The nature of early basinal fluids in the Zambian Copperbelt: A case study from the Chambishi deposit
β Scribed by L.N. Greyling; L.J. Robb; S. Master; M.C. Boiron; Y. Yao
- Publisher
- Elsevier Science
- Year
- 2005
- Tongue
- English
- Weight
- 863 KB
- Volume
- 42
- Category
- Article
- ISSN
- 1464-343X
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β¦ Synopsis
Fluid inclusions from a mineralised lateral secretion quartz vein in the Chambishi open pit in the Zambian Copperbelt represent fluids that immediately postdate stratiform copper mineralisation. Petrographic evidence indicates that this veinset predates deformation in the area. Fluid inclusion microthermometry and Raman spectroscopy of aqueous and aqueo-carbonic inclusions indicate the presence of an early saline H 2 O-NaCl + MgCl 2 Β± CaCl 2 Β± CO 2 Β± CH 4 Β± N 2 fluid (11.9-23.1 wt.% NaCl equiv ) at homogenisation temperatures of 86-129 Β°C. Later fluids occur in fluid inclusion planes, and are linked to early metamorphism of the basin. These fluids are more varied in composition, and are aqueous, aqueo-carbonic, and pure methane inclusions. Aqueous and aqueo-carbonic inclusions are H 2 O-NaCl Β± CaCl 2 Β± MgCl 2 Β± KCl Β± CO 2 , N 2 , CH 4 , H 2 S fluids, with two salinity end-members, namely, a high salinity (18-23 wt.% NaCl equiv )-lower temperature ($130-160 Β°C) fluid, and a lower salinity ($6 wt.% NaCl equiv )-higher temperature ($140-210 Β°C) fluid. Later carbonic inclusion planes contain CH 4 , with N 2 and C 2 H 6 . Later fluids are complex in composition, salinity, and homogenisation temperatures. These fluids are thought to be late-diagenetic fluids on the one hand, and an early (methane productive) metamorphic fluid on the other. Pressure and temperature conditions in the environment immediately after stratiform copper mineralisation were around 480-800 bar and 130-270 Β°C.
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