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Modelling geochemical dispersion above a buried polymetallic volcanogenic massive sulphide deposit in a recently glaciated terrain Bodnar, Matthew Michael

Abstract

Modern society requires a resource supply for the continual development of infrastructure and technology. The discovery of new mineral deposits is challenging as much of North America is covered by Quaternary sediments that obscure bedrock geology. Enhanced methods in exploration geochemistry, capable of detecting mineral deposits through complex cover, must be developed to satisfy global resource demands. Detailed landscape and surficial material mapping over the Lara polymetallic volcanogenic massive sulphide (VMS) deposit were used to establish a landscape evolution model and identify natural processes that govern geochemical responses in shallow soil in glaciated terrain. Upper B horizon soil and physicochemical property measurements were collected along four transects over the deposit and host-rocks and was analyzed by aqua regia ICP-MS/AES, fpXRF and magnetic susceptibility. Select samples were analyzed by sequential extraction and/or for Cu and Zn isotopes to establish the provenance of geochemical responses. Follow-up Ah horizon soil and western hemlock bark samples from a subset of the grid were analyzed by modified aqua regia ICP-MS to determine the role of biochemical cycling. Passive hydrocarbon collector modules were installed at each B horizon soil sample location. Five surficial material domains including till, alluvium and colluvium were identified representing complex alpine glacial and paraglacial processes. Most recent glacial ice flow was valley controlled and sub-parallel to the strike of VMS mineralization as well as a 1-2 m wide pyrite-chalcopyrite stringer zone that occurs 150 m north of the VMS. The highest Zn response occurs over the Lara VMS; however, Cr, Ni, Co and Sc content and magnetic susceptibility indicate this is due to elevated gabbroic content in the till matrix. A response of Zn, Cu, Cd, Mo, Se, Hg, and Te occur over the pyrite zone. Copper isotopes and sequential extraction indicate that geochemical responses are attributed to a clastic source. Zinc, copper, and cadmium in Ah soil and tree bark is controlled by surficial material and geomorphology. Geochemical responses in B horizon soil above the VMS and pyrite zone is interpreted to be caused clastic dispersion of mineralization and mafic host-rocks by glacial transport with negligible input by biochemical cycling.

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