Benchmark copper CMCU3 on the London Metal Exchange touched a record high of $14,533 a metric ton, surpassing an all-time peak of $14,527.50 hit in January, before paring gains slightly to $14,505.50 by 1615 GMT, up 0.6%.
The buying was mainly from Commodity Trade Advisor (CTA) investment funds, largely driven by computer programs, but others were holding back, said Alastair Munro, senior base metals strategist at broker Marex.
"Large parts of the discretionary community remain sidelined, wary of getting involved up here with China downstream backing off," Munro added.
Traders and producers have been shipping large amounts of copper to the U.S. since President Donald Trump mooted import tariffs in February last year. Comex copper stocks stand at a record 766,795 short tons or 695,624 metric tons.
"It's hard to know what will happen on tariffs, but the longer there is uncertainty, the longer prices will remain elevated as material flows to the U.S.," said Albert Mackenzie, an analyst at Benchmark Mineral Intelligence.
Elevated premiums or backwardations for nearby 0#MCU: contracts against longer-dated forwards have attracted some copper back to the LME.
But cancelled warrants, or metal earmarked for delivery, at 51% indicate more than 121,000 tons of copper is likely to leave the LME system over the next few weeks. 0#MCUSTX-LOC.
The premium for cash over the three-month forward climbed above $430 a ton in the middle of August, the highest since 2021. It closed around $74 on Friday.
Another sign of tight supplies outside the U.S. is stocks in warehouses monitored by the Shanghai Futures Exchange at 63,000 tons, down 85% since the middle of March and at their lowest since January 2024.
Copper prices on the SHFE are also in backwardation 0#SCF:, suggesting the industry in top consumer China is concerned about supplies.
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