Rare-element Pegmatite (Petalite)

Abbreviation

REL-Li

Classification

Petalite subtype < Complex type < Lithium subclass < (LCT family) < Rare-element class < Granitic pegmatite

Required Geological Setting

Plutonic rocks

Occurrence

Pegmatites formed by fractional crystallization of S-type granite magma associated with upper Greenschist facies to Amphibolite facies in Barrovian-type middle-P metamorphism. It is considered that the complex type pegmatites are formed by extremely fractionated magma. The petalite subtype pegmatites are formed at slightly shallower 0.15-0.3 Gpa and higher temperature circumstance than the spodumenen subtype as other rare-element class pegmatites emplaced at shallow depth. Most of pegmatites are reported from active continental margin granites in compressional crustal settings such as the Pacific Ocean. Textures of host rocks are clearly cut by pegmatites, and host rocks are subjected to contact metamorphism by granites or pegmatites. Pegmatites are massive and pockets are very rare. The petalite subtype is characterized by abundant Li, Rb, Cs, Be, Nb, Ta, Sn, P, F, and rich in petalite as Li-bearing aluminosilicate. Paragenetic association and chemical composition of the petalite subtype are almost same as the spodumene subtype except that petalite is the dominant Li-bearing aluminosilicate instead of spodumene.

Mineral Assemblages (Major minerals)

Quartz, Orthoclase, Microcline, Albite, Muscovite, (Almandine)

Mineral Assemblages

Petalite, Beryl, Columbite-(Fe), Tantalite-(Fe), (Amblygonite, Lepidolite, Pollucite)