Rainbow Rare Earths Ltd (LSE:RBW, OTC:RBWRF) has upped its overall estimate for the resource at Phalaborwa in South Africa by 16% after bulk density studies.
Tonnage at the site has gone up to 35.1 million tonnes from 30.4m, with the expected life of the project extended by at least a further two years from the current 14 years.
Rainbow's technical team has been focused on the evaluation of the density at depth of the two phosphogypsum stacks that make up the resource at the rare earth project.
US-based global gypsum experts Ardaman and Associates suggested a revised drilling technique based on its experience at over 100 gypsum stacks worldwide.
Using that technique, the in-situ dry density for the stacks increases at depth compared to the conservative bulk density estimate of 1.2 t/m3 used in the existing mineral resource estimate.
Ardaman carried out tests on samples for the site that showed a clear correlation between higher bulk density with increasing depth.
Samples from the drill campaign will now be assayed for grade by SGS in South Africa to allow for an updated JORC-compliant Mineral Resource Estimate.
Rainbow is developing a commercial way to extract rare earths from waste gypsum at Phalaborwa.
George Bennett, Rainbow’s chief executive, commented: "The improvement in the resource tonnage at Phalaborwa is extremely positive.
"While we await the assay results and the JORC compliant Resource classification upgrade, it is clear that the growth in tonnages will lead to an increase in the life of the project by over two years in due course."