Magnetic Measuring Instruments and Methods of Field Work for Magnetic Exploration

In terms of physical properties, there is no difference in the magnetic properties of oil shale, shale, sandstone and mudstone, and the magnetic properties of shale in this area are slightly lower than those of sandstone and mudstone (Table). But can this difference cause magnetic anomalies? The results of the experiment are shown in the figure.

In general, the range of magnetic anomalies in the L2 profile of 2050m is only 5nt, and the amplitude of the magnetic anomaly determined after 5-point smoothing is only 3nt, and the influence of topography has not been considered. The magnitude of the magnetic anomaly in the L1 profile is even smaller. Therefore, the oil shale may not be able to cause identifiable magnetic anomalies based on the test curves alone.

Fig. Half-cut ditch mouth-Houhejiafang section natural potential anomaly curve.

Figure Magnetic anomaly curve of half-cut ditch-Qianlie bridge profile.

Basic knowledge of magnetic exploration.

Magnetic exploration is an important branch of applied geophysics.

Magnetic exploration is based on the magnetic differences between rocks, and solves geological problems by studying the spatial distribution law and change of natural magnetic field. Exploration is the earliest, most theoretically mature, lightest, high efficiency, low cost, and most versatile method among the geophysical prospecting methods, and it is also the most widely used method in mineral exploration.

The phenomenon of magnetism was discovered very early on. There is a magnetic field around the earth, called the geomagnetic field, and the geomagnetic field can be approximated as the magnetic field generated by a magnetic dipole at the center of the earth, and its magnetization axis is about a degree of intersection with the earth's axis of rotation.

There are many factors that affect the magnetic properties of rocks and ores, which can be divided into internal factors and external factors. The internal factors include the composition, slow content, particle size, structure, etc. of magnetic minerals; External factors include magnetizing field strength, temperature, pressure, etc.

Most minerals are paramagnetic and a small amount diamagnetic. The most widely distributed ferromagnetic minerals are iron oxides, such as magnetite, titanomagnetite, hematite, etc.; Among the sulfide minerals there is pyrrhotite; and some ferromagnetic minerals that are widely distributed and have weak magnetism, such as siderite, limonite, etc.

Introduction of magnetometers.

Magnetometer can be divided into relative magnetometer and absolute magnetometer, can also be divided into ground, aviation, ocean, satellite and borehole magnetometer, the magnetometer used in China has: hanging wire magnetometer, optical pump magnetometer, as well as magnetic gradient meter, superconducting magnetometer, etc. Now the electron-based force meter has completely replaced the mechanical magnetometer, and the observation accuracy has also been improved from tens of nanometers in the past to about one nanometer, or even smaller.

Now the most common ones used are the PM-2 proton magnetometer, MCL-2 fluxgate magnetometer, MCL-5 total tank excitation field magnetometer, and MCL-6 three-component magnetometer of Hebei geodetic exploration technology.