Recurring Fair Value Measurements - Additional Information (Details) - USD ($)	3 Months Ended	12 Months Ended
Mar. 31, 2023	Dec. 31, 2022
Recurring Fair Value Measurements
Transfer of assets from level 1 to level 2	$ 0	$ 0
Transfer of assets from level 2 to level 1	0	0
Transfer of liabilities from level 1 to level 2	0	0
Transfer of liabilities from level 2 to level 1	0	0
Transfer into level 3	$ 0	$ 0

Amount of transfers of assets measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

No definition available.

Name:	mtal_FairValueAssetsLevel1ToLevel2TransfersAmount1
Namespace Prefix:	mtal_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of transfers of assets measured on a recurring basis out of Level 2 of the fair value hierarchy into Level 1.

+ References

No definition available.

+ Details

Name:	mtal_FairValueAssetsLevel2ToLevel1TransfersAmount1
Namespace Prefix:	mtal_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of transfers of liabilities measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

+ References

No definition available.

+ Details

Name:	mtal_FairValueLiabilitiesLevel1ToLevel2TransfersAmount1
Namespace Prefix:	mtal_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of transfers of liabilities measured on a recurring basis out of Level 2 of the fair value hierarchy into Level 1.

+ References

No definition available.

+ Details

Name:	mtal_FairValueLiabilitiesLevel2ToLevel1TransfersAmount1
Namespace Prefix:	mtal_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap_FairValueDisclosuresAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of transfers of financial instrument classified as a liability into level 3 of the fair value hierarchy.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(3)
-URI https://asc.fasb.org/extlink&oid=126976982&loc=d3e19207-110258

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationLiabilityTransfersIntoLevel3
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration