Ferromagnetic material, which is subjected to an external magnetic field enhancesthe effect of initiating magnetic field and affects its surrounding area. The strength of magnetic induction mainly depends on the construction material and size of the mass of the element. n the case of rocks, the resulting induction is proportional to the concentration and the sort of the present ferromagnetic mineral, the initiator is the Earth's magnetism. The generated elements field causes deformations in the general magnetic field, allowingto locate or describe the structures, elements and interfaces with different magnetic properties.
Probably the first mention about utilisation of magnetisation effect of the sub-surface ferromagnetic structures on the earth's magnetic field in the localisation of mineral deposits are dated to the 17th century when Swedish miners observed abnormal behaviour of the magnetic compass latch and on the basis of these observations they localised shallow iron ore deposits.
German astronomer and physicist Johann von Lamont was intensively devoted to research of earth's magnetic field and he actively promoted the construction of a global network of magnetic observatories. In 1841 he designed and constructed magnetic variometer which was installed at the observatory in Munich. Later, he designed and constructed the first portable magnetic theodolite which contributed to the forming of magnetometry as a part of explorational geophysics. The primary task of Lamont's theodolite included field measurements of the variations of the earth's magnetic field outside the built observatories, but in 1843 Freiherr von Wrede theoretically started to deal with the possibility of using Lamont´s theodolite o identify and locate changes in the earth's normal magnetic field caused by the presence of rocks containing ferromagnetic minerals. Swedish astronomer and physicist Robert Tobias Thalen improved the measurement methodology for the purposes of geological survey In the next period Thalen contributed to the popularisation of magnetometric survey methods and more successful events in Sweden brought the deserved interest; in other parts of the world the magnetometric methods at that time didn´t attract as much.
A major breakthrough in the design of registration instruments occurred in the second half of the 20th century. Using different physical principles achieved a multiple increase in the sensitivity and data collection speed which also extended application capabilities of the magnetometric methods.