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Understanding the genesis of Zn-Pb-Ag mineralization in the Gorno MVT District (Northern Italy)

The Gorno mining district is an example of Mississippi Valley-type (MVT) deposits in the Italian Orobic Alps. Spanning an area of ~100 km2, it consists of stratabound Zn-Pb-Ag (± fluorite ± barite) mineralization hosted in a lower Carnian stratigraphic succession. Despite Vedra Metals S.r.l.´s acquisition of the exploration license for the deposits has reignited an economic interest, an updated metallogenic model has yet to be developed.

In the carbonate host rocks at Gorno, a complex series of dolomitization, silicification, brecciation, dissolution, and cementation occurred. Microthermometry of primary fluid inclusions in sphalerite and fluorite, alongside sphalerite trace-element geothermometry, indicates formation temperatures ranging from 80 to 140 °C (mean value: ~100 °C). Moreover, fluid inclusion microthermometry and micro-Raman spectroscopy document the involvement of high-salinity brines (up to ~25 eq.wt% NaCl) and gaseous hydrocarbons (e.g. CH4) in ore deposition. Isotopic signatures from ore-related carbonates for carbon (0.5 to 2.5 ‰ PDB), oxygen (-6.6 to -12.1 ‰ PDB), and strontium (0.70840-0.70943) indicate that the ore fluid was likely seawater modified through interaction with the underlying Permian clastic sediments and/or with the metamorphic basement.

The presence of sulfide bodies in association with organic-rich shales implies a notable role of organic carbon in ore deposition. Organic matter and associated hydrocarbons likely served as reactive barriers, leading to the reduction of the ore fluid and initiating the precipitation of sulfide minerals.

Details

Author
Michele Giorno1, Carlo Bertok2, Luca Barale3, Luca Summino2, Mathias Burisch4, Stefano M. Bernasconi5, Jörg Rickli5, Marcus Oelze6, Joachim Krause1, Max Frenzel1, Luca Martire2
Institutionen
1Helmholtz Zentrum Dresden-Rossendorf, Helmholtz Institute Freiberg for Resource Technology, Freiberg, Germany; 2Department of Earth Sciences, University of Torino, Italy; 3Institute of Geosciences and Earth Resources, Turin, Italy; 4Department of Geology and Geological Engineering, Colorado School of Mines, Golden, USA; 5Department of Earth Sciences, ETH Zürich, Switzerland; 6GFZ German Research Centre for Geosciences, Potsdam, Germany
Veranstaltung
GeoSaxonia 2024
Datum
2024
DOI
10.48380/dgp8-3d35