We compare compositional data from a suite of Recent glassy lavas, melt inclusions, and comagmatic syenitic xenoliths from Pico Alto volcano, on Terceira Island, Azores, with the compositions of fresh and hydrothermally altered facies of the Strange Lake rare-metal granite (Quebec-Labrador). Trace-element modeling shows that magmatic enrichment in a pantelleritic magma at Pico Alto can generate HFSE abundances like those observed in early intrusive stages at Strange Lake. Compositional changes accompanying complete crystallization and separation of orthomagmatic fluid from pantellerite magma at Pico Alto mirror the enriched component in HFSE-mineralized granite at Strange Lake. We conclude that HFSE ores can be generated by processes of magmatic enrichment followed by separation of a HFSE-charged orthomagmatic fluid upon final solidification of the silicate melt, and redeposition of these elements in the roof zone of the pluton.

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Canadian Mineralogist
Department of Earth Sciences

Mungall, J.E, & Martin, R.F. (Robert F.). (1996). Extreme differentiation of peralkaline rhyolite, terceira, azores: A modern analogue of Strange Lake, Labrador?. Canadian Mineralogist, 34(4), 769–777.