Geological and geochemical characteristics of the Sawaya'erdun gold deposit, southwestern Chinese Tianshan

The Sawaya'erdun gold deposit in the western segment of the South Tianshan, Xinjiang, China, is a large, low-grade orogenic gold deposit. An abundance of index fossils in the ore-hosting strata, including brachiopoda, corals and Schwagerina, show that the fossil age of the country rocks ranges from Late Carboniferous to Early Permian. Whole rock Rb–Sr and Sm–Nd isochron ages, ranging from 292.43 ± 0.38 to 304.7 ± 11.6 Ma, are concordant with a Late Carboniferous age. Gold mineralization is strictly controlled by a fault zone. Ore minerals are dominated by sulfides, with gold inhomogeneously distributed within them; gangue minerals are quartz, siderite or calcite. Data suggest that the ore-forming fluid was derived predominantly from an active meteoric groundwater system. Ore-forming temperatures are estimated to have been within the range 110 to 220 °C.New 40Ar/39Ar isotope age determinations of auriferous quartz are in excellent agreement with Rb–Sr ages obtained from fluid inclusions in quartz. They suggest gold mineralization at 206 to 213 Ma (Late Indosinian). Such an age is consistent with the age of formation given for other gold deposits in the region, such as Bulong and Dashankou. Combined with K–Ar geochronological data and observed geological features, it is concluded that the Indosinian metallogentic epoch represents a previously unrecognized, major period of gold metallogeny in the southwestern Chinese Tianshan. In some ways, the Sawaya'erdun gold deposit can be compared with the Muruntau gold deposit in Uzbekistan with respect to geological setting, host lithology, mineralization style, mineral assemblages, geochemical association and metallogenic processes involved. Despite this, the Sawaya'erdun gold deposit possesses a number of characteristics typical of only low-temperature metallogenesis.