LE3 .A278 2012

2012

Stanley, Cliff

Acadia University

Bachelor of Science

Honours

Geology

Earth & Environmental Sciences

Weathering of the Bisha volcanic hosted massive sulphide (VHMS) deposit has produced several enrichment zones: (i) a gossanous oxide Au zone above, (ii) a supergene zone of chalcocite replacement of sulphide minerals between, (iii) a hypogene sphalerite-chalcopyrite-bearing massive sulphide body below. These enrichment zones differ from those developed over other VHMS deposits (Ladysmith, Wisconsin; Caribou, New Brunswick; Las Cruces, Spain; Golden Grove, Western Australia) in that supergene Pb mineralization (galena, siderite) occurs immediately above the Cu enrichment zone, and oxide Au grades are ten times that of hypogene mineralization (in contrast to the up to two-fold Au enrichment typically observed at other deposits). In order to understand how these anomalous zones developed, X-Ray diffraction analysis was undertaken on samples from a cross-section to gain insight into the mineralogical changes that took place during weathering. Lithologies within the weathering zone consist of: (i) Au- bearing gossan, (ii) acid leached rocks, (iii) saprolite, (iv) supergene sulphide mineralization, and (v) hypogene massive sulphide. Using lithogeochemical compositions of these rocks, ordinary least squares regression methods were used to obtain ‘best fit’ mineral modes for each weathering zone. These have been plotted on cross-sections to define the weathering patterns present in these rocks, and indicate that lateral groundwater flow is likely responsible for an asymmetric distribution of these zones. With these mineralogical constraints, chemical reactions can now be identified to explain the bulk material transfers responsible for the formation of each weathering zone.

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https://scholar.acadiau.ca/islandora/object/theses:878