Fingerprinting multiple gold mineralization events at the Dome mine in Timmins, Ontario, Canada: Trace element and gold content of pyrite

Abstract

The Dome mine is host to over 16 Moz of orogenic gold deposited during a period of up to 25 Ma through multi-stage enrichment. The earliest economic stage of veining is an extensive set of ankerite veins which were historically considered barren except where overprinted by subsequent veining events. Gold in these veins is intimately associated with pyrite mineralization, and three stages of pyrite growth have been identified (Py1,2,3). The trace element content of each stage of pyrite growth determined by dynamic-secondary ion mass spectrometry and synchrotron radiation x-ray fluorescence reveals that there were three auriferous fluid events, each with a unique gold and trace element fingerprint which can be related to deposits wide mineralization events. Early ankerite vein forming fluids were auriferous, lower temperature (200–250 °C) and deposited Py1 enriched in gold, metals and metalloids (As, Cu, Ni, Zn). Py2 growth is related to deposit wide quartz-tourmaline and quartz-fuchsite veining based on trace element geochemistry, Au:Ag, and associated mineral assemblages. This deposited Ni enriched pyrite, tellurides, galena, and gold with anomalously high Au:Ag ratios. There is also evidence for remobilization of early gold and trace elements from Py1 pyrite during the Py2 forming event. The final stage of gold endowment in the ankerite veins is related to a deposit (and camp) wide quartz veining event. Py3 growth is trace element (As, Ni, Cu) and Au poor with respect to Py1 and Py2, however, this veining event contributed the bulk of the ankerite vein gold endowment. The remobilization of gold and trace elements from sieve textured Py1 in addition to overprinting Py2 and Py3 and their associated gold endowments helps explain the difficulty in applying bulk rock trace element vectors to gold at the Dome mine. The work also provides conclusive evidence for the auriferous nature of early ankerite veining at the Dome mine, and reveals that the system was fertile for a period of over 7 to 25 Ma, a key component for the formation of a world-class deposit.