Workers at the Pribbenow mine in northern Colombia, owned by U.S.-based Drummond, have signed a preliminary two-year contract and will end their strike soon, a union official told Reuters on Tuesday.

"We have a preliminary contract agreement," said Joaquin Romero, president of the Funtraenergetica labor organization which represents 3,500 Pribbenow miners.

"The strike will be lifted when the agreement is signed, probably later today," Romero said.

The open-pit mine produces about 2 million tonnes of coal per month, according to Drummond, a family-run business based in Birmingham, Alabama.

The work stoppage began on July 17 after contract talks broke down over miners' demands for higher pay and better employment security.