Timing and evolution of hydrothermal processes associated with base-metal deposition in alpine-type Pb-Zn deposits (Raibl, NE Italy)

The Triassic platform carbonates of the Eastern and Southern Alps host over 500 Pb-Zn deposits collectively known as Alpine-type (AT) Pb-Zn deposits. The AT deposits represent a subclass of Mississippi Valley–Type systems and one of Europe’s largest provinces for base and strategic metals (e.g. Ge, Ga) resources. Despite their importance, the source of metals, timing of mineralization, and mechanism driving fluid flow in the province remain debated. The Raibl deposit (Italy) displays structural and mineralogical features typical of the class, making it an ideal site to investigate controls on Pb-Zn accumulation. This study provides the first, detailed petrographic and compositional characterization of the hydrothermal carbonates associated with the Pb-Zn mineralization at Raibl and present in-situ U-Pb ages on syn- to post-ore carbonate domains alongside new Pb isotopic data on galena from Raibl and other selected AT deposits. Syn-ore carbonates show a distinctive geochemical signature (Fe and Mn enrichment) and constrain the mineralization to a short interval in the Late Triassic (214.0 ± 5.8 Ma to 205.2 ± 3.3 Ma). These constraints support a revised genetic model involving Late Triassic mobilization of oxidized, metal-bearing brines sourced from Permian clastic units (i.e. Val Gardena Sandstone and the Sesto Conglomerate) during early regional extension and strike-slip tectonic. Epigenetic sulphide precipitation at 2–4 km depth resulted from in-situ reduction of these fluids through interaction with organic-rich, Late Triassic lithologies. The proposed model for Raibl aligns with evidence from the world-class Bleiberg deposit but contrasts with smaller mineralized AT systems (e.g. Gorno) that record Middle Triassic, shallow diagenetic mineralization. Overall, the results suggest diachronous fluid flow and metal deposition across the province, emphasizing the role of local structural and geochemical factors in controlling economic accumulation of base metals.