Summary
Most carbonate-hosted, nonsulphide base metal (CHNSBM) deposits are derived from sulphide mineralization (MVT, SEDEX, Irish-type and vein-type deposits and, to lesser extent, skarns) by a supergene process. Several carbonate-hosted sulphide deposits in the Kootenay terrane, adjacent Cariboo terrane, and elsewhere in BC have near-surface Zn- and Pb-bearing iron oxide-rich gossans. Such gossans form when carbonate-hosted, base-metal sulphide mineralization is subject to intense weathering and metals are liberated by the oxidation of sulphide minerals. The metals can be trapped locally, forming direct-replacement, nonsulphide ore deposits or they can be transported by percolating waters down and away from the sulphide protore, forming wallrock-replacement CHNSBM deposits. Wallrock-replacement deposits can be located in proximity to protore or several hundreds of metres away. The direct-replacement nonsulphide deposits are also know as "red ores" because they consist commonly of Fe-oxyhydroxides, goethite, hematite, hemimorphite, smithsonite, hydrozincite and cerussite; they typically contain >20% Zn, >7% Fe and Pb±As. The wallrock-replacement deposits also know as "white ore" consist of smithsonite, hydrozincite and minor Fe-hydroxides, and contain <40% Zn, <7% Fe and very low concentrations of Pb. Wallrock-replacement deposits are commonly rich in Zn and poor in Pb relative to the direct-replacement CHNSBM deposits.CHNSBM deposits covered by this study are located within the southern part of the Kootenay Arc (including the Salmo district; NTS 082/F03) and adjacent miogeoclinal rocks of the Cariboo terrane (NTS 093A/14E, 15W; see map).
Neither direct-replacement nor wallrock-replacement CHNSBM deposits in BC were properly characterized. The characterization of these deposits is essential for the formulation of integrated exploration programs targeting CHNSBM deposits. Zn or Pb oxides, silicates and carbonates may be also indirect indicator minerals in exploration for MVT, SEDEX, Irish-type, and vein-type Zn-Pb deposits (i.e., Zn-Pb sulphide precursors to CHNSBM deposits). The principal objective of the proposed study is (1) to characterize the mineralogy and chemistry of representative CHNSBM deposits in BC, and (2) assemble the data defining the geological, mineralogical and geochemical and physical attributes of representative CHNSBM deposits located in BC in the form of a BC deposit model (or profile). Such deposit model could be used as a tool for the identification of areas of maximum prospectivity in southern BC and elsewhere in the province.