Geochemical prospecting of fluvial sediments from the Emilia Romagna region for potential secondary CRMs reservoir

The energy transition in Europe is a pivotal aspect of the current agenda, with the supply of Critical Raw Materials (CRMs) being equally crucial. These materials are essential for renewable technologies’ components, such as batteries, wind turbines, photovoltaic systems, fuel cells, and robotics (Bobba et al., 2020). This contribution is framed in a large national project aims to develop innovative methods to secure CRM supplies within EU borders, ensuring a stable and sustainable supply chain. Ensuring an internal supply not only reduces dependence on third countries but also strengthens economic security and promotes technological growth. The study is addressed to evaluate the role of river sediments in providing a resource of critical metals, that in a near future could be commutated in a reserve. The explored area is in the Emilia-Romagna region in the Northern Apennines, Italy. This region is known for its significant geological potential, hosting mafic/ultramafic rocks (ophiolites) associated with the External Ligurian Succession (Kiss et al., 2023). The largest reserves worldwide of metals, such as Cu, Ni, Co, PGE, Cr, Ti, and V are strictly related to these rocks (Barnes, 2023) therefore geochemical and mineralogical investigations were made on mafic sediments from four different river systems (Taro, Nure, Dragone, Scoltenna) of ophiolitic basins. Samples are sieved and grounded to powder before making both glass discs and pressed pellets for XRF analyses of major and trace elements for each of the major grain sizes. Absolute density (ρ) is determined with Helium pycnometer and range between 2.67 and 2.73 g/cm3. Minerals separation is performed using both a Frantz magnetic separator and heavy liquid solution. Each magnetic separated fraction was observed under binocular microscope and fully chemically characterized. Transition metals and Mg are one order of magnitude higher in the magnetic fractions, mainly composed of magnetite, chlorite and serpentine group minerals, compared to the nonmagnetic one, which retains Si, Ca and Sr and is composed mainly of calcite, quartz and feldspars. Heavy liquid separate is ~ 1% weight is mainly constituted by garnet and oxides. XRF results show some CRMs metals such as Cr (up to 1000 ppm), Mn (up to 2000 ppm), Ni (up to 500 ppm) enriched in the sand while others such as Cu (up to 50 ppm) and Zn (up to 150 ppm) are enriched in the mud. These values are “anomalous” compared to the sediments of the Po River as their metals concentration is up to four times higher than those observed in sediments collected along the main course of the Po River and ophiolite-free basins such as the Reno River (Amorosi et al., 2014). Streams and small rivers flowing near ophiolitic rocks (such as those in the Taro, Nure, Dragone, and Scoltenna catchments) show interesting potential for further investigation on the mineral chemistry of the mafic phases in selected granulometric fraction to evaluate the potential metal reserve.