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OPERATING SEGMENT REPORTING - Geographic information (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025
Revenues from External Customers and Long-Lived Assets
Non-current Assets	$ 829,098		$ 680,689
Revenue	74,049	$ 35,696
Paragon Advanced Labs Inc.
Revenues from External Customers and Long-Lived Assets
Revenue			312
Minera Santa Cruz S.A.
Revenues from External Customers and Long-Lived Assets
Revenue	185,813	71,903
USA
Revenues from External Customers and Long-Lived Assets
Non-current Assets	116,919		114,644
Revenue	37,717	22,391
Canada
Revenues from External Customers and Long-Lived Assets
Non-current Assets	249,564		125,364
Revenue	25,316	$ 13,305
Canada \| Paragon Advanced Labs Inc.
Revenues from External Customers and Long-Lived Assets
Investment in Paragon, MSC or McEwen Copper	13,200		13,700
Mexico
Revenues from External Customers and Long-Lived Assets
Non-current Assets	25,848		25,759
Revenue	11,016
Argentina
Revenues from External Customers and Long-Lived Assets
Non-current Assets	436,767		414,922
Argentina \| Minera Santa Cruz S.A.
Revenues from External Customers and Long-Lived Assets
Investment in Paragon, MSC or McEwen Copper	164,700		140,700
Argentina \| McEwen Copper Inc.
Revenues from External Customers and Long-Lived Assets
Investment in Paragon, MSC or McEwen Copper	$ 272,100		$ 274,200