Magnetic and gravity surveys measure changes in the Earth’s magnetic and gravitational fields caused by differences in rock properties below the surface. This gives us important information about the geology below the surface.
Gravity surveys look for small changes in the Earth’s gravitational field that are caused by changes in the density of rocks below the surface. Gravimeters can pick up on stronger gravitational attraction in denser rock formations, like massive sulphides or iron ores. Geologists can use this to find differences in rock density, the depth to bedrock, basin shape, and buried geological structures. Gravity surveys help map differences in density that could be signs of mineral deposits or geological formations like alluvium and bedrock.
Magnetic surveys look at how the Earth’s magnetic field changes in different places. This is because different types of rocks have different magnetic properties, especially those that contain magnetite and other ferromagnetic minerals. Magnetometers can find ore bodies (like nickel, copper, platinum group elements, and chromite), mafic and ultramafic rocks, and structural features that control mineralisation by looking for changes in magnetic intensity and direction. These surveys work well for mapping changes in the types and structures of rocks that are covered by sediment.
Magnetic and gravity surveys work together to give us more information that helps us with geological mapping, mineral exploration, environmental assessment, and resource evaluation. They are non-invasive, low-cost methods that can be done on the ground, from planes, or drones. They are good for finding differences in subsurface density and magnetic properties that point to valuable geological features.
In short, magnetic surveys show differences in rock magnetism and can show structures and ore deposits that are linked to magnetic minerals. Gravity surveys, on the other hand, show differences in rock density, which helps map geological formations, bedrock depth, and possible mineral concentrations.
