Genesis, classification, tectonic setting and economic potential of global granitic pegmatites: A review

Abstract

Granitic pegmatites have attracted a significant interest of petrologists and mineralogists due to their complex genetic characteristics and substantial economic value. Although numerous reviews addressed specific aspects such as genesis, classification, economic potential, and tectonic setting, a comprehensive review integrating all these facets in a single article has been lacking. This study fills that gap by offering a holistic review that synthesizes these key dimensions. It examines prevailing theories on pegmatite genesis, traces the evolution of classification systems, and assesses the economic importance of pegmatites as sources of industrial minerals, strategic metals, and gemstones, as well as their association with different tectonic settings.

The crystallization of the majority of granitic pegmatites is widely acknowledged to occur in the presence of a viscous, volatile-rich polymerized silicate magma, concomitant with supercritical aqueous fluids. Consequently, granitic pegmatites can frequently be conceded as a hybrid rock derived through igneous and hydrothermal processes. Various criteria, such as the emplacement depth of granitic pegmatites, their association with metamorphism and granitic plutons, geochemical signatures, and their relationships with host rocks, have traditionally been employed for the classification of granitic pegmatites. However, none of the classifications has been accepted unequivocally.

Pegmatitic melt is often rich in chemical constituents (including volatiles) that are incompatible in common rock-forming minerals. In addition to rare earth elements, pegmatites are commonly enriched in rare elements such as Li, B, Be, Cs, and Ta. Because they are incompatible in common rock-forming minerals, these elements tend to create specific mineral phases that can host themselves. As a result, the concentration of trace elements such as Li, B, Cs, Ta, and Bi in these bodies are enriched to levels as high as a thousand times higher than the typical crustal abundance.

Granitic pegmatites encompass a diverse array of economic commodities, serving as repositories for industrial minerals and sources for strategic metals like Ta, Cs, Sn, Nb, Be, Sb, W, Co, and rare earth elements. Furthermore, they contribute as reservoirs of fluxing components, including Li, P, F, and B, while serving as sources of precious and semi-precious gemstones and some radioactive minerals. The global distribution of pegmatite ages suggests a linkage between the age of pegmatite formation and supercontinent assembly. The Li, Ce and Ta enriched (LCT) granitic pegmatites form part of the orogenic suites associated with crustal shortening in zones of subduction and instances of continental collision. The Nb, Y, and F-enriched (NYF) pegmatites are mainly interpreted as products of anorogenic suites and formed mainly in extensional settings.