Radioactive method prospecting

Radioactive method for finding uranium ore

Utilizing the greatest feature of the uranium ore body itself - having radioactivity to find uranium ore, it is the most widely used and economically effective method of prospecting. According to the types of radiation generated by detecting uranium and its decaying daughters, the radioactive methods for finding uranium can be roughly classified into the following categories.

1γ method aviation gamma measurement, vehicle gamma measurement, walking gamma measurement, gamma measurement in the hole, gamma measurement in water

2α track etching measurement, ²¹⁰ Po measurement, alpha card measurement, alpha cup measurement, ²²⁶ Ra measurement, etc.

The method of 3β method to find uranium by using β measurement alone is still rare, and most of them adopt β+γ measurement method, such as β+γ measurement in pores and β+γ measurement in core.

In addition, thermoluminescence, uranium isotope method, lead isotope, He gas measurement, Hg vapor measurement, etc., are also used to find uranium under certain geological conditions.

An example of using radioactive methods to find uranium ore

First, method technology

(1) Basic principle of γ energy spectrum measurement

Ground gamma spectroscopy is a method of terrestrial geophysical exploration. It uses the gamma ray energy spectrum of uranium, lanthanide and potassium-40 to make some difference. Using this difference, several suitable spectral segments are selected for ground gamma spectroscopy to estimate the uranium in the ground rock (ore). , strontium, potassium content.

Four energy spectrometers are commonly used in the wild. In order to estimate the content of uranium, thorium and potassium in the rock, the photoreceptor peak of 1.76 MeV of uranium ²¹⁴ Bi, the photopeak of ²⁰⁸ Tl 2.62 MeV and the photoreceptor of 1.46 MeV of ⁴⁰ K were selected respectively; and the corresponding energy was selected respectively. The spectral segments are 1.66-1.86 MeV, 2.52-2.72 MeV, and 1.36-156 MeV, and the ternary equations are listed by energy measurement results:

(1)

In the formula, , , ( =1, 2, 3) are conversion factors, and the set of coefficients needs to be obtained by calibrating the energy spectrum on a known model; The count rate measured by the spectrometer in the corresponding channel (after subtracting the base); , , They are the content of uranium, plutonium and potassium in the rock or soil that needs to be obtained.

Solving the equations (1) can determine the content of uranium, plutonium and potassium in rocks or soil.

γ energy spectrum measurement method

Ground gamma spectroscopy is mainly used to determine the content of uranium, thorium and potassium in floating soil, rock and ore body, and to determine the nature of the anomaly. Its working method is briefly described as:

A. Before the formal work, perform performance check on the gamma spectrometer, select the measurement spectrum, and calibrate the instrument.

B. The main course of the vertical line and structure of the line.

C. At each measurement point, the gamma spectrometer was used for timing counting to determine the count rates of uranium, thorium and potassium channels.

D. Based on the field measurements, the contents of uranium, plutonium and potassium were calculated indoors and various maps were drawn.

(2) Soil natural thermoluminescence measurement method

Method principle

The natural thermoluminescence measurement method of soil is to collect soil samples with a certain depth on the surface of the earth. The high-sensitivity thermoluminescence measuring device is used to measure the thermoluminescence intensity of natural minerals in the sample since the last thermal event, and the difference in strength is used to solve the uranium ore prospecting. And a method of geological problems.

work method

1. Field sampling Field sampling According to the requirements of soil geochemical specifications (DZ/T 0145-94), field samples are collected. According to the specifications, soil samples should be taken from the B layer soil samples. The sampling point is 10 meters away, and each sample takes 80-100g of soil sample.

2. Indoor measurement After sieving the sample, the sample is measured for thermoluminescence intensity (unit: radiation dose unit: μGy/g) using a highly sensitive thermoluminescence measuring instrument (RGD-3A type).

Care should be taken during work to take fresh B-layer soil samples. After the sample is collected, it is packed in black cloth bag or paper bag, protected from light, high temperature and radiation. In addition, the sample must be air-dried naturally, neither heated nor dried.

(3) Helium measurement method

Rn is the only gaseous element of the uranium system, and the direct parent is radium (Ra). The content of maternal elements determines the concentration of radon in rocks and soil to a certain extent. The physical properties of earthworms are very lively, showing a strong ability to migrate, and it is easier to enter the surface soil through rocks ranging from a few meters to hundreds of meters underground. Therefore, in the uranium, radium-rich areas, or geological structural fracture zones, the enrichment of plutonium may be formed, while in the vicinity, the plutonium content is significantly reduced. According to the level of anomaly, the uranium ore body and structural fracture zone can be found.

work method

Helium measurement is divided into two methods: cumulative measurement and instantaneous measurement. The cumulative enthalpy measurement is to embed the sampler (such as α track, fistula, etc.) in the soil. The sampling time is generally 20 days to one month. The abnormal stability and reproducibility are good, but the work efficiency is low. The instantaneous enthalpy measurement is performed by punching and pumping in the field, and the working efficiency is high, and the sensitivity of the method is not bad with respect to the cumulative measurement. This field work uses instantaneous helium measurements.

Field measurements are performed in accordance with the Helium Measurement Specification (EJ/T 605-91). A small hole of 0.5-0.7 m depth was drilled with steel brazing at the measuring point, and then the sampler was inserted into the hole for pumping, and finally measured with an FD-3017 instrument.

2. Research examples of Xiazhuang granite-type uranium ore field (method using thermoluminescence measurement and helium gas measurement)

(1) Test results of 330 deposits

The 330 deposit (also known as the prospective deposit) is the first granite -type uranium deposit discovered in China, and it belongs to the silicified fracture zone type uranium deposit. The deposit has a history of mining for many years. In order to expand its range, 32 lines have been arranged, of which 3 lines are in known areas and 29 lines are in unknown areas. Line 21 is located in a known area of ​​the deposit and has a length of 240 m. The radon measurement and soil natural thermoluminescence measurement grooves are basically similar (Fig. 1). It can be seen from Fig. 1(b) that there are two methods of overlapping anomalies at the -20~2O point, which is the reflection of the No. 92 tectonic belt on the surface, and the amplitude of the groove is measured by thermoluminescence and helium. Small, so it is speculated that the ore-bearing property of the place is not good; at the point of 3O ~ 5O, the anomaly measurement of helium is obvious, but the thermoluminescence measurement has no abnormal display, and is the position where the 92-type structural zone passes. At the position of the 50~7O point, the soil natural thermoluminescence measurement has an abnormal display; in the range of 70 to 200 points, the groove changes of the two methods are relatively large, and the line abnormality coincides well. As can be seen from Fig. 1(a), the range of the abnormality of the thermoluminescence measurement groove is smaller than the range of the abnormality of the helium measurement groove. There are three approximately parallel vertical secondary ore-bearing structural belts in the range of points 5O to 11O in Fig. 1(c), but they are all between the first-order structures and the ore bodies are rich. It can be seen from the measurement results that the radon measurement and the soil natural thermoluminescence measurement reflect the deep underground information, especially the soil natural thermoluminescence method utilizes the long-term accumulation effect of radiation irradiation, which is very stable and can better reflect the uranium mineralization information. According to the above-mentioned known data, in the range of 120-200 points, the abnormal amplitude of thermoluminescence measurement and radon measurement is large, and the agreement is good. It is speculated that there is a uranium ore body in the underground corresponding to the anomaly, and the ore is present. The body is richer and buried shallower.

The 15th line is 200m long and is located in the unknown area 120m southwest of the 21st line. The shape of the two curves on the line is basically similar, and the abnormal coincidence is better (Fig. 2). Comparing the data of known profiles with the measured results, it is speculated that in the range of 10 to 10 points, the anomalies of the two methods are reflected in the fracture zone of No. 92 mineralized structure; there is a compound at the point of 20 to 90 The anomaly may be caused by the ore-bearing structure of the No. 86 tectonic belt and the next level. The anomaly amplitude based on the two methods is large. It is concluded that the ore body may be shallower and the ore-bearing may be more Good; in the range of 90-130, the anomaly coincidence of radon measurement and soil natural thermoluminescence measurement is very good, which may be the reflection of the secondary ore-bearing structure of the No. 86 structural belt on the ground, and the ore-bearing potential may be better.

(2) Test results of known sections in Xiaoshui Mining Area

The type of mineralization in the Xiaoshui mining area belongs to the “intersection point” type uranium mineralization, and the No. 8 line is located in the mining area with a length of 140 m. The two curves of radon measurement and soil natural thermoluminescence measurement have different shapes and have different characteristics (Fig. 3). The characteristics of the radon measurement curve are relatively simple, and can be divided into two jump bands of 0 to 50 points and 60 to 130 points. It can be seen from the known geological section that the 0 to 50 point jump zone corresponds to a smaller tectonic zone; and the 60 to 130 point jump zone corresponds to a larger tectonic zone, and This tectonic belt is closely related to uranium mineralization. The natural thermoluminescence curve of the soil is relatively simple, except that there is a change zone in the range of 20 to 120 points, and the main jump zone is in the range of 20 to 70 points. The jump point corresponds to a depth of about 60 m at the top. Uranium ore body. It is known from the known geological section that the ore body is produced along the tectonic belt and its projection width on the ground is about 40 m.

The measurement results of this section show that when the uranium ore body occurs at the intersection of the tectonic fracture zone and the diabase vein, the radon measurement mainly reflects the location of the structural fracture zone, and the anomaly of the soil natural thermoluminescence measurement reflects The location of the "intersection" type uranium ore body.

Third, discussion

Figure 1 and Figure 2 represent the main uranium deposits in the uranium deposits in the upright structural fracture zone, while Figure 3 shows another major uranium deposit in the ore-bearing tectonic fracture zone and the intermediate-basic rock veins. Types of. These two different types of mineralization differ in the anomalous characteristics of the helium measurement and the soil natural thermoluminescence measurement curve.

It can be seen from the measurement section No. 21 of the 330 deposit that the output form of the uranium ore body in this area is quite special, and almost all of them are arranged in an upright column along the secondary structural fracture zone. The anomalies of natural thermoluminescence of the soil are spike-shaped, mainly reflecting the output position of uranium mineralization; the structural fracture zone is the channel of the helium gas migration, and the helium gas measurement mainly reflects the location of the structural fracture zone. When the two methods are anomalous, the ore body is more likely to produce. The verification results of the 15th measurement section confirm this. However, due to the complex geological conditions in the field, when radon measurements and soil natural thermoluminescence measurements are performed in unknown areas, their abnormalities should be explained as long as the data is reliable. The two exceptions do not have to overlap completely, and a single exception should also be noticed.

It can be seen from the measurement section No. 8 of Xiaoshui Mining Area that the uranium ore body is produced and distributed at the intersection of the structural fracture zone and the intermediate-basic vein, which is the result of the interaction between the structural fracture zone and the intermediate-basic vein. The characteristics of this type of ore body in helium measurement and soil natural thermoluminescence measurement curve are very special. The anomaly of radon measurement clearly reflects the location of the structural fracture zone, while the anomaly of soil natural thermoluminescence measurement corresponds obviously. The location of the uranium ore body.

Fourth, the conclusion

After a large amount of practical research work on the silicified fracture zone type and the “intersection type” uranium deposit in the Xiazhuang uranium ore field, the following points were initially drawn:

(1) Helium measurement and soil natural thermoluminescence measurement The combination of two geophysical methods is an effective and inexpensive method for finding concealed granite-type uranium deposits and expanding old mines. In the silicified fracture zone uranium deposit, the anomaly measured by radon mainly reflects the location of the structural fracture zone, while the anomaly of the natural thermoluminescence measurement of the soil reflects the location of the uranium ore body. When the two anomalies coincide, the class is found. The possibility of uranium ore bodies is even greater. On the “intersection” type uranium ore body, the anomaly measured by radon reflects the location of the structural fracture zone, while the anomaly of the natural thermoluminescence measurement of the soil reflects the intersection of the structure and the intermediate-basic vein, and the location is usually It is the location of the "intersection type" uranium ore body, and the abnormalities of the two methods are basically not coincident.

(2) Through the completion of the “Application Research of Geophysical Prospecting and Prospecting Methods in Xiazhuang Uranium Ore Field”, a set of geophysical prospecting and ore-seeking models for “deep-deep-finding blindness” in Xiazhuang uranium ore field was initially established. The main method is helium. Measurement and soil natural thermoluminescence measurement two methods. It has been proved by practice that this combination is more effective. It has been applied to the “Xianshan Basin volcanic uranium deposit in the Nanxiong Basin of Guangdong Province and the Xiangshan volcanic rock type uranium deposit in Jiangxi Province. application.

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