Contrasting styles of Archaean greenstone gold deposition: Colomac gold mine, Canadian Northwest Territories

摘要

The Colomac mine has produced >15,000 kg of gold form Archaean subvolcanic rocks of the Slave Province of thee Candian Shiield. Two deposit types with distinct styles of gold ore minralisation exist:(1) shallow, low-grade, high-tonnage deposis with primarily sulphide-hosted gold;and (2) deeper, localised, high-grade deposits comprising native gold-quartz veins. Both deposit types formed from H_2O-CO_2-NaCl fluids at temperatures of 250-375deg C and pressures of 1-2 kbar and appear to be a part of a single mineralising system in which the mechanism of gold deposition dictated the style of mineralisation. Colomac provides an opportunity to address the basic causes of gold accumulation in the earth's crust by documenting processes leading to the formation of large, low-grade deposits (fluid-wall rock reaction) versus localised, high-grade deposits (fluid unmixing) in greenstone belts.