A geological model of shear zone gold deposits in the Pietersburg Greenstone Belt, South Africa
- Authors: Franey, N J
- Date: 1987 , 2013-04-17
- Subjects: Greenstone belts -- South Africa , Gold ores -- Geology -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5032 , http://hdl.handle.net/10962/d1007190 , Greenstone belts -- South Africa , Gold ores -- Geology -- South Africa
- Description: The Pletersburg greenstone belt Is located In South Africa, about 300 km northeast of Johannesburg. It hosts a significant amount of gold mineralization and just over 1000 kg of gold have been produced from Its various reefs and secondary deposits. The greenstone belt is interpreted as an Archean ophiolite complex. It comprlses a volcano-sedimentary succession (the Pletersburg Group) which Is subdivided Into a basal greenstone sequence, interpreted as oceanic crust, and an upper sedimentary cover sequence. A number of major shear zones, which are thought to represent thrusts that developed during the subduction of the greenstone sequence, form an integral part of the stratigraphy . Four stages of deformation (D₁-D₄) and four phases of metamorphism (H₁-H₄) (three of which are correlatable with the peak stages of deformation) are recognized. The primary gold deposits are all shear zones related. but they are subdivided into greenstone, sedimentation and granIte-hosted types. Geographically, they occur In three distinct goldfields: Eerstellng, Roodepoort and Marbastad. The greenstone-hosted · Plenaar-Doreen shear complex Is In the Eersteiing goldfield and hosts eight gold occurrences. Within the complex, Girlie North Reef is the 640m-long "pay" section of the Girlie North shear zone. This reef is characterized, macroscopically, by a Quartz-carbonate-chlorite-sulphlde assemblage and, mlcroscoplcally, by the presence of tourmaline, arsenopyrlte and Au. Geochemical evidence Indicates that mineralizing fluids were H₂O and CO₂-bearing and rich In S, K and Al. The wall rock alteratlon was Isochemlcal but Is manifest as a change In mineralogy from a hornblende + plagioclase assemblage to an actlnollte/tremollte + Quartz + clay assemblage. This Is best developed In the hangIng wall of the reef and is thought to have been caused by hydrogen ion metasomatism. The Arsenopyrite Reef was one of the main sediment-hosted shear zone gold producers In the Harabastad goldfield. This reef Is Interpreted as the basal margin of a shear zone whose top contact Is probably represented by the Quartz Vein Reef. The shear zone consists predomonantly of quartz and carbonate, and the two "pay" reefs are characterized by tourmallne. arsenopyrite and Au. No wall rock alteration was identified In this study, Based on the mineralogy and geochemical signature of the Girlie Nortn Reef and the Arsenopyrite Reef, It Is proposed that both were formed at the $The Pletersburg greenstone belt Is located In South Africa, about 300 km northeast of Johannesburg. It hosts a significant amount of gold mineralization and just over 1000 kg of gold have been produced from Its various reefs and secondary deposits. The greenstone belt is interpreted as an Archean ophiolite complex. It comprlses a volcano-sedimentary succession (the Pletersburg Group) which Is subdivided Into a basal greenstone sequence, interpreted as oceanic crust, and an upper sedimentary cover sequence. A number of major shear zones, which are thought to represent thrusts that developed during the subduction of the greenstone sequence, form an integral part of the stratigraphy . Four stages of deformation (D₁-D₄) and four phases of metamorphism (H₁-H₄) (three of which are correlatable with the peak stages of deformation) are recognized. The primary gold deposits are all shear zones related. but they are subdivided into greenstone, sedimentation and granIte-hosted types. Geographically, they occur In three distinct goldfields: Eerstellng, Roodepoort and Marbastad. The greenstone-hosted · Plenaar-Doreen shear complex Is In the Eersteiing goldfield and hosts eight gold occurrences. Within the complex, Girlie North Reef is the 640m-long "pay" section of the Girlie North shear zone. This reef is characterized, macroscopically, by a Quartz-carbonate-chlorite-sulphlde assemblage and, mlcroscoplcally, by the presence of tourmaline, arsenopyrlte and Au. Geochemical evidence Indicates that mineralizing fluids were H₂O and CO₂-bearing and rich In S, K and Al. The wall rock alteratlon was Isochemlcal but Is manifest as a change In mineralogy from a hornblende + plagioclase assemblage to an actlnollte/tremollte + Quartz + clay assemblage. This Is best developed In the hangIng wall of the reef and is thought to have been caused by hydrogen ion metasomatism. The Arsenopyrite Reef was one of the main sediment-hosted shear zone gold producers In the Harabastad goldfield. This reef Is Interpreted as the basal margin of a shear zone whose top contact Is probably represented by the Quartz Vein Reef. The shear zone consists predomonantly of quartz and carbonate, and the two "pay" reefs are characterized by tourmallne. arsenopyrite and Au. No wall rock alteration was identified In this study, Based on the mineralogy and geochemical signature of the Girlie Nortn Reef and the Arsenopyrite Reef, It Is proposed that both were formed at the same time. Textural evidence Indicates that tourmaline, arsenopyrite and Au were all very late In the paragenesis of minerallzatlon. The presence of tourmaline also Indicates a probable granite association. It Is proposed that the maln gold mineralizing event was synchronous with the Intrusion of granitoids (and therefore also with (D₁-D₄) and (H₁-H₄) and that most of the Au was derived from felsic magma. Gold was partitioned Into a magmatic hydrothermal fluid and then transported into the greenstone belt as a chlorIde complex. These magmatiC fluids were channelled up shear zones whIch had already been mineralized with a quartz-carbonate-chlorlte - sulphide assemblage by previous metamorphic fluidS. generated during the dynamic (D₂-related) H₂-phase of metamorphism. The Au was then deposIted as the result of a change In a fluid variable, such as temperature, pH, f0₂, or the activity of Cl (some Au may have been transported In a sulphur complex and so the activity of reduced 5 could also have been Important).
- Full Text:
- Date Issued: 1987
- Authors: Franey, N J
- Date: 1987 , 2013-04-17
- Subjects: Greenstone belts -- South Africa , Gold ores -- Geology -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5032 , http://hdl.handle.net/10962/d1007190 , Greenstone belts -- South Africa , Gold ores -- Geology -- South Africa
- Description: The Pletersburg greenstone belt Is located In South Africa, about 300 km northeast of Johannesburg. It hosts a significant amount of gold mineralization and just over 1000 kg of gold have been produced from Its various reefs and secondary deposits. The greenstone belt is interpreted as an Archean ophiolite complex. It comprlses a volcano-sedimentary succession (the Pletersburg Group) which Is subdivided Into a basal greenstone sequence, interpreted as oceanic crust, and an upper sedimentary cover sequence. A number of major shear zones, which are thought to represent thrusts that developed during the subduction of the greenstone sequence, form an integral part of the stratigraphy . Four stages of deformation (D₁-D₄) and four phases of metamorphism (H₁-H₄) (three of which are correlatable with the peak stages of deformation) are recognized. The primary gold deposits are all shear zones related. but they are subdivided into greenstone, sedimentation and granIte-hosted types. Geographically, they occur In three distinct goldfields: Eerstellng, Roodepoort and Marbastad. The greenstone-hosted · Plenaar-Doreen shear complex Is In the Eersteiing goldfield and hosts eight gold occurrences. Within the complex, Girlie North Reef is the 640m-long "pay" section of the Girlie North shear zone. This reef is characterized, macroscopically, by a Quartz-carbonate-chlorite-sulphlde assemblage and, mlcroscoplcally, by the presence of tourmaline, arsenopyrlte and Au. Geochemical evidence Indicates that mineralizing fluids were H₂O and CO₂-bearing and rich In S, K and Al. The wall rock alteratlon was Isochemlcal but Is manifest as a change In mineralogy from a hornblende + plagioclase assemblage to an actlnollte/tremollte + Quartz + clay assemblage. This Is best developed In the hangIng wall of the reef and is thought to have been caused by hydrogen ion metasomatism. The Arsenopyrite Reef was one of the main sediment-hosted shear zone gold producers In the Harabastad goldfield. This reef Is Interpreted as the basal margin of a shear zone whose top contact Is probably represented by the Quartz Vein Reef. The shear zone consists predomonantly of quartz and carbonate, and the two "pay" reefs are characterized by tourmallne. arsenopyrite and Au. No wall rock alteration was identified In this study, Based on the mineralogy and geochemical signature of the Girlie Nortn Reef and the Arsenopyrite Reef, It Is proposed that both were formed at the $The Pletersburg greenstone belt Is located In South Africa, about 300 km northeast of Johannesburg. It hosts a significant amount of gold mineralization and just over 1000 kg of gold have been produced from Its various reefs and secondary deposits. The greenstone belt is interpreted as an Archean ophiolite complex. It comprlses a volcano-sedimentary succession (the Pletersburg Group) which Is subdivided Into a basal greenstone sequence, interpreted as oceanic crust, and an upper sedimentary cover sequence. A number of major shear zones, which are thought to represent thrusts that developed during the subduction of the greenstone sequence, form an integral part of the stratigraphy . Four stages of deformation (D₁-D₄) and four phases of metamorphism (H₁-H₄) (three of which are correlatable with the peak stages of deformation) are recognized. The primary gold deposits are all shear zones related. but they are subdivided into greenstone, sedimentation and granIte-hosted types. Geographically, they occur In three distinct goldfields: Eerstellng, Roodepoort and Marbastad. The greenstone-hosted · Plenaar-Doreen shear complex Is In the Eersteiing goldfield and hosts eight gold occurrences. Within the complex, Girlie North Reef is the 640m-long "pay" section of the Girlie North shear zone. This reef is characterized, macroscopically, by a Quartz-carbonate-chlorite-sulphlde assemblage and, mlcroscoplcally, by the presence of tourmaline, arsenopyrlte and Au. Geochemical evidence Indicates that mineralizing fluids were H₂O and CO₂-bearing and rich In S, K and Al. The wall rock alteratlon was Isochemlcal but Is manifest as a change In mineralogy from a hornblende + plagioclase assemblage to an actlnollte/tremollte + Quartz + clay assemblage. This Is best developed In the hangIng wall of the reef and is thought to have been caused by hydrogen ion metasomatism. The Arsenopyrite Reef was one of the main sediment-hosted shear zone gold producers In the Harabastad goldfield. This reef Is Interpreted as the basal margin of a shear zone whose top contact Is probably represented by the Quartz Vein Reef. The shear zone consists predomonantly of quartz and carbonate, and the two "pay" reefs are characterized by tourmallne. arsenopyrite and Au. No wall rock alteration was identified In this study, Based on the mineralogy and geochemical signature of the Girlie Nortn Reef and the Arsenopyrite Reef, It Is proposed that both were formed at the same time. Textural evidence Indicates that tourmaline, arsenopyrite and Au were all very late In the paragenesis of minerallzatlon. The presence of tourmaline also Indicates a probable granite association. It Is proposed that the maln gold mineralizing event was synchronous with the Intrusion of granitoids (and therefore also with (D₁-D₄) and (H₁-H₄) and that most of the Au was derived from felsic magma. Gold was partitioned Into a magmatic hydrothermal fluid and then transported into the greenstone belt as a chlorIde complex. These magmatiC fluids were channelled up shear zones whIch had already been mineralized with a quartz-carbonate-chlorlte - sulphide assemblage by previous metamorphic fluidS. generated during the dynamic (D₂-related) H₂-phase of metamorphism. The Au was then deposIted as the result of a change In a fluid variable, such as temperature, pH, f0₂, or the activity of Cl (some Au may have been transported In a sulphur complex and so the activity of reduced 5 could also have been Important).
- Full Text:
- Date Issued: 1987
Anorogenic alkaline ring-type complexes of the Damaraland Province, Namibia, and their economic potential
- Authors: Potgieter, J E
- Date: 1987
- Subjects: Alkalic igneous rocks -- Namibia
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4907 , http://hdl.handle.net/10962/d1001567
- Description: Anorogenic alkaline ring-type complexes form within continental plate settings. Alkaline magmatism is derived from the upper mantle, in which mantle metasomatism plays an important part, as well as from partial melting of the lower crust. Radial and concentric fractures develop during the ascent of alkaline magma. Extrusion of basic and felsic magma takes place along these fractures with felsic volcanics building-up central volcanoes. As a result of emptying of the magma chamber, the superstructure of the volcano collapses and a caldera is formed. During the caldera stage syenitic and granitic material are intruded into ring fractures. Alkaline ring-type complexes may be classified as (i) alkaline qranite and syenite-type and (ii) carbonatite and undersaturated-type. These ring-type complexes occur as distinct igneous provinces. Some major provinces occur in Brazil, Corsica, Namibia, Nigeria, Norway, Saudi-Arabia and Sudan. In Namibia the Damaraland igneous province is of Mesozoic aqe and it contains 15 alkaline ring-type complexes . These complexes are situated along north-eastern trends which correspond to transform directions of the South Atlantic. During the opening of the South Atlantic (Gondwana breakup) Pan-African age lineaments were reactivated which allowed emplacement of anorogenic alkaline magmatism. A zonation of alkaline granite and syenitetype in the west and carbonatite and undersaturated-type ring-complexes in the east correlates with down- and upwarp axes parallel to the line of Gondwana fragmentation. Alkali- and H⁺-metasomatism is related to the alkaline and syenite-type whereas alkali metasomatism (fenitization) is associated with carbonatite and undersaturated-type ring-complexes. Sn, W and Ta mineralization is associated with alkaline granites of some of the alkaline granite and syenite-type ring-complexes. Fe, F, PO₄ , Nb, Th, REE, Sr, Zn and Pb mineralization is associated with carbonatite complexes. Potential exists for: (i) porphyry Cu-Mo and epithermal-type (Au, Ag, Pt-metals, base metals) mineralization in the alkaline granite and syenite-type ring-complexes and (ii) disseminated Cu, Au, Aq and Pt-metals in carbonatite and undersaturated-type ring-complexes
- Full Text:
- Date Issued: 1987
- Authors: Potgieter, J E
- Date: 1987
- Subjects: Alkalic igneous rocks -- Namibia
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4907 , http://hdl.handle.net/10962/d1001567
- Description: Anorogenic alkaline ring-type complexes form within continental plate settings. Alkaline magmatism is derived from the upper mantle, in which mantle metasomatism plays an important part, as well as from partial melting of the lower crust. Radial and concentric fractures develop during the ascent of alkaline magma. Extrusion of basic and felsic magma takes place along these fractures with felsic volcanics building-up central volcanoes. As a result of emptying of the magma chamber, the superstructure of the volcano collapses and a caldera is formed. During the caldera stage syenitic and granitic material are intruded into ring fractures. Alkaline ring-type complexes may be classified as (i) alkaline qranite and syenite-type and (ii) carbonatite and undersaturated-type. These ring-type complexes occur as distinct igneous provinces. Some major provinces occur in Brazil, Corsica, Namibia, Nigeria, Norway, Saudi-Arabia and Sudan. In Namibia the Damaraland igneous province is of Mesozoic aqe and it contains 15 alkaline ring-type complexes . These complexes are situated along north-eastern trends which correspond to transform directions of the South Atlantic. During the opening of the South Atlantic (Gondwana breakup) Pan-African age lineaments were reactivated which allowed emplacement of anorogenic alkaline magmatism. A zonation of alkaline granite and syenitetype in the west and carbonatite and undersaturated-type ring-complexes in the east correlates with down- and upwarp axes parallel to the line of Gondwana fragmentation. Alkali- and H⁺-metasomatism is related to the alkaline and syenite-type whereas alkali metasomatism (fenitization) is associated with carbonatite and undersaturated-type ring-complexes. Sn, W and Ta mineralization is associated with alkaline granites of some of the alkaline granite and syenite-type ring-complexes. Fe, F, PO₄ , Nb, Th, REE, Sr, Zn and Pb mineralization is associated with carbonatite complexes. Potential exists for: (i) porphyry Cu-Mo and epithermal-type (Au, Ag, Pt-metals, base metals) mineralization in the alkaline granite and syenite-type ring-complexes and (ii) disseminated Cu, Au, Aq and Pt-metals in carbonatite and undersaturated-type ring-complexes
- Full Text:
- Date Issued: 1987
Gold metallogeny of Australia
- Authors: Rankine, Graham M
- Date: 1987
- Subjects: Gold ores -- Geology -- Australia , Gold mines and mining -- Australia , Gold -- Metallurgy -- Australia
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4928 , http://hdl.handle.net/10962/d1004676
- Description: The gold metallogeny of Australia is predominantly confined to the Archaean and Palaeozoic Provinces. The Archaean gold occurrences are predominantly hosted in ultramafic-mafic dominated greenstone belts, with less associated tofelsic-volcanic and sedimentary sequences. Most gold occurrences are confined to shear zones or faults, and adjacent discoveries of economic laterite-hosted deposits, host rocks. Recent are presently under investigation and will supply a significant proportion of production in the future. The Proterozoic gold deposits of Australia , are confined to geosyncinal sequences, commonly turbidites (eg: Telfer), with other hydrothermal deposits associated directly to granites. An important feature of the North Australian Craton deposits, is the spatial association of most deposits to granite bodies, although a genetic link has not been established conclusively. The Roxby Downs deposit in South Australia is a unique occurrence of gold in association to copper, uranium and R.E.E. This deposit is tentatively related to intraplate alkaline-magmatism, with further work necessary. The most significant recent discovery of gold mineralization in Australia is in the Drummond Basin in Queensland. This epithermal is tentatively related to mineralization within the Georgetown Inlier. The latter mineralization is Permo-Carboniferous, in a Proterozoic (and possibly Archaean) sequence of schists. It is tentatively suggested that all the gold mineralization in northern Queensland may be related to single tectonic event, a feature which requires further study . Other mineralization in the Phanerozoic includes the turbidite-hosted metamorphogenic deposits of Victoria, the rift related deposits in New South Wales and magmatic related deposits in Queensland. The gold deposits in Australia may in the future be classified in a tectonogeological framework, similiar to the layout of this dissertation, particularly once further data becomes available on recent discoveries.
- Full Text:
- Date Issued: 1987
- Authors: Rankine, Graham M
- Date: 1987
- Subjects: Gold ores -- Geology -- Australia , Gold mines and mining -- Australia , Gold -- Metallurgy -- Australia
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4928 , http://hdl.handle.net/10962/d1004676
- Description: The gold metallogeny of Australia is predominantly confined to the Archaean and Palaeozoic Provinces. The Archaean gold occurrences are predominantly hosted in ultramafic-mafic dominated greenstone belts, with less associated tofelsic-volcanic and sedimentary sequences. Most gold occurrences are confined to shear zones or faults, and adjacent discoveries of economic laterite-hosted deposits, host rocks. Recent are presently under investigation and will supply a significant proportion of production in the future. The Proterozoic gold deposits of Australia , are confined to geosyncinal sequences, commonly turbidites (eg: Telfer), with other hydrothermal deposits associated directly to granites. An important feature of the North Australian Craton deposits, is the spatial association of most deposits to granite bodies, although a genetic link has not been established conclusively. The Roxby Downs deposit in South Australia is a unique occurrence of gold in association to copper, uranium and R.E.E. This deposit is tentatively related to intraplate alkaline-magmatism, with further work necessary. The most significant recent discovery of gold mineralization in Australia is in the Drummond Basin in Queensland. This epithermal is tentatively related to mineralization within the Georgetown Inlier. The latter mineralization is Permo-Carboniferous, in a Proterozoic (and possibly Archaean) sequence of schists. It is tentatively suggested that all the gold mineralization in northern Queensland may be related to single tectonic event, a feature which requires further study . Other mineralization in the Phanerozoic includes the turbidite-hosted metamorphogenic deposits of Victoria, the rift related deposits in New South Wales and magmatic related deposits in Queensland. The gold deposits in Australia may in the future be classified in a tectonogeological framework, similiar to the layout of this dissertation, particularly once further data becomes available on recent discoveries.
- Full Text:
- Date Issued: 1987
Risk analysis assessment of the influence of geological factors on exploration and mining investment alternatives : development of a microcomputer simulation model
- Authors: Mallinson, Clyde A
- Date: 1987
- Subjects: Geology, Economic , Risk assessment -- Computer simulation , Mineral industries -- Economic aspects -- Computer simulation , Prospecting -- Computer simulation
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4904 , http://hdl.handle.net/10962/d1001564
- Description: A microcomputer risk analysis model is developed and used in an exploration - delineation simulation to analyse in particular the effects of geological factors on exploration mining investment alternatives. Analysis of results indicate that geological parameters can have profound effects on such investment alternatives and that the role of the geologist in determining and evaluating the significance of the various geological factors is critical. Simulation examples highlight some of the key geological parameters and show how changes in these parameters influence both the expected mean results and the standard deviations of such means. The risk analysis model provides an ideal means of conveying the importance of the different geoiogical factors on exploration - delineation - mining investment alternatives and may be used as a geological education aid
- Full Text:
- Date Issued: 1987
- Authors: Mallinson, Clyde A
- Date: 1987
- Subjects: Geology, Economic , Risk assessment -- Computer simulation , Mineral industries -- Economic aspects -- Computer simulation , Prospecting -- Computer simulation
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4904 , http://hdl.handle.net/10962/d1001564
- Description: A microcomputer risk analysis model is developed and used in an exploration - delineation simulation to analyse in particular the effects of geological factors on exploration mining investment alternatives. Analysis of results indicate that geological parameters can have profound effects on such investment alternatives and that the role of the geologist in determining and evaluating the significance of the various geological factors is critical. Simulation examples highlight some of the key geological parameters and show how changes in these parameters influence both the expected mean results and the standard deviations of such means. The risk analysis model provides an ideal means of conveying the importance of the different geoiogical factors on exploration - delineation - mining investment alternatives and may be used as a geological education aid
- Full Text:
- Date Issued: 1987
The geology and alteration/mineralization of the Van Rooi's vley W/Sn deposit, Namaqua metamorphic complex, South Africa
- Authors: Smithies, Robert Hugh
- Date: 1987 , 2013-03-01
- Subjects: Mineralogy -- South Africa , Geology -- South Africa -- Namaqualand
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4924 , http://hdl.handle.net/10962/d1004526 , Mineralogy -- South Africa , Geology -- South Africa -- Namaqualand
- Description: Scheelite, wolfram Ite and cassIterIte mIneralizat ion is hosted wIthin numerous quartz-tourmaline-feldspar-fluorite veins at Van Rooi's Vley, N.W. Cape Province . MineralizatIon and hydrothermal alteration within, and around, these veins is hIghly complex and reflects the intricate interaction of hydrotherma l activity upon a structurally deformed sequence of ProterozoIc med ium to high-grade gneisses. Four distinct stages of alteration and mineralization occurred, including a l ate 'epithermal stage'. Although the location of mineralization was strongly controlled by st ructure, the concentration of mineralizati on was controlled by physicochemical variables, of which host-rock geochemistry was particularly important . Further W/Sn mineralization occurs on a local scale, some of which is spatia lly related to minor leucogranite dykes. Leucogranite bodies are not uncommon within the region and some are enriched in Wand Sn. By comparing FIB ra tio s,W/Sn ratios, the alteration mineralogy, the ore mineralogy and the Fe-content of tourmaline, the deposits within the Van Rooi's Vley area can be placed into a 'proximal' to 'distal' classification, with respect to a common source of mineralizing hydrothermal fluids. The Van Rooi's Vley deposit, whilst affiliated to greisen-style deposits, represents a ' distal' quartz-vein lode deposit. , KMBT_363 , Adobe Acrobat 9.53 Paper Capture Plug-in
- Full Text:
- Date Issued: 1987
- Authors: Smithies, Robert Hugh
- Date: 1987 , 2013-03-01
- Subjects: Mineralogy -- South Africa , Geology -- South Africa -- Namaqualand
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4924 , http://hdl.handle.net/10962/d1004526 , Mineralogy -- South Africa , Geology -- South Africa -- Namaqualand
- Description: Scheelite, wolfram Ite and cassIterIte mIneralizat ion is hosted wIthin numerous quartz-tourmaline-feldspar-fluorite veins at Van Rooi's Vley, N.W. Cape Province . MineralizatIon and hydrothermal alteration within, and around, these veins is hIghly complex and reflects the intricate interaction of hydrotherma l activity upon a structurally deformed sequence of ProterozoIc med ium to high-grade gneisses. Four distinct stages of alteration and mineralization occurred, including a l ate 'epithermal stage'. Although the location of mineralization was strongly controlled by st ructure, the concentration of mineralizati on was controlled by physicochemical variables, of which host-rock geochemistry was particularly important . Further W/Sn mineralization occurs on a local scale, some of which is spatia lly related to minor leucogranite dykes. Leucogranite bodies are not uncommon within the region and some are enriched in Wand Sn. By comparing FIB ra tio s,W/Sn ratios, the alteration mineralogy, the ore mineralogy and the Fe-content of tourmaline, the deposits within the Van Rooi's Vley area can be placed into a 'proximal' to 'distal' classification, with respect to a common source of mineralizing hydrothermal fluids. The Van Rooi's Vley deposit, whilst affiliated to greisen-style deposits, represents a ' distal' quartz-vein lode deposit. , KMBT_363 , Adobe Acrobat 9.53 Paper Capture Plug-in
- Full Text:
- Date Issued: 1987
The petrology and geochemistry of the upper critical zone of the Bushveld complex at the Amandelbult section of Rustenberg Platinum Mines Limited, Northwestern Transvaal, South Africa
- Authors: Field, Matthew
- Date: 1987 , 2013-03-06
- Subjects: Geology -- South Africa -- North-Western Transvaal , Petrology -- South Africa -- North-Western Transvaal
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5037 , http://hdl.handle.net/10962/d1007499 , Geology -- South Africa -- North-Western Transvaal , Petrology -- South Africa -- North-Western Transvaal
- Description: A study of petrological and geochemical variations through the upper Critical Zone of the Bushveld Complex at Amandelbult section of R.P,M. was undertaken. The sequence at this locality may be divided into seven "units" two of which appear to be complete, possessing the sequence harzburgite-pyroxenite-norite-anorthosite. The other five Units lack basal, intermediate or upper members. Considerable lateral variations are apparent in this sequence, but these are restricted to the Lower Pseudo Reef-Merensky Reef interval, tne same portion of the succession which is affected by pothole structures. The single most important petrographic feature of genetic significance is the occurrence of annealed, recrystallized anorthosite immediately underlying ulstramafic layers. This, together with the undulatory nature of the contact between the two rock layers, suggests that the ultramafic layer was emplaced as a hot liquid over a pre-existing, crystalline anorthosite floor, and that some remelting of this layer occurred. Variations in the chemical make-up of constituent silicate minerals reveal a number of significant processes which may have been operative in the magma chamber prior to crystallization, Olivine grains, for instance, exhibit extremely wide chemical variations both within single layers and from one layer to the next. These variations are best explained by re-equilibration processes with spinel and base metal sulphides, rather than by wide variations in original liquidus compositions. It appears that the compositions of the initial liquids from which each basal olivine-bearing layer crystallized, were approximately similar. Variations in the iron-magnesium ratio of ortho-pyroxenes indicate well defined continuous fractionation trends in units which are considered to be complete. Magnesian compositions are recorded in ultramfic members, while increasingly iron-enriched values are recorded upwards through the sequence pyroxenite-norite-antorthosite. Plagioclase grains exhibit less well defined fractionation trends, but it is clear that an upward increase in An is encountered through indivitual Units. This is in direct contrast to the trend exhibited by orthopyroxene. A further feature of plagioclase grains is the considerable degree of chemical zonation exhibited by them. In cumulus grains this is commonly manifested as strongly reversed rims, while in intercululus grains normal zoning is ubiquitous. Whole-rock chemical variations through the succession indicate that cyclical variations occur through successive Units, but that these merely reflect changes in modal mineralogy and not liquid fractionation trends. Such trends can be shown for selected element ratios, where these elements are known to partition into a single mineral phase. Rations of pyroxene components such as the nickel/scandium ratio, exhibit a saw tooth pattern through successive Units, while ratios of plagioclase components such as the strontium/alumina ratio have unique, fairly constant values for each individual Unit but different values for successive Units. The latter type of cyclicity is not always strictly confined to lithologically recognized boundaries between Units, and a slight overlap into overlying ultramafic layers is apparent. An investigation of variations in trace element levels in a single layer in five widely separated boreholes revealed that there is some evidence for a lateral fractionation trend from the southwest (more primitive) to the northeast (more evolved), although the small number of data points available preclude definite conclusions. There exists in the data some evidence that the Giant Mottled Anorthosite differs chemically from the other anorthosites in the study section, and that it more closely resembles rocks of the Main Zone. This evidence is particularly apparent in variations of the chromium/aluminium ratio of orthoyroxene grains, and in the An content of plagioclase grains, both of whose trends exhibit distinct inflections at the base of this member. The features of the succession at Amandelbult are best explained by the model of Eales et al. (in press, a), which visualizes the input of a number of pulses of new, hot liquid into a magma chamber containing the fractionated residua of previous influxes. At a critical point in time, just prior to the mafic Merensky Reef input, a large input of gabboic liquid was intruded at high levels in the chamber. The lower portions of this liquid mixed with the residua of earlier mafic inputs, which in turn mixed with new inputs of mafic, typical Critical Zone liquids. Thus the lower portions of the study section represent mixtures of new Critical Zone liquids with the residua of previous such influxes, while the upper portions have the added complication of mixture with a Main Zone-type liquid. The unique chemical character of the Giant Mottled Anorthosite appears to be a direct manifestation of the influence of the Main Zone liquid. , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
- Full Text:
- Date Issued: 1987
- Authors: Field, Matthew
- Date: 1987 , 2013-03-06
- Subjects: Geology -- South Africa -- North-Western Transvaal , Petrology -- South Africa -- North-Western Transvaal
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5037 , http://hdl.handle.net/10962/d1007499 , Geology -- South Africa -- North-Western Transvaal , Petrology -- South Africa -- North-Western Transvaal
- Description: A study of petrological and geochemical variations through the upper Critical Zone of the Bushveld Complex at Amandelbult section of R.P,M. was undertaken. The sequence at this locality may be divided into seven "units" two of which appear to be complete, possessing the sequence harzburgite-pyroxenite-norite-anorthosite. The other five Units lack basal, intermediate or upper members. Considerable lateral variations are apparent in this sequence, but these are restricted to the Lower Pseudo Reef-Merensky Reef interval, tne same portion of the succession which is affected by pothole structures. The single most important petrographic feature of genetic significance is the occurrence of annealed, recrystallized anorthosite immediately underlying ulstramafic layers. This, together with the undulatory nature of the contact between the two rock layers, suggests that the ultramafic layer was emplaced as a hot liquid over a pre-existing, crystalline anorthosite floor, and that some remelting of this layer occurred. Variations in the chemical make-up of constituent silicate minerals reveal a number of significant processes which may have been operative in the magma chamber prior to crystallization, Olivine grains, for instance, exhibit extremely wide chemical variations both within single layers and from one layer to the next. These variations are best explained by re-equilibration processes with spinel and base metal sulphides, rather than by wide variations in original liquidus compositions. It appears that the compositions of the initial liquids from which each basal olivine-bearing layer crystallized, were approximately similar. Variations in the iron-magnesium ratio of ortho-pyroxenes indicate well defined continuous fractionation trends in units which are considered to be complete. Magnesian compositions are recorded in ultramfic members, while increasingly iron-enriched values are recorded upwards through the sequence pyroxenite-norite-antorthosite. Plagioclase grains exhibit less well defined fractionation trends, but it is clear that an upward increase in An is encountered through indivitual Units. This is in direct contrast to the trend exhibited by orthopyroxene. A further feature of plagioclase grains is the considerable degree of chemical zonation exhibited by them. In cumulus grains this is commonly manifested as strongly reversed rims, while in intercululus grains normal zoning is ubiquitous. Whole-rock chemical variations through the succession indicate that cyclical variations occur through successive Units, but that these merely reflect changes in modal mineralogy and not liquid fractionation trends. Such trends can be shown for selected element ratios, where these elements are known to partition into a single mineral phase. Rations of pyroxene components such as the nickel/scandium ratio, exhibit a saw tooth pattern through successive Units, while ratios of plagioclase components such as the strontium/alumina ratio have unique, fairly constant values for each individual Unit but different values for successive Units. The latter type of cyclicity is not always strictly confined to lithologically recognized boundaries between Units, and a slight overlap into overlying ultramafic layers is apparent. An investigation of variations in trace element levels in a single layer in five widely separated boreholes revealed that there is some evidence for a lateral fractionation trend from the southwest (more primitive) to the northeast (more evolved), although the small number of data points available preclude definite conclusions. There exists in the data some evidence that the Giant Mottled Anorthosite differs chemically from the other anorthosites in the study section, and that it more closely resembles rocks of the Main Zone. This evidence is particularly apparent in variations of the chromium/aluminium ratio of orthoyroxene grains, and in the An content of plagioclase grains, both of whose trends exhibit distinct inflections at the base of this member. The features of the succession at Amandelbult are best explained by the model of Eales et al. (in press, a), which visualizes the input of a number of pulses of new, hot liquid into a magma chamber containing the fractionated residua of previous influxes. At a critical point in time, just prior to the mafic Merensky Reef input, a large input of gabboic liquid was intruded at high levels in the chamber. The lower portions of this liquid mixed with the residua of earlier mafic inputs, which in turn mixed with new inputs of mafic, typical Critical Zone liquids. Thus the lower portions of the study section represent mixtures of new Critical Zone liquids with the residua of previous such influxes, while the upper portions have the added complication of mixture with a Main Zone-type liquid. The unique chemical character of the Giant Mottled Anorthosite appears to be a direct manifestation of the influence of the Main Zone liquid. , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
- Full Text:
- Date Issued: 1987
The tectono-metallogenesis during the irumide and pan-African events in South West Africa/Namibia
- Authors: Tregoning, Trevor Denzil
- Date: 1987 , 2013-03-05
- Subjects: Orogeny -- Namibia , Ore deposits -- Namibia , Mines and mineral resources -- Namibia , Geodynamics , Rifts (Geology) -- Namibia
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4922 , http://hdl.handle.net/10962/d1004490 , Orogeny -- Namibia , Ore deposits -- Namibia , Mines and mineral resources -- Namibia , Geodynamics , Rifts (Geology) -- Namibia
- Description: A large portion of South west Africa/Namibia is underlain by 2 great orogens. They are the Irumide (Sinclair/Rehoboth) and Damara Orogenies. The L-shaped Irumide Province forms part of a belt which extends over the subcontinent from Namaqualand to as far as Zambia. The volcano-sedimentary sequences of the Irumide are believed to have formed in intracratonic rifts and pull-apart basins during the period 1400 to 900 Ma. The evolution of the NW trending Sinclair Group proceeded by means of 3 major cycles each beginning with the emplacement of basic to intermediate magmas followed by felsic ones. The cycle ended off with subsidence, deposition of immature clastic debris and final tilting of the volcano-clastic sequence. It was suggested that the extensive calc-alkaline lavas present, developed within a magmatic arc above a subduction zone, but this proposal has not been generally accepted. The NE trending Klein Aub-Witvlei Basins consist essentially of red bed alluvial fans and lacustrine sediments with minor volcanics near the base. The red beds and aeolian sediments were deposited in an arid climatic condition. The regional greenschist facies metamorphism and deformation is attributed to a major tectono-thermal event at 1100 Ma. The Damara Orogen (900 - 550 Ma) forms part of the Pan-African mobile belt system of global proportions. The NE trending intracontinental branch (aulacogen) and 2 coastal branches constitute a triple junction with its focal point near Swakopmund. The NE extension of the intracontinental belt has been linked with the Lufilian Arc hosting the renown Zambian Copper Belt deposits. In South West Africa/Namibia this belt hosts many different mineral occurrences which can be grouped into rift and collision related deposits. The tectonic history of the Damara Orogen supports a geodynamic-evolution-with-time hypothesis and represents a transitional phase in which limited Wilson Cycle Tectonics was active. The Theory of Mantle Advection is invoked to explain rifting, thinning and subsidence. Extensive ensialic rifting resulted in a relatively stable Northern Carbonate Platform and several deep troughs hosting turbiditic sequences. Crustal rupture in the Khomas Trough allowed for the emplacement of ocean floor tholeiites known as the Matchless Amphibolite Belt. Subsequent ocean closure and collision resulted in deformation, metamorphism and generation of predominantly S-type granites. The southern continental plate was partially overridden by the northern plate during final collision at 550 Ma. These low angle thrust faults allowed for the emplacement of the Naukluft Nappe Complex on top of younger Nama sediments. The break up of Gondwanaland during the Mesozoic with the splitting of the Atlantic Ocean was responsible for the intrusion of anorogenic alkaline ring complexes along the extension of the NE trending transform faults within the intracontinental branch of the Damara Orogen. A close relationship between the tectonic setting and mineral deposits has been recognized in both the Irumide and Damara Orogenies. In the Irumide, stratiform syngenetic copper deposits are hosted by alluvial fan, playa and lacustrine sediments. The uninterrupted sedimentation from the Irumide to Damara Orogen resulted in similar stratiform copper deposits during the early stages of rifting. In the Damara Orogen the rifting (extensional) phase is characterized by 4 main mineralizing systems: diagenetic/syngenetic (Kupferschiefer-type), epigenetic/hydrothermal Cu-Pb-Zn (Mississippi Valley-type), volcanogenic cupriferous pyrite (Besshi-type) and volcano-exhalative Pb-Zn (Red Sea-type). The collision (compressional) phase was accompanied by 4 main mineralizing processes: epigenetic/hydrothermal Cu-Pb-Zn, hydrotheral/metasomatic Sn-W-rare earth, metamorphogenic Au and U-bearing anatectic melts. The key to the selection of viable exploration targets lies in the understanding of the field evidence and the geodynamics modelling to explain the evolution of the orogen and its associated mineral deposits.
- Full Text:
- Date Issued: 1987
- Authors: Tregoning, Trevor Denzil
- Date: 1987 , 2013-03-05
- Subjects: Orogeny -- Namibia , Ore deposits -- Namibia , Mines and mineral resources -- Namibia , Geodynamics , Rifts (Geology) -- Namibia
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4922 , http://hdl.handle.net/10962/d1004490 , Orogeny -- Namibia , Ore deposits -- Namibia , Mines and mineral resources -- Namibia , Geodynamics , Rifts (Geology) -- Namibia
- Description: A large portion of South west Africa/Namibia is underlain by 2 great orogens. They are the Irumide (Sinclair/Rehoboth) and Damara Orogenies. The L-shaped Irumide Province forms part of a belt which extends over the subcontinent from Namaqualand to as far as Zambia. The volcano-sedimentary sequences of the Irumide are believed to have formed in intracratonic rifts and pull-apart basins during the period 1400 to 900 Ma. The evolution of the NW trending Sinclair Group proceeded by means of 3 major cycles each beginning with the emplacement of basic to intermediate magmas followed by felsic ones. The cycle ended off with subsidence, deposition of immature clastic debris and final tilting of the volcano-clastic sequence. It was suggested that the extensive calc-alkaline lavas present, developed within a magmatic arc above a subduction zone, but this proposal has not been generally accepted. The NE trending Klein Aub-Witvlei Basins consist essentially of red bed alluvial fans and lacustrine sediments with minor volcanics near the base. The red beds and aeolian sediments were deposited in an arid climatic condition. The regional greenschist facies metamorphism and deformation is attributed to a major tectono-thermal event at 1100 Ma. The Damara Orogen (900 - 550 Ma) forms part of the Pan-African mobile belt system of global proportions. The NE trending intracontinental branch (aulacogen) and 2 coastal branches constitute a triple junction with its focal point near Swakopmund. The NE extension of the intracontinental belt has been linked with the Lufilian Arc hosting the renown Zambian Copper Belt deposits. In South West Africa/Namibia this belt hosts many different mineral occurrences which can be grouped into rift and collision related deposits. The tectonic history of the Damara Orogen supports a geodynamic-evolution-with-time hypothesis and represents a transitional phase in which limited Wilson Cycle Tectonics was active. The Theory of Mantle Advection is invoked to explain rifting, thinning and subsidence. Extensive ensialic rifting resulted in a relatively stable Northern Carbonate Platform and several deep troughs hosting turbiditic sequences. Crustal rupture in the Khomas Trough allowed for the emplacement of ocean floor tholeiites known as the Matchless Amphibolite Belt. Subsequent ocean closure and collision resulted in deformation, metamorphism and generation of predominantly S-type granites. The southern continental plate was partially overridden by the northern plate during final collision at 550 Ma. These low angle thrust faults allowed for the emplacement of the Naukluft Nappe Complex on top of younger Nama sediments. The break up of Gondwanaland during the Mesozoic with the splitting of the Atlantic Ocean was responsible for the intrusion of anorogenic alkaline ring complexes along the extension of the NE trending transform faults within the intracontinental branch of the Damara Orogen. A close relationship between the tectonic setting and mineral deposits has been recognized in both the Irumide and Damara Orogenies. In the Irumide, stratiform syngenetic copper deposits are hosted by alluvial fan, playa and lacustrine sediments. The uninterrupted sedimentation from the Irumide to Damara Orogen resulted in similar stratiform copper deposits during the early stages of rifting. In the Damara Orogen the rifting (extensional) phase is characterized by 4 main mineralizing systems: diagenetic/syngenetic (Kupferschiefer-type), epigenetic/hydrothermal Cu-Pb-Zn (Mississippi Valley-type), volcanogenic cupriferous pyrite (Besshi-type) and volcano-exhalative Pb-Zn (Red Sea-type). The collision (compressional) phase was accompanied by 4 main mineralizing processes: epigenetic/hydrothermal Cu-Pb-Zn, hydrotheral/metasomatic Sn-W-rare earth, metamorphogenic Au and U-bearing anatectic melts. The key to the selection of viable exploration targets lies in the understanding of the field evidence and the geodynamics modelling to explain the evolution of the orogen and its associated mineral deposits.
- Full Text:
- Date Issued: 1987
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