Trace-element composition of pyrite in the Baoshan Cu–Mo–Pb–Zn deposit, southern Hunan Province, China: Insights into the ore genesis

Abstract

The southern Hunan Province in southeastern China is the site of extensive Mesozoic magmatism and the formation of associated polymetallic deposits, among which, the studies for Cu–Pb–Zn mineralization are relatively rare compared with the W–Sn polymetallic deposits. In this study, the Baoshan skarn Cu–Mo–Pb–Zn deposit is investigated as a typical example with sulfide ores hosted in the distal carbonate. By presenting in situ laser ablation–inductively coupled plasma–mass spectrometry trace-element compositions of the ubiquitous pyrite, as well as arsenopyrite, sphalerite, and chalcopyrite, from carbonate strata, granodiorite porphyry, early disseminated and massive Cu–Mo–Pb–Zn ores, and late brecciated Cu ores, we aim to elucidate the relationships between the proximal skarn Cu–Mo and the distal carbonate hosted Pb–Zn mineralization in this deposit. Together with the geological characteristics, our results suggest that the pyrite trace-element compositions can be used to infer the precipitation environment. The pyrite from the early disseminated and massive Cu–Mo–Pb–Zn ores has high As/Sb and low Ni/As ratios, indicating that the ore-forming fluids and materials directly separated from the granodioritic magmas have dominated the sulfide mineralization in this stage, with minor contributions from the carbonate; the Pb–Zn mineralization is most likely precipitated from the same hydrothermal system with the early Cu–Mo mineralization, despite of the distal locations. On the contrary, the pyrite from the late brecciated Cu ores is characterized by low As/Sb and high Ni/As ratios, indicating that the ore-bearing fluids have circulated through the basements beneath the mining area, which should have also leached the ore-forming materials for the subsequent Cu mineralization. In addition to the direct contributions from the magmas and carbonate strata, this study emphasizes the substantial contributions from the basements to the Cu–Mo–Pb–Zn mineralization at Baoshan. This also indicates that the deep locations or the adjacent areas with well-developed fractures can be the potential targets for further exploration.