Potential mineral resources in historically dismissed volcanogenic massive sulfide (VMS) deposits of the Emilia Romagna region (Italy): petrological and geochemical study for Critical Raw Materials (CRMs) exploration and exploitation

The last update on the Critical Raw Materials Act (2023) drawn up by the European Union identified 54 Critical Raw Materials (CRMs), i.e., minerals, elements, or materials that are fundamental to supply for technology and strategic for the green transition, but subjected to fickle supply, e.g., for the fragile geopolitical contest (Kiss et al., 2023). This led many European countries, including Italy, to focus on the metal recovery from dismissed mines, mine wastes, and landfills to accomplish the circular economy politics. Italy has more than 100 historically dismissed mining sites just in the North, and, among them, the ones in the Emilia Romagna region are now under investigation for the various volcanogenic massive sulfide (VMS) deposits (Zaccarini & Garuti, 2008). These are a type of metal sulfide ore deposits that occur as a result of underwater volcanic eruptions, associated with hydrothermal events in submarine environments, and are divided based on ore composition (Cu, Cu-Zn, Cu-Zn-Pb group) and environment formation (Cyprus, Kuroko, Besshi, as mentioned by Zaccarini & Garuti, 2008). In the Emilia Romagna region, these deposits 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; Kiss et al., 2023). These ophiolites represent Jurassic Alpine Tethys oceanic crust fragments obducted in the continental crust (Zaccarini & Garuti, 2008). The stratigraphy of the area is characterized by sequences of pillow lavas associated with serpentine and gabbro breccias, radiolarian cherts, limestones, and abundant serpentinized subcontinental mantle peridotites (Kiss et al., 2023). Basalts, then, show Ocean Continent Transition Zone (OCTZ) chemical features with transitionalMORB affinity and a garnet signature (Dyn/Yb0: 1.2-1.4, Saccani, 2015), in agreement with Cyprus-type VMS deposits (Zaccarini & Garuti, 2008). Major and trace elements bulk rock geochemical analyses were performed in a group of basalts of the Boccassuolo ophiolite and compared with the previous results (e.g., Barrie & Hannington, 1999; Zaccarini & Garuti, 2008; Kiss et al., 2023): the VMS deposits in the Emilia Romagna region belong to the Cu and Cu-Zn types (Cu up to 5818 ppm, 200 times Upper Continental Crust, UCC, composition; Zn up to 7941 ppm, 118*UCC), low to very low Pb contents (< 1 ppm, max. 0.42*UCC). 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 additional information on the enrichment and distribution of VMS deposits in the Region. Barrie C.T. & Hannington M.D. (1999) - Classification of Volcanic-Associated Massive Sulfide Deposits Based on Host-Rock Composition. In: Barrie C.T. & Hannington M.D. (Eds), Volcanic-Associated Massive Sulfide Deposits: Processes and Examples in Modern and Ancient Settings, Rev. Econ. Geol., 8, 2-10. Kiss G.B. et al. (2023) - Tracing the Source of Hydrothermal Fluid in Ophiolite-Related Volcanogenic Massive Sulfide Deposits: A Case Study from the Italian Northern Apennines. Minerals, 13, 8. Saccani E. (2015) - A new method of discriminating different types of post-Archean ophiolitic basalts and their tectonic significance using Th-Nb and Ce-Dy-Yb systematics. Geosci. Front., 6, 481-501, https://doi.org/10.1016/j. gsf.2014.03.006. Zaccarini F. & Garuti G. (2008) - Mineralogy and chemical composition of VMS deposits. Mineral. Petrol., 94, 61-83, https://doi.org/10.1007/s00710-008-0010-9.