The future supply of rare chemical elements is a major concern of the global economy due to the imbalance between supply and demand. Strategic elements are considered those elements that are at greatest risk of supply disruption or are important to a country¿s economy or defense, and include rare earth elements, platinum group elements and trace metals. The demand of rare elements increased enormously in the recent years, due to the large use for the production of new technologies, from consumable of electronic goods, the clean energy and green economy technologies. Even in the frame of a circular economy, the look for alternative resources is a necessary pathway to sustain the evolving technology.
Pegmatites are important reservoirs of rare elements, due to their peculiar petrologic significance and petro-chemical characteristics. Despite the interest for pegmatites has been largely motivated by the exploration for the economic commodities, the ore-forming mechanisms are still poorly understood and, in some cases, controversial. Understanding these mechanisms is indeed extremely important, not only for the direct impact in modeling the transport of rare elements, but also for the development of new techniques for extraction. With the present proposal, we aim to fill this gap by combining a fundamental research, aimed to understand the geochemical behavior (mobilization, transport and accumulation) of rare elements during pegmatite formation, with an experimental development of novel protocols for individuation, sizing and put-into-production of magmatic ore deposits.
The economic exploitation of pegmatite deposits (for gemstones and other raw materials) has been carried out since ancient times with little interest for the formation mechanisms of these rocks. For this reason, the availability of these resources has been always limited to deposits having an excellent surface exposure. With this project, we aim to go deep in the ore-forming processes, which may allow to individuate new non-exposed locations and to improve the efficiency of current extraction techniques (e.g., ionic exchange, fractional crystallization, liquid-liquid extraction). To do this, ore-forming processes in pegmatites, must be carefully investigated. The hypotheses on the formation of pegmatites are poorly understood and, in some cases, controversial (London and Morgan, 2012; Thomas et al., 2012). Even less is known about the ore-forming processes leading to the enrichment in rare elements. Given the difficulty in reproducing in laboratory the conditions at which pegmatites form in nature (especially the timescale of crystallization) and to determine exactly the concentration of rare elements in small sample volumes, only a limited number of experimental studies has been carried out. Some of these studies aimed to reproduce the crystallization conditions of granitic systems using cooling paths that closely simulated those of numerical cooling models and succeeded reproduced the textural and compositional features of pegmatites (London et al., 1989). Other studies investigated the partitioning of some trace elements between fluids and granitic melts, demonstrating the role of volatile species in forming chemical complexes with trace elements and in mobilizing them into the fluid phase (Keppler and Wyllie, 1991). Another trend of experimental studies demonstrated the role of low-temperature hydrothermal fluids in transporting rare elements from rocks in middle ocean ridge settings (Allen and Seyfried, 2005). All together, these studies confirm that the combination of a magmatic source for rare elements and a fluid carrier is required to produce significant enrichments of these elements into an ore deposit. This project is intended to put one step forward in this direction, by connecting all the processes involved in the pegmatitic ore formation, from rare elements mobilization to transport in fluids to accumulation in minerals. The technological progress and the increasing attention to environmental issues demand a review of the criteria for the exploration and sizing of rare elements reserves. In this framework, the use non-conventional reserves characterized by relatively low concentrations of rare elements, but more sustainable in terms of exploitation, requires a deeper examination. The present project is expected to expand our knowledge on rare element reservoirs and mobility, which is at the base of the geochemical characterization of ore deposits. Specifically, we examine the behavior of rare elements in geologic environments where the combined effects of solid-fluid-melt interaction favor the concentration of these elements in viable amounts. This knowledge will be used to develop and test in laboratory new treatment techniques for the efficient extraction of strategic elements from otherwise unexploited minerals and rocks from selected sites.