Formation of Fe-Cu-Au deposit in basin inversion setting in NW China: A perspective from ore-fluid halogen and noble gas geochemistry

Abstract

Abstract The Qiaoxiahala deposit is a significant Paleozoic Fe-Cu-Au deposit in the northern margin of East Junggar, NW China, which has been confirmed to form in a basin inversion setting (dying back-arc basin). The composition of noble gases (Ar, Kr, and Xe) and halogens (Cl, Br, and I) extracted from fluid inclusions, hosted in quartz, calcite, and epidote from various mineralization stages of Qiaoxiahala, are investigated to trace the sources of ore fluids and discuss the ore genesis. Significant multistage mineralization at Qiaoxiahala is identified as magnetite mineralization (stage III), magnetite-pyrite mineralization (stage IV), and chalcopyrite mineralization (stage V). Syn-ore fluid inclusions show salinities varying from 13.2 to 15.3\xa0wt% (NaCl eq.) associated with elevated I/Cl ratios (214\xa0×\xa010−6 to 3950\xa0×\xa010−6), uniformly low Br/Cl ratios (0.78\xa0×\xa010−3 to 1.30\xa0×\xa010−3), and low 40Ar/36Ar ratios (