BOGOTA, Jan 31 (Reuters) - Australian ferronickel miner South32...

BOGOTA, Jan 31 (Reuters) - Australian ferronickel miner South32 (S32) has extended talks with the two unions at its Cerro Matoso mine in Colombia, in a bid to avoid a strike over pay and other benefits, the company and unions said on Thursday.

The extension kicked in after the parties failed to reach an agreement during a 20-day negotiation period. The continuation will run for up to 20 additional days.

If no deal is reached, the Sintramineros and Sintracerromatoso unions will call for their members to vote on whether to strike or go to arbitration.

"The objective is for the parties to reach a beneficial agreement for the workers and for the sustainability of the company," Cerro Matoso, a unit of South32, said in a statement.

Sintramineros President Jorge Burgos said he was optimistic. "We have faith in the dialogue and in the agreement, we have reached agreement on eight of the 27 points," he said.

Sintracerromatoso head Omar Torres said that despite differences, the talks are proceeding at a good pace.

Negotiations with the two unions, which represent 587 of the mine's 860 workers, are conducted separately.

The unions are demanding annual wage increases of between 9 percent and 18 percent. The company has offered inflation plus 0.5 percent.

Inflation in Colombia was 3.18 percent in 2018. South32 produces nickel from ferronickel in an open pit mine near the municipality of Montelibano, in the western department of Cordoba.

Cerro Matoso produced 43,000 tons of ferronickel in the last fiscal year.