Cyanidation of a pyrrhotite-bearing gold ore
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