Granite-related gold mineralization in the Cape Ray fault zone of southwestern Newfoundland

Abstract

Two electrum and base metal sulfide-bearing quartz vein deposits occur in an alaskitic granite (the Windowglass Hill Granite) and an intermixed graphite-chlorite-sericite schist unit (the Windsor Point Group), both within the Cape Ray fault zone of southwestern Newfoundland. Wall rocks to the electrum-bearing quartz veins were subjected to potassic alteration and minor enrichment in chalcophile elements. Ore metals in the showings are Au, Ag, Cu, Pb, and Zn, and their distributions resemble those seen in gold-bearing massive sulfide deposits. The minerals present are galena, sphalerite, chalcopyrite, pyrite, electrum, and rare arsenopyrite, all of which are extensively intergrown. Temperatures of ore formation, or equilibration, estimated from arsenopyrite and other sulfide mineral intergrowths appear to be around 300 degrees C. Sulfur isotope ratios indicate that sulfur in the showings is probably of magmatic origin. Pb isotope ratios in galenas from the showings and felsic volcanic members of the Windsor Point Group are similar and have an oceanic crust-mantle isotopic signature. These precious and base metal-bearing quartz veins were deposited by hydrothermal fluids exsolved as a vapor phase from the Windowglass Hill Granite.