Mineralogical and Geochemical Characterization of Supergene Carbonate-hosted Nonsulphide Zn-Pb Mineralization in Southern and Central British Columbia. Keevil, Halley K.
Carbonate-hosted nonsulphide base metal deposits form in supergene environments as base metal sulphides are oxidized and chemical weathering causes the metals to be leached out and deposited as metal-bearing gossans. The metals can be deposited by direct-replacement as nonsulphide minerals directly above the sulphide ore, or can travel away from the underlying sulphides with percolating water and be deposited as wall-rock-replacement deposits. Direct-replacement deposits, known as “red ores”, are usually rich in iron oxides, occur in association with primary sulphide minerals, and may contain economic concentrations of zinc and lead. Wall-rock-replacement deposits, known as “white ores”, are typically less oxidized, are not associated with primary sulphide minerals, and contain higher concentrations of zinc but lesser amounts of lead and iron. Both forms of mineralization have been recognized as valid exploration targets in British Columbia, but detailed mineralogy and chemistry of representative deposits is needed to better establish exploration models. Petrography, X-ray diffraction, and scanning electron microscopy analyses were completed on select nonsulphide deposits, i.e., Red Bird, Lomond, and Oxide in the Salmo district of the Kootenay terrane, and Cariboo Zinc in the Quesnel Lake district of the Cariboo terrane. Sulphide protore to the nonsulphide deposits of the Salmo district was also studied by analyzing samples from the Reeves MacDonald, HB, and Jersey-Emerald properties. At the Lomond deposit, there is extensive oxidation and cerussite occurs as a lead nonsulphide phase within vugs. At the Red Bird prospect, hemimorphite is the predominant nonsulphide mineral, with remnants of hydrozincite on the crust of oxidized samples. At the Cariboo Zinc property, smithsonite is the most abundant zinc nonsulphide phase, though hemimorphite is also present. Lead nonsulphides on the property consist of anglesite and cerussite. The Oxide prospect is not associated with sulphide ore and the main nonsulphide phases are hemimorphite and hopeite. All of the nonsulphide deposits studied fit the direct-replacement style of nonsulphide mineralization, with the exception of the Oxide prospect, which shows traits of wall-rock-replacement style mineralization. Though the nonsulphide deposits differ to some extent in mineralization styles, all fit the general supergene model of nonsulphide mineralization and further characterization can assist in creating an exploration model for similar deposits in BC and the rest of the Cordillera.
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