Deferred Liabilities, Commitments and Contingencies - Proportions of total Payable Copper (Details)	Mar. 20, 2023 t
Deferred Liabilities, Commitments and Contingencies
Threshold Quantity of Refined Copper delivered to the Purchaser	33,000
Redemptions Backstop Facility
Deferred Liabilities, Commitments and Contingencies
1st Anniversary of the Closing Date to 5th Anniversary	3.00%
5th Anniversary until 33,000 metric tonnes of Refined Copper delivered to the Purchaser (the "Threshold Quantity")	4.875%
Thereafter from the date that the Threshold Quantity has been met	2.25%

Line item represents the deferred liabilities and commitments and contingencies disclosure.

No definition available.

Name:	mtal_DeferredLiabilitiesAndCommitmentsAndContingenciesLineItems
Namespace Prefix:	mtal_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

The percentage of payable copper, time period, fifth anniversary until threshold quantity delivered to Purchaser.

No definition available.

Name:	mtal_PercentageOfPayableCopperTimePeriodFifthAnniversaryUntilThresholdQuantityDeliveredToPurchaser
Namespace Prefix:	mtal_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

The percentage of payable copper, time period, first anniversary of closing date to fifth anniversary.

No definition available.

Name:	mtal_PercentageOfPayableCopperTimePeriodFirstAnniversaryOfClosingDateToFifthAnniversary
Namespace Prefix:	mtal_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

The percentage of payable copper, time period, thereafter from the date that threshold quantity has been met.

No definition available.

Name:	mtal_PercentageOfPayableCopperTimePeriodThereafterFromDateThatThresholdQuantityHasBeenMet
Namespace Prefix:	mtal_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

The threshold quantity of refined copper to be delivered to Purchaser.

No definition available.

Name:	mtal_ThresholdQuantityOfRefinedCopperToBeDeliveredToPurchaser
Namespace Prefix:	mtal_
Data Type:	dtr-types:massItemType
Balance Type:	na
Period Type:	duration

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: