A geological study of the Platreef at Potgietersrus platinum mine with emphasis on the magmatic processes, contamination and metasomatism
- Authors: Appiah-Nimoh, Frederick
- Date: 2009-01-27T07:17:16Z
- Subjects: Platinum group , Metasomatism (Mineralogy) , Magmatism , Geology , Geochemistry , Busveld complex (South Africa)
- Type: Thesis
- Identifier: uj:14821 , http://hdl.handle.net/10210/1946
- Description: M.Sc. , Please refer to full text to view abstract
- Full Text:
- Authors: Appiah-Nimoh, Frederick
- Date: 2009-01-27T07:17:16Z
- Subjects: Platinum group , Metasomatism (Mineralogy) , Magmatism , Geology , Geochemistry , Busveld complex (South Africa)
- Type: Thesis
- Identifier: uj:14821 , http://hdl.handle.net/10210/1946
- Description: M.Sc. , Please refer to full text to view abstract
- Full Text:
A geometallurgical evaluation of the ores of the northern Kalahari manganese deposit, South Africa
- Authors: Chetty, Deshenthree
- Date: 2010-04-19T07:55:36Z
- Subjects: Geology , Manganese ores , Kuruman (South Africa)
- Type: Thesis
- Identifier: uj:6794 , http://hdl.handle.net/10210/3223
- Description: D. Phil. , The Kalahari Manganese Deposit (KMD) is the largest of five erosional relics of the Hotazel Formation that are located near Kuruman in the Northern Cape Province of South Africa. Manganese ores are exploited from the lowermost of three manganiferous beds that are interbedded with banded iron-formation (BIF) and hematite lutite, that together constitute the Hotazel Formation. Two major ore types have been delineated previously, viz. low grade braunite lutite of the Mamatwan-type, and high grade oxidic ores of the Wessels-type, with the latter spatially restricted to the northern KMD. Genesis of the ores was temporally distinct, with the Mamatwan-type ore considered as a sedimentary-diagenetic precursor to the hydrothermally altered Wessels-type ore. Drill core samples from the Nchwaning-Gloria area of the northern KMD were analysed, with the aim to better characterise ore genesis, with emphasis on ore alteration. A second part of the study aimed at the application of mineralogical and geochemical information to aspects of ore smelting for the production of Mn alloy for use in the steel industry. Methods employed were drill core logging, X-ray diffraction (XRD), petrography, electron probe microanalysis (EPMA), major and trace element (including REE) analysis (employing artificial neural networks for evaluation of elemental trends), and stable isotope (C and O) analysis. Significant effort was invested in method development for quantitative mineralogical modal analysis using Rietveld refinement of XRD data. The study shows that a number of ore types can be differentiated in the northern KMD on the basis of mineral assemblage, grade, texture and geochemical characteristics. The ores are broadly classified into least altered (LA), partially altered (PA) and advanced altered (AA) types. The LA ores are low grade (<40 wt%Mn) Mn lutites, with dolomite-group carbonate a significant component in addition to braunite. Serpentine is a ubiquitous trace mineral, and boron is a characteristic trace element hosted predominantly by braunite in these ores. Ores of the PA type comprise either braunite-hausmannite-calcite or hausmannite-calcite assemblages, are fine to coarse grained, and display intermediate Mn grades (40-45 wt%Mn). They exhibit a transitional trace element signature. Advanced altered ores may be classified into five different types, based on mineral assemblages that contain hausmannite and/or braunite as significant minerals. Carbonates occur predominantly in the form of calcite, present in minor to trace proportions. Textures vary from fine to very coarse grained, and high Mn grades (typically >45 wt%Mn), are recorded. Trace elements of significance include Zn, associated with hausmannite, B, associated with massive braunite and a number of trace minerals, and P, typically present in trace quantities of apatite. In terms of ore genesis, mineralogical, geochemical and geological considerations suggest that Mn (and Fe) originated from submarine hydrothermal vents, from which it travelled in hydrothermal plumes, prior to rapid deposition ~2.2 Ga ago. Diagenesis followed soon after deposition, through redox reactions involving organic matter and higher oxides of Mn to produce the braunite-carbonate assemblage primarily observed in LA ores. The carbonate:oxide ratio and nature of the carbonates varied slightly depending on fluctuations in organic matter flux to the sediment, as well as marine bicarbonate concentrations. Metamorphism, in relation to diagenesis and metasomatism, is poorly understood, but is perceived to have resulted in serpentine formation, as observed in LA and PA ores.
- Full Text:
- Authors: Chetty, Deshenthree
- Date: 2010-04-19T07:55:36Z
- Subjects: Geology , Manganese ores , Kuruman (South Africa)
- Type: Thesis
- Identifier: uj:6794 , http://hdl.handle.net/10210/3223
- Description: D. Phil. , The Kalahari Manganese Deposit (KMD) is the largest of five erosional relics of the Hotazel Formation that are located near Kuruman in the Northern Cape Province of South Africa. Manganese ores are exploited from the lowermost of three manganiferous beds that are interbedded with banded iron-formation (BIF) and hematite lutite, that together constitute the Hotazel Formation. Two major ore types have been delineated previously, viz. low grade braunite lutite of the Mamatwan-type, and high grade oxidic ores of the Wessels-type, with the latter spatially restricted to the northern KMD. Genesis of the ores was temporally distinct, with the Mamatwan-type ore considered as a sedimentary-diagenetic precursor to the hydrothermally altered Wessels-type ore. Drill core samples from the Nchwaning-Gloria area of the northern KMD were analysed, with the aim to better characterise ore genesis, with emphasis on ore alteration. A second part of the study aimed at the application of mineralogical and geochemical information to aspects of ore smelting for the production of Mn alloy for use in the steel industry. Methods employed were drill core logging, X-ray diffraction (XRD), petrography, electron probe microanalysis (EPMA), major and trace element (including REE) analysis (employing artificial neural networks for evaluation of elemental trends), and stable isotope (C and O) analysis. Significant effort was invested in method development for quantitative mineralogical modal analysis using Rietveld refinement of XRD data. The study shows that a number of ore types can be differentiated in the northern KMD on the basis of mineral assemblage, grade, texture and geochemical characteristics. The ores are broadly classified into least altered (LA), partially altered (PA) and advanced altered (AA) types. The LA ores are low grade (<40 wt%Mn) Mn lutites, with dolomite-group carbonate a significant component in addition to braunite. Serpentine is a ubiquitous trace mineral, and boron is a characteristic trace element hosted predominantly by braunite in these ores. Ores of the PA type comprise either braunite-hausmannite-calcite or hausmannite-calcite assemblages, are fine to coarse grained, and display intermediate Mn grades (40-45 wt%Mn). They exhibit a transitional trace element signature. Advanced altered ores may be classified into five different types, based on mineral assemblages that contain hausmannite and/or braunite as significant minerals. Carbonates occur predominantly in the form of calcite, present in minor to trace proportions. Textures vary from fine to very coarse grained, and high Mn grades (typically >45 wt%Mn), are recorded. Trace elements of significance include Zn, associated with hausmannite, B, associated with massive braunite and a number of trace minerals, and P, typically present in trace quantities of apatite. In terms of ore genesis, mineralogical, geochemical and geological considerations suggest that Mn (and Fe) originated from submarine hydrothermal vents, from which it travelled in hydrothermal plumes, prior to rapid deposition ~2.2 Ga ago. Diagenesis followed soon after deposition, through redox reactions involving organic matter and higher oxides of Mn to produce the braunite-carbonate assemblage primarily observed in LA ores. The carbonate:oxide ratio and nature of the carbonates varied slightly depending on fluctuations in organic matter flux to the sediment, as well as marine bicarbonate concentrations. Metamorphism, in relation to diagenesis and metasomatism, is poorly understood, but is perceived to have resulted in serpentine formation, as observed in LA and PA ores.
- Full Text:
Basin analysis of the Mesoproterozoic Bushmanland group of the Namaqua Metamorphic Province, South Africa
- Authors: McClung, Craig Randall
- Date: 2008-06-12T05:35:38Z
- Subjects: Geology , Geochemistry , Namaqualand (South Africa)
- Type: Thesis
- Identifier: uj:2666 , http://hdl.handle.net/10210/610
- Description: The Mesoproterozoic Bushmanland Subprovince of northwestern South Africa forms the western continuation of the transcontinental Namaqua-Natal Metamorphic Province, a crustal domain affected by the 1020-1220 Ma Namaquan Orogeny. Cross-cut by several large faults, the Bushmanland Subprovince can be subdivided into a southern Garies Terrain and northern Aggeneys Terrain. The supracrustal rocks of the Aggeneys Terrain (i.e. Bushmanland Group), comprise a thin (<1 km thick) metavolcano-sedimentary succession composed of a very consistent, shallow marine duplex of sandstone-shale to chemogenic metasedimentary and metavolcanic rocks that have undergone multiple phases of deformation and metamorphism. Since the discovery of the Broken Hill-type (BHT) mineralization in the Aggeneys-Gamsberg district (~440 Mt, 5.2% Cu+Zn+Pb) in the early 1970’s, controversy has persisted regarding the stratigraphy of the Bushmanland Group, its lateral correlation throughout the Aggeneys Terrain, environment and age of deposition, as well as classification and origin of its base-metal sulfide ± barite deposits. For these reasons, the present study primarily focuses on two aims, namely: (1) regionally based comprehensive lithostratigraphic, geochemical and geochronologic analysis of the Bushmanland Group to be used in the construction of a basin model; and (2) petrographic and geochemical analyses of Fe-Mn-rich rocks and barites to determine if they are related to base-metal mineralization and if so, to what extent. New lithostratigraphic data for the Bushmanland Group indicate that it can be subdivided into two subgroups and thirteen formations that are directly correlatable throughout the terrain as well as similar supracrustal successions in neighboring portions of the Namaqua Metamorphic Province. The base of the Bushmanland Group (Wortel Subgroup) comprises a thin (250-350 m thick) sequence of interbedded upward-coarsening psammo-pelitic schists and mature quartzite (i.e. meta-orthoquartzites) of the Namies Schist Fm., Pella Quartzite Fm., Bloemhoek Fm. and laterally equivalent Kangnas Fm. In contrast, the metasedimentary rocks of the unconformably overlying Kouboom Subgroup can be separated into facies terrains divided by the Pofadder-Tantalite Valley Shear Zone (PTV Shear Zone). West of the PTV Shear Zone the Kouboom Subgroup is characterized by a thin (205-225 m thick) succession of interbedded mature quartzites and pelitic schists. East of PTV Shear Zone the Kouboom Subgroup encompasses a thick (~1250 m thick) succession of calc-silicate rocks hosted by biotite to calc-silicate-rich schists and metagreywackes. The Koeris Fm., a variably thick (0-650 m) succession of psammitic schists, metaconglomerates and ortho-amphibolites unconformably overlies the Kouboom Subgroup. Geochemical provenance and detrital zircon core populations of the Wortel Subgroup suggest the metasedimentary rocks were derived from the Paleoproterozoic continental island arc rocks of the Vioolsdrift Intrusive Suite and Gladkop Suite, as well as an unidentified sedimentary/metasedimentary succession. Deposition took place in a passive continental margin environment between 1140 to 1650 Ma. In contrast, the unconformably overlying Kouboom Subgroup is characterized by larger plutonic derived zircons of the basement rocks to the Orange River Group, suggesting deposition in a tectonically active environment marked by repeated periods of tectonic uplift. In addition, new age constraints reveal that deposition in the upper part of the Kouboom Subgroup (possibly upper part of the Gams Fm.) was synchronous with emplacement of the Little Namaqualand Suite (~1190 Ma) into the lower portions, i.e. Wortel Subgroup, of the Bushmanland Group. The geochemical attributes and detrital zircon populations of metagreywackes from the Driekop Fm. suggest they were eroded from the newly exposed, i.e. fresh to poorly weathered, intrusions of the Little Namaqualand Suite, indicating a renewed period of tectonic uplift. Lastly, unlike the other lithologic units of the Bushmanland Group, the Koeris Fm. exhibits four detrital zircon age populations at 1125-1325, 1605-1695, 1730-1910 and 1935-2075 Ma. The older sub-populations indicate sediment derivation from various units of the Richtersveld Subprovince and Steinkopf Domain, while the younger sub-populations suggest derivation from various units in the Rehoboth Inlier of Namibia and the Gordonia Terrain to the east. The provenance signature of the younger subpopulation implies that deposition of the Koeris Fm. occurred after continental collision between the Rehoboth Inlier-Kaapvaal Craton and the Namaqua Metamorphic Province. With regards to the base-metal deposits of the Aggeneys-Gamsberg district, petrographic and geochemical analysis of the Bushmanland Group Fe-Mn-rich rocks suggests that they can be subdivided into several types: (1) primary Fe-Mn-rich metasedimentary rocks; (2) magnetite-amphibole-rich Fe-Mn-rich rocks; (3) coticules; and (4) epigenetic Fe-Mn-rich rocks. Primary Fe-Mn-rich metasedimentary rocks occur throughout the western and central portions of the study area and appear to have been formed through the deposition of Fe-Mn-rich hydrogenous precipitates in areas of localized sediment starvation. However, as illustrated by the primary Fe-Mn-rich metasedimentary rocks of the Lemoenpoort prospect, a syn-diagenetic, hot (>250°C), metalliferous hydrothermal fluids infiltrated and altered these hydrogenous Fe-Mnrich metasedimentary rocks, resulting in the deposition of base-metal sulfides, formation of magnetite-amphibolite-rich Fe-Mn-rich rocks, as well as hydrothermal alteration of the siliciclastic wall rocks to form coticules. The spatial restriction of epigenetic Fe-Mn-rich rocks to shear zones, high Fe2O3 T (ca. 65 wt %), low ΣREE (ca. 13 ppm), presence of recrystallized quartz crystals, elevated concentration of Cu in some occurrences and general similarities with some hydrothermal iron/iron-oxide copper-gold (IOCG) deposits, suggests that the epigenetic Fe-Mn-rich rocks may have formed during prograde metamorphism. Low concentrations of SrO (0.5 ± 0.2 wt %), highly radiogenic Sr/ Sr ratios (0.7164 ± 0.0028), elevated δ S (27.3 ± 4.9 ‰) and δ O (7.7 ± 3.1 ‰) values in the barites, as compared to contemporaneous Mesoproterozoic seawater, suggests precipitation of stratiform and stratabound barite layers in the Bushmanland Group occurred through mixing of an evolved continental crustal source and contemporaneous seawater sulfate, 87 86 34 18 modified by bacterial sulfate reduction. Most importantly, δ O values suggest possible minimum temperatures of formation ranging from 18 <150°C for the Gamsberg deposit to >250°C for occurrences in the Aggeneys area. These obvious differences in temperature of formation are in good agreement with the Cu-rich, Ba-poor nature of the sulfide mineralization characteristic of the Aggeneys deposits versus the Cu-poor, Ba-rich character of the Gamsberg deposit. In conjunction with this, the isotopic and petrographic arguments favor a sub-seafloor replacement model for the stratabound barite occurrences of the Aggeneys deposits, while at Gamsberg, deposition at the sediment-water interface as a true sedimentary exhalite appears more acceptable. Data obtained in the present study, combined with the results of previous investigations can be used to develop a comprehensive model for the geological evolution of the Aggeneys Terrain and Namaqua Metamorphic Province. The tectono-sedimentary evolution of the Aggeneys Terrain and Namaqua Metamorphic Province is marked by two important tectonic events separated by an episode of tectonic quiescence. Extrusion and deposition of the metavolcano-sedimentary rocks of the Orange River Group at 1908 Ma marks the start of the Orange River Orogeny. vii Prior to emplacement of the Vioolsdrift Intrusive Suite, the Orange River Group appears to have undergone a period of folding and low-grade metamorphism [D1/M1] that was subsequently followed by emplacement of the Main Phase Vioolsdrift Intrusive Suite roughly dated at 1890 Ma. Rapidly following emplacement of these intrusions, the lower crustal rocks of the Richtersveld Subprovince underwent a second, higher, amphibolite-facies metamorphic event [M1B] from 1870-1840 Ma. This event may have resulted in lower crustal melting and emplacement of the Gladkop Suite into an unknown package of metasediments or metasedimentary rocks south of the present day Orange River at roughly 1820 Ma. The Gladkop Suite was subsequently subjected to high-grade metamorphism at 1800 Ma. The Orange River Orogeny was terminated by emplacement of the Late Phase Vioolsdrift Intrusive Suite at approximately 1765 Ma and later northward-directed thrusting. Following termination of the Orange River Orogeny, deposition of the Bushmanland Group began in a tectonically stable environment marked by punctuated periods of tectonic activity that lasted until emplacement of the Little Namaqualand Suite at 1190 Ma. The detrital zircon populations of the Pella Quartzite Fm. and Koeris Fm. support (a) regional correlation of these stratigraphic units throughout the study area, (b) confirms sediment derivation from various local source terrains and (c) suggests a maximum depositional age of 1650 Ma. Furthermore, new age constraints reveal initiation of the O’okiepian Episode (Namaquan Orogeny), characterized by regional-scale mid- to high-grade contact metamorphism, was synchronous with emplacement of the Little Namaqualand Suite and deposition of the upper Kouboom Subgroup. Furthermore, the detrital zircon populations for the Driekop Fm. (upper Kouboom Subgroup) contain a large population of 1190 Ma (i.e. O’okiepian-age) detrital cores, suggesting a renewed period of tectonic uplift. Analogously, age constraints for the Koeris Fm. indicate a maximum depositional age of 1130 Ma, as well as derivation from a number of local and exotic source terrains indicating that deposition of the Koeris Fm. must have occurred in response to continental collision between the Rehoboth Inlier-Kaapvaal Craton and the Namaqua Metamorphic Province. Furthermore, these new age constraints also constrain the timing of D2-D3 deformation to between 1130-1080 Ma and regional peak metamorphism to 1020- 1040 Ma. , Prof. N.J. Beukes Prof. J. Gutzmer
- Full Text:
- Authors: McClung, Craig Randall
- Date: 2008-06-12T05:35:38Z
- Subjects: Geology , Geochemistry , Namaqualand (South Africa)
- Type: Thesis
- Identifier: uj:2666 , http://hdl.handle.net/10210/610
- Description: The Mesoproterozoic Bushmanland Subprovince of northwestern South Africa forms the western continuation of the transcontinental Namaqua-Natal Metamorphic Province, a crustal domain affected by the 1020-1220 Ma Namaquan Orogeny. Cross-cut by several large faults, the Bushmanland Subprovince can be subdivided into a southern Garies Terrain and northern Aggeneys Terrain. The supracrustal rocks of the Aggeneys Terrain (i.e. Bushmanland Group), comprise a thin (<1 km thick) metavolcano-sedimentary succession composed of a very consistent, shallow marine duplex of sandstone-shale to chemogenic metasedimentary and metavolcanic rocks that have undergone multiple phases of deformation and metamorphism. Since the discovery of the Broken Hill-type (BHT) mineralization in the Aggeneys-Gamsberg district (~440 Mt, 5.2% Cu+Zn+Pb) in the early 1970’s, controversy has persisted regarding the stratigraphy of the Bushmanland Group, its lateral correlation throughout the Aggeneys Terrain, environment and age of deposition, as well as classification and origin of its base-metal sulfide ± barite deposits. For these reasons, the present study primarily focuses on two aims, namely: (1) regionally based comprehensive lithostratigraphic, geochemical and geochronologic analysis of the Bushmanland Group to be used in the construction of a basin model; and (2) petrographic and geochemical analyses of Fe-Mn-rich rocks and barites to determine if they are related to base-metal mineralization and if so, to what extent. New lithostratigraphic data for the Bushmanland Group indicate that it can be subdivided into two subgroups and thirteen formations that are directly correlatable throughout the terrain as well as similar supracrustal successions in neighboring portions of the Namaqua Metamorphic Province. The base of the Bushmanland Group (Wortel Subgroup) comprises a thin (250-350 m thick) sequence of interbedded upward-coarsening psammo-pelitic schists and mature quartzite (i.e. meta-orthoquartzites) of the Namies Schist Fm., Pella Quartzite Fm., Bloemhoek Fm. and laterally equivalent Kangnas Fm. In contrast, the metasedimentary rocks of the unconformably overlying Kouboom Subgroup can be separated into facies terrains divided by the Pofadder-Tantalite Valley Shear Zone (PTV Shear Zone). West of the PTV Shear Zone the Kouboom Subgroup is characterized by a thin (205-225 m thick) succession of interbedded mature quartzites and pelitic schists. East of PTV Shear Zone the Kouboom Subgroup encompasses a thick (~1250 m thick) succession of calc-silicate rocks hosted by biotite to calc-silicate-rich schists and metagreywackes. The Koeris Fm., a variably thick (0-650 m) succession of psammitic schists, metaconglomerates and ortho-amphibolites unconformably overlies the Kouboom Subgroup. Geochemical provenance and detrital zircon core populations of the Wortel Subgroup suggest the metasedimentary rocks were derived from the Paleoproterozoic continental island arc rocks of the Vioolsdrift Intrusive Suite and Gladkop Suite, as well as an unidentified sedimentary/metasedimentary succession. Deposition took place in a passive continental margin environment between 1140 to 1650 Ma. In contrast, the unconformably overlying Kouboom Subgroup is characterized by larger plutonic derived zircons of the basement rocks to the Orange River Group, suggesting deposition in a tectonically active environment marked by repeated periods of tectonic uplift. In addition, new age constraints reveal that deposition in the upper part of the Kouboom Subgroup (possibly upper part of the Gams Fm.) was synchronous with emplacement of the Little Namaqualand Suite (~1190 Ma) into the lower portions, i.e. Wortel Subgroup, of the Bushmanland Group. The geochemical attributes and detrital zircon populations of metagreywackes from the Driekop Fm. suggest they were eroded from the newly exposed, i.e. fresh to poorly weathered, intrusions of the Little Namaqualand Suite, indicating a renewed period of tectonic uplift. Lastly, unlike the other lithologic units of the Bushmanland Group, the Koeris Fm. exhibits four detrital zircon age populations at 1125-1325, 1605-1695, 1730-1910 and 1935-2075 Ma. The older sub-populations indicate sediment derivation from various units of the Richtersveld Subprovince and Steinkopf Domain, while the younger sub-populations suggest derivation from various units in the Rehoboth Inlier of Namibia and the Gordonia Terrain to the east. The provenance signature of the younger subpopulation implies that deposition of the Koeris Fm. occurred after continental collision between the Rehoboth Inlier-Kaapvaal Craton and the Namaqua Metamorphic Province. With regards to the base-metal deposits of the Aggeneys-Gamsberg district, petrographic and geochemical analysis of the Bushmanland Group Fe-Mn-rich rocks suggests that they can be subdivided into several types: (1) primary Fe-Mn-rich metasedimentary rocks; (2) magnetite-amphibole-rich Fe-Mn-rich rocks; (3) coticules; and (4) epigenetic Fe-Mn-rich rocks. Primary Fe-Mn-rich metasedimentary rocks occur throughout the western and central portions of the study area and appear to have been formed through the deposition of Fe-Mn-rich hydrogenous precipitates in areas of localized sediment starvation. However, as illustrated by the primary Fe-Mn-rich metasedimentary rocks of the Lemoenpoort prospect, a syn-diagenetic, hot (>250°C), metalliferous hydrothermal fluids infiltrated and altered these hydrogenous Fe-Mnrich metasedimentary rocks, resulting in the deposition of base-metal sulfides, formation of magnetite-amphibolite-rich Fe-Mn-rich rocks, as well as hydrothermal alteration of the siliciclastic wall rocks to form coticules. The spatial restriction of epigenetic Fe-Mn-rich rocks to shear zones, high Fe2O3 T (ca. 65 wt %), low ΣREE (ca. 13 ppm), presence of recrystallized quartz crystals, elevated concentration of Cu in some occurrences and general similarities with some hydrothermal iron/iron-oxide copper-gold (IOCG) deposits, suggests that the epigenetic Fe-Mn-rich rocks may have formed during prograde metamorphism. Low concentrations of SrO (0.5 ± 0.2 wt %), highly radiogenic Sr/ Sr ratios (0.7164 ± 0.0028), elevated δ S (27.3 ± 4.9 ‰) and δ O (7.7 ± 3.1 ‰) values in the barites, as compared to contemporaneous Mesoproterozoic seawater, suggests precipitation of stratiform and stratabound barite layers in the Bushmanland Group occurred through mixing of an evolved continental crustal source and contemporaneous seawater sulfate, 87 86 34 18 modified by bacterial sulfate reduction. Most importantly, δ O values suggest possible minimum temperatures of formation ranging from 18 <150°C for the Gamsberg deposit to >250°C for occurrences in the Aggeneys area. These obvious differences in temperature of formation are in good agreement with the Cu-rich, Ba-poor nature of the sulfide mineralization characteristic of the Aggeneys deposits versus the Cu-poor, Ba-rich character of the Gamsberg deposit. In conjunction with this, the isotopic and petrographic arguments favor a sub-seafloor replacement model for the stratabound barite occurrences of the Aggeneys deposits, while at Gamsberg, deposition at the sediment-water interface as a true sedimentary exhalite appears more acceptable. Data obtained in the present study, combined with the results of previous investigations can be used to develop a comprehensive model for the geological evolution of the Aggeneys Terrain and Namaqua Metamorphic Province. The tectono-sedimentary evolution of the Aggeneys Terrain and Namaqua Metamorphic Province is marked by two important tectonic events separated by an episode of tectonic quiescence. Extrusion and deposition of the metavolcano-sedimentary rocks of the Orange River Group at 1908 Ma marks the start of the Orange River Orogeny. vii Prior to emplacement of the Vioolsdrift Intrusive Suite, the Orange River Group appears to have undergone a period of folding and low-grade metamorphism [D1/M1] that was subsequently followed by emplacement of the Main Phase Vioolsdrift Intrusive Suite roughly dated at 1890 Ma. Rapidly following emplacement of these intrusions, the lower crustal rocks of the Richtersveld Subprovince underwent a second, higher, amphibolite-facies metamorphic event [M1B] from 1870-1840 Ma. This event may have resulted in lower crustal melting and emplacement of the Gladkop Suite into an unknown package of metasediments or metasedimentary rocks south of the present day Orange River at roughly 1820 Ma. The Gladkop Suite was subsequently subjected to high-grade metamorphism at 1800 Ma. The Orange River Orogeny was terminated by emplacement of the Late Phase Vioolsdrift Intrusive Suite at approximately 1765 Ma and later northward-directed thrusting. Following termination of the Orange River Orogeny, deposition of the Bushmanland Group began in a tectonically stable environment marked by punctuated periods of tectonic activity that lasted until emplacement of the Little Namaqualand Suite at 1190 Ma. The detrital zircon populations of the Pella Quartzite Fm. and Koeris Fm. support (a) regional correlation of these stratigraphic units throughout the study area, (b) confirms sediment derivation from various local source terrains and (c) suggests a maximum depositional age of 1650 Ma. Furthermore, new age constraints reveal initiation of the O’okiepian Episode (Namaquan Orogeny), characterized by regional-scale mid- to high-grade contact metamorphism, was synchronous with emplacement of the Little Namaqualand Suite and deposition of the upper Kouboom Subgroup. Furthermore, the detrital zircon populations for the Driekop Fm. (upper Kouboom Subgroup) contain a large population of 1190 Ma (i.e. O’okiepian-age) detrital cores, suggesting a renewed period of tectonic uplift. Analogously, age constraints for the Koeris Fm. indicate a maximum depositional age of 1130 Ma, as well as derivation from a number of local and exotic source terrains indicating that deposition of the Koeris Fm. must have occurred in response to continental collision between the Rehoboth Inlier-Kaapvaal Craton and the Namaqua Metamorphic Province. Furthermore, these new age constraints also constrain the timing of D2-D3 deformation to between 1130-1080 Ma and regional peak metamorphism to 1020- 1040 Ma. , Prof. N.J. Beukes Prof. J. Gutzmer
- Full Text:
Characterisation of the lowermost manganese ore bed of the Hotazel Formation, Gloria Mine, Northern Cape Province
- Authors: Van Staden, Anelda
- Date: 2009-01-29T12:09:24Z
- Subjects: Geology , Manganese ores , Northern Cape (South Africa)
- Type: Thesis
- Identifier: uj:14853 , http://hdl.handle.net/10210/1975
- Description: 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.
- Full Text:
- Authors: Van Staden, Anelda
- Date: 2009-01-29T12:09:24Z
- Subjects: Geology , Manganese ores , Northern Cape (South Africa)
- Type: Thesis
- Identifier: uj:14853 , http://hdl.handle.net/10210/1975
- Description: 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.
- Full Text:
Die geologie en struktuur van die gebiede Levubu en Bandelierkop in Noord-Transvaal
- Authors: Du Toit, Mattheus Casparus
- Date: 2015-11-05
- Subjects: Geology , Stratigraphy , Lithology
- Type: Thesis
- Identifier: uj:14521 , http://hdl.handle.net/10210/15044
- Description: PhD. (Geology) , The lithology, stratigraphy, metamorphism and structure of the rocks in a highly deformed and metamorphosed terrain, some 5 000 km 2 in extent, south of the Soutpansberg in the Northern Transvaal, are described. The Bandelierkop Formation, which is comprised of Ultramafic-, Mafic- and Pelitic gneisses occur as deformed and metamorphosed remnants in tonalitic grey granitoids known as the Baviaanskloof Gneiss. The Ultramafic- and Mafic gneisses of the Bandelierkop Formation, in which granulite grade mineral assemblages exist, are chemically equivalent to peridotitic and basaltic komatiites and basaltic tholeiites of Archaean greenstone terrains. The greenstone origin for the gneisses is also indicated by the Hout River traverse in which material, at the lower to middle amphibolite facies, becomes progressively metamorphosed and deformed over a distance of 10 km to the granulite grade of metamorphism. The Pelitic gneiss of the Bandelierkop. Formation is chemically similar to greywackes and shales of the Fig Tree Group and Belvue Road Formations of the Swaziland sequence. The area of investigation is divided into two high-grade metamorphic zones separated by an eastnortheast trending Orthopyroxene isograd. The rocks of the Orthopyroxene zone to the north of the isograd were subjected to two events of regional metamorphism (M 1 and M2 ). The area south of the isograd, known as the Orthoamphibole zone, is characterised by the presence of silverygrey anthophyllite blades in Pelitic gneiss which formed during the M3 event. The southern limit of the Orthoamphibole zone, in the south-eastern portion of the area is poorly exposed and thus less well defined.
- Full Text:
- Authors: Du Toit, Mattheus Casparus
- Date: 2015-11-05
- Subjects: Geology , Stratigraphy , Lithology
- Type: Thesis
- Identifier: uj:14521 , http://hdl.handle.net/10210/15044
- Description: PhD. (Geology) , The lithology, stratigraphy, metamorphism and structure of the rocks in a highly deformed and metamorphosed terrain, some 5 000 km 2 in extent, south of the Soutpansberg in the Northern Transvaal, are described. The Bandelierkop Formation, which is comprised of Ultramafic-, Mafic- and Pelitic gneisses occur as deformed and metamorphosed remnants in tonalitic grey granitoids known as the Baviaanskloof Gneiss. The Ultramafic- and Mafic gneisses of the Bandelierkop Formation, in which granulite grade mineral assemblages exist, are chemically equivalent to peridotitic and basaltic komatiites and basaltic tholeiites of Archaean greenstone terrains. The greenstone origin for the gneisses is also indicated by the Hout River traverse in which material, at the lower to middle amphibolite facies, becomes progressively metamorphosed and deformed over a distance of 10 km to the granulite grade of metamorphism. The Pelitic gneiss of the Bandelierkop. Formation is chemically similar to greywackes and shales of the Fig Tree Group and Belvue Road Formations of the Swaziland sequence. The area of investigation is divided into two high-grade metamorphic zones separated by an eastnortheast trending Orthopyroxene isograd. The rocks of the Orthopyroxene zone to the north of the isograd were subjected to two events of regional metamorphism (M 1 and M2 ). The area south of the isograd, known as the Orthoamphibole zone, is characterised by the presence of silverygrey anthophyllite blades in Pelitic gneiss which formed during the M3 event. The southern limit of the Orthoamphibole zone, in the south-eastern portion of the area is poorly exposed and thus less well defined.
- Full Text:
Fluids in metapelitic granulites and Bulai granitoids of the Messina area, central zone of the Limpopo Belt, South Africa
- Authors: Flattery, Yvonne
- Date: 2009-01-28T09:39:06Z
- Subjects: Fluid inclusions , Granulite , Geology , Limpopo Belt (South Africa)
- Type: Thesis
- Identifier: http://ujcontent.uj.ac.za8080/10210/390367 , uj:14835 , http://hdl.handle.net/10210/1959
- Description: M.Sc. , A fluid inclusion study was performed on the following rock types: ● Metapelitic granulites that occur as xenoliths in the Bulai Pluton. ● Metapelitic granulites that occur around the Bulai Pluton. ● Granite from the Bulai Pluton. These rocks outcrop on the farm Boston near Messina in the so called Three Sisters area. The main aims of this study are the following: ● Which fluids are associated with granulite metamorphism? ● Do the fluid inclusions record more than one metamorphic event, if so, what are the P-T conditions of this/these event(s)? ● How do the fluids compare to fluids in the Southern Marginal Zone in terms of composition and density? The metapelites are typically characterised by a peak metamorphic mineral assemblages of (1) quartz, K-feldspar, plagioclase, garnet, biotite, cordierite and sillimanite and (2) quartz, K-feldspar, plagioclase, garnet, orthopyroxene and biotite. The first assemblage have been used by other workers (Van Reenen et al., in prep.) to derive a P-T path for the metapelitic xenoliths and host rock, which is characterised by decompression-cooling. This assemblage also shows typical high temperature metasomatic formation of feldspar around quartz that is in contact with quartz. The peak metamorphic conditions were estimated to be ~850°C and ~7.5 kbar. Fluid inclusions were studied in garnet, quartz inclusions in garnet, and matrix quartz. The following principle fluid types were identified: ● High salinity aqueous fluids. ● CO2-rich (±CH4) carbonic fluids. ii Petrographic evidence indicates that both fluids were present at peak metamorphic conditions under conditions of fluid-fluid immiscibility. The high-salinity aqueous fluid is most likely responsible for the high temperature metasomatic textures. The density of the fluids trapped at peak metamorphic conditions have been reset to lower values at pressures below that of the peak metamorphic conditions. This is probably the result of the emplacement of the Bulai Pluton at shallow crustal levels (2- 3 kbar). Later fluids are dominated by low-density carbonic fluids with significant amounts of CH4. The CH4 is the result of retrograde hydration reactions at relatively low oxygen fugacities.
- Full Text:
- Authors: Flattery, Yvonne
- Date: 2009-01-28T09:39:06Z
- Subjects: Fluid inclusions , Granulite , Geology , Limpopo Belt (South Africa)
- Type: Thesis
- Identifier: http://ujcontent.uj.ac.za8080/10210/390367 , uj:14835 , http://hdl.handle.net/10210/1959
- Description: M.Sc. , A fluid inclusion study was performed on the following rock types: ● Metapelitic granulites that occur as xenoliths in the Bulai Pluton. ● Metapelitic granulites that occur around the Bulai Pluton. ● Granite from the Bulai Pluton. These rocks outcrop on the farm Boston near Messina in the so called Three Sisters area. The main aims of this study are the following: ● Which fluids are associated with granulite metamorphism? ● Do the fluid inclusions record more than one metamorphic event, if so, what are the P-T conditions of this/these event(s)? ● How do the fluids compare to fluids in the Southern Marginal Zone in terms of composition and density? The metapelites are typically characterised by a peak metamorphic mineral assemblages of (1) quartz, K-feldspar, plagioclase, garnet, biotite, cordierite and sillimanite and (2) quartz, K-feldspar, plagioclase, garnet, orthopyroxene and biotite. The first assemblage have been used by other workers (Van Reenen et al., in prep.) to derive a P-T path for the metapelitic xenoliths and host rock, which is characterised by decompression-cooling. This assemblage also shows typical high temperature metasomatic formation of feldspar around quartz that is in contact with quartz. The peak metamorphic conditions were estimated to be ~850°C and ~7.5 kbar. Fluid inclusions were studied in garnet, quartz inclusions in garnet, and matrix quartz. The following principle fluid types were identified: ● High salinity aqueous fluids. ● CO2-rich (±CH4) carbonic fluids. ii Petrographic evidence indicates that both fluids were present at peak metamorphic conditions under conditions of fluid-fluid immiscibility. The high-salinity aqueous fluid is most likely responsible for the high temperature metasomatic textures. The density of the fluids trapped at peak metamorphic conditions have been reset to lower values at pressures below that of the peak metamorphic conditions. This is probably the result of the emplacement of the Bulai Pluton at shallow crustal levels (2- 3 kbar). Later fluids are dominated by low-density carbonic fluids with significant amounts of CH4. The CH4 is the result of retrograde hydration reactions at relatively low oxygen fugacities.
- Full Text:
Formation of major fold types during distinct geological events in the central zone of the Limpopo Belt, South Africa: new structural, metamorphic and geochronologic
- Authors: Boshoff, Rene
- Date: 2009-01-27T07:18:07Z
- Subjects: Geology , Structural geology , Metamorphism (Geology) , Folds (Geology) , Geological time , Limpopo Belt (South Africa)
- Type: Thesis
- Identifier: uj:14827 , http://hdl.handle.net/10210/1951
- Description: M.Sc. , The Limpopo Complex (LC) of southern Africa is one of the best-studied Precambrian granulite facies terrains in the world, yet workers still disagree on fundamental aspects of the geological evolution of this complexly deformed high-grade terrain. Most workers agree that the two marginal zones were exhumed in the late-Archaean, but disagree on the timing of major tectono-metamorphic events that affected the Central Zone (CZ) of Limpopo Belt, and the mechanism/s of its formation. There are currently two main schools of thought: The first school regards the LC as a late-Archaean orogenic zone that resulted from a north-south collision of the Zimbabwe and Kaapvaal cratons. Granitic plutons throughout the entire LC are considered to be accurate time-markers for this orogeny. The second school suggests that the CZ evolved as a result of a major Paleoproterozoic tectono-metamorphic event based mainly on the interpretation of metamorphic mineral ages. The present study focuses on two aims, namely (i) to provide a synthesis of published data as a basis to understand the ongoing age controversy concerning the evolution of the CZ, and (ii) to show that specific fold types in the CZ can be related to either the late-Archaean or the Paleoproterozoic event. New age, structural, metamorphic, and petrographic data are presented to show that (i) major sheath folds reflect the peak tectono-metamorphic event that affected the CZ in the late-Archaean, while (ii) major cross folds developed as a result of a transpressive event in the Paleoproterozoic. The age of formation of the Avoca sheath fold located about 40 km west of Alldays is accurately constrained by the age of emplacement of different structural varieties of precursors to the Singelele Gneiss: penetratively deformed syn- to late-tectonic Singelele gneisses with a zircon SHRIMP age of 2651 ± 8 Ma, date the time of formation of the sheath fold that is characterized by a single population of linear elements that define the central fold axis. The Avoca sheath fold documents top-to-the-NNE movement of material during the exhumation of the high-grade CZ rocks. Weakly foliated late-tectonic L-tectonites with a zircon SHRIMP age of 2626.8 ± 5.4 Ma, outcrop near the centre of the sheath fold, and provide a minimum age for the shear deformation event. An almost undeformed (post-tectonic) variety of the Singelele Gneiss was emplaced after the shear event. A detailed metamorphic study of metapelitic gneisses from the large Baklykraal cross fold, located about 20 km east of the Avoca sheath fold, documents a single decompression-cooling (DC) P-T path for the evolution of this structure. Three studied metapelitic samples characterized by a single generation of garnet provide a Pb-Pb age of 2023 ± 11 Ma, that accurately constrain the time of formation of this major fold to the Paleoproterozoic. A metapelitic sample characterized by two generations of garnet provide a slightly older Pb-Pb age of 2173 ± 79 Ma, that is interpreted to also reflect the late-Archaean event. The Baklykraal cross fold is characterized by two populations of linear elements: the one population defines the shallow N-S oriented fold axes, while the second population is associated with top-to-the-NNE movement of material during exhumation, resulting in folds with a nappe-like geometry. A DC P-T path for the Campbell cross fold (Van Kal, 2004) located just west of Musina, suggests that cross folds developed under significantly lower P-T conditions than is the case with sheath folds, providing an explanation for the lack of significant anatexis associated with the Paleoproterozoic event. The late-Archaean orogeny in contrast, was accompanied by widespread anatexis during a major magmatic event that is characterized by an abnormal high radiogenic signature. This study, for the first time, provides evidence that link specific fold types, and thus deformational events, to different tectono-metamorphic events. The main conclusion is that the CZ was exhumed as the result of two distinct orogenies, one in the late-Archaean, and the other in the Paleoproterozoic.
- Full Text:
- Authors: Boshoff, Rene
- Date: 2009-01-27T07:18:07Z
- Subjects: Geology , Structural geology , Metamorphism (Geology) , Folds (Geology) , Geological time , Limpopo Belt (South Africa)
- Type: Thesis
- Identifier: uj:14827 , http://hdl.handle.net/10210/1951
- Description: M.Sc. , The Limpopo Complex (LC) of southern Africa is one of the best-studied Precambrian granulite facies terrains in the world, yet workers still disagree on fundamental aspects of the geological evolution of this complexly deformed high-grade terrain. Most workers agree that the two marginal zones were exhumed in the late-Archaean, but disagree on the timing of major tectono-metamorphic events that affected the Central Zone (CZ) of Limpopo Belt, and the mechanism/s of its formation. There are currently two main schools of thought: The first school regards the LC as a late-Archaean orogenic zone that resulted from a north-south collision of the Zimbabwe and Kaapvaal cratons. Granitic plutons throughout the entire LC are considered to be accurate time-markers for this orogeny. The second school suggests that the CZ evolved as a result of a major Paleoproterozoic tectono-metamorphic event based mainly on the interpretation of metamorphic mineral ages. The present study focuses on two aims, namely (i) to provide a synthesis of published data as a basis to understand the ongoing age controversy concerning the evolution of the CZ, and (ii) to show that specific fold types in the CZ can be related to either the late-Archaean or the Paleoproterozoic event. New age, structural, metamorphic, and petrographic data are presented to show that (i) major sheath folds reflect the peak tectono-metamorphic event that affected the CZ in the late-Archaean, while (ii) major cross folds developed as a result of a transpressive event in the Paleoproterozoic. The age of formation of the Avoca sheath fold located about 40 km west of Alldays is accurately constrained by the age of emplacement of different structural varieties of precursors to the Singelele Gneiss: penetratively deformed syn- to late-tectonic Singelele gneisses with a zircon SHRIMP age of 2651 ± 8 Ma, date the time of formation of the sheath fold that is characterized by a single population of linear elements that define the central fold axis. The Avoca sheath fold documents top-to-the-NNE movement of material during the exhumation of the high-grade CZ rocks. Weakly foliated late-tectonic L-tectonites with a zircon SHRIMP age of 2626.8 ± 5.4 Ma, outcrop near the centre of the sheath fold, and provide a minimum age for the shear deformation event. An almost undeformed (post-tectonic) variety of the Singelele Gneiss was emplaced after the shear event. A detailed metamorphic study of metapelitic gneisses from the large Baklykraal cross fold, located about 20 km east of the Avoca sheath fold, documents a single decompression-cooling (DC) P-T path for the evolution of this structure. Three studied metapelitic samples characterized by a single generation of garnet provide a Pb-Pb age of 2023 ± 11 Ma, that accurately constrain the time of formation of this major fold to the Paleoproterozoic. A metapelitic sample characterized by two generations of garnet provide a slightly older Pb-Pb age of 2173 ± 79 Ma, that is interpreted to also reflect the late-Archaean event. The Baklykraal cross fold is characterized by two populations of linear elements: the one population defines the shallow N-S oriented fold axes, while the second population is associated with top-to-the-NNE movement of material during exhumation, resulting in folds with a nappe-like geometry. A DC P-T path for the Campbell cross fold (Van Kal, 2004) located just west of Musina, suggests that cross folds developed under significantly lower P-T conditions than is the case with sheath folds, providing an explanation for the lack of significant anatexis associated with the Paleoproterozoic event. The late-Archaean orogeny in contrast, was accompanied by widespread anatexis during a major magmatic event that is characterized by an abnormal high radiogenic signature. This study, for the first time, provides evidence that link specific fold types, and thus deformational events, to different tectono-metamorphic events. The main conclusion is that the CZ was exhumed as the result of two distinct orogenies, one in the late-Archaean, and the other in the Paleoproterozoic.
- Full Text:
Genesis and characteristics of the Wolhaarkop breccia and associated manganore iron formation
- Schalkwyk, Gert Abraham Cornelius
- Authors: Schalkwyk, Gert Abraham Cornelius
- Date: 2009-01-28T09:43:23Z
- Subjects: Geology , Manganese ores , Iron ores , Breccia , Postmasburg (South Africa)
- Type: Thesis
- Identifier: uj:14848 , http://hdl.handle.net/10210/1970
- Description: 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.
- Full Text:
- Authors: Schalkwyk, Gert Abraham Cornelius
- Date: 2009-01-28T09:43:23Z
- Subjects: Geology , Manganese ores , Iron ores , Breccia , Postmasburg (South Africa)
- Type: Thesis
- Identifier: uj:14848 , http://hdl.handle.net/10210/1970
- Description: 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.
- Full Text:
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.
- Full Text:
- 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.
- Full Text:
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.
- Full Text:
- 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.
- Full Text:
Geology and petrology of the Dabolava Region, West-Central Madagascar, with emphasis on granite-hosted gold mineralization
- Rakotoarimanana, Rindrahasy Harilala
- 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.
- Full Text:
- 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.
- Full Text:
Mesoproterozoic volcanism, metallogenesis and tectonic evolution along the western margin of the Kaapvaal Craton
- Authors: Bailie, Russell Hope
- Date: 2010-06-07T06:52:22Z
- Subjects: Geology , Volcanism , Geochemistry , Structural geology , Kaapvaal Craton (South Africa)
- Type: Thesis
- Identifier: uj:6866 , http://hdl.handle.net/10210/3298
- Description: D.Phil. , The western margin of the Archean Kaapvaal Craton, at its contact with the polydeformed and metamorphosed Proterozoic Namaqua Province, is host to four volcanosedimentary successions of Mesoproterozoic age (1.1-1.3 Ga) that occur in close spatial and temporal association to each other. These are the Areachap Group, the Leerkrans Formation of the Wilgenhoutsdrif Group and the two volcanosedimentary successions that comprise the Koras Group. There has been protracted debate as to the exact nature, origin, age and tectonic evolution of these successions, particularly as they occur immediately adjacent to an important crustal suture. A comprehensive whole rock and isotope geochemical study, complemented by zircon-based geochronology where necessary, was thus carried out to characterize and compare the volcanic rocks associated with these four successions. The results are used to assess the role of the four volcanosedimentary successions during the development of the Mesoproterozoic suture between the Kaapvaal Craton and the Namaqua Province during the ~1.2-1.0 Ga Namaquan Orogeny. The geochemical study of the Areachap Group examined a suite of lithologies from different locations along the ~280km long outcrop belt, with the aim of testing the lateral continuity and integrity of this highly metamorphosed and deformed succession. As the bulk of the samples collected were from diamond drill core intersecting volcanogenic massive sulphide (VMS) Zn-Cu deposits it was only appropriate to extend the investigation to assess the metallogenesis and relation of these deposits to their host rock sequences. This included a survey of the sulphur isotope composition of sulphides and sulphates that comprise the Zn-Cu deposits. Furthermore, the architecture and origin of the world-class Copperton deposit, the largest Zn-Cu deposit of the Areachap Group, was examined. For this purpose, available literature data were collated and complemented by new geochemical and geochronological information. Sm-Nd isotopic systematics and U-Pb zircon ages suggest a coeval origin and close genetic link between the metavolcanic rocks of the Leerkrans Formation of the Wilgenhoutsdrif Group and the Areachap Group. Both successions record the establishment of an eastward-directed subduction zone on the western margin of the Kaapvaal Craton. The Areachap Group represents the highly metamorphosed and deformed remnants of a Mesoproterozoic (ca. 1.30-1.24 Ga) volcanic arc that was accreted onto the western margin of the Kaapvaal Craton at ~1.22-1.20 Ga, during the early stages of the Namaquan Orogeny. The igneous protoliths within the Areachap Group are low- to medium-K tholeiitic to calc-alkaline in composition ranging in composition from basaltic through to rhyolitic. Tholeiitic basalts, represented by volumetrically minor amphibolites within the succession have Sm-Nd isotopic characteristics indicative of derivation from a depleted mantle source as denoted by their positive Nd(t) values. The lithogeochemical results highlight the fact that, despite differences in lithological architecture on a local scale, the Areachap Group exhibits coherent geochemical characteristics along its entire strike length.
- Full Text:
- Authors: Bailie, Russell Hope
- Date: 2010-06-07T06:52:22Z
- Subjects: Geology , Volcanism , Geochemistry , Structural geology , Kaapvaal Craton (South Africa)
- Type: Thesis
- Identifier: uj:6866 , http://hdl.handle.net/10210/3298
- Description: D.Phil. , The western margin of the Archean Kaapvaal Craton, at its contact with the polydeformed and metamorphosed Proterozoic Namaqua Province, is host to four volcanosedimentary successions of Mesoproterozoic age (1.1-1.3 Ga) that occur in close spatial and temporal association to each other. These are the Areachap Group, the Leerkrans Formation of the Wilgenhoutsdrif Group and the two volcanosedimentary successions that comprise the Koras Group. There has been protracted debate as to the exact nature, origin, age and tectonic evolution of these successions, particularly as they occur immediately adjacent to an important crustal suture. A comprehensive whole rock and isotope geochemical study, complemented by zircon-based geochronology where necessary, was thus carried out to characterize and compare the volcanic rocks associated with these four successions. The results are used to assess the role of the four volcanosedimentary successions during the development of the Mesoproterozoic suture between the Kaapvaal Craton and the Namaqua Province during the ~1.2-1.0 Ga Namaquan Orogeny. The geochemical study of the Areachap Group examined a suite of lithologies from different locations along the ~280km long outcrop belt, with the aim of testing the lateral continuity and integrity of this highly metamorphosed and deformed succession. As the bulk of the samples collected were from diamond drill core intersecting volcanogenic massive sulphide (VMS) Zn-Cu deposits it was only appropriate to extend the investigation to assess the metallogenesis and relation of these deposits to their host rock sequences. This included a survey of the sulphur isotope composition of sulphides and sulphates that comprise the Zn-Cu deposits. Furthermore, the architecture and origin of the world-class Copperton deposit, the largest Zn-Cu deposit of the Areachap Group, was examined. For this purpose, available literature data were collated and complemented by new geochemical and geochronological information. Sm-Nd isotopic systematics and U-Pb zircon ages suggest a coeval origin and close genetic link between the metavolcanic rocks of the Leerkrans Formation of the Wilgenhoutsdrif Group and the Areachap Group. Both successions record the establishment of an eastward-directed subduction zone on the western margin of the Kaapvaal Craton. The Areachap Group represents the highly metamorphosed and deformed remnants of a Mesoproterozoic (ca. 1.30-1.24 Ga) volcanic arc that was accreted onto the western margin of the Kaapvaal Craton at ~1.22-1.20 Ga, during the early stages of the Namaquan Orogeny. The igneous protoliths within the Areachap Group are low- to medium-K tholeiitic to calc-alkaline in composition ranging in composition from basaltic through to rhyolitic. Tholeiitic basalts, represented by volumetrically minor amphibolites within the succession have Sm-Nd isotopic characteristics indicative of derivation from a depleted mantle source as denoted by their positive Nd(t) values. The lithogeochemical results highlight the fact that, despite differences in lithological architecture on a local scale, the Areachap Group exhibits coherent geochemical characteristics along its entire strike length.
- Full Text:
Metasedimentary manganese ores of the Serra do Navio deposit, Amapa Province, Brazil
- Authors: Chisonga, Benny Chanda
- Date: 2009-01-27T07:18:17Z
- Subjects: Geology , Manganese ores , Petrology , Mineralogy , Fluid inclusions , Geochemistry , Amapá (Territory) Brazil
- Type: Thesis
- Identifier: uj:14828 , http://hdl.handle.net/10210/1952
- Description: M.Sc. , Please refer to full text to view abstract
- Full Text:
- Authors: Chisonga, Benny Chanda
- Date: 2009-01-27T07:18:17Z
- Subjects: Geology , Manganese ores , Petrology , Mineralogy , Fluid inclusions , Geochemistry , Amapá (Territory) Brazil
- Type: Thesis
- Identifier: uj:14828 , http://hdl.handle.net/10210/1952
- Description: M.Sc. , Please refer to full text to view abstract
- Full Text:
MLA-based mineralogical investigation of PGE mineralisation at Lonmin's Akanani Platinum Group Metal Project, Northern Limb of the Bushveld Complex
- Authors: Van der Merwe, Frits
- Date: 2012-06-07
- Subjects: Mineralogy , Geology , Platinum ores , Lonmin Akanan Platinum Group Metal Project , Bushveld Complex (South Africa)
- Type: Thesis
- Identifier: uj:8717 , http://hdl.handle.net/10210/5069
- Description: M.Sc. , Please refer to full text to view abstract
- Full Text:
- Authors: Van der Merwe, Frits
- Date: 2012-06-07
- Subjects: Mineralogy , Geology , Platinum ores , Lonmin Akanan Platinum Group Metal Project , Bushveld Complex (South Africa)
- Type: Thesis
- Identifier: uj:8717 , http://hdl.handle.net/10210/5069
- Description: M.Sc. , Please refer to full text to view abstract
- Full Text:
Ongeluk volcanism in relation to the Kalahari manganese deposits
- Authors: Schutte, Sabine Silke
- Date: 2011-11-30
- Subjects: Geology , Manganese ores , Volcanism , Northern Cape (South Africa) , Kalahari (South Africa)
- Type: Thesis
- Identifier: uj:1746 , http://hdl.handle.net/10210/4101
- Description: D.Phil. , The Ongeluk Formation is a laterally extensive sequence of ≈2200 Ma tholeiitic basaltic andesites in the upper Griqualand West Sequence of the northern Cape Province. The stratigraphic thickness is about 500 m and the Ongeluk Formation underlies the ore-bearing strata of the Kalahari Manganese Field. The formation comprises massive lavas, pillow lavas and hyaloclastite beds in close association. These rocks were extruded under water in a marginal basin within the continental setting of the Kaapvaal Craton. The Hekpoort Basalt Formation of the Transvaal is magmatically cogenetic with the Ongeluk, having indistinguishable geochemistry and sharing a stratigraphically related hiatus in Cr values. The best age estimate for the two formations is 2193 ± 71 Ma, from Rb-Sr data of two previous workers for Hekpoort samples. The Ongeluk Formation shows a mild "regional" geochemical alteration and a profound "Kalahari" alteration beneath the Kalahari Manganese Field. Geochemical screening was used to reconstruct the magmatic composition from a selected dataset. Three stages in the development of regional alteration are ascribed to sea water-rock interaction at different temperatures, and have distinct geochemical signatures. The pervasive Kalahari alteration is characterised by a purple colouration and the decoupled alteration of alkali and high field strength elements. It is due to the development of major hydrothermal systems close to a volcanic vent which are analogous to modern mid-ocean ridge systems. A multi-system isotopic study showed that most of the isotope systems were modified by sea-floor alteration. The similarity of the 2237 ± 23 Ma Pb-Pb errorchron age with the Rb-Sr Hekpoort age reflects changes in U-Pb ratios with minor changes in Pb isotope ratio. Evidence was found in the Rb-Sr system for a minor disturbance at ≈ 1100 Ma, also reported by previous workers. This event is related to the Namaqua tectogenesis, while no isotopic evidence was found for the enigmatic ≈ 2200 to 1750 Ma Kheis orogeny, regarded as the cause of thrust faulting in the region. A genetic connection between the Ongeluk lava and the Kalahari Manganese deposits was established. The manganese ores contain evidence for both marine and hydrothermal contributions to chemical sedimentation. Negative Ce anomalies characterise an oxygenated sea in which the interaction between global oceanic and continental influences is seen. Heavy rare earth enrichment reflects volcanic hydrothermal exhalations from the Kalahari Ongeluk system. Mass balance calculations show that the entire 9 billion tons of Kalahari Manganese ore could have been derived from the Ongeluk Formation. A new model describing the origin and evolution of the Kalahari Manganese Field places a strong emphasis on the role of the syngenetic hydrothermal exhalation and upgrading.
- Full Text:
- Authors: Schutte, Sabine Silke
- Date: 2011-11-30
- Subjects: Geology , Manganese ores , Volcanism , Northern Cape (South Africa) , Kalahari (South Africa)
- Type: Thesis
- Identifier: uj:1746 , http://hdl.handle.net/10210/4101
- Description: D.Phil. , The Ongeluk Formation is a laterally extensive sequence of ≈2200 Ma tholeiitic basaltic andesites in the upper Griqualand West Sequence of the northern Cape Province. The stratigraphic thickness is about 500 m and the Ongeluk Formation underlies the ore-bearing strata of the Kalahari Manganese Field. The formation comprises massive lavas, pillow lavas and hyaloclastite beds in close association. These rocks were extruded under water in a marginal basin within the continental setting of the Kaapvaal Craton. The Hekpoort Basalt Formation of the Transvaal is magmatically cogenetic with the Ongeluk, having indistinguishable geochemistry and sharing a stratigraphically related hiatus in Cr values. The best age estimate for the two formations is 2193 ± 71 Ma, from Rb-Sr data of two previous workers for Hekpoort samples. The Ongeluk Formation shows a mild "regional" geochemical alteration and a profound "Kalahari" alteration beneath the Kalahari Manganese Field. Geochemical screening was used to reconstruct the magmatic composition from a selected dataset. Three stages in the development of regional alteration are ascribed to sea water-rock interaction at different temperatures, and have distinct geochemical signatures. The pervasive Kalahari alteration is characterised by a purple colouration and the decoupled alteration of alkali and high field strength elements. It is due to the development of major hydrothermal systems close to a volcanic vent which are analogous to modern mid-ocean ridge systems. A multi-system isotopic study showed that most of the isotope systems were modified by sea-floor alteration. The similarity of the 2237 ± 23 Ma Pb-Pb errorchron age with the Rb-Sr Hekpoort age reflects changes in U-Pb ratios with minor changes in Pb isotope ratio. Evidence was found in the Rb-Sr system for a minor disturbance at ≈ 1100 Ma, also reported by previous workers. This event is related to the Namaqua tectogenesis, while no isotopic evidence was found for the enigmatic ≈ 2200 to 1750 Ma Kheis orogeny, regarded as the cause of thrust faulting in the region. A genetic connection between the Ongeluk lava and the Kalahari Manganese deposits was established. The manganese ores contain evidence for both marine and hydrothermal contributions to chemical sedimentation. Negative Ce anomalies characterise an oxygenated sea in which the interaction between global oceanic and continental influences is seen. Heavy rare earth enrichment reflects volcanic hydrothermal exhalations from the Kalahari Ongeluk system. Mass balance calculations show that the entire 9 billion tons of Kalahari Manganese ore could have been derived from the Ongeluk Formation. A new model describing the origin and evolution of the Kalahari Manganese Field places a strong emphasis on the role of the syngenetic hydrothermal exhalation and upgrading.
- Full Text:
Origin of high-grade hematite ores at Thabazimbi Mine, Limpopo Province, South Africa
- Netshiozwi, Simon Thizwilondi
- Authors: Netshiozwi, Simon Thizwilondi
- Date: 2009-01-28T09:42:32Z
- Subjects: Hematite , Sedimentation and deposition , Geology , Thabazimbi ( South Africa)
- Type: Thesis
- Identifier: uj:14842 , http://hdl.handle.net/10210/1965
- Description: M.Sc. , High-grade hematite ores at the Thabazimbi Mine, Limpopo Province, occur as stratabound bodies in the Early Paleoproterozoic Penge Iron Formation of the Transvaal Supergroup. Iron ores occur at three distinct positions in the Penge Iron Formation (i) basal ore bodies located immediately above a thin oxidised shale unit that marks the base of the Penge Iron Formation in the Thabazimbi area and that may be interpreted as a structural contact towards the underlying dolostones of the Malmani Subgroup; (ii) ore bodies developed immediately above a prominent mafic sill in the Penge Iron Formation; (iii) small, lenticular ore bodies developed in the iron-formation without apparent structural control. Ore bodies in all three stratigraphic positions formed on the expense of the Penge Iron Formation protore, they share very similar mineralogical and textural attributes and can be subdivided into three major ore types with respect to their mineralogy and physical characteristics, namely, (a) carbonate-hematite ore; (b) hard hematite ore; (c) supergene modified ore. Further subdivision into subtypes is possible based on textural attributes. The first stage of iron ore formation at the Thabazimbi deposit is marked by oxidation of ferrous minerals (carbonates and grunerite) and their replacement by hematite. Efficient leaching and replacement of chert in the iron-formation to produce high-grade hematite ores characterizes the second stage of alteration. Stable isotope and fluid inclusion evidence point to a hydrothermal origin of the iron ores. Two hydrothermal fluids were identified, namely a highly saline Ca-Mg-rich brine (S = 27 wt% NaClequiv, TH = 160ºC) and a Nadominated fluid of intermediate salinity (S = 10 wt% NaClequiv, TH = 130ºC) that is possibly of meteoric origin. The results obtained in this study are used to propose the following sequence of mineralising events for the Thabazimbi iron ore deposit: (i) Deposition of iron-formation and diagenesis; (ii) contact metamorphic alteration related to the intrusion of the Bushveld igneous complex; (iii) metasomatic oxidation, leaching and residual upgrading that is tentatively linked to structurallycontrolled hydrothermal fluid flow; (iv) supergene modification of existing high-grade ore bodies in post-Gondwana times along the old African land surface.
- Full Text:
- Authors: Netshiozwi, Simon Thizwilondi
- Date: 2009-01-28T09:42:32Z
- Subjects: Hematite , Sedimentation and deposition , Geology , Thabazimbi ( South Africa)
- Type: Thesis
- Identifier: uj:14842 , http://hdl.handle.net/10210/1965
- Description: M.Sc. , High-grade hematite ores at the Thabazimbi Mine, Limpopo Province, occur as stratabound bodies in the Early Paleoproterozoic Penge Iron Formation of the Transvaal Supergroup. Iron ores occur at three distinct positions in the Penge Iron Formation (i) basal ore bodies located immediately above a thin oxidised shale unit that marks the base of the Penge Iron Formation in the Thabazimbi area and that may be interpreted as a structural contact towards the underlying dolostones of the Malmani Subgroup; (ii) ore bodies developed immediately above a prominent mafic sill in the Penge Iron Formation; (iii) small, lenticular ore bodies developed in the iron-formation without apparent structural control. Ore bodies in all three stratigraphic positions formed on the expense of the Penge Iron Formation protore, they share very similar mineralogical and textural attributes and can be subdivided into three major ore types with respect to their mineralogy and physical characteristics, namely, (a) carbonate-hematite ore; (b) hard hematite ore; (c) supergene modified ore. Further subdivision into subtypes is possible based on textural attributes. The first stage of iron ore formation at the Thabazimbi deposit is marked by oxidation of ferrous minerals (carbonates and grunerite) and their replacement by hematite. Efficient leaching and replacement of chert in the iron-formation to produce high-grade hematite ores characterizes the second stage of alteration. Stable isotope and fluid inclusion evidence point to a hydrothermal origin of the iron ores. Two hydrothermal fluids were identified, namely a highly saline Ca-Mg-rich brine (S = 27 wt% NaClequiv, TH = 160ºC) and a Nadominated fluid of intermediate salinity (S = 10 wt% NaClequiv, TH = 130ºC) that is possibly of meteoric origin. The results obtained in this study are used to propose the following sequence of mineralising events for the Thabazimbi iron ore deposit: (i) Deposition of iron-formation and diagenesis; (ii) contact metamorphic alteration related to the intrusion of the Bushveld igneous complex; (iii) metasomatic oxidation, leaching and residual upgrading that is tentatively linked to structurallycontrolled hydrothermal fluid flow; (iv) supergene modification of existing high-grade ore bodies in post-Gondwana times along the old African land surface.
- Full Text:
Paleoproterozoic Mississippi Valley-Type Pb-Zn deposits of the Ghaap Group, Transvaal Supergroup in Griqualand West, South Africa
- Authors: Schaefer, Markus Olaf
- Date: 2009-01-28T09:43:16Z
- Subjects: Geology , Carbonate rocks , Mineralogy , Mineralogical chemistry , Fluid inclusions , Isotope geology , Griqualand West (South Africa)
- Type: Thesis
- Identifier: uj:14846 , http://hdl.handle.net/10210/1969
- Description: D.Phil. , Please refer to full text to view abstract
- Full Text:
- Authors: Schaefer, Markus Olaf
- Date: 2009-01-28T09:43:16Z
- Subjects: Geology , Carbonate rocks , Mineralogy , Mineralogical chemistry , Fluid inclusions , Isotope geology , Griqualand West (South Africa)
- Type: Thesis
- Identifier: uj:14846 , http://hdl.handle.net/10210/1969
- Description: D.Phil. , Please refer to full text to view abstract
- Full Text:
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.
- Full Text:
- 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.
- Full Text:
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.
- Full Text:
- 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.
- Full Text:
Textural and geochemical evidence for a supergene origin of the Paleoproterozoic high-grade BIF-hosted iron ores of the Maremane Dome, Northern Cape Province, South Africa
- Van Deventer, Wikus Frederick
- Authors: Van Deventer, Wikus Frederick
- Date: 2010-05-27T06:07:22Z
- Subjects: Geology , Iron ores , Geochemistry , Northern Cape (South Africa)
- Type: Thesis
- Identifier: uj:6850 , http://hdl.handle.net/10210/3281
- Description: M.Sc. , Biofuels have the potential to reduce a country’s dependence on imported oil, to ensure diversity of energy sources, to increase the availability of renewable energy sources and to address global environmental issues. In recognition of the potential benefits of the production and use of biofuels, the Department of Minerals and Energy released the Draft Biofuels Industrial Strategy in December 2006 with the aim to increase the use of biofuels in South Africa to replace 4.5% of conventional transport fuels by 2013. However, there are several barriers that need to be overcome before South Africa can establish a large-scale biofuel industry to achieve the DME’s biofuel target. This includes environmental barriers, such as the availability of land for the cultivation of biofuel feedstocks and potential threats to food security. This study focuses on these environmental barriers and aims to determine the potential for bioethanol production from maize in South Africa to 2013. To this purpose, a bioethanol potential model is developed to simulate the potential for bioethanol production from maize in South Africa between 2008 and 2013. The model incorporates four key elements that all impact on the availability of maize for bioethanol production, namely: maize demand; maize supply; the demand for maize as biomaterial; and the available land area for the cultivation of maize. The study makes further use of the scenario planning method to determine the potential for bioethanol production from maize in South Africa. Four unique bioethanol potential scenarios are designed and simulated within the bioethanol potential model developed for this purpose. Each scenario plays out a different Abstract storyline for the future social, economic and natural environment that will impact on the availability of maize for bioethanol production. The results of the bioethanol potential scenario simulations show that South Africa will be able to produce enough maize to meet the DME’s biofuel target of 1.2 billion liters of bioethanol for all scenarios between 2009 and 2010. From 2011 onwards, the bioethanol potential decreases below the DME’s target value in both the worst case and rapid change scenarios. The study concludes that the production of bioethanol from maize in South Africa will have various social, economic and environmental consequences for the country’s agricultural sector. The depletion of domestic maize supplies will seriously threaten food security and consequently, increase the country’s dependence on maize imports. This will not only affect the country’s maize producing regions, but spread throughout South Africa as the demand for agriculturally productive land for maize production increases. Domestic food security is therefore at risk and South Africa will have to resort to other energy technologies to achieve a sustainable and renewable energy future for road transport.
- Full Text:
- Authors: Van Deventer, Wikus Frederick
- Date: 2010-05-27T06:07:22Z
- Subjects: Geology , Iron ores , Geochemistry , Northern Cape (South Africa)
- Type: Thesis
- Identifier: uj:6850 , http://hdl.handle.net/10210/3281
- Description: M.Sc. , Biofuels have the potential to reduce a country’s dependence on imported oil, to ensure diversity of energy sources, to increase the availability of renewable energy sources and to address global environmental issues. In recognition of the potential benefits of the production and use of biofuels, the Department of Minerals and Energy released the Draft Biofuels Industrial Strategy in December 2006 with the aim to increase the use of biofuels in South Africa to replace 4.5% of conventional transport fuels by 2013. However, there are several barriers that need to be overcome before South Africa can establish a large-scale biofuel industry to achieve the DME’s biofuel target. This includes environmental barriers, such as the availability of land for the cultivation of biofuel feedstocks and potential threats to food security. This study focuses on these environmental barriers and aims to determine the potential for bioethanol production from maize in South Africa to 2013. To this purpose, a bioethanol potential model is developed to simulate the potential for bioethanol production from maize in South Africa between 2008 and 2013. The model incorporates four key elements that all impact on the availability of maize for bioethanol production, namely: maize demand; maize supply; the demand for maize as biomaterial; and the available land area for the cultivation of maize. The study makes further use of the scenario planning method to determine the potential for bioethanol production from maize in South Africa. Four unique bioethanol potential scenarios are designed and simulated within the bioethanol potential model developed for this purpose. Each scenario plays out a different Abstract storyline for the future social, economic and natural environment that will impact on the availability of maize for bioethanol production. The results of the bioethanol potential scenario simulations show that South Africa will be able to produce enough maize to meet the DME’s biofuel target of 1.2 billion liters of bioethanol for all scenarios between 2009 and 2010. From 2011 onwards, the bioethanol potential decreases below the DME’s target value in both the worst case and rapid change scenarios. The study concludes that the production of bioethanol from maize in South Africa will have various social, economic and environmental consequences for the country’s agricultural sector. The depletion of domestic maize supplies will seriously threaten food security and consequently, increase the country’s dependence on maize imports. This will not only affect the country’s maize producing regions, but spread throughout South Africa as the demand for agriculturally productive land for maize production increases. Domestic food security is therefore at risk and South Africa will have to resort to other energy technologies to achieve a sustainable and renewable energy future for road transport.
- Full Text: