C. Biagioni and colleagues have discovered an exceptional assemblage of Tl-Hg-As-Sb-(Ag,Cu)-Pb sulfosalt minerals, showing textural evidence for their mobilization as melts in the barite-pyrite-iron oxide orebodies 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 (up to ~900 ppm), make the barite-pyrite-iron oxide deposits of the Alpi Apuane a reference locality for studying very low-temperature sulfosalt melts in low-grade metamorphic complexes (greenschist facies). This study reveals how sulfosalt melting during low-grade regional metamorphism controls the redistribution of economically valuable and environmentally critical elements such as thallium (a highly toxic element) in sulfide orebodies containing significant amounts of low-melting-point chalcophile elements. The increase in local concentration combined with the change in thallium speciation (from trace level substituting ion to essential constituent element) could significantly influence the environmental release of thallium during weathering of such complex ore deposits.
Magmatic-hydrothermal processes within an evolving Earth: Iron oxide-copper-gold and porphyry Cu Mo Au deposits
Jeremy P. Richards, Dept. of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada; and A. Hamid Mumin, Dept. of Geology, Brandon University, 270 18th Street, Br
|Contact: Christa Stratton|
Geological Society of America