NERCHINSK MINING DISTRICT (29,45o sq.m.) includes all the silver, lead and tin mines and gold-fields between the Shilka and the Argun, together with a few on the left bank of the Shilka. It is traversed by several parallel chains of mountains which rise to 4,500 ft., and are intersected by a complicated system of deep, narrow valleys, densely wooded, with a few expansions along the larger rivers, where the inhabitants with difficulty raise some rye and wheat. The Nerchinsk mountains, not yet fully surveyed, form the watershed between the streams flowing south-east into the Argun and the Onon, Unda and Shilka on the north-west. They consist of crystalline slates and limestones interspersed with granite, syenite and diorite; they contain rich ores of silver, lead, tin and iron, while the diluvial and alluvial valley formations con tain auriferous sands ; asbestos is found near the tin.
The Nerchinsk silver mines began to be worked in 1704, but during the first half of the 18th century their yearly production did not exceed 8,400 oz., and the total amount for the first 15o
years (1704-1854) amounted to 11,540,000 ounces. Transport and climatic difficulties have prevented the exploitation of the minerals in the region and the silver mines were closed in 190o. If the present scheme of linking the mines to the main railway is carried out, production may redevelop. The more easily reached veins of silver have been exhausted and expensive plant would be needed to work the deeper veins. Gold was first discovered in 183o, and between 1833 and 1855 260,000 oz. of gold dust were obtained. In 1864 a large number of auriferous deposits were discovered. Until 1863 all the labour was performed by serfs and convicts, numbering usually nearly four thousand. The output of gold up to 1914 was about 171,000 oz. troy, but is very small at present (1928).