NEVADA – Toronto-based Barrick Gold is the first producer to commercialize thiosulphate recovery of gold, thus eliminating the use of cyanide in the process. The first doré bar – 107 oz – was poured in November 2014 at the Goldstrike mine north of Carlin.
Barrick spent more than 20 years perfecting its thiosulphate process. As the Goldstrike project matured, a larger portion of the ore recovered was carbonaceous. The problem with carbonaceous ore is that it does not lend itself to cyanide recovery. One way to treat it would have been roasting. Instead, the company launched its TCM (total carbonaceous matter) project.
To implement the TCM project took an investment of US$620 million. Major upgrades were made to the leaching circuits at the Goldstrike mill. Plus there was the construction of a thiosulphate plant to manufacture the chemical on site. A new water treatment plant was built to recycle large volumes of thiosulphate to reduce operating costs.
Ore is crushed, ground and autoclaved as before, but the C-I-L circuit has been replaced with one using thiosulphate. The gold in the leached slurry is liberated in a series of seven tanks containing thiosulphate and resin. The process uses calcium thiosulphate, a fertilizer, because it is the most environmentally friendly of the alternate types.
Installation of a section seven-tank thiosulphate circuit, will double throughput to 12,150 t/d.
Click here to read in more detail about the new process in the May 2015 issue of Barrick’s magazine, Beyond Borders.