Comex copper plunged over 19% in minutes after Trump excluded refined metal from his planned import tariff - the largest intraday fall on record. Prices later pared some of the losses.

By Lewis Jackson BEIJING (Reuters) -Benchmark copper prices on the London Metals Exchange rose at the open on Thursday as markets continued to claw back the once-mighty U.S. copper price premium in response to the scaled-down U.

Copper traders were caught flat-footed after refined copper was exempted from Trump's new tariffs. The exemption triggered a 20% drop in copper futures on the COMEX exchange. Traders now face excess inventory, with COMEX stockpiles at a 21-year high.