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.

No description available.

M.Sc., Faculty of Science, University of the Witwatersrand, 1992

No description available.

No description available.

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.

M.Com. (Economics) / The objective of the thesis was to examine the relationship between the grade of ore, physical electricity consumption and working cost in the South African gold mining industry for the period 1965 - 1982. The South African economy is heavily dependent on the gold mining industry, which is a major earner of foreign exchange and a large consumer of labour and agricultural and industrial output. The industry is also important as a source of finance for both the private sector and the Treasury. Curtailment of activity within the industry by closing down the more marginal mines or by shortening the life of the industry' as a whole because of rising costs and/or a hesitant gold price, will harm the South African economy in a number of ways. The industry has no option but to regard the gold price as given. The remaining ore reserves tend to be of a lower grade and/or to be found at greater depth. Controlling the working costs would seem to be almost the only option open to the industry.

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.

M.Sc. (Geology) / The Witwatersrand Supergroup is host to a number of auriferous and uraniferous conglomeratic reefs, which have been extensively exploited along the Witwatersrand Basin margins. The current study investigates the Vaal Reef, in the Klerksdorp gold field with particular focus on conducting a geometallurgical characterization of the ore which may ultimately enhance the recovery of gold and uranium and our understanding of how the ore responds to processing. Six samples were collected from AngloGold Ashanti’s Moab Khotsong mine and prepared for a chemical and mineralogical deportment study. These samples were milled and crushed down to 80% passing -75μm and processed for head chemistry assays, grading analysis as well as heavy liquid separation analysis as part of the chemical deportment. The samples were also submitted for gold cyanide, acid uranium and diagnostic leach tests.....