Critical Raw Materials (CRMs) petro-geochemical investigation in historically dismissed ophiolite-related Volcanogenic Massive Sulfide (VMS) deposits from the Emilia-Romagna region

Critical Raw Materials (CRMs) are essential elements, minerals, or materials for technology and the green transition, whose supply is insufficient to satisfy the global demand (Kiss et al., 2023). This caused several European countries to focus on locally dismissed mine sites. Italy has more than 100, just in the North, and, among them, the diffused Volcanogenic Massive Sulfide (VMS) deposits of the Emilia-Romagna region are now under investigation for potential exploitation of critical metals (i.e. Cu, Zn, PGE, Kiss et al., 2023). They are stratiform accumulations of sulfide minerals that result from underwater volcanic eruptions, associated with hydrothermal events, and classified according to several parameters, i.e. the ore composition (Cu, Cu-Zn, Cu-Zn-Pb groups), formation environment (Cyprus, Kuroko, Besshi), and the host-rock association (mafic, bimodal mafic, siliciclastic-mafic, bimodal felsic, bimodal-siliciclastic, as observed by Kiss et al.. 2023 and references therein). In the Emilia-Romagna region, they occur as pods within small bodies of ophiolitic basalts cropping out as olistoliths in the Northern Apennine External Ligurian units and owe their origin to the metal-rich hydrothermal circulation which developed quartz-sulfide veins when mixed with seawater through a fissures network (Saccani, 2015; Dini et al., 2024). These ophiolites represent Jurassic Alpine Tethys oceanic crust fragments obducted in the continental crust (Saccani, 2015). Sequences of pillow lavas associated with serpentine and gabbro breccias, radiolarian cherts, limestones, and abundant serpentinized subcontinental mantle peridotites define the area (Saccani, 2015). Basalts, there, show Ocean Continent Transition Zone (OCTZ) chemical features with transitional-MORB affinity and a garnet signature (Dyn/Ybn: 1.2-1.4, Saccani, 2015), in agreement with Cyprus-type VMS deposits related to ophiolites (Kiss et al., 2023, Dini et al., 2024). Whole-rock major and trace elements analyses were conducted on a group of basalts from the Toggiano and the Montecreto mine districts (Modena Province) and compared to the few data available for the area (e.g., Kiss et al., 2023 and references therein). Based on the chemical composition, the VMS deposits of the area belong to the Cu and the Cu-Zn types, with Cu up to 6000 ppm (up to 200 time Upper Continental Crust, UCC), and Zn 3000 ppm, i.e. 118 times UCC, with almost no Pb contents (up to 3 ppm, 0.42 times UCC). These results are comparable to Italy‘s most productive Cu-Zn VMS ophiolites deposits (i.e., those in Tuscany, as seen by Dini et al., 2024). Mineralogic analyses on selected samples revealed a sulfide association of pyrite, chalcopyrite, sphalerite, kesterite, and pyrrhotite. In situ analyses are planned to better constrain the VMS ore potential. These preliminary results provide the first relevant geochemical information to map trace metal enrichment distribution in the main rocks of the area. Radiogenic (Sr-Nd-Pb) and stable (S-C) isotopic analyses, as well as mineralogical and in-situ analyses, will provide further information on the enrichment and distribution of VMS deposits in the region. These results are fundamental for creating an updated ore deposits-themed national map.