Rare-element Pegmatite (Spodumene)

Abbreviation

REL-Li

Classification

Spodumene 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 spodumene subtype pegmatites are formed at slightly deep 0.3-0.4 Gpa and lower temperature circumstance than the petalite subtype whereas other rare-element class pegmatites emplaced at shallow depth. This formation condition is almost same as the albite-spodumene type, but more abundant in K-feldspar than albite and quartz. 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 spodumene subtype is characterized by abundant Li, Rb, Cs, Be, Nb, Ta, Sn, P, F, and rich in spodumene as Li-bearing aluminosilicate. Paragenetic association and chemical composition of the spodumene subtype are almost same as the petalite subtype except that spodumene is the dominant Li-bearing aluminosilicate instead of petalite.

Mineral Assemblages (Major minerals)

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

Mineral Assemblages

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