ABSTRACT
The mineralogy and boron content of the shales from the Melville Island Group (Middle-Upper Devonian) and the Imperial Formation (Upper Devonian), Northwest Territories have been determined. Quartz is the dominant mineral (50 to 70 per cent), whereas plagioclase (5 to 10 per cent) and potash feldspar (0 to 10 per cent) are common. Calcite, dolomite and gypsum are common only in the Cape Phillips Formation. Pyrite, goethite, hematite and siderite are detected occasionally in small amounts. Kaolinite (1Md) is the dominant clay mineral (15 to 25 per cent). Illite (1Md) averages 5 to 10 per cent and chlorite (trioctahedral) is present in minor amounts (1 to 2 per cent).
The depositional environment was evaluated by means of degraded illite and the boron content of the strata. The Imperial Formation is marine. The Cape de Bray Member and lower portions of the Weatherall Formation are marine, but this formation grades upward into a deltaic sequence. The Hecla Bay and Griper Bay Formations are largely deltaic with interbeds of marine and nonmarine strata. Several marine transgressions can be recognized in the Griper Bay Formation.
The source rock of the Melville Island Group is possibly largely granite and/or gneiss except for the presence of some possible volcanics in the Griper Bay Formation.
