The Nsuta manganese deposit is located in the Western Region of Ghana, approximately five kilometers south of Tarkwa Goldfields. The deposit has been an important source of manganese ore since mining began in 1916. The purpose of this project was to produce a concise model of the stratigraphy, sedimentology and structural evolution of the deposit in support of future exploration projects. The manganese ores occur as an up to 45m thick carbonate bed in a thick turbidite-greenstone succession that is part of the ~2.2 Ga Birimian Supergroup. Calc-alkaline volcanics, volcaniclastics, turbidites, argillites and phyllites are thought to have been deposited in a backarc basin environment. The entire sedimentary succession, including the manganese orebody, is a thick turbidite package hosted between an upper and lower greenstone unit consisting predominantly of volcaniclastic material. The entire lithological succession at Nsuta is interpreted to have been deposited within the middle to lower reaches of a submarine fan environment. Field evidence suggests a simple stratigraphy, commencing with a lower greenstone unit composed largely of volcaniclastic material. This is followed by an upward-fining lower turbidite unit deposited in response to a marked transgression and sea level rise. Maximum rate of sea level rise provided ideal conditions for manganese precipitation and concentration, as detrital influx ceased. The central portion of the carbonate orebody that formed hosts the manganese orebody. An upward-coarsening turbidite unit follows above the carbonate unit. This upward-coarsening succession reflects a regression and a highstand systems tract in terms of sequence stratigraphic principles. It is capped by an unconformity that formed during a period of rapid relative sea level fall. It is overlain by a second upward-fining turbidite succession. This succession is not fully preserved as there is a sheared contact between it and the overlying upper greenstone unit. Post-depositional deformation and metamorphic alteration are largely attributed to the Paleoproterozoic Eburnean Orogeny. A first phase of compression was directed along a NW-SE axis and produced a series of isoclinal anticlines and synclines (F1) with NE-SW striking axial planes. This was followed by thrusting between the anticlines and synclines. The age of this deformation and closely associated greenschist metamorphism can be accurately constrained between 2.09 Ga and 2.07 Ga. E-W oriented oblique listric faulting has a prominent effect on the appearance of the Nsuta manganese deposit, as it produced a series of imbricate fault blocks dipping to the north. Associated with this period of deformation is small-scale cross folding with axes plunging to the east (F2). The faults post-date the Eburnean Orogeny and must be associated with a second major tectonic event. Finally, a NNE-SSW striking normal fault, locally known as the German Line, caused further block rotation, notably in the northern parts of the mining concession. Late Mesozoic deep lateritic weathering and incision of the lateritic peneplane by modern rivers have resulted in the complex dissected appearance of the Nsuta orebody. However, based on the detailed structural analysis provided in this study, a feasible target for future exploration of manganese ore buried beneath Late Mesozoic and Cenozoic sediments and soils, has been identified. This target is located to the west of Hills A and B. / Dr. J.M. Huizenga Prof. Nic Beukes Prof. J. Gutzmer

M.Sc. / This dissertation describes the N1 manganese ore bed at Gloria Mine in the Kalahari Manganese Field, Northern Cape Province. It also compares the ore bed at Gloria Mine with the correlative bed further to the south at Mamatwan Mine. The ore bed at Gloria Mine can be subdivided into ten texturally distinct zones that are laterally consistent throughout the mine lease area. The mineralogy and geochemistry of the various lithostratigraphic zones are described from two drill cores (GL28 and GL24), situated away from any known structural features or unconformities that could have affected the properties of the Ore. The ore in drill core GL28 has a mineralogical composition similar to that of typical Mamatwan-type ore described at Mamatwan Mine with braunite and kutnahorite as the main minerals. However, in drill core GL24 the ore has a very different mineralogical composition although it is texturally and geochemically rather similar to Mamatwan-type ore. The ore is composed of hausmannite, calcite and jacobsite and is apparently related to a post-depositional alteration event that did not effect Mamatwan-type ore in the Mamatwan Mine area. This altered ore is similar in composition to low-grade leastaltered manganese ores in the cores of fault blocks at Wessels and N’Chwaning Mines i.e. the area known for its hydrothermally altered high-grade manganese ores in the northern part of the Kalahari Manganese Field. In addition to the above, the N1 manganese ore bed at Gloria Mine also underwent ferruginisation close to certain joints and normal faults. No obvious alteration could be detected where the ore bed is unconformably overlain by Dwyka diamictite, nor associated with a thrust fault displacing the ore.

The giant Palaeoproterozoic manganese deposits of the Kalahari manganese field (KMF), Northern Cape Province, South Mrica, have been a world renowned resource of manganese ore for many decades. In recent years, the mineralogical composition, geochemistry and genesis of these deposits have been the objects of many geological investigations, yet their origin remains contentious up to the present day. A characteristic feature of the Kalahari deposits is the intimate association of manganese ore and iron-formation of the Superior-type, in the form of three discrete sedimentary cycles constituting the Hotazel Formation. This striking lithological association is an almost unique feature on a global scale. From that point of view, the present study is effectively the first attempt to shed light on the origin and post-depositional history of the Hotazel succession, using as prime focus the petrographic and geochemical characteristics ofthe host iron-formation. Petrographic and whole-rock geochemical information of iron-formation from the southern parts of the KMF, suggests that the Hotazel iron-formation is almost identical to other iron-formations of the world of similar age and petrological character. The rock exhibits essentially no high-grade metamorphic or low-temperature alteration effects. Mineralogically, it contains abundant chert, magnetite, subordinate amounts of silicate minerals (greenalite, minnesotaite, stilpnomelane) and appreciable concentrations of carbonate constituents in the form of coexisting calcite and ankerite. Such mineralogical composition is indicative of processes occurring in a diagenetic" to burial (up to very low-greenschist facies) metamorphic environment. Bulk-rock geochemical data point towards a simple composition with Si02, total Fe-oxide and CaO being the chief major oxide components. Whole-rock rare-earth element data suggest that the iron-formation precipitated from a water column with chemical signatures comparable to modern, shallow oceanic seawater. The virtual absence of positive Eu anomalies is a feature that compares well with similar data from Neoproterozoic, glaciogenic iron-formations of the Rapitan type, and suggests but only a dilute hydrothermal signal, poten!ially derived from distal submarine volcanic activity. Carbon and oxygen isotope data from iron-formation and Mn-bearing carbonates as well as overlying ferriferous limestone of the Mooidraai Formation, compare well with the literature. The former exhibit variable depletion relative to seawater in terms of both BC and 180, while the latter have signatures comparable to normal marine bicarbonate. Isotopic variations appear to be related to fluctuations in the amount of co-precipitated marine carbonate, in conjunction with processes of coupled organic matter oxidation - FelMn reduction in the diagenetic environment. Oxygen isotope data from quartz-magnetite-calcite triplets suggest that crystallisation took place under open-system conditions, with magnetite being the most susceptible phase in terms of fluid-rock isotopic exchange. Data also suggest that the calcite-magnetite pair may constitute a more reliable geothermometer than the quartz-magnetite one, mainly due to the interlinked diagenetic histories between calcite and magnetite. Iron-formation from the northern parts of the KMF can by categorised into three main classes, namely pristine, altered and oxidised. Pristine iron-formation is identical to the one seen in the southernmost parts of the field. Altered iron-formation corresponds to a carbonate-free derivative of intense oxidation and leaching processes at the expense ofpristine iron-formation, and contains almost exclusively binary quartz-hematite mixtures. The rock appears to have lost essentially its entire pre-existing carbonate-related components (i.e., Ca, Mg, Sr, most Mn and Ba) and displays residual enrichments in elements such as Cr, Th, V, Ni and Pb, which would have behaved as immobile constituents during low-temperature alteration. The low temperature origin of altered iron-formation is supported by oxygen isotope data from quartz-hematite pairs which indicate that isotopically light hematite would have derived from oxidation of magneftte and other ferroussilicate compounds in the presence of a low-temperature meteoric fluid, while quartz would have remained isotopically unchanged. Occasional occurrences of acmite-hematite assemblages suggest localised metasomatic processes related to the action ofNaCI-rich fluids at the expense of altered iron-formation. The conditions of acmite genesis are very poorly constrained due to the very broad stability limits of the mineral in environments ranging from magmatic to surface-related. Oxidised iron-formation constitutes a distinct rock-type and shares common attributes with both the pristine and the altered iron-formation. The rock contains hematite as an important constituent while the amount of magnetite is substantially reduced. With regard to carbonate nlinerals, calcite contents are clearly very low or absent, having being replaced in most instances by a single, Mgenriched, dolomite/ankerite:type species. Oxidised iron-formation contains somewhat higher amounts of iron and reduced amounts of Sr and Ba relative to pristine iron-formation, whereas enrichments in elements such as Ni, Th, Pb, Cr, and V are seen, similar to altered iron-formation. Oxidised iron-formation appears to have originated from processes of dissolution-mobilisationreprecipitation of solutes derived primarily from leaching that produced altered iron-formation. It is proposed that the Hotazel iron-formation and associated manganese deposits were formed as a result of episodic sea-level fluctuations in a stratified depositional environment that gradually evolved into a shallow carbonate platform. A critical parameter in the development of manganese sediment may include regional climatic patterns related to a glacial event (Makganyene diamictite) prior to deposition of the Hotazel strata. This suggestion draws parallels with processes that are believed to have led to the formation of worldwide iron-formations and associated manganese deposits subsequent to Neoproterozoic episodes of glaciation. Submarine volcanism related to the underlying Ongeluk lavas appears to have had very little (if any) metallogenic significance, while evidence for a sudden rise in the oxygen contents of the atmosphere and ambient waters is lacking. With regard to later alteration processes, combination of geological and geochemical data point towards the potential influence of surface weathering prior to deposition of rocks of the unconformably overlying Olifantshoek Supergroup, possibly coupled with fault- and/or thrustcontrolled fluid-flow and leaching of the Hotazel succession during post-Olifantshoek times.

M.Sc. / It is the focus of the study to qualitatively describe and then quantify the mineralogical and geochemical changes associated with the supergene alteration of carbonate-rich braunite lutite (Mamatwan-type ore) immediately below the Kalahari unconformity along the southeastern suboutcrop perimeter of the Hotazel Formation in the Kalahari deposit. It was also the objective of this study to determine the timing and duration of supergene alteration. Samples for polished thin sections were carefully selected from eight representative boreholes to be representative of all the lithostratigraphic zones and ore types. The thin sections were used to study mineralogy by means of reflected light microscopy and scanning electron microscopy. X-ray powder diffractometry on representative powder samples were used to study the mineralogy and geochemistry of the samples. Microprobe analyses were also performed on the representative samples. Finally the samples were submitted for 40Ar/39Ar geochronology. In this supergene enrichment zone carbonates are leached (associated with an increase in porosity) and Mn2+/Mn3+ -bearing minerals (kutnahorite, Mn-calcite an braunite) are altered to supergene Mn4+-bearing mineral phases (todorokite and manganomelane) and minor quartz. This process upgrades ore from 38 wt% Mn to ore with more than 40 wt% Mn. Element fluxes, enrichment and depletion of major and trace elements were quantified by mass balance calculations. Na2O, K2O, Sr, Ba, Zn and H2O were enriched, while Mn3O4, Fe2O3, CaO, MgO, P, B and CO2 were leached from the ore during supergene alteration. Results of this study suggest that the development of Post African I erosional surface may have taken place 45 Ma ago. The bottom of the weathering profile gives a well-defined peak at ca. 5 Ma that may possible coincide with the development of Post African II erosional surface. The major characteristics of the alteration process of the unaltered Mamatwan-type ore to supergene altered braunite lutite can be summarized as follow: • Leaching of Mn carbonates and Mn2+/Mn3+-oxides. • Formation of Mn4+-oxyhydroxides and quartz. • Decrease in relative density of the ore. • Increase in porosity of the ore. • Leaching of Mn3O4, Fe2O3, CaO, MgO, P, B, CO2. • Enrichment of Na2O, K2O, Sr, Ba, Zn, H2O. Chemical weathering processes along the Cenozoic Kalahari unconformity appear to have affected the manganiferous lithologies of the Hotazel Formation from 45 Ma onwards to 5 Ma. The weathering front processes very slowly through the Mn-rich braunite lutite (<10m in 40 Ma; <0.25m/Ma); producing a very uniform and microcrystalline supergene mineral assemblage with distinct characteristics.

M.A. / Hematized iron formation known as the Manganore iron formation is slumped into sinkhole structures in the Campbellrand Subgroup, Transvaal Supergroup, on the Maremane dome. These iron deposits are underlain by manganiferous breccias known as the Wolhaarkop Breccia. Known iron and manganese deposits of this type occur in an arc from Sishen in the north to Postmasburg in the south. The area is not being mined for manganese at the moment due to the relatively high grade of the Kalahari manganese field situated to the north of this area. The iron deposits, though, are some of the richest in the world. The aim is to establish the mode of origin for the Wolhaarkop Breccia. The Wolhaarkop Breccia is interpreted as being a residual ancient manganese wad from a karst environment in manganese rich dolostones of the Campbellrand Subgroup. This siliceous breccia contains authigenic megaquartz and angular poorly sorted clasts of chalcedony and quartz, set in a braunite-hematite matrix. Fluid inclusions in the authigenic quartz of the Wolhaarkop Breccia have been studied to establish the source of the fluid responsible for quartz precipitation in the Wolhaarkop Breccia, and indirectly, for the formation of the Wolhaarkop Breccia. Thermometric data was used to determine the maximum possible pT and depth conditions under which the quartz might have been precipitated. Fluid chemistry was determined using the bulk crush-leach method to shed some light on the fluid origin. It was established that the fluid responsible for chert recrystallization and precipitation of authigenic quartz and chalcedony had a meteoric source. Considering the results of the above-mentioned analysis, it was concluded that the iron and manganese deposits were formed during a cycle of uplift followed by subsidence. During the period of uplift, erosion in a karst environment and enrichment of iron formation in a supergene environment concentrated manganese as a manganese wad, and iron as a residual iron-oxide laterite. Meteoric water was the main fluid present during this period. Later, during a stage of subsidence, the Wolhaarkop Breccia underwent diagenesis and later lower greenschist-facies metamorphism. During a final stage of uplift the deposit was exposed to the atmosphere again, the dolostones were weathered away and the residual Manganore iron formation and Wolhaarkop Breccia were exposed to supergene alteration.

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Thesis (Ph.D.) -- Memorial University of Newfoundland. / Bibliography : leaves 168-183. Also available online.

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In the Middelplaats mine area of the Kalahari manganese field, two drill holes (MP53 and MP54) intersected anomalously high-grade manganese ore sitting stratigraphically just above an igneous body (likely a dike or sill). Manganese ore located within approximate 5 meters of the contact with the underlying igneous rocks has been substantially metasomatically upgraded from 25 percent manganese, to over 40 percent whilst the dominant manganese species within the ore has been altered to hausmannite. This report demonstrates the metasomatic alteration is related to devolatilization (removal and/or remobilization of H₂O, CO₂ and CaO) due to contact metamorphism caused by the underlying igneous rocks. The Middelplaats mine is situated in the southwest corner of the Kalahari manganese field where the paleo basin shallows out and ends. Within the mine area, several stratigraphic units pinch out or are truncated by the side of the basin. This pinching out of lithological formations has led to the underlying Ongeluk Formation being in contact with the much younger units of the Hotazel Formation. Therefore, geochemical investigation into the nature and source of the igneous rocks was also undertaken to see if the rocks from the two drill holes were related to one another and/or the underlying Ongeluk Formation. Results of these geochemical studies have demonstrated that the Middelplaats igneous rocks (dolerites) from the two drill holes (MP53 and MP54) share a co-genetic source region. There is also reasonable geochemical evidence that the source region of the Middelplaats igneous rocks was substantially similar to the source region of the Ongeluk Formation. This may indicate that the source region of the Ongeluk Formation was reactivated at some later stage resulting in the emplacement of doleritic dikes or sills in the Middelplaats mine area. The Middelplaats igneous rocks were also found to have undergone a slight but pervasive potassic alteration; with most of the original plagioclase feldspar showing some level of replacement by a potassium enriched feldspar. Although no source for this potassic fluid was found, the devolatilization reaction within the manganese ore appears to have released some potassium into the surrounding rocks. This additional potassium may be responsible for some localized potassic alteration.