The Usolie rock salt deposit (the eastern part) which is a part of the vast Angara-Lena river basin, covers the territory of the present-day river basins of the upper and middle current of the river Angara, heads of the rivers Lena and Nizhnyaya Tunguska.
In geological structure the Usolie deposit consists of lower cambrian, jurassic and quaternary deposits represented by Usolskaya, Belskaya Budayskaya and Angarskaya suites. Usolskaya suite is the main object of mining in CDPS Usolie and represents rock salt layers, the capacity of which ranges from 11,5 m. up to 84,8 m. The salt layers are located in Usolskaya suite in the interval of 880-1400 m.
The history of salt mining technology development in Usolie mine field covers more than three hundred years. Thus, in 1669 salt production mines were launched in Eastern Siberia by Onisim Mikhalev. Up to the end of the 17th century the salt-producing plant was run by a few different owners, it was owned either by merchants, or dukes, or a monastery.
The cost of the final product was in those years very high, the productivity of salt furnaces was extremely low. Brines had low salt concentration, about 9-12%. It was extracted from the first drill hole 190 meters deep. Until 1862 salt had been produced in 8 black furnaces located in chaotic order, unless the workers’ labor was considered by the chief of the plant Tarasov as harmful and “unfavorable for health”.
The way to improvement of expensive and difficult technologies of evaporated salt production was very long and thorny. Specialists went on duty trips to Eastern Siberia, to the Usolie deposit in order “to establish more optimal ways of salt production”. Thus, in 1875 in order to investigate the state of affairs in the Usolie salt production plant the Finance Ministry sends the mining engineer L. Pershke who gave numerous efficient suggestions for technology improvement. It was him who expressed the idea of brine concentration to the full degree in coolers, which was brought into operation in 1910. As a result the salt concentration there reached 15-18%.
The first drill hole which gave rich brine was drilled in 1924, its depth was 692 meters. However, even it broke only the upper salt layer.
At present brine production is conducted in the eastern part of Usolie field, which is situated on the left bank of the Angara River, close to the town Usolie-Sibirskoe, the Irkutsk region, bordering on the town from the North West.
At present the deposits of the field are equal to more than 4 billion tons of salt, it is one of the largest in the country.