Silver-lead-zinc veins, metamorphic core complexes, and hydrologic regimes during crustal extension

Abstract

The Kokanee Range Ag-Pb-Zn-Au vein and replacement deposits formed during Eocene crustal extension and unroofing of the Valhalla metamorphic core complex, in the hanging wall of the transcrustal Slocan Lake fault. The δ34Ssulfide, δ18Oquartz, δ18Osiderite, and galena Pb isotopic ratios for vein minerals display regional zonations revealing fluid-flow paths of a large, fossil hydrothermal system. Sulfur was derived from local country rocks, but carbon was derived from a deep-seated reservoir, possibly the upper mantle. Lead is a mixture of local, upper-crustal Pb with lower-crustal and depleted upper-mantle Pb. Regional isotopic zonations were controlled by deep fracture zones, such as the Slocan Lake fault, which channeled lower-crustal and mantle Pb and mantle CO2 to higher-crustal levels, where mixing occurred with highly evolved meteoric waters that had leached local sulfur and upper-crustal Ph. This is the first Ag-Pb-Zn vein district for which a genetic link between mineralization and metamorphic core complex unroofing is demonstrated.