Trace element geochemistry and O-S-Pb-He-Ar isotopic systematics of the Lishan Pb-Zn-Cu hydrothermal deposit, NE Hunan, South China

Abstract

The Jiangnan Orogenic Belt, as an important polymetallic metallogenic belt in South China, hosts numerous Au-Sb, W, Cu, Co, and Pb-Zn deposits. The newly discovered Lishan Pb-Zn-Cu deposit (> 0.64 Mt at 1.64% Pb, 2.54% Zn, and 0.42% Cu) in the northeastern Hunan Province is mainly accommodated by the Late Jurassic to Early Cretaceous Mufushan pluton, with vein-type Pb-Zn-Cu orebodies controlled by nearly N-S-trending faults. However, ore genesis, mineralization process, and the contribution of magmatism are unclear despite its closely spatial association with the Mufushan pluton. In this contribution, in-situ trace element, O and S isotopic analyses, as well as Pb, He and Ar isotopic analyses were conducted to determine the sources of ore-forming materials and fluids and potential mineralization process in the Lishan Pb-Zn-Cu deposit. Four stages of hydrothermal processes, from early to late, are recognized: (1) quartz; (2) quartz + fluorite + chlorite + chalcopyrite + pyrite; (3) quartz + fluorite + chlorite + sphalerite + galena + chalcopyrite + pyrite; and (4) quartz + calcite + chalcopyrite + pyrite. The trace element compositions reveal several important substitutions, including 4Zn2+ ↔ 2Sb3+ + Pb2+ + □ (vacancy) in sphalerite, and Ag+ + Sb3+ ↔ 2Pb2+ and (Ag, Cu, Tl)+ + (Bi, Sb)3+ ↔ 2Pb2+ in galena. The Lishan sphalerite is characterized by high contents of Mn (44.3–244 ppm), Fe (5379–19037 ppm), Co (30.0–186 ppm), and Ga (3.81–381 ppm) and low contents of Ag (1.04–20.7 ppm) and Sb (0.03–1.88 ppm). The sphalerite geothermometer combined with Ga/In (1.32–9716) ratios suggest moderate to low mineralization temperatures of 174–251 °C. The δ34S values of sphalerite, galena, chalcopyrite, and pyrite vary between −5.1 and −0.4‰, consistent with those of the magmatic sulfur source. The Pb isotopic compositions (206Pb/204Pb = 18.140–18.378, 207Pb/204Pb = 15.666–15.819 and 208Pb/204Pb = 38.574–39.207) of sulfides demonstrate that the ore metals were most likely derived from the Mufushan granitoids, but contaminated by the Lengjiaxi Group rocks. The oxygen isotopic values of quartz and noble gas isotopic compositions of sulfides indicate that the ore-forming fluids were mainly formed by the mixture of crust-derived magmatic hydrothermal fluid and meteoric water. Combined with principal component analysis, the Lishan sphalerite is different from the trace element characteristics of sphalerite in other types of deposits. In combination with the available data, we propose that the Lishan deposit belongs to a moderate to low temperature hydrothermal vein-type deposit.