Mechanisms of Paleoproterozoic critical metal (Ge, Bi, Te) mobilisation in the Black Angel district, West Greenland

Zn-Pb deposits are host to a large proportion of worldwide resources of Ge and other critical metals. The Black Angel district in central West Greenland hosts several Zn-Pb occurrences, including the historic Black Angel mine, South Lakes and Kangerluarsuk, that show a previously unrecognized endowment of Ge and Bi (± Te) respectively. The carbonate-hosted MVT deposits at Black Angel and South Lakes show strong deformation and associated ore remobilisation at Upper Greenschist facies conditions (ca. 470°C), as indicated by graphite thermometry. Germanium occurs in tectonised and remobilised ore in the form of briartite, which is hosted in sphalerite and galena matrix. We studied how rock deformation and related remobilisation processes in these ore bodies lead to the redistribution of Ge and formation of briartite. Germanium was most likely exsolved from sphalerite as nanoinclusions of briartite during recrystallisation. Subsequent solid-state and fluid-assisted processes lead to formation of micrometre sized grains of briartite in sphalerite matrix, as well as up to millimetre-sized briartite aggregates. However, the nearby clastic-hosted SEDEX deposit at Kangerluarsuk shows native bismuth and tellurides hosted with galena, and no briartite or other Ge enrichment. Thus, two contrasting Zn-Pb systems with a different critical metal endowment are in close proximity to one another.