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'n mineralogiese ondersoek van die goudafsetting In die omgewing van die Fumani-Goudmyn, Gazankulu, Noordoos - Transvaal

Diagenetic carbonates and biogeochemical cycling of organic matter in selected Archean-Paleoproterozoic sedimentary successions of the Kaapvaal Craton, South Africa

  • Authors: Cochrane, Justin Michael
  • Date: 2010-06-03T05:38:44Z
  • Subjects: Stratigraphic geology , Geochemistry , Petrology , Mineralogy , Sedimentation and deposition , Kaapvaal Craton (South Africa)
  • Type: Thesis
  • Identifier: uj:6855 , http://hdl.handle.net/10210/3288
  • Description: M.Sc. , The Kaapvaal craton is one of few regions on earth with an almost continuous record of wellpreserved supracrustal rocks ranging in age from ~3.5 Ga to the late Paleoproterozoic at ~1.75 Ga. In this study diagenetic carbonates from the Paleoarchean Buck Reef Chert and Joe’s Luck Formation of the Swaziland Supergroup, the Mesoarchean Thalu and Promise Formations of the Mozaan/Witwatersrand Supergroups and the Paleoproterozoic Timeball Hill and Silverton Formations of the Transvaal Supergroup were sampled and analyzed. The aim of the study was to determine possible variations in the composition of the carbonates through time and their significance especially with regards to microbial activity in diagenetic systems in early Earth history. Results indicate similar petrographic observations and geochemical signatures in diagenetic carbonates of iron formations in the Buck Reef Chert, Joe’s Luck and Griquatown Iron Formation. The carbonates all tend to be siderites with iron derived from hydrothermal input and all are depleted in 13C relative to Peedee Belemnite standard. It suggested that siderite formed as a result of microbial respiration. Microbes degrade organic matter and reduce iron in this process. This resulted in the depletion in 13C and in the precipitation of siderite. However in order for iron reduction to have occurred the reduced iron first had to be oxidized. This most probably occurred through iron oxidizing chemolithoautotrophs under microaerophilic conditions. Diagenetic carbonate concretions of the Thalu and Promise Formations are manganiferous and are highly depleted in 13C relative to PDB. There is also strong evidence for hydrothermal input of manganese and iron into the system because of positive europium anomalies. The carbonates from both of the formations strongly suggest the presence of some free oxygen. The reasoning behind this conclusion is as follows: The depletion of 13C in the carbonates points to microbial decomposition of organic matter and manganese respiration (the decomposition of organic matter by microbial MnO2 reduction) is shown to be the most reasonable process that led to the formation of the carbonate concretions. The implication is that MnO2 must first have been precipitated and that can only be achieved in the presence of free oxygen with the oxidation reaction often catalyzed by manganese oxidizing chemolithoautotrophs. The carbonates of the Timeball Hill and Silverton Formationsare calcites ad contain little no iron. There is also little or no evidence for hydrothermal input and the basin appears to be a clastic dominated. It is generally accepted that a major rise in oxygen in the oceans and the atmosphere occurred at about 2.32 Ga. This rise in oxygen levels is reflected in the diagenetic calcite concretions of the Silverton Formation. Both iron and manganese reduction where not very effective because of the depletion in the basin water of these two elements, organic carbon taken up in the calcite concretions, indicated by negative δ13CPDB carbonate values, was most probably derived from aerobic and/or nitrate respiration. The most important conclusion from this study is that sufficient free oxygen and hence oxygenic photosynthesis were present to oxidize both Fe and Mn at least as far back as the Paleo-Mesoarchean.
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Geochemistry and mineralogy of supergene altered manganese ore below the Kalahari unconformity in the Kalahari manganese field, Northern Cape Province, South Africa

  • Authors: Du Plooy, Andries Petrus
  • Date: 2009-01-28T09:38:57Z
  • Subjects: Geology , Geochemistry , Mineralogy , Petrology , Manganese ores , Northern Cape (South Africa)
  • Type: Thesis
  • Identifier: uj:14834 , http://hdl.handle.net/10210/1958
  • Description: 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.
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Geological and geochemical study of the quartzofeldspathic rocks from the farm Gotha, Limpopo Province, South Africa

  • Authors: Barnett, Martina
  • Date: 2009-01-27T07:17:45Z
  • Subjects: Geology , Geochemistry , Petrology , Mineralogy , Structural geology , Limpopo (South Africa)
  • Type: Thesis
  • Identifier: uj:14824 , http://hdl.handle.net/10210/1949
  • Description: M.Sc. , This study has served to expand the geological map of surroundings of the Venetia Mine (Limpopo Province, South Africa) incorporating the area lying south of the kimberlite deposit and bounded in the south by the Dowe-Tokwe fault. The most significant structural conclusion stemming from this mapping project is that the Venetia Synform seems to be tectonically separate from the surrounding area and actually forms a klippe (shallowly dipping thrust) against the Krone Metamorphic terrane and the Gotha Complex. Petrographic descriptions of quartzofeldspathic lithologies found in the Krone Metamorphic Terrane to the west of the Venetia klippe (Mellonig, 2004) are identical suggesting that they belong to the Gotha igneous complex. There are no differences in geochemical compositions of monzogranite to granodiorite, tonalite and quartz diorite from Farms Gotha and Venetia. The rocks are I-type granitoids that generally form in continental magmatic arcs. The amount of U and Th in the igneous rocks of the Farms Gotha and Venetia (contained in minerals found within quartz, plagioclase, amphibole and K-feldspar crystal boundaries and the magmatic zircons of the Farm Gotha samples) and the pattern produced by heat producing elements (Council for Geoscience Radiogenic Map), indicate that that the unexpectedly high concentration of these elements are not the result of regional metamorphism, but is the remnant of the final crystallisation phase of the magma of the area. REE plots of the Venetia Mine samples show negative Eu anomalies, indicating the presence of plagioclase and K-feldspar in the magma source of the Venetia mine samples. The assumption is, that most samples retained their original chemical compositions having experienced only weak deuteric alteration and no dynamic metamorphism.
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Geology and petrology of the Dabolava Region, West-Central Madagascar, with emphasis on granite-hosted gold mineralization

  • Authors: Rakotoarimanana, Rindrahasy Harilala
  • Date: 2009-01-28T09:43:01Z
  • Subjects: Geology , Petrology , Gold mine and mining , Dabolava Region (Madagascar)
  • Type: Thesis
  • Identifier: uj:14845 , http://hdl.handle.net/10210/1968
  • Description: M.Sc. , The Dabolava region is an area of approximately 600 km2 and is situated on the western edge of the Precambrian in west-central Madagascar. The geology mainly consists of Proterozoic amphibolite facies metavolcanic rocks, inter-layered with minor metasedimentary rocks, crosscut by granodioritic to gabbroic plutons. The country rocks of the granodiorite and gabbroic plutons are composed of 50% amphibolites, 30% quartzofeldspathic gneisses and 20% metasedimentary rocks, mainly carbonates. The amphibolites consist dominantly of hornblende with plagioclase and minor quartz groundmass, although orthopyroxene, clinopyroxene, chlorite, and biotite are present in certain samples. They have tholeiitic affinities and may have been derived from basaltic lavas. They contain felsic segregations of tonalitic composition that possibly represent migmatitic leucosomes, with hornblende concentrated in associated melanosomes. The amphibolites are highly deformed compared to the plutonic rocks. Meta-quartzofeldspathic rocks of dominant rhyolitic compositions are interlayered within the amphibolites; these may represent felsic volcanics coeval with the metabasalt. Metamorphosed carbonates are also interlayered within the amphibolites. This assemblage of supracrustal rocks is intruded by Neoproterozoic granitoid and gabbroic plutons, and granodiorite dykes. The composition of the majority of the plutons in the area of study is mainly granodioritic, with minor quartz diorite and quartz monzodiorite. They are metaluminous and contain quartz, plagioclase, with minor K-feldspar (microcline); biotite and hornblende constitute the ferromagnesian minerals. The granodiorites have a prominent foliation defined by biotite and hornblende. According to their chemical and mineralogical composition, the granodiorites are classified as I-type in origin. Gold mineralization is associated with the Neoproterozoic granodiorite plutons, mainly the Dabolava and the Ambatomiefy plutons. It is hosted within quartz veins that are generally oriented parallel to the foliation of the host rock. A limited degree of alteration is observed within the granodiorite, with the alteration assemblages consisting of biotite, pseudomorphic chlorite, calcite, and sericite. Gold is associated with hydrothermal biotite and sulphide assemblages consist of pyrrhotite, arsenopyrite with minor pyrite and chalcopyrite, magnetite and ilmenite. The chemistry of analysed gold grains from the Dabolava pluton shows that they mainly consist of 95-97% gold with the remainder composed of Ag, Hg and Cu. A gold concentration of up to 2232 ppm was observed in one of the gold excavations within the Ambatomiefy pluton. Microthermometric studies reveal three fluid types, including a high salinity fluid (type 4), a CO2-rich fluid (type 1-a), and an aqueous type (type 3). It is suggested that the CO2-rich and high salinity fluids were exsolved from the magma. With decreasing temperature a low salinity CO2-H2O-NaCl fluid (type 1-b, type 2) (Th ranges from ~ 220-350° C) resulted from heterogeneous mixting of a CO2-rich fluid and a low salinity aqueous fluid. Therefore, fluid inclusion studies indicate a magmatic origin of the mineralizing fluid(s). A porphyry-type deposit is suggested for the gold mineralization in the study area, as it is associated with I-type granitoid plutons, the mineralizing fluid (s) are of magmatic origin, and gold is associated with chalcopyrite, albeit in minor amounts. Based on the rock associations observed in the field, which consist of metabasalts interlayered with minor coeval metarhyolite, with associated intrusive plutonic rocks, as well as trace element discrimination diagrams, an active continental margin tectonic setting is inferred for the rocks in the study area. Two samples from the granodiorite plutons and one sample from a gabbro body were dated using U-Pb single zircon geochronology. A sample from the Ambatomiefy pluton yielded an age of ~1002±3 Ma, which is interpreted to represent the crystallization age of the pluton. The Dabolava pluton has also been dated, and a similar age of 1008 Ma has been obtained. A gabbro sample from a smaller mafic body in the area has been dated at 982±2 Ma. This defines a ~26 m.y. period of Neoproterozoic magmatic activity. An age of 982.3±2 .9 was also reported from a gabbro body located in the southern part of Madagascar (Amborompotsy-Ikalamavony). These provide evidence of the presence of 1000 Ma magmatic activity in Madagascar. The extent and the significance of this magmatic event are not yet understood although it could be related to the Mesoproterozoic event associated with the assembly of the supercontinent Rodinia. The identification of granitoids of similar age and character in Madagascar and within Gondwana has economic significance regarding the potential of these granitoids for porphyry-type gold mineralization. Therefore, this is useful for future gold exploration.
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Metasedimentary manganese ores of the Serra do Navio deposit, Amapa Province, Brazil

Petrology, geochemistry and geochronology of Neoproterozoic volcanic rocks of the Punagarh and Sindreth Groups, Rajasthan, northwest India

Provenance of the Neoproterozoic to early Palaeozoic successions of the Kango Inlier, Saldania Belt, South Africa

  • Authors: Naidoo, Thanusha
  • Date: 2009-04-28T06:57:55Z
  • Subjects: Geology , Petrology , Geochemistry , Geological time , Cape of Good Hope (South Africa)
  • Type: Thesis
  • Identifier: uj:8308 , http://hdl.handle.net/10210/2437
  • Description: M.Sc. , The configuration of the supercontinent Rodinia, at the end of the Mesoproterozoic to the beginning of the Neoproterozoic (1100-750 Ma), and its subsequent break up into cratonic fragments that would later result in the formation of Gondwana (Early Palaeozoic), is still not completely understood. This is largely due to ambiguity surrounding relationships between cratons, craton evolution and timing of significant tectonic or sedimentary events. Particular to this study is the evolution and palaeogeographic history of the Kalahari Craton and a comprehensive provenance analysis of Neoproterozoic to early Palaeozoic clastic sedimentary rocks from the Kango Inlier (Saldania Belt, South Africa). This includes the Cango Caves and Kansa Groups as well as the Schoemanspoort and the adjacent Peninsula Formation (Table Mountain Group, Cape Supergroup). A well established lithostratigraphy, in addition to recent establishment of age constraints by UPb zircon dating and microfossil evidence, allowed for strategic sampling with the objective of gaining insight to the crustal evolution of SW Gondwana. In this study, a progression from immature, moderately altered rocks in the Cango Caves Group (Upper Neoproterozoic) to mature, strongly altered rocks in the Lower Palaeozoic Kansa Group and overlying formations is observed. Thus, rapid sedimentation of the former is anticipated, while the subsequent formations developed at a passive/rifted margin culminating in the laterally extensive deposition of the Peninsula Formation. Ongoing extensional movement is evident due to chronologically deeper-water facies and the progressive influence of a less fractionated component in the Cango Caves Group, particularly in the Huis Rivier Formation. The association of these rocks with an active margin is not certain since index trace element concentrations are too high for typical arc terranes. Thus, the mixing of a younger (570-600 Ma) magmatic source (close to an active margin) with mafic and felsic rocks of the older Mesoproterozoic Natal- Namaqua Mobile Belt (NMB) is the most likely possibility. A maximum, pre-Cape Granite age of 571 Ma can be assigned to the Huis Rivier Formation (Cango Caves Group) by detrital zircon dating, and thus correlation with the Malmesbury Group can be made. Ediacaran age zircons might be related to the active continental margin (Trans Antarctic Orogen) surrounding southern Gondwana, but this is still hypothetical. The post-Cape Granite Kansa Group and overlying Schoemanspoort Formation were most likely deposited as basin infill subsequent to folding and transtensional tectonics affecting the underlying Cango Caves Group. The Kansa Group may be comparable with the Klipheuwel Formation (southwest South Africa) in terms of its stratigraphic position beneath the Table Mountain Group. Deposition of the Table Mountain Group is much younger than previously believed in light of Ordovician zircon ages (471, 485, 499 Ma) obtained from the underlying Kansa Group. However, the provenance of these thus far unheard of ages for magmatic events in South Africa is a matter of contention. The proximal Ordovician Ross-Delamerian Orogenic event in Antarctica is the most likely source. Peninsula Formation deposition represents a cover sequence i.e. the culmination of small isolated basins (e.g. the Kansa Group and lower Table Mountain Group) into a larger, laterally extensive basin where reworking played a dominant role. This basin is likely to be a rift-related. However, it is not clear which crustal entity rifted away from vi South Africa and if, during the Ordovician an, active continental margin further to the south - bridging the South American Famatina Orogen with the Ross-Delamerian arc in Antarctica - existed. The Natal-Namaqua Mobile Belt appears to be the predominant source throughout the succession as indicated by Nd-isotope data and zircon populations. This implies that simple crustal recycling of Natal-Namaqua basement (or rocks with similar Nd-isotope characteristics) led to the genesis of the magmatic material younger than 1 Ga, observed in this study.
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Pyrite in the Mesoarchean Witwatersrand Supergroup, South Africa

  • Authors: Guy, Bradley Martin
  • Date: 2012-08-20
  • Subjects: Pyrites , Isotope geology , Paragenesis , Formations (Geology) , Petrology , Witwatersrand Supergroup (South Africa)
  • Type: Thesis
  • Identifier: uj:2779 , http://hdl.handle.net/10210/6219
  • Description: Ph.D. , Petrographic, chemical and multiple sulfur isotope analyses were conducted on pyrite from argillaceous, arenaceous and rudaceous sedimentary rocks from the Mesoarchean Witwatersrand Supergroup. Following detailed petrographic analyses, four paragenetic associations of pyrite were identified. These include: 1) Detrital pyrite (derived from an existing rock via weathering and/or erosion). 2) Syngenetic pyrite (formed at the same time as the surrounding sediment). 3) Diagenetic pyrite (formed in the sediment before lithification and metamorphism). 4) Epigenetic pyrite (formed during metamorphism and hydrothermal alteration). It was found that the distribution of the pyrite varies with respect to the stratigraphic profile of the Witwatersrand Supergroup and depositional facies within the Witwatersrand depository. In this regard, the four paragenetic associations of pyrite are either scarce or absent in marine-dominated depositional environments, which occur in the lower parts of the succession and in geographically distal parts of the depository. Conversely, the four paragenetic associations are well represented in fluvial-dominated depositional environments, which occur in the middle and upper parts of the succession and in geographically proximal parts of the depository. However, it is worth noting that diagenetic pyrite in the West Rand Group occurs as in situ segregations in carbonaceous shale, whereas syngenetic and diagenetic pyrite in the Central Rand Group occurs as reworked and rounded fragments in fluvial quartz-pebble conglomerates. The strong association between fluvial depositional environments and sedimentary pyrite (syngenetic and diagenetic pyrite) infers a continental source of the sulfur (sulfide weathering or volcanic activity), whereas the lack of pyrite in marine depositional environments is consistent with the model of a sulfate-poor Archean ocean. The connection between epigenetic pyrite and the fluvial-dominated depofacies is probably related to the elevated concentrations of precursor sulfides (i.e., remobilization of syngenetic and early diagenetic pyrite) and the presence of organic carbon (conversion of metal-rich early diagenetic pyrite into pyrrhotite and base metal sulfides). In support of the petrographic observations above, it was found that the trace element chemistry of each paragenetic association of pyrite yields a distinctive set of chemical compositions and interelement variations (Co, Ni and As contents). Regarding detrital pyrite, two chemical populations can be distinguished according to grain size: 1) small grains (tens of μm’s) with high levels of metal substitution (up to wt. %) and interelement covariation and iv 2) large grains (>100 μm) with low levels of metal substitution (≤200 ppm). These two populations are thought to represent pyrite derived from sedimentary and metamorphosed source areas, respectively (see below). The trace element chemistry of diagenetic pyrite varies relative to the Fe-content of the host rock. Diagenetic pyrite from Fe-rich host rocks, such as magnetic mudstone and banded iron formation (BIF), generally contain low Ni contents (<500 ppm), moderate As contents (<1500 ppm) and relatively high Co contents (up to a few wt. %). Elevated concentrations of As probably reflect desorption of As from clays and Fe-oxyhydroxides during diagenetic phase transformations, whereas anomalous concentrations of Co are tentatively linked to the reductive dissolution of Mn-oxyhydroxides.
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Sm-Nd isotopic disequilibrium between minerals in Merenskycyclic units of the Bushveld Complex, South Africa

Structural-metamorphic studies of distinct fold types related to distinct tectono-metamorphic events in the central zone of the Limpopo Complex, South Africa

  • Authors: Van Kal, Shaun Michael
  • Date: 2009-01-28T09:43:40Z
  • Subjects: Geology , Structural geology , Folds (Geology) , Metamorphism (Geology) , Petrology , Limpopo (South Africa)
  • Type: Thesis
  • Identifier: uj:14850 , http://hdl.handle.net/10210/1972
  • Description: M.Sc. , The Central Zone of the Limpopo Complex displays two major structural features: the roughly east-west oriented Tshipise Straightening Zone Paleoproterozoic in age and a “Cross Folded Zone” to the north of the Straightening Zone comprising large-scale sheath and cross folds suggested to have developed during a Late- Archaean high grade tectono-metamorphic event. This study presents and discusses structural-metamorphic data showing that two closely associated folds (Ga-Tshanzi and Campbell) in the eastern part of the Cross Folded Zone near Musina, record different structural and metamorphic histories that may be applied to the evolution of the entire Central Zone of the Limpopo Complex. The Ga-Tshanzi structure has an ovate-shaped closed outcrop pattern approximately 4km long, and 3km wide with the long axis of the fold pattern oriented in a westerly direction. The fold geometry, characterized by a central fold axis that plunges steeply to the SSW, is very similar to other closed folds in the Central Zone previously interpreted as sheath folds. The Ga-Tshanzi fold deforms rocks of the Beit Bridge Complex (calc-silicate, metaquartzite, metapelite and magnetite quartzite and quartzofeldspathic Singelele Gneiss), and members of the Messina Layered Suite. The ovate structure is characterised by a gneissic fabric comprising peak metamorphic mineral assemblages. This regional gneissic fabric that occurs throughout the Central Zone also defines the shape of the neighbouring Campbell fold. Mineral lineations and fold hinges in the Ga-Tshanzi fold mainly present within metaquartzites and calc-silicates, plunge steeply to the southwest, parallel to its central fold axis indicating a NNE-SSW transport direction during fold formation. A decompression-cooling P-T path calculated for metapelitic gneisses from the Ga-Tshanzi fold shows that the closed fold developed under high-grade, deep crustal conditions. Peak P-T conditions of 7.5kbar/799ºC were followed by decompression and cooling down to 5.23kbar/605ºC. Water activity during this event was low, ranging from 0.122 at peak conditions, and decreasing to 0.037 at the minimum calculated conditions. The Ga-Tshanzi closed fold and the closely associated Campbell cross fold were thus formed at deep crustal levels and partially exhumed along a similar decompression-cooling P-T path to mid-crustal levels during the early orogenic event. The Campbell fold, described as a cross fold in the literature, is approximately 15km long and has a V shaped outcrop pattern that tapers from 12km in the southeast to 2 km in the northwest. This fold is developed in lithologies similar to those of the Ga-Tshanzi fold as well as in Sand River Gneisses. It has a near isoclinal fold geometry with both limbs dipping towards the southwest and a fold axis that plunges moderately to the west-southwest. This fold, that is interpreted to have developed during the same deformational event as the Ga-Tshansi structure has, however, subsequently been affected at mid- to upper crustal levels by shear movement along the Tshipise Straightening Zone displaying widespread development of younger planar and linear structural features. Planar features include north-south-trending high temperature shear zones that crosscut the regional fabric and flexural slip planes particularly evident in quartzites. Linear features from the Campbell fold that are mainly developed in younger shear and flexural slip planes, indicate, in contrast to the Ga-Tshanzi fold, an ENE-WSW directed crustal movement that is in accordance with the sense of movement suggested for the Tshipise Straightening Zone. The calculated decompression-cooling P-T path for sheared metapelitic gneisses from discrete high temperature shear zones deforming rocks of the Campbell cross fold shows that this superimposed shear deformational event occurred under peak P-T conditions of 4.98kbar/681ºC, followed by decompression and cooling down to 3.61kbar/585ºC. Water activity during this shear event was high, ranging from 0.217 at peak conditions and decreases to 0.117 at minimum calculated conditions. Structural and metamorphic data for the two folded areas thus indicate two distinct tectono-metamorphic events: (i) a late Archaean peak metamorphic and deformational event responsible for the formation of the Ga-Tshanzi fold, and similar folds throughout the Central Zone including the Campbell cross fold that was accompanied by steep NNE-SSW transport of crustal material, and (ii) a shear deformational event linked to the Paleoproterozoic Tshipise Straightening Zone that partially obliterated the early structural and metamorphic history of the Campbell fold during mid to upper crustal conditions during relatively shallow ENE-WSW directed movement of crustal material. The fact that this superimposed event had no apparent metamorphic effect on the studied metapelitic rocks of the closely associated Ga-Tshanzi closed fold, suggests that shearing was constrained to discrete north-south orientated zones.
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The nature and origin of the polymetallic Salt River massive sulfide deposit, Northern Cape Province, South Africa

  • Authors: Osburn, Keith Craig
  • Date: 2012-06-07
  • Subjects: Namaqua Metamorphic Province , Sedimentation and deposition , Geology (Kakamas, South Africa) , Salt River sulfide deposit , Petrology , Metamorphic rocks , Geology, Stratigraphic
  • Type: Thesis
  • Identifier: uj:8667 , http://hdl.handle.net/10210/5022
  • Description: M.Sc. , The Salt River deposit is a poly-metallic base metal deposit with a Zn-Cu-Pb metal content that occurs southwest of the town of Kakamas within the Northern Cape Province, South Africa. The Salt River deposit occurs within the Geelvloer Formation of the Bushmanland Subprovince of the Proterozoic Namaqua Metamorphic Province (NMP). This study constitutes the first detailed study of the host rock succession to the Salt River deposit, by investigating the lithostratigraphy, petrography geochemistry and geochronology. During the course of the study, various styles of wall-rock alteration were identified and investigated to determine their effect on the host rock succession. A further aim of this study was to classify the Salt River deposit and compare it to neighboring deposits occurring in the NMP. Geochronological studies were undertaken to define the age of mineralization. Detailed logging of exploration diamond drill core combined with petrographic investigation was used to define thirteen distinct lithotypes. The stratigraphy is dominated by felsic grey gneisses and mafic amphibolites, minor calc-silicate rocks, granitic augen gneisses, pegmatites and two lithologies that represent the metamorphosed equivalents of hydrothermally-altered host rock. Lithostratigraphic investigations yielded a rather uniform succession containing four distinct marker beds defined by their common occurrence and ease of correlation across various boreholes.
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The Paleo-environmental significance of the iron-formations and iron-rich mudstones of the Mesoarchean Witwatersrand-Mozaan Basin, South Africa

  • Authors: Smith, Albertus Johannes Basson
  • Date: 2009-04-28T07:17:48Z
  • Subjects: Geology , Petrology , Mineralogy , Geochemistry , Iron ores , Formations (Geology)
  • Type: Thesis
  • Identifier: http://ujcontent.uj.ac.za8080/10210/370928 , uj:8312 , http://hdl.handle.net/10210/2440
  • Description: M.Sc. , The Mesoarchean Witwatersrand and Pongola Supergroups of South Africa are the oldest, well preserved supracratonic successions worldwide. Various banded iron formation (BIF) and iron-rich mudstone units occur within the West Rand Group of the Witwatersrand Supergroup and the Mozaan Group of the Pongola Supergroup. A granular iron formation (GIF) occurs in a single unit in the Nconga Formation of the Mozaan Group. The Witwatersrand Supergroup and Mozaan Group have been lithostratigraphically correlated and are interpreted to have been part of the same sedimentary basin. The studied BIF units occur in two associations: shale-associated and diamictiteassociated BIF. The GIF seem to have been deposited in shallower environments with greater hydrodynamic activity. The iron-rich mudstone shows a similar stratigraphic setting to that of the shale-associated BIF. The lithostratigraphic setting of the Witwatersrand-Mozaan basin BIFs are similar to what is seen for Superior-type ironformations, with the mudstones and associated BIFs marking marine transgressions. Various mineralogical facies of BIF were identified, including oxide, carbonate and silicate facies BIF, as well as mixed facies between these end members. The GIF is a unique facies and shows abundant petrographic evidence for biological activity. The iron-rich mudstone has been subdivided into iron-silicate rich, magnetite-bearing, carbonate-bearing, magnetite-carbonate-bearing and garnet-bearing subtypes. BIF, GIF and iron-rich mudstone have been subjected to lower greenschist facies metamorphism with some occurences of localized contact metamorphism. The abundance of magnetite shows that oxidation played an important part in BIF deposition, whereas the occurrence of 12C-enriched iron-rich carbonates suggests post depositional reduction of the deposited oxidized iron-rich minerals by organic matter. Al-bearing minerals are rare in the BIFs xxi and abundant in the iron-rich mudstones. Apatite and rare earth element (REE)- phosphates occur throughout. The major element geochemistry shows an inverse proportionality for Fe and Si in all the studied samples. BIFs show slightly higher Fe- and lower Si- and Al-concentrations compared to iron-rich mudstones which show higher Si- and Al- and lower Feconcentrations. The studied BIFs show major element geochemical attributes intermediate to those of Superior- and Algoma-type iron-formations. Provenance studies on some of the iron-rich mudstones illustrate that they were sourced from a mixture of mafic and felsic sources. The rare earth element (REE) geochemistry suggests strong hydrothermal input into the units, and positive correlation with the Fe-concentrations suggests that the Fe was introduced by high temperature hydrothermal fluids. The majority of the REEs are hosted by apatite and the REE-phosphates monazite and xenotime. The REEs were reconcentrated into these phosphates during diagenesis. A comparison of the studied lithostratigraphically correlatable units between the Witwatersrand Supergroup and Mozaan Group makes it possible to construct a depositional model for basin-wide BIF deposition in the Witwatersrand-Mozaan basin. Shale-associated BIF was deposited during the peak of transgression when reduced Ferich hydrothermal bottom waters were introduced into shallow ocean water that was either oxygenated or filled with anoxygenic phototrophic bacteria. Diamictite-associated BIF, in contrast, was deposited during interglacial periods when the melting of glacial ice introduced sunlight, nutrients and oxygen to the reduced, hydrothermally influenced Ferich ocean water. GIF was probably deposited in shallow, above wave base waters cut off from clastic input, and then washed into deeper depositional environments. Iron-rich mudstone was deposited in a similar setting as the shale-associated BIF, but in environments that were not completely cut off from detrital influx. The study shows that it is impossible to construct a general depositional model for Precambrian BIFs, since the lithostratigraphic and depositional settings vary between different examples of BIF.
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