Lithium Origin and Distribution in the Alpine-Cycle Sedimentary Systems of the Northern Apennines (Italy): Geochemical and Mineralogical Constraints on a Potential Unconventional Lithium Resource

The transition to renewable energy and electric vehicles is recognized as a key driver in the global effort to achieve net-zero emissions. High-capacity batteries are a fundamental tool for this transition and we are witnessing a dramatic increase in the demand for the critical raw materials required for their production. Among these, lithium plays a crucial role, with its demand in the European Union (EU) expected to rise by up to twelvefold by 2030. To diversify supply sources and reduce EU’s dependence on imports, it is essential to enhance recycling and to investigate alternative types of resources, the so-called unconventional deposits, with particularly promising prospects offered by lithium recovery from fluids. In Italy, lithium-rich waters have been identified in volcanic/geothermal peri-Tyrrhenian zone and in Apennine external front. The occurrence of sedimentary sequences in the Northern Apennine with associated Li-rich groundwaters (up to 164 mg/L), may represent a potential target for resource exploitation through modern Direct Lithium Extraction techniques. This study provides a geochemical and isotopic (87Sr/86Sr, δ11B, δ7Li) characterization of these waters (natural spring, SPA wells, mud volcanoes fluids) and sedimentary formations, providing the first available Li content and isotopic data for the rocks of this sector of the Apennines. This geochemical and multi-isotope approach, combined with a detailed mineralogical study (XRD, SEM-EDS, LA-ICP-MS, and EPMA) of the main pelitic formations outcropping in the area, has made it possible to investigate the genetic processes of these formations and the mechanisms responsible for the lithium enrichment observed in the associated groundwaters. The results indicate highest lithium content within the Cretaceous pelitic formations of Subligurian and External Ligurian units, reaching content up to 263 mg/kg. Analyses reveal a great micro-scale variability, with Li concentrated in phyllosilicate-rich microlayers (up to 590 mg/kg), showing strong associations with B, K, Al, Fe, Rb and Cs, and suggesting illite as the main Li-hosting phase. Isotope analyses of rocks suggest a mixed carbonate/siliciclastic provenance of these sediments with a possible input of Permian volcanic material from the Eastern Alps. Leaching experiments highlighted a rapid release of Li during water-rock interaction, with a preferential mobilization of 7Li. This finding, coupled with other isotope systematics, suggest that Li in the studied groundwaters (up to 55 mg/L) originates from exchange processes with clays interbedded within the carbonate sequences, with minor contribution of seawater. Overall, the results support the hypothesis of incremental lithium release from these clayey formations into circulating waters, leading to their high concentration within these sedimentary systems. The insights of this work could contribute to promote interest in refining sustainable methods for lithium extraction and recovery from waters and brines, necessaries to support ongoing energy transition, and meet the requirements of the EU Critical Raw Materials Act 2024, and the Italian National Exploration Programme 2025.