RARE-EARTH ELEMENTS IN FLUORAPATITE, SEPARATION LAKE AREA, ONTARIO - EVIDENCE FOR S-TYPE GRANITE - RARE-ELEMENT PEGMATITE LINKAGE

Fluorapatite is an important accessory and, locally, a major mineral i n some extremely evolved, rare-element (Li, Rb, Cs, Be, Nb and Ta) peg matites of the Separation Lake greenstone belt and the spatially assoc iated S-type peraluminous granites of the Treelined Lake complex in th e Umfreville - Conifer Lake granulite zone of the English River Subpro vince, Ontario. The REE characteristics of fluorapatite in geochemical ly primitive pegmatites within the Treelined Lake complex are consiste nt with partitioning of REE with granitic melts that were derived from crustal sources. The chondrite-normalized REE patterns of fluorapatit e in both primary and replacement units (mainly albite-mica pods) of t he Separation Rapids rare-element pegmatites are characterized by mark ed discontinuities at Nd and Er. These unusual REE characteristics in fluorapatite have been modelled based on a granitic source (i.e., the Treelined Lake complex) and the discontinuities at Nd and Er related t o fractionation of monazite and garnet, respectively. Fluorapatite in the sodic wall-zones of the Separation Rapids rare-element pegmatites contains low abundances of REE and is characterized by chondrite-norma lized REE patterns similar to those of the host amphibolites, supporti ng an infiltration of fluid from country rocks during the formation of pegmatites. The occurrence of fluorapatite with similar REE character istics, including discontinuities at Nd and Er, in a miarolitic cavity within the Treelined Lake complex supports a genetic link between the Separation Rapids rare-element pegmatites and the S-type peraluminous granites associated with the granulite-facies metamorphism in the Eng lish River Subprovince.