Geochronology and geochemistry of ore-hosted zircon reveal the genesis of typical Sb-(Au-W) deposits in South China

Abstract

The Xikuangshan and Woxi Sb-(Au-W) deposits are the most important Sb-related mineralization in the Xiangzhong metallogenic province, South China. In this study, trace element, U-Pb dating, and Hf isotopic results of zircon in typical ore samples from the Xikuangshan and Woxi deposits provide new insights into metal/fluid sources and mineralization processes. The zircons in different samples from the Xikuangshan deposit have a similar distribution of zircon U-Pb ages with two major groups: 400–500 Ma and 700–900 Ma, which are consistent with those from their host rocks (Devonian strata) and underlying basement rocks (Lengjiaxi and Banxi Groups). By comparison, the zircons from the Woxi deposit have younger U-Pb ages which are the same as contemporaneous magmatism in South China. The 176Hf/177Hf ratios, εHf(t), and TDM1 further proved an original relationship between the younger zircons (with ages < 500 Ma) and magmatism. The systematic trend in the size and roundness of zircons captured from basement rocks for Xikuangshan might be resulting from gravity separation in the sedimentary process which required a stable and long-lasting mineralization process. On the other hand, the homogenous size and roundness of zircons from the Woxi deposit, regardless of zircon ages and sampling locations, might have been caused by a relatively short and intense mineralization process. The differences in the mineralization process for the two deposits lead to different alteration degrees of zircons and are reflected by the variable concentrations of Y, Hf, Pb, and Th, as well as rare earth elements. In the deposit scale, some samples are considered to be altered at high grade and represent the main mineralization stages for the Xikuangshan and Woxi deposits, as their zircons have variable concentrations of trace and rare earth elements. Combined with previous studies, the sources of zircons and mineralizing material are distinct for the Xikuangshan and Woxi deposits: originated from basement rocks (Xikuangshan deposit) and magmatism (Woxi deposit). In addition, stable and long-lasting deep-circulated meteoric water is considered the mineralizing fluid for the Xikuangshan deposit, whereas the mineralizing fluid for the Woxi deposit might be related to magmatism. This research highlights the use of zircon geochronology and geochemistry in revealing the genesis of Sb deposits, making this method applicable worldwide to similar vein-type mineralization.