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The Salmo lead-zinc deposits : a study of their deformation and metamorphic features MacDonald, Alan Stratton

Abstract

The problematic history of the strata-bound Salmo lead-zinc deposits, which occur in highly deformed, low-grade metasediments of the southern Kootenay Arc of British Columbia, has been investigated via structural analyses, fabric studies, and minor element determinations in three of the deposits: Reeves MacDonald, Jersey and H. B. mines. Three phases of folding have been distinguished: an early phase of near-isoclinal folding, overturned toward the west, produced the major structures; a second phase of upright, more open folding modified the first phase folds by near coaxial refolding, by further closure and local flattening, and ultimately by westward-directed thrusting; a third phase of conjugate mono-clinal folds and kink bands was produced by north-south compression related to northward-directed thrusting. The essentially tabular sphalerite-pyrite-galena ore bodies are involved, on all scales, in the folding and the ores exhibit internal structures ascribed to the differential movement of sulphides and host dolomite and calcite marbles. Regional metamorphism, to lower greenschist facies, was synchronous with Phase 1 folding. Contact metamorphism by granite stocks (K-Ar age: circa 100 m.y. B.P.) postdates all phases of folding, and affects Jersey and H. B. deposits, and possibly also Reeves MacDonald; estimated temperatures are in the range 425-600°C (at 1.5 kb). Seventy-one analyses of minor elements in the sulphides show that pyrite has Co:Ni

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