(Adds comment from Vale, additional details)
By Marta Nogueira
RIO DE JANEIRO, May 16 (Reuters) - Brazilian iron ore miner Vale SA told prosecutors in the state of Minas Gerais that a dam is at risk of rupturing at its Gongo Soco mine, about 40 miles from where its Brumadinho dam collapsed, killing more than 230 people.
According to a document published on Thursday, prosecutors said Vale is predicting the dam in the city of Barao de Cocais may collapse next week if the current rate of movement in the embankment of the mine pit close to the dam is maintained.
The warning underlines ongoing concern about the stability of dams in Brazil's mining heartland of Minas Gerais in the aftermath of the Brumadinho accident, which itself came less than four years after another deadly dam collapse at a joint venture between Vale and BHP Group.
Vale said in a late afternoon statement it remained unclear whether the slippage in the embankment would actually trigger a collapse of the nearby Sul Superior dam, but said it was raising its level of alert and readiness for such an extreme case.
Earlier this week, Vale had identified movement close to the mine, which has not been active since 2016, the prosecutors said. About 500 people seen at risk from a collapse of the dam have been evacuated from their homes since February under orders from mining regulator ANM.
The dam holds 6 million cubic meters of mining waste, roughly half the amount that was released when the Brumadinho tailings dam burst in late January, burying nearby buildings including a company cafeteria and a bed and breakfast.
"If the movement of the northern embankment of the mine pit continues at the same pace, the rupture may happen between May 19 and May 25, which could cause liquefaction of the south dam," the prosecutor's document said.
Liquefaction, in which a dam's barrier gets weakened as it turns to water, has been pegged as a likely cause of the Brumadinho collapse. Like Brumadinho, the dam at Gongo Soco has an upstream structure, known as the cheapest and least stable type of tailings dam design.
Vale shares fell 3.2% on Thursday, accelerating their drop after the reports on the potential dam burst. Prosecutors ordered Vale to issue urgent warnings about the risks to the local population.
Authorities in Brumadinho are still recovering bodies from the collapse of the Vale tailings dam there. (Reporting by Marta Nogueira; Writing by Tatiana Bautzer; Editing by David Gregorio and James Dalgleish)