Large gold deposits are becoming increasingly scarce, grades are declining in known reserves, and deposits are becoming increasingly complex to treat.
The race is on. The industry needs to discover more economically viable means of extracting gold from refractory, low-grade ores and thereby increase reserves.
Since 2012, there have been less than ten major gold deposits discovered globally. Looking at the five years prior to 2012, the number of major discoveries was nearly four times as high. In addition, close to one fifth of the global gold production involves refractory ores. While not all new discoveries are refractory, this indicates that it is becoming increasingly harder to find economically viable large gold deposits.
A need for technologies to treat smaller deposits Industry data show that the amount of gold contained in refractory measured and indicated (M&I) resources is approximately double the amount of contained gold in economically viable refractory gold reserves. The only reason that refractory M&I resources are not considered a "reserve" is that they do not meet cut-off grade for economic extraction.
“Lower processing costs reduce the cut-off grade, allowing more ounces to be processed economically. The only difference between a resource and a proven and probable reserve is that the former is uneconomic and no amount of additional drilling will ever make it economic,” says Peter Flanagan, FLSmidth SVP Executive Accounts.
It is capital intensive to process refractory gold ores with current technologies. Hence, the industry faces challenges with developing new efficient technologies to treat smaller deposits. The aim is to reduce processing cost to convert more resources to economically mineable reserves.
"There are a lot of undeveloped refractory gold deposits that have less than 3 g/t gold head grade, and some are coupled with small resources which translates into short mine lives. Currently, those assets have little to no value as greenfield deposits and need a steep change in technology to unlock value," says Flanagan.
Process low-grade stockpiles earlier for pre-treating refractory gold, the main objective is to oxidise the pyrite and arsenopyrite to liberate gold. Initially, the target is refractory gold-bearing iron sulphides where currently pre-treatment is the only solution to recover sulphide mineral matrix, locked inside the gold. To this end, FLSmidth has developed Rapid Oxidative Leach (ROL), a mechano-chemical pre-treatment process for refractory gold ores.
"When we have proven this technology successful, miners will be looking at a completely different life-of-mine plan; by lowering the cut-off grade, more ore will be converted into reserves, extending mine life." Flanagan explains.
FLSmidth’s ROL pre-treatment process is not merely applicable to new gold deposits. According to Peter Flanagan, there could be significant benefits to existing operations as well. "Many existing refractory operations have low-grade stockpiles that are waiting to be processed at the end of the mine life. By adding ROL pre-treatment to an existing operation, it could become viable to process low-grade stockpiles earlier, rather than processing them at the end of the mine life. Reducing the cut-off grade, you can move those ounces forward to generate cash flow earlier and this will increase the asset’s net present value," says Flanagan.
The ROL pre-treatment process technology can be a breakthrough for the gold industry, displacing current refractory processing methods and prolonging mine lifespans.