RE: RE: gold
I'm no geologist but my understanding is that the so-called "porphyry" material that tends to make up low-grade gold deposits tends to be much cheaper to mine and mill per ton than the hard rock material that high grade gold deposits are made of.
However, I suspect that there is more or less a minimum amount of energy you need per ton to mine a deposit no matter what type of deposit it is, and that's why I suspect that low grade deposits have a lot more risk of being noneconomic if energy prices get very high, which I believe is likely to occur in coming years.
This is no doubt oversimplified, but it takes a certain amount of diesel fuel to transport ore in an ore truck no matter how much gold is in that ore.