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.)
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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.)
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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
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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
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 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