Un exemple de métasomatisme alcalin albite–uranium dans le bassin des Monts Otish, Québec

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.