The Tanco Mine or Bernic Lake mine is an underground

caesium Caesium (IUPAC spelling; also spelled cesium in American English) is a chemical element; it has Symbol (chemistry), symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of , which makes it one of only f ...

and

tantalum Tantalum is a chemical element; it has Symbol (chemistry), symbol Ta and atomic number 73. It is named after Tantalus, a figure in Greek mythology. Tantalum is a very hard, ductility, ductile, lustre (mineralogy), lustrous, blue-gray transition ...

mine, owned and since 2019 owned and operated by Sinomine Resource Group on the north west shore of Bernic Lake,

Manitoba Manitoba is a Provinces and territories of Canada, province of Canada at the Centre of Canada, longitudinal centre of the country. It is Canada's Population of Canada by province and territory, fifth-most populous province, with a population ...

Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

. The mine has the largest known deposit of pollucite and is also the world's largest producer of

. The mine has the largest

reserves in

having estimated reserves of 2.1 million tonnes of ore grading 0.22%

. The mine also has additional reserves amounting to 7.3 million tonnes of ore grading 2.76%

lithium Lithium (from , , ) is a chemical element; it has chemical symbol, symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard temperature and pressure, standard conditions, it is the least dense metal and the ...

. The mine also produces

brine, which is converted into caesium formate which is used mostly as additive for drilling fluids to increase the fluid's

density Density (volumetric mass density or specific mass) is the ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be u ...

. A concentrated solution of caesium formate has a density of 2.3 g/cm³.

History

The pegmatite ore body now mined by the Tanco Mine was discovered in the late 1920s and the first mining started in 1929. Several times the mine was closed, reopened and closed, until in 1969 when it was reopened as a

mine. Cabot Corporation bought the mine in 1993, and began the production of caesium brine from pollucite in 1996. Tanco Mine was purchased by Sinomine in June 2019. Sinomine paid $135 million with an additional 10-year lithium royalty consideration. Tax impact was unexpected.

Geology

The pegmatite found at the north west shore and below the lake floor of Bernic Lake is a

granitic A granitoid is a broad term referring to a diverse group of coarse-grained igneous rocks that are widely distributed across the globe, covering a significant portion of the Earth's exposed surface and constituting a large part of the continental ...

igneous rock Igneous rock ( ), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rocks are formed through the cooling and solidification of magma or lava. The magma can be derived from partial ...

enriched in the incompatible elements, for example caesium, lithium, tantalum and beryllium. Pegmatite forms if

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma (sometimes colloquially but incorrectly referred to as ''lava'') is found beneath the surface of the Earth, and evidence of magmatism has also ...

tic rock slowly crystallizes, and the incompatible elements are concentrated in the residual molten magma. Examples of minerals found in the mine are the lithium-containing spodumene and amblygonite, caesium-containing pollucite, beryllium-containing

beryl Beryl ( ) is a mineral composed of beryllium aluminium Silicate minerals#Cyclosilicates, silicate with the chemical formula Be3Al2(SiO3)6. Well-known varieties of beryl include emerald and Aquamarine (gem), aquamarine. Naturally occurring Hex ...

and tantalum- and niobium-containing simpsonite and tantalite.

Deposit

The pollucite (chemical formula ) deposit associated with the pegmatite is the largest known deposit of this mineral and with 350,000 tons, it accounts for two thirds of the known resources. With an estimated average global use of 30,000 kg/year the reserves of the mine would last for 2,000 to 3,000 years. The mined pollucite contains approximately 24% . The ore body is 1400 m long, 600 m wide and 100 m deep. For several decades the pegmatites at Bernic Lake have supplied the world with the needed caesium.

History

Geology

Deposit

References

Further reading