Summary of significant accounting policies - Investment in affiliates and Mineral properties, development costs (Details) - Ambler Metals LLC	Feb. 28, 2023	Feb. 11, 2020
Schedule of Equity Method Investments [Line Items]
Percentage of ownership	50.00%	50.00%
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Schedule of Equity Method Investments [Line Items]
Percentage of ownership	50.00%	50.00%

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI https://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

Name:	us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant