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.

Raw copper materials will not face the high duty that had been expected, but consumer goods prices may still be impacted.

The once-mighty premium U.S. copper enjoyed over the global benchmark slid on Thursday as markets clawed back months of gains in hours of frenzied trading after President Donald Trump surprised markets with pared-back tariffs.