Genesis of the Hacipushanbei Pb-polymetallic deposit in the East Kunlun Orogen, NW China: Constraints from geochronology and in situ trace-elements and sulfur isotopes of sulfides

Abstract

A recent mineral exploration programme in the East Kunlun Orogen (EKO) identified the new Hacipushanbei Pb-polymetallic deposit. The ores are hosted in faults in granitic rocks and are marked by high Pb grades up to 22.5 %. U–Pb dating of calcites associated with mineralization yields an intersection age of 208 ± 9 Ma, indicating a late Triassic mineralization event. Fluid-inclusion analysis reveals that the ore-forming fluids are characterized by medium-to-high temperature, medium-to-low salinity, and low density. Fluid boiling or immiscibility during ore-formation is also noted. Three sub-generations of pyrite (Py1-1, Py1-2, and Py2) are recognized in the early mineralization stages. In situ trace element analysis shows low Co and Ni contents in Py1-1 and Py1-2 but high contents in Py2. Conversely, Au and As concentrations are the highest in Py1-2. Variations in As contents are systematically coupled with Au. Additionally, sphalerite in the second stage contains higher amounts of Co, Cu, Cd, and In, via a wide range of isomorphic elemental substitutions of X4+(Sn4+ and Ge4+) + X3+(In3+, Sb3+, and Ga3+) + X+(Ag+ and Cu+) ↔ 4Zn2+ and the associated In enrichment. The average δ34S values of in situ and single minerals of Py1-1, Py1-2, Py2, Sp2, Ccp2, and Gn3 are 2.3 ‰, 3.3 ‰, 2.6 ‰, 2.4 ‰, 2.2 ‰, and 0.9 ‰, respectively. These values display a trend of initial increase and then decrease, consistent with thermodynamic fractionation. These data collectively indicate that the ore-forming fluid originated from a deep-seated magma chamber, and subsequent fluid immiscibility led to the formation of high-grade ores. Given the conspicuous association of Pb-polymetallic deposits with magmatic rocks in the EKO, we envisage that our genetic model can be applied, to some extent, to evaluate the potential of some mineral exploration targets.