Dr. Peter Megaw, prominent Tucson exploration geologist, was interviewed by David Morgan in the February issue of The Morgan Report about silver mining. [right, Peter's field trip to Zacatecas Mexico silver mines as part of the AGS Ores & Orogenesis Symp., 10-1-07. Credit, Thomas McCrory]
One of Peter's answers seemed to catch the overall essence of his views: "long-term open-pit silver mining is a marginal to uneconomic enterprise for a number of reasons, historically, and the idea that if you simply mine enough you will ultimately get to the point where your grade trends cross the boundary from unprofitability to profitability is, in my estimation, a very risky proposition."
Peter points to Archie’s Rule as a practical guideline, which says that for a mine to be economic you have to be able to recover twice your "all-in" (mining, milling, smelting, refining, G&A, etc) operating costs at a minimum.