Mineralogy and Geochemistry of the Ergadiji Pb–Zn Deposit in Southwestern China

The Ergadiji Pb–Zn deposit is located in the northern part of the Sichuan–Yunnan–Guizhou (SYG) metallogenic district in southwestern China. This study presents mineralogical observations, electron probe microanalysis (EPMA) of sulfides and Pb–As–Sb sulfosalts, laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) summaries and elemental maps of sphalerite, and in situ S–Pb isotope results obtained by laser ablation multi-collector inductively coupled plasma mass spectrometry (LA–MC–ICP–MS). These datasets describe ore-mineral associations, mineral compositions, and isotopic variability. Germanium (Ge) distribution and possible incorporation pathways are considered within this broader mineralogical and geochemical context. Ge is hosted predominantly by sphalerite, and its enrichment shows a pronounced stage dependence: mean Ge concentrations increase from 41.87 ppm in Stage I to 155.35 ppm in Stage II. This increase is accompanied by a change in sphalerite trace-element systematics. Stage II sphalerite shows moderate positive Ge–Cu and Ge–(Cu + Ag) correlations (R2 = 0.5915 and 0.5661, respectively), while elemental maps show preferential enrichment of Ge–In–Cd toward outer growth zones. Taken together, these observations define a coherent Stage I-to-Stage II evolution in which changes in the hydrothermal system and sphalerite composition increasingly favored Ge incorporation during later growth. The available data are consistent with several possible substitution pathways, including vacancy-assisted substitution (Ge4+ + □ ↔ 2Zn2+), Cu-coupled substitution (2Cu+ + Ge4+ ↔ 3Zn2+), and Cu–Ag-coupled substitution [2(Cu+, Ag+) + Ge4+ ↔ 3Zn2+], but they do not uniquely establish their relative contributions because Ge valence and local coordination were not directly determined at Ergadiji. The stage-related increase in Ge is therefore interpreted as the integrated response of sphalerite to evolving temperature, sulfur and oxygen fugacity, fluid composition, and crystal chemistry, rather than to any single parameter alone. These results constrain the mineral-scale behavior of Ge at Ergadiji and highlight the importance of hydrothermal physicochemical conditions in controlling its incorporation into sphalerite. They also provide a basis for evaluating Ge enrichment and the potential comprehensive utilization of Ge-bearing Pb–Zn resources in the SYG metallogenic district.