THE BIG EASY PROSPECT: A WELL-PRESERVED LATE NEOPROTEROZOIC LOW-SULFIDATION AG-AU DEPOSIT IN THE AVALONIAN TERRANE OF NEWFOUNDLAND, CANADA

The Big Easy prospect is located near Thorburn Lake, approximately 18 km NW of Clarenville, NL. A zone of intense silicification over 1.5 km long, and up to 300 m wide, is recognized on the property, largely within coarse arenite to conglomerate sedimentary rocks of the Musgravetown Group. These sediments contain abundant fragments of intermediate to felsic volcanic rocks, and are currently interpreted to be epiclastic sediments representing intracaldera fill. The silicified sedimentary rocks also contain abundant fine-grained euhedral pyrite. Both silicification and extensive pyritization may have taken place in shallow ponds during the induration of these sediments.

Within the zone of silicification, discrete quartz-chalcedony veins containing Ag-Au mineralization cross-cut the previously indurated epiclastic sediments. These veins contain a very typical “ginguro”-type assemblage of native Ag, acanthite, electrum, naumannite, closely associated with chlorite-white mica alteration and accompanying sulfides and sulfosalts including pyrite, chalcopyrite, and freibergite. Bladed textures of intergrown quartz-adularia are often a component of the mineralized veins, which also display the macroscopic crustiform-cockade textures and brecciation typical of many low-sulfidation epithermal deposits. Only limited diamond drilling has been completed to date, but brecciated quartz-adularia veins in one diamond drill hole (DDH BE-12-12) assayed 1.3 g/T Au and 36.7 g/T Ag over 8.7 m, including 7.9 g/T Au and 130 g/T Ag over 1.2 m (Silver Spruce Resources, News Release, January 16, 2015). Other vein types contain banded opaline or milky chalcedony, which may represent shallow deposition of silica gels in the hydrothermal system.

Work is ongoing to provide a more explicit age for the deposit, but it is currently constrained within the 585-565 Ma age range of many other high- and low-sulfidation epithermal deposits recognized throughout the Avalonian Terrane, including the 575 Ma Hope Brook deposit.