• Latera
• leaching
• lithium
• melt inclusions
• Quaternary
• Roman Magmatic Province
• volcanic

This thesis is aimed at defining the behavior of lithium from the mantle source up to the surface in an area of scientific and (potential) industrial interest such as the potassic-ultrapotassic Roman Magmatic Province. The work focused on samples collected in the area of Latera (western Vulsini Volcanic District), including pyroclastic rocks, lacustrine sediments, and intra-caldera hydrothermal products. Bulk rock and mineralogical analyses, sanidine-hosted melt inclusion micro-analyses, and leaching experiments were conducted on these products, in addition to an extensive gathering of Li concentration data from the literature regarding rocks, glasses, melt inclusions, and minerals from the entire magmatic province.
The results show that Li concentrations in volcanic rocks of the Roman Magmatic Province are higher than what is expected from an ordinary alkaline province, twice the average of global alkaline volcanoes for primitive products and almost threefold in the case of most evolved terms. The occurrence of near-primary melt compositions in the literature (e.g., olivine-hosted melt inclusions, bulk mafic rocks) exhibiting up to 104 ppm Li implies an enrichment of the magma source, likely as a consequence of the mantle metasomatism and introduction of anomalous Li amounts from the subducting slab. High Li values (up to 332 ppm) recorded in most evolved products of the Roman Magmatic Province could thus be the result of such high concentrations in their parent primitive melts, in addition to extensive fractional crystallization because of the incompatible behavior of Li.
Trace element analyses of sanidine-hosted melt inclusions revealed higher Li values in the last trapped melt compared to the glass matrix of pumices, allowing the calculation of ~ 48% Li loss likely caused by the partitioning of Li into the vapor phase before and/or during the eruption, with consequent release to the atmosphere. Being this a very common process, it may be possible that many of the reported Li concentrations in bulk rocks and glasses throughout the Romana Magmatic Province are even underestimated compared to the original Li content in the magma.
Concerning surficial processes, no extreme Li concentration was recorded in sedimentary samples, which were mainly composed of detrital minerals from the nearby volcanic rocks without developing any “sink” mineral capable of accumulating Li (e.g., clays). However, a paleosol sample returned a Li concentration (73 ppm) three times higher than the soil world average. Kaolinitized samples collected in an intra-caldera setting exhibited instead an effective removal of Li from post-caldera lavas, increasing with the hydrothermal alteration degree.
Low-temperature leaching experiments performed on pumice samples revealed an immobile behavior of lithium under near-neutral conditions, becoming slightly more mobile in the case of saline and acid solutions but always being released from the rock in irrelevant amounts. High-temperature leaching experiments, on the contrary, highlighted the most mobile behavior among the analytes considered, reaching ~14% of total Li leached from the rock at 150°C after 32 days of water-pumice interaction and ~30% under more severe conditions (pulverized sample and 170°C) for a shorter time span (14 days), which are among the highest values recorded by experiments of this kind.
The first results from this thesis show that lithium can easily move between different phases (e.g., melt, minerals, rocks, fluids) in several geological environments, but can also be retained. Its pathway from the mantle source to the eruptive event has been reconstructed for Roman-type magmas, in addition to its post-eruptive mobility following water-rock interaction under both low- and high-temperature conditions. Overall, the Roman Magmatic Province seems to be a perfect environment to provide, remobilize, and concentrate lithium, being characterized by voluminous Li-rich products, large caldera basins, and significant hydrothermal circulation. This could have implications for the occurrence of Li unconventional resources in this volcanic area, with special attention to the already documented Li-rich waters in geothermal fields.