The geology and geochemistry of gold mineralization in the Betts Big Pond area, Newfoundland.

Abstract

The ultramafic member of the Lower Ordovician Betts Cove Ophiolite Complex forms an elongate fault bounded belt on the eastern side of the Baie Verte Peninsula. The Betts Big Pond area encompasses the transition between the least altered layered cumulate rocks of the southern part of the ultramafic belt and the metasomatized rocks of the northern part of the ultramafic belt and includes serpentinite, serpentine-carbonate rocks, and talc-carbonate rocks. Au concentrations up to 1300 ppb occur in hematite bearing talc-carbonate rocks in the northern part of the Betts Big Pond area. The occurrence of Au in talc-carbonate racks is consistent with its deposition from Au(HS)$\sb2\sp-$ due to fluid oxidation as a result of the carbonatization of magnetite in the absence of Fe-bearing serpentine. The Au occurrence in serpentinite is consistent with Au deposition from Au(HS)$\sb2\sp-$ as the serpentinizing fluid reacted with a chromite lens. The Long Pond and Arrowhead Pond veins in the northern part of the Betts Cove Complex are interpreted to have formed from fluids of mutually similar composition. C and O isotopic compositions of vein carbonates from the northern Betts Cove Complex are similar to the isotopic composition of C and O of magnesite from talc-carbonate rocks and serpentine-carbonate rocks of the Betts Big Pond area. Talc-carbonate rocks within the alteration halo surrounding Au-vein mineralization at Arrowhead Pond is enriched in SiO$\sb2$; Otherwise it is chemically similar to talc-carbonate rocks. The similarity in chemical and isotopic compositions suggests that Au-vein mineralization may have been emplaced at a similar time as that in talc-carbonate rock in the Betts Big Pond area. (Abstract shortened by UMI.)