Abstract

Pegmatite cutting chlorite schist in the Minas fault at McKay Head, Nova Scotia, consists of Cl-rich (2.7-3.8 wt.% Cl) marialitic scapolite (EqAn (sub 21-32) ) with interstitial, apparently primary analcite, hematite and rutile, and later (including vug-lining) analcite, pyrite, chlorite, titanite and calcite, and cross-cutting epidote veins. Some of the latter phases might have crystallized from residual pegmatitic fluids. Unlike many other primary scapolite-bearing igneous rocks, the McKay Head occurrence has compositional affinities with mafic (rather than felsic) systems: it is enriched in transition metals (e.g. Cr<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 ratios ( approximately 0.05). The presence of interstitial rutile and hematite rather than ilmenite indicates that the pegmatitic fluid was oxygenated late (T approximately 400 degrees C) in its crystallization history. The pegmatite is interpreted to be related to highly sodic hydrothermal solutions derived from (or affected by) early Carboniferous evaporites of the Windsor or Horton groups. Compositionally-similar fluids, perhaps also related to an evaporite source, may be responsible for a regional, early Carboniferous Na-metasomatic event that altered a suite of alkaline granitoid intrusions shortly after their emplacement.

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