On tin and lithium granite systems: A crustal evolution perspective

Abstract

The battery metals tin and lithium (SnLi) are key to renewable energy technologies, with demand driving new interest in the formation and exploration of tin granites and lithium-caesium‑tantalum (LCT) pegmatites. These magmatic-hydrothermal systems originate from highly evolved, reduced, peraluminous, volatile-rich granitic melts which develop elevated concentrations of incompatible metals. Tin granite deposits form either as disseminated magmatic cassiterite, or hydrothermal quartz-cassiterite lodes and greisens, with Li-bearing fluids driving late-stage mica alteration to Li-rich varieties. Conversely, LCT pegmatites record a complex crystallization with Li ores forming during primary magmatic crystallization, and Sn associated with hydrothermal overprints.

The first appearance in the geological record of SnLi granites and pegmatites is linked to the global onset of crustal reworking during Neoarchean terrane assembly, highlighting the key role of crustal evolution processes in their formation. In this contribution, we review our current understanding of SnLi metallogeny from source to sink through the lens of crustal processes. We focus on recent advances in petrological modelling and in situ microanalysis of rock-forming and accessory minerals, to examine tin granite and LCT pegmatite formation from partial melting of a source rock through melt extraction; emplacement, crystallization, and fractionation; to late-stage hydrothermal processes.

Quantitative thermodynamic modelling of crustal melting brings the ability to explore source rock anatexis and resulting melt compositions under various P-T conditions. Melt SnLi concentrations are controlled by mineral breakdown and metal partitioning between restite and melt. Sn and Li are primarily hosted in muscovite and biotite; deep crustal melting driving biotite breakdown releases Sn and Li into the melt, however shallow muscovite-driven melting restricts melt Li enrichment. It is difficult to generate a melt capable of saturating Li ore minerals from melting an ordinary clay protolith, hence either multi-stage melting or source metal pre-enrichment may be required.

Microanalysis allows high-precision geochemical and isotopic characterization of mineral phases. We review and summarize case studies using accessory minerals such as zircon, apatite, and mica, whose compositions are particularly powerful in tracking metal concentration and mobility during magma evolution and the magmatic-hydrothermal transition, with potential applications to exploration efforts. In tandem, the development of novel geochronometers such as cassiterite or columbite UPb help improve constraints on the age and timing of mineralization with respect to magmatism.

Finally, we consider the formation of tin granites and LCT pegmatites in 4D using the framework of long-lived, transcrustal magmatic systems. These models may help describe how prolonged melt generation, extraction, and evolution over protracted timescales allows progressive enrichment of Sn and Li. Combined, such efforts can help answer open questions on the formation of SnLi granite systems, to build improved 4D mineral systems models and inform fresh approaches to prospect for new deposits.