No drilling program, no matter how extensive, can guarantee a given deposit will live up to expectations. And since the capital costs of developing a property can run into billions of dollars, it is no surprise that mine operators strive to minimize their exposure to risk whenever possible. But one of the undesirable implications of the endeavour to decrease risk is a reluctance to use new and promising, but as yet unproven methods and technologies. It is all the more rewarding, then, when the bold and informed choice of such technology pays off, as it has in the case of Kupol, a gold-silver property now owned by Kinross Gold in Russia’s Far East.
Discovered in 1995, Kupol is located about 7,300 kilometres East of Moscow and about 200 kilometres Southeast of Bilibino, the nearest city. The project is marked by the harsh weather conditions characteristic in this very remote region; the annual average temperature is -13º Celsius, but that is positively balmy when compared to the lows of -58º Celsius that are often reached during the eight months of winter.
Still, the challenges and associated costs of running a mine in such a remote and unforgiving environment were compensated for by the high grade of the deposit. Today Kupol averages 14.95 grams per tonne of gold reserves and 180.4 grams per tonne in silver reserves.
The deposit’s promise captured the interest of Bema Gold, an intermediate gold producer based in Vancouver, BC. After purchasing a 75 per cent stake from the autonomous Chukotka regional government in 2002, Bema continued to develop the property, and had completed a feasibility study by May 2005. In July of 2005, the company became aware of a new technology being developed by CANMET, said John Rajala, Kupol’s mill manager at that time.
The technology, developed by gold researcher Guy Deschênes and his colleagues, was called CELP (CANMET Enhanced Leaching Process), and it promised to have a significant impact on Kupol’s operations.
The challenge presented at Kupol involved the high grade of the ore. The recovery of a significant proportion of the silver was going to require a great deal of cyanide, which the operators would then have to destroy. To address this, the original plant designs called for the incorporation of an acidification-volatilization-recycling (AVR) system, by which cyanide would be recovered and reintroduced into the leaching process.
At the time the plant was being designed, AVR was an established technology, however “There were only two such known operations in the entire world,” explained Rajala. “We visited one of them in Argentina.” But while AVR would noticeably decrease the project’s operational costs, it would also require an increased capital outlay, as the unit was expected to cost $5 million. “Today it would probably cost much more,” added Rajala.
To mitigate these costs, Deschênes and his team proposed making a chemical change to the leaching process itself. The plant design would remain largely unaffected, as would the operating costs and the gold extraction rate; however CELP would allow Kupol to cut its cyanide usage in half. In addition, silver extraction rates were expected to increase slightly.
The challenge, explained Deschênes, lay in the silver minerals present in the ore as sulphide and antimony compounds. These minerals are resistant to cyanidation, and slowed down silver extraction significantly. CELP was developed to facilitate the dissolution of silver in these compounds, allowing for faster and more efficient extraction of the metal.