Higher prices in America suit miners with copper assets in the country just fine. The shares of Rio Tinto and Freeport-McMoRan, an American miner which accounts for 60% of domestic copper production, have risen. For the latter, a 50% duty could result in windfall profits of $1.6bn a year, reckons Deutsche Bank, another lender.

The world’s No. 1 miner by market value produced more iron ore and copper over the past year, but flagged possible delays and cost increases at the giant potash project it is building in Canada’s Saskatchewan province.