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.