Light Stable Isotope Evidence for a Metamorphogenic Origin for Bedding-Parallel, Gold-bearing Veins in Cambrian Flysch, Meguma Group, Nova Scotia

Exploration & Mining Geology, Vol. 1, No. 1, 1992

ALAN L. SANGSTER Geological Survey of Canada, 601 Booth Street, Ottawa

Auriferous, bedding-parallel veins occur in zones of carbonaceous, argillaceous and sulfidic turbidites in the Lower to Middle Cambrian sandy flysch of the Goldenville Formation. The S^S values for vein and wall-rock arsenopyrite and pyrrhotite, and for regional pyrite and pyrrhotite, are highly positive. The values are similar to those from Cambro-Ordovician sediment-hosted deposits of other types, and display trends that increase upward in the stratigraphic sequence. The similarity in composition of vein and wallrock sulfides indicates a seawater-sulfate source for sulfur, derived from the enclosing rocks at the time of vein formation. The upward increase in 3^5 values is consistent with closed system sulfate reduction in the anoxic portion of a stratified water-column. Published 613C and 518O values for Meguma Group vein carbonates are unlike those of other gold-vein carbonates, but are similar to those of diagenetic-metamorphic carbonates from the Meguma Group and elsewhere. These data indicate that the source for the vein-related sulfides and carbonates may be the host strata; possibly the arsenic and gold were derived from the same source.