Shares in the FTSE 100's mining contingent, led by Glencore PLC (LSE:GLEN) and Rio Tinto Ltd (LSE:RIO, ASX:RIO, OTC:RTNTF), dropped sharply as copper prices dropped on Donald Trump's plans for 50% tariffs.
The US President confirmed that refined metal, including copper ore and concentrate, will be excluded from new US tariffs on the metal that take effect on Friday.
White House officials announced that the 50% tariff would be applied to semi-finished products, such as copper pipes and wiring.
This sent US copper futures down 5.5% to below $4.50 per pound on Thursday, extending the drop over the past week to around 25%.
The move from the Trump administration unwound a premium in US prices compared to the global benchmark London price, which had led to shipments being diverted Stateside.
"This came as a surprise to market participants," said market analyst Kyle Rodda at Capital.com, "with traders revising the scale of the expected supply shock to copper markets and dialling down the rush to pull copper into the US from other exchanges to front run the higher imposts".
Neil Wilson at Saxo said copper prices in New York "plunged about 20% in a blink of an eye as Trump did another TACO and retreated from imposing swingeing tariffs on imports of the metal".
Glencore shares fell 4.4%, Rio Tinto 3.9%, while copper specialist Antofagasta PLC (LSE:ANTO) plunged 4.8% and Anglo American PLC (LSE:AAL) dropped 3.9%.