REE and background Au/Ag evidence concerning the origin of hydrothermal fluids in the Cape Ray electrum deposits, southwestern Newfoundland

CIM Bulletin, Vol. 78, No. 874, 1985

DEREK H.C.WILTON, Department of Earth Sciences, Memorial University of Newfoundland, St. John's, Newfoundland

The Cape Ray Fault Zone of southwestern Newfoundland contains two notable electrum/base metal sulphide quartz vein lode occurrences hosted by two contrasting lithological units, viz. a graphite schist horizon and a granite. The two occurrences, although in proximity, are not in direct contact, but, based on geochronological, geochemical and isotopic evidence, they were apparently deposited from hydrothermal fluids generated as a vapour phase from the magmatic progenitor of the Windowglass Hill granite. This paper provides further evidence, from REE and background Au andAg data, for the magmatic origin of the hydro-thermal fluids. Wall rocks to the electrum-bearing quartz veins in both the schists and granite have experienced a LREE depletion probably due to leaching by Cl--bearing solutions. Gold and silver contents are typically low in all rock types but there is a slight elevation in gold concentrations in those units in contact with the Windowglass Hill granite. The granite also has the relatively highest gold and silver contents of any unit in the region.

Keywords: Gold mineralization, Rare earth elements, Cape Ray, Electrum deposits, Hydrothermal fluids, Gold, Silver, Granites.