Sulfur- and lead-isotope geochemistry of the Balugou Cu-Pb-Zn skarn deposit in the Wulonggou area in the eastern Kunlun Orogen, NW China

Abstract

The small-scale Balugou Cu-Pb-Zn skarn deposit (45 298 tonnages of ore at 0.1% to 3.99% Cu, 0.20% to 0.43% Pb and 0.76% to 10.92% Zn) is located in the Wulonggou area in the eastern Kunlun orogen, NW China. Ore deposition is spatially and temporally related with the pre-collisional Anisian Balugou granites (~244 Ma). The mineralization hosted by the contact between marble beds within the Paleo-Proterozoic Jinshuikou Group and Balugou granites, was structurally and lithologically controlled. The mineralogy of the Balugou deposit includes an early simple skarn mineral gangue (epidote with little diopside) and a late complicated quartz sulfide assemblage (pyrite, pyrrhotite, chalcopyrite, sphalerite, galena, bornite, quartz, carbonate and chlorite). The δ34S values of eighteen sulfides range from -2.1‰ to +2.8 ‰, with an average of +0.07‰, and the calculated δ34SH2S values for H2S in hydrothermal fluids range from -3.2‰ to +2.4‰, with an average of +0.03‰, suggesting a relatively homogeneous magmatic (±mantle) source, with sulfur produced directly by the Balugou granites. The sixteen sulfides have 206Pb/204Pb ratios from 18.367 4 to 18.384 1, 207Pb/204Pb ratios from 15.634 6 to 15.641 5, and 208Pb/204Pb ratios from 38.455 5 to 38.485 0, which are close to those of K-feldspars from the Balugou granites, but are far away from age-corrected lead isotopic ratios of six wall-rock samples. So it was considered that the Pb sources of sulfides must be almost derived from the Balugou granites rather than the older wall-rocks. Collectively, it’s suggested that the Balugou Cu-Pb-Zn deposit belongs to skarn deposit, and the sulfur and lead deposited in it were leached from the Anisian Balugou granites.