Even if the silver is a relatively small percentage of the total value, if it is used as an offset to the cost of mining the copper, it might make the difference between the negative costs to mine per ton staying about the same vs. being less negative or, possibly causing the cost to mine per ton to be even more negative. This would result in a large difference in perception of the feasability study.

it is possible that they held back on the silver for this very reason, but I kind of doubt it. If they did, they are more clever than I had thought.

Rip