Indonesia is set to consolidate its coal mining sector after reviewing local mines, which are not certified as clean and clear.

Said to be applicable only to the IUPs, the review excludes larger and older-generation firms with so-called contracts of work, Reuters reported.

At the 21st Coaltrans Asia conference in Bali, Indonesia, Mining and Energy Minister Sudirman said the country plans to withdraw licenses of more than 4,000 that have not met certain standards.

Sudirman told Platts: "There are more than 10,000 mines, which are IUPs or Izin Usaha Pertambangan [producers who are not directly under the government], and nearly 40% of them do not have clean and clear certification."

"There are more than 10,000 mines and nearly 40% of them do not have clean and clear certification."

Indonesia exports an estimated $2bn of coal monthly and intends to gain more revenue from the mining sector.

Indonesian Coal Mining Association chairman Pandu Sjahrir did not mention any timeframe for the consolidation process.

According to Sudirman, around 6,000 of the newer mining licenses from the total 10,100 issued had been certified as complying with government rules.

The minister added that there are currently 960 coal firms at production stage.

Said to be IUP permit holders, around 900 of them contribute approximately 80 million tonnes.

The investment coordinating board (BKPM) will take over the licencing from the ministry in 2015.