Indium concentrations as a potential indicator of orebody-intrusion distance in a skarn Pb-Zn system, elucidated by the Fozichong Orefield (South China)

Abstract

Critical metal indium tends to be enriched in skarn Pb-Zn systems, but the spatiotemporal distribution pattern of indium and its controls in a specific skarn Pb-Zn deposit remains unclear. To address this problem, we conducted a combination of geological, mineralogical, and trace element geochemical investigations on the Fozichong skarn Pb-Zn Orefield (South China) that contains two individual Pb-Zn deposits with different distances from ore-causative intrusion (the proximal Longwan and the distal Guyi deposits). Three types of sphalerites with different mineralogical characteristics have been identified that is Sp1 (in the early sulfide stage with chalcopyrite solid solution), Sp2 (with pyrrhotite inclusions), and Sp3 (in the late sulfide stage without solid solution). Further analyses by EPMA (Electron Probe Micro-Analyzer) and LA-ICP-MS (Laser Ablation Inductively Coupled Plasma Mass Spectrometer) reveal that the sphalerite from the two Pb-Zn deposits have different indium concentrations. That is, indium is significantly enriched in the proximal Longwan sphalerite, varying from 1.20 to 287.69 ppm (mean = 78.67 ppm). By contrast, indium is relatively barren in the distal Guyi sphalerite, ranging from 0.04 to 4.79 ppm (mean = 2.11 ppm). The calculated GGIMFis sphalerite geothermometer confirms that the temperatures of proximal Longwan (283 – 392 °C) are higher than those of the distal Guyi (295 – 336 °C). Collectively, the sphalerite proximal to the magmatic intrusion with higher temperatures is concentrated into more indium, but indium in the distal sphalerite significantly decreases by one order of magnitude. Furthermore, the indium contents in sphalerite can be used as a robust indicator of the distance between Pb-Zn orebodies and magmatic intrusion in the skarn Pb-Zn system.

Topics & Concepts