Income taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Deferred tax assets:
Intangible assets	$ 50	$ 91
Exploration mineral interest	27,840	19,488
Net operating losses	37,730	22,498
Foreign capital losses	4,012	4,285
Capital loss carry-forward	1,282	0
Share issuance costs	132	202
Convertible debt	0	960
Other	137	97
Total gross deferred tax assets	71,183	47,621
Less: valuation allowance	(71,063)	(45,619)	$ (35,521)
Net deferred tax assets	120	2,002
Deferred tax liabilities:
Exploration mineral interest	(3,686)	(6,303)
Property, plant and equipment	(322)	(1,081)
Total gross deferred tax liabilities	(4,008)	(7,384)
Net deferred tax liability	$ (3,888)	$ (5,382)