Mobilization of Tl-Hg-As-Sb-(Ag,Cu)-Pb sulfosalt melts during low-grade metamorphism in the Alpi Apuane (Tuscany, Italy)

We report the discovery of an exceptional assemblage of Tl-Hg-As-Sb-(Ag,Cu)-Pb sulfosalts showing textural evidence for their mobilization as melts in the barite-pyrite-iron oxide ore-bodies of the Monte Arsiccio mine (Alpi Apuane, Tuscany, Italy). The relative abundance of rare thallium sulfosalts (including three new mineral species), their peculiar textural features within the orebodies (e. g., migration along matrix grain boundaries, drop-like internal textures, low interfacial angles between sulfosalts and matrix minerals), and the overall high thallium content in pyrite from the entire mining district (to similar to 900 ppm) make the barite-pyrite-iron oxide deposits of the Alpi Apuane a reference locality for studying low-temperature sulfosalt melts in low-grade metamorphic complexes (greenschist facies). Our study reveals how sulfosalt melting during low-grade regional metamorphism controls the redistribution of economically valuable and environmentally critical elements such as thallium in sulfide orebodies containing significant amounts of low-melting-point chalcophile elements.