Physical and Chemical Characterization of the Manganese Ore Bed at the Mamatwan Mine, Kalahari Manganese Field

Physical and chemical characterization of the manganese ore bed at the Mamatwan mine, Kalahari Manganese Field

PAULA CRISTINA CANASTRA RAMOS PRESTON

DISSERTATION

Submitted in fulfillment of the requirements for the degree

MAGISTER SCIENTAE

GEOLOGY

in the

FACULTY OF SCIENCE

at the

RAND AFRIKAANS UNIVERSITY

Supervisor: Prof. N.J. Beukes Co-supervisor: Prof. J. Gutzmer

AUGUST, 2001

TABLE OF CONTENTS

Acknowledgements i Abstract ii

Chapter One: Introduction 1.1 Geographical setting 1 1.2 The Kalahari manganese field 2 1.3 Mamatwan mine 3 1.4 Previous work 4 1.5 Objective of this study 8 1.6 Analytical methods 8

Chapter Two: Geological Setting 2.1 Stratigraphy of the Transvaal Supergroup in Griqualand West 12 2.2 Geology of the Kalahari deposit 13 2.3 The geology at Mamatwan mine 17

Chapter Three: Lithostratigraphy 3.1 Introduction 19 3.2 Existing subdivision of the ore bed 20 3.3 New subdivision of the ore bed 22 3.4 Lateral variation 29 3.5 Discussion 29

Chapter Four: Petrography and Mineralogy 4.1 Introduction 35 4.2 Oxide mineralogy 37

4.3 Carbonate mineralogy 38 4.4 Petrographic description of lithostratigraphic zones 42 4.5 Discussion 52

Chapter Five: Geochemistry 5.1 Introduction 55 5.2 Major elements 55 5.3 Trace elements 61 5.4 Loss on ignition 63 5.5 Depositional Geochemical signatures 63 5.6 Carbonate stable isotope geochemistry 64 5.7 Discussion 70

Chapter Six: Density and Washability 6.1 Density measurements 74 6.2 Washability 77 6.3 Discussion 79

Chapter Seven: Conclusions 7.1 The diagenetic evolution of the Mamatwan-type ore 85 7.2 Cyclicity and lateral consistency of the ore bed 88 7.3 Recommendations for future mining and beneficiation at Mamatwan mine 90

References 96 Appendix I: Drill core logs 102 Appendix II: Whole rock geochemical data 127 Appendix III: Carbonate stable isotope geochemistry 130 Appendix IV: Density measurements 135

Acknowledgements

Without the participation and support of the following people and organizations, this study would not have been possible.

A very special thank-you to my supervisors Prof. J. Gutzmer and Prof. N.J. Beukes. For a geologist, life is too short as there are too many unanswered questions to resolve. They somehow managed to find time in between their many travels and conquests to answer mine.

I will always be indebted to my parents who supported me and encouraged me to continue to learn new things. To my husband Douglas who has always been there and always will be.

The staff and students at the RAU Geology Department provided excellent ‘tea-time’ stories. Special thanks to Lisa Carter, Lynnette Greyling, HermanVan Niekerk, Adrian van Bart, Herman Dorland, Dr. J.M.Huizenga, Angus McIntyre and El-El Coetzee.

SAMANCOR for financial support and E. Swindell, R. Arnot and E.P. Ferreira for their continued interest and participation.

Special thanks to Janet Oosthuizen from Mintek, Uwe Horstmann at the Council for Geoscience and personel from Billiton Process Research for providing valuable information.

Abstract

The Mamatwan mine is situated at the most southern end of the world’s largest land- based resource of manganese, the Kalahari manganese field. The mine is operated by South African Manganese Corporation Limited (SAMANCOR) and is the largest open pit manganese mine in the world. The sedimentary manganese ore bed is interbedded with iron-formation of the Hotazel Formation of the Early Paleoproterozoic Voëlwater Subgroup of the Transvaal Supergroup. The open pit Mamatwan mine has a proven economic ore reserve of between 300 and 400Mt and produces 1.2Mt of manganese ore annually, of which 0.5Mt of ore is beneficiated and shipped through the harbour at Port Elizabeth. The remaining ore is railed to ferro-alloy plants at Meyerton and Newcastle.

Carbonate-rich manganese lutite mined at the Mamatwan Mine is widely known as Mamatwan-type ore. It has a manganese content ranging from 30 – 38%. Only a small portion (15m of a total thickness of 49m) of the ore bed, containing an average of 38% Mn, is being mined and processed at present. The larger portion of the ore bed is not utilized. This study focuses on the physical and chemical characteristics of the ore bed in more detail in order to make suggestions on how to a) reduce waste by upgrading the upper parts of the lower manganese ore bed, or b) to improve the current recovery from the present economic zone. A second part of this study pays special attention to the lithostratigraphy of the lower manganese ore bed. The focus is on the paragenetic sequence and the diagenetic evolution of the braunite lutite that constitutes the manganese ore.

The Mamatwan-type ore can be described as diagenetic to very low-grade metamorphic carbonate-bearing braunite manganolutite. Based on geochemical and mineralogical data, the lower manganese ore body was previously subdivided into eleven lithogically distinct zones. Based on detailed diamond drill core logging and with the aid of geochemical and physical data of two selected drill cores, an additional thirteen subzones were identified in this study. These new subzones were found to be consistent across the entire study area, located to the west and north of the present Mamatwan open pit.

The paragenetic sequence recognised in the ore of the lower manganese ore bed can be subdivided into four stages, namely: (a) sedimentation, which is represented by fine lamination and the presence of fine-grained “dusty hematite”. (b) early diagenesis as represented by micritic carbonate matrix and possibly braunite, (c) late diagenesis or low-grade metamorphism are represented by coarse grained hausmannite, specularitic hematite, partridgeite and Mn-calcite, and supergene alteration that occurs immdediately below the contact of the ore bed to the unconformably overlying Tertiary Kalahari Formation. This supergene altered zone is marked by the presence of Mn4+ oxides such as cryptomelane, manjiroite, romanechite and pyrolusite, in addition to barite.

The results obtained in this study permit definition of two sedimentary cycles within the manganese ore bed at the Mamatwan mine. Both cycles are defined by a carbonate-rich finely laminated zone at the base, overlain by a central manganese-rich economic zone,

ii iii capped by manganese lutite that is enriched in carbonate ovoids. The two manganese- rich zones are known as the M (lower) and X (upper) zone, and are characterized by the replacement of carbonate ovoids by hausmannite. The two Mn-rich zones are chemically and physically almost identical, with the M zone 7.5m thick and the X zone 5.5m thick. However, in the present mining configuration only the M zone is being mined. The most important result arising from the present study is the recommendation to restructure the future mining operation in order to mine not only the M zone, but also the X zone.

iii Introduction 1

Chapter One Introduction

The Mamatwan manganese mine is an open pit operation owned by Samancor Limited. It started operation in 1963 and was initially developed to provide ore with a high manganese to iron ratio, suitable for the local ferro-alloy industry. The mine currently produces approximately 100 000 tons of manganese ore a month (1.2Mt annually) of which some 0.5Mt of beneficiated ore is shipped through the harbour at Port Elizabeth and the remaining ore is railed to ferro-alloy plants at Meyerton and Newcastle (Samancor, 1994).

The manganese ore bed at Mamatwan mine contains low-grade ore with a manganese content ranging from 30 – 38 wt% Mn. The ore bed is some 49m thick but only a 15m thick section, containing on average 38 wt% Mn is currently being mined and processed. The remaining 35 meters of the ore bed are not being utilized. The focus of this project is to suggest a means of utilizing a larger thickness or more zones of the ore bed so as to reduce waste and possibly improve the manganese grade of the ore mined. This is to be achieved by carefully examining the physical and chemical characteristics of the manganese ore bed in the mine lease area.

1.1 Geographical Setting Mamatwan mine is located in the southern-tip of the Kalahari manganese field in the Griqualand West region of the Northern Cape Province, South Africa (Fig.1.1A). The mean elevation in this area is between 1100m to 1400m and the morphology is dominated by flat plains intersected by generally N-S striking ranges of the Asbestos Hills, the Klipfontein Hills and the Gamagara Ridge. The plains are covered by thick calcretes and wind blown Kalahari sands that obscure the sub-outcrop with the exception of Black Rock, a small hillock of the manganese-bearing Hotazel Formation (Fig.1.1B).

Introduction 2

1.2 The Kalahari manganese field The Kalahari manganese field is made up of five structurally preserved erosional relics of the Hotazel Formation, consistng of iron-formation with interbedded units of manganese ore. The largest of the five deposits is the Kalahari deposit (Gutzmer, 1995) (Fig.1.1B), which contains 80% of the worlds known mineable manganese resource (Samancor, 1994). This deposit has a strike length of 41km and a width varying between 5 and 20km (Samancor, 1994). To the east of the Kalahari deposit, lie the Hotazel and Langdon- Annex deposits, which have virtually been mined out. The remaining two deposits, Avontuur and Leinster (Fig.1.1A) are small and of sub-economic grade and lie to the north of the main deposit. Several mines, presently in operation in the Kalahari deposit, are the Mamatwan Mine (open pit), Gloria Mine (underground), N’chwaning II (underground), Wessels (underground), and Langdon West (open pit) (Fig.1.1B). These mines are operated by three companies, SAMANCOR (South African Manganese Corporation Limited), ASSMANG (Associated Manganese Mines of South Africa Ltd.), and National Manganese Ltd.

Two main ore types are present in the Kalahari deposit, namely low-grade primary sedimentary Mamatwan-type ore (MMT) and high-grade Wessels-type ore. The high- grade Wessels-type ore represents a hydrothermal alteration product of low-grade Mamatwan-type ore (Kleyenstüber 1985, Gutzmer & Beukes 1995). Its occurrence is restricted to the faulted northwestern part of the deposit. It is typically coarse-grained and composed mainly of hausmannite, braunite II, bixbyite, and braunite. In contrast, Mamatwan-type ore (MMT) is best described as finely laminated, microcrystalline braunite-lutite composed of Mn-bearing carbonates such as kutnahorite and Mn-calcite together with braunite and hematite. The occurrence of mm-sized carbonate ovoids and stratiform carbonate laminae enhance the finely laminated appearance of the ore. The ∗ presence of coarse crystalline hausmannite and partridgeite , associated with Mn-poor calcite, derived from the metamorphic oxidation of kutnahorite or Mn-calcite

∗ Partridgeite was originally described by De Villiers (1943) as a new mineral species, but was never recognized by the IMA (International Mineralogical Association) and is generally regarded as iron-poor bixbyite. Studies to prove the identity of Partridgeite as a separate mineral are in progress. Introduction 3

(Kleyenstüber, 1984, Nel et al.1986), suggests that the Mamatwan-type ore has been subjected to lower greenschist facies metamorphism at most (Kleyenstüber, 1984).

1.3 Mamatwan mine Mamatwan mine (Fig.1.1B and Fig.1.2A) exploits ore from the lowermost of three braunite-kutnahorite lutite beds, intercalated with iron-formation of the Hotazel Formation of the Transvaal Supergroup (Beukes, 1983). In the mine lease area the manganese ore bed has a thickness of up to 49m and is unconformably overlain by calcrete of the Kalahari Formation (Fig.1.2B). Undulations of the ore bed are a result of gentle folding caused by mild west to east directed compression that resulted in thrust duplication of the Hotazel Formation in the northwestern part of the Kalahari manganese field (Beukes, 1983). Two minor E-W striking faults with displacements of 4m and 2m respectively are present in the southwestern region of the mine area (Fig.1.2A). The ore bed dips gently at 5° to 8° to the west below the Kalahari Formation.

B. Leinster deposit A.

E Botswana Mozambique

24S Avontuur deposit

Namibia

Kuruman z

Lesotho Wessels Mine Black Rock Mine N'chwaning Mine South Africa N N high grade ore Hydrothermally Gloria Mine

0500E altered area Km containing high grade Hotazel Mine Northern Cape Province Wessels-type ore Devon Low grade Griqualand West Region Mine Langdon sedimentary Annex Mine Mamatwan-type ore

Smartt Mine Fault Middelplaats Thrust Fault Mine Mamatwan Mine 0 5 10Km

Figure 1.1 (A) Location of the Griqualand West region in the Northern Cape Province of South Africa. (B) Enlarged view of the Kalahari manganese field showing the five deposits and the location of Mamatwan mine, as well as the distribution of the low grade Mamatwan type ore and high grade Wessels type ore in the main Kalahari deposit. Introduction 4

The lower manganese ore bed is divided into three zones for mining purposes, namely: the top, middle and bottom cuts (Fig.1.2A). The top cut is also referred to as the uneconomic upper zone. It is 29m thick, with a manganese content averaging only 30wt% Mn. The 15m thick middle cut or central economic zone, has a manganese content of 38wt% Mn and the uneconomic bottom cut is only 6m thick and contains an average of about 30wt% Mn. In the open pit mining operation the top cut is stockpiled and is later used as backfill, whereas the bottom cut is left behind in the floor of the pit.

The economic ore is transported to an in-pit primary crusher, which reduces the particle size for transport on a conveyor belt system to the secondary crusher and wet screening plant. Lumpy ore, produced in the screening plant ranges from –63mm to +10mm and has a manganese content of 37wt% to 38wt%, and fines (-10mm) that contain 35wt% to 37wt% Mn (Nel et al., 1986). A tertiary crusher reduces the lumpy ore to smaller particles (-6mm or –19mm) which are fed to the dense medium separation plant. The ore is then sintered to drive off CO2 and to form a hard product with Mn concentrations exceeding 44wt% Mn (Samancor, 1994).

1.4 Previous work Rogers (1907) and Hall (1926), were the first to make mention of the only outcrop of the Hotazel Formation at Black Rock, as being a “black rock” interbedded with “bands of bright red rock” (Rogers, 1907). It was Boardman (1941) that gave a first detailed description of the manganese ore exposed at the Black Rock outcrop and it was his contribution that unvailed the economic potential of the manganese ores buried beneath the Kalahari sand.

Pit outline

M G A O M O Benches A. L A D T 3 TC W 2 A 9 MC N 3 BC B. 3 1 Sand Gravel f 4.5m f Kalahari Kalahari Calcrete Formation Formation f 2m Unconformity f Braunite lutite

Jacobsite-hematite lutite Hotazel Hematite lutite Formation

N Legend Banded Iron Formation BC bottom cut MC middle cut A TC top cut D A M Lava Ongeluk Cryptomelane enrichment along the S 3 lava suboutcrop of the economic ore zone 2 8 against the Kalahari Formation

Fault with fault breccia f f 500m f f Fault

Figure 1.2 (A) Map of Mamatwan mine showing the outline of the open pit, subdivisions into three benches and the location of the two faults 5 (modified after Gutzmer and Beukes, 1996). (B) Stratigraphic succession of the lower manganese ore body at the Mamatwan mine. Introduction 6

Later, the geology of the Black Rock outcrop and general surveys of the geology and extent of the Kalahari deposit and its outliers at Hotazel and Langdon-Annex were published by De Villiers (1960) and Boardman (1964). In the late 1960’s, De Villiers (1970) performed a first regional mineralogical study of the Kalahari deposit and the two graben structures to the east. He inferred a chemo-sedimentary origin for the carbonate- rich manganese ore and considered localized thermal metamorphism and supergene alteration as important factors for the enrichment of some of the ores. Another important genetic process envisaged by Söhnge (1977), was a microbially mediated volcano- sedimentary origin of low-grade ores, followed by structurally controlled alteration caused by circulating meteoric water.

Button’s (1976) review showed the correct stratigraphic position of the interbedded succession of manganese and iron-formations in the Voëlwater Subgroup of the Postmasburg Group. Another study that proved valuable for the understanding of the geology of the Kalahari manganese field was the contribution by Beukes et al. (1982), who recognized the presence of three chemo-sedimentary cycles in the Hotazel Formation. The author stressed that the manganese ores occur in the Hotazel Formation of the Voëlwater Subgroup and constitute the center of the three chemo-sedimentary cycles composed of jaspilitic iron-formation, hematite lutite, jacobsite lutite and braunite lutite and established a tentative sedimentary model for its deposition. This model was later challenged by Cornell and Schütte (1995) who proposed a volcano-sedimentary origin of the Kalahari manganese deposit in a proximal mid ocean ridge-type environment very similar to modern marine hydrothermal manganese deposits.

Kleyenstüber (1984, 1985) focused on the mineralogy of the Voëlwater Subgroup in general and the strata of the Hotazel Formation in particular. He identified a number of previously unnoted minerals and subdivided the ores into three distinct types, namely: low-grade metamorphic Mamatwan-type ore, high-grade Wessels-type ore and uneconomic jacobsitic ore.

Introduction 7

Several other studies have concentrated on the geological setting of specific mines, for example the contributions by Jennings (1986) and Grobbelaar (1985) that provide short descriptions of the geology and mining operations at Middelplaats and Nchwaning mines. Mamatwan mine was the focus of studies by Kleyenstüber (1979) and Nel (1984). An especially important contribution was the comprehensive description of Mamatwan mine published by Nel et al. (1986), a summary of the dissertation of Nel (1984) that provided a first detailed mineralogical and geochemical study of the manganese ore at Mamatwan mine. The results of the latter dissertation resulted in the subdivision of the lower manganese ore bed into eleven macroscopically distinct sub-zones. It is this subdivision that is used to guide the mining operation today.

Studies by Miyano and Beukes (1987, 1988) were dedicated to delineate the physiochemical conditions of the formation of Wessels-type ore. Gutzmer (1993), Burger (1994), Gutzmer and Beukes (1995) and Beukes et al. (1995) established a comprehensive model for this hydrothermal alteration process. It resulted in characteristic lateral zonation of various ore types and grades next to a system of normal faults that acted as feeder channels for hydrothermal fluids.

Kleyenstüber (1985),Tsikos and Moore (1997) were the only to examine the Hotazel banded iron-formation surrounding the manganese ore beds. From geochemical and petrographical data they concluded in favour of a chemo-sedimentary origin for the Hotazel Formation. Tsikos and Moore (1997) further suggest that future emphasis should be placed on constraining the physiochemical processes pertaining to the deposition of the three-fold Fe-Mn succession. Consequently, the role of volcanic activity for the origin of the Hotazel Formation has been reduced to the possibility of constituting a distal – both geographically and temporally – metalliferous source, with only minor influences on subsequent depositional processes.

An interesting new view was recently presented by Tsikos and Moore (1998) and Kirschvink’s et al. (2000), who proposed that the formation of Fe and Mn-rich sedimentary rocks of the Hotazel Formation may have happened in the aftermath of a Introduction 8

Paleoproterozoic Snowball Earth, very similar to the model envisaged for Neoproterozoic iron and manganese formations (Kirschvink, 1992).

1.5 Objective of this study Previous work by Nel (1984) and Nel et al (1986) provided a fundamental understanding of the mineralogy and geochemistry of the manganese ore body at Mamatwan mine. As mentioned earlier, even though the mine has a large proven ore reserve, only a 15m thick zone is considered economical to mine as it contains ore with about 38wt% Mn. The larger part of the ore bed remains, however, unutilised.

The focus of this thesis is to study the physical and chemical characteristics of the ore body in more detail and make suggestions on how to a) reduce waste by upgrading larger portions of the manganese ore bed and/or b) to improve the current recovery from the present economic zone. A second important aspect of the project – which pays special attention to the lithostratigraphy of the lower manganese ore body – involves the paragenetic sequence and the diagenetic evolution of the braunite lutite that constitutes the manganese ore bed.

1.6 Analytical methods Field work included the detailed logging of 22 selected drill cores from the Mamatwan mine lease area and familiarization with the mining process and beneficiation of the manganese ore. As this study required detailed analysis with special focus on the physical characteristics of the lithologies, seven drill cores were logged on a centimeter scale. A further 15 drill cores were logged to test the lateral consistency of the lithostratography over a large area in the ore bed. Of the 22 drill cores, two were selected for in-depth analytical studies, namely: G558, situated to the west of the present day open pit and G552, situated to the northeast of the pit.

Both drill cores were halved using a diamond saw, leaving a representative sample of the drill cores at the Hotazel core shed. Of the two quarters of each drill core, one was Introduction 9

prepared for geochemical analyses, while polished thin sections were prepared and small blocks were selected for density measurements of the second quarter. The remaining material from the second quarter was submitted for washability tests by Billiton Process Research, Randburg.

Twenty six polished thin sections from drill core G552 and 34 from drill core G558 were carefully selected to be representative of all lithostratigraphic zones and sub-zones. They were studied using reflected light microscopy on a Leica DMLP research microscope at the Department of Geology at RAU and a JEOL JSM 5600 Scanning Electron Microscope at the Central Analytical Facility at RAU.

For geochemical work, homogeneous powder samples for each zone and sub-zone of the ore bed were prepared. A jaw crusher was used to produce <1.5cm sized chips. These chips were then milled in a Sieb Technik disc swing mill using a Cr-steel body and rings. The resulting large volume of sample material for each zone and sub-zone of each drill cores was homogenized by quartering. Small aliquots of the 20 samples of each drill core were used for whole rock geochemical analyses, X-ray powder diffraction and carbonate carbon stable isotope analyses.

Whole rock geochemical analyses were performed on powdered sample material by B&B/Set Point Laboratories (Johannesburg), using standard X-ray fluorescence techniques. Fused beads were used for major elements and pressed powder pellets for trace elements and Na. A second set of samples was analyzed by Mintek (Randburg) for comparison, using a variety of suitable techniques (ICP-MS, ICP-OES, AAS). Loss of ignition measurements were performed at the Department of Geology at RAU at a temperature of 1200°C in a muffle furnace.

A PHILIPS PW 1710 diffractometer at the Central Analytical Facility at RAU was used to conduct X-ray powder diffractometry. The measurements were carried out with the following diffractometer settings: Tube anode material: Co-Kα radiation (wavelength kα- Introduction 10

1.789Å); Generator tension: 40kV; Generator current: 30mA; Angle range: 5-80° 2Θ; Step size: 0.02°2Θ; Scan rate: 4s per step; Scan type: step.

Carbon and oxygen stable isotope analyses of carbonates were performed at the Council for Geosciences (CGS) in Pretoria under guidance of Dr. U. Horstmann. The technique used was modified after McCrea (1950). Twenty mg of each powdered sample and 2ml of 100% H3PO4, prepared after the method of Coplen et al. (1983), were enclosed separately in a reaction vessel. After evacuation, both sample and acid were thermally equilibrated in a water bath for about 1 hour and subsequently reacted. Equilibration/reaction temperature was 50°C for all samples. The samples were reacted for 18-25 hours.

Capturing of the CO2 gas was carried out by the author, using the following procedure:

The liberated CO2 was purified cryostatically through cold traps using dry ice and liquid nitrogen in order to remove water and other condensable gases. The yield was measured and found in all cases to be about 100%, which indicated complete reaction of the sample material as far as can be judged from the given mineralogical composition of carbonate species.

The isotope analyses were performed by Dr. U. Horstmann using a Finnigan MAT-251 gas-source mass-spectrometer with a sequential, multi-port, sample inlet system. Sample isotope ratios were measured against a working gas, taken from a commercially available

CO2 gas bottle, which was calibrated and controlled against internal laboratory standards included in each batch of samples.

The occurrence of more than one carbonate phase in most of the samples posed a problem for the analytical procedure as well as for the interpretation of the results. A physical mineral separation was impractical and therefore whole samples had to be reacted. The sequential reaction of carbonates as routinely applied to calcite-dolomite mixture could not be applied. The reaction of kutnahorite with H3PO4 was completed below 50ºC, much faster than for dolomite. The factor for the fractionation of oxygen Introduction 11

pertaining to the reaction of ankerite with phosphoric acid at 50ºC was therefore used to correct the results. A calibration curve was calculated for carbon and oxygen respectively and used to correct the mass-spectrometric analytical results. Repeated analysis of internal standards (MHS1 and MDS1) indicated a analytical reproducibility of ±0.1 per mil (1σ) for both δ13C and δ18O values. Calibration values and calculated regression lines are listed in appendix III.

Whole rock density measurements were conducted on both small chips (<1cm) and medium (±5cm) sized blocks at the Deparment of Geology at RAU, using a Sartorius laboratory scale (Appendix IV).

Geological Setting 12

Chapter Two Geological Setting

2.1 Stratigraphy of the Transvaal Supergroup in Griqualand West The manganese ore bed of Mamatwan mine forms part of the late Archean to Paleoproterozoic Transvaal Supergroup in Griqualand West (Fig.2.1). It is the earliest of three manganiferous cycles, bound by iron-formations of the Hotazel Formation in the Voëlwater Subgroup of the Postmasburg Group (Beukes, 1983).

The Transvaal Supergroup in Griqualand West is subdivided into two groups, namely the Ghaap Group, composed essentially of chemical sedimentary rocks, and the overlying Postmasburg Group, which is a mixed volcanic and chemo-sedimentary succession (Fig.2.2) (Beukes, 1986).

The Postmasburg Group, which hosts the Hotazel Formation, consists from the base upwards of the Makganyene Diamictite, followed by andesitic pillow lavas, hyaloclastites and jaspilites of the Ongeluk Formation (Fig.2.2). The conformably overlying Hotazel Formation is composed of three manganiferous units each constituting the center of three symmetrical iron-formation - hematite lutite - braunite lutite - jacobsite lutite cycles (Fig.2.3) (Beukes, 1983). The lower manganese ore bed contains virtually all the manganese ore reserves and accounts for all production in the Kalahari manganese field today. The lower manganese bed reaches a maximum known thickness of about 49m at Mamatwan mine and ranges between 4-8m in the Wessels and Nchwaning (Fig.1.1) mining areas. Limestone and dolomite of the Mooidraai Formation conformably overlie the Hotazel Formation (Tsikos, 1999). Together, they constitute the Voëlwater Subgroup of the Postmasburg Group. The Mapedi/Gamagara unconformity separates the Voëlwater Subgroup from overlying iron ore pebble conglomerates, shales and siltstone of the Mapedi Formation. The top of the Transvaal Supergroup is represented by the Neylan conglomerate overlying the quartzites of the Lucknow Formation (Dorland, 1999).

Geological Setting 13

2.2 Geology of the Kalahari deposit The manganese ores of the Kalahari deposit occur in a shallow, elongated, NNW-SSE trending structurally preserved basin, dipping gently from east to west and extending approximately 41km long in NS and between 5 and 20km in EW direction (Fig.2.1B) (Grobbelaar et al. 1995). The deposit can be subdivided into a large south-eastern area hosting low-grade sedimentary Mamatwan-type ore, and a much smaller north-western area of hydrothermally reconstituted high-grade Wessels-type manganese ore (Fig.1.1B) (Kleyenstüber, 1984).

The low-grade Mamatwan-type ore constitutes approximately 93% of the ore reserve of the Kalahari manganese field and has a manganese content of 20-38 wt % Mn (Kleyenstüber, 1984). The Mamatwan-type ore is dark brown to brown/grey in colour with white and pink carbonate ovoids and laminae occurring throughout. The major oxide minerals are braunite and hausmannite, while the carbonates in the ore are kutnahorite and calcite. The high-grade Wessels-type ore has a manganese content of 45- 60 wt % Mn and is believed to have been hydrothermally upgraded from Mamatwan-type ore by hydrothermal fluids introduced along a series of north-south oriented normal faults (Gutzmer & Beukes, 1995). Wessels-type ore is black, massive, coarse crystalline and displays signs of recrystallization and alteration. Original carbonates present in the Mamatwan-type ore are replaced by a mineralogically complex assemblage of coarse crystalline oxides, such as braunite II and hausmannite and more than one hundred other minerals (Gutzmer & Beukes, 1995).

NE-SW trending dykes and sills that occur throughout the Kalahari manganese field are of pre-Gamagara/Mapedi age as they do not penetrate the Mapedi Formation. Duplication of the Ongeluk, Hotazel and Olifantshoek successions in the north-western corner of the Kalahari deposit is due to the Black Ridge thrust which is part of the nappe of the Kheis Orogeny (Grobbelaar et al. 1995). The south-eastern part of the basin is structurally less complex with only minor NW-SE normal faults displacing the Hotazel Formation by a few metres in the Mamatwan mine area.

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MONTEVILLE F U D G A O S R R LOKAMMONA F T G D T I B M BOOMPLAAS F U S H C

VRYBURG F S N 0 20 40 km VENTERSDORP/ ALLANRIDGE LAVA

Figure 2.1. A. Small scale geological map showing the Griqualand West basin and the Transvaal basin on the Kaapvaal Craton. B. Geological map of the Transvaal Supergroup in Griqualand West showing distribution of major stratigraphic units, the location of the Kalahari manganese field and the N-S trending Black Ridge thrust (modified after Beukes, 1983). 15 P U P O U ) R O A G P R G R ( U

G E Formation LITHOLOGY O E B P R G U U G A S S calcrete, sand, marl, clay Kalahari Kalahari Unconformity O O

R diamictite

A Dwyka

K Dwyka Unconformity K

E conglomerate, quartzite S

O Volop I H

S E T

H V V (1) 1.93 N Hartley A andesitic lava K V F V I L

O Neylan quartzite, conglomerate Neylan unconformity Lucknow quartzite

shale, siltstone Mapedi/ Gamagara aluminous shale Fe-pebble conglomerate Mapedi / Gamagara Unconformity Mooidraai dolomite R L

2.39 E (2) : E

T braunite-lutite O A

V Fe-lutite G W Hotazel R Fe-rhythmite U

B V V S V andesitic basalts A V M Ongeluk V hyaloclastite T S V V pillow lavas O P Makganyene diamictite Makganyene Unconformity S L E Griquatown Fe-lutite W U

(3) 2.43 E H S

E Fe-rhythmite B Kuruman S Manganore A Iron-Formation (4) 2.55 Gamohaan dolomite and limestone L A

A Kogelbeen dolomite and limestone V S

N Klippan ch ch ch cherty dolomite A ch ch ch R D T N

A Papkuil dolomite and limestone R L L

E c c c B Klipfontein c c c cherty dolomite

P c c c P M A A A

C Fairfield H G

dolomite, limestone

Reivilo

Monteville dolomite, shale - S Lokammona shale, dolomite T D I shale, dolomite M Boomplaas F I H R C quartzite, shale D S Vryburg (5) 2.70 Unconformity P

R V V O

D V V S basaltes, rhyolites R V E V graywackes, shale T

N V V E V Figure 2.2. The lithostratigraphy of the Transvaal Supergroup in Griqualand West showing the stratigraphic setting of the Hotazel Formation (Gutzmer, 1996, Dorland, 1999). Radiometric ages from literature sources: (1) Cornell et al. 1998. (2) Bau et al. 1999 (3) Trendall et al. 1990. (4) Sumner and Bowring 1996 and (5) Altermann and Nelson 1998. 16

Prograding Shallow part of carbonate slope platform sequence

Platform slope

Carbonate turbidites

Pink dolomite Mooidraai Fm

Cherty ankeritic and kutnahoritic toe-of-slope dolomite slump breccia B

Chertfied and p

p sideritized distal Sand u

u carbonate turbidites Gravel

o o

r r

o G G

r Mn1 Cycle 3

g Kalahari

b Basin with

g Calcrete

u volcanogenic- Formation r

S sedimentary cycles

t s Cycle 2 a Mn2 Unconformity

a Hotazel Fm

: e

o V Cycle 1 P Braunite- lutite

R e g re ss io n Jacobsite-hematite lutite Hematite lutite Hotazel Mn3 Formation

on si es gr Banded Iron Formation ns ra T

Volcanic Cycles Ongeluk Lava Lava Ongeluk lava

Carbonate-rich Manganese ore Limestone Carbonate-poor IF Iron Formation

Ongeluk lava

Figure 2.3. A. Profile of the Hotazel and Mooidraai Formations illustrating the stratigraphic setting of the three manganese units interbedded with iron-formation. Note cyclical repetition of lithofacies in the Hotazel Formation. B. Stratigraphic succession at Mamatwan mine. Note the unconformity at the base of the Tertiary Kalahari Formation. The lower manganese ore body is up to 49m thick at Mamatwan mine (modified after Nel et al., 1986). Geological Setting 17

2.3 The geology at Mamatwan mine The Mamatwan mine is situated in the most southern part of the Kalahari deposit. Only the lowermost of the three manganese ore beds in the Hotazel Formation is exposed at Mamatwan mine and comprises of braunite lutite (Mamatwan-type ore). It ranges in thickness from 30m in the eastern part of the mine, to 49m in the west. This decrease in thickness to the east is the result of removal of the upper parts of the ore bed by erosion along the unconformity at the base of the Tertiary Kalahari Formation. The ore bed dips 8º to the west, therefore preserving more of the stratigraphy of the Hotazel Formation towards the west. The Mamatwan mine is structurally simple with the exception of gentle folding causing undulations of the ore body and two WNW-ESE trending faults in the southwestern parts of the mine area (Fig. 1.2.).

The manganese ores at Mamatwan mine show the effects of at least four post- depositional alteration events (Fig.2.4) (Gutzmer, 1996). The first event is tentatively attributed to stratabound metasomatic fluid infiltration during low-grade metamorphism. ∗ It led to the replacement of Mn carbonates by hausmannite, partridgeite and manganite (Gutzmer and Beukes, 1996) (Fig.2.4B). This event is thought to have affected manganese ores throughout the Kalahari manganese field. Two periods of structurally controlled hydrothermal metasomatic alteration along faults and joints succeed stratabound metasomatism (Gutzmer and Beukes, 1996). The first of these involved the introduction of epithermal fluids along veins and joints, causing local reduction and bleaching of the manganese ore that is observed along normal faults throughout the Kalahari manganese field (Fig.2.4C). The second period introduced low temperature, oxidizing ground water ascending along reactivated faults and caused intensive oxidation and carbonate leaching of the adjacent manganese ore (Fig.2.4D). The final event, caused by supergene alteration by descending groundwater took place along the Kalahari unconformity and led to the formation of cryptomelane, pyrolusite and goethite (Fig.2.4E) (Kleyenstüber, 1993).

∗ Partridgeite was originally described by De Villiers (1943) as a new mineral species, but was never recognized by the IMA (Internation Mineralogical Association) and is generally regarded as iron-poor bixbyite.

Geological Setting 18

lithostatic pressure A. Deposition A: Deposition of braunite lutite (or a precursor) as part of the succession of Mooidraai dolomite V W chemogenic sediments of the Hotazel X Formation. BIF Y Hotazel Formation Z Diagenetic or braunite lutite Mn 1 M metamorphogenic B : Metamorphic overprint; stratabound fluid fluid flow causes C local oxidation of flow results in local oxidation of kutnahorite. carbonates to hausmannite, manganite Ongeluk lava H and partridgeite. N L

B. Metamorphism

C. Hydrothermal alteration adjacent to veins and joints C: Ferruginization and bleaching of ores along joints and faults by hydrothermal fluids that deposit hematite, pyrite,

braunite-lutite chalcopyrite, calcite, kutnahorite, chalcedony, and talc.

hydrothermal fluid flow

D. Pre-Kalahari alteration and hydrobrecciation D: Over-pressured ground water ascends along reactivated faults, leading to intensive brecciation and oxidative

altered ore altered ore alteration of manganese ores along faults. Fault breccias are cemented by sparitic calcite or dolomite, chalcedony, and quartz.

ascending groundwater (?)

E. Post-Kalahari calcretization and supergene weathering Descending meteoric water

Kalahari Formation Kalahari E: Post-Kalahari supergene alteration. supergene ore unconformity

Figure 2.4. Epigenetic alteration of manganese ores at Mamatwan mine (modified after Gutzmer et al. 1996). Lithostratigraphy 19

Chapter Three Lithostratigraphy

3.1 Introduction Twenty-two diamond drill cores were selected for this study in the area where mining is to take place in the next 5-10 years. Two of these cores, G558 and G552 (Fig.3.1), were selected for detailed studies. Drill core G558 represents a complete section of the lower manganese ore bed with a thickness of 46m and is located to the west of the present open pit. G552 is representative of the lower 35m of this bed with the top most part removed by erosion prior to deposition of the Tertiary Kalahari Formation. The top of the lower ore bed has, in both drill cores, been affected by supergene enrichment, but more so in G552, which is situated in the eastern part of the mine closer to the present land surface (Fig.3.1).

G540

G466 G531

G511 G548 E-W section N-S section

G416

G433 G429

G515

G478 250m

G559 N G445

G565 G327

G512

Figure 3.1 Map of Mamatwan mine illustrating the exact location of 22 drill cores selected for this study in the mine lease area. Drill cores G558 and G552 that are especially marked were elected for detailed studies. Note the location of N-S and E-W cross sections illustrated in Figures 3.7 and 3.8.

Lithostratigraphy 20

Low-grade Mamatwan-type ore is present in both cores. It appears finely laminated with a dark brown to dull-grey colour. The ore consists of fine grained braunite lutite with ellipsoidal and spheroidal ovoids, which range from less than 1mm up to 5mm in size. These white, pink and grey ovoids contribute to a spotted appearance of the ore. Carbonate laminae accentuate the sedimentary bedding. Nel’s (1984) subdivision of the ore bed into eleven lithologically distinct zones (Fig.3.2) was based on macroscopically distinct variations of the ore, with regards to presence, distribution, colour and size of these carbonate ovoids and laminae. During this study a more detailed examination of the lower manganese ore bed at Mamatwan mine enabled further subdivision of the eleven zones as defined by Nel (1984).

3.2 Existing subdivision of the ore bed The subdivision of the ore bed into eleven lithologically distinct zones, as well as the tentative identification of three sedimentary cycles within the ore bed at the Mamatwan mine by Nel (1984), was based on vertical variations of physical characteristics of the ore on a macroscopic scale (Fig.3.2). The subdivision was backed by the visual examination of numerous drill cores, as well as mineralogical and whole rock geochemical data (mostly major elements). Nel (1984), gave detailed descriptions of the different ore zones. His findings are summarized as follows.

The ore bed is immediately underlain by the O-zone, a reddish-purple hematite lutite containing red carbonate laminae. This transition bed (O-zone) grades upwards into the L-zone, which is a light purple lutite containing pink carbonate laminae and small red- brown carbonate ovoids. The brown-purple lutite of the B-zone follows with small brown ovoids and white carbonate laminae. The N-zone is best described as a grey coloured manganese lutite with alternating bands of brown and white concretionary ovoids and thin white carbonate laminae. The overlying H-zone is finely laminated and contains light-grey carbonate laminae. Brown carbonate ovoids are present in the carbonate rich laminae. The C-zone is also laminated and composed of a light-grey carbonate-rich manganese lutite containing white carbonate laminae and small brown and

average cycle thickness zone lithology (m) H Purplish red hematite lutite with pink and white carbonate transition H F laminae. bed

Light grey massive carbonate-rich manganolutite with 4.2 small white carbonate ovoids and thin white and pink V carbonate laminae.

Dark grey and light grey banded braunite lutite with 2.2 W small white and brown carbonate ovoids. e n o

Dark grey braunite lutite with abundant large concentrically z

3 e

banded white carbonate ovoids. r

3.8 X o

e d

Brown to white carbonate nodules. Contorted marker. a r g

Massive dark grey to brownish gray speckled braunite o l

lutite with abundant brown carbonate ovoids of various e

4.4 Y p

size and outlined by coarser grained braunite and hematite. p u

Massive dark grey speckled hematitic braunite lutite with abundant brown carbonate ovoids of various size 4.9 Z outlined by coarser grained braunite and hematite.

Dark grey massive braunite lutite with large white 2 5.0 M carbonate ovoids with inclusions of hausmannite. e n o z Dark grey and light grey banded braunite lutite with white e r

carbonate laminae and abundant small brown and white o 5.5 C e

carbonate ovoids with some dark grey braunite bearing d a ovoids. r g

c i m o n o

Irregularly banded hausmannite bearing braunite lutite c e

consisting of light grey braunite lutite beds with small l a r

brown carbonate ovoids alternating with reddish brown t

5.6 H n hausmannite bands displaying crosscutting contacts with e c braunite lutite beds.

Dark grey braunite lutite with beds rich in large white carbonate ovoids alternating with beds containing brown 3.6 N carbonate ovoids. Some braunite ovoids and thin white 1 carbonate laminae. e

Purplish grey braunite lutite with abundant brown d

L a

3.0 r carbonate ovoids. e g n

o w z

o l e

r Light purple jacobsite hematite lutite with prominent l o a s

B brown and pink carbonate laminae and small reddish brown a

3.0 b carbonate ovoids.

H Purplish red hematite lutite with prominent pink carbonate transition H O laminae. bed

Figure 3.2. Lithostratigraphic subdivision of the manganese ore bed at Mamatwan mine as established by Nel (1984). Lithostratigraphy 22 white carbonate ovoids. The M-zone is a massive dark-grey manganese lutite with abundant white and grey carbonate ovoids.

The Z-zone is a massive dark grey manganese lutite containing brown carbonate ovoids of different sizes as well as white carbonate laminae. The Z-zone has a typical speckled appearance caused by many different ovoid sizes. The Y-zone has a brown lutite matrix with brown carbonate laminae and many small ovoids, as well as small pinkish coloured carbonate lenses. The overall appearance of the X-zone is described as a dark grey finely laminated carbonate rich manganese lutite with large white carbonate ovoids that have a concentric internal texture. The W-zone is grey-brown and finely laminated, made up of alternating dark and light grey laminae with small white and brown carbonate ovoids. The V-zone is massively textured and grey in colour, very carbonate-rich with fine white and pink carbonate laminae and small white carbonate ovoids. The F-zone is brown- purple in colour and contains prominent pinkish-white carbonate laminae.

The R-zone overlies the manganese ore bed unconformably and is a steel-grey coloured breccia with manganese ore and calcrete of the Tertiary Kalahari Formation. This zone is not part of the normal lithostratigraphy but rather represents the supergene altered portion of the original ore bed.

3.3 New subdivision of ore bed Detailed studies of the ore bed at Mamatwan mine have revealed the possibility to further subdivide the X, Y, M and C zones into subzones that are macroscopically distinct and laterally consistent. All existing subdivisions as described by Nel (1984) remain essentially valid but are further refined. The new subdivision is based on factors such as ovoid shape, size, colour and structure or the ore (finely to more massively bedded/laminated). All changes are gradational and no sharp contacts are present between the different subzones.

The X-zone is divided, from top to bottom, into the X1, which is approximately 1,5m thick, the X2 and X3 subzones, which are both 2m thick. The X1 zone (Fig.3.4A)

Zone AT Description

5m Supergene-enriched ore below Kalahari unconformity. E

Banded braunite lutite with alternating bands of small and large (2mm and greater) pink V 3m carbonate ovoids. Ovoids are of ellipsoidal shape and larger ones are zoned with white core and pink rim.

Braunite lutite containing alternating bands of small and medium sized (1mm-2mm) pink W 3.5m and white carbonate ovoids. Banded appearance at the top grades into laminated appearance towards the bottom, with the presence of thin white carbonate laminae.

X1 1.5m Massive braunite lutite, containing large spherical, dark grey carbonate ovoids and lenticles.

X X2 Braunite lutite with irregular-shaped, grey and white, medium to large carbonate ovoids, as 2m well as white carbonate lenticles. Mottled appearance. X3 2m Braunite lutite containing medium and small, pink spherical ovoids, with occasional larger zoned ovoids. Y1 1m Laminated dark grey braunite lutite with small white carbonate ovoids and thin white carbonate laminae. Y2 2m Braunite lutite with brown and grey carbonate laminae with interspersed small and medium sized red carbonate ovoids. Y

Y3 Braunite lutite with light grey, brown and white carbonate laminae, with occasional small white carbonate ovoids and thin red carbonate laminae. Laminated appearance. 5m

Y4 Braunite lutite with brown and grey bands and many small and medium-sized red ovoids. Banded appearance with 1m distinct red colour. Z Banded appearance with alternating bands rich in small and medium sized white ovoids 3.5m and thin white carbonate lenses.

M1 1.5m Massively textured braunite lutite, containing medium sized, grey and white carbonate ovoids and lenses. M2 0.5m Massively textured braunite lutite with alternating bands of white carbonate ovoids and lenses.

M M3 Massively textured braunite lutite, with alternating bands containing irregular shaped white 3.5m ovoids and bands characterized by white carbonate lenses. Irregular shape of carbonate ovoids is responsible for mottled appearance.

M4 Massively textured braunite lutite, containing small to medium sized and irregular shaped 2m white carbonate ovoids. Very few thin white carbonate lenses. Mottled appearance. C1 1m Laminated braunite lutite with brown and black laminae. Abundant medium-sized red carbonate ovoids. C C2 Laminated braunite lutite with light brown and black laminae. Abundant white carbonate 5m laminae and occasional red carbonate ovoids in black laminae. Overall red-brown laminated appearance.

3.5m Laminated braunite lutite with many medium sized white carbonate ovoids and thin white N carbonate laminae.

Laminated brownish-red jacobsite lutite, with medium sized carbonate ovoids and pink-white B 2m carbonate laminae.

L Laminated hematite lutite with thick pink carbonate laminae. 3m

Figure 3.3. New lithostratigraphic subdivision of the manganese ore bed at Mamatwan mine. AT-average thickness of zone/subzone in study area. 24 A

1cm

Figure 3.4 Photographs of hand specimens illustrating the typical appearance of X1-X3 subzones. A. Medium-sized spheroidal ovoids in fine-grained lutite matrix, typical for the X1-subzone. B. The X2-subzones shows lens shaped ovoids. C. X3-subzone, with small ellipsoid ovoids. All samples from drill core G558. Lithostratigraphy 25 consists of a very dark brown manganese lutite (Fig.3.3), with abundant spheroidal carbonate ovoids, 1mm to 3mm in size. Larger ovoids are more spherical than smaller ovoids that tend to be ellipsoidal in shape. The larger ovoids also have a dark shiny core and a light grey rim. Smaller ovoids are flattened, elliptically parallel to bedding, creating a laminated appearance in the ore.

The estimated volume ratio of carbonate ovoids to matrix is 2:3 in the X1 subzone. In contrast to the X1 subzone the X2 subzone (Fig.3.4B) has a similar very dark lutite matrix but contains irregular-shaped (lens-like) carbonate ovoids of 1mm to 3mm in diameter. The ovoids are grey in colour and oftern surrounded by a thin white rim. The distribution of the flattened lens-shaped ovoids creates an overall laminated appearance. The ovoid to matrix volume ratio is estimated at 2:3. The X3 subzone (Fig.3.4C) also has a very dark lutitic matrix, with small ellipsoidal carbonate ovoids. The pink and white ovoids are less than 1mm in size. Alternating ovoid-rich and ovoid-poor bands are present, resulting also in a distinct laminated appearance of the ore. The ovoid : matrix ratio is again 2:3.

The Y-zone is subdivided from top to bottom into the Y1, Y2, Y3 and Y4 subzones. Y1 is not always easily identified as it is only 1m thick. Y3 is always the most prominent, being very carbonate rich, well laminated and on average 5m thick. Y2 and Y4 are very similar in appearance; both contain prominent red ovoids. They are 2m and 1m thick respectively.

The Y1 subzone (Fig.3.5A) consists of a dark-brown finely laminated lutite matrix with tiny highly compacted ellipsoidal brown carbonate ovoids. This zone is not always well developed. The Y2 subzone (Fig.3.5B) consists of a very dark grey lutite matrix containing compact, red ellipsoidal ovoids less than 1mm in diameter. A banded appearance arises from the intercalation of ovoid-rich bands (2-3mm in size) with bands containing only a few scattered and smaller ovoids (up to 1mm in size). The estimated ratio of ovoids : matrix is 3:2. Subzone Y3 (Fig.3.5C) consists of a finely laminated varicolored (grey, red and dark brown) matrix containing thin but distinct (1-2mm thick)

A B

1cm 1cm

C D

1cm 1cm

Figure 3.5 Photographs of representative samples of subzones in the lithostratigraphic Y zone. A. Finely laminated dark brown lutite of the Y1 subzone. B. The Y2 subzone is characterised by small red ellipsoid ovoids. C. the Y3 subzone is finely laminated greyish pink lutite, with very small red ovoids. D. Y4 subzone is very similar to the Y2 subzone. Both contain bands of small red ovoids. Drill core G552 (A). G558 (B,C,D).

6 Lithostratigraphy 27 red laminae and very thin (less than 1mm) white laminae. Very small red ovoids (less than 0.5mm in diameter) are present. The Y4 subzone (Fig.3.5D) consists of a very dark brown lutite matrix containing compact, red ellipsoidal ovoids that are smaller than 1mm in diameter. Banding is very similar to that in the Y2 subzone. The estimated ovoid : matrix ratio is 1:1.

The M-zone consists, from top to bottom, of the M1, M2, M3 and M4 subzones. The M1 subzone has a thickness of 1,5m followed by a the M2 subzone, which is 0.5m thick and is not always recognized. Subzone M3 has a thickness of 3,5m and subzone M4 is 2m thick. Altogether the M-zone is approximately 7,5m thick.

The M1 subzone (Fig.3.6A) consists of a very dark lutite matrix containing ovoids that are less than 2mm in size. The ovoids are grey in colour and slightly flattened and evenly distributed. The estimated ovoid to matrix ratio is 3:7. The M2 subzone (Fig.3.6B) also consists of a very dark lutite matrix but contains spheroidal grey ovoids as well as thin flat carbonate lenses, 10mm long and 2mm thick. A distinct bedded appearance is the result of the alternation of layers containing thin flat lenses with layers containing spheroidal ovoids. The estimated carbonate (ovoid + lenses) to matrix ratio is 2:3. The M3 subzone (Fig.3.6C) consists of a very dark brown lutite matrix containing distinct layers of medium sized, mottled pink and white coloured carbonate ovoids, alternating with layers with thin white carbonate lenses. The M4 subzone (Fig.3.6D) consists of a dark-grey lutite matrix containing red, pink and white, irregular-shaped small to medium- sized carbonate ovoids. A mottled appearance is due to the random distibution of size and colour of these ovoids.

The C-zone is divided into 2 zones, namely an upper C1 subzone, which is only 1m thick, and a lower finely laminated C2 subzone, which is approximately 5m thick. The C1 subzone is composed of a finely laminated dark brown matrix containing small brown carbonate ovoids and occasionally some thin (1mm) white carbonate laminae. The C2 subzone is composed of alternating brown, white, red and dark brown laminae, with brown laminae being the most abundant. The brown laminae are thicker than the other

A B

1cm 1cm

C D

1cm 1cm

Figure 3.6 Photographs of samples representing subzones of the M zone. A. M1 Subzone containing small to medium, spheroidal ovoids in a fine-grained black lutite matrix. B. The M2 subzone represents lens-like carbonate ovoids in a fine-grained matrix. C. The M3 subzone consists of alternating bands of lens-like ovoids, with bands of pink and white mottled ovoids. D. The M4 subzone has a mottled pink-red appearance with compact, small, irregular shaped ovoids.

8 Lithostratigraphy 29 types of laminae and contain small red-brown spheroidal ovoids. The dark brown lutite laminae contain small spheroidal red-brown carbonate ovoids. The white laminae range between 2mm and 5mm in thickness and are spaced at regular intervals, some more than 150mm apart. Only occasionally red laminae are present. These are between 1mm and 3mm thick and are the least abundant.

3.4 Lateral variation Mining at Mamatwan mine is at present guided by grade rather than lithostratigraphy. This is mainly due to the fact that fine details of appearance of the ore are not easily recognised on the working faces of the open pit. However, the results of this study suggest that the lithostratigraphy is consistent across the study area, even on a small scale. This is illustrated by EW (Fig.3.7) and NS (Fig.3.8) sections across the study area. The cross sections illustrate the gentle undulation of the ore bed (due to folding) and minor displacement by normal faulting (Fig.3.8). The central economic zone (zones M and C) in all drill cores of both E-W and N-S sections has been highlighted and the top of the C zone is used as a marker bed for comparison of all drill cores. The E-W section (Fig.3.7) clearly shows the suboutcrop in the east and increasing preservation of the ore body to the west. In drill core G429 only the central economic zone and the basal low- grade zone ore is preserved. Overlying the M zone of the central economic zone is a zone of supergene enriched ore (E-zone) of up to 5m thick..

The N-S section (Fig.3.8) across the western part of the mine lease area (west of present pit) shows an average thickness of the lower manganese ore body of 45m. The EW striking fault is clearly delineated between G515 (north of the fault) and G558, with a 4m displacement to the south. The lithostratigraphic zones are consistent throughout this section and the presence of the V and W zones of the upper low-grade zone are noted. The development of the E-zone (supergene enriched) is not very prominent.

3.5 Discussion The lateral variation of the different zones of the manganese ore bed at Mamatwan mine area was found to be negligible. Most subzones and all zones defined by Nel (1984) are

Depth G429 G416 38m G475 G433 40m G421 G453 3.09m E 3.00m Calcrete 5.25m E 42m Calcrete 1.82m E 0.75m 0.09m E 44m 2.20m X1 0.46m Y2 1.34m Y1

4.87m 46m 3.99m M3 2.02m X2 X 8.12m E E 4.33m Y3 Y M 48m 1.25m X3 6.72m Y3 Y 1.74m Vein 0.79m Y1 0.79m Y4 2.77m M4 50m 1.74m 1.41m Z 4.10m Y2 1.41m Y1 1.10m X1 52m 1.8m Y4 1.52m M1

1.65m X2 2.13m Y2 Y 1.31m M2 X 2.37m Z 54m 6.43m C2 C 2.53m X3 3.81m Y3 Y M 56m 1.25m M1 3.40m M3 0.69m M2 1.10m Y1 6.10m Y3 58m 1.76m Y4 2.7m M3 M 1.70m M4 E W 4.02m N 60m 4.15m Y2 2.80m Z 0.92m Y4 M4 Y 3m 62m 5.33m C2 C 1.23m M1 3.54m Z 3.12m B 3.34m Y3 64m 3.65m M3 M 1.59m M2 0.78m Y4 66m 3.30m N 7m C2 C 3.74m L 3.18m Z 1m M4 68m 3.60m M3 M B 1.04m M1 3.25m 70m 0.61m 5.60m C2 C M2 2.05m M4 2.20m M3 M 3.m N 1.10m L 72m

1.14m M4 74m 2.m B 1.09m C1 3.03m N 6.00m C2 C 76m 1.65m L C 2.53m B 78m 5.20m C2

3.93m N 80m 2.32m L

82m 2.94m N 1.87m B 0.35m L 84m 2.81m B 86m

88m 3.70m L

90m

92m 0

94m Figure 3.7. E-W profile of the lower manganese ore body in the study area. Highlighted in red isthe central economic zone, comprising the M and C zones. The dotted line indicates the top of the C-zone which is used as a marker for comparison. Depth G444 34m G515 F 36m 4.40m W 38m G416 G558 G559 3.83m E 1.04m X1 40m 0.25m E 1.33m E 1.80m X2 X 3.09m 1.63m X1 E V 1.10m X3 42m 3.45m 2.28m V 2m X2 X 1.68m 44m Y2 2.20m X1 Y 2m X3 3.14m W 1.69m Y3 46m 3.94m W 2.02m X2 X 0.92m Y4 1.40m Y1 48m G466 1.69m X1 1.25m X3 1.44m 1.89m X1 Y2 Y 3.38m Z 0.79m Y1 2.18m X2 X 50m 7m Y3 1.05m Y4 2.22m X2 X 4.10m Y2 1.8m Z 1.95m X3 2.57m M1 52m 1.52m X3 0.58m M2 Y 54m 2.3m M2 10m Supergene 3.39m Y2 2.88m Y2 Enriched M3 3.81m 3.66m M 56m BIF Y3 Y 2.85m M3 M 58m 3.40m Y3 1.76m Y4 Y 1.76m M4 2.52m M4 60m 1m E 0.95m C1 8.08m Y3 2.80m Z 4.62m 62m 2m V Z C 1.23m M1 5.39m 64m C2 7.35m C2 C 0.52m Y4 2.03m M1 5.30m W 3.65m M3 M 66m 2.08m Z 1.08m M2 3.02m 1m M4 N 1.18m M1 68m M 0.83m M2 2.78m M3 3.26m N S N 2.45m X1 70m 2.26m B 3.00m M3 M 5.60m C2 C 2.68m M4 72m 2.30m X2 X 2.47m B 2.08m M4 1.40m L 74m 3.10m X3 5.4m L 3.03m N 76m 7.30m C2 C 0.95m Y1 5.50m C2 C 78m 2.53m B 4.40m Y2 80m Y 2.32m L 2.42m N 2.10m N 82m 4.07m Y3 2.23m B 1.80m B 84m

2.33m L 3.41m L 86m 3.46m Z 88m 0.90m M2 90m

92m 4m M3 M

94m 0.70m M4

96m 5.55m C2 C 98m

100m 2.37m N 102m B

104m 2.70m Figure 3.8. N-S profile of the lower manganese ore body in the study area. Highlighted in red, the central 3

economic zone, comprising the M and C zones. The dotted line indicates the top of the C-zone which is used as a 1 106m 4.15m L marker for comparison. The fault line indicates the displacement direction. 108m

110m 32

-2400 -2200 -2000 -1800

-7600 0

Legend -7800 -25 Kalahari Calcrete E -8000 -50 V W -8200 X1 -75 X2 X3 -8400 Y1 -100 Y2 Y3 0 Y4 Z M1 -7600 -25 M2 M3 -7800 M4 -50 C1 C2 -8000 N -75 B

-8200 L Lutite -100 -8400

Figure 3.9. Cut-away 3-D model of the lower manganese ore bed west of the Mamatwan open pit. Notice the gentle folding and the lateral consistency of all lithostratigraphic zones. Lithostratigraphy 33 consistent across the mine lease area. A 3-D model (Fig.3.9) of the lower manganese ore bed illustrates this lateral consistency as well as the gentle folding noticed in the N-S and E-W cross sections. Because of this apparent lateral consistency only two drill cores (G558 and G552) were sampled for detailed mineralogical/petrographical/geochemical studies. It appears reasonable to extrapolate results, obtained from these two cores to the entire study area.

Two sedimentary cycles rather than three, as previously stated by Nel (1984), were identified in the manganese ore bed (Fig. 3.10). The first and older cycle commences with the Mn-poor N zone followed by the carbonate rich laminated C zones and ends with the M zones. The Mn-poor Z zone separates the two cycles. The second cycle follows a similar lithostratigraphic pattern starting with a carbonate rich laminated Y zone, which is overlain by the X zones and ends in the carbonate rich W and V zones (Fig3.10).

Most important for understanding the sedimentary cyclicity inherent to the lower manganese ore bed as well as the mining of the bed, is the fact that the X and M zones are very similar in macroscopic appearance. Both the X1 and M1 subzones have a massive appearance and contain abundant medium sized (less than 2mm) grey and white carbonate ovoids and lenses. The X2 and X3 zones are similar in appearance to the M3 and M4 zones respectively.

Ave. Zone Thick 34

5m E

t V 3m

/ W

3.5m

n o

z X1 1.5m Large spherical, dark grey carbonate ovoids and lenticles.

d X X2 Irregular-shaped, grey and white, medium to large a 2m

r carbonate ovoids and white carbonate lenticles. Mottled appearance. g X3 2m Medium and small, pink spherical ovoids, with

w occasional large zoned ovoids. o

l Y1 1m Laminated with small white carbonate ovoids and thin white carbonate laminae.

e Y2 2m Brown and grey laminae with small and medium sized red carbonate ovoids. p

p Y U

Y3 Light grey, brown and white laminae, with occasional small white carbonate ovoids and thin red carbonate laminae. Laminated appearance. 5m

Y4 1m Brown and grey bands with many small and medium-sized red ovoids.

Z 3.5m

M1 1.5m Medium-sized, grey and white carbonate ovoids and lenses.

c i

u M2 0.5m Alternating bands of white carbonate ovoids and lenses.

o e M Bands containing irregular shaped white ovoids and carbonate lenses l M3 n mottled appearance.

d 3.5m

l Small to medium sized and irregular shaped

a M4 2m

few carbonate lenses. Mottled appearance.

t e

n C1 Brown and black laminae. Abundant medium-sized red

n 1m

o carbonate ovoids. z C C C2 Light brown and black laminae. Abundant white carbonate 5m laminae and occasional red carbonate ovoids in black laminae. Red-brown laminated appearance.

d c

a N 3.5m

l b B 2m

a o L

B z 3m

Figure 3.10 Lithostratigraphic profile of the lower manganese ore bed illustrating the new subdivision in relation to the general lay-out of the open cast mining operation (upper low-grade zone, central economic zone and the basal low-grade zone). Subzones of the X and M zones are highlighted to illustrate their similarity. Petrography and mineralogy 35

Chapter Four Petrography and Mineralogy

4.1 Introduction Mamatwan-type manganese ore can be described as finely laminated and microcrystalline braunite lutite (Nel et al., 1986; Kleyenstüber, 1984), composed of finely intergrown Mn- bearing carbonates (kutnahorite, rhodochrosite, Mn-calcite), braunite and hematite. This mineral assemblage is thought to be of diagenetic origin (Gutzmer & Beukes, 1997). The distribution, shape and colour of early diagenetic Mn-carbonate ovoids and carbonate laminae within this microcrystalline braunite lutite matrix permit distinction between different lithostratigraphic zones. The presence of variable quantities of hausmannite and hematite in these carbonate ovoids and laminae results in their variable grey, red or white colour. The occurrence of hausmannite and calcite as replacement products of early diagenetic kutnahorite and Mn-calcite ovoids and laminae reflect late diagenesis to lower greenschist facies alteration of the ore (Kleyenstüber, 1985; Gutzmer & Beukes, 1996).

Sixty polished thin sections were studied using transmitted and reflected light microscopy as well as scanning electron microscopy. The sections were carefully selected to be representative of all the lithostratigraphic zones. Combined results of X-ray powder diffraction and petrographic studies of samples representing each subzone, illustrated that the low grade Mamatwan-type ore is essentially composed of braunite, kutnahorite, calcite, hematite, hausmannite and trace amounts of partridgeite (Table 4.1A&B), cryptomelane, jacobsite, pyrolusite and romanechite. Trace amounts of barite were identified in the supergene enriched zone below the Kalahari Formation only by scanning electron microscopy.

G558 Braunite Kutnahorite Hematite Calcite Hausmannite Cryptomelane Jacobsite Dolomite A E xx xxx xx xx \ xxxx \ ? V xxxx xxx xx x \ \ \ \ W xxxx xxx xx xx \ \ \ \ X1 xxxx xxx x x xx \ \ \ X2 xxxx xxx x xx x \ \ \ X3 xxxx xxx xx xx \ \ \ \ Y2 xxxx xxx xx xxx x \ \ \ Y3 xxxx xxx xx xxx \ \ \ \ Y4 xxxx xxx xx xx \ \ \ \ Z xxxx xxx x x \ \ \ \ M1 xxxx xxx x x x \ \ \ M2 xxxx xxx xx x xx \ \ \ M3 xxxx xxx x x xx \ \ \ M4 xxxx xxx xx xx x \ \ \ C2 xxx xxx x xx xxx \ \ \ N xxxx xxx x xx x \ \ \ B xxxx xxx xx xx \ \ x \

G552 Braunite Kutnahorite Hematite Calcite Hausmannite Cryptomelane Pyrolusite Jacobsite Hollandite B E \ \ xx xxx \ xxxx x \ \ Y1 xxxx \ xx xxx \ \ \ \ x Y3 xxxx xx xx xxx \ \ \ \ \ Y4 xxxx xxx x xx x \ \ \ \ Z xxxx xxx x xx x \ \ \ \ M1 xxxx xxx x x x \ \ \ \ M2 xxxx xxx x \ xx \ \ \ \ M3 xxxx xxx x xx x \ \ \ \ M4 xxxx xxx x x \ \ \ \ \ C1(G565) xxx xxx xx x xxx \ \ \ \ C2 xxxx xxx x xx xxx \ \ \ \ N xxxx xxx x xx xx \ \ \ \ B xxxx xxx xx xx x \ \ x \ 3 6 Petrography and mineralogy 37

As already reported by Nel et al. (1986) the mineralogy of the lower manganese ore bed was found to be consistent in all the lithostratigraphic zones. The occurrence of hausmannite and partridgeite is restricted to zones X, M and C (Table 4.1).

4.2 Oxide mineralogy 2+ 3+ Braunite (Mn Mn6 SiO12 ) is undoubtedly the most abundant oxide mineral in the ore. It occurs mainly as microcrystalline matrix constituent intimately intergrown with micritic carbonates. Microscopically, braunite occurs in minute grains (<10µm) of rounded shape that appear to be cogenetic to matrix kutnahorite, and possibly hematite. Subordinate amounts of braunite appear recrystallized to subhedral/euhedral polygonal crystals in carbonate ovoids or laminae.

Hausmannite (Mn3O4), representing a replacement mineral of carbonate ovoids and laminae, is restricted to certain lithostratigraphic zones in Mamatwan-type ore. It is the manganese mineral species with the highest manganese content occurring in the Kalahari manganese field. The mineral is always much coarser grained than braunite, hematite or jacobsite, ranging in size up to 50µm. Hausmannite is usually associated with calcite, partridgeite and recrystallized hematite. It apparently formed by oxidation of manganese- rich carbonates in the Mamatwan-type ore during late diagenesis or low-grade metamorphism (Kleyenstüber, 1985).

Microcrystalline hematite (<5µm) is finely dispersed in the matrix. Most hematite is enclosed in braunite, very little, if any, hematite is enclosed in matrix kutnahorite. The very fine-crystalline and rounded hematite grains (<5µm) are thought to be of primary sedimentary origin. They are certainly older than the braunite itself.

Recrystallised hematite (grain size up to 10µm) forms euhedral crystals associated with kutnahorite ovoids in the Y and C zones (Figure 4.7E & G). Larger platy hematite crystals are associated with hausmannite and Mn-calcite in ovoids of the X, Z and M zones (Figure 4.8B). Specularitic hematite associated with the ovoids is thought to

Petrography and mineralogy 38

represent a product of recrystallization of primary microcrystalline hematite during late diagenesis or metamorphism (Kleyenstüber, 1984)

Jacobsite (MnFe2O4) is a ferromagnetic manganese oxide restricted to the transition zones of the lower manganese ore bed into the surrounding hematite lutite.

Cryptomelane (KMn8O16) and manjiroite (NaMn8O16) belong to the manganomelane group of minerals. These manganese oxide mineral phases are concentrated in the supergene enriched zone but also occur in microscopic veinlets that crosscut the ore bed below the zone of macroscopically visible supergene alteration (Fig.4.4D). The formation of manganomelane is most probably related to supergene alteration below the

Kalahari unconformity (Kleyenstüber, 1993).

Trace amounts of barite (BaSO4) were identified by scanning electron microscopy in the supergene enriched zone below the Kalahari unconformity as clusters of platy crystals (<10µm) that appear to fill pore spaces less than 0.5mm in diameter. This mineral has not been reported by previous studies from the Mamatwan area.

4.3 Carbonate mineralogy

Kutnahorite [Ca(Mn,Mg)(CO3)2] is the most abundant carbonate species in the Mamatwan-type ore (Nel et al., 1986). Kleyenstüber (1985) identified three distinct kutnahorite species by X-ray diffraction and electron microprobe analysis, namely: kutnahorite, Ca-kutnahorite and Mg-kutnahorite. The most common is kutnahorite and Mg-kutnahorite that constitute the matrix as well as ovoids. These two carbonate species are intimately intergrown with braunite. The scanning electron X-ray mapping technique revealed the heterogeneity of kutnahorite in the mamatwan type ore. These pseudomicritic carbonate grains show a patchy distribution especially for Ca and Mg. These patches are tentatively identified as Ca-kutnahorite or Mg-kutnahorite (Fig. 4.6). Detailed SEM studies revealed that the matrix kutnahorite is intergrown with minor Mn- calcite. The matrix carbonate is very fine-grained with anhedral grains averaging 15µm in size, intimately intergrown with even smaller braunite grains.

Petrography and mineralogy 39

Some kutnahorite ovoids are partly replaced by hausmannite. Such ovoids display signs of recrystallization to form larger (>0.125mm) crystals (Figure 4.8A&B), accompaniesd by a depletion of MnO at the expense of CaO (Kleyenstüber, 1984).

The presence of various generations and species of carbonate in the manganese ore body poses interesting questions as to their interrelations and origin. The microcrystalline nature of kutnahorite, the predominant carbonate species in the matrix and ovoids, strongly suggests that this carbonate species was the first to crystallize. Kleyenstüber (1985) suggested a primary sedimentary origin but work by Bau and coworkers (M.Bau, oral comm., 1997) on the rare earth element geochemistry of the mamatwan type ore strongly suggests that manganese carbonates originated diagenetically at the expense of sedimentary Mn4+ oxihydroxides. An early diagenetic origin for the microcrystalline kutnahorite is thus most likely.

According to unpublished data, Beukes (1985), the early diagenetic kutnahorite matrix can be subdivided further into two different generations. True kutnahorite represents the earliest carbonate phase but is often rimmed by Mg-kutnahorite that may represent an early diagenetic “dolomitization” process. This early stage of carbonate formation is followed by up to three generations of Mn-calcite. The earliest of the three is Mn-rich, containing about 15 to 17wt% MnO, followed by an intermediate generation typically containing about 9 to 11wt% MnO. The last generation is restricted to cross-cutting veins with only 5 to 6wt% MnO. Beukes (1985) further indicated that stratigraphic position defines a certain control on the chemical composition of carbonates. Carbonates with high Mn content (Mn-rich kutnahorite, Mn-calcite, Ca-rhodochrosite and rhodochrosite) are preferentially developed in the upper and lower portions of the ore bed, in association with hematite lutite and jacobsitic hematite lutite. An increase in the amount of manganese oxides (braunite) was found to correspond to a decrease in the Mn content of the coexisting carbonates irrespective of their identity as calcite or kutnahorite. This implies that Mn-calcite and Mn-poor kutnahorite, are associated with subzones and layers most enriched in braunite.

100µm Mn

100µm 100µm Ca

100µm 100µm Fe Figure 4.1. X-ray maps of a typical sample from the Y4 zone, illustrating compositional zoning of carbonate ovoids. Of special interest is the Mn map which illustrates zoning within the kutnahorite ovoids.. 41

10 m 10 m Mn Ca

10 m 10 m Fe Si

10 m 10 m

Mg Al Figure 4.2. X-ray map representative of X2 zone samples from G558 illustrating the presence of calcite within kutnahorite matrix (Ca), as well as a variation in Mn and Mg concentration in kutnahorite. Fe concentration coincides with Mn and Si maps. An angular grain containing high concentrations of Mg-Al-Si is thought to represent chlorite. Petrography and mineralogy 42

Numerous carbonate species exist within ovoids but the most common is kutnahorite (Fig.4.1 and 4.2). The ovoids tend to be zoned, ranging from a Mg-kutnahorite core, followed by a Mn-rich kutnahorite, and finally Ca-kutnahorite (Fig.4.1). Mn-calcite is another very common carbonate species observed as euhedral grains within large ovoids, always closely associated with hausmannite. It could not be determined whether this Mn- calcite is always a reaction product of kutnahorite and braunite to form hausmannite and Mn-calcite, or if it formed at an earlier stage together with kutnahorite.

4.4 Petrographic description of lithostratigraphic zones E zone The E zone represents the supergene enriched zone below the Kalahari unconformity and its mineralogy and petrography is thus very distinct from the carbonate rich Mamatwan- type ore that constitutes all other zones described below. It represents the most recent geological event that continues to affect the manganese ores of the Kalahari manganese field. In this zone the original braunite is altered to a microcrystalline mixture of manjiroite, cryptomelane, pyrolusite and goethite, amongst others (Gutzmer & Beukes, 1996). At Mamatwan mine this alteration event can be observed along the eastern suboutcrop perimeter of the manganese ore bed below the calcretized sediments of the Kalahari Formation (Fig.4.3). The supergene altered ore is dull grey in colour, with many crosscutting veins filled with clay, sand and/or calcrete. The E zone reaches up to 5m in thickness below the Kalahari unconformity (Nel et al., 1986) and overprints the original mineralogy and texture of the ore. The composition of the zone depends to some degree on the zone or subzone of the primary ore bed that is intersected by the Kalahari Unconformity at any given locality on the mine.

The E zone was studied in drill core G552. In this drill core the E zone overprints the X zone and alteration is such that the original texture and mineralogy of the X zone is no longer recognisable. In this example the E zone consists of very fine-grained manganomelane (manjiroite- cryptomelane) which replaces the former braunite

Petrography and mineralogy 43

Figure 4.3. Photograph taken in the Mamatwan open pit, facing W, showing the lower manganese ore body capped by the E-zone below the calcretized Kalahari sediments. Supergene enriched zone E, extends for 5m from the unconformity seen above.

lutite components and now constitutes a porous matrix (Fig.4.4A). Replacement of carbonate commences along grain contacts, forming a compact rim around every carbonate grain. Complete replacement leads to the formation of manganomelane aggregates up to 1mm in diameter (Fig.4.4B). Hematite appears to remain largely unaffected by the supergene oxidation and residual hematite grains (15µm) in diameter are preserved within the replaced ovoids.

The E zone is not as well developed in drill core G558, located further to the west of the suboutcrop, where the manganese ore bed is not immediately exposed below the Kalahari unconformity. In this case the E zone forms at the expense of the V zone of the ore bed. The matrix carbonates and braunite of the V zone are transformed into coarse-grained aggregates (0.25mm) of manganomelane with minor amounts of carbonate and braunite remaining. Barite (BaSO4) was observed in small secondary pores (<0.5cm) as clusters of platy crystals. It is not obvious whether the formation of barite is associated with any other supergene mineral phase.

Petrography and mineralogy 44

The differences in mineralogy between the E zone in cores G552 and G558 are attributed to their stratigraphic setting and the exact composition of the protore, as well as the different intensity of supergene alteration in the two intersections.

V zone The V zone consists of fine-grained, subhedral braunite grains (<10µm), interspersed with coarser grained anhedral kutnahorite (<20µm). Very fine-grained euhedral hematite crystals (<5µm) are usually enclosed in braunite and only sometimes occur enclosed in carbonate. Typical medium and large (>1mm) kutnahorite ovoids are abundant within the matrix. The ovoids sometimes contain a core of fine-grained braunite. Evidence of mild supergene enrichment is observed in the V zone, preserved beneath the E zone in core G558, as manganomelane-filled veinlets (0.06mm wide) (Fig.4.4D) and somewhat larger calcite-manganomelane veinlets (1mm wide). In the latter replacement of cryptomelane after coarse calcite is evident (Fig.4.4E).

W zone The W zone is especially rich in carbonate and contains tiny (<0.125mm) dark-brown kutnahorite ovoids. The matrix is composed of fine-grained braunite (<10µm), with larger (10µm) randomly distributed euhedral hematite crystals. Medium to large red- brown kutnahorite ovoids (0.75mm) also occur. Fine-grained braunite crystals are concentrated in and around these ovoids (Fig.4.4F).

X zone The X1 subzone consists of a matrix of finely intergrown subhedral braunite (<10µm) and anhedral carbonate grains (<15µm). Kutnahorite ovoids (<1mm) contain fine-grained euhedral disseminated braunite crystals, locally concentrated as a rim around carbonate ovoids. Other ovoids contain coarse-grained hausmannite and partridgeite intergrown with euhedral sparitic Mn-calcite and minor amounts of hematite (Fig.4.4G). X-ray maps illustrate the compositional variations of carbonates in the matrix and ovoids (Fig.4.5). The matrix carbonates contain greater amounts of manganese and magnesium, representing most probably Mg-kutnahorite, while carbonate in the ovoids is Ca-

A B 45

0.25mm 0.6mm

C D

0.25mm 0.25mm

E F

0.25mm 0.25mm

G H

0.25mm 0.25mm

Figure 4.4. A: Reflected light photomicrograph illustrating a very fine-grained supergene enriched zone below the Kalahari unconformity. B: Magnified view of typical replacement textures of carbonate ovoids. Manganomelane needles replacing euhedral carbonate crystals. C: E zone (G558), pyrolusite (pink) replaces carbonate along grain boundaries. D: V zone (G558) red brown carbonate ovoids in braunite rich (grey) matrix, cryptomelane filled veinlet showing evidence of compaction. E: V zone (G558), vein filled by sparite carbonate that is replaced by cryptomelane along grain boundaries. F: W zone (G558) ellipsoidal ovoid (red-brown), rimmed by hematite (white) within a braunite (grey) and kutnahorite (brown) matrix. G: X1 subzone (G558), ellipsoid ovoid replaced by hausmannite (blue-grey), partridgeite (yellow) and hemaite (white). Carbonate (black) occurs in ovoid as well as in the braunite rich (grey) matrix. H: Romanechite (white-grey) filled stylolite within braunite and carbonate matrix of the X1 subzone. Petrography and mineralogy 46

kutnahorite or Mn-calcite. An unusual characteristic of this zone is the presence of stylolites along which supergene romanechite is concentrated (Fig.4.4H). This feature was observed in both drill cores. Sedimentary compaction of laminae is evident around carbonate ovoids (Fig.4.7B) indicating that the ovoids formed prior to complete lithification.

The matrix of the X2 subzone contains large amounts of subhedral braunite (<15µm) and less carbonate than that of the X1 zone. A series of X-ray maps illustrates the high abundance of braunite, associated with very fine grained Mg-kutnahorite (Fig.4.6). Very fine-grained euhedral hematite (<2µm) is scattered throughout the braunite matrix. Medium sized red-brown kutnahorite ovoids (0.3mm) with very fine-grained braunite and hematite inclusions are abundant (Fig.4.7C). Dark brown irregular shaped kutnahorite ovoids are surrounded by thin rims of euhedral braunite crystals (Fig.4.7D). Larger spheroidal ovoids (<2mm) show replacement of kutnahorite by hausmannite and Mn- calcite. Recrystallized euheral hematite (10µm) grains are present in these larger ovoids.

The matrix of the X3 subzone consists of fine-grained braunite (<10µm) and kutnahorite. Euhedral hematite crystals appear concentrated in and around carbonate ovoids. Elliptical ovoids are red-brown in colour with occasional hematite inclusions. Many lens-like (flattened) ovoids occur and are dark brown in colour. These flattened ovoids contain abundant hematite crystals (Fig.4.7E).

Y-zone Subzone Y1 is especially carbonate-rich and finely laminated with many small and medium sized carbonate ovoids (<1mm) surrounded by a fine-grained braunite-bearing matrix (<10µm). Some of the larger ovoids contain hematite inclusions (<5µm). A small amount of cryptomelane is present in the Y1 subzone of drill core G552 as it immediately underlies the supergene enriched E zone.

Subzone Y2 is composed of fine-grained braunite and kutnahorite, with abundant rather coarse (>10µm) euhedral hematite crystals. Bands of small red spheroidal ovoids are

10 m 10 m Mn Mg

10 m 10 m Ca Fe

10 m 10 m Si Al Figure 4.. Series of X-ray maps of ovoid rim fromX1 subzone, G558. The rims of euhedral braunite crystals appear to project into the ovoid. The ovoid is composed of coarser grained Mn-calcite while the matrix constituted by Mg-kutnahorite.Note small amounts of a Mg-Al-silicate, possibly chlorite. Petrography and mineralogy 48

present, as well as layers predominantly composed of hematite and kutnahorite (Fig.4.7F).

In contrast to Y2, the Y3 subzone consists of abundant small, spheroidal carbonate ovoids (<0.125mm) with very fine-grained braunite (<10µm) and coarser hematite crystals scattered throughout the surrounding carbonate matrix. Larger red carbonate ovoids (0.2mm) occur. They contain needle-shaped hematite crystals (Fig.4.7G). The Y3 subzone is generally very carbonate rich, mainly in the form of very small ovoids and carbonate laminae. The Y4 subzone is very similar in composition to the Y2 subzone. It is composed of a fine-grained braunite-rich matrix with scattered hematite crystals, with many small red ellipsoidal carbonate ovoids (<0.2mm) (Fig.4.7H).

Z zone Small hematite crystals are scattered throughout the fine-grained braunite (<10µm) and carbonate (<20µm) matrix in the Z zone. Carbonate ovoids (<2mm) are replaced by medium to large grains of hausmannite (<50µm) in association with calcite (<20µm) and rare hematite (<20µm) (Fig.4.8A). Abundant red-brown carbonate ovoids are present.

M zone The M1 subzone contains large to medium-sized ovoids (2mm) composed largely of hausmannite and hematite. Other ovoids are composed of kutnahorite, but contain Mn- calcite, hausmannite and partridgeite inclusions (Fig.4.8B). The ovoids are hosted by alternating bands of very fine (<10µm) and fine-grained (20µm) matrix of braunite and carbonate.

Subzone M2 consists of medium and large ovoids and a coarse grained braunite, hausmannite and carbonate matrix (Fig.4.8C). Larger ovoids contain large hematite crystals and hausmannite, whereas smaller ovoids are composed essentially of kutnahorite and contain only small hausmannite crystals.

10 m 10 m Mn Ca

10 m 10 m

Fe Mg

10 m 10 m Mn(L) Si

Figure 4.7. Series of X-ray maps of braunite-kutnahorite matrix (X2 subzone, G558). Note the apparent compositional heterogeneity of the matrix carbonates with respect to Mg. A B 50

10mm

C D

0.25mm

E F

0.25mm 0.25mm

G H

0.25mm 0.25mm

Figure 4.7. Photomicrographs illustrating petrographic characteristics in X and Y zone. A: X1 zone (G558), BSE-SEM image illustrating a cryptomelane filled stylolite. B: BSE-SEM image of X1 subzone, showing kutnahorite ovoids with a hausmannite core. C: X2 subzone with coarse grained braunite and carbonate matrix, ellipsoidal ovoid (red-brown) with small braunite inclusions. D: BSE-SEM image of X2 subzone showing irregular shaped carbonate ovoids in a braunite and carbonate matrix. Concentrations of fine-grained braunite surround some of the ovoids. E: subzone X3, flattened carbonate ovoids (brown) surrounded by concentrations of hematite (white) in a braunite and carbonate matrix. F: Y2 subzone, ovoids in a carbonate and braunite matrix with small hematite crystals. G: |Y3 zone, many poorly defined carbonate ovoids (brown and red) with abundant prismatic hematite crystals (white), in a fine-grained carbonate rich matrix. H: Y4 subzone, red spheroidal ovoids in a braunite and carbonate matrix (bottom half), and small compact ovoids (brown) in carbonate rich matrix (top half). B 51 A

0.25mm 0.25mm

C D

0.25mm 0.25mm

E F

0.25mm 0.25mm

G H

0.25mm 0.25mm

Figure 4.8. Photomicrographs illustrating petrographic characteristics of the Z, M, C and N zones. A: Z zone, medium grained hausmannite (grey) and calcite (black) filled ovoid in a braunite and carbonate matrix. B: M1 subzone, ellipsoid ovoid containing coarse grained hausmannite, partridgeite, hematite and calcite. C: M2 subzone, coarse grained hausmannite and calcite replace matrix carbonate. D: M3 subzone, ovoid containing coarse grained calcite crystals (black) and hausmannite in a braunite-kutnahorite matrix. E: M4 subzone, fine-grained braunite and carbonate matrix with hausmannite ovoids. Small hematite crystals (white) scattered throughout. F: C2 subzone, small and medium hausmannite ovoids in a kutnahorite matrix with very little braunite. G:C2 subzone, carbonate laminae (red-brown) with hematite crystals. Braunite and carbonate matrix. H: N zone, fine-grained braunite and carbonate matrix with hausmannnite-calcite ovoid. Petrography and mineralogy 52

The M3 subzone is characterized by medium and large spherical and lens-shaped ovoids. Large ovoids contain hausmannite and large (0.125mm) euhedral Mn-calcite crystals (Fig.4.8D). The matrix consists of fine-grained braunite with abundant carbonate and hematite.

Subzone M4 is marked by a matrix of fine-grained braunite, kutnahorite and hematite. Large and medium sized ellipsoidal ovoids are replaced by hausmannite and calcite, and contain abundant hematite crystals (Fig.4.8E).

C zone The C1 subzone contains many small (<1mm) ellipsoidal red ovoids in a fine-grained braunite and kutnahorite matrix (<10µm). Fine-grained hematite (<5µm) is enclosed in the braunite and kutnahorite matrix and laminae. The braunite in the matrix varies from fine-grained (<10µm) to a coarser grained (20µm) in alternating bands. Hausmannite crystals are observed in some ovoids. The C2 subzone contains many medium and small spheroidal ovoids (2mm) that are replaced by hausmannite (Fig.4.8F). It also contains abundant hematite-rich laminae (Fig.4.8G). The matrix is composed of microcrystalline braunite, kutnahorite and hematite.

N zone In the N zone, medium sized ovoids are typically composed of a hematite core and hausmannite rim (Fig.4.8H). These ovoids are hosted by a fine-grained braunite and kutnahorite matrix. Many lenticles and laminae of hausmannite and hematite are present.

B zone The B zone is very carbonate rich, with finely dispersed braunite. Many red small and medium carbonate ovoids are present, some of which contain hematite crystals.

4.5 Discussion The lower manganese ore body of the Hotazel Formation is the oldest of three similar orebodies intercalated with Superior-type banded iron-formation. The ores display

Petrography and mineralogy 53

primary sedimentary features such as: fine lamination and “dusty” hematite. However, the ore has been diagenetically altered as shown in the carbonate mineralogy and textures (Nel et al., 1986). Mg-kutnahorite matrix and braunite are regarded to be of early diagenetic origin (Fig.4.9). The matrix kutnahorite grains are anhedral and ±15µm in size, they are often homogenous in composition and rarely intergrown with calcite grains of similar grain size and shape. Some examples, however, show thin rims of more manganiferous and less Ca-Mg-rich carbonate. Braunite grains are usually smaller than tightly intergrown carbonate grains and of more spherical or subhedral shape. Dusty hematite is almost exclusively enclosed in these braunite grains, confirming the very early origin of the hematite.

Carbonate ovoids and laminae apparently postdate the formation of the Mg-kutnahorite- braunite matrix. The ovoids are interpreted as diagenetic microconcretions. Variable degrees of flattening and deformation suggest that carbonate microconcretions formed prior to final compaction and lithification, i.e. during early diagenesis. Most of the ovoids have a massive internal texture, but some display crude concentric zonation (Fig.4.1). Zoned ovoids are composed of a nucleus of Mg-kutnahorite, very similar in composition to the surrounding matrix carbonate, and a rim of (Mg-poor) kutnahorite. Small amounts of recrystallised braunite and hematite appear to be closely associated with the microconcretions and are thus also regarded to be of diagenetic origin.

Replacement of carbonate ovoids and laminae by coarser grained hausmannite, specularitic hematite, partridgeite and Mn-calcite is attributed to late diagenetic or very low-grade metamorphic stratabound fluid flow (Fig.4.9) (Kleyenstüber, 1984; Gutzmer and Beukes, 1996). It is important to note that ovoids replaced by hausmannite- partridgeite and/or Mn-calcite are always distinctly larger and less well defined than remnant carbonate ovoids in the same sample. This observation along with the fact that we only see hausmannite-partrigdeite and Mn-calcite in all the Mn-rich zones (X and M zones), could suggest that Gutzmer & Beukes (1996) were incorrect in assuming that this occurrence was related to stratabound metamorphic fluid flow. It appears rather as if the metasomatic replacement process commenced in the carbonate ovoids and extended

Petrography and mineralogy 54

further into the immediately surrounding matrix, replacing not only kutnahorite but also braunite. Therefore, hausmannite-partrigdeite and Mn-calcite are most probably of late diagenetic origin and not related to a separate metamorphic event.

Finally, the ore is affected by supergene alteration where exposed immediately below the Tertiary Kalahari Unconformity. Cryptomelane, manjiroite, romanechite, pyrolustite and barite are products of supergene enrichment in the E zone (Figure 4.9). Several other mineral phases, including goethite and todorokite were previously identified by Gutzmer (1996) and ascribed to supergene alteration (Gutzmer, 1996). However, these minerals are not present in the samples analyzed during this study.

Supergene Sedimentation Late diagenesis Early diagenesis Alteration Carbonates Kutnahorite Mg-kutnahorite Mn-calcite Calcite Oxides & Hydroxides Specularite Hematite Braunite Hausmannite Partridgeite Pyrolusite Todorokite Cryptomelane Manjiroite Romanechite Sulphates Barite

Present in certain zones Abundant throughout Very abundant throughout Figure 4.9.Mineral paragenesis at Mamatwan mine that formed during diagenesis and metamorphism.

Geochemistry 55

Chapter Five Geochemistry 5.1 Introduction Whole rock geochemical analyses were conducted on representative samples from drill cores G552 and G558. Each sample analysed represents a complete intersection from quartered drill core, of the entire length of each zone/subzone as defined by detailed logging. These samples were crushed and powdered to analytical fineness. The resulting large amount of powdered sample material for each zone was homogenized and split by quartering. Aliquots of representative samples were sent for whole rock geochemical analyses and stable isotope analyses.

Whole rock, major and trace element data were obtained from two laboratories, namely: Set Point Laboratories (Johannesburg) (Appendix II) and MINTEK (Randburg) (Tables 5.1 & 5.2), for comparison. The two laboratories used different analytical methods. Set Point Laboratories used only XRF (on fused beads and pressed powder pellets) to obtain results reported, whereas MINTEK selected most suitable analytical techniques for different elements, including AAS, ICP-OES and ICP-MS. The differences observed are tentatively attributed to the fact that XRF is a matrix dependent analytical method and difficulties arise especially when analyzing unusually heavy matrices such as Fe and Mn ores (Gutzmer, 1996). The results may thus warrant the conclusion that the analytical approach by MINTEK – namely to choose the most suitable analytical technique for each element analysed and not to rely on one instrumental method - is preferred for the analyses of manganese ores. Therefore, only the data set supplied by MINTEK will be used for discussion purposes. The two sets of results show noticeable discrepancies, especially for trace element concentrations. To illustrate these differences comparative tables for both major and trace elements were constructed for zones X1, M1 and C2 (Figures 5.1 & 5.4).

5.2 Major elements A comparison of major element concentrations (Fig.5.1) illustrates that the data from Mintek and Set Point are well comparable with the exception of results reported for

Mn3O4 .

Table 5.1. Major and trace element composition of representative samples of all lithostratigraphic zones in drill core G558 (all data reported supplied by MINTEK, with the exception of L.O.I.). G558 Major elements (all data in wt%) * * L.O.I 98.0

3.80 8 12.0 3

8 7.40 LLD 7 LLD LLD 1 LLD 9.00 LLD 1 LLD 3 LLD 9 LLD 4.30 LLD LLD 5 Method ICP ES ICP ES IC-OES AAS ICP-OES ICP-OES ICP-OES AAS ICP

G558 Trace elements (all data in ppm)

73.0

53.0 47.0

69.0

Method ICP-OES ICP-OES ICP-OES ICP-OES ICP-MS ICP-MS ICP-MS ICP-MS ICP-MS ICP-MS ICP-MS

* Total Fe expressed as Fe2O3 and total Mn expressed as Mn3O4, in order to calculate reliable analytical totals to test quality of data reported. 5 L.O.I. Loss on ignition at 1200 C. 6 LLD-lower than limit of detection. Table 5.2. Major and trace element composition of representative samples of all lithostratigaphic zones in drill core G552 (all data reported supplied by MINTEK, with the exception of L.O.I.).

(all data in wt%) *Fe2 O3 * Mn3 O4 CaO K2 O SiO2 Al2 O3 MgO Na2 O Ba Cl P2 O5 L.O.I Total % % % % % % % % % % E 9.13 35.2 20.6 2.37 4.05 <0.5 1.59 0.21 LLD 0.04 0.08 -23.3 97.1 Y1 7.89 29.8 29.0 0.28 4.75 <0.5 0.64 0.17 LLD 0.02 0.07 -24.0 97.1 Y3 7.47 22.9 32.0 LLD 3.71 <0.5 2.42 LLD LLD 0.05 0.04 -28.4 97.5 Y4 14.2 41.0 18.0 LLD 5.02 <0.5 1.97 LLD LLD 0.05 0.04 -18.3 99.1 Z 8.68 44.6 16.1 LLD 5.24 <0.5 3.98 LLD LLD 0.01 0.09 -19.0 98.2 M1 7.59 52.5 12.6 LLD 5.64 <0.5 3.78 LLD 0.13 0.06 0.07 -16.5 99.4 M2 8.63 55.0 10.9 LLD 5.29 <0.5 3.89 LLD LLD 0.03 0.05 -16.6 100.9 M3 5.56 56.4 11.9 LLD 5.84 <0.5 3.45 LLD LLD 0.24 0.07 -15.9 99.4 M4 5.93 52.7 14.3 LLD 5.24 <0.5 3.19 LLD LLD 0.03 0.04 -17.4 99.3 C1 (G565) 6.20 58.2 11.9 LLD 3.63 <0.5 3.76 LLD LLD 0.08 0.06 -15.5 99.8 C2 4.97 52.5 17.2 LLD 3.86 <0.5 2.48 LLD LLD 0.03 0.05 -16.7 98.3 N 8.07 50.1 14.9 LLD 5.18 <0.5 3.34 LLD LLD 0.03 0.03 -16.8 99.0 B 12.2 41.0 16.7 LLD 6.25 <0.5 3.6 LLD LLD 0.03 0.07 -18.7 99.1 Mehod ICP-OES ICP-OES AAS ICP-OES ICP-OES ICP-OES AAS ICP-MS Chem Trc-ICP

(all data in ppm) Sample# E <25.0 <25.0 <25.0 45.1 <0.5 290 75 110 11 4.8 Y1 <25.0 <25.0 <25.0 40.9 <0.5 140 5.5 110 12 590 4.1 Y3 <25.0 <25.0 <25.0 34.4 2.4 120 2.2 110 17 370 5.7 Y4 <25.0 <25.0 <25.0 42.2 2 150 1.9 120 11 680 4.6 Z <25.0 <25.0 59.3 43.3 2.3 500 6.4 120 20 230 3.1 M1 <25.0 <25.0 70.1 55.1 0.51 910 1.5 95 18 210 3.2 M2 <25.0 <25.0 <25.0 59.0 <0.5 (0.13wt%) 0.5 100 29 210 3.7 M3 <25.0 <25.0 40.2 47.4 <0.5 500 <0.5 100 21 150 6.9 M4 <25.0 <25.0 <25.0 38.8 0.5 330 <0.5 75 13 130 4.0 C1 (G565) <25.0 <25.0 62.2 65.4 5.9 75 <0.5 53 308 140 3.5 C2 <25.0 104 <25.0 42.6 12 390 23 59 11 210 4.5 N <25.0 <25.0 <25.0 40.3 11 920 25 73 6.7 210 4.3 B <25.0 <25.0 <25.0 41.8 5.1 170 32 97 11 210 7.1 Method ICP-OES ICP-OES ICP-OES ICP-OES ICP-MS ICP-MS ICP-MS ICP-MS ICP-MS ICP-MS ICP-MS

* Total Fe expressed as Fe2O3 and total Mn expressed as Mn3O4, in order to calculate reliable analytical totals to test quality of data reported. L.O.I. Loss on ignition at 1200 C.

LLD-lower than limit of detection. 7 Geochemistry 58

However, maximum discrepancy of 4.5 wt% between Mintek and Set Point results for total Mn expressed as Mn3O4 (Fig.5.1) is cause of concern. Manganese concentrations reported by XRF at the SAMANCOR Laboratory (Hotazel) compare very well with the XRF results of MINTEK. Results reported for all other major elements show only minor or insignificant differences between the two datasets. In most cases, differences are well below 1wt%, but CaO is up to 2wt% different for the C2 zone. XRF (MINTEK) results are consistently higher for Mn and lower than XRF (Set Point Laboratories) results for CaO in the Mn-rich zones.

Table 5.3. Comparison between Mn concentrations reported by Mintek, Set Point and the SAMANCOR in-house laboratory in Hotazel.

G558 Mintek Set Point Hotazel G552 Mintek Set Point Hotazel Sample # Mn wt% Mn wt% Mn wt% Sample # Mn wt% Mn wt% Mn wt% E 18.8 21.6 19.4 E 27.1 30.5 27.2 V 27.9 27.0 28.4 Y1 21.4 25.0 22.2 W 27.1 30.1 27.5 Y3 16.4 18.8 16.8 X1 35.9 34.0 35.2 Y4 29.5 31.9 29.7 X2 40.12 39.7 39.9 Z 32.1 30.7 31.7 X3 31.21 30.8 31.0 M1 37.7 36.17 36.9 Y2 24.5 26.3 24.4 M2 39.6 38.34 38.9 Y3 17.2 17.9 17.3 M3 40.6 38.96 39.6 Y4 30.2 31.4 30.1 M4 37.9 35.47 37.2 Z 33.3 31.4 33.4 C1(G565) 41.9 40.0 41.6 M1 37.3 35.0 36.6 C2 37.7 36.3 37.1 M2 40.4 39.2 39.1 N 36.1 33.8 35.9 M3 42.4 42.6 42.5 B 29.5 32.3 29.1 M4 38.7 37.7 38.2 C2 38.8 35.8 38.2 N 33.2 32.6 30.1 B 28.4 29.6 27.9

The main components of the manganese ore are Mn, Fe and Ca, present in carbonate and oxide minerals. Both drill cores show very similar chemostratigraphic trends reinforcing the observation that lithostratigraphic divisions are consistent throughout the study area (Fig.5.2). Greatest Mn concentrations are observed in zones X, M and C. The highest concentrations are observed in the X2 and M3 subzones with 55.2wt% and 59.1wt%

Mn3O4, respectively. The silica content is consistent throughout the ore bed with a slight

4 X1 subzone 2 Mintek results D=1.3 in wt % 6.11 49.9 48.6 14.8 0 4.99 <0.5 3.8 0.07 -2 -4 -6 -8 -10 -12 -14 Fe 2 O3 Mn3O4 CaO K2O SiO2 Al2O3 MgO P2 O5

% M1 subzone

t 3.5 w

n i

2.5

) t

n 2 i

o 1.5 P

D=1.3

t 1 e

S 0.5

- Mintek results 12.7 0

k in wt % 7.85 51.8 50.5 5.97 <0.5 4.19 0.05 e

t -0.5 n i -1

M Fe 2 O3 Mn3O4 CaO K2O SiO2 Al2O3 MgO P2 O5 (

C2 subzone 5 4 3

2 D=1.1 1 Mintek results 15.8 0 4.3 in wt % 5.15 53.9 52.8 <0.5 2.67 0.03 -1 -2 Fe 2 O3 Mn3O4 CaO K2O SiO2 Al2O3 MgO P2 O5

Figure 5.1 Comparison of major element concentrations reported by Mintek and Set Point Laboratories of the X1, M1 and C2 subzones of drill core G558. Positive values represent higher concentrations reported by Mintek and negative values represent higher concentrations reported by Set Point Laboratories. Values attached to columns report Mintek results.

Lighter bar for Mn34O concentrations reported by the SAMANCOR laboratory in Hotazel. 60

Mn3O4 % Fe 2 O3 % CaO % Mn/Fe atom % 0 0

0 5 0 0 0

2 0

2 4

2 2 1 2 4

3 8

3 4

2 5

1 1

1 Thick. 2 Zones 1 1 E 0.25m

V 3.45m

d r

o e

E r

3.14m o

W r

X1 1.69m d

r X X2 2.18m E

X3 1.95m

Y2 3.39m

Y3 8.08m

Y4 0.52m

Z 2.08m

M1 1.18m

M2 0.83m

M M3 3.00m

M4 2.08m

C C2 5.50m

N 2.42m

B 2.23m

L 2.33m G558 G552

Figure 5.2 Mn34O , Fe23O and CaO concentration profiles for drill cores G558 and G552. Highest Mn contents are present in the X, M and C zones with the highest Ca concentration in the Y zone. The Fe content is relatively low and remains constant throughout the ore body. Note that there are two distinct Mn-rich zones (M-C and X) separated by the manganese-poor Y zone. Note also excellent consistency of concentrations between the two cores studied. Geochemistry 61

increase corresponding to the X and M zones, which is attributed to the abundant braunite content in those zones. The iron content remains below 12wt% throughout the ore bed with the exception of the Y4 subzone, where an iron content of almost 20wt% is reached. This trend is observed in both drill cores. The carbonate content, as reflected by the L.O.I., reaches a high of almost 30wt% in the Y3 subzone, with corresponding very low

Mn concentrations of 24wt% Mn3O4 (Fig. 5.2).

An inverse correlation of –0.83 is observed between the Mn3O4 and CaO concentrations in the manganese rich zones (X, M, C, N) only. No other covariation is observed between major element concentrations. This indicates that independent geochemical mechanisms controlled the introduction of these elements into the rock, most probably during sedimentation and/or diagenesis.

The supergene enriched E zone differs from all the other zones in that it is highly enriched in Na and K (Table 5.1).

5.3 Trace elements Greatest differences between Mintek and Set Point results were encountered for Cr and Ti, with differences exceeding 100ppm between data sets (Fig.5.3). Other trace elements illustrating considerable deviations between data sets are Ba, Sr, Ni, V and Co, whereas Zn, Pb and Zr show only negligible differences in concentration between the two data sets. The differences encountered are consistent throughout the data sets and can thus almost certainly be attributed to the different methods and/or in calibration of the instrumentation used. Such problems are mostly due to the unusually heavy matrix composition of the Mn ores, as compared to typical Si and Al-rich rock samples for which XRF-calibration standards are widely available (Gutzmer, 1996).

Some general observations can be made, despite the variations in results from the two methods used by Mintek and Set Point Laboratories. Firstly, the Ba content shows a marked increase in zones X2, M4, C2 and N (G558) and M1, M2 and N in G552 in both data sets (Table 5.1 & 5.2). An unusual concentration of Zn is observed in zone C2 (Table 5.1 & 5.2). The high Ba and Zn values are related to zones of high Mn content.

250 X1 subzone 200

150

100

50 Mintek results <25.0 1.8 15 in ppm <25.0 40.7 58.3 1 230 230 170 6.1 -50

-100

-150 Cu Zn Ni Co Pb Ba V Ti Cr Sr Zr

100 M1 subzone

50 m

p Mintek results <25.0 3.6 8.3 p

in ppm <25.0 <25.0 53.3 6.7 150 110 160 2.6

n i

-50

)

t n

i -100 o

p -150

e Cu Zn Ni Co Pb Ba V Ti Cr Sr Zr

n i

M 80 ( C2 subzone 60 40

20 Mintek results <25.0 69 <25.0 1300 2.9 7.2 in ppm 50.5 6.8 130 130 4.3 -20

-40

-60

-80

-100

-120 Cu Zn Ni Co Pb Ba V Ti Cr Sr Zr Figure 5.3 Plots comparing trace element concentrations in data sets supplied by Mintek and Set Point Laboratories, for the X1, M1 and C2 subzones of drill core G558. Concentrations reported by Mintek are arbitrarily chosen to normalise against, i.e. positive values on the Y-axis represent higher concentrations reported by Mintek and negative values represent higher values reported by Set Point Laboratories. The differences between the two results are illustrated by the length of bars. Values printed below/above bars report Mintek concentrations in ppm. Geochemistry 63

The supergene enriched E zone shows notably higher concentrations of Pb, Sr and Ti.

5.4 Loss on ignition Set Point Laboratories conducted loss on ignition measurements at temperatures of only 850°C (12 hours). Using this L.O.I value, analytical totals remain too low for all data sets. Further L.O.I measurements were thus conducted at the Department of Geology at RAU at 1200°C (2 hours). These results showed improved totals, as the mass change values showed an average increase of 1% for the manganese-rich zones. This is explained by the fact that only at temperatures above 1000°C, most manganese bearing minerals in the Mamatwan type ore transform into Mn3O4 and carbonates dissociate to

CO2 and oxide (Gutzmer, 1996). Repeated L.O.I determination on selected samples indicated a reproducibility of ±1% relative for data determined at RAU.

5.5 Depositional geochemical signatures Manganese oxides possess a strong positive surface charge and therefore a strong absorbtion capacity for different cation species. The amount and type of cations absorbed by Mn oxides is strongly affected by the chemical composition of the associated fluid and trace element signatures and may thus be useful as diagnostic criteria to identify depositional environments for manganese deposits (Nicholson, 1992). The discrimination plot by Nicholson (1992) (Figure 5.4) to distinguish between either fresh water, shallow marine or marine environments was applied to the low-grade Mamatwan-type ore of the Hotazel Formation. The carbonate-rich ores as identified in the lithostratigraphic classification in chapter three, are very rich in Mg but almost completely devoid of Na, and therefore the deposit can be classified as either a shallow marine or marine deposit. Only results for the supergene enriched E and Y1 altered zones are separated from the main cluster of results. These zones exhibit a higher Na concentration and lower Mg concentration due to the supergene alteration caused by the introduction of meteoric water below the Kalahari unconformity.

Geochemistry 64

Figure 5.4. Diagnostic plot to differentiate marine and fresh water manganese deposits (after, Nicholson, 1992).

5.6 Carbonate stable isotope geochemistry A total of 30 whole rock samples, representing all lithostratigraphic zones of both drill cores (G558 & G552), were submitted for carbon and oxygen isotope analysis at the Council for Geoscience (CGS) in Pretoria. X-ray powder diffraction analysis identified the carbonate phases present as kutnahorite (most abundant) and Mn-calcite. Quantitative analyses to determine the abundance of the carbonate species within the samples were not available. Therefore, the amount of sample material needed for one analysis had to be estimated. The carbonate content was estimated to be between 50 and 60 vol. %, and 20 to 25mg of sample material were therefore sufficient to yield at least

100µmol CO2. The occurrence of more than one carbonate phase (kutnahorite, Mn- calcite, calcite) in most of the samples, posed a severe problem for the analytical procedure and inhibited the interpretation of the results to a certain degree. Physical mineral separation of the carbonates, however, was impossible due to the exceedingly fine-grained nature of the ore.

The δ13C and δ18O signatures for both drill cores are presented in Table 5.5. It is obvious that both δ13C (-14‰ to –6.4‰) and δ18O (15‰ to 20.3‰) show a very large range of values but variations appear to be consistent between the lithostratigraphic zones for both drill cores. There is, however, very good consistency between results obtained for the same lithostratigraphic zones in different drill cores. This observation can be used

Geochemistry 65

to suggest that the spread of isotopic composition is due to syndepositional or diagentic variations that affected specific stratigraphic units of the orebody and that the variations are not structurally controlled or related to hydrothermal or metasomatic alteration processes.

Table 5.5. Stable isotope geochemistry of whole rock samples representing lithological zones in drill cores G558 and G552.

13 13 18 18 18 18 δ % δ % δ % δ C % δ O % δ O % C O O G558 PDB PDB SMOW G552 PDB PDB SMOW

* G565

Almost identical stable isotopic compositions and trends are observed in both drill cores (Table 5.5). The supergene enriched E-zone has the least depleted δ13C values of –5.8‰ (G558) and –5.7‰ (G552). The carbonate-rich Y3-zone has a δ13C value of –6.6‰ (G558) and -6.4‰ (G552), in comparison to the depleted δ13C values of the Mn-rich M1-zone, -13.5‰ (G558) and –13.3‰ (G552).

δ13C and δ18O are negatively correlated (Figure 5.6 and 5.7), i.e. more depleted δ18O values are associated with less depleted δ13C values. A good negative correlation is also recognized between δ13C and the Mn concentration (Fig.5.5). These results exclude, however, results for supergene altered zones which contains calcite formed from recent meteoric water.

Geochemistry 66

Figure 5.5. Composition of carbonate δ18 O and δ13C for different lithostratigraphic zones in drill cores G558 and G552. A good negative correlation is displayed for all zones but the supergene enriched zones E and Y1 (G552).

Compared to other large Mn-carbonate deposits in the world, the isotopic signature of the Kalahari Mn field (Fig.5.8) shows very similar δ13C carbonate signatures but unusually low δ18O values. Literature data used in Fig.5.8 are all from marine Mn carbonate deposits ranging in age from Late Paleoproterozoic (Moanda, Nsuta) and Neoproterozoic (Penganga) to Mesozoic (Úrkút, Nikopol). Depositional environments for Mn deposits range from deep-water outer shelf platform (Penganga) to very shallow marine (Nikopol). Mn carbonates present in all the deposits are thought to have formed as a result of reduction of sedimentary Mn4+oxihydroxide, by organic matter. Manganese carbonates 13 thus have a δ C signature that should be a mixture between pore water, inorganic CO2 18 and organic carbon and a δ O signature determined by pore water oxygen (in CO2 and

H2O) as well as oxygen liberated by the reduction of MnO2.

13 18 18 G558 d C PDB d O PDB d O SMOW Zones Thickness -16 -14 -12 -10 -8 -6 -4 -16 -14 -12 -10 -8 -6 -4 5 1 0 1 5 2 0 2 5

E 0.25m

V 3.45m

W 3.14m

X1 1.69m

X2 2.18m

X3 1.95m

Y2 3.39m

Y3 8.08m

Y4 0.52m

Z 2.08m

M1 1.18m M2 0.83m

M3 3.00m

M4 2.08m

C2 5.50m

N 2.42m

B 2.23m

2.33m L

Figure 5.6. d13C and d18O whole rock carbonate signature plotted against lithostratigraphy for drill core G558 (Note the excellent negative 18 13 6

covariation between d O and d C). Zone E is affected by supergene enrichment and shows distinctly different isotopic composition. 7 13 18 18 G552 d C PDB d O PDB d O SMOW -1 4 -1 2 -1 0 -8 -6 -4 -2 0 - 2 0 - 1 5 - 1 0 - 5 0 0 5 1 0 1 5 2 0 2 5 3 0 Zones Thickness

E 2.86m

Y1 1.58m

Y3 4.09m

Y4 1.09m

Z 3.48m

M1 0.84m M2 1.18m

M3 3.54m

M4 1.52m C1 0.27m

C2 6.889m

N 3.23m

B 2.35m

L 3.08m

13 18 Figure 5.7. d C and d O whole rock carbonate signature plotted against lithostratigraphy for drill core G552. Zones E and Y1 are affected 6 by supergene enrichment and show distinctly different isotopic compositions. Note the excellent negative covariation between d18O and d13C. 8 Geochemistry 69

The negative δ13C signatures of the Mn-rich carbonates of the Hotazel Formation may in analogy be used to indicate diagenetic origin for kutnahorite, Mn-calcite and calcite (Bau, pers. comm., 1997).

Figure 5.8. Carbonate stable isotopic compostion of various large manganese carbonate deposits (modified after Hein & Bolton, 1993).

A similar negative covariation between Mn and δ13C observed in this study was previously only reported by Polgári et al. (1991) for the Úrkút manganese carbonate deposit in Hungary. The covariation was tentatively attributed to coupled manganese oxyhydroxide reduction and organic matter oxidation, that has been described by Okita (1987), Okita and Shanks (1988), and Okita et al. (1988) for other sedimentary Mn carbonate deposits. Based on the covariation, Okita and Shanks (1988) proposed conversion of primary Mn-oxihydroxide precipitates to Mn carbonates as a normal consequence of diagenetic oxidation of sedimentary, organic matter. The δ13C-values observed for the above-mentioned deposits are intermediate between organic matter and marine inorganic dissolved carbonate values, and indicate contributions of carbon from both reservoirs.

Geochemistry 70

Covariation between the Mn concentration and δ13C values are not apparent in the Mn- rich zones (X, M, N and C), (Fig.5.9C). However, when all zones are considered a good negative correlation coefficient of –0.85 is calculated. This is tentatively attributed to the late diagenetic replacement of early diagenetic carbonates i.e. kutnahorite, hausmannite, partridgeite and Mn-calcite that is not observed outside zones with highest manganese content. For similar reasons the Ca concentration shows a good positive correlation with δ13C when all zones are considered and a poor positive correlation for the Mn-rich zones.

Of special interest is the covariation observed in the Ca-rich Y zone where SiO2, Fe2O3, 13 Mn3O4 and CaO concentrations show distinct covariation with δ C. CaO shows a very 13 good positive correlation of 0.96 with δ C, whereas SiO2, Fe2O3 and Mn3O4 all show moderate to good negative correlation. The very distinct negative correlation between δ13C and δ18O signatures, and the very low δ18O values for the Hotazel Formation can only find tentative explanations in this thesis and certainly demands further, more detailed investigation.

5.7 Discussion Whole rock geochemistry The great consistency attained between both drill cores and the close similarity of trends for specific lithostratigraphic zones illustrate that each one of the two both drill cores may be regarded as representative for the entire study area. The similarities shown by zones X and M for all major chemical components (Mn3O4, Fe2O3 and CaO) illustrate that X has a similar geochemical character to the currently mined M zone. To a lesser extent, the silica content, which is related to the manganese silicate mineral braunite, also follows similar trends for both X and M zones for each drill core.

Isotopic data Similar trends were observed for both drill cores (Fig. 5.6 & 5.7). δ13C and δ18O show a negative correlation to one another and the Mn concentration. In comparison to other large Mn carbonate deposits in the world the Kalahari manganese field (Fig.5.8) shows very similar δ13C carbonate signature but unusually low δ18O values.

Geochemistry 71

Table 5.6. Correlation coefficients for major elements and the δ13C signature for different subsets of data. A: entire data set (excluding supergene altered zones); B: carbonate rich Y zone only; C: Mn-rich X, M, N, C zones only. Note that for the entire data set, a negative correlation is observed between Mn and δ13C, and a positive correlation between CaO and δ13C.

A All lithostratigraphic zones, G558 and G552

SiO2 Fe2O3 Mn3O4 MgO CaO P2O5 δ δ13 -0.34 0.17 -0.85 -0.46 0.87 0.22

P2O5 0.34 0.2 -0.2 0.34 0.08 CaO -0.42 0.06 -0.93 -0.46 MgO 0.42 -0.16 0.35

Mn3O4 0.13 -0.38 Fe2O3 0.5

B Y zone only, G558 and G552 SiO2 Fe2O3 Mn3O4 MgO CaO P2O5 δ δ13 -0.78 -0.84 -0.99 0.32 0.96 0.04

P2O5 0.5 0.04 0.08 0.93 -0.11 CaO -0.91 -0.94 -0.98 0.17 MgO 0.24 -0.24 -0.19

Mn3O4 0.86 0.86 Fe2O3 0.86

C Zones X, M, N, C, G558 and G552 SiO2 Fe2O3 Mn3O4 MgO CaO P2O5

δ13 -0.4 -0.51 -0.38 -0.4 0.56 0.01

P2O5 0.62 -0.24 0.35 0.48 -0.47 CaO -0.36 -0.09 -0.89 -0.49

MgO 0.62 0.47 0.08

Mn3O4 0.08 -0.27 Fe2O3 0.14

A B -2 -2

-4 -4

-6 -6

C 3 -8 1

C -8 3

d 1 X1/8 -10 d -10 X3/8 X2/8 M4/8 M4/2 -12 M3/2 -12 M2/2 M3/8 M2/8 M1/2 -14 -14 M1/8 -16 -16 0 20 40 60 80 0 20 40 60 80

Mn3 O4 wt% Mn3 O4 wt%

C D -2 -2

-4 -4

-6 Y3/2 -6 Y3/2

C 3 Y3/8 Y3/8 1

C 3

1 d -8 Y2/8 -8 Y2/8 d

Y4/8 Y4/8 -10 Y4/2 Y4/2 -10

-12 -12 0 10 20 30 40 50 0 10 20 30 40

Mn3 O4 wt% CaO wt%

13 Figure 5.9 Plots illustrating the relationship between d C and the Mn content in all zones excluding supergene alteration (A), 7

2 Mn-rich X and M zones (B),and the carbonate-rich zone Y © as well as the Ca content of zone Y (D). Geochemistry 73

Unusually low δ18O values were also reported by Bau et al. (1999) for the Mooidraai dolomite immediately overlying the Hotazel Formation. These were attributed by the authors to cold (glacial) climatic conditions and a resulting unusually heavy δ18O composition of the world’s ocean water reservoir. The same explanation may also hold true for the manganiferous Hotazel Formation but this explanation is certainly not conclusive. Even more interesting is the negative covariation between δ13C and δ18O values. This covariation almost certainly reflects depositional and early diagenetic processes as also suggested by the negative covariation between δ18O and Mn concentrations. It may be related to the amount of oxygen supplied by sedimentary manganese oxihydroxide precipitates, in relation to oxygen supplied by oceanic or diagenetic water, or dissolved inorganic CO2 during the early diagenetic formation of the Mn carbonates (Okita et al 1988).

74 Density and Washability of the Ore Bed Chapter Six Density and Washability

6.1 Density measurements Whole rock density measurements were performed at the Department of Geology, RAU. Medium-sized lumpy ore (±5cm) and small chip samples (0.5-1cm) were carefully selected to be representative of each ore zone (lumpy samples) and of specific characteristic components such as ovoids, lenses and laminae (chip samples). Details of the analytical technique and descriptions of chip samples are presented in Appendix IV.

The densities obtained for the lower manganese ore bed range between 2.7 g/cm3 to 4.0 g/cm3 (Fi.6.1). As expected chip samples (0.5-1cm) from one lithostratigraphic zone show greater variation than large lumpy ore samples which report a consistent average for any one zone. The manganese rich X and M zones are marked by the greatest density, and the lowest variability, whereas the carbonate-rich Y zone has the lowest whole rock density (Figures 6.1 and 6.2). The greatest variability of densities for small chip samples is typical for carbonate-rich zones Y and C. This is explained by the fact that the carbonate-rich zones contain macroscopically distinct carbonate laminae, lenses and ovoids (low density) that could be separated as distinct chip samples from the braunite lutite laminae (high density), depending on the crushing size. Providing the crushing size remains small enough to separate the individual carbonate laminae, ovoids and lenses from the heavier oxides in the lutite laminae, the greater the variation in density within the Y zone is observed (Y3 zone in Fig.6.1).

The systematic variation in whole rock densities displayed in Figure 6.1 is consistent with the distribution and relative abundance of oxide and carbonate minerals in the different lithostratigraphic zones. Hausmannite, especially abundant in the Mn-rich X, M and C zones, has a very high density of 4.8 g/cm3. Calcite and Mn-calcite that are abundant in carbonate laminae in the Y, C and N zones, in contrast, have densities below 3.0g/cm3. Mn-carbonates have an intermediate density of 3.1–3.7 g/cm3 (kutnahorite, rhodochrosite respectively) and are the most abundant mineral phase present throughout the ore body.

s 3 75

e G558 Density g/cm

n Mineral phases

o Small Chips Lumpy ore (Listed in order of decreasing abundance) Z chips 2.6 3.4 4.2 2.6 3.4 4.2 Cryptomelane (matrix), kutnahorite (matrix), calcite E E-1 E-2 (vein), hematite (scattered grains), braunite (matrix). V-1 V V-2 Braunite (matrix), kutnahorite (matrix and ovoids), V-3 hematite (scattered grains), calcite (matrix). V-4 W-1 Braunite (matrix), kutnahorite (matrix and ovoids), W-2 hematite (scattered grains), calcite W W-3 W-4 Carbonate laminae containing hematite. W-5 X1-1 Braunite (matrix), kutnahorite (matrix and ovoids), X1-2 hausmannite (ovoids), Mn-calcite (ovoids), hematite X1 X1-3 (matrix and ovoids). X1-4 X2-1 Braunite (matrix), kutnahorite (matrix and ovoids), X2-2 hausmannite (ovoids), Mn-calcite (ovoids), hematite X2 X2-3 (matrix and ovoids). X2-4 X3-1 Braunite (matrix), kutnahorite (matrix and ovoids), X3 X3-2 Mn-calcite (ovoids). Hausmannite, hematite X3-3 (scattered grains). Y2-1 Y2-2a Braunite (matrix), kutnahorite (laminae, matrix, ovoids) Y2 Y2-2b Mn-calcite (ovoids, laminae), hematite (scattered grains, Y2-3 laminae). Y2-4 Y3-1 Y3-2 Braunite (matrix), kutnahorite (laminae, ovoids, matrix) Y3 Y3-2.5 Mn-calcite (laminae, matrix), hematite (laminae, ovoids). Y3-3 Y3-4 Y4-1 Y4-2 Braunite (matrix), kutnahorite (matrix, ovoids), hematite Y4 Y4-2.5 (ovoids, matrix), Mn-calcite (ovoids). Y4-3 Z1 Z2 Braunite (matrix), kutnahorite (matrix, ovoids), Z Z3 hematite (scattered grains), Mn-calcite (ovoids). Z4 Z5 M1-0 Braunite (matrix), kutnahorite (matrix, ovoids), M1 M1-1 Mn-calcite (ovoids), hematite (scattered grains). M1-2 M2-1 Braunite (matrix), kutnahorite (matrix, ovoids), M2 M2-2 hausmannite (ovoids), Mn-calcite (ovoids), hematite (ovoids). M2-3 M3-1 Braunite (matrix), kutnahorite (matrix, ovoids), M3 M3-2 hausmannite (ovoids), Mn-calcite (ovoids), hematite M3-3 (ovoids). M4-2 Braunite, kutnahorite, hematite, Mn-calcite, hausmannite. M4 M4-3 C2-1 C2-2 C2 C2-3 Braunite (matrix), kutnahorite (laminae), hematite C2-4 (laminae), hausmannite (ovoids laminae). C2-5 C2-6 C2-7 N-1 N-2 Braunite (matrix), kutnahorite (matrix, ovoids), Mn-calcite (laminae, ovoids), hematite (ovoids). N N-3 N-4 B-1 B Braunite (matrix), kutnahorite (matrix), hematite. B-2 Figure 6.1.Drill core G558. Range and average of whole rock density for all lithostratigraphic zones for the lower ore body of Mamatwan mine. Note the distinct difference between results for lumpy and chip samples. Density variations for small sample chips is indicated by bars. Detailed desciptions of small sample chips are listed in Appendix IV. Note that carbonate-rich, laminated zones (Y3, Y4, C2, N) show very large variations in density of chip samples whereas chips from Mn-rich zones show negligible variation. 76

s 3

e G552 Density g/cm Mineral phases n

o Chip Chips Lumpy ore (Listed in order of decreasing abundance)

Z samples 2.8 3.2 3.6 4 2.6 3 3.4 3.8 E-1 Cryptomelane (matrix), calcite (veinlet), hematite E (scattered grains), pyrolusite. E-2 Y1-1 Y1 Braunite (matrix), Mn-calcite (laminae, matrix) Y1-2 hematite (scattered grains, laminae). Y3-1 Braunite (matrix), kutnahorite (matrix, ovoids, Y3 laminae), Mn-calcite (laminae, ovoids), hematite Y3-2 (grains, laminae). Y4-1 Braunite (matrix), kutnahorite (matrix, ovoids), Y4 Y4-2 Mn-calcite (ovoids), hematite (ovoids, rare). Y4-3 Z-1 Z-2 Braunite (matrix), kutnahorite (matrix, ovoids), Z Mn-calcite (ovoids), hematite (matrix, ovoids), Z-3 hausmannite (ovoids). Z-4 M1-1 Braunite (matrix), kutnahorite (matrix, ovoids), M1 hematite (ovoids, matrix), Mn-calcite (ovoids), M1-2 hausmannite (ovoids). M2-1 Braunite (matrix), kutnahorite (matrix, ovoids), M2 M2-2 hematite (matrix, ovoids), hausmannite (ovoids). M2-3 M3-1 Braunite (matrix), kutnahorite (matrix, ovoids), M3 M3-2 hausmannite (ovoids), hematite (matrix, ovoids), Mn-calcite (ovoids). M3-3 M4-2 Braunite (matrix), kutnahorite (matrix, ovoids) M4 M4-1 hematite (matrix, ovoids), Mn-calcite (ovoids). C-1 C-2 Braunite (matrix), kutnahorite (matrix), C2 C-3 hematite (matrix, laminae, ovoids), hausmannite (laminae, ovoids). C-4 C-5 N-1 N-2 Braunite (matrix), kutnahorite (matrix, ovoids), N Mn-calcite (ovoids, laminae), hausmannite N-3 (ovoids). N-4 B-1 Braunite (matrix), kutnahorite (matrix), B-2 B hematite (matrix, laminae, ovoids), Mn-calcite B-3 (ovoids), hausmannite (ovoids). B-4

Figure 6.2. Drill core G552. Whole rock density plotted against lithostratigraphy and mineralogical composition for the lower ore bed at Mamatwan Mine. Note the distinct difference between results for lumpy ore and chip samples. Density variations of small sample chips are indicated by bars. Detailed descriptions of small sample chips are found in Appendis IV.Note the large density variation in the chip samples from carbonate-rich zones and negligible variation in the Mn-rich zones. 77 Density and Washability of the Ore Bed

The mineral phase with the greatest density however is hematite (5.2 g/cm3 ), a mineral that is present in variable amounts in all zones. It is especially abundant as fine-grained constituent in thin carbonate laminae in the Y and C zones. It also occurs widespread in the carbonate matrix and in ovoids in all other zones.

The manganese concentration is positively correlated with the whole rock density (Figure 6.3). This observation can be explained by the high manganese content and density of

hausmannite (Mn3O4), which accounts for the unusually high Mn concentrations in the X and M zones.

Figure 6.3. Binary plot illustrating positive covariation between Mn concentration (in wt%) and whole rock density (g/cm3). Note that only data from the V – N zones of the main ore body are plotted. Supergene altered zones (E, Y1) are omitted. Data for drill cores G558 and G552 combined.

6.2 Washability Washability tests were conducted by Billiton Process Research for all lithostratigraphic zones from drill cores G552 and G558. A novel and confidential method developed by BPR was used to test heavy medium separation for these samples. The details of this method were not revealed to the author and cannot be discussed in this thesis. However, the results are presented in Tables 6.1 and 6.2.

A few interesting observations were made regarding the washability of the different zones of the lower manganese ore bed. Only a small increase of the Mn grade is

cum. mass recovery Mn grade 78 A.

)

(

)

(

Relative density of suspension (g/cm3)

cum. mass recovery Mn grade B.

)

(

)

(

t e

Relative density of suspension (g/cm3)

cum. mass recovery Mn grade C.

)

(

)

(

d a

r m

e v

a u

Relative density of suspension (g/cm3)

Figure 6.4. Cumulative recovery values and Mn grade for variable densities. Drill core G558. A. X2 zone; B. Y3 zone; C. M2 zone. Note the very flat grade curve for all plots, indicating only minor changes in Mn content with increasing density. Note that even a marginal increase in grade always associated with a very steep drop in mass recovery. 79 Density and Washability of the Ore Bed characteristic for all zones, and this increase was obtained only at very low recoveries. This is illustrated in figure 6.4, where the cumulative recovery and Mn-grade are plotted against the density of the heavy medium used. The results illustrate that increasing the density of the heavy medium, has only a marginal effect on the Mn concentration while having a very distinct effect on recoveries. Heavy medium separation holds most promise for carbonate-rich zones that are marked by thick Mn-poor carbonate laminae, lenses, and ovoids. The latter have a distinctly lower density compared to oxide-rich laminae (matrix). However, results obtained for the washability of the carbonate-rich Y and C zones suggest that heavy media separation of the zones results in an increased Fe concentration rather than a significant increase in Mn content (Fig.6.5.D,E).

Individual plots were produced for specific density parameters that were used during the washability tests of each zone (Fig.6.5A, B, C, D, E). These plots indicate that the ideal density for maximum recovery (>40 mass %) and reasonable Mn grade (>30wt%) would be a sink value of 3.6 g/cm3 (Fig.6.5C). Highest Mn grades (>36 wt%) were attained with a density of 3.8 g/cm3 sink (Fig.6.5B). However, recovery is then less than 40 mass %.

6.3 Discussion

The variation in density measurements observed between different size samples (lumpy ore, chips), illustrate the influence of different mineral phases of each lithostratigraphic zone for ore processing purposes. The Mn-rich zones (X, M), consisting mostly of few mineral species, have little variation in density regardless of grain size. In contrast the carbonate rich zones contain a variety of mineral phases, each containing different densities at a small grain size. Washability tests conducted by Billiton Process Research (Table 6.1 & 6.2) illustrate that the increase in Mn concentration was very low throughout the different densities tested for Mn-rich zones. Mn-poor, carbonate rich (V, W, Y, Z, C) zones in contrast, responded by a significant increase in Fe concentration (Fig.6.5). From the results attained, the heavy media separation technique is considered to be a poorly suited method for upgrading the lower manganese ore bed material mainly

80 Density and Washability of the Ore Bed due to the fact that density variations are low in the Mn-rich zones and the Mamatwan- type ore in general is too fine grained to release components of greatly differing densities.

For the purpose of this study it is very important to note that on average the Mn-rich zones X and M, show virtually identical behaviour during the washability tests. It should therefore be possible to process the X zone in the same manner as the currently mined M zone. The C and N zones also produce reasonable Mn grade (>3.6 wt% Mn) at a sink value of 3.6 g/cm3 but at a low recovery (20-30 mass %). All other zones (V, W, Y, Z, B and L) show only poor grades (<32 wt% Mn) for reasonable recoveries (> 40 mass%).

81 A. B.

Recovered sample Concentrations of Mn and Fe in recovered sample

Assay results for recovered fraction

Bulk rock concentrations in wt %

Molar Mn/Fe* ratios

Figure 6.5 Plots illustrating the relation of recovery to Mn concentration in sink fraction vs. bulk rock Mn and Fe, content and Mn/Fe ratio with bulk rock for each lithostratigraphic zone at specific heavy medium densities. Drill core G558. A. Sink 4.0, B. Sink 3.8, C. Sink 3.6, D. Sink 3.4, E. Float 3.4. Note the similar trends observed for zones X and M. D. 82

Figure 6.5. Continued 83

Table 6.1. Washability results for drill core G558. Table A lists the mass recovery for each zone for specific densities. Table B. summarises the Mn grade for each zone at a specific density and Table C lists the corresponding Fe concentration for each zone at specific densities. The coloured blocks indicate the highest values attained for each zone. (Mn grade expressed as total Mn).

Mass Recovery A E V W X1 X2 X3 Y2 Y3 Y4 Z M1 M2 M3 M4 C2 N B L sink 4.0 0 0 0 8.54 6.48 0.48 0 0 0 0 4.59 7.11 10.74 1.66 4.78 9.62 11 0 sink 3.8 0 0.52 0 9.03 21.02 0.48 0 0 4.64 9.37 26.11 49.74 39.07 13.58 38.05 9.62 0 0 sink 3.6 0 9.44 14.32 41.97 50.74 8.83 0.2 0.05 56.76 26.64 41.92 39.84 47.41 75.08 26.83 30.44 11 2.42 sink 3.4 0 59.32 25.7 33.28 16.01 68.45 11.9 1.64 28.42 60.67 0 0 0 0 24.39 56.92 67.35 29.58 float 3.4 0 30.72 59.98 7.19 5.76 22.23 87.9 98.31 10.19 3.31 0 0 0 0 5.94 30.2 21.64 68 float 3.6 0 0 0 0 0 0 0 0 0 0 27.39 3.31 2.78 9.67 0 0 0 0

Highest Mass Recovery (in %)

Mn Grade B E V W X1 X2 X3 Y2 Y3 Y4 Z M1 M2 M3 M4 C2 N B L

Sink 4.0 0 0 0 47 45.8 35.9 0 0 0 0 45.7 43.6 45.5 40.4 47 40.1 30.9 0 Sink 3.8 0 28.3 0 42.5 43.4 35.9 0 0 32.6 33.4 40.5 43 43 40.7 41.5 40.1 0 0 Sink 3.6 0 30.9 30.2 37.5 38.8 36 0 0 30.9 34.9 36.5 36.6 38.9 37.7 38.4 36.1 30.9 20.7 Sink 3.4 0 29.9 30.4 30.5 33.4 31.5 27.8 26.5 27.6 31.9 0 0 0 0 34.1 31.5 28.1 19 float 3.4 0 25.60 25.80 27.10 27.10 27.30 23.80 18.40 19.30 28.20 0 0 0 0 38.24 24.7 21.5 18 float 3.6 0 0 0 0 0 0 0 0 0 0 33.10 28.30 32.40 33.60 0 0 0 0

Highest Mn grade

C Fe Grade E V W X1 X2 X3 Y2 Y3 Y4 Z M1 M2 M3 M4 C2 N B L Sink 4 .0 0 0 0 5.2 4 0 0 0 0 0 6.1 6.1 3.5 4.8 3.7 0 0 0 Sink 3 .8 0 5.1 0 4.3 4 4.7 0 0 6.4 12.7 7.7 5.7 3.6 4.3 4 4.7 0 0 Sink 3 .6 0 9.7 12.7 4.3 4.3 4.3 0 0 12.9 8 5.8 7 4.3 5.3 4.1 5.5 9.6 18.5 Sink 3 .4 0 8.6 5.6 4.9 5.3 4.9 1.5 3.4 12 5.6 0 0 0 0 4.1 6.5 9.5 19.1 Float 3.4 0 8.1 4.5 5.3 5.7 4.7 5.8 5.7 4.6 5.5 0 0 0 0 4 5.5 12.1 15.9 Float 3.6 0 0 0 0 0 0 0 0 0 0 6 10.7 5.6 5.3 0 0 0 0

Highest Fe grade 84

Table 6.2. Washability results for drill core G552. Table A. lists the mass recovery for each zone at different densities. Table B, summarises the Mn grade for each zone at different densities and Table C lists the corresponding Fe concentration for each zone at different densities. The coloured block mark the highest values observed for each zone.

A Mass Recovery

E Y1 Y3 Y4 Z M1 M2 M3 M4 C1 C2 B Sink 4.0 0 0 0 2.51 2.64 0 7.91 6.63 0.97 5.61 2.65 0 Sink 3.8 0 0 0 17.3 3.45 1.94 32.8 33 23.9 44.9 14 0 Sink 3.6 0 0 23.8 12.2 66.6 43.8 55.9 54.6 27.8 46.6 20.3 Sink 3.4 0 0.68 1.1 56.4 47.1 29.3 13.4 3.68 20.3 16.2 27.1 54 0 99.3 98.9 0 34.6 2.19 2 0.78 0.18 5.45 9.71 25.7 Highest Mass Recovery (in %)

B Mn Grade E Y1 Y3 Y4 Z M1 M2 M3 M4 C1 C2 B Sink 4.0 0 0 0 31.7 31.7 0 43.1 47.6 42.4 44.7 46.3 0 Sink 3.8 0 0 0 32.9 36.1 36.2 40 41.6 41.1 43.3 43.6 0 Sink 3.6 0 0 0 31.9 34.8 36.1 36.7 37.4 37.2 38.3 38.4 32 Sink 3.4 0 32.6 24.5 29.4 30.8 32.9 30.2 30.8 33.3 31.9 33.7 29.6 17.9 28.2 25.6

Highest Mn grade

Fe Grade C

E Y1 Y3 Y4 Z M1 M2 M3 M4 C1 C2 B Sink 4.0 0 0 5.1 Sink 3.8 0 7.7 5.9 Sink 3.6 0 6.9 4.3 Sink 3.4 11 5.5 4.9 5.7 4.3 8.3

Highest Fe grade Conclusions 85

Chapter Seven Conclusions

The focus of this study was to define the physical and chemical characteristics of the lower manganese ore bed of the Hotazel Formation at Mamatwan mine. The aim was to provide a set of data that may be used to explore new avenues of selective mining and beneficiation of the manganese ore and to improve the information available for modeling the origin and post-depositional evolution of the Kalahari manganese deposit. In addition to the fact that some of the resulting information may well find an application in the mining industry, there is also some information that is largely of academic interest. The latter shall be discussed first, while recommendation for the mining and beneficiation of low-grade manganese ores at Mamatwan mine will be discussed separately.

7.1 The diagenetic evolution of the Mamatwan-type ore The manganese ore bed at Mamatwan mine displays a series of sedimentary and diagenetic characteristics. The primary sedimentary characteristics are defined by fine laminations and the preservation of “dusty” hematite. The cyclicity observed throughout the ore bed is characteristic of a sedimentary process (Nel et al., 1986). The systematic change from Mn-rich to Mn-poor lithologies differentiates between two sedimentary cycles, which are well defined by physical properties as well as chemical and isotopic characteristics. Diagenetic phases including various carbonates and oxides predominate the mineralogy. They prevail throughout the ore bed and can be classified as either early or late diagenetic in origin as outlined in figure 7.1.

The microcrystalline Mg-kutnahorite matrix and closely associated braunite are regarded to be of early diagenetic origin. Carbonate ovoids (diagenetic micro-concretions) and laminae post-date the formation of this Mg-kutnahorite-braunite matrix, but formed prior to final compaction and lithification as illustrated by the spheroidal shape of the carbonate ovoids throughout the ore bed (Fig.7.1). Coarse-grained hausmannite, specularitic hematite, partridgeite and Mn-calcite in ovoids and laminae are attributed to late diagenesis and are largely restricted to the two Mn-rich zones (X and M) in the ore bed (Fig.7.1).

86 Paragenetic Sequence

Mineral phase Description Photograph

I Sedimentation

Hematite Dusty hematite finely scattered in the braunite Fe2 O3 lutite matrix.

II Early diagenesis

10 m Braunite Very fine-grained rounded 2+ 3+ to subhedral grains and Mn Mn 6 SiO12 aggregates that are very abundant throughout. Closely associated with kutnahorite to form the matrix 0.25mm

Braunite (grey) interspersed with kutnahorite (black).

Ca-Kutnahorite Various forms of Mg-Kutnahorite carbonate species coexist throughout the ore body Mn-calcite as fine-grained aggre- [Ca(Mn,Mg)(CO3 )2 ] gates in matrix; as small carbonate ovoids (zoned) and as carbonate laminae and lenses. 100 m SEM image of zone ovoids.

III Late diagenesis/Low-grade metamorphic facies

Hausmannite Coarse grained crystals replace Mn carbonate ovoids and carbonate 3O4 laminae. Replacement product of kutnahorite and braunite. Always originates in ovoid core.

0.25mm Large ovoid replaced by hausmannite (grey-blue).

Mn-calcite Coarse grained euhedral crystals associated with (Ca, Mn)CO3 hausmannite.

Calcite Finely intergrown with Mg-kutnahorite matrix CaCO3 0.25mm Ovoid containing hausmannite and euhedral Mn-calcite crystals.

Figure 7.1. Paragenetic sequence of the Lower-Mn ore body of the Mamatwan Mine.

½... 87

Partridgeite Closely intergrown with -Mn 2 O3 hausmannite.

0.25mm

Large aggregates ofpartridgeite (yellow) intergrown with hausmannite replaced ovoid.

Specularite Coarse grained euhedral crystals.Formed during Fe 2 O3 recrystallization of original hematite “dust”.

0.25mm Kutnahorite (red) ovoids surrounded by prismatic specularite (white). IV Supergene Enrichment

Cryptomelane Most abundant in the supergene enriched zone. KMn8O16 Occurs as fine grained Manjiroite masses that replace NaMn 8 O16 diagenetic carbonate and braunite.

0.06mm Carbonate ovoids and matrix replaced by cryptomelane

Fills small pore spaces in Barite the supergene enriched BaSO4 zone. Occurs as clusters of platy crystals.

SEM image illustrating clusters of platy barite crystals.

Romanechite Observed in stylolites of 4+ Ba (Mn ,Mn2+ ) O . the X zone (G558)and also x-1 8 16 xH2 O in the supergene enriched E zone in small veinlets.

Pyrolusite Identified only by XRD,. SEM image illustrating a stylolite filled with romanechite. 4+ Mn O 2 Was not identified microcopically in this study.

Figure 7.1. Continued. Conclusions 88

It is very important to note that these replaced ovoids are distinctly larger and have less distinct outlines than the original early diagenetic carbonate ovoids, therefore suggesting that the metasomatic replacement process extended into the immediately surrounding matrix replacing not only kutnahorite but also braunite (Fig.7.1). The replacement of kutnahorite by hausmannite and calcite is illustrated by the following equation:

3CaMn(CO3)2 + ½O2 ! Mn3O4 + 3CaCO3 + 3CO2

7.2 Cyclicity and lateral consistency of the ore bed Nel (1984) distinguished eleven lithological zones in the lower manganese ore bed and grouped these to constitute three chemosedimentary cycles. This subdivision provided a suitable bases for the mining operation at Mamatwan mine. The more detailed study on a much smaller area conducted here, has essentially confirmed Nel’s (1984) subdivisions. However it also led to further subdivision of some of the major zones into laterally consistent and texturally distinct subzones (X1,2,3, Y1,2,3,4, M1,2,3,4, C1,2 ). Furthermore, it revealed the presence of only two chemo-sedimentary cycles and not three as defined by Nel (1984). The lateral consistency of these subzones is illustrated by E-W and N-S cross-sections using selected drill cores (Fig.7.2). Undulations of the ore bed (Fig.7.2A and B) are related to gentle folding.

Results obtained for the two drill cores examined in detailed are virtually identical, indicating that the physical and chemical characteristics of the ore body are laterally very consistent across the mine lease area. It is therefore suggested to use the results obtained for G558 – the more complete section through the ore bed investigated here – as future reference for the physical and chemical properties of the lower manganese ore bed in the Mamatwan mine lease area. This specifically pertains to whole rock major and trace element geochemistry, whole rock density and whole rock washability of the ore bed.

A Pit outline

G429 M G A’ A O -1070 M O Benches A. L A D Legend T A. W 3 TC 2 BC bottom cut A 9 MC N MC middle cut 3 B 3 C 1 TC top cut G466 G511 G492 G453 f Cryptomelane enrichment along the -1095 -1095 -1095 -1095 -1095 4.5m f suboutcrop of the economic ore zone -1100 against the Kalahari Formation B’ Kalahari Formation f f Fault with fault breccia

f f f Fault 2m -1120 -1120 -1120 -1120 -1120 f

-1145 -1145 -1145 -1145 -1150 500m N

-1170 A -1170 -1170 D A M S 3 2 8

-1195 Legend

A A` Tertiary Kalahari calcrete B. Calcrete veins E zone Supergene enriched BIF G466 G416 G515 G559 G444 G512 -1095 -1095 -1095 -1095 -1095 -1095 V zone -1100 W zone

X1 zone

X2 zone

-1120 -1120 -1120 -1120 -1120 -1120 -1120 X3 zone

Y1 zone Y2 zone Lower Mn Y3 zone -1145 -1145 -1145 -1145 -1145 -1145 ore bed -1150 Y4 zone Z zone

M1 zone

-1170 -1170 -1170 -1170 M2 zone

M3 zone M4 zone

C1 zone -1195 -1200 C2 zone N zone B B` B zone L zone

Figure 7.2. A: W-E cross-section of the manganese ore bed at Mamatwan mine showing gentle folding. B: N-S cross-section of the 8 manganese ore bed at the Mamatwan mine showing gentle folding. C: Insert of Mamatwan mine map illustrating N-S (B-B’) and W-E (A-A’) 9 cross-sections as well as WNW-striking normal faults. Conclusions 90

The presence of two compositional (depositional) cycles in the lower manganese ore bed at the Mamatwan mine is clearly illustrated in Figure 7.3. The two cycles, centered around the Mn-rich X and M zones, are defined not only by geochemistry and mineralogy but also by whole rock density and stable isotope geochemistry. Both depositional cycles commence with carbonate-rich manganese lutite containing carbonate ovoids, followed by manganese-rich lutite containing abundant carbonate and hausmannite-filled ovoids. Both cycles terminate in a carbonate rich, finely laminated zone. The center of the two cycles, namely, the manganese-rich X and M zones are characterized by the abundance of hausmannite. Directly below the manganese-rich M zone is the laminated C zone, characterised by similar geochemical characteristics as the M zone. This zone is not similar mineralogically or lithostratigraphically to the M or X zones, but it exhibits an unusually high manganese concentration that is attributed to the abundance of hausmannite.

Subdivisions of the manganese rich X and M zones can be physically compared to one another. The X1 subzone appears to be similar in character to the M1 zone, the X2 similar to M3 and X3 very similar to M4. Zones containing the highest Mn3O4 concentration are X2 and M3 zones with values of 55.7% and 58.9%, respectively and Mn/Fe ratios of 9 for X2 and 11 for M3.

7.3 Recommendations for future mining and beneficiation at Mamatwan mine The close similarity between the X zone and the currently mine M zone with regards to physical properties and chemical composition is obvious (Table 7.1). Both zones are unusually Mn-rich, both have high Mn/Fe ratios and both have high densities with low internal variability attributed to the abundance of hausmannite. X and M zones also showed the most promising Mn-grade (>36 wt%) at reasonable recoveries (>40 mass %) (Table 7.1). The additional 5.5m thick X zone and the 7m thick M zone, together contribute 12.5m’s of Mn-rich ore. However, only the X1 and M2 subzones showed an increase in the Mn grade, the other subzones actually decreased in Mn grade after undergoing washability tests.

13 18 d 3 G558 d C PDB O PDB Density g/cm Mn3O4 % Fe 2 O3 % CaO % Mn/Fe atom %

-16 -14 -12 -10 -4 0 0

0 5 0 0 -8 -6 0 -16 -12 1

5 -14 -10 -6 -4 2 0 2.5 4

0 -8 0

Zones 2 4

2 2

Thickness 1 2 4

3 8

3 4

2 5 1 1

1 2 1 1

E 0.25m

V 3.45m

W 3.14m

X1 1.69m

X2 2.18m

X3 1.95m

Y2 3.39m

Y3 8.08m

Y4 0.52m

Z 2.08m

M1 1.18m M2 0.83m

M3 3.00m

M4 2.08m

C2 5.50m

N 2.42m

B 2.23m

Medium chips 2.33m L

Figure 7.3. Geochemical, isotopic and physical data acquired for drill core G558, which is representative of the low-grade Mamatwan-type ore at the

Mamatwan Mine. Note the presence of two depositional cycles reflected by geochemical as well as physical characteristics. Note also that both cycles 9

are centered around the Mn-rich M and X zones and that both these zones have virtually identical properties. 1 Table 7.1. Comparison between X and M zones for all chemical and physical properties examined in this study. All samples from drill core G558. Washability values were selected as to make highest mass recovery. Note the different density values for which highest mass recovery was observed.

Ave. Mineralogy Whole rock geochemistry Whole rock. Washability Carbonate stable Isotopes Texture Density Thick. 3 Highest 13 18 Mn Fe23O CaO Mn/Fe g/cm mass recovery Mn wt% d C (PDB) d O (PDB) Massive braunite lutite, Braunite (matrix), Wt% Wt% Wt% Molar ratio containing large spherical, Kutnahorite (matrix & ovoids) dark grey carbonate ovoids Hausmannite (ovoids) 35.98 6.11 14.8 12.25 3.50 41.97 -9.5 -11.8 X1 1.5m and lenticles. Mn-calcite (ovoids), 37.47 Hematite (matrix & ovoids) (Sink3.6)

Braunite lutite with Braunite (matrix), irregular-shaped, grey and Kutnahorite (matrix & ovoids) white, medium to large Hausmannite (ovoids) 12 50.74 X2 2m carbonate ovoids, as well as Mn-calcite (ovoids), 40.16 6.05 9.64 3.73 38.70 -10.4 -10.5 white carbonate lenticles. Hematite (matrix & ovoids) (Sink 3.6) Mottled appearance. Partridgeite (ovoids)

Braunite lutite matrix Braunite (matrix) containing medium and Kutnahorite (matrix & ovoids) 2m small, pink spherical ovoids Mn-calcite (ovoids) X3 31.23 6.83 18.3 6.64 3.58 68.45 31.40 -10.6 -13 with occasional large Hausmannite (ovoids) (Sink 3.4) zoned ovoids. Partridgeite (ovoids) Hematite (scattered grains)

Massively textured braunite Braunite (matrix) lutite, containing medium Kutnahorite (matrix, ovoids) 1.5m sized, grey and white Mn-calcite (ovoids) M1 37.40 7.85 12.7 6.91 3.74 41.92 36.50 -13.5 -10.8 carbonate ovoids and Hematite (scattered grains) (Sink 3.6) lenses.

Massively textured braunite Braunite (matrix) lutite, with alternating Kutnahorite (matrix,ovoids) Hausmannite (ovoids) M2 0.5m bands of white carbonate 40.50 9 10.6 6.52 3.83 49.74 42.98 -13 -10.2 ovoids and lenses. Mn-calcite (ovoids) (Sink 3.8) Hematite (ovoids) Partridgeite (ovoids) Braunite lutite, with Braunite (matrix) alternating bands containg Kutnahorite (matrix, ovoids) irregular shaped white ovds Hausmannite (ovoids) M3 3.5m 42.40 5.19 11.1 11.88 3.95 47.41 -12.4 -11.4 and bands characterized by Partridgeite (ovoids) (Sink 3.6) 38.80 white carbonate lenses. Mn-calcite (ovoids) Mottled appearance. Hematite (ovoids) Braunite lutite, containing Braunite (matrix) small to medium sized Kutnahorite (matrix, ovoids) 2m irregular shaped white Hematite (ovoids, matrix) M4 carbonate ovoids. Few thin Mn-calcite (ovoids, lenses) 38.80 6.22 13.2 9.05 3.8 75.08 37.60 -11.3 -12.6 white carbonate lenses. Hausmannite (ovoids) (Sink 3.6) Mottled appearance.

2 93

-2100 -2200 -2000

-7600 -25

-7800 -50

-8000 -75

-8200 -100

-8400

-7600

-25 -7800

-50 -8000 -75 Legend

-8200 E zone -100 X zones -8400 M zones -2100 -2200 -2000

Figure 7.4 Cut-away 3-D model illustrating the lateral consistency of the manganese rich X and M zones. The E zone shows the topography, notice especially the depression in the northwestern corner of the mine lease area. Conclusions 94

Washability tests illustrate that a substantial (>5wt%) increase in Mn grade cannot be obtained for most zones, even at dramatically low (<20 mass %) ore recoveries. This is especially true for the X and M zones. The whole rock Mn grade for the X and M subzones, excluding the X1 and M2 subzones, is only less than 5 wt% lower than the samples that were subjected to washability testing. This indicates that the heavy medium separation technique is not suited for this type of material. An alternative solution to possibly increase the Mn grade would be to actively practice selective mining methods and mine only the X and M zones and continue to sinter the final ore product.

Figure 7.5. Map of Mamatwan Mine illustrating the suboutcrop of the X zone against the Kalahari Formation and the present outline of the pit. Note that the pit will intersect the X zone very soon, in a westerly direction.

The X and M zones and their respective subzones were found to be laterally consistent throughout the entire mine lease area. A 3-D model depicting the E, X and M zones reveals an apparent depression/syncline in the north-western corner of the mine lease area (Fig.7.4). The suboutcrop in the east against the Kalahari Formation is a result of erosion and is therefore responsible for the absence of the X zone in the area mined at present at Mamatwan. However, the X zone will be encountered immediately to the west of the

Conclusions 95

present open pit, at a depth of ±38m up to 68m (in the depression) in the north-western corner of the mine lease area (Fig.7.5).

Based on the data acquired during this study, the 5.5m thick X zone is identified as an additional section of the ore body that is an attractive target for selective mining at Mamatwan mine in the near future. The chemical and physical properties closely resemble those of the M zone, which is currently being mined and beneficiated. Although the X zone is not as thick as the current mined economic zone, it does have the advantage of being located closer to surface. A simple sketch (Fig.7.6) illustrates how open pit mining could be modified to get the added benefit of the X zone by either opening up a second pit or advancing the stripping of the calcrete ahead of the present upper cut across the X zone, before mining the M zone in the middle cut.

Figure 7.6. Sketch illustrating the suggested modification of present day mining method to access and exploit the X zone in a separate open pit.

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102

Appendix I: Drill core logs

22 drill cores of the manganese ore bed were logged in detail at Mamatwan Mine.

Figure I.1: G327 Figure I.2: G416 Figure I.3: G429 Figure I.4: G444 Figure I.5: G453 Figure I.6: G466 Figure I.7: G475 Figure I.8: G478 Figure I.9: G492 Figure I.10: G511 Figure I.11: G512 Figure I.12: G515 Figure I.13: G531 Figure I.14: G540 Figure I.15: G548 Figure I.16: G552 Figure I.17: G558 Figure I.18: G559 Figure I.19: G565 Figure I.20: G421 Figure I.21: G433 Figure I.22: G445 103

G327 Depth Thickness

30.98m

5.10m Calcrete Co-ordinates: X: 2112.916m 36.08m Y: 30 28284.77m 2.15m E

38.23m Elevation Z: 1093.89m

2.89m X2 X

41.12m

2.08m Y2 Y

43.20m

3.98m Z

47.18m 1m M0 48.18m 1m M1 49.18m

1.68m M2 M 50.86m

4m M3

54.86m

2.15m C1 57.01m

C 5.50m C2

62.51

3.59m N

66.10m

3.44m B

69.54m 1.21m L 70.75m

Figure I.1. Drill core G327 104 G416

Depth Thickness

40.69m

3.09m E Co-ordinates: X: 2310.92m Y: 30 27780.37m 43.78m Elevations Z: 1092.92 2.20m X1

45.98m

2.02m X2 X

48.00m 1.25m X3 49.25m 0.79m Y1 50.04m

4.10m Y2

54.14m Y

3.81m Y3

57.95m

1.76m Y4 59.71m

2.80m Z

62.51m 1.23m M1 63.74m

3.65m M3 M

67.39m 1m M4 68.39m

5.60m C2 C

73.99m

3.03m N

77.02m

2.53m B

79.55m

2.32m L

81.87m

Figure I.2. Drill core G416 105

G429

Depth Thickness 39.59m Co-ordinates X: 1765.13m Y: 30 27854.64m Elevation Z: 1094.98m

5.25m E

44.84m

3.99m M3

M 48.83m

2.77m M4

51.60m

6.43m C2 C

58.03m

4.02m N

62.05m

3.12m B

65.17m

3.74m L

68.91m

Figure I.3. Drill core G429 106

G444 Depth Thickness 34.45m Co-ordinates X: 2222.136m Y: 30 28369.193m 4.40m W Elevation Z: 1093m

38.85m 1.04m X1 39.89m

1.80m X2 X 41.69m 1.10m X3 42.79m 1.68m Y2 44.47m Y 1.69m Y3 46.16m Y4 47.08m 0.92m

3.38m Z

50.46m

2.57m M1

53.03m 0.58m 53.61m M2

3.66m M3 M

57.27m

2.52m M4

59.79m

7.35m C2 C

67.14m

3.26m N

70.40m

2.47m B

72.87m 1.40m L 74.27m

Figure I.4. Drill core G444 107

G453

Depth Thickness

42.70m Calcrete 43.45m 0.75m Co-ordinates X: 0.09m E 1843.914m 1.34m Y1 Y: 30 27797.042m 44.88m Elevation Z: 1094.092m

4.33m Y3 Y

69.21m 0.79m 50.00m Y4 1.41m Z 51.41m

1.52m M1 52.93m 1.31m M2 54.24m M 3.40m M3

57.64m

1.70m M4 59.34m

5.33m C2 C

64.67m

3.30m N

67.97m

3.25m B

71.22m 1.10m L 72.32m

Figure I.5. Drill core G453 G466 108 Depth Thickness 49.81m Co-ordinates X: 2308.67m Y: 30 27563.63m Elevation Z: 1092.11m

10m Supergene Enriched BIF

59.81m 1m E 60.81m

2m V

62.81m

5.30m W

68.11m

2.45m X1

70.56m

2.30m X2 X

72.86m

3.10m X3

75.96m 0.95m Y1 76.91m

4.40m Y2 Y 81.31m

4.07m Y3

85.38m

3.46m Z

88.84m 0.90m M2 89.74m

4m M3 M

93.74m 0.70m M4 94.44m

5.55m C2 C

99.99m 99.99m 109

2.37m N

102.36m

2.70m B

105.06

4.15m L

109.21m

Figure I.6. Drill core G466 (continued from previous page) G478 110 Depth Thickness 40.50m Co-ordinates X: 2483.08m Supergene Y: 30 28016.18m 7m Enriched BIF Elevation Z: 1091.57m

47.50m 1.32m E 48.82m

3.47m V

52.29m

4.53m W

56.82m 1.1m X1 57.92m

X2 3.89m X

64.81m

2m X3 63.81m 1m Y1 64.81m

2.32m Y2

67.13m Y

6.04m Y3

73.17m 0.68m 73.85m Y4

3.27m Z

77.12m 1.06m 78.18m M1 78.71m 0.53m M2 M 2.76m M3

81.47m 1.21m M4 82.68m 1.66m C1 84.34m

4.87m C2

89.21m 111

2.89m N

92.10m

2.96m B

95.06m

4.66m L

99.72m

Figure I.8. Drill core G478 (continued from previous page) 112

G492

Depth Thickness 43.60m Co-ordinates X: 1978.35m Y: 30 27689.7m 5.41m Calcrete Elevation Z: 1092.93m

49.01m

2.66m E

51.67m 0.81m Y1 52.48m

6.10m Y3 Y

58.58m 0.80m Y4 59.38m

3.30m Z

62.68m

1.24m M1 63.50m 0.82m 64.32m M2

2.70m M3 M

67.02m

2.40m M4

69.42m 70.01m 0.59m C1

6.86m C2 C

76.87m

2.37m N

79.24m

1.90m B 81.14m

2.40m L 82.10m

Figure I.9. Drill core G492 G511 113

Depth Thickness 46.90m Co-ordinates X: 2135.98m 0.8m V 47.70m Y: 30 27649.41m Elevation Z: 1091.98m

5.35m W

53.05m 1.73m X1

54.78m

5m X2 X

59.78m 1.70m X3

61.48m

2.32m Y1

63.80m

2.52m Y2 Y 66.32m

5.02m Y3

71.34m 1.03m Y4 72.37m

2.74m Z

75.11m

2.44m M2

77.55m

M 3.69m M3

81.24m 1m M4 82.24m 82.61m 0.37m C1

5.63m C2 C

88.24m

3.41m N

91.65m 114

3.10m B

94.75m

4.87m L

99.62m

Figure I.10. Drill core G511 (continued from previous page) 115 G512

Depth Thickness 33.80m 34.45m 0.65m Calcrete 1.82m V Co-ordinates X: 2131.3m 36.27m Y: 30 28426.84m 2.70m W Elevation Z: 1092.88m

38.97m

1.56m X1 40.53m

2.46m X2 X

42.99m 1m X3 43.99m 1.54m Y2 45.53m 1m Y3 Y 46.53m

1.57m Y4 48.10m

3.53m Z

51.63m 52.37m 0.74m M1

3.20m VEIN

55.57m M 1.30m M3 56.87m 1.40m M4 58.27m

1.80m C1 60.07m

C 6.99m C2

67.06m

3.94m N

71.00m

2.95m B

73.95m

2.85m L

76.80m

Figure I.11. Drill core G512 116

G515

Depth Thickness 36.50m Co-ordinates X: 2284.61m

3.83m E Y: 30 27955.96m Elevations Z: 1093.19m

40.33m

1.63m X1 41.96m

2m X2 X

43.96m

2m X3

45.96m 1.40m Y1 47.36m 1.44m Y2 48.80m Y 55.80m 7m Y3 1.05m Y4 56.85m

1.8m Z 58.65m

2.3m M2

60.95m

2.85m M3 M

63.80m

1.76m M4 65.56m 0.95m C1 66.51m

C 5.39m C2

71.90m

3.02m N

74.92m

2.26m B

77.18m

5.4m L

82.58m

Figure I.12. Drill core G515 117

G531

Depth Thickness 46.70m Co-ordinates X: 1826.08m

2.10m E Y: 30 27563.45m

48.80m Elevation Z: 1093.13m

2.16m M3

50.96m M

1.77m M4

52.73m

7.70m C2 C

60.43m

1.70m N 62.13m

2.05m B

64.18m

6.42m L

70.60m

Figure I.13. Drill core G531 118

G540

Depth Thickness 47.80m

Co-ordinates X: 1977.23m 3.78m E Y: 30 27476.21m Elevation Z: 1091.92m 51.58m 1.55m Y3 Y 53.13m

3.64m Z

56.77m 1.47m M1 58.24m 0.95m M2 59.19m M

3.49m M3

62.68m 1.2m M4 63.88m 0.78m 64.66m C1

7.07m C2 C

71.73m

3.30m N

75.03m

3.86m B

78.89m

3.74m L

82.63m

Figure I.14. Drill core G540 119

G548

Depth Thickness 43.65m 0.64m Co-ordinates X: 1794.46m 44.29m E 44.77m 0.48m Calcrete Y: 30 27683.77m

2.93m E

47.70m

2.65m Z

50.35m 0.80m M1 51.15m 1.30m M2 52.45m

4.40m M3 M

56.85m

1.45m M4 58.30m 0.73m C1 59.03m

5.64m C2 C

64.67m

3m N

67.67m

3.10m B

70.77m

5.70m L

76.47m

Figure I.15. Drill core G548 120

G552

Depth Thickness 43.95m Co-ordinates X: 1929.01m 2.86m E Y: 30 27604.97m

46.81m 1.58m Y1 48.39m

4.09m Y3 Y

52.48m 1.09m Y4 53.57m

3.48m Z

57.05m 0.84m M1 57.89m 1.18m M2 59.07m

3.54m M3 M

62.61m 1.52m M4 64.13m 64.40m 0.27m C1

6.889m C2 C

71.29m

3.23m N

74.52m

2.35m B

76.87m

3.08m L

79.95m

Figure I.16. Drill core G552 121

G558 Depth Thickness 40.20m 0.25m 40.45m E

3.45m V Co-ordinates X: 2334.03m Y: 30 28027.07m 43.90m

3.14m W

47.04m 1.69m X1 48.73m 2.18m X2 X

50.91m 1.95m X3 52.86m

3.39m Y2

56.25m

8.08m Y3

64.33m 64.85m 0.52m Y4 2.08m Z 66.93m 1.18m M1 68.11m 0.83m 68.94m M2

3.00m M3 M

71.94m

2.08m M4 74.02m

5.50m C2 C

79.52m

2.42m N 81.94m

2.23m B 84.17m

2.33m L 86.50m

Figure I.17. Drill core G558 G559 122

Depth Thickness 39.75m 1.33m E 41.08m Co-ordinates X: 2312.79m 2.28m V Y: 30 28144.19m 43.36m

3.94m W

47.30m

1.89m X1 49.19m

2.22m X2 X 51.41m

1.52m X3 52.93m

2.88m Y2

55.81m Y

3.40m Y3

59.21m

4.62m Z

63.83m

2.03m M1

65.86m 1.08m M2 66.94m M 2.78m M3

69.72m

2.68m M4

72.40m

7.30m C

79.40m

2.10m N

81.80m

1.80m B 83.60m

3.41m L

87.01m

Figure I.18. Drill core G559 G565 123

Depth Thickness 41.60m 1.04m E 42.64m Co-ordinates X: 2416.39m Y: 30 28288.79m 2.42m V

45.06m

2.80m W

47.86m

2.03m X1

49.89m X 1.94m X2 51.83m 1.23m X3 53.06m

2.33m Y2

55.39m Y

2m Y3

57.39m 0.78m Y4 58.17m

5.12m Z

63.29m

1.90m M2

65.19m

3.12m M3 M 68.31m 1.43m M4 69.74m

1.54m C1 71.28m

6.42m C2

77.70m 1.03m N 78.73m

3.84m B

82.57m

2.12m L 84.69m

Figure I.19. Drill core G565 124

G421 Thickness Co-ordinates X: 2185.871m Y: 30 27839.071m Elevation Z: 1093.291m

8.12m E

1.41m Y1

2.13m Y2

6.10m Y3

0.92m Y4

3.54m Z

1.59m M2

3.60m M3 M

2.05m M4

6.00m C2 C

3.93m N

1.87m B 0.35m L

Figure I.20. Drill core G421 125

G433

Depth Thickness 41.91m Co-ordinates: X: 2062.5m 1.82m E Y: 30 27812.5m 43.73m 44.19m 0.46m Y2

6.72m Y3 Y

50.91m

1.8m Y4

52.71m

2.37m Z

55.08m 1.25m M1 56.33m 0.69m M2 57.02m

2.7m M3 M

59.72m

3m M4

62.72m

7m C2 C

69.72m

3.m N

72.72m

2.m B

74.72m

1.65m L 76.37m

Figure I.21. Drill core G433 126 G445

Depth Thickness 34.25m Co-ordinates X: 2.27m E 220.442m Y: 30 8223.679m 36.52m 1.09m X1 Elevation Z: 1092.979m 37.61m

1.72m X2 X 39.33m

2.49m X3

41.82m

2.28m Y2 44.10m Y 1.25m 45.35m Y4

3.83m Z

49.18m

2.40m M2 51.58m

3.78m M3 M

55.36m

1.86m M4 57.22m

Vein 2.71m

59.93m

4.42m C2 C

64.35m

3.46m N

67.81m

2.70m B

70.51m

4.15m L

74.66m

Figure I.22. Drill core G445 127

Appendix II: Whole rock geochemical data

Contents: . Table II.1: Major and trace element chemistry for samples form drill core G558 (Set Point Laboratories). Table II.2: Major and trace element chemistry for samples from drill core G552 (Set Point Laboratories). Table II.1. Major and Trace element chemistry for samples from drill core G558 (Set Point Laboratories) G558 Major Elements Sample # *Fe2O3 FeO *Mn3O4 CaO K2O P2O5 SiO2 Al2O3 MgO Na2O Cl S L.O.I Total % % % % % % % % % % % % % % V 11.9 LLD 37.52 19.3 0.12 0.08 5.7 0.2 3.3 0 0.01 0.02 -22.2 100.35 W 7.97 LLD 41.71 21.4 0.22 0.09 5.1 0.3 3.6 LLD 0.02 0.02 -22.2 102.35 X1 5.94 LLD 47.19 14.8 0.13 0.06 4.8 0.5 3.6 LLD 0.01 0.03 -18.2 95.26 X2 5.93 LLD 55.15 11.9 0.17 0.07 5.3 0.3 3.5 LLD 0.01 0.05 -14.8 97.18 X3 6.91 LLD 42.79 18.6 0.23 0.07 5.7 0.4 3.5 LLD 0.02 0.03 -19.9 98.15 Y2 7.09 LLD 36.44 23.4 0.05 0.08 4.4 0.2 2.6 LLD 0.02 0.02 -23.3 97.60 Y3 6.68 LLD 24.94 30.0 0.03 0.09 3.9 0.2 2.8 LLD 0.02 0.03 -28.1 96.79 Y4 17.5 LLD 43.65 14.1 0.02 0.10 5.7 0.3 2.5 LLD 0.02 0.02 -14.6 98.51 Z 8.83 LLD 43.65 15.3 0.02 0.07 5.5 0.2 3.9 LLD 0.02 0.03 -17.8 95.32 M1 7.75 LLD 48.59 13.1 0.29 0.06 5.7 0.5 3.9 LLD 0.02 0.03 -15.6 95.54 M2 8.59 LLD 54.40 10.9 0.26 0.06 4.9 0.2 3.2 LLD 0.02 0.04 -13.3 95.87 M3 5.35 LLD 59.13 11.9 0.24 0.06 6.0 0.4 3.2 LLD 0.01 0.04 -13.6 99.93 M4 6.02 LLD 52.35 13.4 0.04 0.06 4.8 0.1 3.1 LLD 0.01 0.11 -16.0 95.99 C2 5.28 LLD 49.67 17.1 0.32 0.06 4.7 0.2 2.5 LLD 0.01 0.10 -15.8 95.54 N 7.51 LLD 45.26 17.0 0.09 0.07 4.8 0.3 2.7 LLD 0.02 0.18 -17.9 95.83 B 11.9 LLD 41.17 17.3 0.09 0.08 5.7 0.4 3.0 LLD 0.02 0.03 -19.3 98.99 Sample # Cu Zn Ni Co Pb Ba V Ti Cr Sr Zr ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm E 7 2 32 26 1 146 28 51 72 1020 1 V 1 LLD 42 25 1 80 36 65 94 295 LLD W 15 9 47 23 1 29 27 36 87 183 LLD X1 6 38 44 29 LLD 165 41 36 109 121 LLD X2 17 43 53 32 1 1394 44 94 130 156 LLD X3 14 LLD 47 28 LLD 94 37 51 93 205 LLD Y2 14 1 43 21 LLD 127 29 65 81 474 1 Y3 LLD LLD 24 23 LLD 93 20 22 58 394 LLD Y4 5 LLD 55 37 LLD 4 38 51 108 156 LLD Z 12 10 49 20 1 20 41 51 111 101 LLD M1 13 27 49 23 1 64 32 65 122 122 LLD M2 10 30 50 23 1 375 39 51 130 126 LLD M3 18 16 59 20 LLD 389 39 80 135 88 LLD M4 14 LLD 49 22 1 1275 43 36 114 69 LLD C2 15 76 51 19 LLD 1362 33 65 113 98 LLD N 10 11 41 18 1 2241 37 65 100 121 LLD B 15 11 45 26 1 108 29 51 99 130 LLD

L.O.I - loss on ignition LLD - lower than limit of detection

* Total Fe expressed as Fe2O3, and Mn is expressed as Mn3O4, in order to calculate reliable analytical totals to test the 1 2 quality of data reported. 8 Table II.2 Major and Trace element che mistry for samles from drill core G552 (Se t Point Laboratories).

G552 Major Elements Sample # *Fe2O3 FeO *Mn3O4 CaO K2O P2O5 SiO2 Al2O3 MgO Na2O Cl S L.O.I Total % % % % % % % % % % % % % % E 9.04 LLD 42.36 21.2 2.09 0.10 4.5 0.4 1.6 LLD 0.01 0.04 -20.8 102.14 Y1 7.58 LLD 34.72 29.5 0.30 0.10 4.7 0.3 0.7 LLD 0.01 0.03 -24.1 102.04 Y3 7.25 LLD 26.23 32.2 0.06 0.09 3.8 0.3 2.4 LLD 0.03 0.03 -28.7 101.09 Y4 14.0 LLD 44.40 18.9 0.10 0.09 5.5 0.4 2.1 LLD 0.03 0.02 -17.7 103.24 Z 8.47 LLD 42.68 16.7 0.08 0.07 5.2 0.3 3.8 LLD 0.02 0.02 -19.3 96.64 M1 7.33 LLD 50.20 13.4 0.04 0.06 5.4 0.3 3.5 LLD 0.02 0.02 -15.7 95.97 M2 8.11 LLD 53.21 11.3 0.14 0.06 5.1 0.4 3.3 LLD 0.02 0.02 -14.1 95.76 M3 5.73 LLD 54.07 12.8 0.13 0.06 5.9 0.3 3.2 LLD 0.01 0.02 -14.7 96.92 M4 5.93 LLD 49.24 15.0 0.11 0.06 5.5 0.2 3.2 LLD 0.01 0.03 -16.7 95.98 C1 (G565) 5.81 LLD 55.58 12.4 0.14 0.06 3.5 0.2 4.1 LLD 0.01 0.02 -14.0 91.72 C2 4.83 LLD 50.42 17.0 0.18 0.06 3.6 0.2 3.1 LLD 0.01 0.04 -16.5 95.94 N 7.91 LLD 46.98 15.7 0.04 0.06 5.1 0.3 3.1 LLD 0.02 0.07 -16.2 95.48 B 12.1 LLD 44.94 17.4 0.05 0.08 6.0 0.3 3.4 LLD 0.02 0.03 -18.3 102.62 G552 Trace elements Sample# Cu Zn Ni Co Pb Ba V Ti Cr Sr Zr E 12 5 42 26 2 231 68 65 95 1561 1 Y1 6 3 37 22 1 111 24 36 67 497 1 Y3 3 1 27 19 1 100 24 7 63 453 1 Y4 8 LLD 49 18 LLD 2 36 51 107 277 1 Z 6 LLD 48 27 LLD 382 36 80 139 146 LLD M1 7 10 44 24 LLD 835 34 80 129 153 LLD M2 20 28 45 26 1 1259 50 65 130 142 LLD M3 18 14 60 18 LLD 393 47 65 131 89 LLD M4 10 11 42 19 LLD 265 42 51 116 85 LLD C1 (G565) 19 94 59 22 1 7 42 36 125 97 LLD C2 13 53 41 21 1 312 37 36 102 162 LLD N 7 10 44 21 LLD 843 38 65 111 135 LLD B LLD 7 37 22 1 86 35 36 108 140 LLD

L.O.I - loss on ignition LLD - low er than limit of detec tion * Total Fe expres sed as Fe2O3, and Mn is express ed as Mn3O4, in order to calculate reliable analytical totals to test the

quality of data r eported. 9 130

Appendix III: Carbonate stable isotope geochemistry

Contents:

Table III.1: Carbonate stable isotopic data for whole rock samples from drill cores G558 and G552 Table III.2: Calibration data.

All data as reported by Horstmann (2000) 131

Table III.1 Analytical results of aliquot C/O isotope determinations

Mineral composition by XRD (RAU)

δ13 δ18 δ18

C ‰ O‰ O‰ Sample t[h] T[°C] high low tube PDB PDB SMOW calcite calcite braunite Analysis hematite jacobsite Mncalcite Mncalcite kutnahorite partridgeite weight [mg]weight hausmannite cryptomelane

G552-B C2915 20.0 18 50 0 0.300 0 -11.551 -13.274 17.176 x x x x x x C2916 20.0 18 50 0 0.296 0 -11.506 -13.177 17.276 avg.: -11.528 -13.226 17.226 diff.: 0.045 0.097 0.099 G552-C2 C2911 20.0 15 50 0 0.279 0 -11.710 -14.327 16.091 x x x x x C2912 20.0 15 50 0 0.292 0 -11.696 -14.288 16.131 avg.: -11.703 -14.307 16.111 diff.: 0.014 0.038 0.039 G552-E C2826 20.0 16 25 0 0.245 0 -5.537 -5.110 25.593 x x x C2827 20.0 nr 25 0 0.247 0 -5.524 -5.328 25.367 avg.: -5.531 -5.219 25.480 diff.: 0.013 0.218 0.225 C2920 20.0 17 50 0 0.233 0 -5.770 -5.121 25.581 C2921 20.0 17 50 0 0.221 0 -5.772 -5.058 25.646 avg.: -5.771 -5.090 25.613 diff.: 0.002 0.063 0.065 G552-M1 C2901 20.0 15 50 0 0.264 0 -13.305 -10.932 19.591 x x x x x C2902 20.0 15 50 0 0.274 0 -13.295 -10.904 19.620 avg.: -13.300 -10.918 19.605 diff.: 0.010 0.028 0.029 G552-M2 C2903 20.0 15 50 0 0.225 0 -13.034 -9.611 20.952 x x x x C2904 20.0 15 50 0 0.233 0 -13.019 -9.596 20.968 avg.: -13.027 -9.604 20.960 diff.: 0.015 0.015 0.015 G552-M3 C2905 20.0 18 50 0 0.246 0 -12.108 -11.636 18.865 x x x x x C2906 20.0 18 50 0 0.250 0 -12.110 -11.640 18.861 avg.: -12.109 -11.638 18.863 diff.: 0.002 0.004 0.004 G552-M4 C2907 20.0 18 50 0 0.286 0 -11.521 -12.917 17.545 x x x x C2908 20.0 18 50 0 0.264 0 -11.522 -12.977 17.482 avg.: -11.521 -12.947 17.514 diff.: 0.000 0.060 0.062 G552-N C2913 20.0 15 50 0 0.264 0 -11.891 -13.278 17.172 x x x x x C2914 20.0 15 50 0 0.266 0 -11.884 -13.278 17.172 avg.: -11.888 -13.278 17.172 diff.: 0.008 0.000 0.000 G552-Y1 C2891 20.0 20 50 0 0.394 0 -5.126 -9.211 21.365 x x x x x C2892 20.0 20 50 0 0.410 0 -5.119 -9.156 21.422 avg.: -5.123 -9.184 21.393 diff.: 0.007 0.055 0.057 G552-Y3 C2893 20.0 20 50 0 0.523 0 -6.420 -15.152 15.240 x x x x C2894 20.0 20 50 0 0.503 0 -6.446 -15.197 15.194 avg.: -6.433 -15.175 15.217 diff.: 0.026 0.045 0.046

132

Table III.1 continued

Mineral composition by XRD (RAU)

δ13 δ18 δ18

C ‰ O‰ O‰ Sample t[h] T[°C] high low tube PDB PDB SMOW calcite calcite braunite Analysis hematite jacobsite Mn-calcite kutnahorite partridgeite weight [mg]weight hausmannite cryptomelane

G552-Y4 C2895 20.0 22 50 0 0.301 0 -9.926 -14.419 15.996 x x x x x C2896 20.0 22 50 0 0.313 0 -9.906 -14.345 16.073 avg.: -9.916 -14.382 16.034 diff.: 0.021 0.075 0.077 G552-Z C2897 20.0 22 50 0 0.328 0 -11.117 -11.948 18.543 x x x x C2898 20.0 22 50 0 0.327 0 -11.121 -11.944 18.547 avg.: -11.119 -11.946 18.545 diff.: 0.004 0.004 0.004 G558-B C2824 20.0 16 50 0 0.324 0 -11.102 -13.546 16.896 x x x x x x C2825 20.0 16 50 0 0.324 0 -11.123 -13.579 16.862 avg.: -11.113 -13.562 16.879 diff.: 0.020 0.033 0.034 G558-C2 C2818 20.0 nr 50 0 0.282 0 -11.255 -13.600 16.840 x x x x x C2819 20.0 nr 50 0 0.281 0 -11.243 -13.609 16.831 avg.: -11.249 -13.605 16.835 diff.: 0.012 0.009 0.009 G558-E C2803 20.0 1 25 0 0.265 0 -5.701 -6.965 23.680 x x x x x x C2804 20.0 1 25 0 0.256 0 -5.696 -6.983 23.662 avg.: -5.699 -6.974 23.671 diff.: 0.005 0.018 0.019 G558-M1 C2797 20.0 21 50 0 0.257 0 -13.023 -10.517 20.018 x x x x x C2798 20.0 21 50 0 0.211 0 -13.545 -11.903 18.590 avg.: -13.284 -11.210 19.304 diff.: 0.521 1.386 1.428 C2917 20.0 18 50 0 0.255 0 -13.526 -10.837 19.689 C2918 20.0 18 50 0 0.274 0 -13.529 -10.829 19.697 avg.: -13.527 -10.833 19.693 diff.: 0.003 0.008 0.008 G558-M2 C2809 20.0 21 50 0 0.193 0 -12.972 -10.227 20.318 x x x x x C2810 20.0 21 50 0 0.206 0 -12.976 -10.236 20.308 avg.: -12.974 -10.231 20.313 diff.: 0.004 0.009 0.010 G558-M3 C2812 20.0 17 50 0 0.195 0 -12.384 -12.223 18.259 x x x x x C2813 20.0 17 50 0 0.224 0 -12.028 -11.325 19.185 avg.: -12.206 -11.774 18.722 diff.: 0.356 0.898 0.926 C2922 20.0 17 50 0 0.224 0 -12.383 -11.406 19.102 C2923 20.0 17 50 0 0.223 0 -12.368 -11.367 19.142 avg.: -12.375 -11.387 19.122 diff.: 0.015 0.039 0.040 G558-M4 C2814 20.0 17 50 0 0.283 0 -11.319 -12.573 17.899 x x x x C2815 20.0 17 50 0 0.285 0 -11.311 -12.583 17.889 avg.: -11.315 -12.578 17.894 diff.: 0.008 0.010 0.010 G558-N C2822 20.0 16 50 0 0.279 0 -11.420 -13.632 16.807 x x x x x C2823 20.0 16 50 0 0.313 0 -11.419 -13.641 16.798 avg.: -11.419 -13.637 16.803 diff.: 0.001 0.009 0.009 G558-V C2775 20.0 24 50 0 0.110 0 -9.413 -12.155 18.330 x x x x C2776 20.0 24 50 0 0.120 0 -9.423 -12.142 18.344 avg.: -9.418 -12.149 18.337 diff.: 0.010 0.013 0.014 G558-W C2805 20.0 18 50 0 0.383 0 -9.157 -13.487 16.957 x x x x C2806 20.0 18 50 0 0.370 0 -9.158 -13.515 16.928 avg.: -9.158 -13.501 16.943 diff.: 0.002 0.027 0.028 G558-X1 C2807 20.0 18 50 0 0.316 0 -9.491 -11.761 18.737 x x x x x C2808 20.0 18 50 0 0.318 0 -9.500 -11.779 18.718 avg.: -9.496 -11.770 18.727 diff.: 0.010 0.018 0.019

133

Table III.1 continued

Mineral composition by XRD (RAU)

δ13 δ18 δ18

C ‰ O‰ O‰ Sample t[h] T[°C] high low tube PDB PDB SMOW calcite calcite braunite Analysis hematite jacobsite Mn-calcite, kutnahorite partridgeite weight [mg]weight hausmannite cryptomelane

G558-X2 C2828 25.0 nr 50 0 0.310 0 -10.424 -10.507 20.029 x x x x x C2829 25.0 nr 50 0 0.320 0 -10.421 -10.545 19.990 avg.: -10.423 -10.526 20.009 diff.: 0.002 0.038 0.039 G558-X3 C2786 20.0 22 50 0 0.348 0 -10.344 -13.115 17.340 x x x x C2799 20.0 21 50 0 0.331 0 -10.250 -12.825 17.639 avg.: -10.297 -12.970 17.489 diff.: 0.093 0.290 0.299 C2924 20.0 19 50 0 0.348 0 -10.617 -12.938 17.523 C2925 20.0 19 50 0 0.338 0 -10.637 -13.054 17.403 avg.: -10.627 -12.996 17.463 diff.: 0.020 0.116 0.119 G558-Y2 C2788 20.0 25 50 0 0.399 0 -7.957 -14.651 15.757 x x x x x C2800 20.0 21 50 0 0.390 0 -7.857 -14.456 15.958 avg.: -7.907 -14.553 15.858 diff.: 0.100 0.195 0.201 C2926 20.0 19 50 0 0.422 0 -8.086 -14.573 15.837 C2927 20.0 19 50 0 0.422 0 -8.176 -14.662 15.746 avg.: -8.131 -14.617 15.791 diff.: 0.089 0.089 0.092 G558-Y3 C2789 20.0 25 50 0 0.499 0 -6.565 -15.094 15.300 x x x x C2790 20.0 25 50 0 0.480 0 -6.570 -15.112 15.281 avg.: -6.568 -15.103 15.291 diff.: 0.005 0.018 0.019 G558-Y4 C2793 20.0 19 50 0 0.207 0 -9.388 -13.781 16.654 x x x x C2794 20.0 19 50 0 0.219 0 -9.392 -13.693 16.744 avg.: -9.390 -13.737 16.699 diff.: 0.005 0.087 0.090 G558-Z C2795 20.0 19 50 0 0.285 0 -11.353 -11.717 18.782 x x x x C2796 20.0 19 50 0 0.284 0 -11.351 -11.682 18.817 avg.: -11.352 -11.700 18.799 diff.: 0.001 0.034 0.035 G565-C1 C2816 20.0 17 50 0 0.238 0 -11.710 -12.424 18.053 x x x x x C2817 20.0 nr 50 0 0.259 0 -11.734 -12.429 18.047 avg.: -11.722 -12.426 18.050 diff.: 0.024 0.005 0.005

134

Table III.2. Calibration data

Carbon

standard analysis expected raw dev corrected dev slope: NBS19 old C2879 1.95 1.954 0.004 1.971 0.021 0.9937 NBS18 old C2880 -5.04 -5.012 0.028 -5.039 0.001 intercept: IAEA-CO-1 C2885 2.48 2.446 0.034 2.467 0.013 -0.0050 IAEA-CO-8 C2886 -5.75 -5.719 0.031 -5.751 0.001 MD4 C2883 2.35 2.334 0.016 2.354 0.004 MHS1 avg. -2.82 -2.806 0.014 -2.819 0.001 MDS1 avg. 1.35 1.324 0.026 1.338 0.012

Oxygen

standard analysis expected raw dev corrected dev slope: NBS19 old C2879 -2.200 -2.350 0.150 -2.207 0.007 0.9851 NBS18 old C2880 -23.050 -22.976 0.074 -23.145 0.095 intercept: IAEA-CO-1 C2885 -2.440 -2.601 0.161 -2.462 0.022 -0.1757 IAEA-CO-8 C2886 -22.670 -22.450 0.220 -22.612 0.058 MD4 C2883 -10.000 -10.012 0.012 -9.986 0.014 MHS1 avg. -14.6 -14.502 0.098 -14.543 0.057 MDS1 avg. -7.1 -7.176 0.076 -7.106 0.006

δ 13 3 Carbon - C PDB

2 y = 0.9937x - 0.005 1 R2 = 1 0

-1

-2

-3

Analysed (raw ) -4

-5

-6

-7 -6 -5 -4 -3 -2 -1 0 1 2 3

Exp e cte d

18 0 Oxygen - δ O PDB

y = 0.9851x - 0.1757 -5 R2 = 1

-10

-15 Analysed (raw )

-20

-25 -25 -20 -15 -10 -5 0

Exp e cte d 135

Appendix IV: Density measurements

Contents: Table IV.1. Detailed descriptions of small chip samples from drill core G558 used for density measurements.

Table IV.2. Detailed descriptions of small chip samples from drill core G552 used for density measurements

Table IV.3. Whole rock densities obtained for lumpy ore samples from drill core G552 and G558.

Density determinations Chip samples: chips smaller than 1cm in diameter were selected to represent all major characteristics of the examined zone. i.e., ovoids (red/white/grey), carbonate laminae (white/red) and matrix (brown/ dark grey). The unique characteristics are described in detail in tables IV.1 and 2.

Lumpy ore samples: approximately 5cm in size, were chosen to obtain average densities for each lithostratigraphic zone. Duplicate samples for each zone were measured and the average density calculated.This average is listed in table IV.3.

Analytical Technique

The weight of the samples was measured first in air and then submerged in water. The exact temperature of the water was measured with a calibrated thermometer. The water density for a specific temperature was taken from Küster and Thiel (1993). The density of the samples was calculated by applying the law of Archimedes, based on the weight of the sample in air and the amount of water of known temperaturedisplaced by the sample when submerged. P P GG = G /(GG-GW) * T P Where G density of sample

GG weight of sample in air

GW weight of sample in water P T Density of water 136

Table IV.1. Detailed description and density of small chip samples from drill core G558.

Sample Density Description number g/cm3 G558 E-1 2.90 Small lenses (white rim and dark interior) in manganomelane matrix E-2 3.05 Small shiny grey ovoids in massive manganomelane matrix V-1 3.52 Laminated; small zoned ovoids (grey and red) and large white lenses V-2 3.63 Zoned, spheroidal ovoids with dark cores in massive lutite V-3 3.71 Large, pink, zoned ovoids in massive lutite V-4 3.74 Many compact, pink, spheroidal ovoids in lutite matrix W-1 3.68 Very small pink, spheroidal or round or irregular shaped ovoids in lutite matrix W-2 3.71 Pink spheroidal ovoids in lutite matrix W-3 3.62 Very compact, small pink spheroidal ovoids in lutite matrix W-4 3.53 Very compact, small, pink, spheroidal ovoids in lutite matrix W-5 4.25 Very small compact ovoids, with thin red-pink laminae in lutite matrix X1-1 3.63 Spheroidal, grey, zoned ovoids in a massive lutite matrix. X1-2 3.89 Laminated; spheroidal grey ovoids and dark grey lenses in lutite matrix X1-3 3.74 Thin flattened grey ovoids and lenses in lutite matrix X1-4 3.78 Thin flattened grey ovoids and zoned lenses (white-core, grey-rim) X2-1 3.60 Large, grey, shiny, zoned ovoids in massive lutite matrix X2-2 3.92 Irregular shaped white carbonate lenses and ovoids in lutite X2-3 3.78 Thin white lenses and a yellow-brown weathered laminae X2-4 3.74 Zoned, irregular ovoids (grey and white) in lutite matrix X3-1 3.71 Rounded and irregular shaped white ovoids in lutite matrix X3-2 3.60 Small ovoids and lenses (pink) in lutite matrix X3-3 3.65 Small ovoids and lenses (pink and white) in lutite matrix Y2-1 3.61 Laminated; very small red ovoids and lenses Y2-2a 3.56 Laminated; black lutite Y2-2b 3.48 Laminated; very small, compact red ovoids Y2-3 3.38 Laminated; medium sized red ovoids Y2-4 3.27 Laminated; very small red and white ovoids and thin brown laminae Y3-1 3.36 Very small ovoids in massive black lutite Y3-2 306 Very small ovoids in light grey lutite band Y3-2.5 4.65 1.5mm thick white and red laminae in black lutite Y3-3 3.65 2mm thick red and white laminae in black lutite

137

Sample Density Description number g/cm3 G558 Y3-4 3.04 Small compact ovoids in laminated grey and black lutite Y4-1 3.30 2mm thick red band in grey lutite Y4-2 3.57 Small red ovoids in laminated black lutite matrix Y4-2.5 3.76 Very small white ovoids in a massive black lutite matrix Y4-3 2.94 Thin red lense in 2cm thick brown and white laminae Z-1 3.42 Medium sized white ovoids and thin lenses in lutite matrix Z-2 3.54 Medium sized white ovoids (fewer) and more abundant lenses Z-3 3.38 White irregular shaped ovoids in grey lutite matrix Z-4 3.56 Medium sized zoned, grey and white ovoids in lutite matrix Z-5 3.55 Flattened grey ovoids and thin lenses in lutite matrix M1-0 3.67 Large grey and white spheroidal ovoid and lenses in a black lutite matrix M1-1 3.73 Medium flattened, grey and white ovoids in lutite M1-2 3.58 Medium sized, zoned ovoids (grey-core; white-rim). M2-1 3.72 Large and medium sized zoned ovoids and lenses in black lutite matrix M2-2 3.77 Thin white and grey lenses in lutite matrix M2-3 3.81 Large and medium sized zoned ovoids (grey-core; white-rim) M3-1 3.99 Irregular shaped white ovoids in black lutite matrix M3-2 3.86 Flattened grey ovoids and long thin lenses in black lutite matrix M3-3 3.61 Very large irregular shaped, white lenses in black lutite matrix M4-2 3.71 Very small irregular shaped, white ovoids in black lutite matrix M4-3 3.74 Irregular shaped ovoids and thin white lenses in black lutite matrix C2-1 3.50 Laminated; thick brown-red laminae with very small ovoids C2-3 3.89 Laminated; red ovoids in black lutite matrix C2-4 3.05 Interlaminated brown and black bands C2-5 3.83 Irregular shaped pink and brown ovoids in a black laminated matrix C2-6 3.29 Laminated; white and black laminae C2-7 3.82 Irregular shaped grey ovoids and thin lenses in a black matrix N-1 3.72 White laminae in a black lutite matrix N-2 3.75 Pink and white, compact ovoids in black lutite matrix N-3 3.28 A 6mm thick pink laminae in black lutite matrix N-4 3.59 Compact pink and white ovoids and thin lenses B-1 3.66 Red ovoids in black-brown matrix B-2 3.29 Pink and white carbonate lenses in black-brown lutite matrix

138

Table IV.2. Detailed description of small chip samples used from drill core G552.

Sample Density Description number g/cm3 G552 E-1 2.85 Massive black lutite containing very small shiny ovoids E-2 2.98 Massive black lutite containing very small shiny ovoids Y1-1 3.01 Laminated; white calcite vein (<1mm) in grey-black lutite Y1-2 2.89 Laminated; very small ovoids in black lutite Y3-1 2.95 Laminated grey lutite Y3-2 3.09 1mm thick red laminae in grey lutite matrix Y4-1 3.73 Laminated; medium sized spheroidal red ovoids in black lutite Y4-2 3.16 Laminated; medium sized red ovoids and brown laminae in black lutite Y4-3 3.47 Laminated; medium sized red ovoids in black lutite matrix Z-1 3.19 Pink and white ovoids and small lenses in black lutite matrix Z-2 3.55 Irregular shaped ovoids and lenses (white and red) in black lutite Z-3 3.5 Very small irregular shaped, white ovoids in black lutite Z-4 4.0 Flattened grey ovoids and few lenses in black lutite M1-1 4.04 Medium sized zoned ovoids (grey-core; white-rim) in black lutite matrix M1-2 3.69 Large scattered zoned ovoids (grey-core; white-rim) in black lutite matrix M2-1 3.79 Large zoned ovoids and flattened ovoids within black lutite matrix M2-2 3.97 Medium sized, zoned ovoids and lenses in black lutite matrix M2-3 4.11 Flattened grey ovoids and lenses in black lutite matrix M3-1 3.84 Irregular shaped white ovoids in black lutite matrix M3-2 3.46 Irregular shaped white and pink ovoids in black lutite matrix M3-3 4.12 Compact irregular shaped white ovoids in black lutite matrix M4-1 3.45 Irregular shaped pink and white ovoids in black lutite matrix M4-2 4.02 Irregular shaped white ovoids and lenses in black lutite matrix C2-1 3.2 Red irregular shaped ovoids in brown lutite matrix C2-2 2.86 White carbonate laminae C2-3 3.32 Laminated; white carbonate laminae and brown laminae C2-4 3.63 Irregular shaped small ovoids within brown-grey lutite band C2-5 3.94 Red and brown ovoids and lenses in dark black lutite band N-1 3.84 Medium sized spheroidal white ovoids in brown-black lutite N-2 3.74 Small white compact ovoids in brown-black lutite N-3 3.67 White carbonate lenses in brown-black lutite N-4 3.7 White carbonate lenses in brown-black hematite lutite

139

B-1 3.75 Small grey and white ovoids in brown-black hematite lutite B-2 3.65 5mm thick pink carbonate laminae in brown-black lutite matrix B-3 3.8 Small red-brown, compact ovoids in brown-black lutite matrix B-4 3.84 6mm thick pink-white laminae in brown-black lutite matrix

140

Table IV.3. Average density of lumpy ore samples from drill cores G558 and G552 representing all lithostratigraphic zones and subzones. All results reported in g/cm3 G558 G552 Zones Density Zones Density E 2.99 E 2.83 V 3.41 Y1 2.66 W 3.39 Y3 3.07 X1 3.5 Y4 3.65 X2 3.73 Z 3.58 X3 3.51 M1 3.52 Y2 3.31 M2 3.82 Y3 3.1 M3 3.75 Y4 3.45 M4 3.61 Z 3.52 C2 3.38 M1 3.74 N 3.57 M2 3.83 B 3.46 M3 3.94 L 3.44 M4 3.8 C2 3.47 N 3.66 B 3.27

Estimated reproducibility of results from repetitive measurements : approximately 0.0