Survey Track: Geology, Geophysics, Mapping and Core · Module 2 of 4 · about 15 min
Seeing underground: geophysics
Geophysics measures physical properties of rock from the surface or the air, so crews can see where to drill. Magnetic surveys map rocks with magnetic minerals like magnetite. Gravity surveys map changes in rock density. Both are often flown from aircraft or drones to cover big areas fast.
Electrical methods look for conductive or chargeable rock. Induced polarization (IP) is a standard tool for disseminated sulfides, such as porphyry copper, because those minerals hold a charge briefly after current is switched off. Magnetotellurics (MT) uses natural electromagnetic fields to map resistivity deep into the crust.
USGS runs the Earth Mapping Resources Initiative (Earth MRI), which funds new geologic mapping, airborne geophysics and lidar to find areas with potential for critical minerals across the U.S.
Geophysics finds anomalies, not ore. Many things cause an anomaly, so the next step is always ground checks, geology and drilling. Field crews lay out lines, run instruments, keep notes on anything that could add noise, like fences and power lines, and back up data every night.
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Module quiz
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