The announcement follows the release of revised year-end tonnage figures for the mine, which came into production in 2000. The new reserve figure is 845,000 tonnes grading 21.18% U3O8, compared with 668,000 tonnes grading 17.33% U3O8 at the end of 1999.
Underground drilling over the course of the year in the No. 3 and No. 4 zones account for much of the new tonnage, but re-interpretation of existing drill data for the No. 1 and No. 2 zones also contributed. The No. 2 zone is the only one being mined so far.
Zone 2 is being mined using remote-controlled raise-boring, with ore trucked to the Key Lake mill, 80 km to the south. Production in 2000 was just over 5,000 tonnes U3O8, and the mine is expected to produce around 6,800 tonnes in 2001. At full production, it should turn out just over 8,000 tonnes annually. Cameco owns 70% of McArthur and is the project operator. The remaining interest is held by
Production has been higher than estimated in the mine model, suggesting that the reserve grades have been understated. Cameco estimates grades in its McArthur River drill holes by down-hole radiometric probing, rather than by chemical assaying. The radiometric profiles are corrected for the effect of radon gas in the holes and converted into implied grades.
McArthur River is an unconformity-type uranium deposit hosted in Proterozoic-age Athabasca sandstone and in the underlying pelitic gneisses.
The mineralization is mainly held in a fault that cuts both rock types. This fault, named P2, strikes northeast and dips about 45 southeast, and separate mineralized zones occur over a length of 1,800 metres along the fault.
Grades can run as high as 70% U3O8 in individual samples and up to 30% U3O8 over core lengths of a few metres. These grades, which were originally determined in drill cores, have proved to hold up in underground mining.
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