Granitic pegmatites

This review focusses on P-T conditions, mineralogical indicators of melt or fluid composition, and textural evolution. Studies of stable and radiogenic isotopes have revealed that the source materials for pegmatites are likely to have been more heterogeneous or varied than previously thought, especially for peraluminous pegmatites, but that pegmatites overall bear a clear intrusive relationship with their hosts, as opposed to an origin in situ. The P-T conditions of crystallization of some Li-rich pegmatites have been constrained by Li aluminosilicate stability relations in combination with stable isotope or fluid inclusion techniques. Experimental work has elucidated the effects of such components as Li, B, P and F on liquidus relations in the haplogranite system, and has provided corroboration that pegmatites owe their distinctive textures and mineral/chemical zonation to relatively rapid crystallization of melt from the margins inwards in conditions far from equilibrium. Studies of fluid inclusions, crystal-vapour equilibria and wallrock alteration have helped to define the timing and compositions of vapour phases in pegmatites and to aid in the economic evaluation of deposits.