Genesis of the Maoping carbonate-hosted Pb-Zn deposit, northeastern Yunnan Province, China: evidences from geology and C-O-S-Pb isotopes

The Maoping Pb-Zn deposit (similar to 3 Mt Pb + Zn reserves with grades of 12-30 wt%) is one of the largest Pb-Zn deposits in the Sichuan-Yunnan-Guizhou (SYG) metallogenic province, which has contributed a tremendous amount of lead and zinc resources for China. To obtain a further understanding of the sources of ore-forming materials and ore genesis of the deposit, S-Pb isotopes of sulfides and C-O isotopes of ore-stage calcites were systematically collected from representative orebodies at different elevations with a Finnigan MAT-253 mass spectrometer. The calcites separated from the sulfides of the No I and No II orebodies shared identical delta(13)C(PDB)values (- 5.3 to - 0.8 parts per thousand) and delta(18)O(SMOW)values (+ 14.5 to + 21.8 parts per thousand) with those of the calcites in the SYG region, suggesting that CO(2)in regional ore-forming fluids possibly had a homologous C-O source that originated from a ternary mixture of the dissolution of marine carbonate rocks, degassing process of the Emeishan mantle plume, and dehydroxylation of sedimentary organic matter. The No. I-1 and No. I-2 orebody was hosted in the same strata, but the sulfur source of No. I-1 orebody (+ 13.1 to + 19.0 parts per thousand) with equilibrated sulfur fractionation (delta S-34(sphalerite) < delta S-34(galena)) and No. I-2 orebody (+ 18.0 to + 21.8 parts per thousand) with sulfur equilibrium fractionation (delta S-34(sphalerite) > delta S-34(galena)) were different. They were derived from the allopatry thermochemical sulfate reduction (TSR) of overlying Carboniferous sulfates in the ore-hosting strata and local TSR of sulfates in the ore-bearing Upper Devonian Zaige Formation, respectively. The narrow and uniform Pb isotopic ratios of single galena grains collected from sulfides with(206)Pb/Pb-204 of 18.713-18.759,Pb-207/Pb-204 of 15.772-15.776 and(208)Pb/Pb-204 of 39.383-39.467 indicate a well-mixed metal source(s) that consist of Proterozoic Kunyang and Huili Group basement rocks and Devonian to Middle Permian ore-hosting sedimentary rocks. Besides, the late Permian Emeishan basalts are difficult to contribute metals for regional Pb-Zn mineralization despite a closely spatial relationship with the distribution of the Pb-Zn deposit. This is supported by Pb isotopic ratios plotting above the average upper crustal Pb evolution curves and staying far away from that of the age-corrected Emeishan basalts. Hence, taking into account of the similarities in tectonic setting, ore-hosting rock, ore assemblage, wall rock alteration, ore-controlling structure, and ore-forming materials and the differences in relationship with regional magmatism, fluid inclusion characteristic and ore grade between the Maoping deposit and typical MVT Pb-Zn deposit, the ore genesis of the Maoping deposit should be an MVT like Pb-Zn deposit.