Tectonic control of quartz vein orientations at the Trout Lake stockwork molybdenum deposit, southeastern British Columbia; implications for metallogeny in the Kootenay Arc

Abstract

Quartz vein orientations and crosscutting relationships are used to evaluate the structural evolution of the Trout Lake stockwork molybdenum deposit, located in the Kootenay arc region of southeastern British Columbia. There are five main vein trends. Early veins trend 135 degrees + or - 15 degrees (trend 1) and are parallel to the regional foliation. These are followed by orthogonal 045 degrees + or - 15 degrees trending veins (trend 2) and a conjugate set of veins trending 005 degrees + or - 15 degrees and 095 degrees + or - 15 degrees (trends 3 and 5). The youngest veins are subhorizontal (trend 4). Molybdenite grades are highest in the orthogonal vein sets (trends 1 and 2). A similar distribution of vein orientations is also observed for Pb-Zn-Cu-Ag-Au vein-type deposits in adjacent parts of the Kootenay arc.The veins are interpreted as being related to a northeasterly directed compressive stress field produced by collisions of allochthonous terranes with North America. Trend 2 and trend 1 veins represent the primary and secondary axes of a stored elastic stress field that was released during uplift. The temporal order of the two vein trends is reversed owing to host-rock anisotropy. The trend 4 veins formed as a result of the release of stored elastic stress perpendicular to the tertiary stress axis. Fracturing in both the Trout Lake and regional base and precious metal deposits is attributed largely to thermal expansion of pore fluids.The Trout Lake molybdenum deposit is considered to be part of a postkinematic granite-related metallogenic event which formed stockwork Mo deposits, skarn W deposits, and remobilized stratiform Pb-Zn-Ag into discordant vein-type deposits during an episode of Middle to Late Cretaceous uplift.