## 2 Materials and Methods  
### Magnetic Susceptibility and Its Measurement: Physical Basis  
The magnetization of a physical body induced by an external magnetic field is a vector quantity that represents the magnetic moment per unit of volume [7]. The magnetic properties of matter are determined by the structure of atomic orbits and the magnetic moments of the electrons. It is well known that the main magnetic property of the substance itself is its ability to acquire a magnetization in an applied magnetic field--the magnetic susceptibility (we use \(\kappa\) for it as a common designation in geomagnetic research practice). Mathematically, \(\kappa\) is a dimensionless quantity representing the coefficient of proportionality between the intensity of the inductive magnetization and the intensity of the external (magnetizing) field. In magnetic prospecting practice, magnetization is used as a parameter that indicates the material (mineral) composition of a rock. The magnetic susceptibility of rocks varies widely from 0 to 10 SI units. In the magnetic survey practice, magnetic susceptibility is measured in 10\({}^{-5}\) SI units. According to their magnetic properties, all substances are divided into three groups: diamagnets, paramagnets, and ferromagnets, differing in magnetic susceptibility range and sign. The magnetic susceptibility of diamagnets is very low and is about 10\({}^{-5}\) SI. It is negative, as the magnetization vector within diamagnets is directed against the external magnetizing field). Many minerals, such as quartz, rock salt, graphite, gold, silver, lead, copper, and rocks, such as marble, are diamagnetic. Paramagnetic substances are also characterized by low magnetic susceptibility. Most sedimentary, igneous, and metamorphic rocks contain paramagnetic minerals. Ferromagnetic substances have the highest magnetic susceptibility (up to several SI units). The reason for this is the exchange coupling between their atomic spins. Even in the absence of an external magnetic field, the magnetic moments of all atoms of a substance are parallel to each other, forming domains, the distinguishing feature of which is remanent magnetization. An example of ferromagnets magnetite (Fe\({}_{3}\)O\({}_{4}\)), which has a very high magnetic susceptibility of about 1.5 to 80,000 \(\times\) 10\({}^{-5}\) SI units). Other examples of ferromagnetic minerals are hematite (Fe\({}_{2}\)O\({}_{3}\)), maghemite (a magnetic modification of iron oxide Fe\({}_{2}\)O\({}_{3}\)--\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\)), titanomagnetic (Fe\({}_{2}\)TiO\({}_{4}\)), and pyrrhotite, which is a magnetic modification of iron sulfide (Fe\({}_{n}\)S\({}_{n+1}\), where \(n=6\dots\) 11). Thus, the cause of the magnetism of rocks is their chemical composition and crystalline structure of the minerals therein, especially ferromagnetic ones. High magnetic susceptibility values are typical for rocks containing large amounts of ferromagnetic minerals. For instance, the magnetic susceptibility of some ferruginous quartzites can reach 1-3 SI. Ferromagnetic minerals, especially magnetite, are often found in igneous rocks. Such intrusive rocks as granites and granodiorites are characterized by lower \(\kappa\) values due to their acidic composition. Higher \(\kappa\) values are typical for rocks of medium composition (diorites) and basic composition (gabbro). However, in most rocks, magnetite is an accessory mineral in the rock composition, i.e., it occurs in very small quantities and therefore does not affect the rock classification. Almost all sedimentary rocks are non-magnetic. Limestones, dolomitic limestones, and dolomites have the lowest magnetic susceptibility. Specific exceptions are possible, e.g., when sandstones or siltstones formed near the drift source contain relatively large amounts of magnetite grains and have high magnetic susceptibility values as a result. In magnetic survey practice, minerals and rocks are often classified by their magnetization. Some useful examples of such classification were made by [PERSON] [8] and [PERSON] [9].