A NEW approach to interpreting old data is helping BHP make smarter, better informed decisions about where to drill for precious minerals, and far more accurate exploration outcomes.
In South Australia, this fresh approach to interpreting decades-old data has led to the discovery in 2018 of copper deposits at the company’s Oak Dam West site, 65km southeast of Olympic Dam. Jamie King, BHP’s Head of Exploration who has worked for BHP for more than 15 years, was invited back to Australia from Chile to search for Olympic Dam-style copper deposits in this state, using the lessons gathered from a country with some similar geological challenges to our own.
“I was transferred to the BHP Adelaide office in late 2016 with the specific objective of reviewing the copper exploration portfolio around our Olympic Dam mine,” he says. “From the portfolio of historic exploration projects BHP still had exploration licences over, Oak Dam West was clearly highlighted as a standout opportunity and begged the question, ‘why had previous exploration teams not completed the drill test and made a discovery?’.”
Exploration teams from Western Mining Corporation had done ground gravity surveys in the area in the late 1970s and some drilling in the 1980s, but no further work was done before BHP bought the company in 2005. While King can’t be sure why WMC did not follow up on Oak Dam West, he says the depth of the target at more than 700m below the surface may be a factor. “And, don’t forget, the same team had just discovered what was to become one of the largest ore bodies in the world just up the road at Olympic Dam,” he says.
Decades later, King had the original geoscientific data and core samples to go on. Now it was a matter of his team taking advantage of advanced geophysics modelling to re-analyse the information and better define the existence of a drill target and its quality. BHP’s Chief Technology Officer, Diane Jurgens, last year told a mining conference in London:
“Oak Dam shows that with new technology and new skills, our geologists can identify opportunities that were hidden to explorers in decades past.” King says the critical process that led the 2018 exploration team to revisit Oak Dam West was a “minerals systems” approach that modelled the gravity data in three dimensions, integrated it with geochemistry and interpreted it together with the latest understanding of how the exploration team believe this type of ore body formed. “This approach focused the team on recognising the presence of critical ore-forming processes that are very evident in the historical data, regardless of the lack of copper in the original drilling,” he says.
King says the discovery of “significant copper mineralisation” at Oak Dam has already had flow on effects for the mineral industry in South Australia with renewed excitement and hope for more discoveries in the region. New drilling on the site began in Quarter 4 of 2019 and is ongoing and, as the distance between drill holes is reduced, and more information is accumulated, hopes are high the company can report a new exploration target. “If the discovery continues to be positive and economic viability is confirmed, it has the potential to complement Olympic Dam’s giant copper resource,” he says. “The current phase of exploration drilling is designed to inform BHP’s next steps with the project.”