China's Coal Market

Alex turnbull is a fund manager based in singapore, and someone who has done quite a bit of research into china's coal market. He says the country does actually have a decent amount of coal within its borders, but it also imports a lot of its coal supplies. So i guess my question is, why do that happen? Why not just dig up what they have already? With any commodity which is reasonably low dollar value per ton, it's best to think of it as not a price where if you want to buy an ounce of gold from someone, its sufficiently high value,. They can mail it to you or export it quite easily. But with things that are relatively low