RE:Conservative or Not...
If Selby puts out an NPV even approximating 7-8B then I believe that CNC should double or triple overnight.
Assuming an AISC of $3.1/lb seems rather optimistic, as opposed to conservative. Sub-3 seems impossible, without substantial metallurgical work to determine the potential for and quantify the amount of byproduct opex credits.
Your capex number seems reasonable, I think, but wouldn't be shocked if it came in +/- 20% in either direction.
GL. I recognize I'm a contrarian here but do believe that CNC is probably a good position to hold for the long run.