I did some time ago a benchmarking study on 12 Canadian gold...

I did some time ago a benchmarking study on 12 Canadian gold mines, which dominantly employ Longhole Open Stoping with some also using Cut and Fill mining. The relationship between opex and capex versus mining width is striking. Unfortunately the operating performance information does not provide average width mined, but annual treatment rate is strongly related to mining width as productivity increases with such width. Treatment rate can be seen as a proxy for mining width. The mines in the sample extracted ore from very narrow veins (e.g. Harte, Macassa) to locally very wide at tens of metres (e.g. Seabee, Young-Davidson, Meliadine).

Anyway, see below the relationship between Opex (blue) and Capex (red) with production rate. These are total operating cost including processing and G&A. Processing cost will be all in the same ball park for these mines, G&A highly determined by economies of scale and the balance for mining cost. Capex is predominanty underground development to open up new stopes.

Cost Rates as a Function of Annual Treatment Rate Given the above, the suggested cost rates for Antler seem optimistic, in particular as it will have to employ Cut and Fill for the narrower sections of the shoots. The scoping studies also totally ignore the need for delineation drilling underground to plan the stope outlines. I also am of the opinion that using Longhole Open stoping for such a high grade deposit leading to dilution of 45% of the grade is stupid. Rather use the less productive, more expensive Cut and Fill method that allows dilution to be reduced to 10-15%. The additional cost is easily made up by improved grade. I also looked into costs forecast in the economic assessments and actual cost achieved. It confirmed how the "independent" consultants always err on the positive. The graph below shows that, on average, actual cost exceed forecast by 29%. When the three outliers below the regression line are ignored as being not representative (Westwood closing down and capex cut to the bone, Red Lake having been taken over by a new operator cutting cost), then the actual (opex + capex) is on average 88% above forecast. Ouch.