Temperature as a major control on Cd enrichment in a skarn system: A case study of the Yiliu Pb-Zn-As deposit, South China

The Yiliu Pb-Zn-As deposit is located in the Nanling Metallogenic Belt (NMB), South China, representing an extremely As-enriched skarn system, but the endowment of critical metals, such as Cd and In, and their recording metallogenic physicochemical condition have never been investigated. To address these questions, we conducted a series of field survey, microscopic observation, electron probe micro-analyzer (EPMA) and laser ablation inductively coupled plasm mass spectrometer (LA-ICP-MS) studies. The lenticular orebodies are closely associated with the altered Devonian limestone and Yanshanian Baoshan and Benggangling granitic intrusions, and the massive and disseminated ores comprise arsenopyrite, pyrite, sphalerite, chalcopyrite, galena and tetrahedrite, in a decreasing order. We identified three generations of sphalerite, that is, Sp1, Sp2 and Sp3, with different colors and mineral assemblages. EPMA and LA-ICP-MS data show that two groups of minor and trace elements are hosted in the Yiliu sphalerites: (1) Fe, Cd, Mn and In mainly occurring as lattice-bound (solid-solution) or homogeneously distributed nanoparticles, and (2) Cu, Sn, Pb, Sb and Ag mainly occurring as micro-mineral inclusions. It is notable that a relatively high Cd (4814-10149 ppm, mean = 6133 ppm) against low In (10-301 ppm, mean = 67 ppm) concentration is identified in all the three sphalerite generations. Calculation of sphalerite crystallization temperatures by GGIMFis geothermometer show that a clearly decreasing trend from the earlier Sp1 (273-319 degrees C; median = 296 degrees C) to the later Sp2 (267-301 degrees C; median = 286 degrees C) and Sp3 (278-290 degrees C; median = 282 degrees C). And there is a decrease for Cd concentrations from Sp1 to Sp2 and Sp3, i.e., 4903-10149 ppm (median 6964 ppm) for Sp1, and 4814-7078 ppm (median 5435 ppm) for Sp2 and 5756-6894 ppm (median 6420 ppm) for Sp3, respectively. Additionally, the enrichment of Cd is also affected by the content of Fe whose enrichment is controlled by the relatively high temperature. Collectively, we deduce that the temperature acts as the major control for Cd enrichment in the sphalerite of the Yiliu Pb-Zn-As deposit, and the higher temperature facilitate Cd enrichment in a skarn system.