(Recasts with Vale plan to decommission dams, cutting output, changes dateline from RIO DE JANEIRO/BRUMADINHO)
BRASILIA/BRUMADINHO, Brazil, Jan 29 (Reuters) - Vale SA , the world's largest iron ore miner, on Tuesday vowed to take as much as 10 percent of its ore output offline in order to decommission 10 more dams like the one that burst last week, killing scores of workers and nearby residents.
Chief Executive Fabio Schvartsman said it would temporarily paralyze operations using those dams and spend 5 billion reais ($1.3 billion) to decommission them over the next three years.
The move came as prosecutors began arresting Vale executives over the Friday collapse of a tailings dam in the Brazilian town of Brumadinho, which was buried in a torrent of mining waste that killed at least 84 people and left hundreds more missing.
"We decided the company should, once and for all, do what it takes to remove any doubt about the safety of Vale's dams," Schvartsman told journalists in Brasilia.
The burst Brumadinho dam was one of 19 "upstream" tailings dams owned by Vale, all in the state of Minas Gerais, built with a method banned in Peru and Chile for safety reasons. Vale had already begun the process of decommissioning nine of them.
Schvartsman said Vale's board had already approved the decision to decommission the 10 remaining dams of that kind and suspend the related mining operations as necessary, relocating 5,000 workers to other parts of the company.
Those operations currently produce 40 million tonnes of iron ore and 11 million tonnes of pellets per year, he said.
Vale forecast total iron output of 390 million in 2018.
($1 = 3.7201 reais)
(Reporting by Jake Spring in Brasilia and Gram Slattery in Brumadinho; Additional reporting by Marta Nogueira, Pedro Fonseca, Gabriel Stargardter in Rio de Janeiro; Lisandra Paraguassu and Ricardo Brito in Brasilia; Marcelo Teixeira in Sao Paulo Editing by Brad Haynes and Matthew Lewis)