The petrogenesis of the volcanic rocks of the Witwatersrand triad in the Klerksdorp area, Transvaal
- Authors: Bowen, Michael Peter
- Date: 1985
- Subjects: Volcanic rocks , Witwatersrand triad , Klerksdorp , Transvaal , Northwest Province , South Africa , Chemical analysis , Magma , Geology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4909 , http://hdl.handle.net/10962/d1001569
- Description: Several hundred chemical analyses of early Proterozoic lavas of the Witwatersrand triad (incorporating the Dominion Group, Witwatersrand Supergroup and Ventersdorp Supergroup) in the Klerksdorp area, have revealed the presence of various distinct magma types. These essentially correspond to formally defined lithostratigraphic units, but several inconsistencies have necessitated the use of informal nomenclature. The lavas have been regionally metamorphosed to low-grade, greenschist facies assemblages. Original igneous textures are preserved, despite a metamorphic overprint. Metamorphism has resulted in a certain degree of random chemical remobilization. Ba, Sr, Rb, K₂0, Na₂0 and CaO have been highly mobile, and their usefulness in petrogenetic modelling is extremely limited. In contrast, Zr, Nb, Y, LREE's, Cr, Ni, Ti0₂ P₂0₅ and Al₂0₃ have remained immobile. Ti/Zr and Ti/P ratios together constitute efficient discriminating variables for characterizing the different magma types. Lava compositions range from primitive Mg-rich tholeiites to rhyolites, the bulk being tholeiitic andesites. Al₂0₃ contents do not exceed 15%, a feature which reflects the tholeiitic, as opposed to calcalkaline, character of these lavas. Two magma-types are present within the Dominion Group, which is a typical example of bimodal volcanism. The Dominion basic lavas are overlain by the Dominion acid porphyries, with a limited amount of interfingering. The basic lava suite is highly fractionated, with compositions ranging from Mg-, Cr- and Ni-rich tholeiites (close to primary mantle melts) to evolved tholeiitic andesites. The most primitive liquids evolved by 45% fractional crystallization of hornblende, followed by a further 70% crystallization of an orthopyroxene-plagioclase assemblage containing up to 3% sulphides. The Dominion porphyries are rhyolitic, display very limited compositional variation, and probably represent a crustal melt related to the same magmatic event which produced the basic lavas. The only lavas from the Witwatersrand Supergroup present in the Klerksdorp area are those of the Crown Formation (Jeppestown amygdaloid). These are tholeiitic dacites which display extremely limited compositional variation, and are unrelated to any of the other magmas of the Witwatersrand triad. The Ventersdorp Supergroup comprises 4 magma-types: The Kliprivierberg Group lavas at the base are subdivisible into 3 sub-types on the basis of Zr contents. (Zr>11Oppm) are the most evolved. They are tholeiitic andesites which display fairly limited compositional variation. It is likely that more evolved compositions are present in other areas where the porphyritic lavas which characterize this unit are better developed. The overlying Orkney lavas are characterized by 110ppm>Zr>90ppm. They are tholeiitic andesites of similar composition to the Alberton lavas, but have lower incompatible element levels, higher siderophile element levels, and are of extremely uniform composition. The uppermost Loraine/Edenville lavas range from magnesian tholeiites to tholeiitic andesites. They are distinguished by Zr< 90ppm, and contain the most primitive magmas af the Witwatersrand triad, with up to 17,5% MgO, 2600ppm Cr, 600ppm Ni and M-values up to 77. The most primitive liquids evolved by 38% fractional crystallization of orthopyroxene ∓ chromite, followed by 35% fractional crystallization of an extract containing clinopyroxene and plagioclase. The absence of olivine precipitation is a result of the inherently high Si0₂ content of the magma. The Loraine/Edenville, Orkney and Alberton lavas do not lie on a common liquid line of descent, but are probably consanguinous. The Platberg Group overlies the Kliprivierberg Group, and has a coarse-clastic sedimentary unit, the Kameeldoorns Formation, at the base. Three petrographically distinct porphyritic lava sequences overlie the Kameeldoorns Formation, namely the informal "Goedgenoeg formation", the Makwassie quartz-feldspar porphyries and the Rietgat Formation. Despite petrographic differences, the Goedgenoeg and Rietgat lavas are chemically indistinguishable and thus form a single magma-type. The Makwassie porphyries are dacitic in composition with a high proportion of feldspar and quartz phenocrysts. Rational variation trends are attributed to a nett loss of Si0₂ during secondary alteration. The porphyries are probably of crustal origin. The Goedgenoeg/Rietgat lavas display unusual chemistry and a broad, irrational compositional spectrum. They contain very high incompatible element levels, high nonnative quartz, as well as high MgO, M-values, Cr and Ni relative to the other tholeiitic andesites of the Witwatersrand triad. It is tentatively suggested that they are hybrid magmas containing both crust and mantle components, the former possibly represented by the Makwassie porphyries. Field evidence suggests that Platberg volcanism commenced directly after Klipriviersberg volcanism ceased, and was accompanied by a period of enhanced tectonic activity. The Platberg lavas thus probably reflect a crustal melting cycle associated with the Klipriviersberg magmatic event. The Allanridge lavas are the youngest rocks of the Witwatersrand triad. They are separated from the Platberg Group by a unit of flat-lying sediments, the Bothaville Formation, which was deposited after an extended period of peneplanation. The Allanridge lavas form a separate magma-type. They are tholeiitic andesites of similar composition to the Alberton lavas, but have higher incompatible element levels and are not consanguinous. The compositional similarities amongst the basic magma-types of the Witwatersrand triad suggests that all were generated in an hydrous mantle. Interelement ratio differences between the various magma-types nevertheless support the concept that the mantle was chemically heterogeneous during the early Proterozoic.
- Full Text:
- Date Issued: 1985
- Authors: Bowen, Michael Peter
- Date: 1985
- Subjects: Volcanic rocks , Witwatersrand triad , Klerksdorp , Transvaal , Northwest Province , South Africa , Chemical analysis , Magma , Geology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4909 , http://hdl.handle.net/10962/d1001569
- Description: Several hundred chemical analyses of early Proterozoic lavas of the Witwatersrand triad (incorporating the Dominion Group, Witwatersrand Supergroup and Ventersdorp Supergroup) in the Klerksdorp area, have revealed the presence of various distinct magma types. These essentially correspond to formally defined lithostratigraphic units, but several inconsistencies have necessitated the use of informal nomenclature. The lavas have been regionally metamorphosed to low-grade, greenschist facies assemblages. Original igneous textures are preserved, despite a metamorphic overprint. Metamorphism has resulted in a certain degree of random chemical remobilization. Ba, Sr, Rb, K₂0, Na₂0 and CaO have been highly mobile, and their usefulness in petrogenetic modelling is extremely limited. In contrast, Zr, Nb, Y, LREE's, Cr, Ni, Ti0₂ P₂0₅ and Al₂0₃ have remained immobile. Ti/Zr and Ti/P ratios together constitute efficient discriminating variables for characterizing the different magma types. Lava compositions range from primitive Mg-rich tholeiites to rhyolites, the bulk being tholeiitic andesites. Al₂0₃ contents do not exceed 15%, a feature which reflects the tholeiitic, as opposed to calcalkaline, character of these lavas. Two magma-types are present within the Dominion Group, which is a typical example of bimodal volcanism. The Dominion basic lavas are overlain by the Dominion acid porphyries, with a limited amount of interfingering. The basic lava suite is highly fractionated, with compositions ranging from Mg-, Cr- and Ni-rich tholeiites (close to primary mantle melts) to evolved tholeiitic andesites. The most primitive liquids evolved by 45% fractional crystallization of hornblende, followed by a further 70% crystallization of an orthopyroxene-plagioclase assemblage containing up to 3% sulphides. The Dominion porphyries are rhyolitic, display very limited compositional variation, and probably represent a crustal melt related to the same magmatic event which produced the basic lavas. The only lavas from the Witwatersrand Supergroup present in the Klerksdorp area are those of the Crown Formation (Jeppestown amygdaloid). These are tholeiitic dacites which display extremely limited compositional variation, and are unrelated to any of the other magmas of the Witwatersrand triad. The Ventersdorp Supergroup comprises 4 magma-types: The Kliprivierberg Group lavas at the base are subdivisible into 3 sub-types on the basis of Zr contents. (Zr>11Oppm) are the most evolved. They are tholeiitic andesites which display fairly limited compositional variation. It is likely that more evolved compositions are present in other areas where the porphyritic lavas which characterize this unit are better developed. The overlying Orkney lavas are characterized by 110ppm>Zr>90ppm. They are tholeiitic andesites of similar composition to the Alberton lavas, but have lower incompatible element levels, higher siderophile element levels, and are of extremely uniform composition. The uppermost Loraine/Edenville lavas range from magnesian tholeiites to tholeiitic andesites. They are distinguished by Zr< 90ppm, and contain the most primitive magmas af the Witwatersrand triad, with up to 17,5% MgO, 2600ppm Cr, 600ppm Ni and M-values up to 77. The most primitive liquids evolved by 38% fractional crystallization of orthopyroxene ∓ chromite, followed by 35% fractional crystallization of an extract containing clinopyroxene and plagioclase. The absence of olivine precipitation is a result of the inherently high Si0₂ content of the magma. The Loraine/Edenville, Orkney and Alberton lavas do not lie on a common liquid line of descent, but are probably consanguinous. The Platberg Group overlies the Kliprivierberg Group, and has a coarse-clastic sedimentary unit, the Kameeldoorns Formation, at the base. Three petrographically distinct porphyritic lava sequences overlie the Kameeldoorns Formation, namely the informal "Goedgenoeg formation", the Makwassie quartz-feldspar porphyries and the Rietgat Formation. Despite petrographic differences, the Goedgenoeg and Rietgat lavas are chemically indistinguishable and thus form a single magma-type. The Makwassie porphyries are dacitic in composition with a high proportion of feldspar and quartz phenocrysts. Rational variation trends are attributed to a nett loss of Si0₂ during secondary alteration. The porphyries are probably of crustal origin. The Goedgenoeg/Rietgat lavas display unusual chemistry and a broad, irrational compositional spectrum. They contain very high incompatible element levels, high nonnative quartz, as well as high MgO, M-values, Cr and Ni relative to the other tholeiitic andesites of the Witwatersrand triad. It is tentatively suggested that they are hybrid magmas containing both crust and mantle components, the former possibly represented by the Makwassie porphyries. Field evidence suggests that Platberg volcanism commenced directly after Klipriviersberg volcanism ceased, and was accompanied by a period of enhanced tectonic activity. The Platberg lavas thus probably reflect a crustal melting cycle associated with the Klipriviersberg magmatic event. The Allanridge lavas are the youngest rocks of the Witwatersrand triad. They are separated from the Platberg Group by a unit of flat-lying sediments, the Bothaville Formation, which was deposited after an extended period of peneplanation. The Allanridge lavas form a separate magma-type. They are tholeiitic andesites of similar composition to the Alberton lavas, but have higher incompatible element levels and are not consanguinous. The compositional similarities amongst the basic magma-types of the Witwatersrand triad suggests that all were generated in an hydrous mantle. Interelement ratio differences between the various magma-types nevertheless support the concept that the mantle was chemically heterogeneous during the early Proterozoic.
- Full Text:
- Date Issued: 1985
The petrology of the basalts of the Dordabis Formation in the vicinity of Dordabis in central S.W.A./Namibia|
- Authors: Williams-Jones, Ian Eric
- Date: 1985 , 2013-03-14
- Subjects: Basalt -- Namibia , Petrology -- Namibia , Geochemistry -- Namibia
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5062 , http://hdl.handle.net/10962/d1013277
- Description: The late Proterozoic volcanic and sedimentary sequence in the Dordabis area SWA/Namibia has been named the Dordabis Formation and subdivided, on the basis of field, petrological and petrographic evidence, into the Opdam and Bitterwater Members. Relict phases including augite and minor plagioclase only occur in the Bitterwater metalavas, as recrystallisation is complete in the Opdam metal avas. The composition of the relict feldspars ranges from labradorite in the ophitic basalts to oligoclase in the blastoporphyritic metalavas. The feldspars in the Opdam member are albitic in composition (An content 0,0 to 1,7) . Epidote compositions are typical of those occurring in metabasic rocks. Samples with high-iron whole-rock compositions are accompanied by high concentrations of Fe3+ in concomitant epidotes. Sixty three samples were analysed using X-ray fluorescence spectrometry to determine concentrations of major and 16 trace elements. Although greenschist facies metamorphism, metasomatism and shearing have produced scatter in the more mobile element concentrations, variation trends in other elements closely resemble modelled low-pressure fractional crystallisation trends. The Dordabis metalavas are petrologically classified as sub-alkaline, tholeiitic continental basalts. Low K/Rb ratios and low ratios of less incompatible to more incompatible elements probably reflect a source that has either been metasomati ca lly enriched or that has undergone little previous partial melting. Overlapping whole-rock variation trends indicate that the generally more evolved Opdam and primitive tholeiitic Bittenwater lavas are cogenetic. A comparison of the Dordabis Formation with the Sinclair Sequence and the Koras Group shows that their ages, petrology, petrography, associ a ted sedimentary suites and depositional environments are similar. It is concluded that they may possibly be coeval equivalents.
- Full Text:
- Date Issued: 1985
- Authors: Williams-Jones, Ian Eric
- Date: 1985 , 2013-03-14
- Subjects: Basalt -- Namibia , Petrology -- Namibia , Geochemistry -- Namibia
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5062 , http://hdl.handle.net/10962/d1013277
- Description: The late Proterozoic volcanic and sedimentary sequence in the Dordabis area SWA/Namibia has been named the Dordabis Formation and subdivided, on the basis of field, petrological and petrographic evidence, into the Opdam and Bitterwater Members. Relict phases including augite and minor plagioclase only occur in the Bitterwater metalavas, as recrystallisation is complete in the Opdam metal avas. The composition of the relict feldspars ranges from labradorite in the ophitic basalts to oligoclase in the blastoporphyritic metalavas. The feldspars in the Opdam member are albitic in composition (An content 0,0 to 1,7) . Epidote compositions are typical of those occurring in metabasic rocks. Samples with high-iron whole-rock compositions are accompanied by high concentrations of Fe3+ in concomitant epidotes. Sixty three samples were analysed using X-ray fluorescence spectrometry to determine concentrations of major and 16 trace elements. Although greenschist facies metamorphism, metasomatism and shearing have produced scatter in the more mobile element concentrations, variation trends in other elements closely resemble modelled low-pressure fractional crystallisation trends. The Dordabis metalavas are petrologically classified as sub-alkaline, tholeiitic continental basalts. Low K/Rb ratios and low ratios of less incompatible to more incompatible elements probably reflect a source that has either been metasomati ca lly enriched or that has undergone little previous partial melting. Overlapping whole-rock variation trends indicate that the generally more evolved Opdam and primitive tholeiitic Bittenwater lavas are cogenetic. A comparison of the Dordabis Formation with the Sinclair Sequence and the Koras Group shows that their ages, petrology, petrography, associ a ted sedimentary suites and depositional environments are similar. It is concluded that they may possibly be coeval equivalents.
- Full Text:
- Date Issued: 1985
Turbidite-hosted gold deposits
- Authors: Leeming, Prudence Mary
- Date: 1985
- Subjects: Gold ores , Turbidites
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5010 , http://hdl.handle.net/10962/d1005939 , Gold ores , Turbidites
- Description: Turbidite-hosted gold deposits contribute a significant proportion to world lode gold production and have also provided substantial gold to alluvial resources. Turbidity current deposits occur throughout geological time within Archaean greenstone belts, Proterozoic orogenic belts and rifted passive continental margins, and Palaeozoic geosynclines. Representing the end member of the sedimentary cycle, turbidites have the attribute of preservation not only on an individual bed basis but also due to below wave base accumulation in submarine deeps. Cyclic deposition according to the Bouma sequence punctuates turbidite deposition by a series of diastems. Accumulation of organic, pelagic and chemical sediments may concentrate gold to protore enrichment levels i n a primary sedimentary environment. Dewatering during diagenesis and low-grade metamorphism under reducing conditions may redistribute gold with transport as low energy organo- and thio-complexes. Gold may precipitate with diagenetic pyrite and silica near black shale and/or partially replace fine carbonate detritus. Gold solubility increases with high grade amphibolite facies metamorphism (T 400ºC) when efficient leaching of gold and transport by simple chloro- and hydroxychloro - complexes to lower greenschist regions takes place. Reduced permeability of turbidite strata induces hydrofracturing which focuses dewatering solutions. Gold is deposited due to pressure and temperature decrease or local changes in physico - chemico conditions caused by the reaction of fluids with wall rocks (reactive beds in turbidites are predominantly carbonaceous strata). The largest of turbidite - hosted goldfields are confined to back -arc or marginal sea basins with restricted oceanic circulation. The richest concentrations of gold occur proximal to the original source within the greenschist facies formations lowermost in a thick turbidite sequence and exhibit strong combined structural and lithological association. Turbidites represent important strata for the concentration and preservation of gold not only during sedimentation and diagenesis but also during later deformation and metamorphism.
- Full Text:
- Date Issued: 1985
- Authors: Leeming, Prudence Mary
- Date: 1985
- Subjects: Gold ores , Turbidites
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5010 , http://hdl.handle.net/10962/d1005939 , Gold ores , Turbidites
- Description: Turbidite-hosted gold deposits contribute a significant proportion to world lode gold production and have also provided substantial gold to alluvial resources. Turbidity current deposits occur throughout geological time within Archaean greenstone belts, Proterozoic orogenic belts and rifted passive continental margins, and Palaeozoic geosynclines. Representing the end member of the sedimentary cycle, turbidites have the attribute of preservation not only on an individual bed basis but also due to below wave base accumulation in submarine deeps. Cyclic deposition according to the Bouma sequence punctuates turbidite deposition by a series of diastems. Accumulation of organic, pelagic and chemical sediments may concentrate gold to protore enrichment levels i n a primary sedimentary environment. Dewatering during diagenesis and low-grade metamorphism under reducing conditions may redistribute gold with transport as low energy organo- and thio-complexes. Gold may precipitate with diagenetic pyrite and silica near black shale and/or partially replace fine carbonate detritus. Gold solubility increases with high grade amphibolite facies metamorphism (T 400ºC) when efficient leaching of gold and transport by simple chloro- and hydroxychloro - complexes to lower greenschist regions takes place. Reduced permeability of turbidite strata induces hydrofracturing which focuses dewatering solutions. Gold is deposited due to pressure and temperature decrease or local changes in physico - chemico conditions caused by the reaction of fluids with wall rocks (reactive beds in turbidites are predominantly carbonaceous strata). The largest of turbidite - hosted goldfields are confined to back -arc or marginal sea basins with restricted oceanic circulation. The richest concentrations of gold occur proximal to the original source within the greenschist facies formations lowermost in a thick turbidite sequence and exhibit strong combined structural and lithological association. Turbidites represent important strata for the concentration and preservation of gold not only during sedimentation and diagenesis but also during later deformation and metamorphism.
- Full Text:
- Date Issued: 1985
An investigation of the groundwater seepage and irrigation return flow of the Middleton area of the Great Fish River
- Authors: Reynders, Anthony Gerard
- Date: 1984 , 2013-04-11
- Subjects: Irrigation -- South Africa -- Great Fish River , Seepage , Groundwater flow -- South Africa -- Great Fish River
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5035 , http://hdl.handle.net/10962/d1007380 , Irrigation -- South Africa -- Great Fish River , Seepage , Groundwater flow -- South Africa -- Great Fish River
- Description: From introduction: This study is concerned with the factors responsible for mineralisation of water in the Great Fish River, in particular the irrigation return flow and groundwater seepage components. A small irrigated area in the lower Fish River Basin was chosen for a detailed study of irrigation water input, groundwater and seepage water fluctuati ons, and the affect of soils and rocks on river water mineralisation. , KMBT_363 , Adobe Acrobat 9.53 Paper Capture Plug-in
- Full Text:
- Date Issued: 1984
- Authors: Reynders, Anthony Gerard
- Date: 1984 , 2013-04-11
- Subjects: Irrigation -- South Africa -- Great Fish River , Seepage , Groundwater flow -- South Africa -- Great Fish River
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5035 , http://hdl.handle.net/10962/d1007380 , Irrigation -- South Africa -- Great Fish River , Seepage , Groundwater flow -- South Africa -- Great Fish River
- Description: From introduction: This study is concerned with the factors responsible for mineralisation of water in the Great Fish River, in particular the irrigation return flow and groundwater seepage components. A small irrigated area in the lower Fish River Basin was chosen for a detailed study of irrigation water input, groundwater and seepage water fluctuati ons, and the affect of soils and rocks on river water mineralisation. , KMBT_363 , Adobe Acrobat 9.53 Paper Capture Plug-in
- Full Text:
- Date Issued: 1984
The geology, mineralogy and chemistry of the Grahamstown clay deposits
- Authors: Smuts, Johann, 1951-
- Date: 1984
- Subjects: Clay minerals -- South Africa -- Grahamstown , Mineralogy -- South Africa -- Grahamstown , Geochemistry -- South Africa -- Grahamstown
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5080 , http://hdl.handle.net/10962/d1015969
- Description: The Grahamstown clay deposits extend in a broad belt from 26°23 to 26°50 East longitude and from 33°15 to 33°22 South latitude along two distinct geomorphological features, the Grahamstown Peneplane (650 m) and the Coastal Plain (520m). The clay deposits traverse four different lithologies including the Bokkeveld Shale, Witteberg Shale, Dwyka Tillite and Ecca Shale. The two planes invariably have a covering of silcrete which is also present over most of the clay deposits except where erosion has taken place. X-ray fluorescence analysis shows that chemically there is a fairly wide variation between and witnin the deposits. The greatest variation is in the Si0₂/Al₂0₃ ratio which appears to be controlled by the parent lithology and to some extent by the amount of leaching. K²0 shows an increase in concentration with depth and therefore indicates the limits of hydrolysis and leaching and of the clay. X-ray diffraction study shows the Peneplane and Coastal Plain deposits to be quite distinct. The Peneplane deposits consist of kaolinite, illite and quartz and the Coastal Plain deposits of kaolinite, illite, quartz and pyrophyllite. The presence of pyrophyllite is not fully understood as there is no indication of major faulting, metamorphism or pyrophyllite in the parent rock. The pyrophyllite most probably represents a transformation product of kaolinite. The kaolinite from the various deposits shows a considerable variation in crystallinity in both the X-ray diffraction traces and electron photomicrographs. The most poorly crystalline kaolinites are from the Coastal Plain deposits and the difference in crystallinity is most probably due to differences in the degree of hydrolysis and the parent rock material in the case of the tillite. Genetically all of the deposits are residual types generated by hydrolysis and subsequent leaching of micas and feldspars. The principal elements leached are silicon, iron and potassium. The hydrolysis and leaching took place over a long period of time in the flat lying areas of the Peneplane and Coastal Plain. The deposits are exploited economically and the clay is used principally in the tile, pottery and whiteware industries with some usage in the paper, refractory and brickmaking industries. The price commanded by raw kaolin is not very high and as a result the clay industry in Grahamstown is not as viable economically as it could be.
- Full Text:
- Date Issued: 1984
- Authors: Smuts, Johann, 1951-
- Date: 1984
- Subjects: Clay minerals -- South Africa -- Grahamstown , Mineralogy -- South Africa -- Grahamstown , Geochemistry -- South Africa -- Grahamstown
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5080 , http://hdl.handle.net/10962/d1015969
- Description: The Grahamstown clay deposits extend in a broad belt from 26°23 to 26°50 East longitude and from 33°15 to 33°22 South latitude along two distinct geomorphological features, the Grahamstown Peneplane (650 m) and the Coastal Plain (520m). The clay deposits traverse four different lithologies including the Bokkeveld Shale, Witteberg Shale, Dwyka Tillite and Ecca Shale. The two planes invariably have a covering of silcrete which is also present over most of the clay deposits except where erosion has taken place. X-ray fluorescence analysis shows that chemically there is a fairly wide variation between and witnin the deposits. The greatest variation is in the Si0₂/Al₂0₃ ratio which appears to be controlled by the parent lithology and to some extent by the amount of leaching. K²0 shows an increase in concentration with depth and therefore indicates the limits of hydrolysis and leaching and of the clay. X-ray diffraction study shows the Peneplane and Coastal Plain deposits to be quite distinct. The Peneplane deposits consist of kaolinite, illite and quartz and the Coastal Plain deposits of kaolinite, illite, quartz and pyrophyllite. The presence of pyrophyllite is not fully understood as there is no indication of major faulting, metamorphism or pyrophyllite in the parent rock. The pyrophyllite most probably represents a transformation product of kaolinite. The kaolinite from the various deposits shows a considerable variation in crystallinity in both the X-ray diffraction traces and electron photomicrographs. The most poorly crystalline kaolinites are from the Coastal Plain deposits and the difference in crystallinity is most probably due to differences in the degree of hydrolysis and the parent rock material in the case of the tillite. Genetically all of the deposits are residual types generated by hydrolysis and subsequent leaching of micas and feldspars. The principal elements leached are silicon, iron and potassium. The hydrolysis and leaching took place over a long period of time in the flat lying areas of the Peneplane and Coastal Plain. The deposits are exploited economically and the clay is used principally in the tile, pottery and whiteware industries with some usage in the paper, refractory and brickmaking industries. The price commanded by raw kaolin is not very high and as a result the clay industry in Grahamstown is not as viable economically as it could be.
- Full Text:
- Date Issued: 1984
The petrology of the Merensky cyclic unit and associated rocks and their significance in the evolution of the Western Bushveld Complex
- Authors: Kruger, Floris Johan
- Date: 1984
- Subjects: Petrology -- Africa, Southern Petrofabric analysis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5006 , http://hdl.handle.net/10962/d1005636
- Description: A brief review of the various models proposed to account for the Bushveld Complex shows that there are two main hypotheses. These are the Multiple Intrusion hypothesis and the In Situ Crystallization hypothesis. The latter also allows for multiple additions to the crystallizing magma, and several variants involving the number of these inputs , their composition, volume and timing have been proposed. To facilitate description and investigation of the study section, the stratigraphic nomenclature of this part of the Rustenberg Layered Suite is revised and clarified. It is proposed that the boundary between the Critical Zone and Main Zone be placed at the base of the Merensky cyclic unit, and thus the whole of the Merensky and Bastard cyclic units are included in the Main Zone. Furthermore, the extremely confused terminology for smaller units within the Merensky and Bastard cyclic units is resolved by discarding the term Reef as a formal term and substituting lithological terms such as Merensky pegmatoid, Merensky pyroxenite, Bastard pyroxenite and Merensky mottled anorthosite etc. It is recommended that the term Reef be retained as an informal term to designate the mineralized horizon which may be mined, regardless of lithology. The term "pegmatoid" is restricted to stratiform or lensoid masses of coarse grained feldspathic pyroxenite or harzburgite which are part of the layered sequence. The transgressive vertical pipe-like, coarse-grained ultramafic "iron-rich bodies are termed "ultramafic pegmatites ". The main features of the Merensky and Bastard cyclic units are the regular chemical and mineralogical changes that occur with respect to stratigraphic height in these units. In the Merensky cyclic unit there is a smooth iron enrichment in the orthopyroxenes upward in the succession and a transition from pyroxenite at the base to mottled anorthosite at the top of the unit. The Bastard cyclic unit is broadly similar to the Merensky cyclic unit. A variety of textures and chemical features are in disequilibrium in some samples but not in others, and great complexity is evident wh en individual samples are studied in detail. The initial ⁸⁷Sr/⁸⁶Sr ratios of plagioclase separates and whole rocks from the study section show a distinct step-like increase in the Merensky cyclic unit to .70806 at the base of the, Merensky cyclic unit to .70806 at the base of the Bastard cyclic unit. In contrast , samples from below the Merensky cyclic unit have a constant initial Sr-isotopic ratio, as do the samples from the Bastard cyclic unit. These isotopic and chemical data, and available published geologic relationships suggest that a major new influx of basic magma occurred after the Footwall unit was deposited and that this mixed with the residual magma in the chamber and then precipitated the Merensky and Bastard cyclic units. The crystal settling theory as outlined by Wager and Brown (1968) fails to account for the chemical and stratigraphic variations observed in the study section. The theory of bottom crystallization, initially proposed by Jackson (1961), more adequately explains the features observed. Applying a model outlined by Irvine (1980a & b), it has been established from chemical data, that the Merensky cyclic unit crystallized from a magma layer with a thickness roughly equivalent to the average thickness of the cyclic unit itself (±10m). A similar exercise on the Bastard unit was not possible. The formation of the Footwall unit is still enigmatic. Infiltration metasomatism and sintering can modify the petrographic and chemical characteristics of rocks and minerals after deposition at the liquidus stage. During the solidification of the crystal mush a separate vapour phase may form in the crystal mush, which could move up through the crystal pile. This process may ultimately be responsible for the generation of potholes and pegmatoidal horizons, such as the Merensky pegmatoid. The upward increase in the initial ⁸⁷Sr/⁸⁶Sr ratio within the Merensky cyclic unit is strong evidence that infiltration metasomatism has played an important part in the generation of the Merensky cyclic unit. This process, coupled with fluid enrichment, may also result in the formation of pegmatoid layers. Sintering appears to have been a common process in the mottled anorthosites of the study section and may have severely reduced the amount of trapped interstitial liquid in these rocks.
- Full Text:
- Date Issued: 1984
- Authors: Kruger, Floris Johan
- Date: 1984
- Subjects: Petrology -- Africa, Southern Petrofabric analysis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5006 , http://hdl.handle.net/10962/d1005636
- Description: A brief review of the various models proposed to account for the Bushveld Complex shows that there are two main hypotheses. These are the Multiple Intrusion hypothesis and the In Situ Crystallization hypothesis. The latter also allows for multiple additions to the crystallizing magma, and several variants involving the number of these inputs , their composition, volume and timing have been proposed. To facilitate description and investigation of the study section, the stratigraphic nomenclature of this part of the Rustenberg Layered Suite is revised and clarified. It is proposed that the boundary between the Critical Zone and Main Zone be placed at the base of the Merensky cyclic unit, and thus the whole of the Merensky and Bastard cyclic units are included in the Main Zone. Furthermore, the extremely confused terminology for smaller units within the Merensky and Bastard cyclic units is resolved by discarding the term Reef as a formal term and substituting lithological terms such as Merensky pegmatoid, Merensky pyroxenite, Bastard pyroxenite and Merensky mottled anorthosite etc. It is recommended that the term Reef be retained as an informal term to designate the mineralized horizon which may be mined, regardless of lithology. The term "pegmatoid" is restricted to stratiform or lensoid masses of coarse grained feldspathic pyroxenite or harzburgite which are part of the layered sequence. The transgressive vertical pipe-like, coarse-grained ultramafic "iron-rich bodies are termed "ultramafic pegmatites ". The main features of the Merensky and Bastard cyclic units are the regular chemical and mineralogical changes that occur with respect to stratigraphic height in these units. In the Merensky cyclic unit there is a smooth iron enrichment in the orthopyroxenes upward in the succession and a transition from pyroxenite at the base to mottled anorthosite at the top of the unit. The Bastard cyclic unit is broadly similar to the Merensky cyclic unit. A variety of textures and chemical features are in disequilibrium in some samples but not in others, and great complexity is evident wh en individual samples are studied in detail. The initial ⁸⁷Sr/⁸⁶Sr ratios of plagioclase separates and whole rocks from the study section show a distinct step-like increase in the Merensky cyclic unit to .70806 at the base of the, Merensky cyclic unit to .70806 at the base of the Bastard cyclic unit. In contrast , samples from below the Merensky cyclic unit have a constant initial Sr-isotopic ratio, as do the samples from the Bastard cyclic unit. These isotopic and chemical data, and available published geologic relationships suggest that a major new influx of basic magma occurred after the Footwall unit was deposited and that this mixed with the residual magma in the chamber and then precipitated the Merensky and Bastard cyclic units. The crystal settling theory as outlined by Wager and Brown (1968) fails to account for the chemical and stratigraphic variations observed in the study section. The theory of bottom crystallization, initially proposed by Jackson (1961), more adequately explains the features observed. Applying a model outlined by Irvine (1980a & b), it has been established from chemical data, that the Merensky cyclic unit crystallized from a magma layer with a thickness roughly equivalent to the average thickness of the cyclic unit itself (±10m). A similar exercise on the Bastard unit was not possible. The formation of the Footwall unit is still enigmatic. Infiltration metasomatism and sintering can modify the petrographic and chemical characteristics of rocks and minerals after deposition at the liquidus stage. During the solidification of the crystal mush a separate vapour phase may form in the crystal mush, which could move up through the crystal pile. This process may ultimately be responsible for the generation of potholes and pegmatoidal horizons, such as the Merensky pegmatoid. The upward increase in the initial ⁸⁷Sr/⁸⁶Sr ratio within the Merensky cyclic unit is strong evidence that infiltration metasomatism has played an important part in the generation of the Merensky cyclic unit. This process, coupled with fluid enrichment, may also result in the formation of pegmatoid layers. Sintering appears to have been a common process in the mottled anorthosites of the study section and may have severely reduced the amount of trapped interstitial liquid in these rocks.
- Full Text:
- Date Issued: 1984
A review of asbestos resources
- Authors: Abbott, Paul
- Date: 1983
- Subjects: Asbestos Asbestos -- Geology Silicate minerals Mineralogy Chrysotile
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4910 , http://hdl.handle.net/10962/d1001570
- Full Text:
- Date Issued: 1983
- Authors: Abbott, Paul
- Date: 1983
- Subjects: Asbestos Asbestos -- Geology Silicate minerals Mineralogy Chrysotile
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4910 , http://hdl.handle.net/10962/d1001570
- Full Text:
- Date Issued: 1983
Economic geology of sulphide nickel deposits
- Authors: Harrison, P A
- Date: 1983
- Subjects: Nickel sulfide , Ore deposits , Geology, Economic , Silicate minerals , Geochemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5022 , http://hdl.handle.net/10962/d1006349
- Description: From Chapter 1: It has been a long standing belief that many nickel sulphide ores are derivatives of magmatic processes in ultramafic and mafic rocks, and that they segregate from these magmas as immiscible sulphide droplets which are then concentrated into an orebody by gravitational settling either during intrusion or extrusion, or during the early stages of crystallization of the magma (Naldrett, 1981). Some geologists however, have suggested alternative mechanisms to explain the concentration of nickeliferous sulphides in the mafic and ultramafic hosts. These include hydrothermal replacement (Fleet, 1977), exhalative volcanic processes (Lusk, 1976), or major metamorphic upgrading of low grade, initially magmatic deposits (Barrett et al., 1977). It is not the purpose of this study to verify or disprove these hypotheses, but in so far as the initial concentration of sulphides in most deposits is concerned, these effects are relatively unimportant (Naldrett, 1981). The nickel sulphide ores associated with these mafic and ultramafic host rocks, invariably consist of nickeliferous pyrrhotite as the dominant phase, together with lesser, but variable, amounts of magnetite, pentlandite, chalcopyrite, cubanite, and platinum group elements (Reynolds, 1982).
- Full Text:
- Date Issued: 1983
- Authors: Harrison, P A
- Date: 1983
- Subjects: Nickel sulfide , Ore deposits , Geology, Economic , Silicate minerals , Geochemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5022 , http://hdl.handle.net/10962/d1006349
- Description: From Chapter 1: It has been a long standing belief that many nickel sulphide ores are derivatives of magmatic processes in ultramafic and mafic rocks, and that they segregate from these magmas as immiscible sulphide droplets which are then concentrated into an orebody by gravitational settling either during intrusion or extrusion, or during the early stages of crystallization of the magma (Naldrett, 1981). Some geologists however, have suggested alternative mechanisms to explain the concentration of nickeliferous sulphides in the mafic and ultramafic hosts. These include hydrothermal replacement (Fleet, 1977), exhalative volcanic processes (Lusk, 1976), or major metamorphic upgrading of low grade, initially magmatic deposits (Barrett et al., 1977). It is not the purpose of this study to verify or disprove these hypotheses, but in so far as the initial concentration of sulphides in most deposits is concerned, these effects are relatively unimportant (Naldrett, 1981). The nickel sulphide ores associated with these mafic and ultramafic host rocks, invariably consist of nickeliferous pyrrhotite as the dominant phase, together with lesser, but variable, amounts of magnetite, pentlandite, chalcopyrite, cubanite, and platinum group elements (Reynolds, 1982).
- Full Text:
- Date Issued: 1983
Geochemical exploration in arid and semi-arid environments
- Authors: Van Berkel, Ferdinand
- Date: 1983 , 2013-04-02
- Subjects: Geochemical prospecting , Arid regions
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4920 , http://hdl.handle.net/10962/d1004389 , Geochemical prospecting , Arid regions
- Description: Anomalous element distributions within the regolith result from chemical adjustments of the earth's surface to prevailing climatic conditions. Because of the lack of moisture in the arid environment, chemical equilibrium related to paleoclimates is largely maintained. Mechanical or clastic dispersion dominates arid weathering and hence the exploration approach is largely dictated by the degree of preservation of the paleoregolith. Arid environment geochemists thus have to contend with surface materials ranging from laterite and calcrete in areas where the imprint of aridity is minimal, to more conventional sample media such as bedrock, stream sediment and lithic soils in actively dissecting areas. Extraction techniques are designed specifically to isolate clastic dispersion trains. Thick mantles of aeolian and water-borne overburden characterise desert lowlands and are a challenge to the exploration geochemist. Techniques showing the most promise in these areas include groundwater geochemistry, vapour geochemistry, surface microlayer geochemistry, geobotany and biogeochemistry which attempt to isolate gaseous and weak hydromorphic, ore-related trace-element dispersions. Termite mound sampling yields convincing results and appears to be an under-utilised geochemical approach. , KMBT_363 , Adobe Acrobat 9.53 Paper Capture Plug-in
- Full Text:
- Date Issued: 1983
- Authors: Van Berkel, Ferdinand
- Date: 1983 , 2013-04-02
- Subjects: Geochemical prospecting , Arid regions
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4920 , http://hdl.handle.net/10962/d1004389 , Geochemical prospecting , Arid regions
- Description: Anomalous element distributions within the regolith result from chemical adjustments of the earth's surface to prevailing climatic conditions. Because of the lack of moisture in the arid environment, chemical equilibrium related to paleoclimates is largely maintained. Mechanical or clastic dispersion dominates arid weathering and hence the exploration approach is largely dictated by the degree of preservation of the paleoregolith. Arid environment geochemists thus have to contend with surface materials ranging from laterite and calcrete in areas where the imprint of aridity is minimal, to more conventional sample media such as bedrock, stream sediment and lithic soils in actively dissecting areas. Extraction techniques are designed specifically to isolate clastic dispersion trains. Thick mantles of aeolian and water-borne overburden characterise desert lowlands and are a challenge to the exploration geochemist. Techniques showing the most promise in these areas include groundwater geochemistry, vapour geochemistry, surface microlayer geochemistry, geobotany and biogeochemistry which attempt to isolate gaseous and weak hydromorphic, ore-related trace-element dispersions. Termite mound sampling yields convincing results and appears to be an under-utilised geochemical approach. , KMBT_363 , Adobe Acrobat 9.53 Paper Capture Plug-in
- Full Text:
- Date Issued: 1983
Geology and mine planning
- Authors: Maturana-Bascope, M
- Date: 1983
- Subjects: Geology , Mining geology , Geology, Economics
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5027 , http://hdl.handle.net/10962/d1006896
- Description: From introduction: This dissertation aims to review the main aspects involved in mine planning, in order to provide the geologists with the main criteria to obtain a preliminary estimate of the minability of an in situ orebody, and to make the geologists aware of the information they can contribute to the planning engineers. Furthermore, an understanding of the basic principles behind mine planning may help the exploration geologist to select more realistic targets of exploration.
- Full Text:
- Date Issued: 1983
- Authors: Maturana-Bascope, M
- Date: 1983
- Subjects: Geology , Mining geology , Geology, Economics
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5027 , http://hdl.handle.net/10962/d1006896
- Description: From introduction: This dissertation aims to review the main aspects involved in mine planning, in order to provide the geologists with the main criteria to obtain a preliminary estimate of the minability of an in situ orebody, and to make the geologists aware of the information they can contribute to the planning engineers. Furthermore, an understanding of the basic principles behind mine planning may help the exploration geologist to select more realistic targets of exploration.
- Full Text:
- Date Issued: 1983
Geology of the central and southern domains of the Koras Group, northern Cape Province
- Sanderson-Damstra, Christopher Gerald
- Authors: Sanderson-Damstra, Christopher Gerald
- Date: 1983 , 2013-04-17
- Subjects: Geology -- South Africa -- Cape of Good Hope
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5017 , http://hdl.handle.net/10962/d1006203 , Geology -- South Africa -- Cape of Good Hope
- Description: The Central and Southern Domains of the Koras Group, situated on the Doornberg Lineament, are the structurally preserved remnants of a once more widespread late-syntectonic cover sequence. Detailed examination of the field relationships, lithology and petrography together with new geochemical data (30 analyses) has resulted in the proposal of a new geological succession consisting mainly of two cycles of bimodal basaltic-rhyolitic volcanics with interbedded, immature conglomerates and lithic greywackes. These two cycles, named the Boomrivier and Leeudraai Formations, are overlain by the immature, polymictic orthoconglomerates and red arkosic sandstones of the Kalkpunt Formation. The first volcanic cycle commenced with the Lambrechtsdrif basaltic andesites and was followed, after a short hiatus, by the Swartkopsleegte rhyodacites. The second cycle comprises the Rouxville basalts and basaltic andesites and the Swartkop and Kenilworth rhyolites. Field evidence suggests that eruption of the rhyolitic and basaltic volcanics in the second cycle was contemporaneous. Geochemically, the volcanics can be classified as an "average-K" to high-K, tholeiitic, subalkaline association which exhibits general similarities to other Southern African bimodal associations e.g., the tholeiitic lavas of the Wilgenhoutsdrif Group. The Koras Group is petrologically similar to the Sinclair Sequence which is presently considered to be its coeval equivalent, but the dominantly calc-alkaline character of the Sinclair rocks distinguishes them from the dominantly tholeiitic Koras lavas. In a short literature review, the four main hypotheses for the petrogenesis of bimodal associations: liquid immiscibility, crystal fractionation, two-stage partial melting and separate magma sources, are described and the most feasible explanation for the origin of the Koras lavas is thought to be a "separate magma source" hypothesis in which two cycles of mantle-derived basalts and crustal-derived rhyolites were produced in a zone of high heat flow and erupted in an area of crustal weakness. The middle- or late-Proterozoic Koras Group was formed during unstable tectonic conditions, in a depositional setting that was probably controlled by late folding of the underlying pre-Koras sequences as well as the major strike-slip movement and subordinate dip-slip faulting in the Doornberg Lineament.
- Full Text:
- Date Issued: 1983
- Authors: Sanderson-Damstra, Christopher Gerald
- Date: 1983 , 2013-04-17
- Subjects: Geology -- South Africa -- Cape of Good Hope
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5017 , http://hdl.handle.net/10962/d1006203 , Geology -- South Africa -- Cape of Good Hope
- Description: The Central and Southern Domains of the Koras Group, situated on the Doornberg Lineament, are the structurally preserved remnants of a once more widespread late-syntectonic cover sequence. Detailed examination of the field relationships, lithology and petrography together with new geochemical data (30 analyses) has resulted in the proposal of a new geological succession consisting mainly of two cycles of bimodal basaltic-rhyolitic volcanics with interbedded, immature conglomerates and lithic greywackes. These two cycles, named the Boomrivier and Leeudraai Formations, are overlain by the immature, polymictic orthoconglomerates and red arkosic sandstones of the Kalkpunt Formation. The first volcanic cycle commenced with the Lambrechtsdrif basaltic andesites and was followed, after a short hiatus, by the Swartkopsleegte rhyodacites. The second cycle comprises the Rouxville basalts and basaltic andesites and the Swartkop and Kenilworth rhyolites. Field evidence suggests that eruption of the rhyolitic and basaltic volcanics in the second cycle was contemporaneous. Geochemically, the volcanics can be classified as an "average-K" to high-K, tholeiitic, subalkaline association which exhibits general similarities to other Southern African bimodal associations e.g., the tholeiitic lavas of the Wilgenhoutsdrif Group. The Koras Group is petrologically similar to the Sinclair Sequence which is presently considered to be its coeval equivalent, but the dominantly calc-alkaline character of the Sinclair rocks distinguishes them from the dominantly tholeiitic Koras lavas. In a short literature review, the four main hypotheses for the petrogenesis of bimodal associations: liquid immiscibility, crystal fractionation, two-stage partial melting and separate magma sources, are described and the most feasible explanation for the origin of the Koras lavas is thought to be a "separate magma source" hypothesis in which two cycles of mantle-derived basalts and crustal-derived rhyolites were produced in a zone of high heat flow and erupted in an area of crustal weakness. The middle- or late-Proterozoic Koras Group was formed during unstable tectonic conditions, in a depositional setting that was probably controlled by late folding of the underlying pre-Koras sequences as well as the major strike-slip movement and subordinate dip-slip faulting in the Doornberg Lineament.
- Full Text:
- Date Issued: 1983
Metallogenetic evolution of the Canadian Cordilleran Orogen
- Authors: Mathe, H L M
- Date: 1983
- Subjects: Orogeny -- Canadian Cordillera , Plate tectonics -- Canadian Cordillera , Metallogeny -- Canadian Cordillera , Geology, Structural -- Canadian Cordillera
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5025 , http://hdl.handle.net/10962/d1006890
- Description: From Introduction: The Canadian Cordilleran Orogenic Belt forms part of the circum-Pacific orogenic zone. It underlies an area of about 1,54 million sq. kilometres, is over 2400 kilometres long and 800 kilometres wide. The region is characteristically mountainous, much of it glaciated and alpine, containing plateaux, trenches, valleys, and fjords. The mountains, in general, rise to elevations between 2100 m and 3600 m above sea level, although Mount Logan in the St. Elias Mountains attains an altitude of 6000 m. The Canadian Cordillera is divided into two dominant orogenic belts: the eastern Columbian Orogenic Belt comprising defonned miogeosynclinal rocks and the western Pacific Orogenic Belt comprising allochthonous eugeosynclinal rocks. The Cordillera is further subdivided into five longitudinal tectonic belts within which rocks are broadly similar in type, age, and history. These belts are, from east to west: the Rocky Mountain Belt, the Omineca Crystalline Belt, the Intermontane Belt, the Coast Plutonic Complex, and the Insular Belt (Wheeler et al., 1972a). The Canadian Cordillera is important in that it contains: one of the world's largest lead-zinc-silver mine, Sullivan; the second-largest molybdenum mine, Endako; one of the most important concentrations of porphyry copper deposits, Highland Valley; Canada's largest tungsten mines, Cantung and Mactung; and Canada's second-largest silver district, Keno Hill (Sutherland Brown et a1., 1971). In addition, it contains several large massive sulphide and lead-zinc deposits.
- Full Text:
- Date Issued: 1983
- Authors: Mathe, H L M
- Date: 1983
- Subjects: Orogeny -- Canadian Cordillera , Plate tectonics -- Canadian Cordillera , Metallogeny -- Canadian Cordillera , Geology, Structural -- Canadian Cordillera
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5025 , http://hdl.handle.net/10962/d1006890
- Description: From Introduction: The Canadian Cordilleran Orogenic Belt forms part of the circum-Pacific orogenic zone. It underlies an area of about 1,54 million sq. kilometres, is over 2400 kilometres long and 800 kilometres wide. The region is characteristically mountainous, much of it glaciated and alpine, containing plateaux, trenches, valleys, and fjords. The mountains, in general, rise to elevations between 2100 m and 3600 m above sea level, although Mount Logan in the St. Elias Mountains attains an altitude of 6000 m. The Canadian Cordillera is divided into two dominant orogenic belts: the eastern Columbian Orogenic Belt comprising defonned miogeosynclinal rocks and the western Pacific Orogenic Belt comprising allochthonous eugeosynclinal rocks. The Cordillera is further subdivided into five longitudinal tectonic belts within which rocks are broadly similar in type, age, and history. These belts are, from east to west: the Rocky Mountain Belt, the Omineca Crystalline Belt, the Intermontane Belt, the Coast Plutonic Complex, and the Insular Belt (Wheeler et al., 1972a). The Canadian Cordillera is important in that it contains: one of the world's largest lead-zinc-silver mine, Sullivan; the second-largest molybdenum mine, Endako; one of the most important concentrations of porphyry copper deposits, Highland Valley; Canada's largest tungsten mines, Cantung and Mactung; and Canada's second-largest silver district, Keno Hill (Sutherland Brown et a1., 1971). In addition, it contains several large massive sulphide and lead-zinc deposits.
- Full Text:
- Date Issued: 1983
Metallogenic evolution of the southern Appalachian Orogenic Belt and Mississippi Valley
- Authors: Maassen, Larry W
- Date: 1983 , 2013-04-03
- Subjects: Metallogeny -- Appalachian Region , Metallogeny -- Mississippi River Valley , Plate tectonics -- Appalachian Region , Plate tectonics -- Mississippi River Valley
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5018 , http://hdl.handle.net/10962/d1006210 , Metallogeny -- Appalachian Region , Metallogeny -- Mississippi River Valley , Plate tectonics -- Appalachian Region , Plate tectonics -- Mississippi River Valley
- Description: Plate tectonic theory provides logical explanations for the major tectonic events in the eastern US during Paleozoic time. The details of these tectonic events are becoming more apparent with the accumulation of new data, especially radiometric age dates. When plate tectonic theory is applied to specific tectonic events for which there is no substantial evidence, such as intracontinental hotspot rifting environments and Precambrian subduction zones, the proposed models may become very speculative. A misconception concerning the geology of the central US is that this region is structurally stable. However, geologists are currently paying considerable attention to the interlocking network of faults that in a general way follow the 38th parallel of latitude from west-central Virginia into Central Missouri (and may extend farther to the east and west). Most of the displacement along this zone occurred during the Precambrian, but different parts have moved during several periods of post-Precambrian time. In the basement the lineament may be a wide fracture zone that extends deep into the crust and is thus responsible for the magmatic iron deposits of the Southeast Missouri and may be either directly or indirectly responsible for the localization of the Mississippi Valley type deposits that occur sporadically along its length. Whether or not plate-tectonic processes operated during the Precambrian is open to speculation and the lineament may or may not be related to plate tectonic activity, but it is obvious that throughout time inherent zones of weakness are important in the localization of ore deposits. The occurrence of several major mineral districts at the intersections of the 38th parallel lineament with other major structural features, particularly in some uplifted areas and fault zone intersections, suggests that other similar structural uplifts and fault-zone intersections should be investigated for undiscovered new districts or extensions of known districts. Small uneconomic mineral occurrences along fault zones intersecting the lineament may merit further examination as they may be indications of undiscovered deposits at depth. The overall tectonic environment in the Appalachian region was an important control on the localization of massive sulfide, gold, titanium, and tungsten deposits. The deposits occur in clusters, either in Late Precambrian spreading centers and associated rift systems related to the breakup of proto-Pangea, or in Eocambrian and Devonian low-potassium tholeiitic volcanic and plutonic rocks associated with the volcanic island arc systems which developed during the closing of the Iapetus Ocean. Feiss and Hauck (1980) are confident that moderate sized (1-10 million ton) massive sulfide deposits are yet to be found at depth in these regions of the southern Appalachians, but large (greater than 20 million ton) massive sulfide deposits are unlikely to exist. The Mississippi Valley carbonate-hosted deposits of lead-zinc-baritefluorite, that occur to some extent throughout the Paleozoic section, and the Silurian "Clinton" iron ores owe their origin and distribution to normal sedimentary and diagenetic processes resulting from the transgressions of the epeiric seas. Others, such as the residual deposits of managnese iron, and aluminum, owe their existence to the afore mentioned processes, but must also have had subsequent exposure to the concentrating mechanism of weathering in a stable environment. The Mississippi Valley type occur primarily around paleo-basement highs and paleoshorelines; therefore, the formation of domes and arches within the continental interior during bathygenic episodes was a major factor controlling the localization of these deposits. These broad upwarps were preferential sites for reefal development and facies changes, and, during epeirogenic periods, these positive features have resulted in erosion and karsting of the the carbonate rocks by meteoric waters and have thus been prepared for mineralization. Deposits of this type are most common below a pre-Middle Ordovician unconformity and should be sought along major domes and arches, and along major lineaments. The association of Applachian type deposits with arches is indeterminate because a structure as subtle as an arch would be difficult to detect following overprinting by the deformation of the Alleghany orogeny; however, there is no reason to suspect that this type of positive feature did not play a role in their location. In conclusion, plate movements were a major control on the Paleozoic tectonic history of the eastern US and were also the primary control on the localization of the base metal, gold, tungsten, chromite, and titanium deposits of the southern Appalachians. However, important sedimentary and diagenetic deposits were localized primarily by arch, dome, and basin development during bathygenic episodes. Whether these submergent episodes are the result of plate motion or whether plate motion is indirectly related to submergent episodes, as suggested by Sloss and Speed (1974), remains a problem that needs to be investigated and debated further. , KMBT_363 , Adobe Acrobat 9.53 Paper Capture Plug-in
- Full Text:
- Date Issued: 1983
- Authors: Maassen, Larry W
- Date: 1983 , 2013-04-03
- Subjects: Metallogeny -- Appalachian Region , Metallogeny -- Mississippi River Valley , Plate tectonics -- Appalachian Region , Plate tectonics -- Mississippi River Valley
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5018 , http://hdl.handle.net/10962/d1006210 , Metallogeny -- Appalachian Region , Metallogeny -- Mississippi River Valley , Plate tectonics -- Appalachian Region , Plate tectonics -- Mississippi River Valley
- Description: Plate tectonic theory provides logical explanations for the major tectonic events in the eastern US during Paleozoic time. The details of these tectonic events are becoming more apparent with the accumulation of new data, especially radiometric age dates. When plate tectonic theory is applied to specific tectonic events for which there is no substantial evidence, such as intracontinental hotspot rifting environments and Precambrian subduction zones, the proposed models may become very speculative. A misconception concerning the geology of the central US is that this region is structurally stable. However, geologists are currently paying considerable attention to the interlocking network of faults that in a general way follow the 38th parallel of latitude from west-central Virginia into Central Missouri (and may extend farther to the east and west). Most of the displacement along this zone occurred during the Precambrian, but different parts have moved during several periods of post-Precambrian time. In the basement the lineament may be a wide fracture zone that extends deep into the crust and is thus responsible for the magmatic iron deposits of the Southeast Missouri and may be either directly or indirectly responsible for the localization of the Mississippi Valley type deposits that occur sporadically along its length. Whether or not plate-tectonic processes operated during the Precambrian is open to speculation and the lineament may or may not be related to plate tectonic activity, but it is obvious that throughout time inherent zones of weakness are important in the localization of ore deposits. The occurrence of several major mineral districts at the intersections of the 38th parallel lineament with other major structural features, particularly in some uplifted areas and fault zone intersections, suggests that other similar structural uplifts and fault-zone intersections should be investigated for undiscovered new districts or extensions of known districts. Small uneconomic mineral occurrences along fault zones intersecting the lineament may merit further examination as they may be indications of undiscovered deposits at depth. The overall tectonic environment in the Appalachian region was an important control on the localization of massive sulfide, gold, titanium, and tungsten deposits. The deposits occur in clusters, either in Late Precambrian spreading centers and associated rift systems related to the breakup of proto-Pangea, or in Eocambrian and Devonian low-potassium tholeiitic volcanic and plutonic rocks associated with the volcanic island arc systems which developed during the closing of the Iapetus Ocean. Feiss and Hauck (1980) are confident that moderate sized (1-10 million ton) massive sulfide deposits are yet to be found at depth in these regions of the southern Appalachians, but large (greater than 20 million ton) massive sulfide deposits are unlikely to exist. The Mississippi Valley carbonate-hosted deposits of lead-zinc-baritefluorite, that occur to some extent throughout the Paleozoic section, and the Silurian "Clinton" iron ores owe their origin and distribution to normal sedimentary and diagenetic processes resulting from the transgressions of the epeiric seas. Others, such as the residual deposits of managnese iron, and aluminum, owe their existence to the afore mentioned processes, but must also have had subsequent exposure to the concentrating mechanism of weathering in a stable environment. The Mississippi Valley type occur primarily around paleo-basement highs and paleoshorelines; therefore, the formation of domes and arches within the continental interior during bathygenic episodes was a major factor controlling the localization of these deposits. These broad upwarps were preferential sites for reefal development and facies changes, and, during epeirogenic periods, these positive features have resulted in erosion and karsting of the the carbonate rocks by meteoric waters and have thus been prepared for mineralization. Deposits of this type are most common below a pre-Middle Ordovician unconformity and should be sought along major domes and arches, and along major lineaments. The association of Applachian type deposits with arches is indeterminate because a structure as subtle as an arch would be difficult to detect following overprinting by the deformation of the Alleghany orogeny; however, there is no reason to suspect that this type of positive feature did not play a role in their location. In conclusion, plate movements were a major control on the Paleozoic tectonic history of the eastern US and were also the primary control on the localization of the base metal, gold, tungsten, chromite, and titanium deposits of the southern Appalachians. However, important sedimentary and diagenetic deposits were localized primarily by arch, dome, and basin development during bathygenic episodes. Whether these submergent episodes are the result of plate motion or whether plate motion is indirectly related to submergent episodes, as suggested by Sloss and Speed (1974), remains a problem that needs to be investigated and debated further. , KMBT_363 , Adobe Acrobat 9.53 Paper Capture Plug-in
- Full Text:
- Date Issued: 1983
The concept of grade in mineral deposits
- Authors: Esterhuizen, Anton G
- Date: 1983 , 2013-04-04
- Subjects: Mines and mineral resources , Ore deposits , Mineralogy , Geology, Economic
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5020 , http://hdl.handle.net/10962/d1006331 , Mines and mineral resources , Ore deposits , Mineralogy , Geology, Economic
- Description: The grade of a mineral deposit is determined by the effectiveness of a geological ore forming process, which is the result of the interaction between an ore forming mechanism and the environment in which it operates. Properties of a mineral deposit controlled by ore forming processes include the distribution, density and nature of ore minerals and gangue, and the metal content and impurities of the ore minerals. More efficient ore forming processes tend to develop in the larger mineralizing systems giving rise to richer deposits. As the geological environment within which a mineral deposit evolves becomes more complex a greater number of variables interact to determine the grade of the deposit. This is reflected in the greater variability of the grade distribution, resulting in greater difficulties in obtaining reliable estimates of the recoverable grade, and increased difficulties in the processing of ores. In response to economic fluctuations the working grade of heterogeneous orebodies, that form in geologically complex environments, can often be altered to ensure the continued viability of a mining venture. In contrast the evenly mineralized orebodies that tend to develop in geologically simple environments do not have this flexibility. All the important decisions in the mining industry, such as feasibility studies, choice of ~ining and processing methods, selection and planning, are made on the basis of, or are related to, grade estimates. If the geological controls of grade are fully understood, then it is possible to optimize the selection of the various mining alternatives, leading to the efficient exploitation of ore deposits.
- Full Text:
- Date Issued: 1983
- Authors: Esterhuizen, Anton G
- Date: 1983 , 2013-04-04
- Subjects: Mines and mineral resources , Ore deposits , Mineralogy , Geology, Economic
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5020 , http://hdl.handle.net/10962/d1006331 , Mines and mineral resources , Ore deposits , Mineralogy , Geology, Economic
- Description: The grade of a mineral deposit is determined by the effectiveness of a geological ore forming process, which is the result of the interaction between an ore forming mechanism and the environment in which it operates. Properties of a mineral deposit controlled by ore forming processes include the distribution, density and nature of ore minerals and gangue, and the metal content and impurities of the ore minerals. More efficient ore forming processes tend to develop in the larger mineralizing systems giving rise to richer deposits. As the geological environment within which a mineral deposit evolves becomes more complex a greater number of variables interact to determine the grade of the deposit. This is reflected in the greater variability of the grade distribution, resulting in greater difficulties in obtaining reliable estimates of the recoverable grade, and increased difficulties in the processing of ores. In response to economic fluctuations the working grade of heterogeneous orebodies, that form in geologically complex environments, can often be altered to ensure the continued viability of a mining venture. In contrast the evenly mineralized orebodies that tend to develop in geologically simple environments do not have this flexibility. All the important decisions in the mining industry, such as feasibility studies, choice of ~ining and processing methods, selection and planning, are made on the basis of, or are related to, grade estimates. If the geological controls of grade are fully understood, then it is possible to optimize the selection of the various mining alternatives, leading to the efficient exploitation of ore deposits.
- Full Text:
- Date Issued: 1983
The geological evolution and mineralised environments of the Tasman Geosyncline
- Authors: Pelham, D A
- Date: 1983 , 2013-04-03
- Subjects: Geosynclines -- Tasmania , Geology -- Tasmania , Ore deposits -- Tasmania , Mineralogy -- Tasmania
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5030 , http://hdl.handle.net/10962/d1006936 , Geosynclines -- Tasmania , Geology -- Tasmania , Ore deposits -- Tasmania , Mineralogy -- Tasmania
- Description: From introduction: The Tasman Geosyncline covers the eastern part of the continent of Australia, an area of over 2 million km'. The area has been a major source of Australian gold and tin production, and though it contains important base metal sulphide deposits, these are overshadowed in scale by the very large stratabound Proterozoic deposits (for example, Mt Isa, Broken Hill and McArthur River). This dissertation deals with the metallic mineral deposits of the Tasman Geosyncline, and as such does not include the extensive post Palaeozoic continental successions, with their important coal reserves, that overlie the deformed geosyncl i nal sequences.
- Full Text:
- Date Issued: 1983
- Authors: Pelham, D A
- Date: 1983 , 2013-04-03
- Subjects: Geosynclines -- Tasmania , Geology -- Tasmania , Ore deposits -- Tasmania , Mineralogy -- Tasmania
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5030 , http://hdl.handle.net/10962/d1006936 , Geosynclines -- Tasmania , Geology -- Tasmania , Ore deposits -- Tasmania , Mineralogy -- Tasmania
- Description: From introduction: The Tasman Geosyncline covers the eastern part of the continent of Australia, an area of over 2 million km'. The area has been a major source of Australian gold and tin production, and though it contains important base metal sulphide deposits, these are overshadowed in scale by the very large stratabound Proterozoic deposits (for example, Mt Isa, Broken Hill and McArthur River). This dissertation deals with the metallic mineral deposits of the Tasman Geosyncline, and as such does not include the extensive post Palaeozoic continental successions, with their important coal reserves, that overlie the deformed geosyncl i nal sequences.
- Full Text:
- Date Issued: 1983
The significance of unconformities in the development of Witwatersrand gold and uranium placers
- Authors: Beater, Christian Douglas
- Date: 1983 , 2013-04-03
- Subjects: Placer deposits , Gold ores -- Geology -- South Africa -- Witwatersrand , Uranium ores -- Geology -- South Africa -- Witwatersrand
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4925 , http://hdl.handle.net/10962/d1004535 , Placer deposits , Gold ores -- Geology -- South Africa -- Witwatersrand , Uranium ores -- Geology -- South Africa -- Witwatersrand
- Description: Most of the economic gold and uranium placers are developed on low angle disconformities in the Central Rand Group and concentrations of gold and uranium are usually at their optimum on unconformity surfaces. Examples include the Kimberley Reef and South Reef of the East Rand, the Main Reef Leader of the Central Rand, the Carbon Leader of the Carletonville goldfield, the Vaal Reef of the Klerksdorp goldfield and the Basal/Steyn placers of the Welkom goldfield. The individual goldfields represent fluvial fans which are composed of a large number of tectonogenetic sedimentary packages separated by unconformities. The tectonic responses between cycles of sedimentation produced unconformities and tectonically controlled cyclic sedimentation is one of the key factors culminating in the preparation and deposition of auriferous placers within the Witwatersrand succession. Unconformities, which represent breaks in sedimentation, result in the preconditioning of palaeosurfaces and redistribution of sediments and heavy minerals on them. Winnowing of sands produced heavy mineral residual accumulations on erosion surfaces which were generally preserved by small-pebble lags or algal mats. Reworking of units truncated by the unconformities provided additional gold, uranium and heavy minerals to unconformity surfaces.
- Full Text:
- Date Issued: 1983
- Authors: Beater, Christian Douglas
- Date: 1983 , 2013-04-03
- Subjects: Placer deposits , Gold ores -- Geology -- South Africa -- Witwatersrand , Uranium ores -- Geology -- South Africa -- Witwatersrand
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4925 , http://hdl.handle.net/10962/d1004535 , Placer deposits , Gold ores -- Geology -- South Africa -- Witwatersrand , Uranium ores -- Geology -- South Africa -- Witwatersrand
- Description: Most of the economic gold and uranium placers are developed on low angle disconformities in the Central Rand Group and concentrations of gold and uranium are usually at their optimum on unconformity surfaces. Examples include the Kimberley Reef and South Reef of the East Rand, the Main Reef Leader of the Central Rand, the Carbon Leader of the Carletonville goldfield, the Vaal Reef of the Klerksdorp goldfield and the Basal/Steyn placers of the Welkom goldfield. The individual goldfields represent fluvial fans which are composed of a large number of tectonogenetic sedimentary packages separated by unconformities. The tectonic responses between cycles of sedimentation produced unconformities and tectonically controlled cyclic sedimentation is one of the key factors culminating in the preparation and deposition of auriferous placers within the Witwatersrand succession. Unconformities, which represent breaks in sedimentation, result in the preconditioning of palaeosurfaces and redistribution of sediments and heavy minerals on them. Winnowing of sands produced heavy mineral residual accumulations on erosion surfaces which were generally preserved by small-pebble lags or algal mats. Reworking of units truncated by the unconformities provided additional gold, uranium and heavy minerals to unconformity surfaces.
- Full Text:
- Date Issued: 1983
The factors affecting the interpretation of geochemical surveys in mineral exploration
- Authors: Fletcher, B A
- Date: 1982
- Subjects: Geochemistry , Geochemistry -- Environmental aspects , Mining geology , Minerals , Ore deposits , Geochemical prospecting
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5014 , http://hdl.handle.net/10962/d1006142
- Description: [From introduction] Exploration geochemistry is an indirect method of detecting mineral deposits by measuring the abundance and distribution of ore elements and elements closely associated with ore in natural materials at or near the earth's surface. The method relies on the assumption that a mineral deposit is reflected by unusual element abundances or distribution patterns (geochemical halos), and that these indications of mineralization can be detected by geochemical surveys involving the collection and analysis of natural materials. The interpretation of geochemical surveys in mineral exploration involves: 1) The use of geological and statistical inference, based on a knowledge of the normal behaviour and distribution of indicator elements in the exploration area, to recognize apparent geochemical anomalies in field and analytical data and to predict the type of geochemical halo reflected by the anomalies. 11) The use of geological inference, based on a knowledge of the characteristics of geochemical halos and their relationship to mineral deposits, to predict the presence and probable location of an ore body. The interpretation process is, however, complicated by the absence of a simple universal formula that relates the abundance and distribution of elements in natural materials to the presence or absence of a mineral deposit. The interpretation of a geochemical survey must, thus, be based on an empirical approach which avaluates each survey as an individual problem. The objective of this dissertation is to illustrate the factors affecting the "nuts and bolts" approach to the interpretation of geochemical surveys in mineral exploration. The discussion is aimed at providing field geologists responsible -for the planning and execution of geochemical surveys with some basic guidelines for interpreting the surveys. I hope that the contents of this dissertation will help field geologists to "look in the last place first".
- Full Text:
- Date Issued: 1982
- Authors: Fletcher, B A
- Date: 1982
- Subjects: Geochemistry , Geochemistry -- Environmental aspects , Mining geology , Minerals , Ore deposits , Geochemical prospecting
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5014 , http://hdl.handle.net/10962/d1006142
- Description: [From introduction] Exploration geochemistry is an indirect method of detecting mineral deposits by measuring the abundance and distribution of ore elements and elements closely associated with ore in natural materials at or near the earth's surface. The method relies on the assumption that a mineral deposit is reflected by unusual element abundances or distribution patterns (geochemical halos), and that these indications of mineralization can be detected by geochemical surveys involving the collection and analysis of natural materials. The interpretation of geochemical surveys in mineral exploration involves: 1) The use of geological and statistical inference, based on a knowledge of the normal behaviour and distribution of indicator elements in the exploration area, to recognize apparent geochemical anomalies in field and analytical data and to predict the type of geochemical halo reflected by the anomalies. 11) The use of geological inference, based on a knowledge of the characteristics of geochemical halos and their relationship to mineral deposits, to predict the presence and probable location of an ore body. The interpretation process is, however, complicated by the absence of a simple universal formula that relates the abundance and distribution of elements in natural materials to the presence or absence of a mineral deposit. The interpretation of a geochemical survey must, thus, be based on an empirical approach which avaluates each survey as an individual problem. The objective of this dissertation is to illustrate the factors affecting the "nuts and bolts" approach to the interpretation of geochemical surveys in mineral exploration. The discussion is aimed at providing field geologists responsible -for the planning and execution of geochemical surveys with some basic guidelines for interpreting the surveys. I hope that the contents of this dissertation will help field geologists to "look in the last place first".
- Full Text:
- Date Issued: 1982
The geology, geochemistry and silicate mineralogy of the upper criticial zone of the north-western Bushveld Complex, at Rustenburg Platinum Mines, Union Section
- Authors: De Klerk, William Johan
- Date: 1982 , 2013-03-20
- Subjects: Mineralogy -- South Africa -- North-Western Transvaal , Geochemistry -- South Africa -- North-Western Transvaal , Geology -- South Africa -- North-Western Transvaal , Platinum mines and mining -- South Africa -- North-Western Transvaal , Rustenburg Platinum Mines
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5013 , http://hdl.handle.net/10962/d1006140 , Mineralogy -- South Africa -- North-Western Transvaal , Geochemistry -- South Africa -- North-Western Transvaal , Geology -- South Africa -- North-Western Transvaal , Platinum mines and mining -- South Africa -- North-Western Transvaal , Rustenburg Platinum Mines
- Description: Rustenburg Platinum Mines, Union Section, is located in the mafic phase of the north-western sector of the Bushveld Complex. This part of the Complex is characterised by transgressions of Upper zone ferrogabbros across the lower sequence of mafic rocks. These transgressions have effectively isolated a roughly triangular segment of Lower, Critical and Main zone rocks. It is in the upper part of the Critical zone that the Merensky Reef, with a strike length of 9,5 km, is found to suboutcrop below a 2-3 m black turf soil cover and it constitutes the orebody being mined at Union Section. Underground mining and development have exposed a stratigraphic succession from the Middle Group chromitites to within the lower part of the Main zone gabbros. A detailed investigation of a 100 m stratigraphic succession was undertaken in the upper part of the Critical zone, which includes the Bastard Reef, Merensky Reef, Pseudo Reef, UG 2 and UG 1 layers. Stratigraphic descriptions are presented for both a normal and potholed succession, as well as a description of pothole characteristics. The variations of Merensky Reef thickness, pothole distribution and structure of the are body are also discussed. Forty seven whole-rock major- and trace-element analyses were carried out on selected samples from both normal and potholed successions, although more emphasis was placed on the former. These samples were taken from just below the UG 1 to above the Bastard Reef. Trace elements determined included Sr, Rb, Y, Nb, Zr, Cr, Co, Ni, Cu and V. The cyclical nature of the layering is clearly defined by breaks in the trends of both the major- and trace element analyses, although some elements are strongly influenced by the modal proportions of the mai n mineral phases. Although major breaks are observed for individual elements , insignificant variation of the Mg/Mg+Fe 2 + ratio is observed throughout. New electron microprobe data are presented for the main silicate phases olivine , orthopyroxene, clinopyroxene and plagioclase , while only a limi ted number of analyses were carried out on the spine l phase. There would appear to be a reversal of the expected fractionation trend from the hanging wal l of the UG 2 to the Pseudo Marker layer. There is an upward increase of the Fo content of the olivine from F0₇₆ , ₇₋₈₁,₆ . A similar trend is observed for the orthopyroxene analyses . The Merensky unit, as a whole, exhibits a gradual decrease in the Mg end member of the Ca-poor pyroxenes from En ₇₈,₅₋₇₄ . was found to be markedly more calcic Cumulus plagioclase (An ₇₂, ₈-₈₁, ₇) than the intercumulus phase (An₅₆,₃₋₇₁, ₉) ' A further feature of the cumulus plagioclase is that strong zonation was observed with the cores of individual crystals being consistently lower in Ca relative to their margins . , KMBT_363 , Adobe Acrobat 9.53 Paper Capture Plug-in
- Full Text:
- Date Issued: 1982
- Authors: De Klerk, William Johan
- Date: 1982 , 2013-03-20
- Subjects: Mineralogy -- South Africa -- North-Western Transvaal , Geochemistry -- South Africa -- North-Western Transvaal , Geology -- South Africa -- North-Western Transvaal , Platinum mines and mining -- South Africa -- North-Western Transvaal , Rustenburg Platinum Mines
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5013 , http://hdl.handle.net/10962/d1006140 , Mineralogy -- South Africa -- North-Western Transvaal , Geochemistry -- South Africa -- North-Western Transvaal , Geology -- South Africa -- North-Western Transvaal , Platinum mines and mining -- South Africa -- North-Western Transvaal , Rustenburg Platinum Mines
- Description: Rustenburg Platinum Mines, Union Section, is located in the mafic phase of the north-western sector of the Bushveld Complex. This part of the Complex is characterised by transgressions of Upper zone ferrogabbros across the lower sequence of mafic rocks. These transgressions have effectively isolated a roughly triangular segment of Lower, Critical and Main zone rocks. It is in the upper part of the Critical zone that the Merensky Reef, with a strike length of 9,5 km, is found to suboutcrop below a 2-3 m black turf soil cover and it constitutes the orebody being mined at Union Section. Underground mining and development have exposed a stratigraphic succession from the Middle Group chromitites to within the lower part of the Main zone gabbros. A detailed investigation of a 100 m stratigraphic succession was undertaken in the upper part of the Critical zone, which includes the Bastard Reef, Merensky Reef, Pseudo Reef, UG 2 and UG 1 layers. Stratigraphic descriptions are presented for both a normal and potholed succession, as well as a description of pothole characteristics. The variations of Merensky Reef thickness, pothole distribution and structure of the are body are also discussed. Forty seven whole-rock major- and trace-element analyses were carried out on selected samples from both normal and potholed successions, although more emphasis was placed on the former. These samples were taken from just below the UG 1 to above the Bastard Reef. Trace elements determined included Sr, Rb, Y, Nb, Zr, Cr, Co, Ni, Cu and V. The cyclical nature of the layering is clearly defined by breaks in the trends of both the major- and trace element analyses, although some elements are strongly influenced by the modal proportions of the mai n mineral phases. Although major breaks are observed for individual elements , insignificant variation of the Mg/Mg+Fe 2 + ratio is observed throughout. New electron microprobe data are presented for the main silicate phases olivine , orthopyroxene, clinopyroxene and plagioclase , while only a limi ted number of analyses were carried out on the spine l phase. There would appear to be a reversal of the expected fractionation trend from the hanging wal l of the UG 2 to the Pseudo Marker layer. There is an upward increase of the Fo content of the olivine from F0₇₆ , ₇₋₈₁,₆ . A similar trend is observed for the orthopyroxene analyses . The Merensky unit, as a whole, exhibits a gradual decrease in the Mg end member of the Ca-poor pyroxenes from En ₇₈,₅₋₇₄ . was found to be markedly more calcic Cumulus plagioclase (An ₇₂, ₈-₈₁, ₇) than the intercumulus phase (An₅₆,₃₋₇₁, ₉) ' A further feature of the cumulus plagioclase is that strong zonation was observed with the cores of individual crystals being consistently lower in Ca relative to their margins . , KMBT_363 , Adobe Acrobat 9.53 Paper Capture Plug-in
- Full Text:
- Date Issued: 1982
The stratigraphy and structure of the Kommadagga subgroup and contiguous rocks|
- Authors: Swart, Roger
- Date: 1982
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4919 , http://hdl.handle.net/10962/d1004378
- Description: The Lake Mentz and Kommadagga Subgroups were deposited in a marine environment and are characterised by a heterogeneous sequence of sediments, which range in grain size from clays to grits. During the first phase of deposition the Kweekvlei Shale and Floriskraal Formations were deposited in a prograding shoreline environment, whereas the succeeding Waaipoort Shale Formation is interpreted as represnting a reworked shoreline . The final phase of deposition of the Cape Supergroup was a regressive one in which the Kommadagga Subgroup was formed. The coarsening upward cycle of this subgroup represents a deltaic deposit. A significant time gap appears to exist before the deposition of the glacial-marine Dwyka Tillite Formation. Structurally, the area was subjected to deformation by buckle folding at about 250 Ma into a series of folds with southward dipping axial planes. Only one phase of deformation is recognised in the study area . A decrease in pore space, mineral overgrowths,formation of silica and calcite cements and development of autigenic minerals such as opal, stilpnomelane, analcite, prehnite, muscovite and various clay minerals are the characteristic diagenetic features of the sediments. The mineralogical evidence suggests that the maximum temperature and pressure of burial was 150 C and 4 to 5 Kbar respectively.
- Full Text:
- Date Issued: 1982
- Authors: Swart, Roger
- Date: 1982
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4919 , http://hdl.handle.net/10962/d1004378
- Description: The Lake Mentz and Kommadagga Subgroups were deposited in a marine environment and are characterised by a heterogeneous sequence of sediments, which range in grain size from clays to grits. During the first phase of deposition the Kweekvlei Shale and Floriskraal Formations were deposited in a prograding shoreline environment, whereas the succeeding Waaipoort Shale Formation is interpreted as represnting a reworked shoreline . The final phase of deposition of the Cape Supergroup was a regressive one in which the Kommadagga Subgroup was formed. The coarsening upward cycle of this subgroup represents a deltaic deposit. A significant time gap appears to exist before the deposition of the glacial-marine Dwyka Tillite Formation. Structurally, the area was subjected to deformation by buckle folding at about 250 Ma into a series of folds with southward dipping axial planes. Only one phase of deformation is recognised in the study area . A decrease in pore space, mineral overgrowths,formation of silica and calcite cements and development of autigenic minerals such as opal, stilpnomelane, analcite, prehnite, muscovite and various clay minerals are the characteristic diagenetic features of the sediments. The mineralogical evidence suggests that the maximum temperature and pressure of burial was 150 C and 4 to 5 Kbar respectively.
- Full Text:
- Date Issued: 1982
The tectonic framework of magmatism and mineralization in the western United States
- Authors: Empsall, J S
- Date: 1982 , 2013-04-03
- Subjects: Plate tectonics -- United States , Magmatism -- United States , Mineralogy -- United States
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5019 , http://hdl.handle.net/10962/d1006328 , Plate tectonics -- United States , Magmatism -- United States , Mineralogy -- United States
- Description: KMBT_363 , Adobe Acrobat 9.53 Paper Capture Plug-in
- Full Text:
- Date Issued: 1982
- Authors: Empsall, J S
- Date: 1982 , 2013-04-03
- Subjects: Plate tectonics -- United States , Magmatism -- United States , Mineralogy -- United States
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5019 , http://hdl.handle.net/10962/d1006328 , Plate tectonics -- United States , Magmatism -- United States , Mineralogy -- United States
- Description: KMBT_363 , Adobe Acrobat 9.53 Paper Capture Plug-in
- Full Text:
- Date Issued: 1982