SANTIAGO, July 10 (Reuters) - Workers at Antofagasta Minerals's Zaldivar copper mine in Chile have voted in favor of strike action after rejecting a pay offer, the deposit's sole union said on Friday.

The union said the pay offer, reached during collective negotiations whose start date was not disclosed, had been rejected by 99% of voters and a strike had been set for July 15, although usually government mediation takes place first. (Reporting by Aislinn Laing Editing by Chris Reese and Sandra Maler)