Work experience

(1) Prospecting deployment and task selection

1. From early detailed investigation work in conjunction with geology in the mining area to carrying out area-wide census

Detailed investigation Although many achievements have been made in sexual work, sometimes geophysical prospecting cannot meet the geological requirements (for example, finding deeper mines, delineating ore bodies in detail, finding ore bodies with small physical differences, etc.). More importantly, this limitation It demonstrates the pioneering role of geophysical prospecting in discovering new mining areas and new deposit types. With the large-scale development of airborne geophysical prospecting and ground magnetic methods, geophysical prospecting has played a leading role in finding magnetic minerals. Some electrical methods (such as self-electricity and electrical profile methods) and radioactive method area measurements have been used to find non-ferrous metal minerals. Played a pioneering role. Since geophysical prospecting first carried out area surveys, great results were achieved in discovering new mineral deposits. From the late 1950s to the late 1970s, a large number of iron ore, copper ore, lead-zinc ore, polymetallic ore and other results were discovered or expanded. be proven.

2. From direct prospecting to both direct and indirect prospecting

With the changes in prospecting tasks in the mid-to-late 1960s, the method of direct prospecting with geophysical prospecting methods is no longer fully adaptable. ; Later, the task of looking for iron ore and copper-rich ore took over again, which alleviated this contradiction. By the 1980s, with the changes in geophysical prospecting tasks and the accumulation of experience, the idea of ??indirect prospecting using geophysical prospecting to identify mineralized alteration zones and various ore-controlling factors became increasingly clear, and then direct prospecting and indirect prospecting were proposed. strategic thinking. In terms of practice, geophysical prospecting requires mapping, studying ore-controlling structures, and researching and establishing geological-geophysical models of mineral deposits. Typical examples include the use of gravity, magnetic and electrical methods to successfully delineate rock masses related to ore control when searching for deep non-ferrous metal ores in the middle and lower reaches of the Yangtze River, Hunan, Guangxi and other places; seismic methods were also used in the Jiurui area of ??Jiangxi The method has been used to study hidden rock masses; in the old mine of Gejiu Tin Mine in Yunnan, gravity and electrical sounding were used to detect the hidden contact zone of the rock mass, thereby finding the large-scale tin polymetallic deposit in Gaosong with a depth of 1,000 meters; when looking for gold deposits in Jiaodong and other places Electrical and magnetic methods are used to effectively trace the broken zones of gold-bearing ores under coverage. For many non-metallic minerals, indirect prospecting starts from the beginning. For example, when looking for diamond ores, magnetic methods are used to delineate kimberlite rock bodies; when looking for salt ores and gypsum ores, electrical methods, gravity and other methods are used to study structures, etc.

3. From only attaching importance to survey work to paying equal attention to the role of geophysical prospecting in detailed surveys and explorations

As mentioned above, in the late 1950s, the role of geophysical prospecting in geophysical prospecting was emphasized. The department has had the problem of not paying enough attention to the role of geophysical prospecting in detailed surveys and exploration, while geophysical prospecting in the industrial sector is better in this regard. In the 1980s, with the need to find blind mines, expand the scale of known deposits, and shorten the exploration cycle, the proportion of geophysical prospecting in detailed geological surveys and exploration has increased. Because this type of work is sometimes technically difficult, it is difficult for the geophysical team to have the geophysical force to do so. Moreover, since it is necessary to closely coordinate with the progress of the geological survey, it is difficult for the geophysical team to be on call at all times, making this aspect of work unsatisfactory.

4. From only conducting research on mining area data to carrying out regional mineralization prediction

Before the 1970s, comprehensive research on geophysical data was mainly conducted around field work reports, and then realized One explanation is often not deep and comprehensive enough. The data should be re-interpreted and re-understood, especially the secondary development of geophysical data in mining areas, which can lead to many new understandings and discoveries, and the effect will be twice the result with half the effort. Continuously researching and queuing up aeromagnetic-based anomalies, and screening out Class B anomalies that can be verified, is a model for this type of work. Since the late 1970s, the geophysical prospecting community has taken the initiative to use regional geophysical prospecting data of various scales to study regional ore-controlling structures, combine geological, geochemical prospecting, and remote sensing data to conduct mineralization predictions, and circle various levels (especially levels III and IV). The metallogenic zones and prospecting sections provide the most important basis for regional planning of mineral geology. This type of work (comprehensive mapping, comprehensive interpretation and mineralization prediction) is officially listed as an integral part of geological and mineral zoning work, and is included in the "Basic Requirements for Mineralizing Prospect Zoning (Trial)" issued by the Ministry of Geology and Mineral Resources in 1983.

Since the 1990s, all provinces and regions and seven key cross-provincial areas have carried out comprehensive mapping, interpretation and mineralization prediction. These results have become the basis for the deployment of geological prospecting work and the study of mineralization laws by geologists. valuable information.

5. Fully consider the results of regional geophysical and geochemical exploration when determining geophysical survey tasks and survey areas

Before the mid-1960s, the determination of geophysical survey tasks and survey areas It is mainly proposed based on existing geological data and experience. This often has certain limitations, which can result in insufficient basis for selection and unsatisfactory ore prospecting results. In the mid-to-late 1960s, geophysical surveys (including anomaly verification) deployed based on large-area aeromagnetic data, area-based geochemical data and geological data achieved good results. After the 1980s, the general survey of metal mineral exploration was mainly deployed based on regional geochemical prospecting, aeromagnetic, regional gravity and geological data, especially based on the results of comprehensive information mineralization prediction, so as to determine the ore to be prospected with more basis. species, possible types, main ore-controlling factors, possible distribution areas, etc. This can not only better delineate the prospecting work area, but also better determine the work tasks. The detailed investigation work is to delineate the survey area and select methods based on the results of geophysical and geochemical prospecting surveys, which will be more scientific and more effective. After the 1990s, the general survey of metal mineral prospecting (1:10,000 to 1:20,000) was mainly based on comprehensive information to demarcate prospecting areas, which were generally slightly larger than the anomaly range of geochemical prospecting and could better utilize geophysical prospecting to find hidden potential. The role of mines and blind mines. These have been reflected in the "Work Requirements for Geophysical Exploration and Geophysical Exploration of Solid Minerals" issued by the Ministry of Geology and Mineral Resources in 1989.

(2) Only by selecting appropriate and optimized combinations of methods can the advantages of geophysical prospecting be truly realized

There have been some twists and turns as to which combination of geophysical prospecting methods is the best for prospecting. In the early 1950s, there was a practice of using magnetic method, self-electricity and electrical profile method in non-ferrous metal ores, some of which were successful; some were disseminated or non-magnetic ores, and the "three treasures were combined". "Put" does not work well. Later, in order to conduct a rapid census, the method was relatively simple, and the same method was used for both census and detailed investigation, but it failed due to multiple solutions. For example, in the 1950s, a study was conducted on cases where strong magnetic anomalies confirmed the absence of magnetite. After measuring the physical properties, it was found that basic rocks, ultrabasic rocks, and some volcanic rocks are all very magnetic; another example is that in the mid-1950s, After using the self-electricity method to work on a large scale, a large number of non-mineral anomalies were encountered. Another example is the equipotential line method, which also found a large number of non-mineral anomalies, and no minerals were found in many verified anomalies. By the end of the 1950s and the beginning of the 1960s, from the study of physical properties and the accumulation of experience in verifying anomalies, we realized the multi-explanatory nature of geophysical anomalies, and therefore attached great importance to the use of comprehensive methods. Anomalies found during the census should be checked using another method; in many cases, several methods are used to conduct targeted surveys in order to find multiple types of minerals and provide comprehensive explanations. There have also been situations where too many methods and parameters were duplicated in the same area and at the same time in general and detailed surveys. Generally, method effectiveness tests should be conducted on known mines before work in order to select the appropriate method.

By the 1980s, due to a large amount of practice, research on the geological and geophysical characteristics of various mineral deposits and understanding of some foreign geophysical models of mineral deposits, our country's geophysical workers had basically We have mastered the geological and geophysical characteristics of the main mineral deposits in my country, established a geological-geophysical model of the known mineral deposits, and then summarized and deduced the geological-geophysical model of the mineral deposits to be found. Based on this, we can select methods more scientifically. scale, accuracy, etc., and can predictably consider surveying new types of mines and new mineral species.

(3) When interpreting geophysical data, the complexity of geological conditions and the uncertainty of geophysical interpretation must be fully estimated.

The first thing encountered in direct prospecting is the qualitative nature of anomalies. , whether it is caused by minerals, and then make inferences about the shape, occurrence, burial depth, etc. of the abnormal body. There are multiple solutions and uncertainties in both qualitative and quantitative inferences, the complexity of the geological situation (the surface and underground geological phenomena are inconsistent, the known mines are not the only types in the work area, what you can see with the naked eye does not exist microscopically, etc. ), all of which increase the difficulty and complexity of geophysical interpretation.

The main experiences in geophysical anomaly interpretation are as follows.

1. From the known to the unknown, pay attention to the discovery of new types of minerals and new mineral species

“From the known to the unknown” is a commonly used and effective basic method in explanation. Since there may be several mineral species and types in an area, and there may be ones that are different from known minerals, it is necessary to pay attention to those anomalies that are different from the known mineral anomalies, and are located in different geological environments or mineralization characteristics. It cannot be simply denied. For example, the Wushan Copper Mine in Jiangxi, the Tonglushan Copper Mine in Hubei, the Ximaanshan Copper Mine in Anhui, and the Yulong Copper Mine in Tibet were all initially prospected as iron ores. However, it was only after verification of magnetic anomalies that the copper ores were found to be more valuable than iron ores. value. For another example, the Qixiashan lead-zinc mine in Jiangsu was originally a small-scale manganese mine. A large-scale lead-zinc mine was discovered after verification of electromagnetic and geochemical anomalies. For another example, the Daxigou Iron Mine in Shaanxi was first treated as magnetite based on aeromagnetic anomalies, but the scale was very small. Then geologists identified the existence of siderite, which was much larger than magnetite. Hebei Fanshan Phosphate Mine first worked as an iron ore. When magnetic anomalies were verified, thick phosphate ore bodies were found in the depths and reached a large scale.

2. Be good at analyzing the complexity of mineralization geological conditions

Surface geological conditions are of great significance to the qualitative explanation of geophysical anomalies, but the measured anomalies are geological bodies in both vertical and horizontal directions. In the superposition field, in addition to separating superposition anomalies, we must also fully understand the complexity of geological conditions. For example, at the Baiyinnuoer skarn-type lead-zinc mine in Inner Mongolia, new ore bodies were found under the volcanic rocks in the southwest of the mining area through induced electricity, and the reserves were expanded to millions of tons. There are many cases like this when looking for iron ore. The surface is volcanic rock or diorite, but contact iron ore is found underground. Another example is the geochemical exploration anomaly of the Bajiazi lead-zinc deposit in Liaoning, which only showed mineralization and has no industrial significance. Later, electrostatic survey, magnetic survey and geochemical prospecting were put into use, and blind ores were found based on electrostatic and other anomalies, reaching a medium size or above. Another example is the Shanmen Silver Mine in Jilin. After first using IP, magnetic methods, and geochemical prospecting, IP anomalies were discovered. It was believed that the primary IP anomalies were caused by graphitization and pyritization, and the secondary anomalies may be caused by sulfide minerals. It was verified in 1982 to find gold deposits. At that time, silver was not analyzed and the gold deposit had not been broken through. After analyzing silver in 1984, it was found that graphitized and pyritized marbles are silver-containing mineral layers, and the silver reserves reached a large scale.

3. Pay attention not only to medium and strong anomalies, but also to weak and slow anomalies

In the early days of the work, strong magnetic anomalies were mainly studied. The explanation for the search for magnetic minerals in the 1970s came from the emphasis on , intensity abnormality to pay more attention to weak and slow abnormality, there are successful examples in many iron ore areas. Due to the influence of oblique magnetization and gentle ore bodies, the magnetic anomaly is slower and the positive anomaly deviates from the ore head. Failure to pay attention to this will cause the verification hole to be hollowed out. For example, Anhui Longqiao Iron Mine has learned this lesson. In the interpretation of complex anomalies that overlap multiple geological bodies (ore bodies) and complex shapes, it is necessary to study and extract weak and slow anomalies after separation. For example, the copper ore body in Xima'anshan, Anhui Province has a complex shape (crescent shape), and the anomalies are regular. However, no ore was struck in the center; later, through multi-hole verification and the reasonable application of in-hole geophysical prospecting methods such as in-hole radio wave method, combined with the re-interpretation of ground magnetic survey data, the ore body was finally delineated. Another example is that after extracting residual magnetic anomalies at the Hebei Shuichang and Beijing Shachang iron mines, they found ore bodies in deep synclines and expanded their reserves. There are similar lessons learned in the explanation of anomalies in methods such as gravity, self-electricity, and induced electricity.

4. In the qualitative explanation of anomalies, pay attention to the measured physical properties, combine quantitative forward and inverse data, and use comprehensive methods as much as possible

In the early stage of the work, the "simple comparison method" is mainly used to Anomalies are compared with surface geology or geological bodies shown on geological maps, and then qualitative explanations are made without actual measurement of physical properties. There have been many success stories in doing so, but there have also been many mistakes. For example, in the early verification of aeromagnetic anomalies in the Daxinganling Mountains, it was believed that the acidic volcanic rocks seen on the surface could not cause strong magnetic anomalies. After drilling, they were still volcanic rocks. Only by measuring physical properties did we find that the acidic volcanic rocks in the area have a large residual magnetism. For another example, the magnetic anomalies in Dahongshan in Yunnan and Meishan in Jiangsu are located in volcanic rock areas, and were inferred to be rock mass anomalies. After physical properties were measured in the anomaly areas and semi-quantitative forward and inversion calculations were performed, it was concluded that the anomalies were likely to be iron ore deep underground. Finally, Verify seeing a large iron mine. There are similar cases in other regions. It started with magnetic methods, and later gravity, electrical methods, etc. also paid attention to measured physical properties to determine abnormal properties.

When the surface is covered, in order to determine the possible causes of anomalies, using comprehensive data to reduce multiple solutions has been a successful experience for many years. The comprehensive explanation of geophysical anomalies and geochemical anomalies has a great qualitative effect on the anomalies of various non-ferrous metal mines; The comprehensive interpretation of gravity and magnetic survey data is very effective in qualitative and quantitative inference of magnetic iron ore; the comprehensive interpretation of resistivity method, autoelectricity, magnetic method anomalies and electrostatic anomalies is very effective in determining whether it is a sulfide mineralization body. Examples of this are many and known.

5. It is necessary to fully estimate the complexity of geophysical explanations (qualitative and quantitative explanations) of anomalies

Quantitative and semi-quantitative inferences under the conditions of complex shapes and various interferences It is much more difficult than inference under simple shapes and simple conditions, and its reliability is reduced or even errors may occur. For example, the Dahongshan Iron Mine in Yunnan has multiple layers of superimposed anomalies. It was initially inferred that the burial depth was only about 100m, but when it was drilled to 450m, only a thin ore layer of nearly 3m was found. After decomposing the anomaly into three levels, it was inferred that the main ore body was below 340m. , and finally saw the 181m main ore body at 590m. Another example is that the Tiantang Polymetallic Mine in Guangdong was not discovered during verification in 1961 due to an incorrect judgment of its occurrence. The Beichagoumen Lead-Zinc Mine in Hebei also failed to study the occurrence of induced electric anomalies even though the occurrence was verified. The main ore body was discovered after many years of delay based on electrostatic anomalies. There are many examples of incorrect quantitative inferences leading to failed verification. In particular, the lack of reliable prior geological knowledge, a single method, and imprecise inferences will all make the interpretation unreliable.

(4) Experience in anomaly verification

The purpose of anomaly verification is to identify the subject of the anomaly source and its mineralization properties. Verification of anomalies is the only way to confirm inferred conclusions. It is a key link in whether geophysical prospecting is effective or not, and it is also the last link in direct geophysical prospecting. After a large number of anomalies are screened and studied, the ones with the most prospecting prospects are selected and submitted for verification. The essence of screening research is the process of qualitative and quantitative explanation of anomalies. The more scientific the explanation, the more reliable the conclusion, and the more ideal the verification results will be.

Cutting off the work before identifying the main body of the anomaly source and the main mineralization characteristics, and lacking the spirit to persevere in verifying the anomaly, are often one of the reasons for the delay in the discovery of many mineral deposits.

The Ministry of Geology and Mineral Resources formulated the "Measures for the Management of Geophysical and Geochemical Exploration Anomalies and Verification Work" in 1983, which basically established the relevant technical requirements and management system for verification, and provided unified standards for anomaly classification and verification work. Facilitated anomaly verification work. Then, in 1993, the Ministry of Geology and Mineral Resources formulated the "Requirements and Assessment Standards for Anomaly Verification of Geophysical and Geochemical Exploration" to further standardize the verification work of anomalies.

How can we most effectively verify anomalies and avoid detours? We have a lot of experience and lessons, mainly as follows.

1. The degree of abnormality verification is divided into three levels (Level III is reconnaissance inspection, Level II is detailed inspection, and Level I is engineering verification)

Generally, it should be carried out step by step and upgraded step by step. , but the key is Level III. Level III inspection will classify the abnormality as a non-mining abnormality (Category D), and the abnormality will no longer be taken seriously for a long time. Although the work should generally be carried out according to the gradual upgrade method, there are some cases ( For example, if mineralization or ore body outcrops have been seen on the surface, it can also go from level III to level I. For some complex situations, there are often multiple verification processes from level III to level II or multiple level I. For example, Guangdong Paradise. The verification of the polymetallic mine in 1961 failed due to errors in inferring the occurrence of the ore body; in 1967, systematic work was carried out and verification was carried out again, and the ore body was finally hit at 300m. Another example is the Yangerzhuang Iron Mine in Hebei due to neglect of slope. Due to the influence of magnetization, the location of the ore body was inferred incorrectly, and no ore was found in the three holes. The ore was only hit after verification.

2. Verify the reason why the abnormal first hole (or first batch of holes) did not find the ore. Make specific analysis

Except for non-mining anomalies, there are often cases where the inference is wrong and the construction location is not in place, resulting in no ore being found in the first hole.

Common problems in inference include: complex ore body shape (such as Ma'anshan copper mine in Anhui Province); excessive error in inferred burial depth (such as Tianhu Iron Mine in Xinjiang); incorrect inference of ore body occurrence (such as Tiantang Polymetallic Mine in Guangdong) ; Affected by oblique magnetization, the ore body does not correspond to positive anomalies (such as Yangerzhuang Iron Mine in Hebei Province and Longqiao Iron Mine in Anhui Province); drilling happens to be at the point where the ore body pinches out (there are many examples of this in iron ores, and once Use in-hole magnetic survey to discover blind ore beside the hole); when using comprehensive anomalies, the main anomaly is improperly selected (for example, the Dongxing Salt Mine in Anhui first arranges holes according to the center of the gravity anomaly to find no ore, and then arranges holes according to the type of electrical sounding curve to see the salt layer ); Another example is the magnetic anomaly of the Huangshaping lead-zinc mine in Hunan. At first, only iron ore was found. Later, it was confirmed that the self-electricity anomaly was found. Lead-zinc ore was also found, thus opening up the situation; another example is the early stage of the Zhangjiawa iron mine in Shandong. Gravity and magnetic anomalies were found during the work. The gravity anomalies were first verified and only diorite and skarn were found, but no further investigation was conducted. After many years, the magnetic anomalies were verified again before the ore body was discovered.

There are even more cases where the construction is not in place and the purpose of verification is not achieved. Some verifications failed because the construction unit did not drill according to the anomalies suggested by geophysical prospecting (for example, the Qibaoshan copper and polymetallic mine in Liuyang, Hunan, was drilled according to anomalies and found minerals, but the last four holes were drilled according to the exploration mesh, and no minerals were found); Although some holes were laid on the anomalies, the direction of the oblique holes was not designed correctly, and the ore could not be drilled; in other cases, the holes were drifted during drilling construction and passed along the edge of the ore layer; and in some cases, the verification holes did not reach the designed depth and drilling was stopped. Those that fail to achieve the purpose of verification.

3. Dare to persist in verifying promising anomalies to the end

There are some verification holes where no ore is found in the first hole, and the cause of the anomaly cannot be explained (there are many such examples, For many reasons (as mentioned before), the discovery of the mine was delayed for many years because they were afraid of taking risks and did not dare to verify it again. For example, it took many years to find the main ore body in Xiangyang Iron Mine in Anhui, Xishangzhuang Iron Mine in Shandong, and Shachang Iron Mine in Beijing. There are some anomalies in which the main ore body was discovered only after drilling several holes. For example, the main ore body was discovered only after the eighth hole in the Wangwangzhuang Iron Mine in Shandong, the Ashele Copper Mine in Xinjiang, the Longqiao Iron Mine in Anhui, and the Kangjiawan Iron Mine in Hunan were hidden. In lead-zinc mines, the ore or main ore body is only seen in the seventh hole. There are also many examples of mineral anomalies where the ore (or main ore body) was discovered only after drilling 2 to 4 holes.

4. Pay attention to the re-interpretation after verification, geophysical and geochemical exploration in the well

After verification, it is a scientific attitude to re-interpret the anomaly based on the geological conditions of the borehole and measured physical property data. and courage. When re-explaining after verification, you must first determine whether the verification has achieved its purpose. If it has not achieved its purpose, you must find out the problems in the verification. The ore observer should determine whether the anomaly is caused by the ore encountered during drilling, whether there is any blind ore that has not yet been discovered, and provide suggestions for laying new verification holes. The actual problem is that after the geological units are verified, there are few dedicated personnel to systematically reinterpret the geological units, and few geophysical exploration teams are arranged to conduct it. Due to reasons such as insufficient attention to this work and specific organizational work, it is often difficult to explain in a timely manner after verification.

After verification, in-hole geophysical and geochemical exploration should be carried out regardless of whether ore is found or not. It will be better able to discover blind ores beside the well and at the bottom of the well, which will be helpful for the final determination of abnormal properties and further expansion of the search. Mine clues are of great significance. my country's in-hole magnetic survey has found ore bodies and blind ore bodies that were missed when verifying abnormality in many iron and copper mining areas, thereby increasing the success rate of verification. In-hole geophysical exploration methods such as in-hole electromagnetic waves, in-hole radio waves, and well-ground transient electromagnetic methods have all played an important role in verifying anomalies and finding blind ores underground.