b'FeatureMore than oreDelivering new resources an economic and material risk imperative for us to lean in with geophysics in this space.As we produce new resources from our existing operations and develop new mines over the coming decades the trendsTackling this new problem space requires us to collaborate deeply towards deeper extraction are clear, our open pits are gettingacross traditional silos between resource geology, geotechnical deeper, presenting new geotechnical and hydrogeologicalengineering, mine planning, hydrogeology, and closure. We need challenges with our pit wall stability and de-watering. At theto work with these stakeholders to ensure that the systems are same time a significant portion of future mines, both globallyin place to ensure that we collect rock mass data early enough to and within the BHP portfolio, will be deep underground mines.be a phase ahead of the decisions we inform. We need ways for The future of these mines is likely to reside predominantly inteams to articulate the value of information associated with early mass mining methods as only these can yield the vast quantitiesdata and acquisition. Finally, we need to figure out how best to of metals that we need. use our geophysical capabilities to provide impactful information and knowledge in this new context.However, the success of high column cave mines globally has so far been mixed with poor rock mass characterisation,We have a unique opportunity to leverage the 3D and 4D specifically around structure and geomechanical properties,access that we have to the Earth during mine development to and the knock-on impacts for model building and mine designbuild a truly smart, instrumented rock mass, for both design being identified as a key cause of underperformance. Withand monitoring of cave behaviour over time. There have the increased pressure on timelines this is often due to minebeen several studies published recently leveraging downhole planning decisions getting ahead of the characterisation. Asfibreoptic cable (DAS) for seismic imaging in cave mines. our mine-planners tell us, we need to be a phase ahead of themUsing drill holes for sensors sets up an optimal geometry for or forever behind. Fortunately, geophysics is well placed toacquiring structural data from seismic in areas of steep dip, help us front-load our rock mass characterisation. We can startand can be further extended to include cables shot-creted to as early as exploration to delineate resource and structures andmine walls. This flexibility gives us the opportunity to build up later in-fill this initial characterisation as we gain more accessan increasingly robust image and geo-mechanical property to the earth via drill holes and development infrastructure.picture over time. Experimenting with combining data from Given time pressures the focus of our geoscience teamsthe surface, downhole and cross hole, extending to other tends to be on drilling out the resource to required spacingphysical properties, and calibrating with core and wireline for resource classification. While we will intensively drill thepetrophysics all present rich avenues for industry research deposit itself to meet JORC classification expectations, drillingover the coming decades. By embedding these cables during of the surrounding host rock and cover tends to be sparser andmine development, we also build a robust network of stress the cost of obtaining that data from the surface can be in theand temperature sensors that can be used during operations high hundreds of millions of dollars. This information, however,to monitor and optimise cave propagation. At BHP we have is critical to placing infrastructure such as mine-access, and torecently completed an initial experiment combining a sparse predicting how the cave will behave. A cave mine will not justsurface seismic acquisition with downhole DAS cable at our propagate through the deposit but also through the cover,Oak Dam project. The images in Figure 2 are from the feasibility therefore, understanding behaviour of and the expectedstudy work, showing the advantages of collecting down hole dilution from cover material is critical to mine planning.data for imaging steep dips and we are anxiously awaiting and Surface subsidence also has implications for both infrastructurehope to publish the results in the not-too-distant future!placement, closure and interactions and local water pathways. The high cost, time and access constraints of drilling along withAs I said earlier, there are opportunities to leverage this 3D the opportunity cost associated with failure of the cave mine orgeometry to trial other physical measurements that might collapse of infrastructure due to poorly informed design createotherwise be inaccessible such as Muon tomography. Muons Figure 2.Synthetic seismic feasibility modelling for down hole vs. surface seismic imaging highlighting downhole advantage in imaging of steep dips. Adapted from H. Schijns etal. 2023.APRIL 2023 PREVIEW 56'