South Africa has the world's deepest gold mines and an earth tremor at one of Sibanye-Stillwater's mines killed seven miners in one incident alone in May.
Mitsui has said it will trim its thermal coal assets in the long term but would continue to invest in coking coal - a key raw material for steel-making.
Glencore expected to achieve annual cash savings of more than $300 million in its coal business by the end of 2018, but now it expects savings of more than $450 million by year-end.