MODE OF OCCURRENCE, CHEMICAL VARIATION AND GENESIS OF MORDENITE AND ASSOCIATED ZEOLITES FROM THE MORDEN AREA, NOVA SCOTIA, CANADA

Abstract

Selected zoned and homogeneous amygdales and veins of zeolite from the earliest Jurassic North Mountain Basalt, in Nova Scotia, have been examined in thin section and by SEM, XRD and electron-microprobe analysis. Zoned sequences of zeolites in amygdales and veins in the North Mountain basalt show a succession of clinoptilolite-Na → mordenite → heulandite, clinoptilolite-Ca, or epistilbite → stilbite, barrerite, or stellerite, and are interpreted as developing under falling temperatures. Locally, fractures within zeolites have been filled with smectite and at least three different Mg–Fe–Na-aluminosilicates. Barite, Cu, Ni and Au precipitates occur throughout some zoned amygdales. The high temperatures required for the precipitation of labradorite and mordenite, the repetitive zonation in some amygdales, and the occurrence of metal precipitates all suggest an origin for the zeolites by active hydrothermal circulation, not by burial metamorphism as implied by previous authors. Formation of mordenite was favored by hydrothermal circulation of alkaline lake waters and extraction of Na from underlying evaporites of the Blomidon Formation.