It was Brazil's worst ever environmental disaster.
The 2015 collapse of the Fundao dam left 19 dead, and villages obliterated.
Six years on, the legal wrangling continues.
On Tuesday (July 27) a court in London reopened a $6.9 billion lawsuit against BHP.
The mining firm co-owned the dam, along with Brazilian giant Vale.
Last year a UK court had struck out the lawsuit, saying it was an abuse of process.
An appeals court upheld that decision in March.
But on Tuesday, three judges reversed course, and granted permission to appeal.
Lawyers successfully argued that the earlier appeals judge had not properly dealt with arguments about why the case should proceed.
Claimants argue they are entitled to sue BHP in the UK, and that Brazilian litigation is so complex it cannot provide redress in any realistic timeframe.
The final ruling will help establish whether multinationals can be sued at home for the conduct of overseas subsidiaries.
A final verdict may mean going all the way to the UK's Supreme Court.