This thesis presents the application of the state-of-the-art processing, interpretation and modeling to the 3D reflection seismic data that were acquired between 1988 and 2003 across the West Rand and West Wits line goldfields of the Archean Witwatersrand Basin. The re-processing of the old 3D seismic data using new imaging techniques, such as 3D Kirchhoff prestack time migration (KPSTM), has led to better imaging of the ore body, structures (faults and dikes), and steeply dipping stratigraphy. Detailed interpretations of the highly auriferous Ventersdorp Contact Reef (VCR) using advanced complex seismic trace and horizon - based seismic attributes, have led to discoveries of ore blocks (~ 1 km long and ~ 250 m wide) that are bound by multi-fault segments of the first-order scale Bank and West Rand faults, leading to an increase of the resource portfolio and potentially, the quantity of the reserves. In particular, the edge detection attributes have resolved faults with throws as small as 10 m and complex structural architectures such as intersecting and cross-cutting faults, and fault bifurcations which are difficult to detect using conventional techniques (e.g., amplitude, dip and azimuth). Potential conduits, such as faults and dikes for migration of water and methane into underground workings were also mapped using edge detection attributes. These results have the potential to play into safe mine planning. The interpretation of the merged 3D seismic datasets, integrated with underground maps, boreholes, absolute and relative geochronological data, has added to our understanding of the gross structural architecture and Neoarchaean tectonic evolution of the goldfields. On a first-order scale (400 m - 2.5 km) the data resolved: (1) the northerly-trending disharmonic Libanon Anticline with a wavelength of 8 km and amplitude of 2 km, which was formed during deformation in the Umzawami Event (ca 2.73 Ga); and (2) the north-northeast trending, west-dipping (65°–70°W) listric West Rand and Bank faults, which were formed during a major extensional event, herein termed the Hlukana- Platberg Event (2.70-2.64). On a second-order scale (25 m - 400 m) the datasets resolved: (1) the Tandeka and Jabulani thrusts 1.5 km below the West Rand and Bank faults in the depth interval of 6-8 km; and (2) a series of drag synclines and rollover anticlines in the immediate footwall and hangingwall of the West Rand and Bank faults. Further to this, the seismic sections across the goldfields provided evidence that the first- and second-order scale faults, thrust and folds were dissected, eroded and overlain by the Transvaal Supergroup above an angular unconformity. The oldest approximate age for the Transvaal Supergroup is given as 2.58 Ga, thus constraining the age of the faults, thrust and folds to the Neoarchaean or pre- 2.58 Ga.

The ~2.98 - 2.87 Ga Pongola Supergroup in South Africa is subdivided into the lower volcano-sedimentary Nsuze Group, and the upper sedimentary Mozaan Group, the latter comprising a several kilometres thick succession of fluvial to shallow marine sandstones and shales. Thin beds of gold and uranium-bearing conglomerates are locally present in the Mandeva Formation near the base of the Mozaan Group and have been mined at Denny Dalton in northern KwaZulu-Natal. The style of mineralization strongly resembles that of the Witwatersrand goldfields, however appears to be of low grade and limited tonnage. The ~1 m thick basal conglomerate, the “Mozaan Contact Reef” (MCR, herein referred to as CG 1), at Denny Dalton hosts erratic gold and uranium mineralization. The conglomerate is laterally discontinuous and occupies east-northeast trending scour channels. Polymict, matrix-supported conglomerates are common, while clast-supported conglomerates are rare. Well rounded, pebble to cobble-sized clasts of vein quartz and chert are hosted in a sandy matrix of quartz, pyrite and sericite. Where mineralized, the CG 1 hosts abundant rounded pyrite grains, interpreted as detrital in origin, with subordinate U-bearing minerals, such as brannerite and uraniferous leucoxene. Rounded detrital pyrite occurs in three phases, compact, porous and radial. Gold forms inclusions within massive pyrite grains, which are concentrated in shoots associated with the basal parts of the channel scours. SEM-EDX results, as well as the high reflectivity of the gold show a high Ag content, indicative of a primary origin for the gold within the pyrite grains. Uranium within CG 1 is hosted primarily as secondary inclusions of uranium within black chert pebbles within the basal cobble-sized regions of the conglomerate. Geochemical comparison of the chert pebbles at Denny Dalton with similar chert from the Nondweni Greenstone Belt indicates that the uranium is secondary in origin as no U anomalies occur in the Nondweni chert. Geochemical and SEM analysis of the uppermost conglomerate (CG 4) indicate the presence of uraninite and coffinite within the uppermost horizon as both fillings of voids within, and coatings on, detrital pyrite grains. Palaeocurrent data indicate a likely source terrain for the detrital material to the west of the inlier. This orientation, as well as differing mineralogical and sedimentological aspects between the Mandeva Formation and the correlative Sinqeni Formation within the main Pongola basin, indicate a separate and more proximal provenance for the auriferous conglomerates of the White Umfolozi Inlier. The Mandeva Formation is a fluvial to shallow marine sequence that has been affected by cyclic sea-level changes. The basal conglomerates of the Denny Dalton Member were deposited in a proximal braided alluvial plain environment. The conglomerates fine upwards into trough cross-bedded quartz arenites which appear to have been deposited as shallow marine sands in a shoreface environment. They are overlain with a sharp contact by a laterally extensive unit of polymictic conglomerate which represents a transgressive ravinement surface within the wave zone and marks the onset of a major marine transgression into the Pongola basin. The conglomerate is overlain by massive grits and coarse-grained quartz arenite. This unit is overlain with a sharp and locally sheared contact by shales and subordinate banded iron formation which can be traced into other parts of the Pongola basin and indicates continued rapid transgression onto large parts of the Kaapvaal Craton with deeper marine, sub-storm wave base sediments being deposited in quiet-water environments on a sediment-starved shelf. The heavy mineral assemblage as well as bulk geochemical data is consistent with a granitoid-greenstone source terrain for the conglomerates and sandstones. The geochemical composition of chert pebbles from the CG 1 is similar to the composition of cherts present in the Nondweni Greenstone Belt that is situated ~30 km west of the White Umfolozi Inlier. Multiple sulphur isotope (ä34S, ä33S) values for detrital pyrite from the MCR are consistent with an origin from mantle-like rocks, such as hydrothermal sulphide-quartz veins in a granitoid-greenstone setting. Palaeocurrent, mineralogical and geochemical data all point to a likely granitoid-greenstone provenance to the west of the White Umfolozi Inlier. / Thesis (M.Sc.)-University of KwaZulu-Natal, 2009.

D.Phil. / Lode-gold deposits usually occur in granite-greenstone terranes of low- to medium-grade of metamorphism. Such deposits are well studied in terms of their petrogenesis, ore mineralogenesis and structural control. Gold occurrences associated with high-grade terranes are, however, also known from the Yilgam Block in Australia (Griffin's Find) and Northern Marginal Zone of the Limpopo Belt in Zimbabwe (Renco), but the genesis of these deposits are not as well understood as that of their lower grade counterparts. The Doornhoek lode-gold deposit, situated in the granulite terrane of the Southern Marginal Zone of the Limpopo Belt in South Africa displays an important sequence of structural and metamorphic events that proved to be very useful in understanding the formation of metamorphic gold deposits formed under upper-amphibolite - granulite facies conditions. Structurally the Doornhoek gold deposit is situated in a large low-angle D, fold plunging towards the west at 10-15 °. The fold structure and the mineralised zone are affected by D2-strike-slip shear zones which occur both within and along the outer contacts of the ore zone. The gold deposit is also affected by southward verging D3 shear zones which thrusted Baviaanskloof Gneiss over and onto the Doomhoek Ore Body. The Doomhoek Gold Deposit is also situated in a highly altered zone of metasomatised rocks within the zone of rehydration of the Southern Marginal Zone. The actual Ore Body is represented by a remnant of BIF, mafic and ultramafic rocks surrounded by Baviaanskloof Gneiss. The alteration process, caused by high-temperature fluids channeled along the D2 shear zones was responsible for the formation of the different metasomatic lithologies. These altered rocks initially experienced a regional hydration event followed by the high-temperature metasomatic event. The very intense metasomatic activity was synchronous with the growth of prograde-zoned garnet and gold mineralisation associated with quartz veins. This scenario is suggested by the fact that gold associated with Zn, Ge, As, Y, Zr and Ni was trapped in the mineralised inner-ring of the zoned garnet, by the REE pattern and presence of Th232 and U238 in the biotite-garnetiferous formation, and by the mobility of major elements such as A1 203, K2O, SiO2 and TiO2 associated with the metasomatic activity. The alteration is probably related to externally derived magmatic fluids mixed with metamorphic aquitards that were active in both open and close system conditions along deep seated D2 shear zones. These fluids are characterised by the presence of high-density CO 2-rich and high salinity fluid inclusions. The gold mineralisation is closely associated with pyrrhotite, magnetite, lollingite, arsenopyrite, chalcopyrite, ilmenite, pentlandite, sphalerite and gold. The gold has a very low fineness (520), typical of gold precipitated from hydrothermal solutions at high-grade conditions. The textural relationships of the ore minerals hosted by the quartz veins, furthermore demonstrate a prograde pattern of mineralisation, similar as in the case of mineralisation trapped within different zones of the zoned garnet porphyroblast. The dark inner-ring of the garnet is characterised by high concentrations of sulphides, oxides and gold. The mineralising event initially deposited sphalerite and arsenopyrite at low temperatures of up to 569 °C with temperatures increasing to 673 °C, and even up to 750°C when lollingite was formed. Most of the gold is related to As-rich arsenopyrite, lollingite and graphite at temperatures ranging from upper-amphibolite facies to lower-granulite facies metamorphic conditions. The Doornhoek gold deposit is an example of a high-grade lode-gold deposit formed during a prograde hydrothermal event and demonstrates unequivocally the possibility of economic gold mineralisation during granulite facies conditions. This observation has important implications for gold exploration in high-grade geological terranes that to date have been mostly ignored by the gold mining industry.

submitted partial fulfilment of the requirements for the degree of MASTER OF SCIENCE in the Faculty of ENGINEERING in the University of the Witwatersremd, Johannesburg August 1991 \

No description available.

Extraction of platinum group elements (PGE) is a major source of revenue in South Africa and the reserves represent about 75 per cent of world reserves. Most of the remaining Platinum Group Mineral (PGM) reserves are located in the UG-2 chromitite layer of the Bushveld Igneous Complex. Platinum concentrators experience significant losses of PGE in their secondary milling circuits due to insufficient liberation of platinum-bearing particles. The chromium oxide (Cr2O3) content in UG-2 concentrates is typically 3%, which results in operational problems in the downstream smelting process. Ways of improving the design of the secondary milling circuit were investigated, with the purpose of improving PGE recovery and reducing Cr2O3 entrainment in the subsequent flotation stage. Batch-scale laboratory and pilot plant tests were carried out to investigate the optimal design of a secondary milling circuit configuration. The optimal design consisted of a conventional hydrocyclone to de-slime the feed, followed by gravity separation with a spiral concentrator circuit to separate the ore into lights (silicates-rich) and heavies (chromite-rich) fractions. Separate milling of the light and heavy fractions made it possible to grind the silicate-rich fraction finer and to avoid over-grinding of the chromite. The total milling energy was redistributed between the silicates and chromite ball mills with 88% of the energy input to the silicates mill and 12% to the chromite mill thus reducing chromite over-grinding. The effects on the recovery of PGE, and the entrainment of Cr2O3 were measured in combined batch rougher flotation tests. The results indicated a 2% improvement in the secondary rougher flotation PGE recovery for the densifier underflow sample as compared to the standard MF-2 circuit, and most significantly the Cr2O3 entrainment was reduced by over 30% overall. Attritioning of the chromite-rich heavies fraction and ball milling of the silicates-rich lights fraction resulted in a 52% reduction of Cr2O3 in the rougher flotation concentrate and a 0.4% increase in PGE recovery (0.4%) as compared to the standard circuit. The improved reduction in chromite entrainment may be attributed to the lower fines generation with attritioning (52.8%- 106μm) as compared to ball milling with a 12% energy input (83.6% -106μm). Over 50% of the chromite minerals remained in the +106μm of the attritioned heavies product as compared with 21% for the ball milled spiral heavies stream. This accounted for a significant proportion of the overall chromite reduction in the flotation concentrate and supported the motivation for the inclusion of a separate grinding circuit for the chromite and silicate particles. Pilot plant testwork on a VHG (very high grade) spiral concentrator circuit followed by laboratory milling and rougher flotation tests confirmed the above conclusions. A 3.7% improvement in PGE recovery was noted with a 32% Cr2O3 reduction in the secondary rougher flotation concentrate as compared to the standard circuit. The statistical reliability of the laboratory and pilot plant data were quantified at various stages of the testwork due to the heterogeneous nature of the feed material and representative sampling. The repeat analyses on selected flotation tests for the high grade ore revealed that the variances were below 0.5%, 4%, and 7% for the head grades, PGE and Cr2O3 recoveries respectively. The flotation results for the standard and significantly improved milling circuits had variances in the 4E recoveries for the low grade ore and pilot plant ore of below 5.5% and 1% respectively. Low variances (<1%) in the Cr2O3 recoveries were noted for the low grade and pilot plant ores. A preliminary cost estimate was undertaken based on the pilot plant data to determine what value the proposed circuit could add for an additional 3.7% PGE recovery. An additional revenue of approximately R50 000 per day could result based upon the platinum mineral recovery only. The other precious metals, i.e. palladium and rhodium were neglected and would further increase the overall revenue. The minimum payback period for the estimated capital investment would be approximately 4 years. This confirmed the benefit of this improved secondary milling circuit design as a viable option. A closed-circuit operation of the silicates mill should offer more significant benefits compared to the open circuit option; however, this was not considered in the current testwork. This project has confirmed the benefit of separate ball milling and the use of a spiral concentrator as an effective gravity separation device in the secondary milling circuit for a chromite-rich (>50%) UG-2 platinum ore. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2011.

This project is an investigation of the UG2 cyclic unit of the Upper Critical Zone at Lebowa (Atok) / Thesis (M. Sc.)-University of KwaZulu-Natal, Westville, 2008.

M.Sc. (Geology) / The Sishen Iron Ore Mine is situated in the Northern Cape Province at the northern extremity of the Maremane dome. The stratigraphy of the Sishen Iron Ore Mine consist of carbonate rocks of the Campbellrand Subgroup which are unconformably overlain by the Wolhaarkop Breccia. The Wolhaarkop Breccia grades upwards through a shaly unit into an succession of iron formation known as the Manganore Iron Formation. The positive correlation of the Manganore Iron Formation with the Asbesheuwels Subgroup, of which it represents the oxidized equivalent, assigns a collapse origin to the Wolhaarkop Breccia. The siliciclastic Gamagara Formation overlies the Manganore Iron Formation unconformably. The unconformity cuts through the Manganore stratigraphy into the carbonate rocks of the Campbellrand Subgroup. The Gamagara Formation consist of a basal unit of conglomerates and argillite of varying thickness in the form of stacked upward fining alluvial cycles. These are overlain by two well 'developed upward coarsening progradational shale to quartzite deltaic cycles. A massive argillite unit marks the upper contact of the Gamagara Formation with the overlying Makganyene and Ongeluk Formations. This unit represents a milonite along a thrust plane and the Ongeluk lava and parts of the Makganyene diamictite were thrusted over the Gamagara Formation which is a correlative of the Mapedi Formation of the 01ifantshoek Group...

Ph.D. / The economically important sedimentary manganese deposits of the Paleoproterozoic Kalahari and Postmasburg manganese fields, are situated in close geographic vicinity to each other in the Griqualand West region of the Northern Cape Province, South Africa. This thesis describes aspects of mineralogy, petrography and geochemistry of the manganese ores with the purpose to establish genetic models for genesis and alteration of manganese ores of both manganese fields. The Kalahari manganese field, situated some 60 km northwest of Kuruman, is the largest known land-based manganese deposit. Manganese ores occur interbedded with iron-formations of the Hotazel Formation of the Voelwater Subgroup of the Late Archean-Paleoproterozoic Transvaal Supergroup. The sediments of the Voelwater Subgroup are preserved in five erosional relics, of which the Kalahari manganese deposit is by far the largest and the only one of economic importance. Two types of ore are mined, low-grade sedimentary Mamatwan-type ore and high-grade Wesselstype ore. Mamatwan-type ore is represented by microcrystalline laminated braunite-lutite composed of kutnahorite, Mn-calcite, braunite and hematite, modified by the occurrence of late diagenetic or metamorphic hausmannite, partridgeite, manganite and calcite. Mamatwan-type ore contains up to 38 mass % Mn and constitutes about 97 % of the ore reserves in the Kalahari manganese deposit. High-grade Wessels-type ore, with a manganese content of between 42 to 48 mass % Mn (on average), constitutes about 3 % of the ore reserves. It occurs only in the northwestern part of the main Kalahari deposit, and in small deposits at Hotazel and Langdon, in association with a system of north-south striking normal faults. The Wessels alteration event is thought to be related to the Kibaran orogenetic event (about 1.1 Ga). Fault zones are ferruginized and alongside faults sedimentary Mamatwan-type ore has been hydrothermally upgraded to Wessels-type ore. Metasomatic fronts are defined by changing mineral associations. These associations clearly illustrate that decreasing degrees of alteration relate to increasing distance from the fluid feeders. Areas of unaltered Mamatwan-type ore are preserved in the core of fault blocks. Wessels-type ore consists mostly of hausmannite, bixbyite, braunite II and manganite and subordinate gangue minerals such as clinochlore and andradite but the mineral assemblage associated with the Wessels alteration event is unusually diverse. More than 100 minerals have been identified, amongst them 8 new mineral species and an unusual, ferrimagnetic, Fe-rich variety of hausmannite. Mass balance calculations illustrate that the upgrading of the Wessels-type manganese ore is a consequence of leaching of CaO, MgO, CO 2, and Si02 from a low-grade Mamatwan-type precursor. This metasomatic process results in increasing secondary porosities, compaction of the orebody to two thirds of its original thickness and consequently residual enrichment of manganese in the ores. Three younger alteration events are observed in the Kalahari manganese deposit. These are only of minor economic importance. Wallrock alteration associated with the Mamatwan alteration event is characterized by reductive leaching of Fe and Mn around syntectonic veins and joints with pyritechalcopyrite- carbonate mineralization. The alteration is explained by infiltration of epithermal solutions that were introduced along veins or joints. The timing of the alteration event has tentatively been placed into the Pre-Karoo era. The Smartt alteration event is associated with intensive faulthosted brecciation and replacement of braunite and carbonates of the Mamatwan-type ore by todorokite and manganomelane, a process that causes considerable upgrading of the manganese ore next to a fault breccia at Mamatwan mine, and the formation of stratiform cross-fibre todorokite veins at Smartt mine. The Smartt alteration event postdates the Mamatwan alteration event and has tentatively been correlated with Pre-Kalahari groundwater circulation. Supergene alteration of the ores took place in Kalahari and Post-Kalahari times. It is characterized by the occurrence of cryptomelane, pyrolusite and other typically supergene manganese oxides along the suboutcrop of the Hotazel Formation beneath the Cenozoic Kalahari Formation. The Postmasburg manganese field is situated about 120 km to the south of the Kalahari manganese field on the Maremane dome. Two arcuate belts of deposits extend from Postmasburg in the south to Sishen in the north. Two major ore types are present. The ferruginous type of ore is composed mainly of braunite, partridgeite and bixbyite and occurs along the centre of the Gamagara Ridge, or Western belt. The siliceous type of ore consists of braunite, quartz and minor partridgeite and occurs in small deposits along the Klipfontein Hills (or Eastern belt) and the northern and southern extremities of the Gamagara Ridge. Geological and geochemical evidence suggest that the manganese ores represent weakly metamorphosed wad deposits that accumulated in karst depressions during a period of lateritic weathering and karstification in a supergene, terrestrial environment during the Late Paleoproterozoic. The dolomites of the Campbellrand Group of the Transvaal Supergroup are host and source for the wad accumulations. Contrasting geological settings are suggested for the accumulation of the siliceous and the ferruginous types of ore respectively. The former originated as small pods and lenses of wad in chert breccia that accumulated in a karst cave system capped by the hematitized Manganore iron-formation of the Transvaal Supergroup. The cave system finally collapsed and the hematitized iron-formation slumped into the sinkhole structures. The ferruginous type of ore accumulated as mixed wad-clay sediment trapped in surficial sinkhole depressions in the paleokarst surface. The orebodies are conformably overlain by the Doornfontein hematite pebble conglomerate or aluminous shales belonging to the Gamagara Formation of the Late Paleoproterozoic Olifantshoek Group. Well preserved karst laterite paleosol profiles, described from the basal section of the Gamagara Formation, provide a strong argument for the terrestrial, supergene origin of the manganese ores. The manganese ores in the Postmasburg manganese field were affected by diagenesis and lower greenschist facies metamorphism. Metamorphism resulted in recrystallization to braunite in the siliceous ores of the Eastern belt, and to massive or mosaic textured braunite and idioblastic partridgeite in the ferruginous environment of the Western belt. Secondary karstification and supergene weathering are evidence for renewed subaerial exposure of the manganese ore and their host rocks. The metamorphic mineral assemblage is replaced by abundant romanechite, lithiophorite and other supergene manganese oxides. Comparison between the Kalahari- and the Postmasburg manganese field shows that sedimentary manganese accumulation took place in entirely different depositional environments and owing to different mechanisms. Their close geographic relationship appears to be coincidental. Apparent similarities arise as a consequence of regional geological events that postdate the deposition of the manganese ores. These similarities include the lower greenschist facies metamorphic overprint, an event tentatively related to thrusting and crustal thickening during the Kheis orogenetic event, and syn- to Post-Kalahari supergene alteration. The correlation of structurally controlled hydrothermal alteration events in the Kalahari manganese field and the Postmasburg manganese field remains difficult due to the absence of the necessary geochronological constraints.

M.Sc. (Geology) / Within the Black Reef Formation, which forms the basal unit of the Transvaal Supergroup, an auriferous and uraniferous reef occurs. This is known as the Buckshot Pyrite Leader reef. This reef is a conglomerate-hosted gold and uranium deposit, which is similar to the Witwatersrand reefs as they both contain significant amounts of pyrite and have similar depositional environments. This study seeks to identify the geometallurgical characteristics of the gold uranium and thorium that are hosted in the Black Reef at the Modder East operation in Springs. In terms of methodology, a detailed petrographic study was completed on the samples taken from underground and the surface run of mine samples. Mineralogy was conducted on these samples using SEM-based automated technology, namely the FEI Mineral liberation analyser (MLA). Using this, I could further characterise the gold and uranium bearing phases found across the Black Reef. Additionally, mill testing, grading analysis, major and trace element chemistry, density separation, gold and uranium dissolution as well as flotation testing was conducted on the ore in order to determine its geometallurgical characteristics. Through the combination of these methods, this study aims to evaluate the Au, U and Th within the Black Reef with regards to: the metallurgy; the extraction process in relation to the mineralogy of the samples; and the possible implications that these factors could have on the overall recovery of the economic minerals.