GERMANIUM ENRICHMENT MECHANISM: AN EXAMPLE FROM THE MAOPING CARBONATE-HOSTED Zn-Pb-(Ge) DEPOSIT, SW CHINA

Germanium (Ge), as a critical metal, is in high demand due to its growing usage in emerging industries and green technologies. The Sichuan-Yunnan-Guizhou Zn-Pb metallogenic region, located on the southwestern margin of the Yangtze block, is one of the most important producers of Ge in China. The Maoping Zn-Pb deposit in the Sichuan-Yunnan-Guizhou region contains Ge-bearing sphalerite, whose crystal chemistry and process of Ge incorporation are poorly resolved. Sphalerite occurring in two hydrothermal stages (Sp-II and Sp-III) is recognized in this deposit. Laser ablation inductively coupled plasma mass spectrometry was used to map the concentrations of key elements (including Mn, Fe, Cu, Ga, Ge, As, Ag, Cd, In, Sn, Sb, Hg, and Pb) in Sp-II and Sp-III, and their distributions were qualitatively compared, followed by a quantitative assessment through application of the structural similarity index. The results suggest that Ge positively correlates with Cu in Sp-II, but with Ag in Sp-III, differences that may be related to the temperature of formation. The metamorphic basement is the main source of Ge in the Maoping deposit. Additionally, coal seams in this deposit could potentially be important contributors to Ge enrichment. A model for Ge mineralization was proposed in which the mixing of the Ge-bearing metamorphic fluids with the Ge-bearing basin brines precipitated sphalerite, and the Ge was incorporated into Sp-II and Sp-III via 2Cu(+) + Ge4+ <-> 3Zn(2+) and 2Ag(+) + Ge4+ <-> 3Zn(2+), respectively, under medium sulfur fugacity and low oxygen fugacity conditions.