Geochemistry and Au mineralization within the Kakagi-Rowan Lakes greenstone belt : a study of the Angel Hill Gold Zone

Abstract

The Angel Hill Gold Zone of the West Cedartree Gold Project has been exposed over 300 meters along the internal contact of ultramafic and gabbroic rocks within the Kakagi Sill. The sill lies within the Kakagi-Rowan Lakes greenstone belt and has intruded the mafic metavolcanic rocks of the Snake Bay Formation and the felsic to intermediate etavolcanic rocks of the Emm Bay Formation. The Snake Bay Formation consists of pillowed and massive basalts and fine-grained tuffs. The Emm Bay Formation stratigraphically overlies the Snake Bay Formation and consists of tuffs and tuff breccias. Trace element geochemistry and primitive mantle normalised plots suggest that both the rocks of the Kakagi Sill and the Snake Bay F ormation are comprised of metasomatsed island arc tholeiite basalts whereas the rocks of the Emm Bay Formation are characterised of a back island arc affinity. The Angel Hill Gold Zone occurs as extensive carbonate and quartz flooding within a zone of brittle deformation termed the master fault. A distinguishing feature of the gold zone is the presence of extensive fuchsite alteration forming large mats up to 20 meters wide. Mineralization in the Angel Hill Gold Zone consists of free gold and sylvanite occurring as inclusions within and rimming pyrite grains, as well as precipitated along small fractures in quartz. Associated mineralization includes pyrite as well as galena and sphalerite. Textural relationships and stable isotope analyses of carbonate (o1 80 1 3 .6 to 1 7 .9 %o), quartz (o 1 80 8.8 to 1 3. 1 %o), pyrite (o34S -0.8 to 1 .0 %o), sphalerite (o34S 1 .3 to 5.4 %o), and galena (o34S 5 .9 to 7.3 %o) suggest multiple episodes of brittle deformation and fluid influx within a protracted lode gold system. The combination alteration assemblages and stable isotope characteristics suggest that the Angel Hill Gold Zone formed as a result of listwanite metasomatism with input of fluids from both magmatic and metamorphic sources. These fluids propagated as a result of the brittle faulting that occurred due to a competency contrast between the ultramafic footwall and the gabbro hangingwall during regional deformation.