Various occurrences and differential enrichment of Ge in sphalerite: An example from the Shanshulin Pb-Zn deposit, SW China

Abstract

Germanium (Ge) is commonly enriched in low-temperature Pb-Zn deposits. However, the distribution and enrichment mechanisms of Ge vary significantly for individual deposits. This study employs SEM and LA-ICP-MS analysis techniques to investigate the occurrence and substitution of Ge within sphalerite, as well as to identify the factors controlling Ge enrichment. In the Shanshulin Pb-Zn deposit, three generations of sphalerite were identified: early stage (Sp1a + Sp1b) and late stage (Sp2). Sp1a is dark brown, and Sp1b is light brown, often in close association with or enclosing pyrite. Sp2 is light yellow to white and typically found in close contact with galena. LA-ICP-MS time-resolved depth-intensity profiles reveal that Ge can exist either within the sphalerite lattice or as Ge-rich nanoparticles. The substitution mechanisms for Ge incorporation into the sphalerite may include Ge⁴⁺+2(Ag⁺, Cu⁺) ↔ 3Zn²⁺ and Ge²⁺ ↔ Zn²⁺ or Ge⁴⁺ + □ (□ represents vacancy) ↔ 2Zn²⁺. In the Shanshulin deposit, the chemical reactions and mass exchanges between gaseous sulfur species and minerals or fluids may induce variations in the temperature and fS₂ of ore-forming fluids. The concentrations of Fe, Mn, Cu, and Ga in sphalerite are influenced by temperature, while the concentration of Ge is jointly regulated by the temperature and composition of the ore-forming fluids. The difference in Ge enrichment among different Pb-Zn deposits in the northwestern Guizhou is controlled by temperature which influences the substitution mechanisms of Ge.