"the opinions and anlysis in no way address the effect of falling energy prices on the cost of production."

Concur, but I might add that this is most likely due to the fact that nobody in the know expects oil prices to remain this low. I fully expect that the refiners are locking in many barrels at current prices and expecting to refine them into $3+ gasoline to sell in Q2 and beyond of 2015, just as they did between 2009 and 2010.

The time scale of mine development makes it unlikely that such a dip in energy costs will have much effect on the long-term feasibility of a proposed mine. Unless real trends indicating a sustained depression of petroleum prices emerge, developers must assume that oil prices will rebound, especially when domestic producers start to roll back output to reflect lower demand and subsequent prices.