Mongolia’s coal export s grew more than fourfold in the first half of 2017, with the country benefiting from China’s ban on imports of the commodity from North Korea and curbs on deliveries into smaller ports.

Coal made up around half the country’s total export trade over the period, figures from Mongolia’s National Statistics Office showed on Monday.

China’s ban on coal from North Korea, as well as the restrictions on deliveries into smaller ports, has helped boost Mongolia’s total earnings from coal to $1.28 billion over the first half.

Minerals comprised 82 percent of all exports during the period, as overall export volumes jumped 41.7 percent from the same period in 2016 to a total value of $3.1 billion.

China has been forced to seek alternative sources of coal after banning imports from North Korea as part of a tougher sanctions regime imposed as punishment for its nuclear missile tests.