RIO DE JANEIRO (Reuters) -Mining companies Vale and BHP, together with their joint venture Samarco, may soon reach an agreement with Brazilian authorities to pay around 100 billion reais ($17.87 billion) for the collapse of a dam in the city of Mariana, said four sources familiar with the discussions.

Three of the sources expect a final agreement to be reached in October.

The amount is more than the 82 billion reais in new resources offered in the companies' last proposal in June to compensate for the 2015 disaster, which caused a wave of toxic tailings that killed 19 people, left hundreds homeless, flooded forests and polluted a river.

($1 = 5.5955 reais)

(Reporting by Marta Nogueira and Rodrigo Viga Gaier; Editing by Chris Reese and Kylie Madry)