magnetics

• Magnetic surveys are carried out along transects or grids to determine, with a magnetometer, geomagnetic field strength. They can be airborne, marine or hand held. 
• Geologists study the variation in magnetic fields or the magnetic anomaly. 
• Minerals rich in iron, nickel and cobalt produce positive magnetic anomalies. Ultramafic/mafic intrusions may contain ore deposits formed by gravity settling, magnetite may also be present. 
• Magnetic surveys do not show depth or composition or structure of the ore body. 
• Magnetic surveys are used for finding buried steel and waste drums or detecting iron and steel obstructions. They can find unmarked mineshafts and map igneous intrusive rocks.