Isotopic (H─O─S─Pb) geochemistry and zircon U─Pb geochronology of the Kaladaban Pb─Zn deposit, in Xinjiang, NW China

Abstract

The Kaladaban Pb─Zn─Cu volcanogenic massive sulphide deposit (VMS), located within the Altyn region of Xinjiang in NW China, is an economically significant deposit with known reserves of 414,400 t Zn with a grade of 4.14%, 265,200 t Pb with a grade of 2.52%, and 149,200 t Cu with a grade of 1.10%. The mineralization is hosted in basalt, rhyolite, and rhyolite porphyry, with the latter two rock types yielding zircon U─Pb ages of 516 and 505 Ma, respectively, representing the timing of crystallization. Samples of the host volcanic rocks show fractionated rare‐earth element (REE) patterns and enrichment in both large‐ion lithophile elements (e.g., Ba, Rb, U, and light REEs) and high‐field‐strength elements (e.g., Th, Hf, and Zr). These features are similar to those of oceanic island basalt. δ18O values of ore fluids from quartz in orebodies range from +8.1‰ to +13.4‰, and fluid δ18Dwater values vary from −68.5‰ to −99.1‰, indicating a mixture of magmatic hydrothermal and seawater. δ34S values range from +8.5‰ to +14.9‰, suggesting that S that in the Kaladaban ore minerals had a mixed origin of magmatic hydrothermal fluids and sulphate‐reduced seawater. Ratios of 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb from metal minerals in Kaladaban deposit are 18.513–18.740, 15.633–15.727, and 38.236–38.398, respectively, indicating extremely radiogenic characteristics, similar to the host volcanic rocks. We infer that the Kaladaban Pb─Zn deposit formed in an active continental margin setting related to southward subduction of the North Altyn oceanic crust during the early Palaeozoic.