Segment information (Details)	3 Months Ended	12 Months Ended
Mar. 31, 2023 segment location	Dec. 31, 2022 segment location	Dec. 31, 2021 location segment
Segment information
Number of business segments \| segment	1	1	1
Number of Geographical Locations \| location	1	1	1

The number of geographical locations in which assets held.

No definition available.

Name:	mtal_NumberOfGeographicalLocations
Namespace Prefix:	mtal_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration