In drift mining
, the height of working stalls - the tunnel the miners dig to get coal - is no bigger than the thickness of the coal seam.
Although cheaper, drift mining is often a more environmentally-intrusive way of removing coal from the ground than deep coal mining.
Rather than tunnelling down, drift mining is done by cutting into the side of the earth, with tunnels that can be accessed on foot.
The contract covers work at a new main level at the Kiruna mine in northern Sweden, and includes 21 kilometres of drift mining
, skip shafts, loading chutes, crushing chutes and pumping stations, as well as raise drilling of 25,000 metres of shafts.
Rising coal prices have renewed interest in drift mining
, where the seams are accessed by tunnels driven from hillsides rather than costly vertical shafts.