Fish Lake porphyry copper-gold deposit, central British Columbia

Special Volume, Vol. SV 46, No. 1995, 1995

The Fish Lake porphyry copper-gold deposit is situated 130 km southwest of Williams Lake, British Columbia, near the southwestern edge of the Intermontane Belt. The deposit is spatially and genetically related to the Late Cretaceous Fish Lake Intrusive Complex. This Complex consists of the steeply-dipping, lenticular Fish Creek quartz diorite stock surrounded by an east-west swarm of subparallel quartz feldspar porphyry dikes. The greater part of the deposit, however, is hosted by adjacent andesite flows and volcaniclastic rocks of probable Early Cretaceous age. The Fish Lake deposit contains a global geological reserve of 1148 million tonnes with an average grade of0.22% Cu and 0.41 gl t Au. It is oval in plan and is 1500 m long, 8(}() m wide and extends to a maximum depth of 880 m. Potassium silicate alteration forms a central alteration zone co-extensive with the coppergold mineralization. An irregular zone of phyllic alteration is developed at the boundary between the potassium silicate alteration zone and the surrounding propylitic altered rocks. Later sericite-iron carbonate-clay alteration forms numerous narrow zones throughout the deposit. Pyrite and chalcopyrite are the principal sulphide minerals within the deposit and bornite occurs widely in subordinate amounts. Native gold occurs as microscopic grains, as inclusions and along microfractures in chalcopyrite, tetrahedrite/ tennantite and pyrite. An irregular pyrite halo several hundred metres wide surrounds the northern and eastern sides of the deposit, and is more or less co-extensive with the phyllic alteration zone.

Mots Clés: Porphyry, Copper-gold deposit, Fish lake