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Opaque mineralogy of a representative cross-section of deformed and metamorphosed turbiditic slate and metasandstone of the Meguma Group has been investigated optically and by electron microprobe. A strong stratigraphic control over the presence and abundance of certain opaque minerals is recognized, which may prove useful for environmental evaluation such as acid drainage potential. Abundant pyrite and pyrrhotite in the lower Halifax Formation reflect concentration of early diagenetic pyrite resulting from the reduction of seawater sulphate under anoxic conditions. Magnetite is restricted to the Goldenville Formation. Dmcnitc and rutile occur throughout the succession, and minor chalcopyrite, arsenopyrite, covellite, hematite and glaucodot were also noted.  Pyrrhotite and ilmenitc, as well as spcssartine, chlorite and chloritoid porphyroblasts, developed during pro-grade metamorphism before and/or during cleavage formation, which also resulted in removal of early diagenetic pyrite. Later pyrite formed by replacement or immobilization of pyrrhotite during retrograde metamorphism. Colloform pyrite, arsenopyrite and chalcopyrite are the youngest mineral phases.   R&3xC9;SUME  On a etudie la structure meniralogique opaque d'un echantillon representatif de metagres et d'ardoisc turbiditique deformes et melamorphises du groupe de Meguma, optiquement ainsi qu'e l'aide d'une microsonde electronique. On a ainsi reconnu un contrdle stratigraphique prononce sur la presence et l'abondance de certains mineraux opaques, ce qui pourrait s'averer utile pour une evaluation environnementale, comme celle du potentiel de drainage acide. Les quantites abondantes de pyrite et de pyrrhotine dans la partie inferieure de la Formation d'Halifax temoignent d'une concentration de pyrite diagcenetique precoce provenant de la reduction du sulfate d'eau salie dans des conditions anoxiques. La magnetite se limite a la Formation de Goldenville. On releve la presence d'ilmenite et de rutile partout dans la succession, en plus de petites quantites de chalcopyrite, d'arsenopyrite, de covellite, d'hematitc et de glaucodot.  La pyrrhotine et l'ilmenite, tout comme la spcssartine, la chlorite et les porphyroblastes chloritoldes, sont apparus au cours d'un metamorphisme progradc avant ou pendant la formation du clivage, qui a provoque en plus un retrait de la pyrite diagenetique precoce. La pyrite ulterieure s'est formic par remplacement ou remobilisation de la pyrrhotine au cours d'un retrometamorphisme. La pyrite colloforme, l'arsenopyrite et la chalcopyrite representent les phases minerales les plus recentes.  [Traduit par la redaction]

The opaque mineralogy of metasedimentary rocks of the Meguma Group, Beaverbank-Rawdon area, Nova Scotia