Lithium isotopic constraints on the petrogenesis of the Jiajika two-mica granites and associated Li mineralization

Abstract

Petrogenesis of two-mica granites and the associated Li mineralization from the Jiajika super-large Li deposit in Sichuan Province, southwest China, remains equivocal. This study analyzed Li contents and isotopic compositions of metasedimentary rocks (schists and slates) and two-mica granites in this deposit to investigate the issue. The metasedimentary rocks show large variations in Li (71.7 ppm to 1792 ppm) and δ7Li (–14.1 ‰ to +7.9 ‰), while the two-mica granites have Li contents from 60.2 ppm to 388 ppm and δ7Li values from –3.1 ‰ to +1.9 ‰. Integrated with bulk geochemistry and available Nd–Hf isotopes from this deposit, the two-mica granites probably originated from partial melting of the middle-upper crustal pelitic metasediments. The lower average δ7Li value of metasedimentary rocks (–2.9 ‰) than that of two-mica granites (–0.4 ‰) is possibly attributed to 6Li-rich garnets entering residuum during incongruent melting. We speculate that Li isotopic fractionation might have occurred during crustal anatexis. The partial melting that contributed to the transfer of volatiles and rare-metal elements into the granitic melts played an important role in Li mineralization. Li isotopes can potentially guide Li deposit prospecting as Li-bearing veins are likely to occur in regions with light 6Li.