Tectonic setting and geochronology of the Sarsuk Au polymetallic deposit in Xinjiang, NW China: Constraints from pyrite Re–Os, zircon U–Pb dating and Hf isotopes

Abstract

The Sarsuk Au polymetallic deposit is located in the Ashele volcano-sedimentary basin of the south Altay Orogenic Belt (AOB), Northwest China. Within the deposit, rhyolite porphyry and diabase are widespread, and emplaced into the strata. The orebodies of the Sarsuk deposit are hosted by the rhyolite porphyry, while diabase cuts through the rhyolite porphyry and part of the orebody. Rhyolite porphyry11Rhyolite porphyry displays two events where only the older (384Ma) one is metallogenically relevant for the sarsuk, the young rhyolite porphyry (302Ma) is not relevant for the formation of the sarsuk deposit. yields a zircon U-Pb age of 384 ± 1.2 Ma (MSWD = 0.69), and the diabases yield a zircon U-Pb age of 380 ± 0.74 Ma (MSWD = 3.1). Four auriferous pyrite samples from vein sulfide ores and one pyrite sample from massive ores display a Re–Os isochron age of 383 ± 11 Ma (MSWD = 1.2). These data show that the bimodal Devonian magmatism and rhyolite porphyry hosted ore bodies emplaced in a narrow interval during 384–380 Ma. Diabases have the geochemical characteristics of tholeiitic basalts, with relatively high Mg# values (49.4–61.4), Cr and Ni, a slight positive Eu anomaly (δEu = 0.98–1.12), and relatively low concentrations of Sr and (La/Yb)N. Rhyolite porphyries have similar characteristics to those of sanukitoide in terms of high Mg# values (47.6–55.7), an obvious negative Eu anomaly (δEu = 0.33–0.35), and enrichments of large ion lithophile elements and light rare earth elements. The aforementioned chemical characteristics indicate that the Sarsuk deposit was located in the arc environment of a subduction zone during the Early to Middle Devonian. Hf isotope analyses of the diabases exhibited εHf(t) values of + 4.86 to + 8.96. The two-stage Hf model age (TDM2) was 805–1064 Ma. Hf isotope analyses of the rhyolite porphyry exhibited a εHf(t) value range of + 1.78 to + 8.49, and the two-stage Hf model age (TDM2) was 449–528 Ma. The original diabase and rhyolite porphyry magmas were derived from a mixing of the depleted mantle and juvenile crust material. The pyrite Re/Os system indicated that crust-derivedand S-rich sediments also contributed to the ore formation. Accordingly, based on the results of this study and a review of the regional magmatic framework, we can conclude that the Sarsuk deposit was formed at 383 Ma in an island arc subduction environment. Furthermore, we establish that the magmatic rocks and ore are co-genetic.