The approval was given by the MRAM’s Mineral Resources Profession Committee.
As part of the expansion, the mining capacity at the BNU will be increased to 1.5 million tons in 2015 and two million tons in 2016.
Guildford Coal managing director Peter Kane said: "MRAM’s approval to increase our mining capacity is a significant development for Guildford.
"It allows us to ramp up production at the BNU Mine beyond the recently announced targeted production figures for 2015, if it makes economic sense to do so."
Meanwhile, the company said that washing and laboratory testing of the second trial batch of coal from the BNU confirmed that the project’s coal can be washed to produce a low-ash premium quality hard coking coal with low sulphur.
The lab tests were carried out at Alfred H Knight and Bureau Veritas laboratories in Ulaanbaatar.
Further test work is being conducted at the China Coal Research Institute in Beijing.
