The origin and significance of non-aqueous CO2 fluid inclusions in the auriferous veins of Bin Yauri,northwestern Nigeria |
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| Authors: | I Garba S O Akande |
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| Institution: | (1) Department of Geology, Imperial College, SW7 2BP London, UK;(2) Department of Geology and Mineral Sciences, University of Ilorin, Ilorin, Nigeria |
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| Abstract: | Non-aqueous CO2 and CO2-rich fluid inclusions are found in the vein quartz hosting mesothermal gold-sulphide mineralization at Bin Yauri, northwestern
Nigeria. Although mineralizing fluids responsible for gold mineralization are thought to be CO2-rich, the occurrence of predominantly pure to nearly pure CO2 inclusions is nevertheless unusual for a hydrothermal fluid system. Many studies of similar CO2-rich fluid inclusions, mainly in metamorphic rocks, proposed preferential loss (leakage) of H2O from H2O-CO2 inclusions after entrapment. In this study however, it is proposed that phase separation (fluid immiscibility) of low salinity
CO2-rich hydrothermal fluids during deposition of the gold mineralization led to the loss of the H2O phase and selective entrapment of the CO2. The loss of H2O to the wallrocks resulted in increasing oxidizing effects. There is evidence to suggest that the original CO2-rich fluid was intrinsically oxidized, or perhaps in equilibrium with oxidizing conditions in the source rocks. The source
of the implicated fluid is thought to be subducted metasediments, subjected to dehydration and devolatilization reactions
along a transcurrent Anka fault/shear system, which has been described as a Pan-African (450–750 Ma) crustal suture. |
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