Mineral chemistry and sources of fluid and sulfur at the Katbasu gold deposit in South Tianshan, NW China

Abstract

Katbasu is a gold (and copper) deposit located in an arc on the southern margin of the Ili-Central Tianshan micro-continent. An in-situ method was conducted to acquire trace element concentrations to elucidate the origins and chemistry of the fluid in the Katbasu deposit. This included oxygen isotopes in quartz, as well as sulfur isotopes and trace elements concentrations in pyrite. Trace elements in gold deficient veins have higher concentrations compared to those in the gold bearing veins. The δ18O values of gold deficient veins are between 3.9 and 8.1‰, which imply a magmatic oxygen isotope signature. In contrast, oxygen isotopes in gold bearing veins range between −1.3 and 5.8‰, indicating the involvement of meteoric water in the mineralization system. This data, combined with evidence from alteration style and metal assemblages, shows that the ore-forming fluids at the Katbasu gold deposit is of a magmatic origin. The data also indicates that meteoric water diluted the magmatic fluid and caused an oversaturation of gold, causing precipitation of native gold grains. Trace elements in pyrite show no difference among the veins analyzed. However, they have distinctly different trace element patterns of pyrite from orogenic gold deposits. Based on the δ34S values of pyrite (8.3–12.9‰), and the lack of coeval regional metamorphism, we conclude that the enriched 34S at the Katbasu gold deposit is derived from a subducted slab during the Late Carboniferous.