The United States will impose a 50 per cent tariff on copper pipes and wiring, President Donald Trump said on Wednesday, but details of the levy fell short of the sweeping restrictions that were expected and left out copper input materials such as ores, concentrates and cathodes.

U.S. Comex copper futures plunged 19.5 per cent after the announcement, quickly unwinding a premium over the London global benchmark that had grown in recent weeks. Traders had assumed U.S. copper mines would see a financial benefit from the tariff.

Trump first teased the tariff in early July, implying that it would apply to all types of the red metal, ranging from cathodes produced by mines and smelters to wiring and other finished products.

But a proclamation released by the White House said the tariff, which

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