Concentrations of metals in Rio Doce river after catastrophic dam burst "do not significantly differ" from tests by Brazilian Geological Service in 2010.
The volume of water behind the dam has been rising and concerns had been raised in recent weeks about what could happen as snow melts and its capacity is exceeded.
The miner expects to lower production costs to $1.08 per pound during the 2017 financial year, from a projected $1.21 per pound in the year ending June 2016.