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

A recent mineral exploration programme in the East Kunlun Orogen (EKO) identified the new Hacipushanbei Pbpolymetallic 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 delta 34S values of in situ and single minerals of Py1-1, Py1-2, Py2, Sp2, Ccp2, and Gn3 are 2.3 %o, 3.3 %o, 2.6 %o, 2.4 %o, 2.2 %o, and 0.9 %o, 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.