Tepid turnout for Peru rally against Newmont mine

* Mediation effort bogged down

* Humala struggles to overcome opposition

* Newmont mine would be costliest ever in Peru

LIMA, Aug 21 (Reuters) - Weak turnout on Tuesday hobbled the latest in a string of protests to stop a $5 billion gold mine in the northern Peruvian region of Cajamarca and denounce the government's ban on rallies against U.S.-based Newmont Mining Corp's Conga project.

Only several hundred people marched, local media reports said, and throngs of police, helped by 300 soldiers, patrolled the streets. A high-level security source in Peru's government said the atmosphere was "calm" and that a repeat of clashes that killed five protesters in July was not expected.

Milton Sanchez, who represents a community group opposed to the mine, said rallies were being held in provinces not included in the government's ban on rallies. He lives in Celendin, where marching in groups is currently prohibited.

"Everything is tranquil," he said by telephone.

President Ollanta Humala has shuffled his Cabinet since November in a bid to win local support for the project, but he has made little headway pushing forward with what has become the defining issue of his young presidency.

A six-week mediation effort headed by two prominent Catholic leaders has bogged down as the government refuses to accept their call to lift a ban on civil liberties in several provinces of Cajamarca, and the mine's opponents continue to reject what would be the costliest mining project Peru's history. [ID: nL2E8IS1WS]