It had $US25.9 billion ($A35.48 billion) of debt at the end of 2015. The miner's five-year credit default swaps, instruments used by investors to insure exposure to a company or country's debt, were at 182 basis points, according to Markit data. They closed at 194 basis points on Wednesday. "I think (the deal with the Brazil government is) having a more material impact on the stock," Macquarie analyst Alon Olsha said, noting that other miners were also gaining due to higher copper prices. BHP Billiton's Samarco joint venture will pay up to $US2.3 billion ($A3.15 billion) over six years after reaching a settlement with Brazilian authorities over a deadly dam spill in November. BHP shares were up 33 cents, or 1.91 per cent, to $17.58 at 9.05am.