Deciphering the diagenetic evolution of the lower Carnian succession in the Gorno and Pian Resinelli sulphide mining districts (Southalpine Domain, N Italy)

Abstract

The stratabound Mississippi Valley-type (MVT) sulphide deposits of the Gorno and Piani Resinelli mining districts are hosted in the lower Carnian carbonate succession, mainly peritidal limestones, of the Lombardian Basin (Southalpine Domain, Northern Italy). In addition to the formation of the well-known sulphide deposits, these carbonate sediments experienced a complex diagenetic evolution, including different stages of dolomitization, silicification, dissolution, brecciation, calcite cement precipitation. Stratigraphic and petrographic features suggest that, apart from an early calcite cementation and a first penecontemporaneous dolomitization affecting the supratidal beds, diagenetic processes and sulphide precipitation, are intimately and genetically associated. They document the occurrence of a Carnian hydrothermal system developed shortly after deposition at shallow burial depth, confirmed by fluid inclusion microthermometry and U-Pb radiometric datings.