Base metals prices rose in Wednesday's London Metal Exchange floor trading, supported by copper gaining on tight supply, traders said. Technical tightness mostly drove copper, with the benchmark cash/threes spread backwardation widening some $10 to $235 a tonne - the highest for 8-1/2 years.
"We saw technical buying and then the dollar weakened a little against the euro," a trader said.
"If the market advances further in Asia tomorrow then prices could mount a real challenge of $3,300 and possibly beyond, although there's still wariness of another slide."
Three-months last traded at $3,287, a $37 advance from Tuesday's kerb close.
Traders said LME copper was gripped by tightness through to September, with warehouse inventories at 31-year lows.
However, prices have tried to breach $3,300 three times since Friday, but lacked the buying momentum to do so.
The market scored an all-time high of $3,336 on April 12.
Mine supply is rising, which will push refined metal into surplus at some point, but potential short sellers are absent.
Zinc bounced back after a three-day run of big inventory increases ended with a 350-tonne fall.
The price closed at $1,292 from a previous $1,260.
Aluminium extended a rise from $1,700, ending at $1,735, up $25.
Nickel rose $195 to $16,195, lead was at $967/968, versus $966, and tin at $7,590, against $7,600.