Rb-Sr geochronology of single gold-bearing pyrite grains from the Katbasu gold deposit in the South Tianshan, China and its geological significance

Abstract The newly discovered Katbasu gold deposit in the South Tianshan region has a gold reserve of 76 t at an average grade of 3.84 g/t. It is the first large gold deposit in the central segment of the South Tianshan. Gold mineralization is hosted within granite, and is associated with potassic, phyllic and chloritic alteration. Gold-bearing pyrite occurs as disseminations in the host rock and as quartz-sulfide veins cross-cutting the potassic and phyllic alteration assemblage. Rubidium (Rb) - strontium (Sr) analyses on sericite within five individual pyrite grains from a phyllic alteration sample yield an isochron age of 322.5 ± 6.8 Ma (MSWD = 3.2). The host granite has a SIMS U-Pb zircon age of 351.4 ± 1.1 Ma (MSWD = 0.13). The Rb-Sr isochron age represents the mineralizing age of the Katbasu gold deposit, which significantly postdates the ore-hosting granite but is consistent with the age of regional porphyry type mineralization at ~ 320 Ma in the South Tianshan. Discovery of the Katbasu gold deposits indicates huge potential for gold exploration in the central segment of the South Tianshan as it is geologically similar to the western and eastern segments of the South Tianshan, which both host many world-class gold deposits.