochemistry of Mn ores is rather complex and cannot be presented in

sufficient detail. Lower oxides (braunite) and silicates (rhodonite) form during metamorphism and

hydrothermal alteration processes (Roy, 1968). A total of 70 samples were collected for

geochemical analysis. The geochemical analysis includes data from XRF, XRD and ICP-MS. This

data is used to identify the elemental grade of both major oxides, to identify unknown minerals

plus the trace metals concentration found in the Mn samples respectively.

From the XRF data variograms of the Mn and the barium (Figure 36 & 37) were drawn up to see

the origin of these two elements. The variograms do show a correlation to each other i.e. both have

a similar trend. There are two possible geological processes that took place to form the manganese

layers as observed from the variogram that shows two sills. Both variograms show a pure nugget

behaviour due to the uncertainty at a distance of zero. This shows that the behaviour of the

elements used is highly unpredictable at short sampling distances and more data would be required

than was sampled in this study.

Figure 36: The variogram for the Mn showing two possible geological processes

39 | P a g e

Figure 37: Variogram for barium showing two possible source

A graph is made just to observe the metal concentrations (Figure 38) in 10 samples collected from

the lithological units in the mapping area. As observed the selected samples contain an exceptional

amount of nickel and some minor lead concentrations. Nickel is a hydrothermal metal in this study

as there occurs no nickel in the sediments but the copper which is low is probably both of

hydrothermal and sedimentary origin as observed in the DOF to the east.

Figure 38: Plot showing the metal concentrations in selected samples

40 | P a g e

The soil sampled shows a lower Mn concentration then that in the rocks (Figure 39). The Mn

concentration is up to 0.2 Wt. % in soils while in rocks it is up to 32 Wt. %

Figure 39: Mn concentration in soil of two extensive traverses. The oval marks the manganese occurrence area

41 | P a g e

The Mn samples contain high barium concentration as observed in figure 40. All four layers plot

in the ranges from 100-10000 ppm Ba and the Fe/Mn ration is between 0.01 and 10. In figure 30,

it is observed that the Mn nodules plot where the black star is shown. There occurs no link

between the nodules and the Olulilwa Mn samples. Figure 40 below shows how the Ba

concentration is related to this ratio. There is no correlation between the barium and the Mn

concentration. This plot also that the Ba and the Mn content was increased due to the hydrothermal

event.

Figure 40: Plot of Fe/Mn vs Ba, the Mn nodules put for comparison (Cabral et al, 2011)

The ternary diagram (Figure 41) discriminates between hydrothermal or hydrogenous depending

on the Co+Cu+Ni concentration (Bonatti, 1972). It. has been recognized that hydrothermal oxides

are depleted in Co, Cu, Ni and Zn relative to hydrogenous deposits. The points fall in the

hydrothermal section. The points are mostly in the diagenetic-hydrothermal region. The same can

be said on the Si vs Al plot (Figure 42) where the samples plot on the hydrothermal region.

Mn nodules

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Figure 41: Plot of Fe vs. Mn vs. (Co+Cu+Ni)*10 from Bonatti et al. (1972). Purple-BMF 1, Red-BMF 2, Green-BMF 3 and Blue-BMF 4

Figure 42: Plot of Si vs Al from Peter (1988)

In the REE patterns we observe that the Mn found close to the fault (Figure 43-blue) are enriched

with H-REEs. The banded Mn have a negative Ce anomaly and are slightly enriched in L-REEs.

The massive Mn are depleted in H-REEs and show no Ce anomaly. The Eu anomaly is fluctuating,

sometimes positive or negative.

Diagenetic

Hydrothermal

Hydrogenous

Hydrogenous

Hydrothermal

43 | P a g e

Figure 43: Plot showing the REE patterns. Red-Massive Mn. Blue-Fault Mn and Green-Banded Mn

0.1

1

10

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Sam

ple

/ P

AA

S

Mn1

Mn2

Mn4

BMF6

BMF9

OLULIWA1

BMF-M 7

BMF-M 8

BMF-M 10

44 | P a g e

CHAPTER 6: DISCUSSION

6.1 Introduction This chapter aims to give a clear explanation on what the results show and whether these results

confirm the hypothesis or not.

6.2 Geology The SEDEX deposits are bedded or laminated, tabular sulphide-rich bodies in carbonaceous and/

or pyritic, fine-grained, clastic rocks showing a diagnostic laminated bedding-parallel sulphide

texture of sphalerite, galena and pyrite (Large et al., 2002). The manganese occurrence is hosted

within siltstones and shows a syngenetic texture (Figure 17 & 20). The rocks contains some pyrite,

galena and sphalerite but at a very low concentration. The occurrence is not dominated by

sulphides but by oxidized minerals such as braunite, jacobsite and hausmannite. The formation of

the Mn likely indicates that it was in an environment where there was high oxygen. Most SEDEX

deposits are located close to major growth faults (syn-sedimentary faults), which have tapped

hydrothermal fluid from depths of 2-10 km in the basin. Ore fluids are generally linked to

metalliferous formational waters that were heated within the sedimentary basin under the elevated

geothermal conditions of the typically extensional tectonic settings (Flavianu, 2010). From the thin

sections it shows that the hydrothermal fluids were rich in Mn, K⁺ and Ca²⁺. This hydrothermal

fluid came in after the syngenetic event and remobilized it causing brecciation and disruption in

continuous textures such as colloform.

The minor presence of carbonates and sulphides suggest that the Mn deposition experienced

initially reduced environments and then the conditions changed to highly oxygenated

environments. Preliminary paragenetic interpretation for the Mn oxides suggests that braunite

typically represents an early paragenetic phase (Jones et al., 2013). Besides braunite, we observe

hausmannite and jacobsite which suggest a hydrothermal and metamorphic origin for these Mn

oxides (Cabral et al, 2011; Jones et al, 2013; Nicholson, 1992)

6.3 Geochemistry Mn mineralogy is notoriously difficult to interpret since many Mn minerals have stability fields

spanning ambient to mesothermal temperatures and are observed in both hydrothermal and

supergene paragenesis (Roy, 1968). Detailed geochemistry must be done to determine the identity

of the true nature of the deposit.

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Bonatti (1972) has observed that hydrothermal deposits have a low concentration of Co, Cu and

Ni (Figure 38 & 41). In our samples we have a low concentration these metals although Ni is high

which might be explained by the hydrothermal fluid that came in. From the geochemical data it is

observed that the nature of the Mn deposit is hydrothermal and diagenetic (Figure 41 & 42). The

high Ba concentration which is observed in the samples suggests a hydrothermal event that

increased the both Ba and Mn content (Figure 40).

REE patterns are used to distinguish between primary hydrothermal Mn and supergene enrichment

in REEs (Ce). Enrichment in REEs reflects the effects of prolonged exposure to oxidised surface

waters during weathering. The banded samples show a negative Ce anomaly (Figure 43) which

probably reflects the dominance of barite and, by inference, that the barite obtained its sulphate

component primarily from sea water. The Eu values for the Mn rock sample are unreliable owing

to the high Ba contents, which hamper quantitative determination of Eu (Dulski, 1994). Maynard

(2010) has shown that most Neoproterozoic Fe–Manganese deposits do not show significant Eu

anomalies and attributes this primarily to sea water dilution. This characteristic is seen in the

banded Mn samples collected from Olulilwa.

The REEs patterns of metasedimentary rocks are although to be relatively unaffected by regional

high grade metamorphism and therefore should reflect the primary environment of deposition

(Grauch, 1989):

Flat shale normalized REE pattern with weak positive Ce- detrital origin

LREE higher than H-REE reflects that of present day oxic sea water

Low Ce- high Barite therefore sulphate obtained from the sea water

Proposed genetic model:

The 3rd order basin found in Olulilwa is bounded by faults on both sides where fluids flowed in

and settled at the bottom of the basin. This fluid came in with clastic slope facies. During the

glacial period the water level dropped the Fe²⁺ and Mn²⁺ were dissolved in reduced ocean water.

As conditions changed after the glacial period, the Fe-Mn precipitated as the ice cover melted and

oceans became oxidized (Figure 44). When the water levels rose so did the pH allowing the Mn to

precipitate as high pH is favoured by Mn. After the diagenetic sequence hydrothermal fluids were

brought in that had no involvement with sedimentary processes. The hydrothermal fluid

46 | P a g e

remobilized the syngenetic ores and caused brecciation. The oxygen levels increased and the

hydrothermal phases became oxidized. The depositional environment of this proposed genetic

model is similar to that of Rosh Pinah (Mouton. 2006).

Figure 44: Depositional environment of Rosh Pinah from Mouton (2006).

Separation of Mn and iron

A great puzzle in Mn sedimentary geochemistry is not the chemical processes as such but the

mechanism by which Mn compounds become separated from other sediments (Krauskopf, 1976).

Mn compounds occur in small sizes but the large size found Mn ores are separated by sedimentary

processes from Fe-deposits. Another long period of erosion is proposed but the behaviour of Mn

and iron is so similar that conditions under which the Mn and iron may be quantitatively separated

are restricted. In acidic solutions, when exposed to air the solution becomes basic and both metals

47 | P a g e

precipitate but if the pH increases iron compounds reach their stability limit before Mn compounds

and so are precipitated before Mn thus the solution becomes more Mn rich (Figure 35) (Krauskopf,

1976). This is seen in nature like spring deposits, SEDEX deposits show zonation of iron closer to

the feeder zone than the Mn zone (Figure 36). Precipitation of Mn after iron has separated out can

be affected in many of the usual ways e.g., a solution becomes more alkaline or conditions become

reducing (Krauskopf, 1976).

Mn-iron separation by diagenesis occurs when there is a reduction of Mn-iron, causing them to go

into solution and become mobile, this solution reaches the oxidized environment and both

precipitate first iron then Mn (Evans, 1993).

Figure 45: Eh-pH diagram showing the stability fields of Fe and Mn minerals from Evans (1993)

48 | P a g e

CHAPTER 7: CONCLUSION

This research project aimed at studying the geology and the geochemistry of the manganese

occurrence at Olulilwa. The primary objective was to come up with a possible genetic model. All

the objectives have been achieved.

The Damaran rocks formed at the rift-drift transition when continental margins subsequently

thermally subsided, lithosphere extensional stress was released through development of oceanic

rift systems and associated transgression inundated adjacent shelf areas. Mn and iron developed

adjacent to pelagic conditions on top of long lived continental lithosphere. Glaciation played an

important role in the Mn formation in the Neoproterozoic where it enhanced the formation of large

Manganese deposits.

The manganese occurrence is on the northern platform of an intra-cratonic sedimentary basin. As

observed in the field and the geochemical data, both hydrothermal and exhalative process played

a part in the formation of the manganese occurrence. The elevated levels of Ba in the deposits

indicate that the prospect originated as product of sedimentary exhalative processes. Therefore in

conclusion, the occurrence is a SEDEX deposit that has been reworked by hydrothermal fluid rich

in Mn, K⁺ and Ca²⁺. Tectonics in the form of thrusts and folds affected the area and may have

contributed as pathways for the remobilization of the Mn.

Recommendations As the area is not well studied and this is the first geological work done on the manganese

occurrence, the author recommends that:

An extensive structural study should be done in the area

Drilling can be done to determine the depth and grade of the manganese occurrence

Exploration must be carried out to the east as the zonation is lateral and the feeder vent

might be to the eastern side where there could be copper.

49 | P a g e

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53 | P a g e

APPENDIX Table 2: XRF detection limits of selected elements

Element Detection Limit (ppm)

Si 10

Ti 2.5

Al 10

Fe 2.5

Mn 0.5

Mg 0.25

Na 25

K 50

P 25

Nb 0.001

Zn 0.0005

Y 0.0005

Sr 0.001

U 0.0005

Rb 0.001

Th 0.0005

Pb 0.0005

Ga 0.0005

Ni 0.002

Ce 0.0005

Sc 0.0005

V 0.0005

Ba 0.0005

La 0.0005

54 | P a g e

Table 3: The structural readings taking in the field

Foliation Strike in ° Dip in ° Dip Direction 280 82 S

280 40 S

296 80 S

287 52 S

287 86 S

286 42 S

298 50 S

298 82 S

290 88

274 64 S

299 38 S

303 42 S

270 28 S

286 86 S

307 86 S

296 80 S

287 52 S

287 86 S

270 32 S

290 86 S

282 88

286 88

288 82 S

274 88

296 78 S

294 72 S

288 78 S

Close to the BMF and the BMF layers

288 86 N

282 64 N

284 88

274 78 N

281 86 N

306 86 N

288 86 N

279 80 N

290 72 N

286 58 N

278 76 N

290 76 N

292 72 N

280 82 N

55 | P a g e

277 86 N

279 86 N

Table 4: The sub-round granite clasts measurements from the breccia

Clasts X-

axis

[cm]

Y-

axis

[cm]

Z-

axis

[cm]

granite 6.8 5

granite 6.1 3

granite 5 4.1

granite 31.3 9 17

granite 20.5 7

granite 40 25

granite 9 16

granite 10 23

granite 11 23

granite 26 10 14

granite 18 9 12

granite 13 5 7

granite 17 7

granite 6 5

granite 6 6.5

granite 10 6

granite 17 7

granite 23 10

granite 16 8

granite 24 12

granite 9 5.5

granite 11 7

granite 17 9

granite 6 3

56 | P a g e

granite 7 4

granite 12 4 6

Table 5: Coordinates of 40 selected samples for geochemical analysis

33K UTM Elevation BMF #

331320 8025770 1113 1

331320 8025770 1113 1

331334 8025763 1113 1

331232 8025768 1117 1

331333 8025753 1117 1

331356 8025765 1117 1

331347 8025770 1118 1

331381 8025764 1104 1

331390 8025763 1102 1

331407 8025750 1103 1

331274 8025749 1147 2

331274 8025749 1147 2

331280 8025745 1141 2

331280 8025745 1141 2

331294 8025747 1137 2

331313 8025747 1138 2

331310 8025746 1131 2

331242 8025749 1119 2

331356 8025757 1118 2

331408 8025749 1103 2

331211 8025729 1165 3

331211 8025729 1165 3

331211 8025729 1157 3

331213 8025929 1161 3

331222 8025726 1154 3

331224 8025726 1161 3

331236 8025725 1157 3

331243 8025730 1160 3

331271 8025730 1158 3

331284 8025720 1142 3

331202 8025696 1179 4

331202 8025698 1177 4

331209 8025701 1176 4

331209 8025701 1176 4

331219 8025704 1122 4

57 | P a g e

Table 6: The XRF analysis of 10 selected samples from MME

Sample

No.

Si

%

Mn

%

Al

%

Mg

%

Ca

%

K

%

S

%

Ba

%

P

%

Fe

%

Ti

%

Sr

%

Zn

%

Zr

%

Pb

ppm

Cu

ppm

Ni

ppm

Cr

ppm

Sn

ppm

1 31.62 18.06 6.52 3.11 0.93 1.93 - 0.44 - 3.66 0.56 0.01 0.06 0.02 21 18 315 65 40

2 45.81 0.13 3.19 - 0.34 2.44 0.04 0.09 - 1.34 0.19 - 0.01 0.02 16 13 24 76 -

3 26.44 9.76 6.45 4.57 3.95 2.41 - 0.06 - 4.58 0.37 0.03 0.08 0.01 17 26 248 27 48

4 31.75 8.13 8.11 3.80 1.30 4.51 0.08 0.11 0.12 4.07 0.69 0.01 0.04 0.02 30 13 199 86 42

5 28.60 7.66 4.89 2.79 3.19 3.59 - 0.13 - 2.41 0.42 0.02 0.25 0.03 65 73 113 65 34

6 29.76 10.62 6.83 3.94 0.92 2.56 0.09 0.10 0.10 3.38 0.51 0.02 0.95 0.02 835 37 201 74 29

7 28.42 4.40 7.17 5.39 0.74 3.84 0.08 3.89 0.67 0.01 0.11 0.02 45 144 98 64 35

8 14.62 7.06 3.23 - 21.14 1.29 - 0.34 - 2.12 0.19 0.02 0.10 0.01 84 37 117 37 34

9 26.67 2.21 4.63 4.17 4.56 4.52 - 0.15 0.09 5.58 0.50 0.01 0.18 0.02 26 43 96 65 37

10 21.16 32.22 4.31 3.73 1.57 0.75 0.07 0.10 - 2.33 0.23 0.01 0.10 0.01 43 - 287 88 74

Table 7: Soil analysis

lat lon Mn Fe Cu Pb Zn Ba

-17.802 13.40553 925.1 29988.86 20.35 < LOD 41.12 722.32

-

17.8065

13.40549 672.29 26615.43 36.68 < LOD 46.84 748.03

-17.811 13.40545 896.71 37306.66 18.81 10.71 59.77 461.65

-

17.8156

13.40541 657.77 27780.98 42.55 11.63 76.49 677.17

-

17.8201

13.40537 1863.05 80434.63 25.08 < LOD 67.76 517.99

-

17.8246

13.40533 722.12 28214.23 34.45 12.49 66.87 470.38

-

17.8291

13.40529 637.93 32220.38 34.66 12.16 78.81 906

-

17.8336

13.40525 1514.87 113077.1 59.16 11.61 131.94 877.02

-

17.8382

13.40521 1618.2 106719 57.45 163.51 146.07 1300.15

-

17.8427

13.40517 642.41 26017.97 28.25 < LOD 59.14 668.64

-

17.8472

13.40513 22578.6 103802.9 52.81 399.67 1173.48 1654.97

331219 8025704 1122 4

331217 8025700 1166 4

331225 8025701 1171 4

331237 8025700 1166 4

331247 8025696 1158 4

58 | P a g e

-

17.8517

13.40509 1336.29 31174.56 37.79 22.22 145.78 927.1

-

17.8562

13.40505 639.03 25486.36 18.61 12.66 66.67 1139.09

-

17.8607

13.405 799.19 38031.9 48.99 12.81 50.67 866.07

-

17.8653

13.40497 787.82 41753.07 32.16 < LOD 52.32 547.81

-

17.8698

13.40493 644.15 38914.59 69.42 21.36 49.48 467.69

-

17.8743

13.40488 447.83 45055.68 46.67 13.84 38.87 376.82

-

17.8788

13.40485 519.64 36510.69 < LOD 13.92 41.73 696.65

-

17.8833

13.40481 556.73 30325.32 < LOD < LOD 31.92 761.92

-

17.8878

13.40477 563.42 26690.86 107.05 < LOD 18.85 709.52

-

17.8924

13.40473 712.9 35209.5 315.74 49.97 37.79 507.22

-

17.8969

13.40468 344.86 29625.78 < LOD < LOD 8.78 367.09

-

17.9014

13.40464 259.79 29485.72 < LOD < LOD 19.43 211.11

-

17.9059

13.4046 458.71 35888.48 < LOD < LOD 17.58 572.31

-

17.9104

13.40456 806.85 19791.14 165.34 < LOD 17.98 337.42

-17.915 13.40454 319.28 22572.4 < LOD < LOD 14.57 395.88

-

17.9195

13.40448 209.85 20672.82 < LOD < LOD 8.66 344.98

-17.924 13.40444 438.26 30119.5 17.97 < LOD < LOD 560.48

-

17.9285

13.4044 377.58 25688.13 < LOD < LOD 9.89 503.73

-17.933 13.40436 426.53 32281.56 < LOD < LOD 9.76 463.14

-

17.9375

13.40432 460.89 41743.53 19.3 < LOD 18.68 500.81

-

17.9421

13.40428 359.21 25075.11 21.16 < LOD 13.62 490.66

-

17.9467

13.42312 323.74 29114.21 23.94 < LOD 27.52 650.75

-

17.9422

13.42316 562.77 36993.52 31.02 < LOD 44.34 592.45

-

17.9377

13.42312 625.68 35252.58 35.34 < LOD 41.01 643.51

59 | P a g e

-

17.9332

13.42324 574.34 30455.04 23.47 < LOD 30.73 632.71

-

17.9287

13.42328 457.87 29277.65 20.47 < LOD 17.19 647.24

-

17.9241

13.42334 295.98 30361.23 < LOD < LOD 26.89 540.05

-

17.9196

13.42336 284.43 20701.58 19.14 < LOD 9.26 323.49

-

17.9151

13.4234 275.98 27725.75 < LOD < LOD 12.72 415.69

-

17.9106

13.42344 320.26 21221.19 15.48 < LOD 19.9 432.36

-

17.9061

13.42348 300.04 28873.21 21.09 < LOD 16.7 299.29

-

17.9015

13.42358 609.26 21661.54 34.62 76.35 177.69 510.3

-

17.8022

13.4244 533.66 12069.45 15.67 < LOD 21.51 423.77

-

17.8067

13.42436 690.02 21850.22 17.6 < LOD 35.27 506.14

-

17.8112

13.42431 548.16 25988.59 18.13 < LOD 48.03 692.2

-

17.8157

13.42427 718.78 27039.14 27.31 6.33 53.37 467.18

-

17.8202

13.42424 574.56 23685.89 46.1 10.8 49.23 465.01

-

17.8248

13.4242 583.43 22051.93 23.83 < LOD 44.6 615.1

-

17.8293

13.42416 502.57 20510.65 36.51 < LOD 43.93 475.86

-

17.8338

13.42411 595.4 35703.98 38.53 < LOD 49.13 564.02

-

17.8383

13.42408 962.24 45183.29 < LOD < LOD 76.5 258.63

-

17.8428

13.42407 1361.65 46398.69 17.6 32.75 98.72 796.56

-

17.8473

13.424 745.5 24739.84 < LOD 19.28 61.46 1082.96

-

17.8519

13.42396 1276.21 36425.93 30.46 24.69 179.02 792.76

-

17.8564

13.42392 328.56 13182.22 19.18 98.93 230.78 996.25

-

17.8609

13.42388 881.21 46730.02 53.33 15.96 72.53 757.2

-

17.8654

13.42384 1075.6 44651.84 91.67 < LOD 68.09 656.79

60 | P a g e

-

17.8699

13.42379 630.57 40823.67 46.65 12.12 38.31 484.71

-

17.8744

13.42375 544.43 40302.41 < LOD < LOD 42.28 414.13

-17.879 13.42371 664.33 39666.68 36.99 < LOD 43.26 421.58

-

17.8835

13.42368 538.32 36904.36 < LOD < LOD 31.66 609.4

-17.888 13.42364 497.56 38791.84 22.73 < LOD 30.24 532.01

-

17.8925

13.4236 519.21 27837.4 < LOD < LOD 14.07 407.9

-17.897 13.42355 269.29 21246.47 < LOD < LOD 18.19 373.09

61 | P a g e

Table 8: The ICP-MS data analysis from Actlabs

Analyte

Symbol

MnMn

FeCo

NiCu

ZnLa

CePr

NdSm

EuGd

TbDy

HoEr

TmYb

Lu

Unit Sy

mbol

%ppm

%ppm

ppmppm

ppmppm

ppmppm

ppmppm

ppmppm

ppmppm

ppmppm

ppmppm

ppm

Detect

ion Lim

it0.00

31

0.010.1

0.10.01

0.10.5

0.010.1

0.020.1

0.10.1

0.10.1

0.10.1

0.10.1

0.1

Analysi

s Meth

odFUS

-ICPAR

-MSAR

-MSAR

-MSAR

-MSAR

-MSAR

-MSAR

-MSAR

-MSAR

-MSAR

-MSAR

-MSAR

-MSAR

-MSAR

-MSAR

-MSAR

-MSAR

-MSAR

-MSAR

-MSAR

-MS

Mn1

94622.5

5.615.3

22.4540

15.930.8

3.714.6

30.6

3.80.6

3.70.8

2.30.3

1.60.2

Mn2

76819.8

3.810

26.245.6

10.920.6

2.49.22

1.80.3

20.3

1.90.4

1.10.2

0.90.1

Mn3

87330.9

1.93.3

4.61152

3.79.66

0.62.39

0.40.1

0.6< 0.

10.4

< 0.1

0.2< 0.

10.2

< 0.1

Mn4

25317.3

0.93.3

6.119.6

5.310

1.25.19

1.10.3

1.50.2

1.80.4

1.20.2

10.2

BMF6

37.9> 10

0000.99

12.924.9

10.5891

22.635.2

4.316.1

2.80.6

3.10.4

2.50.5

1.40.2

1.20.2

BMF9

39.1> 10

0000.86

1328.8

10.1784

17.732.9

3.814.5

2.90.6

3.40.5

3.10.6

1.90.3

1.60.3

OLULIW

A130.9

> 10000

1.6323.6

55.426.1

33836.6

46.86.3

23.74.4

15.1

0.74.1

0.82.4

0.31.9

0.3

BMF-M

742

> 10000

1.039.2

187.6

58621.6

354.2

15.32.8

0.63.1

0.42.5

0.51.4

0.21.2

0.2

BMF-M

840.3

> 10000

1.6311.2

305.8

69016.2

313.6

13.52.3

0.52.4

0.31.8

0.41

0.10.8

0.1

BMF-M

1045.1

> 10000

1.4311.7

36.432.3

30618.4

35.74.3

16.93.6

0.84.2

0.63.4

0.71.9

0.31.5

0.2

RTM1

1280

4.8121.5

37.270.3

20321.8

44.65.9

22.94.5

1.44.6

0.63.9

0.82.2

0.31.8

0.3

RTM2

58700

0.7511.2

22.412.8

41615.7

33.53.9

15.13.2

0.83.4

0.53.2

0.71.9

0.31.6

0.2

RTM3

241000

0.273.8

6.24.22

112032.9

69.87.8

26.63.5

0.62.5

0.31.3

0.20.6

< 0.1

0.5< 0.

1

RTM4

98800

2.4515

36.511.8

> 5000

19.435.2

4.717.6

3.30.6

3.60.5

2.60.5

1.30.2

0.90.2

RTM5

3940

0.725.3

10.910.3

41112.2

23.63.2

11.82.3

0.51.8

0.20.9

0.20.4

< 0.1

0.4< 0.

1

RTM6

6690

1.4612.4

21.823.6

65.319.4

38.85.2

20.34.1

0.83.6

0.42

0.41

0.10.9

0.2

RTM7

186000

1.629.3

233.02

98327.6

53.86.5

233.9

0.94.2

0.63.6

0.82.2

0.31.8

0.3

RTM8

14400

3.7319.5

47.47.09

2120

19.447

5.420.1

40.8

3.90.5

2.70.5

1.30.2

10.2

62 | P a g e

XRD analysis

63 | P a g e

64 | P a g e

65 | P a g e

66 | P a g e

67 | P a g e