Benchmark March futures ended the day up 0.15 cent at $2.0690 a lb, at the Comex division of the New York Mercantile Exchange, after dealing from $2.0540 to $2.0725, a new life-of-contract peak.
Spot December set a new record for copper in the day at $2.2990 a lb, but then slid 8.60 cents to settle at $2.1940 as investors liquidated their long positions ahead of the contract's expiration at the end of business today.
Comex final copper volume was estimated at 10,000 lots, above on Tuesday's official count at 8,028 lots.
Brokers noted the market's run-up to record levels this year has been fuelled by aggressive fund buying with little attention toward the fundamentals.
"People seem to want to find a reason to buy this market, but they ignore any change that would legitimately be a reason to sell," said one copper broker.
"The Codelco news boosted the market yesterday and it started up today.
We gave up some of those gains today as it now seems unlikely there is going to be a strike," he added, referring to the news that contract workers at Chile's Codelco, the world's largest copper producer, were threatening to go on strike unless the state-owned miner agreed to pay them a bonus amid soaring world copper prices.
"We had the price go up when Asarco was on strike, the price went up when Falconbridge's Kiddie Creek facility was on strike and all this stuff gets settled and the market never goes down, so there is going to be a day when the funds decide to sell it and it's going to be a day or a series of days that we have rarely seen before."
Keeping a lid on any advance today was a rebound in the US dollar against the euro after a stronger-than-expected United States consumer confidence report.
US consumer confidence improved in December to 103.6 from a November reading of 98.3, which had been downwardly revised from 98.9.
Economists polled by Reuters on average had forecast the index to likely rise 101.8.
In afternoon trading in New York, the euro was down slightly at $1.1820, off over a cent from session highs at $1.1932.
London Matel Exchange three-month copper finished the day up $33 at $4,483 a tonne, after the market was unable to sustain a new record high at $4,511.50 a tonne reached in the session.