Michael Berry:

"TGR: One thing on copper. It's around $3.46 or $3.50/pound (lb) right now. It appears to have solid support around $3/lb. Is that a profitable level for copper miners?

MB: It all depends. Is it oxide copper? Is it open pit? Is it underground? Are there by-products like molybdenum and gold? Is it a porphyry or a massive sulphide? What country is it in? Peru, Indonesia and some other countries right now are not very welcoming to copper miners. While $3.50/lb ought to work, it all depends on the grade and the factors mentioned above.

Normally, companies produce what we call a preliminary economic assessment that tries to do an early discounted cash flow with as much as we know about the deposit. "

The interview:

http://www.kitco.com/ind/GoldReport/20121122.html