NEXT IGA EVENT
LECTURE
Dr. Tom Molyeux (Exploration Consultant) will present a lecture:
Geology of the Bushveld Complex, South Africa
VENUE: Room 4, Dept. of Geology, Muesum Building, Trinity College Dublin, Dublin 2.
TIME: 6.00pm
MAP:
View Larger Map Abstract The Bushveld Complex is an ultramafic, mafic and granitic complex in the famous Kaapvaal Craton of South Africa. This craton has escaped subduction for >3.5 billion years and also supports The Archaean Barberton Mountainland and the fabulous gold-uranium bearing rocks of The Witwatersrand Basin. The Bushveld Complex has an age of ~2.05 billion years and outcrops over an area of ~65 000 km2. Though all of this area may not be underlain by Bushveld rocks the volume of the original Bushveld ultramafic and mafic magma has been estimated to be as much as 1 million km3. This is similar to the volume of magma in The Deccan Trap and Breto-islandic volcanic provinces. The Bushveld magmatic event may have been the product of an underlying mantle plume. In this context The Great Dyke/Graben to the north has an estimated age of 2.4by and The Trompsburg Complex aligned to the south has an estimated age of 1.3by. I have calculated that a movement of ~1cm/year would put a possible mantle plume at the measued ages under these three bodies. The Bushveld ultramafic/mafic rocks outcrop in three principal intrusions: The East, West and Northern bodies. There are other some minor bodies as well. The Eastern and Western bodies apparently were formed from an initial intrusion of Ultramafic magma followed by three major intrusions of mafic magma. A later phase of granitic magma(s) was then intruded upwards through the consolidated mafic layers. The Eastern and Western intrusions are ~8km thick and consist of an unmineralised Lower Zone, The Critical Zone contains magnificent chromitite layers and with The UG 2 Chromitite Seam and Merensky Reef containing huge PGE reserves at the top. Then comes ~3km thickness of unmineralised noritic and gabbroic rocks of The Main Zone. The Upper Zone is ~1.5km thick and contains the world-renowned FeTiV magnetite layers. The Mafic rocks of The Complex contain ~80% of the world's reserves of Cr, ~70% of it's PGE's and 40-50% of the world's vanadium reserves.'Black and Grey 'Granites' are also quarried from suitable Bushveld mafic rocks. The Bushveld Granite contains lesser reserves of tin, fluorite and dimension stone. The value of, and demand for minerals of The Bushveld Complex has increased enormously over the last ~50 years. Bushveld chromitite is in far greater demand for alloying in steels. Bushveld PGEs are now used very extensively in auto-catalysts, and in jewellery, particularly in The East. Bushveld vanadium is used in non-expanding or shrinking FeV alloys, in barnicle-repelling paints for the hulls of ships and with Li in highly efficient batteries. The mineral reserves of The Bushveld Complex are enormous and are of very great importance in South Africa as they are slowly taking the place of the dwindling minable gold reserves of fabulous The Witwatersrand Basin Dr. Tom Molyneux Tom graduated from Trinity College Dublin in 1958 before moving to South Africa to study for an MSc, followed by a doctorate from the University of Pretoria, which was awarded in 1971. He then worked for The Anglo American Corp. Plc. and their associated companies, giving him wide experience in mineral exploration including diamond exploration in Tanzania, exploration of the Bushveld Complex and surrounding areas, exploration in the British Isles, Mauretania and the Iberia Peninsula while based in London, gold geology in Botswana, Uranium in the Namib Desert and surrounds, exploration of the bushveld satellites, base metal exploration in this area, supervised training for Amgold geologists, as well as a deep drilling programme into the Ventersdrop Copntact Reef, target generation & assesment of the Bushveld and also managed to find time to teach Economic Geology at the University of Washington from 1984 -1985. Tom then worked as a contractor for Geoscience, South Africa compiling maps, mineral deposit databases and reports and since then has been an independant geological and geochemical consultant based here in his native Ireland, which has taken him to places such as Africa and Iran and is still often concerned with the Bushveld gold deposits. Tom's experience of and love for the Bushveld Complex definitely classes him as an expert in the complicated geology associated with teh area.
View Larger Map Abstract The Bushveld Complex is an ultramafic, mafic and granitic complex in the famous Kaapvaal Craton of South Africa. This craton has escaped subduction for >3.5 billion years and also supports The Archaean Barberton Mountainland and the fabulous gold-uranium bearing rocks of The Witwatersrand Basin. The Bushveld Complex has an age of ~2.05 billion years and outcrops over an area of ~65 000 km2. Though all of this area may not be underlain by Bushveld rocks the volume of the original Bushveld ultramafic and mafic magma has been estimated to be as much as 1 million km3. This is similar to the volume of magma in The Deccan Trap and Breto-islandic volcanic provinces. The Bushveld magmatic event may have been the product of an underlying mantle plume. In this context The Great Dyke/Graben to the north has an estimated age of 2.4by and The Trompsburg Complex aligned to the south has an estimated age of 1.3by. I have calculated that a movement of ~1cm/year would put a possible mantle plume at the measued ages under these three bodies. The Bushveld ultramafic/mafic rocks outcrop in three principal intrusions: The East, West and Northern bodies. There are other some minor bodies as well. The Eastern and Western bodies apparently were formed from an initial intrusion of Ultramafic magma followed by three major intrusions of mafic magma. A later phase of granitic magma(s) was then intruded upwards through the consolidated mafic layers. The Eastern and Western intrusions are ~8km thick and consist of an unmineralised Lower Zone, The Critical Zone contains magnificent chromitite layers and with The UG 2 Chromitite Seam and Merensky Reef containing huge PGE reserves at the top. Then comes ~3km thickness of unmineralised noritic and gabbroic rocks of The Main Zone. The Upper Zone is ~1.5km thick and contains the world-renowned FeTiV magnetite layers. The Mafic rocks of The Complex contain ~80% of the world's reserves of Cr, ~70% of it's PGE's and 40-50% of the world's vanadium reserves.'Black and Grey 'Granites' are also quarried from suitable Bushveld mafic rocks. The Bushveld Granite contains lesser reserves of tin, fluorite and dimension stone. The value of, and demand for minerals of The Bushveld Complex has increased enormously over the last ~50 years. Bushveld chromitite is in far greater demand for alloying in steels. Bushveld PGEs are now used very extensively in auto-catalysts, and in jewellery, particularly in The East. Bushveld vanadium is used in non-expanding or shrinking FeV alloys, in barnicle-repelling paints for the hulls of ships and with Li in highly efficient batteries. The mineral reserves of The Bushveld Complex are enormous and are of very great importance in South Africa as they are slowly taking the place of the dwindling minable gold reserves of fabulous The Witwatersrand Basin Dr. Tom Molyneux Tom graduated from Trinity College Dublin in 1958 before moving to South Africa to study for an MSc, followed by a doctorate from the University of Pretoria, which was awarded in 1971. He then worked for The Anglo American Corp. Plc. and their associated companies, giving him wide experience in mineral exploration including diamond exploration in Tanzania, exploration of the Bushveld Complex and surrounding areas, exploration in the British Isles, Mauretania and the Iberia Peninsula while based in London, gold geology in Botswana, Uranium in the Namib Desert and surrounds, exploration of the bushveld satellites, base metal exploration in this area, supervised training for Amgold geologists, as well as a deep drilling programme into the Ventersdrop Copntact Reef, target generation & assesment of the Bushveld and also managed to find time to teach Economic Geology at the University of Washington from 1984 -1985. Tom then worked as a contractor for Geoscience, South Africa compiling maps, mineral deposit databases and reports and since then has been an independant geological and geochemical consultant based here in his native Ireland, which has taken him to places such as Africa and Iran and is still often concerned with the Bushveld gold deposits. Tom's experience of and love for the Bushveld Complex definitely classes him as an expert in the complicated geology associated with teh area.