Multistage germanium-rich sphalerite and wurtzite mineralization from the Qingshan carbonate-hosted Zn-Pb deposit, SW China

As a critical raw material for green technologies, germanium (Ge) is frequently concentrated in sphalerite (cubic ZnS). In nature, ZnS also occurs as its hexagonal polymorph, known as wurtzite; however, the distribution and incorporation of Ge in wurtzite still remains poorly understood. Using laser ablation−inductively coupled plasma−mass spectrometry analysis, this study investigates Ge distribution in sphalerite and wurtzite from three mineralization stages at the Qingshan carbonate-hosted Zn-Pb deposit, Southwest China. Stage I sphalerite (Sp-1) is enriched in Ge (109−672 ppm), whereas Stage II sphalerite (Sp-2) displays Ge-rich (dark Sp-2a; 174−899 ppm) and Ge-poor (light Sp-2b; ≤14.8 ppm) domains. Colloform wurtzite precipitated in Stage III (Wz-3) contains 58.0−722 ppm Ge, followed by euhedral sphalerite (Sp-3) with the highest Ge contents (467−1393 ppm). Combining transmission electron microscopy with trace element content correlations reveals that Ge is a structurally bound element in both sphalerite and wurtzite, incorporated via direct substitution mechanisms such as Ge2+ ↔ Zn2+ and Ge4+ + vacancy ↔ 2Zn2+. Ab initio calculations demonstrate no correlation between ZnS crystal structures (cubic/hexagonal) and Ge incorporation levels. The strongly positive δ34S values in Wz-3 (+17.2‰ to +19.2‰) suggest that the colloform texture is independent of low temperatures (<100 °C) and bacterial sulfate reduction. Increasing sulfur fugacity triggered wurtzite-to-sphalerite phase transition (Wz-3→Sp-3) and may have enhanced the incorporation of Ge in Sp-3. We propose a Ge enrichment process involving coupled dissolution-reprecipitation. This study highlights the importance of coupling micro- to nano-scale textural and chemical observations in ZnS minerals for understanding Ge enrichment.