Fluid evolution and characterisation of mineralising solutions in the Central African Copperbelt

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dc.contributor.authorGreyling, Lynnette Natasha
dc.date.accessioned2009-07-08T08:12:58Z
dc.date.available2009-07-08T08:12:58Z
dc.date.issued2009-07-08T08:12:58Z
dc.description.abstractThe reconstruction of the fluid evolution of the Zambian Copperbelt is presented, where extensive stratiform copper-cobalt mineralisation is hosted in the metasediments of the Katanga Supergroup located in the Lufilian Arc in the Democratic Republic of the Congo and Zambia. Fluid inclusions are characterised from three different tectonic settings at selected deposits within the Zambian Copperbelt in terms of basinal, early orogenic, and late orogenic settings. Fluid inclusion microthermometry, Raman microspectroscopy, laser ablation inductively coupled plasma mass spectrometry, and stable isotope analysis are used to investigate the nature of basinal, early orogenic, and late orogenic fluids. NaCl-CaCl2, MgCl2-KCl brines are found to have circulated the sedimentary pile immediately after stratiform copper mineralisation and are the earliest fluids documented from the Copperbelt. MgCl2-KCl brines were also trapped together with CO2-CH4-N2 fluids during these times. Basinal fluids were trapped under minimum pressure temperature conditions of 350 bar and 120°C. Four distinct early orogenic fluids are found at the Chambishi, Nchanga, and Nkana deposits and consist of NaCl-CaCl2-MgCl2-KCl, CaCl2-KCl, NaCl-CO2-CH4-N2, and pure carbonic fluids. It is seen that these fluids at pressures of 550-800 bar and temperatures of 153-260°C which corresponds to depths of ~5.6-8.2 km. Late orogenic fluids from the Mufulira and Nkana deposits are the hottest and most complex fluids documented during this study and contain mixtures of hypersaline NaCl- CaCl2-MgCl2 ± KCl and NaCl-CaCO3-saturated ±N2 brines. Fluids were trapped at minimum temperatures of 240°C and 1750 bar pressure. In addition to these fluids, a low salinity CaCl2-MgCl2-CO2-CH4 fluid is also present during late orogenesis. Minimum depth estimates for late orogenic fluids are around 6.61 km. The highest salinities of all three fluid types are found within these late orogenic fluids in addition to the highest levels of Pb, Zn, Cu, Co and Sr. This indicates the prolonged presence and equilibration of these fluids with the host rock. Moreover, late orogenic fluids are also more oxidised compared to relatively more reduced basinal fluids. A key to the widespread and paragenetically complex nature of the Copperbelt ores may be related to the longevity of fluid flow and the progressive ability of fluids to transport metals. The marked increase in Pb and Zn in later fluids may be relevant to the formation of regional epigenetic Pb-Zn deposits further afield of the Copperbelt, such as ii at Kabwe and Kipushi. The late orogenic fluids seen in the Copperbelt compare favourably with mineralising fluids of the epigenetic Pb-Zn Kabwe deposit in terms of metal composition, temperature and moderate salinities. It is envisaged that early stratiform mineralisation is followed by continuing fluid circulation in the basin whereby metals are scavenged by hotter fluids which continue to act as mineralising agents.en
dc.identifier.urihttp://hdl.handle.net/10539/7078
dc.language.isoenen
dc.titleFluid evolution and characterisation of mineralising solutions in the Central African Copperbelten
dc.typeThesisen
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