BERNIC LAKE (RU: Берник-Лейк) is the deposit of the rare metal pegmatites within Canada, which is unique in composition; it contains the ores of tantalum, cesium, and lithium. It has been discovered during the start of the 20th century; till the 1930, it was being developed for cassiterite (it is also known under the Mongari and Tanco names). During the 1929-61, it was studied (operated since the 1958) as the deposit of the complex lithium-cesium-beryllium ores. During the 1966, there has been determined the high content of tantalum. It is represented by the series of the pegmatitic bodies, which are embedded within the amphibolitized diabases and andesites of the Late Archean. The main body has the ellipsoidal shape (Figure), submerges northward in slightly inclined manner under the level of the lake Bernic.
The pegmatites are plagioclase-microcline, with the complex of the tantalum, cesium, lithium, and beryllium minerals. The association of the tantalum minerals includes the tin-containing tantalite (wodginite), tapiolite, microlite, and pseudo-ixiolite; the minerals of lithium are represented by spodumene, lepidolite, amblygonite, and petalite; cesium concentrates itself within pollucite; there may be also found beryl, cassiterite, columbite, molybdenite, and so on. The reserves are: 0.9-1.3 million tonnes of the tantalum ores, with the content 0.15-0.22% of the Ta2O5; 5.1 million tonnes of the lithium ores (5 million tonnes within spodumene, with the content 2.2% of the Li2O, and 107.7 thousand tonnes within lepidolite, with the content 2.24% of the Li2O); 0.9-1.0 million tonnes of the beryllium ores, with the content 0.22% of the BeO. The total reserves of pollucite are 450 thousand tonnes (90 thousand tonnes of the Cs2O), the content of rubidium within pollucite and lepidolite is 1800 tonnes (1976).
Since the 1969, the deposit is being developed by the underground method (the depth is up to 200 metres) by the "Tantalum Mining Corporation of Canada Ltd." ("Tanco"); it includes the tantalum mining-beneficiation combined enterprise and the beneficiation plant for the processing of the spodumene ores. The extraction of the ore is 180 thousand tonnes (1979). There is included the processing of the ores with small-crystalline tantalite, and also the obtainment of the lithium, cesium, and beryllium concentrates. The extraction of tantalum from the ores is 80%. The tantalum concentrate contains 50-52% of the Ta2O5, 3.5% of the Nb2O5, and 9% of the SnO2. The production of the Ta2O5 is 275 tonnes in the form of concentrate. The productive capacity of the beneficiation plant for the processing of spodumene is 910 tonnes of the ore per day.
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