Abstract
Typically found in rare-metal granites and pegmatites, lithium micas are increasingly considered a resource for lithium as global demand surges. In a recently discovered major lithium resource within the Macusani Volcanic Field in Peru, lithium mica crystal clasts hosted by a tuffaceous mudstone represent an important ore constituent. The mm-scale mica clasts comprise a zinnwaldite core and a lepidolite rim. Compositionally similar to micas in global peraluminous, rare-metal-rich leucogranites and LCT pegmatites, they exhibit enrichment in incompatible, fluid-mobile lithophile elements relative to micas in other volcanogenic and intrusive units in the Macusani Volcanic Field. The compositions of the mica crystal clasts record high degrees of magmatic differentiation and exsolution of a magmatic vapor phase during their crystallization in a ligand-rich, peraluminous crystal mush. (40)Ar/(39)Ar dating of zinnwaldite-lepidolite crystal clasts reveals cooling between 8823 ± 9 and 8717 ± 44 ka, coinciding with a regional magmatic lull in the Central Andes of southern Peru. A general slowdown in magmatic activity and a hiatus in volcanism may have contributed to extreme differentiation and pre-eruptive volatile build-up. This study provides crucial insights for lithium exploration, highlighting volcanogenic-sedimentary lithium mica deposits as a promising exploration target in peraluminous volcanic fields.