LME Copper was down 1.4%, while prices on the Comex exchange plunged more than 20% last week after President Trump’s decision to exempt refined forms of the metal from fresh US import tariffs, ING's commodity experts Ewa Manthey and Warren Patterson note.

Copper slides as Trump exempts refined forms from tariffs

"Just last week, futures in New York surged to an all-time high. A significant premium for New York futures over London evaporated. A week ago, that premium reached over 30%. The collapse of an arbitrage trade has left the US with a huge buildup of Copper stockpiles."

"Copper inventories at Comex warehouses are at their highest in 21 years. That stockpile might now be re-exported. This will be bearish for LME prices with more Copper showing up in LME warehouses."

"Trump imposed 50% tariffs on semi-finished Copper products, such as pipes, rods, sheets, and tubes, and Copper-intensive goods like pipe fittings, cables, connectors, and electrical components, effective last Friday. But, he exempted less-processed goods, including ore, concentrates, cathodes and anodes."