Open pit and underground mining

Mining methods have been changing. In 1990, 55% of world production came from underground mines, but by 1999 this had shrunk dramatically to 33%.

From 2000 the new Canadian mines increased it again, and with Olympic Dam it is now back to one third (Table 6.1). In situ leach (ISL or ISR) mining has been steadily increasing its share of the total, mainly due to developments in Kazakhstan.

Where orebodies lie close to the surface, they are usually accessed by open cut mining, involving a large pit and the removal of much overburden (overlying rock) as well as a lot of other waste rock. Where orebodies are deeper, underground mining is usually employed, involving construction of access shafts and tunnels but with less waste rock removed and less environmental impact. In either case, grade control is usually achieved by measuring radioactivity as a surrogate for uranium concentration. (The radiometric device detects associated radioactive minerals, which are decay products of the uranium, rather than the uranium itself.)

At Ranger in north Australia, Rossing in Namibia, and most of Canada’s Northern Saskatchewan mines through to McClean Lake, the orebodies have been accessed by open cut mining. Other mines such as Olympic Dam in Australia, McArthur River, Rabbit Lake and Cigar Lake in Northern Saskatchewan, and Akouta in Niger are underground, up to 600 metres deep. At McClean Lake and probably Ranger, mining will be completed underground.