Source of lead in the gold-bearing quartz-fuchsite vein at the Dome mine, Timmins area, Ontario, Canada

The quartz-fuchsite vein at the Dome mine, Timmins area, Canada, is characterized by a consistent spatial association of gold and galena. A lead isotope study was carried out to trace the source of the lead in the galenas, and to evaluate possible source reservoirs for the gold. Although other sources cannot be entirely ruled out, the lead isotope composition of most of the galenas and of local quartz-feldspar porphyries suggests that most of the lead in the vein-galenas was derived from the Dome mine porphyries. However, lead isotope systematics do not allow unique constraints to be placed on the gold source. Conceptual genetic models commonly advocate gold source reservoirs such as shallow to deep seated igneous intrusions, the middle to lower crust or the mantle for Archean lode gold deposits. A likely scenario is that ore-bearing hydrothermal fluids originated at depth, and were preferentially channeled along the porphyries to the site of ore deposition. The hydrothermal fluids leached lead from the porphyries, and deposited gold and galena together in the quartz-fuchsite vein. Two galena samples have “anomalous” lead compositions and are colinear with the main galena cluster suggesting one or more contamination episodes, broadly between 1250 and 2480 Ma, resulting in further addition of radiogenic lead to the galenas.