There are a lot of myths about KSM, spread by professional bashers, so it might be interesting to gather some basic information about porphyries.
According to the United States Geological Survey database of worldwide porphyry deposits, the 2008 median grade of 422 porphyry deposits was 0.44% copper Only 2/3 of these deposits contained gold and their avarage gold grade was0.21 g/t Gold. For comparison, 0.44% Cu and 0.21 g Gold are worth some 45$ these days, whereas KSMs reserves show a value of 49$. So there is evidence, that KSM, although being one of the largest porphyries ever found, has above average grades, regardless the eternal bashers claiming it to be low grade.
For further information, please google for the paper called
"Characteristics of Porphyry Copper Deposits", published by solgold.
Especially the chapters about exploration and mining options are an extreme good read that put the bashers arguments (too deep) in the right perspective.
Mitchell has something about 0,16% Copper, very poor grades. And as far as I now it is a fact that the gold recovery is poor (about 50-60% under laboratory conditions). The "resources" are calulated with a 70% recovery.
I guess at the moment the market is either not confident that the copper and gold prices stay at least at the current levels or expects production and capex costs to rise together with POG.
But if you look at the larger deposits found in the last decade, they all share high capex, the easy deposits are already found.
A Codelco spokesman said, that they needed at least a copper price of 2.80 for bringing new projects in production.
That means the following:
A lot of big copper and gold mines will be depleted during the next decade. If the market wants this supply to be substituted, he has to pay the price for making the new deposits economic.
There is nothing out there but KSM, Cerro Casale, Galore Creek, Donlin Creek that would substitute a big depleted mine.