Origin, metamorphic remobilisation and structural control of the Buca della Vena orebody (Alpi Apuane, Italy)

Research on the ore-forming event(s) and their relationships with the Apennine deformation and metamorphism of the Alpi Apuane ore district (NW Tuscany, Italy) was abandoned with the closure of mining activities. The discovery of a remarkable thallium (Tl) anomaly associated with the pyrite ± baryte ± Fe-oxides ores has renewed scientific interest in this ore district during the last fifteen years. This work provides a detailed field and underground geological-structural investigation of one of these orebodies (previously exploited at the Buca della Vena mine), performed from cartographic to micro-scales, and integrated with available drill-log data, providing new insights into ore-forming events and late remobilisation during metamorphic processes. Our investigation suggests that the current ore settings were acquired during successive geological events related to a Permian hydrothermal-magmatic phase, and more recent Apennine-related deformations. The Permian hydrothermal activity related to the post-Variscan magmatic cycle produced the proto-ore associated with tourmalinisation and hydrothermal alteration halo in the Palaeozoic host-rock. The proto-ore was then partially exhumed, undergoing supergene alteration and minor syn-sedimentary Fe-oxide mineralisation during the upper Norian-Hettangian. Finally, the earlier hydrothermal and syn-sedimentary ores and the host rocks were involved in the Apennine orogenesis, suffering recrystallisation and partial remobilisation, acquiring their current mineralogical, textural, and structural settings.