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

Published online by Cambridge University Press:  05 July 2018

J. V. Owen  and
J. D. Greenough
J. V. Owen
Affiliation:
Department of Geology, Saint Mary's University, Halifax, N.S. Canada B3H 3C3
J. D. Greenough
Affiliation:
Department of Geological Sciences, Okanagan University College, 3333 College Way, Kelowna, B.C., Canada V1V 1V7
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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 (EqAn21–32) 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 (~0.05). The presence of interstitial rutile and hematite rather than ilmenite indicates that the pegmatitic fluid was oxygenated late (T~400°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.

Keywords

scapolitepegmatiteevaporitesMinas faultNova Scotia
Type
Research Article
Information
Mineralogical Magazine , Volume 63 , Issue 3 , June 1999 , pp. 387 - 397
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1999

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