Geological, mineralogical, geochemical and physical characterization of carbonate-hosted nonsulphide Zn-Pb mineralization in southern British Columbia (NTS 82F, 93A)
- Suzanne Paradis and George Simandl

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.

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.

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).

Posters and Presentations
2011: Geology and geochemistry of carbonate-hosted nonsulphide Zn-Pb mineralization in southern and central BC (BCGS Geofile 2011-4)
- Mineral Exploration Roundup Conference 2011 Poster

2011: Hand-held, portable XRF in exploration for carbonate-hosted sulphide and nonsulphide Pb-Zn deposits (BCGS Geofile 2011-6)
- Mineral Exploration Roundup Conference 2011 Poster

2011: Mineralogy of Supergene Carbonate-Hosted Nonsulphide Zn-Pb Mineralization in Southern and Central British Columbia
- Mineral Exploration Roundup Conference 2011 Poster (pdf, 6.3 MB)
Technical Articles
2011: "Geology and mineralogy of carbonate-hosted nonsulphide Zn-Pb mineralization in southern and central British Columbia"
- Summary of Activities 2010, Report 2011-1 p. 143-168 (pdf, 35.2MB)

2011: "Physical properties of carbonate-hosted nonsulphide Zn-Pb mineralization in southern and central British Columbia"
- Summary of Activities 2010, Report 2011-1 p. 169-180 (pdf, 6.9 MB)
Final Deliverables
2011: "Carbonate-hosted, Nonsulphide Zn-Pb (sugergene) Mineral Deposit Profile B09"
- BCGS Geological Fieldwork 2010, Paper 2011-1 p. 189-194 (pdf, 7.3 MB)

B.Sc. Honours Thesis - H.A. Keevil
Mineralogical and Geochemical Characterization of Supergene Carbonate-hosted Nonsulphide Zn-Pb Mineralization in Southern and Central British Columbia - University of British Columbia, 2011 - Available digitally through the University of British Columbia (pdf, 6.3 MB)

Abstract: 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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