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.
In order to continue mining, the hydaulic operations either shut down or changed to the drift mining method.
Drift mining in California was extensive in the latter part of the 19th century, and first part of the 20th century.
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.
Budge now had a track record in opencast and drift mining
but if it was to convince investors that it was a serious bidder for British Coal it still needed to demonstrate the ability to operate deep mines, Further successful parliamentary lobbying eventually convinced the government to let private operators bid for those collieries British Coal had already placed on a care-and-maintenance basis.
Rising coal prices have renewed interest in drift mining
, where the seams are accessed by tunnels driven from hillsides rather than costly vertical shafts.