Work

Genesis of the Maweishan Pb–Zn deposit, eastern China and controls on the distribution and formation of sphalerite-hosted critical metal (Cd, Ga, and In) mineralization

Year: 2025

Type: article

Abstract: Garnet U–Pb dating of samples from the Maweishan deposit of the Xuancheng ore district within of the Middle and Lower Yangtze River metallogenic belt of eastern China yields a well-defined lower-intercept age of 132.3 ± 1.4 Ma (Fig. A), consistent with a zircon U–Pb age of a proximal quartz diorite intrusion (132.4 ± 0.9 Ma). This strongly suggests that the quartz diorite is genetically associated with the formation of the Maweishan deposit rather than the deposit being a distal part of the Qiaomaishan skarn system. The flat LA-ICP-MS signal spectra for sphalerite within the system suggests that the critical metals Cd, In, and Ga were incorporated into the sphalerite structure through isomorphic substitution or are present as homogeneously distributed nanoparticles (Fig. B). The strong correlation between Ga and Cu (Fig. C) suggests that Ga was incorporated by coupled substitution in the form Cu + + Ga 3+ replacing 2Zn 2+ . The narrow range of δ 34 S values for sulfides within the system (Fig. D), all of which are slightly heavy compared to the range expected for magmatic-derived fluids (–5 to + 5‰), suggests that the metals within the deposit and the fluids that formed the deposit were predominantly derived from a magmatic source, namely the proximal quartz diorite, but with minor amounts also derived from the surrounding country rock. • The Maweishan deposit formed at 132.3 ± 1.4 Ma, indicating that the Maweishan system is not a distal part of the Qiaomaishan system. • Sphalerite incorporated Cd 2+ by direct substitution for Zn 2+ , whereas In 3+ was incorporated as homogeneous nanoparticles through adsorption or capture. • The sphalerite also contains Ga 3+ incorporated as a result of the coupled substitution of (Cu, Ag) + for 2Zn 2+ . • The metals in the Maweishan deposit are derived primarily from the quartz diorite, with a small amount derived from the surrounding country rocks. • This study demonstrates the significant critical metal potential of this style of mineralization within the MLYB. Skarn-type Pb (lead)–Zn (zinc) polymetallic deposits are not only important sources of Pb and Zn but also critical metals such as Cd, In, Ge, and Ga. Significant numbers of skarn-type (or magmato-hydrothermal) Pb–Zn deposits have been identified within the Xuancheng ore district of the Middle and Lower Yangtze River metallogenic belt of eastern China. However, these Pb–Zn deposits are understudied compared to the well-documented porphyry-type Cu–Au, skarn-type Cu–W and Cu–Mo deposits within this district. In addition, the controls and nature of the deportment of critical metals within Pb–Zn deposits also remain poorly constrained, including identification of substitution processes and the sources of these metals within these Pb-Zn systems. The potential genetic link between the Maweishan deposit and the adjacent Qiaomaishan deposit also remains uncertain, with some research considering that the Maweishan deposit is a distal part of the Qiaomaishan skarn system whereas other research suggests that these are independent skarn systems. This study addresses these issues using new evidence of the timing of mineralization obtained by the in-situ U–Pb dating of the garnet from the Maweishan deposit. This garnet yields a well-defined lower-intercept U–Pb age of 132.3 ± 1.4 Ma, consistent with a zircon U–Pb age for the proximal Maweishan quartz diorite (132.4 ± 0.9 Ma). This, combined with the spatial relationships of alteration and mineralization within the deposit, strongly suggests that the proximal quartz diorite is genetically related to the formation of the Maweishan deposit and this deposit is not a distal manifestation of the Qiaomaishan skarn system. Sphalerite from the Maweishan deposit also contains high levels of the critical metals Cd [3480–5107 parts per million (ppm)], In (78.3–407 ppm) and Ga (22.4–348 ppm). The Cd 2+ within this sphalerite was incorporated into the mineral lattice by direct substitution for Zn 2+ , whereas the uniform concentrations of In 3+ in all three types of sphalerites is indicative of incorporation by the adsorption or capture of homogeneous In nanoparticles. The Ga 3+ within the Maweishan deposit was predominantly incorporated into sphalerite as a result of coupled substitution with Cu + replacing 2Zn 2+ , with the Ag + + Ga 3+ coupled substitution for 2Zn 2+ also involved in the incorporation of Ga into the Sp2 sphalerite. The narrow range of sulfur isotopes (δ 34 S from 4.9 ‰ to 8.3 ‰, average of 5.8 ‰) for sulfides within the Maweishan deposit combined with the new garnet trace element data and elemental maps presented in this study suggests that the metals and fluids that formed the Maweishan were primarily derived primarily from the proximal quartz diorite. These sulfur isotopic data also indicate that a small amount of metals or sulfur were derived from the surrounding country rocks. These data provide new insights into critical metal mineralization associated with Pb–Zn deposits in the Xuancheng ore district, where regional folding concentrated ore-forming fluids that generated both 139 Ma Cu–W and 132 Ma Pb–Zn mineralization events, indicating that this structural zone is an ideal area for future exploration within the Xuancheng district and in other areas with similar characteristics.

Source: Ore Geology Reviews

DOI: 10.1016/j.oregeorev.2025.106600