Subsequent Events - Working Capital Loans - Senior Syndicated Facility Agreement (Details) - Subsequent Event	Feb. 28, 2023 USD ($) facility	Mar. 10, 2023 USD ($)
Maximum
Subsequent Event
Amount of facility		$ 75,000,000
Facility C \| Minimum
Subsequent Event
Issuance fee (in percent)	2.00%
Syndicated Facility Agreement [Member]
Subsequent Event
Number of Credit Facilities \| facility	3
Additional interest rate on overdue payments (in percent)	2.00%
Syndicated Facility Agreement [Member] \| Facility A
Subsequent Event
Amount of facility	$ 205,000,000
Debt Service Cover Ratio	1.50
Percentage of excess cash to be applied for repayment	30.00%
Maturity term (in years)	5 years
Variable margin	3.00%
Syndicated Facility Agreement [Member] \| Revolving Credit Facility [Member]
Subsequent Event
Amount of facility	$ 25,000,000
Maturity term (in years)	3 years
Variable margin	3.00%
Syndicated Facility Agreement [Member] \| Facility C
Subsequent Event
Amount of facility	$ 40,000,000
Syndicated Facility Agreement [Member] \| Facility C \| Maximum
Subsequent Event
Issuance fee (in percent)	3.00%

Represents the Debt Service Cover Ratio.

No definition available.

Name:	mtal_DebtServiceCoverRatio
Namespace Prefix:	mtal_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the percentage of additional interest rate per annum for overdue payments.

+ References

No definition available.

+ Details

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

- Definition

Represents the percentage of issuance of fee per annum on the amount of each outstanding performance guarantee.

+ References

No definition available.

+ Details

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

- Definition

Represents the number of credit facilities (collectively, the "Senior Facilitates").

+ References

No definition available.

+ Details

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

- Definition

Represents the percentage of excess cash to be applied for repayment of debt.

+ References

No definition available.

+ Details

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

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=mtal_SyndicatedFacilityAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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