Petrology, mineralogy, and geochemistry of the Carboniferous Katbasu Au-Cu deposit, western Tianshan, Northwest China: Implications for petrogenesis, ore genesis, and tectonic setting

Abstract

The Katbasu Au-Cu deposit in the Chinese western Tianshan is hosted in the ca. 355 Ma granite intrusion. This paper reports whole-rock geochemical and zircon Hf-O isotopic data for the granites and the mafic enclaves as well as in situ S isotopic data for the sulfides from the Katbasu Au-Cu deposit. Our results provide constraints on the petrogenesis and ore genesis of the Katbasu Au-Cu deposit. Geochemical characteristics suggest that the Katbasu granites are metaluminous rocks, exhibiting mineral assemblages and geochemical characteristics of I-type granites. The granites have positive zircon εHf(t) values of 7.1–10.2 and zircon δ18O values of 6.2–7.2‰, suggesting a juvenile crustal origin. Mixing processes between felsic and mafic magmas were involved in their generation. The mafic enclaves are enriched in LILEs and depleted in HFSEs, and have zircon εHf(t) values of 7.5–15.8 and zircon δ18O values of 5.4–6.9‰, suggesting that they were derived from a subduction-modified mantle and underwent subsequent crustal contamination and/or magma mixing processes. In situ S isotopic analyses show that pyrite grains from the pre-ore stage and post-ore stage have positive δ34S values of 7.0–8.5‰ and 8.2–9.0‰, respectively. Pyrite and chalcopyrite grains from an early magmatic-hydrothermal Cu-Au mineralization stage show δ34S values of 8.8–11.1‰, and pyrite grains from the main orogenic Au mineralization stage have positive δ34S values of 5.9–8.4‰. The heavy S isotope characteristics of magmatic-hydrothermal Cu-Au mineralization indicate that the magma source might be metasomatized by subduction materials, whereas the heavy S isotope characteristics of the late orogenic Au mineralization suggest that the ore-forming materials mainly originated from the metamorphic devolatilization of the source rocks. The ca.352–349 Ma early magmatic-hydrothermal Cu-Au mineralization in the Katbasu deposit formed in a subduction tectonic setting, whereas the ca. 323–311 Ma late orogenic Au mineralization formed in an orogenic environment during the final stage of subduction.