Colloform sulfides host significant germanium (Ge) resources in South China. The Banbianjie deposit, situated in southwest China, is a carbonate-hosted Zn-Ge deposit (0.8 Mt. @ 1.78 to 9.50 % Zn and > 800 t @ 100–110 ppm Ge) and is rich in colloform sphalerite with widespread occurrence of Ge-rich nanoparticles. Previous studies documented that Ge enrichment in sphalerite may be correlated to internal mechanisms, however, the impact of external factors, such as source and fluid mixing, on Ge enrichment is poorly understood. In this study, we applied in situ trace elements and S-Pb isotopic compositions to interpret the external controls influencing Ge distribution. New laser-ablation inductively coupled mass spectroscopy (LA-ICP-MS) analyses reveal that sphalerite contains very heterogeneous Ge contents from 221 to 1916 ppm (mean = 843 ppm Ge), positively correlating with Fe, Mn, and Pb and negatively with Cd concentrations. Sulfur isotopic compositions infer a predominant sulfur source (~ 􀀀 10 ‰) and a subordinate sulfur source (~ 􀀀 1 ‰). The Pb isotopic ratios of sphalerite plot on the upper crust curve, indicating a crustal source for the metals. The sulfur isotope geothermometer estimates the formation temperatures of sphalerite mainly below 250 ◦C and pH changes may cause the transition of sulfide phases. Trace elements and δ34S values indicate a predominant Ge-rich fluid and a subordinate Cd-rich fluid. The influxes of Cd-rich fluid are correlated with local Ge-poor zonings in sphalerite. We propose that fluid mixing can locally influence the Ge contents in sphalerite.