RU2623841C2 - Method of geophysical intelligence in searching for relaxing deposits on aquatories in the areas of "living" ripes and in the wave-wide zone - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: studying the map of the anomalous magnetic field of the Earth in the investigated area, obtained from the results of the previously performed high-precision magnetic survey in a prospective for the discovery of placers of minerals in the water area. In the area of the "living" ripe, a seismoacoustic monitoring station is set up to record micro-earthquakes and a daily change in acoustic emission. Determining the periods of activation and calm of the fault zone, as well as the period of activity of the wave zone. During the lull (after the activation period), a repeated high-precision magnetic survey is performed on the profile that suppresses the magnetic field anomalies on the old map, or they perform a repeated survey on the whole explored perspective area. Calculate the differences in the magnetic field (between old and repeated surveys) obtained before and after activation, allocate local anomalies on them. By the magnitude of the difference anomalies, it is judged about the presence of placers containing magnetic minerals. Samples are taken at the center of each anomaly and analyzed for the presence of a useful component. On the contours of significant anomalies in which, based on the results of the analysis of samples, the presence of anomalous contents of useful components is confirmed, the boundaries of the deposit are determined.

EFFECT: reduction of sampling volumes, reduction of field work time.

Description

The invention relates to the field of prospecting and exploration of mineral deposits by geophysical methods, in particular to the search for placer deposits.

The invention can most effectively be used in the search for deposits on the shelf.

It is known that alluvial concentrations of minerals, in addition to the actually useful component (for example, gold, tin, diamonds, etc.), contain significant amounts of heavy minerals, in particular magnetite, titanomagnetite, ilmenite, the presence of which leads to the formation of magnetic field anomalies [ one].

However, in addition to the anomalies created by the clusters of magnetic minerals, there are a number of other magnetically disturbing objects in areas of their localization that are not directly related to minerals. For example, these are bedrocks on which placer formations are deposited.

Of the known geophysical methods for searching for alluvial deposits, the closest in technical essence is the magnetic survey method described in the manual for magnetic exploration [1], in which the use of magnetic properties of accompanying heavy minerals, which are indicators of useful components, is common with the claimed invention. The disadvantages are the same: difficulties in identifying anomalies by their natural sources.

The specified disadvantage of the known methods of using magnetic exploration is eliminated in the claimed invention by conducting comprehensive studies in assessing the nature (sources) of anomalies, including:

- the presence of the original, obtained in advance (5-10 days, better several months, etc. before the experiment - repeated surveys), maps of the anomalous magnetic field of the Earth (ΔТ) _а ;

- the use of seismic methods for monitoring acoustic emission, the sensors of which are located in the zone of the “living” fault or in bedrocks, to estimate the time of their activation and calm due to the geodynamic processes of the tide and / or surf;

- timing of repeated magnetic surveys (error 1-1.5 nT);

- repeated surveys on a profile crossing the anomalies of the original map or areal surveys over the entire study area;

- assessment of the influence of tidal forces on the structure of placers and, accordingly, on the anomalies of the magnetic field ΔT on routes or areas of past magnetic surveys;

- assessment of the difference in the magnetic field on repeated routes or areas performed before and after the activation of the fault or bedrock, with high accuracy.

Difference anomalies are created due to the fact that due to the activation of the fault and tidal forces, magnetically active minerals move and form new magnetic sources with a different structure.

The aim of the present invention is the allocation of magnetic anomalies caused by placers of magnetic minerals, which are often associated with valuable valuable minerals (gold, cassiterite, diamonds, etc.), among other natural anomalies, including those created by bedrock.

This goal is achieved by the fact that geological and geophysical maps (primarily magnetic fields) select areas that are prospective for the detection of placers in the coastal waters in the zone of the “living” fault — an acoustic source that influences (in addition to the ocean tides and wave-breaking zone) activation alluvial mineral deposits, including magnetic, their "loosening" and moving in space.

With the help of acoustic surveying, the fault zone is mapped and / or the places of maximum acoustic emission exit are found, where the seismic-acoustic station is installed, with the help of which daily monitoring is performed [2].

According to the results of daily monitoring of the acoustic emission energy created by geodynamic processes, tides and surf, the time of activation of the fault or rock mass and the time of "lull" are selected, high-precision magnetic surveys are performed during the lull - before activation, if there are no old high-precision surveys, and after ( or only after - if there is an “old” high-precision map of the magnetic field), and the difference between these two maps is calculated to assess the effect of activation of the fault or rock mass along with the tides of the earth's crust and the tides of the ocean in placers.

Obviously, it is more convenient to perform both surveys within 1-2 days. However, the presence of an old (possibly obtained months or even years before the time of assessment) high-precision map will allow more reliable calculation of the difference between two maps, the anomalies of which are created by a substance capable of changing its magnetic properties under mechanical (acoustic) exposure.

The source of acoustic emission is natural factors: a “living” fault and / or microearthquake in bedrocks created by the accumulation of elastic recoil energy in microcenters, earth tides, etc.

Obviously, in the zone of the “living” fault, the acoustic impact and, accordingly, the difference magnetic field will be greater, because these sources of exposure are summarized. In the absence of “living” faults or when their impact is not recorded on the studied area (for example, assessed by daily monitoring in two seismographs remote at the ends of the area), the method can be used only by weak daily activation of bedrocks. However, in this case, repeated surveys will need to be performed in a few days, the number of repetitions can be determined by the results of daily monitoring: the difference between repeated and primary measurements of the magnetic field, using the example of a separate anomaly or a separate profile.

Anomalies of the magnetic field in the difference field on the profile or map are highlighted by exceeding the absolute value of the difference by 1-3 times the mean square difference calculated in the nonanomalous zone. You can also use the shooting error. Shooting is carried out according to the instructions for magnetic exploration (1981).

The contours of the anomalies selected by the difference map are transferred to the magnetic field map and anomalies are quantitatively interpreted to estimate the depth of the lower edge (bottom) of the placer formation [1]. Further, on a rare network, testing is performed (not necessarily for all anomalies) and the parameters (content of useful components) of the placer formation are evaluated. Anomalies of useful components are determined by the excess of their contents over the background by 1-3 errors in determining their concentration.

Effect: localization of promising areas for the discovery of new alluvial deposits, preliminary contouring of the discovered deposits, reduction of the volumes of testing, reduction of the time of field work, a significant decrease in the cost of exploration.

Literature

1. Magnetic exploration: Handbook of geophysics / Ed. V.E. Nikitsky, Serkerov S.A. Gravity and magnetic exploration: Textbook for universities. - M .: Subsoil.

2. Burdakova E.V., Glinskaya N.V., Mishchenko O.N., Palamarchuk V.K., Pryalukhina L.A. The lull among the precursors of earthquakes // Materials of the XVI Conference “Structure, Properties, Dynamics and Minerageny of the East European Lithosphere.” - Voronezh, 2010 // Vol. I, 160-162 p.

Claims (1)

The method of geophysical exploration when searching for placer deposits in water areas in the areas of “living” faults and in the wave-breaking zone using the map of the Earth's anomalous magnetic field (ΔT) _{a of the} studied area, obtained from the results of previously performed high-precision magnetic surveys in prospective for the detection of placers of mineral resources of the water area characterized in that in the area of the “living” fault, a seismic-acoustic monitoring station is installed to record micro-earthquakes and daily change in acoustics emission, by the energy of the ongoing processes, determine the activation period and the quiet period of the fault zone, as well as the period of activity of the wave-breaking zone, during the quiet (after the activation period) repeated high-precision magnetic surveys are carried out on a profile that suppresses magnetic field anomalies on the old map, or survey over the entire studied prospective area, the differences of the magnetic field (between the old and repeated surveys) obtained before and after activation are calculated, local anomalies are distinguished on them, according to the magnitude of the difference anomalies is judged on the presence of placers containing magnetic minerals, samples are taken in the center of each anomaly, samples are analyzed for the presence of a useful component and along the contours of significant anomalies (i.e. if the absolute value of the anomaly | ΔT | ≥ (1 ÷ 3) σ, where σ is the mean square error of the survey), in which the analysis of the samples confirms the presence of anomalous (exceeding the background) contents of useful components, determine the boundaries of the deposit.