The treasure at the bottom of NSW's Mt Boppy mine has traditionally been metallic, but a precious resource of a different kind has put the pit at the centre of delicate negotiations.

More than 550 million litres of water has pooled at the bottom of the Mt Boppy pit since mining ceased in 2015, turning the 124-year-old mine into a kind of industrial oasis in the drought-stricken region around Cobar.