ASSET RETIREMENT OBLIGATION (Details) - CAD ($) $ in Thousands	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023
ASSET RETIREMENT OBLIGATION
Opening balance	$ 987	$ 952
Increase due to reassessment of the rehabilitation obligation	514
Effect of change in discount rate	(56)	18
Accretion expense	18	17
Ending balance	$ 1,463	$ 987

Noncurrent portion of the carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

No definition available.

Name:	nmg_IfrsAssetRetirementObligationsNoncurrent
Namespace Prefix:	nmg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant