"To start mining today you have to look at the commodity prices 3-4 years from now."
What? Where do you come from! No one can look forward to what prices will be 3-4 years from now for such a decision. Forecasted income can only look from present values.
What happens is, preliminary economic assessments, and feasibilities studies look at a discount to present metals prices for development decisions, and they use a discount in case prices fall from present values On that basis, and that basis alone do they put a shovel in the ground.
Forecasted prices would lead to all manner of corruption, no?
Geez!