Reverse telescoping in a distal skarn system (Campiglia Marittima, Italy)

• Campiglia Marittima was considered a classical example of exoskarn.
• This work argues significant departure from the classical model.
• We propose a new model with a reverse telescoping interpretation.
• The reverse telescoping model could be applied to other skarn deposits.

The Campiglia Marittima Fe-Cu-Zn-Pb(-Ag) skarn deposit has long been regarded as a reference example of an exoskarn showing a symmetric outward mineralogical zoning of both skarn and ore minerals with respect to an axial mafic porphyry dike. Detailed field and underground mapping, along with three-dimensional reconstruction of the geometries of skarn and magmatic bodies, integrated with new petrographic, mineralogical and geochemical data, argue against this model. The shapes of the skarn bodies and the growth versors of skarn minerals in particular, are ascribed to the focusing of metasomatic fluids in sigmoid-shaped volumes of fractured host marble. After skarn formation, a mafic magma was emplaced, forming dikelets and filling residual pockets in the skarn. Field evidence and geochemical data show that the “hot” mafic magma interacted with the previously formed Zn-Pb(-Ag) skarn, triggering textural reworking and chemical redistribution of Zn-Pb sulfides as well as contributing to a late Fe-Cu mineralization. Campiglia Marittima skarn-ore system behaved at odd: a telescoping process is recorded, yet in a reverse way.

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