BENEFIT PLANS: (Details) (USD $) In Millions	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010
SCC Defined Benefit Pension Plans
Defined benefit plan, Net periodic benefit cost
Interest cost	$ 0.3	$ 0.3
Expected return on plan assets	(0.3)	(0.3)
Maximum amortization of net loss (gain)	0.1	0.1
SCC Post-retirement Health Care Plan
Defined benefit plan, Net periodic benefit cost
Maximum total periodic benefit cost	0.1	0.1
Minera Mexico Pension Plans
Defined benefit plan, Net periodic benefit cost
Interest cost	0.3	0.8
Service cost	0.5	1.0
Expected return on plan assets	(1.7)	(1.4)
Amortization of net loss (gain)	(0.8)	(0.5)
Amortization of prior services cost		0.1
Net periodic benefit costs	(1.7)
Maximum amortization of transition obligation (assets), net	(0.1)	(0.1)
Maximum amortization of prior services cost	(0.1)
Minera Mexico Post-retirement Healthcare Plan
Defined benefit plan, Net periodic benefit cost
Interest cost	1.9	2.1
Service cost		0.2
Amortization of transition obligation (assets), net	0.8	(0.7)
Net periodic benefit costs	2.7	1.6
Maximum amortization of net loss (gain)	0.1	0.1
Maximum amortization of services cost	$ (0.1)