Abstract

Metallographic studies of uraniferous occurrences in the Otish basin (Quebec) have shown that these mineralizations are characterized by the association albite–uranium (successively, brannerite–uraninite). This paragenesis corresponds to a sodium metasomatic event related to Hudsonian (1730 ± 30 Ma) gabbroic sills and dykes that intrude both Archean granitic basement and the overlying Aphebian detritic cover. The mineralization (1723 ± 3 Ma) is interpreted as a late Hudsonian event and is in many ways comparable to other occurrences in the Precambrian shields of Brazil, Scandinavia, and the Ukraine. A comparison of these different occurrences with the Otish mineralization has resulted in the recognition of several characteristics common to late-orogenic metallogenic events from mid-Proterozoic time in Canada and elsewhere up to late Hercynien in Europe. To explain specific assemblages of tellurides, selenides, and sulphides within a dolomitic gangue, one suggests that deep basinal Na-rich brines were mobilized to form mineralizing fluids during a regional tectono-magmatic event. The pitchblende–calcite association in the Otish basin corresponds to the latest mineralized event (306 Ma) caused by a remobilization of the primary Na–U metallogeny.

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