Falling exchange rates could provide a boost to low cost commodity producers as Chinese production and a rising renminbi provide price support at the top of the curve. Commodity currencies have fallen significantly against the dollar in the last six months. Since the beginning of 2013 the South African rand has fallen by 30%, the Australian dollar by 18%, the Brazilian real by 14% and the Chilean peso by 13%. Since mining companies operating in those countries make their sales in USD, but pay part of their costs in the local currency, this has the effect of increasing margins as…