First Reliable ReOs Ages of Pyrite and Stable Isotope Compositions of Fe(-Cu) Deposits in the Hami Region, Eastern Tianshan Orogenic Belt, NW China

The Eastern Tianshan Orogenic Belt (ETOB) in NW China is composed of the DananhuTousuquan arc belt, the Kanggurtag belt, the AqishanYamansu belt and the Central Tianshan belt from north to south. These tectonic belts have formed through arccontinent or arcarc collisions during the Paleozoic. A number of Fe(-Cu) deposits in the AqishanYamansu belt, including the Heifengshan, Shuangfengshan and Shaquanzi Fe(-Cu) deposits, are associated with CarboniferousEarly Permian volcanic rocks and are composed of vein-type magnetite ores. Metallic minerals are dominated by magnetite and pyrite, with minor chalcopyrite. Calcite, chlorite, and epidote are the dominant gangue minerals. Pyrite separates of ores from those three deposits have relatively high and variable Re contents ranging from 3.7 to 184 ppb. All pyrite separates have very low common Os, allowing us calculation of single mineral model ages for each sample. Pyrite separates from the Heifengshan Fe deposit have an 187Re187Os isochron age of 310 +/- 23Ma (MSWD = 0.04) and a weighted mean model age of 302 +/- 5Ma (MSWD = 0.17). Those from the Shuangfengshan Fe deposit have an isochron age of 295 +/- 7Ma (MSWD = 0.28) and a weighted mean model age of 292 +/- 5Ma (MSWD = 0.33). The Shaquanzi Fe-Cu deposit has pyrite with an isochron age of 295 +/- 7Ma (MSWD = 0.26) and a weighted mean model age of 295 +/- 6Ma (MSWD = 0.23). Pyrite separates from these Fe(-Cu) deposits have 34SCDT ranging from 0.41 parts per thousand to 4.7 parts per thousand except for two outliers. Calcite from the Heifengshan Fe deposit and Shaquanzi Fe-Cu deposit have similar C and O isotope compositions with 13CPDB and 18OSMOW ranging from 5.5 parts per thousand to 1.0 parts per thousand and from 10 parts per thousand to 12.7 parts per thousand, respectively. These stable isotopic data suggest that S, C, and O are magmatic-hydrothermal in origin. The association of low-Ti magnetite and Fe/Cu-sulfides resembles those of IronOxideCopperGold (IOCG) deposits elsewhere. Our reliable ReOs ages of pyrite suggest that the Fe(-Cu) deposits in the AqishanYamansu belt formed at approximate to 296 Ma, probably in a back-arc extensional environment.