As a rule of thumb, fully allocated cost per tonne (which includes depreciation and depletion allowances) is about 2x the cash cost, which is why I said in a prior post that $50 was a reasonable estimate. VALE itself mentioned the $50 figure on an investor CC a couple of years ago.
The $42 figure for 2012 cited in #msg-98658507 was an average for VALE’s mining operations in general rather than the IO operations, specifically. Moreover, ceratin costs (e.g. labor) are higher now than they were in 2012.