Hydrothermal germanium mineralization at South Lakes Glacier in the Black Angel Zn-Pb district, West Greenland

• Germanium at South Lakes Glacier is mainly hosted by briartite. • Briartite formed by precipitation from a Cu-Ge-bearing hydrothermal fluid. • Phengite and quartz are unusually enriched in Ge. • Metamorphism in the Black Angel district reached 510 ± 40 °C at 4.3 ± 1.5 kbar. Metamorphosed Zn-Pb deposits can host significant amounts of critical metals, but their enrichment and source are often not well understood. The Black Angel district in central West Greenland hosts several marble-hosted Paleoproterozoic Zn-Pb occurrences, including the Black Angel mine. The sphalerite-pyrite-galena dominated massive sulfides in the district host briartite, a rare Cu-thiogermanate mineral. Detailed petrographic studies, electron microprobe and laser ablation-inductively coupled plasma-mass spectrometry and micro-XRF-mapping were applied to breccia-hosted massive sulfide from the South Lakes Glacier prospect in the Black Angel district to study the formation of briartite and the distribution of Ge in the ore. Whole rock analyses reveal Ge grades of 120 ppm in the ore. Briartite, occurring as clusters of µm-sized grains, as well as anhedral grains of up to three millimeters in diameter, formed by precipitation from Cu-Ge-bearing hydrothermal fluids coevally with Ge-rich chalcopyrite and is the main host for Ge. Unusually Ge-rich phengite and quartz post-dating briartite reflect a shift in Ge behaviour from sulfide-hosted to silicate-hosted. The epigenetic ore assemblage was overprinted by metamorphism leading to solid-state and dissolution-precipitation sulfide remobilization as well as the formation of a syn -metamorphic ore stage. Remobilization led to widespread sulfide breccia formation at South Lakes Glacier. Biotite and graphite geothermometry reveal peak metamorphic temperatures of ∼500°C.