Mineral properties and development costs (Narrative) (Details) (USD $)	3 Months Ended		6 Months Ended		122 Months Ended		122 Months Ended	1 Months Ended		8 Months Ended					1 Months Ended
	May 31, 2014	May 31, 2013	May 31, 2014	May 31, 2013	May 31, 2014	Jan. 11, 2010	May 31, 2014 Approximations [Member]	Jan. 31, 2011 Ambler Property [Member]	Jan. 31, 2010 Ambler Property [Member]	Aug. 05, 2012 Ambler Property [Member]	Jan. 31, 2012 Ambler Property [Member]	Aug. 05, 2011 Ambler Property [Member]	Jan. 11, 2010 Ambler Property [Member]	Dec. 31, 2009 Ambler Property [Member]	Oct. 31, 2011 Bornite Property [Member]	Oct. 19, 2011 Bornite Property [Member]	Oct. 19, 2011 Bornite Property [Member] Minimum [Member]	Oct. 19, 2011 Bornite Property [Member] Maximum [Member]
Mineral property interest percentage						100.00%							100.00%	51.00%			16.00%	25.00%
Mineral Property, Shares Issued, Shares									931,098
Mineral Property, Shares Issued, Value									$ 5,000,000
Payments for mineral property	0	0	0	0	4,116,000			12,000,000							4,000,000
Consideration for Ambler property						29,000,000					29,000,000
Fair value of cash payments to acquire mineral properties								11,100,000			10,300,000
Discount rate used								8.00%
Mineral property, fair value of consideration										26,500,000
Transaction costs												100,000
Net smelter return royalty													1.00%				1.00%	2.50%
Purchase price of the net smelter royalty													10,000,000
Accretion expense	0	0	0	0	2,530,000
Net proceeds royalty																15.00%
Discount on consideration																40,000,000
Mineral properties expense	$ 489,000	$ 2,231,000	$ 1,069,000	$ 3,033,000	$ 52,326,000		$ 52,300,000