Early New York trading was active, with key December copper vaulting $1.26 a lb resistance, but gains were later pared.
"All eyes will be on the labour situation at SPCC in Peru in order to determine the next move for copper. If a strike does occur, we should see some more short-covering, which in turn could bring in some strong technical buying...," Man Financial said in a report.
December futures on the New York Mercantile Exchange's COMEX division ended up 0.90 cent at $1.2595 a lb, after trading in a range of $1.2430 to $1.2790 that marked highest price since August 20.
September was up 0.85 cent at $1.2590, spot August climbed 0.95 to $1.2610 and the rest rose 0.75-0.95 cent.