Mineral properties and development costs (Narrative) (Details) (USD $)	3 Months Ended		119 Months Ended		116 Months Ended	1 Months Ended		8 Months Ended					1 Months Ended
	Feb. 28, 2014	Feb. 28, 2013	Feb. 28, 2014	Oct. 17, 2011	Nov. 30, 2013 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	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	2,530,000
Net proceeds royalty														15.00%
Discount on consideration														40,000,000
Mineral properties expense	$ 580,000	$ 802,000	$ 51,837,000		$ 51,800,000