Episodic Ore Redistribution in Carlin-Type Gold Deposits in Southeastern Yunnan Province, SW China

Abstract The central-southern Youjiang basin in southeastern Yunnan hosts numerous Carlin-type gold deposits, such as the pyroclastic-hosted Bieli and the siliciclastic-hosted Bielidong deposits. In both deposits, gold occurs as lattice-bound Au+ in sulfide minerals of different paragenetic stages: sedimentary framboidal pyrite (PyS), diagenetic dissolution-reprecipitation porous pyrite (PyDR), hydrothermal early ore pyrite (Py1), main ore pyrite/arsenopyrite (Py2/Apy2), and late ore pyrite (Py3). The textures show there were multiple pulses of fluid flow related to the formation of the deposits. Sedimentary and diagenetic pyrite has negligible Au (1 ppm) and As (0.5 wt %) contents and extremely negative δ34S (−49.7 to −21.4‰) values, which differ markedly from early ore Py1 (Au = 0.05–4.20 ppm; As = 0.32–4.16 wt %; δ34S = −3.54 to 10.5‰), main ore sulfide minerals (Py2 and Apy2; mean Au = 9.28 and 39.2 ppm, mean As = 3.16 and 44.6 wt %, mean δ34S = 4.68 and 12.1‰), and late-stage Py3 (Au = 2.27–27.4 ppm; As = 7.80–9.49 wt %; δ34S = 8.62–13.5‰). The main ore sulfide minerals display positive δ34S values (4.68–12.1‰) and pronounced mass-independent sulfur isotope signatures (Δ33S = –2.80 to +8.16‰). The chemical composition and the δ34S and Δ33S values of ore sulfides indicate that the fluids were derived from a sedimentary source, most probably the Precambrian metamorphic rocks beneath the Phanerozoic basin. Both deposits formed by the same process, and the fluids came from the same source. Differences between the deposits are largely related to the local host rocks. The mobilization of the fluids seems to be the far-field effect of tectonic processes at the margins of the South China block.