The World Gold Council’s "Above-ground stock" page directly supports the core numeric claim: central banks hold 38,666 tonnes, jewellery accounts for 97,645 tonnes, and total above-ground stock is 219,891 tonnes. Dividing 38,666 by 219,891 gives about 17.6%, which the same source rounds to 18%. That means the statement "roughly 17% of mined supply" is close but slightly understates the share. The World Gold Council’s "Gold Market Primer: Market size and structure" further corroborates that central banks hold nearly 39,000 tonnes and that jewellery is about 44% of stock. The cited X post repeats these figures consistently with the World Gold Council data.