Bor-Under (previously in Russian it was called Bor-Undur, Mong. Bor-Ondor, “brown high”) is a city with the status of a somon in the south-west of Khentii aimag in the south of the territory of the Darkhan somon.
The name of the locality, after which the name of the city was given, goes back to the highest mountain of this region, Ikh-Bor-Under-Obo (Mong. Ikh Bor-Ondor ovoo, “big brown high obo”), about 1450 m above sea level and located in 2.5 km northwest of the Soviet settlement.

History
Fluorite deposits were explored by Soviet geologists in the 1950s, in 1973 the Soviet-Mongolian joint venture (now Mongolrostsvetmet) was established, as a result of massive assistance from the USSR, a mine, fluorite quarries and an enrichment enterprise were built. The first fluorite concentrate was obtained in the second half of December 1985. A railway line was built connecting the city with the Trans-Mongolian Mainline, through which all products were exported to the USSR. A city was built, which has a panel building traditional for the Soviet era. The status of the city was assigned to the village by a resolution of the Great People’s Khural (parliament) of the Mongolian People’s Republic on October 20, 1981. In the early 1990s, the city-forming enterprise and the city itself experienced a period of deep crisis. The company is currently operating normally.
The city is located on the border of semi-desert and dry steppe natural zones.

The city consists of several parts – a village left from Soviet times with a predominantly five-story brick and panel building traditional for the Soviet era, as well as yurt quarters located to the west and north-west of the city proper (consisting of Mong. Khashaa yards with wooden fences 2 m high and yurts and small residential houses located inside them). At a distance of 1 km to the north-east of the Soviet settlement there is an industrial site, on which there is an enrichment enterprise and a mine. There is a railway station 400 m southwest of the Soviet settlement, from which a branch line goes south to the Airag station on the Trans-Mongolian railway, and north goes to the industrial site.
Most of the administrative territory of the city (95 km²) belongs to the category of mining land, the territory the actual urban development is 30 km².

The population of the city declined after the departure of Soviet specialists in the early 1990s and the fall in the volume of extraction and enrichment of raw materials, in 1994 it was only 2695 people, but then, as production was restored, the population grew. According to the census in November 2010, the population of the city reached 9298 people. In subsequent years, there was a tendency for a slight decrease in the population of the city. This is the second largest city of the Khentii aimag (after the administrative center of the aimag, the city of Underkhaan with a population of 15 thousand people).

Education
There are 2 secondary schools in the city, in which in 2014 there were 1740 students. The system of preschool education includes 3 kindergartens, which were attended by 825 children in 2014.

Economy
The basis of the city’s economy is the extraction and enrichment of ore fluorites. In addition to fluorite mined in the vicinity of the city, the only enrichment enterprise in the country is supplied with raw materials from deposits in the Dornogovi aimag. The enterprise is owned by the joint venture Mongolrostsvetmet, which is owned by the governments of Russia (49%) and Mongolia (51%). All the concentrate obtained at the enterprise is exported by rail to Russia, Ukraine and other countries. In 2009, using Russian equipment and technologies, the mining and processing enterprise was modernized, which increased its productivity to 140 thousand tons of concentrate per year
The city receives electricity through a 110 kV high-voltage line from the city of Choir. The reconstruction of the mining and processing enterprise made it possible to reduce the unit costs of electricity by 25% and increase production in the face of limited energy resources.
In 2007, the number of livestock owned by the townspeople was 39,218 heads, but in the vicinity of the city there was not enough pasture capacity for such a number of livestock. In subsequent years, the growth of livestock continued, so in 2012 it amounted to 51 thousand heads, in 2013 already 62.1 thousand heads, and in 2014 – 74.5 thousand heads.