What lies beneath? 3D seismic survey plays its part to reveal Mount Isa’s underground secrets
During September, Mount Isa Mines’ Exploration team supplemented the 2D seismic survey completed in 2020 with a cutting-edge 3D seismic survey, deploying the latest ground-breaking technology.
These surveys are the first steps in a process that will eventually tell us what future mining possibilities could exist for Mining Lease 8058 and investigate possible extensions to the life of the asset.
Seismic surveys create images of the earth through the analysis of vibrations from sound waves. These sound waves can penetrate solid rock, deep into the inner layers of the earth.
Approximately 8,000 nodes were distributed throughout the survey area, with 12,000 locations used across the survey.
The sound waves are produced by trucks that create a vibration in the ground. Lines of receivers are set out on the surface to pick up and record the sound waves as it bounces back to the surface. The nature of these sound waves varies depending on the underground features enabling specialists to develop a picture of the underground formations.
Alex Brown, Principal Geologist for the Mount Isa Mines’ Exploration Department says the data received from a seismic survey can’t actually tell us if the rock formations are copper or zinc deposits. Supplementary interpretation work from the geologists is required for this.
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These receivers, also called nodes, are small yellow boxes, each containing accelerometers, a battery and a logging computer. They are spiked into the ground so the accelerometers can measure the vibrations bouncing back from the rocks beneath.
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The vibration trucks, weighing 38 tonnes each, serve as the vibration source. Each truck lowers a plate down on hydraulic jacks so that when the plate is on the ground, it lifts the truck up, and with the truck's full weight vibrating through the plates, sound waves are sent down into the ground.
“We know that certain formations shown in the survey results indicate the possibility of copper or zinc-lead mineralisation. The purpose of a seismic survey is to gain a picture of what the underground landscape looks like so we can identify which areas will make promising drilling targets,” says Alex.
“Drilling is very expensive and at the end all we have is a small sample of a core, and the deposits surrounding the core can be completely different within as little as a handful of metres. This seismic survey will be able to leverage knowledge from our existing drilling, and hopefully reduce the number of drill holes we need to make a discovery.”
“Something many people misunderstand about the exploration process is exactly how long it takes to go from the first surveys to the actual mining of the deposits,” says Alex.
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Three vibration trucks covered a survey area of 3 kilometres wide and 5 kilometres long over 24 days jointly stopping 10,000 times to create 10,000 source point (plate vibrations).
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The vibration trucks move 12 meters at a time with the vibrations lasting approximately 30 seconds per source point.
“The project scope began at the end of 2018, with works proceeding in early 2019. This included various regulatory approvals and stakeholder engagement though exploration agreements with the Native Title Holders and other land users.”
“The 2D seismic survey took place in October 2020 and the results were received in January 2021. This was followed up with the 3D seismic survey in September 2022.”
“We will receive the data in early 2023, and the seismic experts and the Exploration Team will work together to interpret the data with the rest of the information available to determine areas for further investigation via drilling, “says Alex.
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The command centre is parked high on a hill so optimal signal and communication to ground staff can be maintained. The surveyed area covered a significant area south of X41.
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The data sent back from the receivers (nodes) are displayed on the command centre’s screens. From here the sources (vibration trucks) are controlled and instructed on which areas to attend to next making sure that they do not interfere with each other’s sound wave production.
“There are no guarantees, but if we get some promising results, we expect to have identified which areas we want to drill by the middle of 2023 which means drilling could potentially start in the second half of 2023.”
If we were to discover significant mineralisation in the first round of drilling, it would most likely take another two to three years to gather enough information for the engineers to determine how to mine it. Therefore, the entire process is likely to carry on into 2025.”
Mount Isa Mines undertakes continuous exploration activities as part of our business development and to identify opportunities for future operational expansions.