GEOCHEMISTRY OF THE DOME MINE ANKERITE VEINS; INSIGHTS INTO FLUID FLOW PATHWAYS AND THE MULTI-STAGE ENRICHMENT OF A WORLD-CLASS OROGENIC GOLD DEPOSIT

Over the last 100 years the Dome mine in the world-class Timmins gold camp has produced over 16 Moz. This gold endowment is the result of multistage enrichment of which the first stage is a massive set of ankerite veins which extend over 5,400m in strike and 1,500m vertically, and are overprinted by subsequent mineralization events. The extensive mining history of the Dome mine provides a unique three-dimensional view into the geometry of the deposit both from underground and open pit workings. A deposit wide study of the Dome ankerite veins, with samples and mapping from historical and modern mine workings was undertaken to characterize their genesis, geochemistry, and to provide insights into the fluid history of the deposit. The ankerite veins have contributed ~20% of the ore at the Dome mine and were deposited between ~2,690 and 2,679 Ma into the Vipond formation of the Tisdale Assemblage metavolcanics, primarily along flow boundaries. Grade is variable across their extensive strike length ranging from <1 to 98 g/t, and is intimately associated with pyrite mineralization. Three stages of pyrite growth have been identified, each with a distinct gold and trace element fingerprint. These stages of pyrite growth can be related to three deposit wide fluid events. The δ¹³C and δ¹⁸O values for dolomite from the ankerite veins show a trend of increasing δ¹⁸O_VSMOW values from 10.8 to 14.9‰ down dip of the ankerite veins and to the Northwest away from the Dome Fault Deformation Zone (DFDZ). The DFDZ is a region of intensely deformed and carbonatized ultramafic and felsic rock. It hosts the highest producing structure at the Dome mine, the Quartz-Fuchsite Vein, and is a long-lived structure which likely acted as a fluid conduit for the ankerite forming metamorphic fluids. Carbonate alteration related to the early ankerite vein forming fluids played an important role in the mineralization history of the deposit by facilitating a rheological and geochemical regime in the DFDZ and mine volcanic sequences favoring auriferous vein formation during subsequent fluid events.