posted on Oct 04, 10 09:05AM
I'm looking at a projected cost/revenue summary from last summer. Total costs, all in, are projected at $42/tonne, and that's right through to dore bars. Costs might well be higher (I don't know the "cushion factor" built into the budget), because of the diesel generator and inflation and all that, but the Canadian dollar exchange rate has improved since then, also.
The yields are not as high as you used, tmw, because this is not raw ore being processed. The tailings have been chemically changed by the earlier process work, and that adverse chemistry may also be enhanced by weathering that has occurred over the last century. There's an oxide layer on each tailings particle that inhibits exposure to the cyanide leach solution. The reason for the addition of the larger ball mill is to hopefully mechanically remove enough of the oxide layer to enhance recoveries/yield.
A number of bench-scale laboratory tests were run at a big mining consulting lab in the U.S., each with different process chemistry (different cyanide concentrations, solution pH, additives, etc.), and the worst case of all of the reported yields was used for the financial projections for the project. As the worst case was believed to be profitable, the project went ahead. Those worst case recoveries were 58% of the gold, and 35% of the silver. There is every reason to believe that those recoveries can be substantially improved upon, and that is where the art of running a mill comes into play. Jim's mill manager has 35 years experience running Merrill-Crowe mills. The fine-tuning process never ends.
Using these worst case recoveries, at 220 tonnes/day throughput, the ballpark yield would be 7 oz/day gold, and 500 oz/day silver. Inflating the cost/tonne processed to $50/tonne, you get costs at $11,000/day. Using $1200 gold and $20 silver, revenues would be $18,400. That's over $2million/year profit, with very conservative assumptions, IMHO.
Lar
