Metamorphism of arsenopyrite-pyrite-sphalerite-pyrrhotite lenses, western Cape Breton Island, Nova Scotia

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Authors:Lynch, Gregory; Mengel, Flemming
Author Affiliations:Primary:
Geological Survey of Canada, Quebec Geoscience Centre, Sainte-Foy, QC, Canada
Other:
Geologisk Museum, Denmark
Volume Title:Canadian Mineralogist
Source:The Canadian Mineralogist, Vol.33(Part 1), p.105-114. Publisher: Mineralogical Association of Canada, Ottawa, ON, Canada. ISSN: 0008-4476
Publication Date:1995
Note:In English with French summary. Geol. Surv. Can. Contrib. No. 20592. 34 refs.; illus., incl. 1 plate, 2 tables, geol. sketch maps
Summary:Polymetallic sulfide lenses occur in Ordovician-Silurian sequences of clastic and volcanic rocks of the western Cape Breton Highlands, Nova Scotia. The rocks have been affected by thrusting and metamorphism during late Silurian to Devonian Acadian deformation. The sulfides occur as highly sheared and recrystallized lenses concordant to bedding. Mineral compositions of equilibrium sphalerite - arsenopyrite - pyrrhotite - pyrite intergrowths provide a sliding-scale indicator of P-T-f(S2) variations during metamorphism. The arsenopyrite contains between 33 to 29 atom % As, a range reflecting recrystallization within a changing thermal regime, at temperatures between 510° and 300°C. Pyrrhotite with up to 47.3 atom % Fe is recorded; however, most of the pyrrhotite is relatively sulfur-rich, likely owing to low-temperature inversion or partial oxidation. The dominant composition of sphalerite, between 13-14 mol % FeS, indicates intermediate-to high-pressure conditions. Pressure estimates of 5.5 to 6.9 kilobars are consistent with upper-greenschist metamorphic assemblages found in the surrounding rocks. Decreasing fugacity of sulfur accompanied retrogression in the sulfide lenses as a consequence of the buffering capacity of the coexisting pyrite and pyrrhotite.
Subjects:Arsenides; Arsenopyrite; Cambrian; Crystal growth; Electron probe data; Geologic barometry; Geologic thermometry; Intergrowths; Lenses; Metamorphism; Microstructure; Mineral composition; P-T conditions; Paleozoic; Pyrite; Pyrrhotite; Recrystallization; Retrograde metamorphism; Shear; Sphalerite; Sulfides; Canada; Cape Breton Highlands; Cape Breton Island; Eastern Canada; Inverness County Nova Scotia; Maritime Provinces; Nova Scotia; Cheticamp Granite; Core Shack; Fisset Brook Nova Scotia; Galena Mine
Coordinates:N463000 N464000 W0605000 W0610000
Abstract Numbers:95M/4695
Record ID:1999051548
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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