UPDATE 3-Chile's Collahuasi back to normal after work stoppage

* Company says production largely unaffected by stoppage

* About a third of 1,500 unionized workers joined protest

SANTIAGO Oct 29 (Reuters) - Workers at the world's third-largest copper deposit, Chile's Collahuasi mine, ended a partial strike begun early on Saturday after reaching an agreement with management over bonus payments, the company and union said.

"An agreement was reached over the application of the bonus," the company said in a statement. "Copper production was largely unaffected by the illegal stoppage. After the agreement was reached, operations have been completely normalized."

The union said via Twitter it had called off the protest.

"We have begun to return to our jobs and I think tomorrow (Sunday) we'll be 100 percent back," union leader Victor Cubillos told Reuters.

About 250 workers refused to start their morning shift to protest what they called an insufficient bonus payment. They were joined by night-shift workers, meaning about a third of the mine's roughly 1,500 unionized workers staged the protest, blocking access to the mine.

Collahuasi, which accounts for about 3 percent of global mined copper output, is owned by miners Xstrata and Anglo American .

Collahuasi produced 504,000 tonnes of copper in 2010, when output was hit by a monthlong strike. The mine expects to produce 500,000 tonnes of copper this year.

Relations between the union and management have been tense over the bonus payments since last year's strike. Saturday's protest came as the union prepared to hold elections.