Scapolite pegmatite from the Minas fault, Nova Scotia: tangible manifestation of Carboniferous, evaporite-derived hydrothermal fluids in the western Cobequid highlands?

Pegmatite cutting chlorite schist in the Minas fault at McKay Head, Nova Sc otia, consists of Cl-rich (2.7-3.8 wt.% Cl) marialitic scapolite (EqAn(21-3 2)) with interstitial, apparently primary analcite, hematite and rutile, an d later (including vug-lining) analcite, pyrite, chlorite, titanite and cal cite, and cross-cutting epidote veins. Some of the latter phases might have crystallized from residual pegmatitic fluids. Unlike many other primary sc apolite-bearing igneous rocks, the McKay Head occurrence has compositional affinities with mafic (rather than felsic) systems: it is enriched in trans ition metals (e.g. Cr less than or equal to 53 ppm), and has very low LILE concentrations (e.g. Rb<10 ppm; U<1 ppm; Th<2 ppm; Ba<20 ppm) and Rb/Sr rat ios (similar to 0.05). The presence of interstitial rutile and hematite rat her than ilmenite indicates that the pegmatitic fluid was oxygenated late ( T similar to 400 degrees C) in its crystallization history. The pegmatite is interpreted to be related to highly sodic hydrothermal sol utions derived from (or affected by) early Carboniferous evaporites of the Windsor or Horton groups. Compositionally-similar fluids, perhaps also rela ted to an evaporite source, may be responsible for a regional, early Carbon iferous Na-metasomatic event that altered a suite of alkaline granitoid int rusions shortly after their emplacement.