Metal source and ore-forming process of the Maoping carbonate-hosted Pb-Zn deposit in Yunnan, SW China: Evidence from deposit geology and sphalerite Pb-Zn-Cd isotopes

The Maoping carbonate-hosted Pb-Zn deposit (25 Mt ores @ 12-35% Zn + Pb) is a representative and the thirdlargest Pb-Zn deposit in the Sichuan-Yunnan-Guizhou Pb-Zn metallogenic province (SYGMP). In this study, PbZn-Cd isotope analyses were performed on sphalerite from Maoping, in order to understand the ore metal source and metallogenesis in the SYGMP. The sphalerite samples have narrow ranges of Pb isotope ratios: 206Pb/204Pb = 18.675-18.751, 207Pb/204Pb = 15.758-15.768, and 208Pb/204Pb = 39.287-38.436. This implies thorough mixing of two Pb sources, which we interpreted to be the Devonian-Carboniferous ore-hosting carbonate wallrocks and the Neoproterozoic Kunyang/Huili Group (Gp.) clastic and metamorphic rocks. The Maoping sphalerite samples have uniform 866Zn (-80.07 to + 0.25%o) and 8114Cd (-0.10 to + 0.27%o) values, which further support complete source mixing. In the 866Zn vs. Cd/Zn plot, the Maoping sphalerite data fall close to the field of basement rocks and distal to the carbonate wallrocks, indicating that the ore zinc was mainly derived from the metamorphic basement with heavier 866Zn values and low Cd/Zn ratios with certain contributions from the minor carbonate wallrock with lower 866Zn values and high Cd/Zn ratios. In the 8114Cd vs. 1/Cd plot, all Maoping sphalerite samples fall inside the Mississippi Valley-type (MVT) field, and the deposit shares many geological and sulfide geochemical (incl. isotopic) features with MVT deposits. Thus, the Maoping Pb-Zn mineralization is best classified as MVT, and the sulfide precipitation in structural (fault-fold) traps was caused by binary mixing of a metal-bearing and a reduced S-bearing fluid.

Automated summary

The study of the Maoping carbonate-hosted Pb-Zn deposit in the Sichuan-Yunnan-Guizhou Pb-Zn metallogenic province revealed a thorough mixing of Pb sources from Devonian-Carboniferous ore-hosting carbonate wallrocks and Neoproterozoic clastic and metamorphic rocks. The deposit is classified as MVT type, with sulfide precipitation in structural traps caused by binary mixing of metal-bearing and reduced S-bearing fluids.