Besshi-type deposits range in age from early Proterozoic to early Tertiary, of which the largest number are late Proterozoic, early Palaeozoic or Mesozoic in age. No Archaean examples of Besshi-type deposits are known, probably due to insufficient availability of sialic crust for erosion and clastic marine sedimentation before the start of the Proterozoic. All Besshi-type deposits are contained within sequences of clastic sedimentary rock and intercalated basalts in a marine environment. The basalts and amphibolites are principally tholeiitic in composition. Besshi-type deposits characteristically form stratiform 1enses and sheet-like accumulations of semi-massive to massive sulphide. The main ore assemblage consists dominantly of pyrite and/or pyrrhotite with variable amounts of chalcopyrite, sphalerite and trace galena, arsenopyrite, gold and e1ectrum, barite being absent in general. The median Besshi-type deposit (n=75) contains 1.3 million tonnes (Mt) of massive sulphide with a Cu grade running at 1.43%. It is suggested that Besshi-type deposits form by both exhalative and synsedimentary replacement processes when considering geological features and comparisons with modern analogues in the Guaymas Basin, Middle Valley and Escanaba Trough. The currently forming metalliferous sediments in the Red Sea provide for a brine pool model explaining the lack of footwall feeder zones below sheet-like deposits. Where thick sulphide lenses are contained in some Besshi-type deposits, combinations of exhalative precipitation and sub-sea-floor replacement of permeable sediments and/or volcanic rocks, take place in the upper parts of submarine hydrothermal systems.

This study involves the application, interpretation and utilization of regional geochemical data for target generation in the North West Province, South Africa. A regional soil geochemical survey programme has been carried out by the Council of Geoscience South Africa since 1973. A number of 1:250 000 sheet areas have been completed, but there are no interpretative maps which could aid in mineral exploration and other purposes. In order to utilize the valuable and expensive data, the project was motivated through data acquisition and interpretation to generate exploration targets. The study area is confined to Mafikeng, Vryburg, Kuruman and Christiana in the Northwest Province, where potential exploration and mining opportunities exist in areas of great geological interest. These include geological events such as the Bushveld Complex, the Kalahari manganese field and the Kraaipan greenstone belts. The aim of this project was to utilize geochemical data together with geophysical and geological information to verify and identification of possible obscured ore bodies or zones of mineralization, and to generate targets. Another objective was the author to be trained in the techniques of geochemical data processing, interpretation and integration of techniques such as geophysics, in the understanding of the geology and economic geology of the areas. Approximately 5 kg of surface soil was collected per 1 km2 by CGS from foot traversing. Pellets of the samples were prepared and analyzed for TiO2, MnO and Fe2O3, Sc, V, Cr, Ni, Co, Cu, Zn, As, Y, Ba, Nb, Rb, Th, W, Zr, Pb, Sr and U using the simultaneous wavelengthdispersive X-ray fluorescence spectrometer technique at the Council for Geoscience, South Africa. For each element the mean +2 standard deviations were used as a threshold value to separate the negative from the positive anomalies. The integration of geological, geophysical and geochemical information was used to analyze and understand the areas of interest. A number of computer programmes were extensively used for data processing, manipulation, and presentation. These include Golden Software Surfer 8®, Arc-View 3.2a®, TNT-Mips®, JMP 8 ®, and Microsoft Excel®. Through geochemical data processing and interpretation, together with the low resolution aeromagnetic data, gravity data and geological data, seven (7) exploration target areas have been generated: These have been numbered A to G. It is concluded that there is good potential for Cr, PGMs, vanadium, nickel, iron, copper, manganese, uranium and niobium in the targets generated. The results provide some indication and guide for exploration in the target areas. In Target A, Cu, Cr, Fe, Ni and V anomalies from the lower chromitite zone of far western zone of the Bushveld Complex, which has be overlain buy the thick surface sand of the Gordonia Formation. Target B occurs over the diabase, norite, andesitic lava and andalusite muscovite hornfels of the Magaliesberg Formation. This target has the potential for Cu, Fe and Ni mineralization. The felsic rocks of the Kanye Formation and the Gaborone Granite in target C have shown some positive anomalies of niobium, uranium, yttrium and rubidium which give the area potential for Nb, REE and U exploration. Target D is located on the Allanridge Formation, and has significant potential for Ni-Cu mineralization, and is associated with the komatiitic lava at the base of the Allanridge Formation in the Christiana Area. The light green tholeiitic, calc-alkali basalt and andesitic rocks of the Rietgat Formation are characterized by a north-south trending yttrium anomaly with supporting Ba and Y anomalies (Target E). This makes the area a potential target for rare earth elements. Calcrete on the west of the Kuruman has a low b potential target for vanadium. It is believed that the area might be potential for potassium-uranium vanadate minerals, carnotite which is mostly found in calcrete deposits. This study has proved to be a useful and approach in utilizing the valuable geochemical data for exploration and future mining, generated by Council for Geoscience Science. It is recommended that further detailed soil, rock and geochemical surveys and ultimately diamond drilling be carried out in the exploration target areas generated by this study.

Ph.D. (Geology) / Shear zone controlled hydrothermal alteration zones in the northern Kaapvaal craton (NKC) are developed in host rocks of vastly different chemical composition and metamorphic grade. Some carry appreciable Au and base metals and some are barren. Alteration zones in three different distinctive crustal zones were examined in detail to determine the controls of these two types of alteration. 1. The Matok Complex is situated in the southern marginal zone (SMZ) of the Limpopo Belt (LB), close to the zone of rehydration. Two major stages of hydrothermal alteration could be identified in local shear zones, a pervasive propylitization and a subsequent vein controlled quartzalbite alteration. The two-stage alteration occurred sometimes between the emplacement of the Matok Complex (2670 Ma) and the intrusion of unaltered mafic dykes (1900 Ma). Calculated isotopic compositions of the hydrothermal fluids indicate that magmatic ± meteoric waters as well as juvenile C02 were responsible for the establishment of the alteration zones. The fluids most probably were late magmatic fluids associated with the Matok magmatism. The propylitic alteration was accompanied by introduction of small amounts of CU + Au and represents an alteration type identical to that developed in porphyry copper deposits. The subsequent quartz-albite alteration was caused by extremely saline fluids which depleted the rocks of all the major and trace elements with exception of Si, Al, Na and Zr. 2. This chemical alteration pattern' contrasts with those developed in two alteration zones associated with economic gold mineralization in greenstone belts of the NKC (Sutherland and Pietersburg belts). At the Birthday and Eersteling gold mines, a biotite-calcite-quartz alteration is developed. The chemical pattern of the alteration is...

M.Sc. (Geology) / Please refer to full text to view abstract

The Kalahari Goldridge mine is located within the Archaean Kraaipan Greenstone Belt about 60 km SW of Mafikeng in the Northwestern Province, South Africa. Several gold deposits are located within approximately north - south-striking banded iron-formation (BIF). Current opencast mining operations are focused on the largest of these (D Zone). The orebody is stratabound and hosted primarily in the BIF, which consists of alternating chert and magnetite-chloritestilpnomelane-sulphide-carbonate bands ranging from mm to cm scale. The ore body varies in thickness from 15 to 45 m along a strike length of about 1.5 km. The BlF is sandwiched between a sericite-carbonate-chlorite schist at the immediate footwall and carbonaceous meta-pelites in the hanging-wall. Further west in the footwall, the schists are underlain by mafic meta-volcanic amphibolite. Overlying the hanging-wall carbonaceous metapeiites are schist units and meta-greywackes that become increasingly conglomeratic up the stratigraphy. Stilpnomelane-, chlorite- and minnesotaite-bearing assemblages in the BlFs indicate metamorphic temperatures of 300 - 450°C and pressures of less than 5 kbars. The BIF generally strikes approximately 3400 and dips from 60 to 75°E. Brittle-ductile deformation is evidenced by small-scale isoclinal folds, brecciation, extension fractures and boudinaging of cherty BIF units. Fold axial planes are sub-parallel to the foliation orientation with sub-vertical plunges parallel to prominent rodding and mineral lineation in the footwall. Gold mineralization at the Kalahari Goldridge deposit is associated with two generations of subhorizontal quartz-carbonate veins dips approximately 20 to 40°W. The first generation consists of ladder vein sets (Group lIA) preferentially developed in Fe-rich meso bands, whilst the second generation consists of large quartz-carbonate veins (Group lIB), which crosscut the entire ore body extending into the footwall and hanging-wall in places. Major structures that control the ore body are related to meso-scale isoclinal folds with fold axes subparallel to mineral elongation lineations, which plunge approximately 067°E. These linear structures form orthogonal orientation with the plane of the mineralized shallowdipping veins indicating stretching and development of fluid - focusing conduits. A second-order controlling feature corresponds to the intersection of the mineralized veins and foliation planes of host rock, plunging approximately 008°N and trending 341°. G0ld is closely associated with sulphides, mainly pyrite and pyrrhotite and to a lesser extent with bismuth tellurides, and carbonate gangue. The ore fluid responsible for the gold deposition is in the C-O-H system with increased CH₄ contents attributed to localized hydrolysis reaction between interbedded carbonaceous sediment and ore fluid. The fluid is characterized by significant C0₂ contents and low salinities below 7.0 wt % NaCl equivalent (averages of 3.5 and 3.0 wt % NaCl equivalent for the first and second episodes of the mineralization respectively) . Calculated values of f0₂. ranging from 10⁻²⁹·⁹⁸ to 10⁻³²·⁹⁶ bars, bracket the C0₂-CH₄ and pyrite-pyrrhotite-magnetite buffer boundaries and reveal the reducing nature of the ore fluid at deposition. Calculated total sulphur content in the ore fluid (mΣs), ranges from 0.011 to 0.018M and is consistent with the range (10⁻³·⁵ to 10⁻¹M) reported for subamphibolite facies ore fluids. The close association of sulphides with the Au and nature of the fluid also give credence that the Au was carried in solution by the Au(HS)₂ - complex. Extensive epigenetic replacement of magnetite and chlorite in BIF and other meta-pelitic sediments in the deposit by sulphides and carbonates, both on meso scopic and microscopic scales gives evidence of an interaction by a CO₂- and H₂S-bearing fluid with the Fe-rich host rocks in the deposit. This facilitated Au precipitation due to changes in the physico-chemical conditions of the ore fluid such as a decrease in the mΣs and pH leading to the destabilization of the reduced sulphur complexes. Local gradients in f0₂ may account for gold precipitation in places within carbonaceous sediments. The fineness of the gold grams (1000*Au/(Au + Ag) ranges from 823 to 921. This compares favourably with the fineness reported for some Archaean BIFhosced deposits (851 - 970). Mass balance transfer calculations indicate that major chemical changes associated with the hydrothermal alteration of BIF include enrichment of Au, Ag, Bi, Te, volatiles (S and CO₂), MgO, Ba, K and Rb but significant depletion of SiO₂ and minor losses of Fe₂O₃. In addition, anomalous enrichment of Sc (average, 1247%) suggests its possible use as an exploration tool in the ferruginous sediments in the Kraaipan greenstone terrane. Evidence from light stable isotopes and fluid inclusions suggests that the mineralized veins crystallized from a single homogeneous fluid source during the two episodes of mineralization under the similar physicochemical conditions. Deposition occurred at temperatures rangmg from 350 to 400°C and fluid pressures ranging from 0.7 to 2.0kbars. Stable isotope constraints indicate the following range for the hydrothermal fluid; θ¹⁸H₂O = 6.65 to 10.48%0, 8¹³CΣc = -6.0 to -8.0 %0 and 8³⁴SΣs = + 1.69 to + 4.0%0 . These data do not offer conclusive evidence for the source of fluid associated with the mineralization at the Kalahari Goldridge deposit as they overlap the range prescribed for fluid derived from devolatization of deep-seated volcano-sedimentary piles near the brittle-ductile transition in greenstone belts during prograde metamorphism, and magmatic hydrothermal fluids. / KMBT_363 / Adobe Acrobat 9.54 Paper Capture Plug-in

The Makganyene Formation forms the base of the Postmasburg Group in the Transvaal Supergroup in the Griqualand West Basin. It consists of diamictites, sandstones, banded iron-formations (BIFs), shales, siltstones and carbonates. It is generally accepted that the Makganyene Formation rests on an erosive regional unconformity throughout the Northern Cape Province. However this study demonstrates that this stratigraphic relationship is not universal, and conformable contacts have been observed. One of the principal aims of this study is to identify the nature of the Makganyene basal contact throughout the Griqualand West Basin. Intensive fieldwork was carried out from Prieska in the south, to Danielskuil in the north. In the Sishen and Hotazel areas, only borehole material was available to assess the stratigraphy. The Griquatown Fault Zone delimits the boundary between the deep basin and platform facies. The Koegas Subgroup is only present south of the Griquatown Fault Zone, where it pinches out. However, the transition Griquatown BIFs-Koegas Subgroup occurs in lacustrine deposits on the Ghaap platform (Beukes, 1983). The Griquatown Fault Zone represents the edge of the basin, which corresponds to a hinge rather than a fault zone. The Makganyene Formation rests with a conformable contact on the Koegas Subgroup south of the Griquatown Hinge Zone, and north of it the Makganyene Formation lies unconformably on the Asbestos Hills Subgroup. The Makganyene Formation displays lateral facies changes that reflect the paleogeography of the Griqualand West Basin, and the development of ice sheets/shelves. The Ghaap platform is characterised by coarse immature sand interbedded with the diamictites. The clasts in this area contain local Asbestos Hills material and no dropstones are present. Such settings are typical of sediments that are being deposited below a grounded ice mass. At the Griquatown Hinge Zone, the sandstone lenses are smaller, and the clasts consist of chert, of which a great number are striated and faceted. In the Matsap area, the presence of dropstones is strong evidence for the presence of a floating ice shelf that released its material by basal melting. Further south, the Makganyene Formation contains stromatolitic bioherms that only form if clastic contamination is minimal and therefore the ice that transported the detritus to the basin did not extend far into open sea conditions. The base of the Hotazel Formation also contains diamictite levels. Dropstones have been identified, implying a glacial origin. The Hotazel diamictites are interbedded with hyaloclastites and BIFs. The Makganyene glacial event, therefore, was not restricted to the Makganyene Formation, but also included the Ongeluk Formation, through to the base of the Hotazel Formation. Petrographic studies of the Makganyene Formation and the base of the Hotazel Formation reveal mineral assemblages that are diagnostic of early to late diagenetic crystallisation and of low-grade metamorphism not exceeding the very low green-schist facies. The facies identified display the same sense of basin deepening, from shallow high-energy Hotazel area on the Ghaap platform, to the deep basin in the Matsap area. Whole-rock geochemical analyses reveal that the elemental composition of the Makganyene Formation is very similar to that of the Asbestos Hills BIFs, which were the most important source of clastic detritus for the Makganyene Formation. However, minor amounts of carbonates of the Campbellrand Subgroup, as well as a felsic crustal input from the Archean granitoid basement, made contributions. On the Ghaap platform, the Makganyene diamictite is enriched in iron, calcium, and magnesium, while in the deeper parts of the basin the diamictites are enriched in detrital elements, such as titanium and aluminium, which occur in the fine clay component. The Hotazel diamictite displays a distinct mafic volcanic input, related to the extrusion of the Ongeluk basaltic andesites, which was incorporated in the glacial sediments. Sequence stratigraphy is based on the recognition of contacts separating the different systems tracts that compose a depositional sequence. However, because the basal contact of the Makganyene Formation has not been properly identified in previous work, no correct model has been proposed so far. Therefore correlations between the Griqualand West and the Transvaal basins, based on lithostratigraphic similarities and extrapolations of unconformities, have to be reviewed, especially since the publication of new radiometric ages contradict all previously proposed correlations. It is proposed here that the Transvaal Supergroup in the Griqualand West Basin represents a continuous depositional event that lasted about 200 Ma. The Makganyene glacial event occurred during changing conditions in the chemistries of the atmosphere and ocean, and in the continental configuration. A Snowball Earth event has been proposed as the causative process of such paleoenvironmental changes. However, evidence presented here of less dramatic glacial conditions, with areas of ice-free waters, implies an alternative to the Snowball Earth event. The paleoenvironmental changes are thought to represent a transition from an anaerobic to aerobic atmosphere, that was responsible for the global cooling of the surface of the Earth, Such a glacial event may have aided in the large-scale precipitation of iron and manganese in areas of intense upwellings.

PhDENV (Geology) / Department of Mining and Environmental Geology / The study focused on the geology, structural setting and mineralisation of copper-sulphide deposits in the Musina area, located in the Central Zone of the Limpopo Mobile Belt of South Africa. The Messina copper deposits are located in the eastern part of Limpopo Province near the border with Zimbambwe. The deposits stretch from northeastern to southwestern direction for about 15 km. Previous copper mining in the area took place at Artonvilla, Messina, Harper, Campbell and Lilly copper deposits. The current study, however, focused on two main deposits, Campbell and Artonvilla. The origin, nature and mode of formation of the Cu-sulphide deposits in the Musina area have not been established with certainty. Two principal hypotheses on the origin of the Messina copper sulphide deposits have been proposed, viz; a magmatic-hydrothermal model, and meteoric waters model. Consequently, the mode of formation and mineralisation style of the Messina Cu-sulphide deposits remain contentious. Therefore, the main objective of the study was to investigate the nature and mode of formation of Cu-sulphide deposits in the Musina area. Different research methods have been applied in the current study so as to unpack the contradictory positions on the genesis of the Messina copper deposits. This included fieldwork, remote sensing data acquisition, laboratory work, and data analysis and interpretation. Fieldwork involved soil geochemical survey as well as rock and ore sampling within the study area. A total of 295 soil samples, 33 rock specimens and 21 ore samples were collected for laboratory investigation. Laboratory work consisted of a range of methods that included; geochemical analysis, petrographic and cathodoluminescence microscopy, ore mineralogy and ore microscopy, fluid inclusion geothermometry and isotope geochemistry. The work was done in different laboratories including: Mining and Environmental Geology Laboratory, Unviersity of Venda; Department of Geology Laboratory, University of Johannesburg; MINTEK Laboratory in Johannesburg; Société Générale de Surveillance Laboratory in Johannesburg, South Africa; Department of Applied Geology, Geoscience Institute, Göttingen University, Germany and Department of Geology, University of Georgia, Athens, United States of America. Remote sensing data was acquired from Southern Mapping Company, Johannesburg, South Africa. Interpretation of Remote sensing data was done at the University of Applied Sciences, Oswestfalen-Lippe, Germany. Data analysis and interpretation of laboratory results involved the use of: Desktop ArcGIS 10.4.1 for geochemical data interpretation; ENVI 5.1 and ArcGIS 10.4.1 Softwares for remote sensing data; and Triplot version 4.1.2 software for ternary plot for compositional variation of rocks. Soil geochemical survey revealed geochemical anomalies for Pb, Zn, Cu, As and Ni over the known copper deposits in the area as well as over six other areas that have not been associated with any sulphide mineralisation. Such new anomalous areas have been identified as target areas for future exploration of sulphide ore mineralisation. Petrographic studies of the rocks confirmed the host rocks to be amphibolite-quartz granulite, biotite-garnet-quartz granulite, amphibolite, quartzite, hornblende gneiss, quartzo-feldspathic gneiss, potassium-feldspathic gneiss and cal-silicate gneiss. These rocks were subjected to hydrothermal alteration during ore mineralisation within the area. It was further noted that epidote alteration was quite intensive in ore samples, while in unmineralised rock samples it was less intensive. Remote sensing data interpretation revealed spatial distribution and intensity of epidote alteration within the study area and in places coincided either with the known copper deposits or structural features, thus led to the identification of target areas for future mineral exploration in the Musina area. The current study established that the process of ore mineralisation in the Messina copper deposits took place in two distinct phases: first the formation of garnet, graphite, magnetite and hematite during regional metamorphism of the Limpopo Mobile Belt; and secondly, sulphide ore mineralisation resulting in the formation of copper ore comprising, veined, disseminated and brecciated ores. Sulphide ore mineralisation consisted mainly of pyrite, chalcopyrite, sphalerite, bornite, chalcocite and minor pyrrhotite and galena as well as traces of pentlandite, tennantite, mollybdenite, cobaltite and tetrahedrite. This confirms that the Messina copper deposits had complex sulphide ore mineralisation that is typical of hydrothermal mode of ore mineralisation from a magmatic source. The study further establishes the paragenitic sequence of ore mineralisation, comprising four stages: Stage I (Garnet- graphite – Fe oxides); stage II (Quartz- pyrite); stage III (Pyrite- sphalerite - chalcopyrite); and stage IV (Carbonates). Stage III represented the main stage of sulphide ore mineralisation in the area, while Stage IV comprising calcite, dolomite and ankarite marked the final stage of hydrothermal ore mineralisation. Paragenetic sequence identified three generations of quartz; first generation being associated with garnet, graphite, magnetite and hematite, second generation with pyrite and third generation with pyrite, sphalerite and chalcopyrite. Previous studies, however, indicated that there was only one generation of quartz that formed at the temperature between 210o to 150°C, but the current study established that the entrapment temperature of first generation quartz ranges from 315o to 200°C; second generation quartz from 235o to 135°C and third generation quartz from 240o to 115°C. At the same time, sulphur isotope investigation of chalcopyrite-pyrite pair from Campbell deposit registered a temperature of 359°C. The study therefore concluded that the temperature of ore formation within the Messina copper deposits ranged between 359°C and 115°C. The presence of halite and calcite as daughter minerals within the fluid inclusions was noted and this apparently is indicative of high salinity of fluid inclusions, which is considered as a product of direct exolution of crystalizing magma. Raman spectroscopy revealed the composition of gases in the fluid inclusions to be CH4 and N2 with 80% and 20% composition respectively, however, some inclusions were gas-poor. The presence of gases in the fluid inclusions is an indication that there was boiling at the time of entrapment. A narrow range of 34S values of -0.5 to 0.5‰ obtained in this study further confirms the magmatic source of Sulphur as Sulphur from the host rock was found to have high 𝛿34S value of 8.2‰. A genetic model for copper ore mineralisation within Musina area is proposed. The deposits are of polymetallic vein type that are genetically associated with porphyry copper deposits. According to this model, copper ore bodies were formed from hydrothermal fluids originating from magma and were epigenetic in nature. Geological structures in the area acted as conduits for hydrothermal fluids that resulted in the alteration of the host rocks and mineralisation of copper sulphide ore. Thus, the Messina coper deposits are of magmatic hydrothermal origin although the apparent location of a batholith is still unknown and the study recommends further viii research work on the location of the batholith that is presumed to have been the magmatic source. The study further recommend dating of later rocks as well as orebody s it is essential for understanding the process of ore formation in this area. For further exploration, areas that have undergone “moderate” to “high” degree of epidote alteration and lie in close proximity to geological structures such as faults and thrust folds that could have acted as conduits for hydrothermal fluids and resulted in sulphide ore mineralisation and registered high geochemical anomalies for Pb, Zn, As and Ni should be targeted. In support of further mineral exploration within the study area, the study recommend a detailed geostatistical application for the purpose of delineating homogeneous areas based on the combination of lineaments, interpolated soil geochemical maps and thematic maps. / NRF