The physical and chemical evolution of fluids in rare-element granitic pegmatites associated with the Lacorne pluton, Quebec, Canada.

Co-magmatic rare-element (Be, Li, Nb, Ta) granitic pegmatites associated with the Lacorne monzogranite pluton of the Preissac-Lacorne batholith (Québec) range from a least evolved beryl-type in the pluton through a transitional beryl + spodumene-type to a most evolved spodumene-type in mafic country rocks. They possess internal lithologic fabrics and primary fluid inclusions that provide evidence for saturation of the magma with aqueous fluids immediately after the formation of aplite in the beryl pegmatite, and pene-contemporaneously with formation of the beryl + spodumene and spodumene pegmatites. [...] The results of this study show that aqueous fluid saturation can take place at an early stage of pegmatite emplacement, and that magma evolution is matched by changes in the solute chemistry of the exsolving aqueous fluid. They also show that evolution to a more volatile-rich composition (H2O + F + Li) may have contributed to the increased mobility of later magma batches, thereby helping to explain the regional zonation of the pegmatites, from beryl-type within the pluton to spodumene-type in the adjacent amphibolite