Cyanidation of a pyrrhotite-bearing gold ore

G. Deschênes1*, D. Hall2 and M. Fulton1

1Mining and Mineral Sciences Laboratories, CANMET, Natural Resources Canada, 555 Booth Street, Ottawa, Ontario, Canada, K1A 0G1
2Placer Dome Canada, Musselwhite Mine, P.O. Box 7500,Thunder Bay, Ontario, Canada, P7B 6S8

Received 30 July 2002; accepted 21 November 2003


The Musselwhite Mine in Canada processes a free milling gold ore at 5.5-5.8g/t Au and 4.2% pyrrhotite. A laboratory investigation was conducted to improve cyanidation. The pyrrhotite was determined to be 50% monoclinic and 50% hexagonal. A leach using 8ppm dissolved oxygen yielded only 82.3% gold extraction with a 0.29kg/t NaCN consumed. The addition of lead nitrate, directly to the leach, showed 94.2% gold extraction with only 0.16kg/t NaCN consumption. A gold extraction of 95.0% was obtained by adding oxygen with lead nitrate. The laboratory results were found to be similar to current plant practice. Plant data indicated that the enhancement of leaching kinetics has resulted in a 0.61% increase of gold recovery, from 95.20% in 1999 to 95.81% in 2000. Benefits of the oxygen system were more pronounced in the hot summer months when higher slurry temperatures depleted dissolved oxygen content and pyrrhotite is more reactive. Other modifications include the installation of cone spargers. The results of July 2000 versus those of July 1999 displayed a 2.0% improvement in recovery with the use of oxygen (i.e. a reduction of 0.08g/t Au in the leach residue). In 2000, the improvement of gold recovery represented an additional gross revenue of $CDN0.5 Million (€0.304 Million). Cyanide consumption decreased slightly by approximately 8%.

Keywords: Gold; Cyanide; Leaching; Lead nitrate

* Corresponding author
   E-mail : gdeschen@nrcan.gc.ca