CONCENTRATION OF RISK: (Details)	12 Months Ended
	Dec. 31, 2011 refinerie smelter mine	Dec. 31, 2011 Cash equivalents	Dec. 31, 2011 Cash equivalents United States	Dec. 31, 2011 Cash equivalents Peru	Dec. 31, 2011 Cash equivalents Mexican Operations.	Dec. 31, 2011 Accounts receivable trade Five largest customers	Dec. 31, 2010 Accounts receivable trade Five largest customers	Dec. 31, 2009 Accounts receivable trade Five largest customers	Dec. 31, 2011 Accounts receivable trade Largest customer	Dec. 31, 2010 Accounts receivable trade Largest customer	Dec. 31, 2009 Accounts receivable trade Largest customer	Dec. 31, 2011 Total sales Five largest customers	Dec. 31, 2010 Total sales Five largest customers	Dec. 31, 2009 Total sales Five largest customers	Dec. 31, 2011 Total sales Largest customer	Dec. 31, 2010 Total sales Largest customer	Dec. 31, 2009 Total sales Largest customer
CONCENTRATION OF RISK:
Number of open-pit copper mines	4
Number of underground poly metallic mines	5
Number of smelters	2
Number of refineries	8
Concentration of risk
Percentage of total cash			86.90%	9.10%	4.00%
Percentage invested in one institution			25.20%	84.30%	96.10%
Percentage of cash in US dollars		97.70%
Percentage of accounts receivable and total sales						35.90%	49.10%	37.40%	10.80%	16.30%	11.20%	28.70%	29.60%	35.10%	7.30%	9.90%	8.50%