BHP's manager for Australian exploration, Jamie King, told one of the final sessions of PDAC overnight the 2018 copper-gold discovery had been transferred out of exploration division for the next phase of its evolution."The project has been handed over to Minerals Australia planning and technical team, who will advance the project to the next phase of resource definition and inform our future decisions. And we are all very excited to start that next round of drilling, hopefully in the middle of this calendar year 2021," he said.King's presentation provided the best look yet at the size and geometry of Oak Dam, which will have analysts crunching the numbers to estimate potential ore volumes. A new map and three cross sections incorporate the results of 21,000m of drilling in FY 2020. About 40,000m has now been drilled. Mineralisation now stretches about 1km from east to west, about 2km from north to south and extends from a depth of about 600m to 1600m.King said the FY 2020 drilling continued to strengthen the model at Oak Dam of a cone of mineralisation with a barren core."We continued to test the model by stepping out further to the north and to the south and at depth, but encouragingly the model still held together," he said.The 2020 round of drilling established mineralisation extends into a "fault nose" where the best result was an intercept of 312m at 2.14% copper. Drilling also defined a new volume of mineralisation to the north, separated by at least one fault from the main zone. The northern zone is shallower and drilling to date has averaged a lower grade.Oak Dam West and Oak Dam East (separated by about 3km) were originally defined as prospects and drilled by Western Mining Corporation in the early 1980s. All previous drilling by WMC and other explorers found no copper at Oak Dam West and only minor copper at Oak Dam East.Oak Dam West was the least favoured target because it did not have a magnetic anomaly. A coincident magnetic and gravity anomaly, as found at Oak Dam East, are generally regarded on the Gawler Craton as an essential feature of IOCG targets.Despite all these reasons to ignore Oak Dam West, BHP drilled the prospect in 2018 and was rewarded with a spectacular intercept of 425.7 metres at 3.04% copper and 0.59 grams per tonne gold with discovery hole AD23.Kind revealed the decision to drill Oak Dam West was based on mineral systems thinking about IOCGs, as described by retired Geoscience Australia senior scientist, Roger Skirrow, and BHP's own studies on the geochemical footprint of Olympic Dam.He said the geochemistry of Oak Dam West, particularly the distribution of cerium, lanthanum and arsenic, strongly suggested the prospect was in the heart of an IOCG copper system and encouraged BHP to drill deeper than previous explorers.
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