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 [email protected]
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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).
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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
42 | P a g e
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.
45 | P a g e
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