Contribution of carbonaceous strata to intrusion–related Au mineralization: Evidence from trace elements and S–Pb isotopes in pyrite from the Qukulekedong Au–Sb deposit, East Kunlun, NW China

The large intrusion–related Qukulekedong Au–Sb deposit was recently discovered in the East Kunlun Orogenic Belt (EKOB). Mineralization occurs in the Late Triassic granitoid intrusion and its surrounding carbonaceous siltstone. Pyrite is an important Au-rich mineral in the deposit, and can be classified into three types: Py1, Py2 and Py3. The lattermost Py3 represents the main metallogenic episode. In–situ trace elements and S–Pb isotopes of pyrites indicate that the Py3 has a relatively high Au content (mean 7.84 ppm), high Co/Ni ratios (mean 4.93), with δ 34 S values around 0‰ (-2.03 to 1.69‰) and matched Pb isotopic ratios to the intrusions, suggesting that Au and other ore-forming material were most likely derived from a magmatic source. Carbonaceous siltstone contains organic carbon up to 3.39 wt%. According to the evidence of paragenetic minerals, texture, and S isotopes, the carbonaceous material may have played a key role in the precipitation of Au and pyrite in the carbonaceous strata. The Au–As decoupling of pyrite in intrusions may be attributed to the Au precipitation and crystallization of arsenopyrite, which was caused by the decreasing of oxygen fugacity. Overall, the new understanding highlights the importance of carbonaceous strata in intrusion–related Au ore-forming processes, the combination of carbonaceous strata and Late Triassic intrusions provides a new exploration direction for Au prospecting in the EKOB and similar settings.