INVISIBLE GOLD IN SULFIDES FROM THE CAMPBELL MINE, RED LAKE GREENSTONE-BELT, ONTARIO - EVIDENCE FOR MINERALIZATION DURING THE PEAK OF METAMORPHISM

The Au content of pyrite and arsenopyrite from the Campbell mine, Red Lake mining camp, Ontario, has been established by secondary-ion mass spectrometry (SIMS). All Au contents significantly exceed the minimum detection-limits of the technique (36 ppb in arsenopyrite, 193 ppb in pyrite). Arsenopyrite is characterized by high contents of ''invisible '' Au (up to 0.56 wt%). Coarse-grained arsenopyrite displays Au zoning , and fine-grained arsenopyrite generally displays a uniform Au conten t. Gold is present in low concentrations in pyrite (up to 168 ppm), an d elevated Au is related to As-rich zones. The host rocks at the mine have experienced low-pressure amphibolite-grade metamorphism. We consi der it unlikely that compositional zoning could survive metamorphic re crystallization. Textural relations between gahnite and auriferous ars enopyrite, and the presence of auriferous arsenopyrite inclusions in g arnet, indicate that the introduction of Au was synchronous with peak conditions of metamorphism.