Coloration mechanism of Fe in sphalerite based on LA-ICP-MS and DFT: A case study of the Huize super-large Ge-rich Ag–Pb–Zn deposit in Sichuan–Yunnan–Guizhou

Abstract

The Fe content is a crucial factor influencing the color of sphalerite. This study focuses on sphalerite from the Huize super-large Ge-rich Ag–Pb–Zn deposit in the Sichuan–Yunnan–Guizhou border region. Based on LA-ICP-MS in-situ analysis and quantum chemical calculations using Density Functional Theory (DFT), we investigated the Fe–Zn substitution patterns and their impact on sphalerite color, identified the isomorphous and interstitial doping modes of iron in sphalerite, and further elucidated the coloration mechanism and mineralization process of sphalerite. The research shows that black sphalerite from the Baizuo Formation in this deposit has the highest Fe content, while red-brown sphalerite from the Dengying Formation has the highest Fe content among its counterparts. When the number of Fe atoms in the ZnS electronic structure exceeds six, the reflection coefficient in the red-brown spectral range is significantly higher than that in other visible light bands, while the absorption coefficient is lower. The isomorphous substitution and interstitial insertion of Fe in sphalerite are key factors leading to its color variation. Fe predominantly enters the (110) and (100) cleavage planes in the form of isomorphous substitution, forming isomorphous mixed crystals, with the (110) cleavage plane being more sensitive to Fe substitution. The study suggests that the mineralization temperature corresponding to different mineralization stages affects the Fe content in sphalerite, which in turn determines its color presentation. This further supports the evolution process of the ore-forming fluid from medium–to–high temperature, and low salinity to medium temperature, and medium salinity, and finally to low temperature, and medium–to–low salinity. This paper provides a new theoretical perspective for revealing the coloration mechanism of sphalerite.