Gold-bismuth occurrences in the Kennedy igneous province, North Queensland: constraints on tectonic, magmatic and hydrothermal processes in intrusion-related gold deposits

• Main Author: Graham-Ruzicka, Julie Louise
• Format: Thesis
• Language: unknown
• Published: 2014
• Subjects: Queensland; Yukon; Alaska
• Online Access: https://researchonline.jcu.edu.au/43773/1/43773-graham-ruzicka-2014-thesis.pdf; https://researchonline.jcu.edu.au/43773/2/43773-graham-ruzicka-2014-appendix-1-maps.pdf

The Kennedy Igneous Province (KIP) in north Queensland, Australia is host to a gold mineralising event (8.5Moz) associated with Carboniferous–Permian aged magmatism. Gold production was mainly from the shallowly emplaced (<5km) hydrothermal breccia pipe hosted gold deposits like Kidston, Mt Leyshon and Mt Wright. The Kidston and Mt Leyshon deposits share characteristics with intrusion-related gold systems of the Tintina Gold Province, Yukon and Alaska. This suggests north Queensland is prospective for intrusion-related gold deposits or intrusion-related gold systems. The thesis focused on whether two gold occurrences, the Empire Stockworks and Douglas Creek gold mineralisation, share similarities with other intrusion-related gold systems. Empire Stockworks gold mineralisation is temporally and spatially associated with rhyolite dykes located on the eastern margin of the Empire dacite hydrothermal breccia pipe. A number of Empire Stockworks characteristics are similar to other shallow intrusion-related gold systems. The geochemistry of the Empire Stockworks rhyolite dykes suggest they are weakly to strongly oxidised (Fe₂O₃\FeO, 0.5-8), sub-alkaline (<10wt. % Na₂O+K₂O and~60 to 85wt. % SiO₂), peraluminous, moderately to highly fractionated (Rb/Sr >1, -ve Eu compared to REECN) intrusions derived from a crustal source (depleted in Ba, Nb, La, Ce, Sr, P and Ti compared to primitive mantle). The veins are associated with potassic alteration and contain <2% sulphide. The mineralising fluid was CO₂ poor with variable salinities from ~5 to 45 equivalent wt. % NaCl. The best estimate of conditions of mineralisation is ~260-437ºC at 1.5kbar. This estimate is based on a primary L-V inclusion entrapment temperatures calculated using an entrapment pressure (1.5kbar) from a primary ms-L-V inclusions, in a Stage 2 quartz K-feldspar vein, that homogenised by halite disappearance. Further work is required to confirm the entrapment conditions. Mineralisation contains gold associated with Bi-chalcogenides, although the ...