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

Abstract

The Maoping Pb–Zn deposit (~ 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 δ13CPDB values (− 5.3 to − 0.8 ‰) and δ18OSMOW values (+ 14.5 to + 21.8 ‰) with those of the calcites in the SYG region, suggesting that CO2 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 ‰) with equilibrated sulfur fractionation (δ34Ssphalerite δ34Sgalena) 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 206Pb/204Pb of 18.713–18.759, 207Pb/204Pb of 15.772–15.776 and 208Pb/204Pb 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.