The Ranger uranium orebody, the richest in the Southern Hemisphere, was discovered in late 1969, when an aerial radiometric survey conducted by Geophysical Resources Development Co., a company based in Sydney, on contract to Noranda Aluminum, Inc., detected a large spike in gamma radiation when passing over Mount Brockman, known as Djidbidjidbi to the Mirarr traditional owners of the area. The instrument that detected the anomaly was a Nuclear Enterprises gamma ray spectrometer using a Thallium doped Sodium Iodide cylindrical crystal. At time of discovery the aircraft was flying at an altitude of 100 meters. The anomaly could still be detected at almost 3000 feet.