Summary of significant accounting policies - Narrative (Details)	3 Months Ended
	Mar. 31, 2024 USD ($) model asset_group	Dec. 31, 2023 USD ($)
Restricted Cash and Cash Equivalents Items [Line Items]
Number of asset groups | asset_group	2
Impairment, long-lived asset, held-for-use	$ 0
Long-lived asset, asset group, undiscounted cash flow model, useful life	40 years
Long-lived asset, asset group, remaining useful life	49 years
Long-lived asset, asset group, cash flows supporting carrying value, term	16 years
Number of cash flow models | model	2
Sensitivity analysis of fair value, commodity, favorable change in price, percent	15.00%
Sensitivity analysis of fair value, commodity, adverse change in price, percent	15.00%
Sensitivity analysis of fair value, commodity, adverse change in payables, percent	10.00%
Sensitivity analysis of fair value, metal recoveries, favorable change in price, percent	5.00%
Sensitivity analysis of fair value, metal recoveries, adverse change in price, percent	5.00%
Sensitivity analysis of fair value, operating costs, adverse change in price, percent	10.00%
Sensitivity analysis of fair value, operating costs, favorable change in price, percent	10.00%
Sensitivity analysis of fair value, construction costs, favorable change in price, percent	5.00%
Sensitivity analysis of fair value, construction costs, adverse change in price, percent	5.00%
Restricted cash	$ 9,600,000	$ 9,700,000
Waste Disposal Obligation Securities
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	2,900,000
Bank Guarantee
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	$ 5,500,000