CONCENTRATION OF RISK: (Details)	12 Months Ended
	Dec. 31, 2012 item	Dec. 31, 2012 Cash equivalents	Dec. 31, 2012 Cash equivalents United States	Dec. 31, 2012 Cash equivalents Peru	Dec. 31, 2012 Cash equivalents Mexican Operations	Dec. 31, 2012 Cash equivalents Europe	Dec. 31, 2012 Accounts receivable trade Five largest customers	Dec. 31, 2011 Accounts receivable trade Five largest customers	Dec. 31, 2010 Accounts receivable trade Five largest customers	Dec. 31, 2012 Accounts receivable trade Largest customer	Dec. 31, 2011 Accounts receivable trade Largest customer	Dec. 31, 2010 Accounts receivable trade Largest customer	Dec. 31, 2012 Total sales Five largest customers	Dec. 31, 2011 Total sales Five largest customers	Dec. 31, 2010 Total sales Five largest customers	Dec. 31, 2012 Total sales Largest customer	Dec. 31, 2011 Total sales Largest customer	Dec. 31, 2010 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			69.70%	5.40%	1.40%	23.50%
Percentage invested in one institution			32.60%	63.50%	36.50%	100.00%
Percentage of cash in US dollars		99.20%
Percentage of accounts receivable and total sales							40.00%	35.90%	49.10%	10.40%	10.80%	16.30%	28.80%	28.70%	29.60%	7.40%	7.30%	9.90%