Mineralisation, Alteration Assemblages, Geochemistry and Stable Isotopes of the Intermediate-Sulfidation Epithermal Kylo Deposit, Drake Goldfield, North-Eastern NSW, Australia

Abstract

The intermediate-sulfidation epithermal Kylo deposit is part of the Drake Goldfield of north-eastern NSW. The mineralization is gold-dominant with minor silver and significant levels of zinc, copper and lead. Kylo has a resource of 2.298 Mt @ 1.23g/T Au and 1.35 g/T Ag. Mineralization mainly occurs in the form of vein stockworks. Petrographic and SEM analysis show that there are at least three mineralization events, with Au mineralization strongly associated with at least a deposit-scale alteration event. Quantitative XRD analysis shows a strong positive correlation between Au-mineralization and argillic-phyllic alteration. Electrum was found as inclusions in massive sphalerite in the main mineralization stage. Correlation analysis for the assay data indicates that Au has a strong relation with Ag and moderate correlation with Pb. Petrographic and geochemical analysis has identified three lithologies, rhyolite, rhyodacite/dacite and andesite, with Au mineralization more associated with the rhyodacites, while at deeper levels some of the andesites also show a relatively strong correlation with Au. Sr shows a significant strong depletion, due to the intense and pervasive alteration at Kylo. The andesitic volcanics show moderate LREE enrichment with small negative Eu anomalies, and relative depletion in Nb, Ta and Ti, indicating an island arc tectonic setting. The carbon and oxygen isotopes of late-stage vein carbonates suggest that the fluid was derived from a magmatic source with a significant influence of low-temperature alteration, while the sulfur isotopes indicate a magmatic sulfur source.