Research Projects

The shift to low-carbon technologies has intensified demand for critical rare metals, positioning Li-Cs-Ta (LCT) pegmatites as key targets for exploration. Although many LCT pegmatites are spatially associated with highly fractionated, peraluminous granites, this link is not universal. Fertile pegmatites may occur without such granites (e.g., Müller et al., 2017), and conversely, fractionated granites may lack associated pegmatites. These inconsistencies challenge the idea of a simple genetic link between granites and pegmatites (Simmons, 2008). Furthermore, where a geochemical continuum between granite and pegmatite is absent, the pegmatite generation via fractional crystallization becomes uncertain (e.g., Martins et al., 2012). A further complication lies in the globally recurring age gaps between granite emplacement and pegmatite crystallization, challenging the notion that pegmatites invariably represent terminal granite fractionates (e.g., Melleton et al., 2012). Overall, these patterns point to deeper controls on rare-metal enrichment, such as source rock composition, partial melting reactions, and melt segregation mechanisms- beyond fractional crystallisation alone. The Allapatna rare-metal pegmatite belt in the Western Dharwar Craton (WDC) offers a suitable geological context to examine these questions. The fertile pegmatites here have been attributed to the adjacent Allapatna Granite, a Neoarchean, amphibole-bearing intrusive of moderate geochemical evolution. However, this granite yields a Rb-Sr isochron age of ~2803 Ma (Sarbajna et al., 2018), notably older than the electron microprobe-derived chemical age of uraninite (~2340 Ma) from the pegmatites. These discrepancies call for a careful re-evaluation of the granite’s fertility and its genetic link to the pegmatites using a process-oriented framework integrating thermodynamic modelling and mineral-scale geochemistry. This study aims to reconstruct the melt evolution pathway, from crustal anatexis to pegmatite crystallization, through whole-rock chemistry, mineral (mica, garnet, apatite) trace-element signatures, and open-system phase equilibria modelling. A central goal is to simulate partial melting and fractional crystallization processes to generate model melt compositions comparable to observed pegmatites. Three questions guide this investigation: (1) What partial melting reactions and source lithologies favor the generation of rare-metal-enriched melts? (2) How do melt segregation regimes, batch versus accumulated fractional melting, affected the concentration of strategic metals (Li, Cs, Ta, Nb, Sn, W)? (3) Do the traceelement signatures and mineral chemistry of the pegmatites reflect derivation from the Allapatna granite or any other distinct anatectic event? Addressing these will refine the petrogenetic model for granite-pegmatite systems in high-grade Archean terranes and establish diagnostic geochemical criteria to guide rare-metal exploration in poorly understood regions.

LCT Pegmatites, Granite–Pegmatite Evolution, Partial Melting, Thermodynamic Modelling, Trace Element Geochemistry, Rare-Metal Fertility