Texture and geochemistry of sphalerite from the Chitudian Pb-Zn-Ag deposit, southern margin of the North China Craton: Implications for the enrichments of Cd, Ga, and In

The Chitudian Pb-Zn-Ag deposit, located in the southern margin of the North China Craton (SNCC), is a typical magmatic-hydrothermal deposit, where sphalerite is the predominate ore mineral with significant concentrations of critical metals, including Ga, In, and Cd. However, previous studies paid little attention to the critical metals in the deposit. This study carried out in-suit elemental analysis on the sphalerite from the Chitudian deposit, aiming to constrain the spatial distribution and enrichment mechanism of critical metals. In the Chitudian deposit, five types of sphalerite were identified (Z-Sp, Y-Sp1, Y-Sp2, X-Sp1, and X-Sp2), which differ in color, texture, and chemical composition. The concentrations of Cd, Ga, and In of these sphalerites range from 1440 to 5145 ppm, 0.53 to 528 ppm, and 0.75 to 2113 ppm, respectively. In detail, Cd is mainly concentrated in the sphalerites from the hydrothermal vein-type orebodies relative to skarn-type orebodies. Indium is progressively depleted from granite-proximal locations to granite-distal locations, and the Fe-rich sphalerite is an excellent host of In. Gallium enrichment is only observed in the tectonically deformed location of the sulfide ore vein, where the Ga-rich sphalerite is poor in Fe and shows a complex texture. Microanalysis conducted on the Ga-rich sphalerite sug-gested that Ga, together with In, Sn, and Cu, are removed from the deformed sphalerite by mineral-fluid interaction and subsequently sequestered by the late sphalerite cement. Considering that the Ga-rich sphal-erite is close to the Ga-bearing coal bed of the Meiyaogou Formation, it is likely that the coal bed could be a potential source for Ga. These results highlight that tectonic deformation followed by hydrothermal fluid overprinting is favorable for the enrichment of critical metals in sphalerite-rich deposits.