Gold Exploration in the Timmins District Using Field and Lithogeochemical Characteristics of Carbonate Alteration Zones

Special Volume, Vol. SV 24, No. 1982, 1982

All gold deposits within the Tisdale Group are spatially associated with carbonate alteration zones; however, not all carbonate alteration zones are host to gold mineralization. Within the komatiitic and magnesium tholeiitic volcanic rocks at the base of the Tisdale Group, discordant and stratabound carbonate alteration zones occur throughout. The alteration zones consist of a ferroan dolomite - quartz inner assemblage which is enveloped by calcite-quartz and an outer chlorite-rich subzone. Factors which control the distribution of carbonate alteration include joint systems, flow contacts, synvolcanic faults and bulk composition of the host rock. Two environments of carbonate alteration can be recognized: 1) The subsea-floor alteration zones developed within the volcanic rock succession where hydrothermal fluids did not discharge directly onto the sea floor. Insignificant gold production has come from this alteration environment. 2) Seafloor zones, which represent points of hydrothermal fluid discharge into the hydrosphere, are spatially associated with felsic volcanic rock complexes and are host to syngenetic, auriferous cherty dolomite. Carbonatized, magnesium tholeiitic basalts, which are host to the auriferous, cherty dolomite, are enriched in antimony (>0.35 ppm), boron (>30 ppm), gold (>5 ppb) and lithium (> 35 ppm), but are depleted in copper ( 5 ppb), lead(> 10 ppm), arsenic(> 70 ppm) and antimony (>1 ppm). The habit, petrographic characteristics and certain geochemical characteristics of the altered volcanic rocks suggest that the hydrothermal fluid was of sea-water origin.
Keywords: Gold, gold mining, gold exploration, Timmins, Carbonate alteration zones, volcanic rocks