You are right in terms of variation per point, but based on today's environment, exchange rate will have the biggest impact, followed by capex and opex.  Copper & gold numbers, taken seperately, will not create a big variation compared to 2013 as they will use the long terms consensus price (around $3.10 for copper vs. $3.25 and around $1300 for gold vs. $1445).  If this drags longer, they might be able to increase the gold price in a near future, but even if they use $1600, the change in valuation would still be small compared to the other parameters.

MoneyK