Newly discovered germanium minerals in Huize and Maoping MVT PbZn deposits in Southwest China: Implications for the germanium enrichment mechanism and exploration

The Sichuan-Yunnan-Guizhou (Chuan-Dian-Qian) region represents the largest Mississippi Valley-type (MVT) Pb-Zn-Ge metallogenic province in China, including giant Huize and Maoping deposits. Research has suggested that Ge is incorporated primarily into the sphalerite lattice in the form of element substitution, and few Ge-bearing minerals have been reported in these deposits. We identified numerous sphalerite colors in Huize and Maoping and further found Ge-bearing minerals in black (C1) sphalerite. These Ge-bearing minerals are randomly distributed and have regular mineral morphologies, suggesting potential co-precipitation with C1 sphalerite rather than formation during later metamorphism and oxidation. One Ge-bearing mineral, argutite (GeO₂), is found in Huize C1 sphalerite, which occurs in an isolated distribution or is locally associated with pyrite and hematite. Two Ge-bearing minerals, brunogeierite (GeFe₂O₄) and argutite (GeO₂), are found in the Maoping C1 sphalerite. Brunogeierite is more abundant than argutite and is commonly associated with pyrite and rarely with argutite. The petrography and elemental composition confirmed that the C1 sphalerite in Huize and Maoping is the earliest formed sphalerite with the highest formation temperature. This suggests that high temperatures favor the precipitation of argutite and brunogeierite. However, slight variations in sulfur and oxygen fugacity may have resulted in discrepancies in the occurrence of Ge-bearing minerals between the Huize and Maoping deposits. According to the fluid mixing metallogenic model in the Chuan–Dian–Qian region, we posit that Ge-oxide mineral precipitation benefited from the initial stage of fluid mixing between Ge-bearing reduced fluid and oxidized basinal brine. This is also consistent with the findings that argutite and brunogeierite are exclusively associated with C1 sphalerite. As fluid mixing progresses, Ge is incorporated into the sphalerite lattice via element substitution. The newly discovered independent Ge minerals (argutite and brunogeierite) present greater economic potential than Ge-rich sphalerite does, thereby offering significant insights into the enrichment mechanism of Ge and the further utilization of Ge resources.