A four-point prospecting method and system for iron-rich ore in thick overburden areas

Abstract

The present invention discloses a four-point prospecting method and system for iron-rich ores in thick-covered areas, which relates to the field of deep prospecting technology in geological exploration. The method comprises the following steps: delineating prospecting areas based on aeromagnetic anomaly maps and Bouguer gravity anomaly maps; obtaining polarized magnetic anomaly maps and residual gravity anomaly maps based on aeromagnetic anomaly data and Bouguer gravity anomaly data, and determining key anomaly areas; laying out gravity and magnetic profiles in key anomaly areas, establishing a preliminary inversion model, obtaining optimal geological information through multiple gravity and magnetic joint inversions, and determining prospecting target areas; determining target layer positions and faults within the prospecting target areas, and delineating geological body stratification boundaries; and identifying low-resistance anomaly features using wide-area electromagnetic methods, obtaining low-resistance anomaly areas, and determining the buried depth of the ore body. The present invention has the characteristics of accurate information recognition, high positioning accuracy, and a large detection depth, effectively solving the technical difficulties in prospecting for iron-rich ores in thick-covered areas.

Description

Technical Field

[0001] The present invention relates to the technical field of deep prospecting in geological exploration, and in particular to a four-point prospecting method and system for iron-rich ores in thick-covered areas. Background Art

[0002] Iron accounts for a significant portion of metal consumption, accounting for approximately 95% of total metal consumption. Furthermore, steel products are widely used in all aspects of modern life, serving as a vital pillar of social development and a key metal material for modern industry. However, the supply of iron ore resources is tight, and the supply has long been unable to meet the demand for steel production. While significant potential remains for iron ore exploration deep within major mineralization belts, the depth of the deposits and the limited surface visibility make prospecting extremely challenging. Consequently, accurate and efficient methods are urgently needed to identify hidden iron ore deposits in thickly covered areas.

[0003] The existing prospecting methods generally use geophysical methods, which mainly include regional gravity and magnetic survey methods, large-scale gravity and magnetic survey methods, two-dimensional seismic methods, and wide-area electromagnetic methods. Among them, the regional gravity and magnetic survey method can only delineate the approximate prospecting range by observing and analyzing gravity and magnetic anomalies caused by differences in rock (ore) density and magnetism, but cannot accurately locate ore bodies. The large-scale gravity and magnetic survey method uses potential field conversion processing and forward and inverse calculations to extract geological information and determine prospecting targets, but it only targets key areas. If the key areas are not selected accurately, potential ore bodies may be missed. Under complex geological conditions, it is difficult to accurately delineate prospecting targets. The two-dimensional seismic method uses the velocity distribution of seismic waves in different lithologies to delineate the boundaries of major geological bodies. However, in actual applications, seismic wave propagation is interfered with by various factors, such as the heterogeneity of the underground medium and the undulating terrain, resulting in the inability to effectively identify some geological bodies. The wide-area electromagnetic method identifies the low-resistance anomaly characteristics of metal sulfides from the high-resistance surrounding rock, thereby obtaining information on hydrothermal alteration activity related to deep concealed rock bodies and then determining the buried depth of the ore body. However, since this method cannot delineate the approximate prospecting range and target area, it cannot fully understand the geological conditions, which affects the accuracy of prospecting.

[0004] It can be seen that the various existing geophysical prospecting methods have limitations. In thick-covered areas, due to the deep burial of the ore deposits and weak surface information, it is difficult to effectively identify hidden iron ore deposits, accurately delineate the target area for rich iron ore prospecting and determine its burial depth. It is difficult to meet the prospecting needs under complex geological conditions. In addition, the existing technology is difficult to effectively combine the above-mentioned various geophysical prospecting methods and it is difficult to integrate their respective advantages, resulting in the current low accuracy of prospecting. Summary of the Invention

[0005] In response to the shortcomings of the existing technology, the present invention provides a four-position prospecting method and system for iron-rich ores in thick-covered areas. The present invention uses four comprehensive geophysical exploration methods, namely gravity, magnetic, electric, and seismic, to search for skarn-type iron-rich ores in thick-covered areas. It has the characteristics of high positioning accuracy, large detection depth, and good prospecting effect.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a four-point prospecting method for iron-rich ores in thick overburden areas, comprising:

[0008] According to the aeromagnetic anomaly map and Bouguer gravity anomaly map, aeromagnetic anomaly data and Bouguer gravity anomaly data are obtained, and the effective magnetic anomaly range is determined, and the prospecting prospect area is delineated according to the effective magnetic anomaly range;

[0009] Based on aeromagnetic anomaly data and Bouguer gravity anomaly data, we obtain polar magnetic anomaly maps and residual gravity anomaly maps, and identify key anomaly areas in prospecting areas; obtain geological information and determine initial prospecting targets; lay out gravity and magnetic profiles in key anomaly areas, establish a preliminary inversion model, and obtain optimal geological information through multiple gravity and magnetic joint inversions to determine prospecting targets;

[0010] Calibrate the formation velocity value in the prospecting target area, calculate the target layer burial depth data, determine the target layer position and fault, and delineate the geological body stratification boundary;

[0011] Based on the stratification boundaries of geological bodies, the wide-area electromagnetic method is used to identify low-resistance anomaly characteristics, obtain low-resistance anomaly areas, and determine the buried depth of the ore body.

[0012] As a further technical solution, the magnetic anomaly characteristics are obtained based on the aeromagnetic anomaly data, and the effective magnetic anomaly range is determined in combination with the Bouguer gravity anomaly data. According to the effective magnetic anomaly range, the anomaly areas are respectively delineated on the aeromagnetic anomaly map and the Bouguer gravity anomaly map, and the superposition of the two anomaly areas is the prospecting prospect area.

[0013] As a further technical solution, the aeromagnetic anomaly data is subjected to polarization processing to obtain polarized magnetic anomaly data, and a polarized magnetic anomaly map is generated; the Bouguer gravity anomaly data is subjected to a sliding average method to obtain regional gravity anomaly data, and the regional gravity anomaly data is subtracted from the Bouguer gravity anomaly data to obtain residual gravity anomaly data, and a residual gravity anomaly map is generated.

[0014] As a further technical solution, the drill column charts on the gravity and magnetic profiles are connected and assigned density and magnetic parameters. The Bouguer gravity anomaly is forward calculated according to the density of the geological information of the remaining sections, and then the contact relationship between the strata and rock masses is inverted to establish a preliminary inversion model; the preliminary inversion model is fine-tuned using magnetic parameters, and the polarized magnetic anomaly data is forward calculated. The preliminary inversion model is then modified again in combination with the Bouguer gravity anomaly data and the residual gravity anomaly data. Finally, the optimal geological information is obtained through multiple gravity and magnetic joint inversions, and the prospecting target area is determined.

[0015] As a further technical solution, a two-dimensional seismic profile is arranged on the prospecting target area, and combined with the drilling information, the correspondence between the main stratigraphic boundaries and the seismic profile reflection phase axis is constructed, and the stratigraphic velocity value is calculated by the depth of the target layer and the time value of the seismic time profile next to the borehole.

[0016] As a further technical solution, the reflection wave time of the target layer is obtained according to the laid-out two-dimensional seismic profile, and the target layer burial depth data is obtained by combining the formation velocity value with the time-depth conversion formula.

[0017] As a further technical solution, a wide-area electromagnetic apparent resistivity section is obtained by the wide-area electromagnetic method. In the wide-area electromagnetic apparent resistivity section, with high resistivity as the background, the low-resistance anomaly features are U-shaped contour lines, V-shaped contour lines or strip shapes.

[0018] In a second aspect, the present invention provides a four-point prospecting system for iron-rich ores in thick overburden areas, comprising the following modules:

[0019] The qualitative module is configured to obtain aeromagnetic anomaly data and Bouguer gravity anomaly data based on the aeromagnetic anomaly map and the Bouguer gravity anomaly map, determine the effective magnetic anomaly range, and delineate the prospecting area based on the effective magnetic anomaly range;

[0020] The targeting module is configured to: obtain polar magnetic anomaly maps and residual gravity anomaly maps based on aeromagnetic anomaly data and Bouguer gravity anomaly data, and identify key anomaly areas in prospecting areas; obtain geological information and determine initial prospecting targets; lay out gravity and magnetic profiles in key anomaly areas, establish a preliminary inversion model, obtain optimal geological information through multiple gravity and magnetic joint inversions, and determine prospecting targets;

[0021] The layer determination module is configured to: calibrate the formation velocity value in the prospecting target area, calculate the target layer burial depth data, determine the target layer position and fault, and delineate the geological body layer boundaries;

[0022] The depth determination module is configured to: based on the geological body stratification boundaries, use the wide-area electromagnetic method to identify the low-resistance anomaly characteristics, obtain the low-resistance anomaly area, and determine the buried depth of the ore body.

[0023] One or more technical solutions of the present invention have the following beneficial effects:

[0024] The present invention is based on the four geophysical prospecting methods of gravity, magnetism, electricity and seismic. Through qualitative analysis - delineating prospecting areas, target determination - determining prospecting target areas, layer determination - delineating the stratification boundaries of major geological bodies, and depth determination - determining the buried depth of rich iron ore, the four physical prospecting methods are effectively combined, realizing prospecting based on the organic combination of geology, geophysical prospecting and drilling, solving the problem that various geophysical prospecting methods in the prior art are difficult to effectively combine. In addition, the four-determination prospecting method provided by the present invention has the characteristics of accurate information recognition, high positioning accuracy and large detection depth, which effectively solves the technical problems of prospecting rich iron ore in thick coverage areas. On the other hand, it can solve the limitation problems of existing geophysical prospecting methods in use and meet the prospecting needs under complex geological conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0026] Figure 1 This is a flow chart of the four-point prospecting method of the present invention;

[0027] Figure 2 This is the 1:50,000 aeromagnetic anomaly map of the Qihe-Yucheng area of ​​the present invention;

[0028] Figure 3 This is the 1:50,000 local Bouguer gravity anomaly map of the Qihe-Yucheng area of ​​the present invention;

[0029] Figure 4 This is the polar magnetic anomaly map of Laiwu area of ​​the present invention;

[0030] Figure 5 This is the residual gravity anomaly map of Laiwu area in the present invention;

[0031] Figure 6 is a 2.5D joint inversion inference diagram of the gravity and magnetic profile of the present invention, wherein (a) is the profile magnetic survey curve; (b) is the profile gravity curve; and (c) is the 2.5D gravity and magnetic joint inversion inference geological interpretation profile.

[0032] Figure 7 This is a schematic diagram of a two-dimensional seismic depth profile of the present invention;

[0033] Figure 8 This is a schematic diagram of the wide-area electromagnetic apparent resistivity cross section of the present invention. DETAILED DESCRIPTION

[0034] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0035] Example 1

[0036] like Figure 1 As shown, this embodiment provides a four-step prospecting method for iron-rich ores in thick overburden areas. Prospecting is achieved through four steps: characterization, target determination, layer determination, and depth determination. The specific steps of the method are as follows:

[0037] S1: Qualitative: According to the aeromagnetic anomaly map and the Bouguer gravity anomaly map, obtain the aeromagnetic anomaly data and the Bouguer gravity anomaly data, and determine the effective magnetic anomaly range, and delineate the prospecting prospect area according to the effective magnetic anomaly range.

[0038] According to geological data, skarn-type iron-rich deposits in western Shandong are primarily located at the interface between intermediate-basic intrusive rocks and host rocks during the Yanshanian Period of the Mesozoic Era. These intrusive rocks primarily include gabbro diorite, biotite diorite, and diopside diorite, while the host rocks are the Majiagou Group limestone. Mineralization is most pronounced in rock masses, which occur as caprocks and sills. Mineralization is most favorable in the dipped areas of rock masses. Iron ore bodies are often found in xenolithic host rocks and at the intersections of rock masses. Locally raised areas and sudden changes in relief within layered intrusions are particularly important ore-controlling locations.

[0039] In step S1, Figure 2 and Figure 3 As shown in the figure, the prospecting areas are delineated based on the 1:50,000 aeromagnetic anomaly map and the 1:50,000 Bouguer gravity anomaly map. Specifically, according to the aeromagnetic anomaly data on the aeromagnetic anomaly map, the magnetic anomaly characteristics are as follows: the sedimentary strata are non-(micro)magnetic, and the resulting magnetic anomaly is negligible; Mesozoic diorite has medium-to-high magnetic characteristics, with a magnetic susceptibility κ varying between (100 and 5000)×10-64πSI and a residual magnetization intensity Jr ranging from (10 to 1000)×10-3A / m; magnetite is strongly magnetic, with an average magnetic susceptibility κ of 160,000×10-64πSI and an average residual magnetization intensity Jr of 180,000×10-3A / m; the magnetic parameters of the above geological bodies determine that rich iron ore appears as a high magnetic anomaly on the aeromagnetic anomaly map. Due to the varying thickness of the overlying strata, the resulting magnetic anomaly intensity also varies, making it impossible to determine a quantitative magnetic anomaly index. Therefore, in this embodiment, the effective magnetic anomaly range is determined in combination with Bouguer gravity anomaly data.

[0040] Based on the Bouguer gravity anomaly data on the Bouguer gravity anomaly map, gravity anomalies are characterized by density differences between different underground geological bodies (generally speaking, density values ​​for Quaternary < sandstone < limestone < diorite < magnetite), which cause iron-rich deposits to appear as high gravity areas on the Bouguer gravity anomaly map. Analysis of the magnetic and density parameters of rocks (or ores) indicates that gravity-magnetic homologous areas with high gravity and high magnetic properties have the potential to form rich iron deposits (effective magnetic anomaly range). Based on the effective magnetic anomaly range, anomaly areas are delineated on both the aeromagnetic anomaly map and the Bouguer gravity anomaly map. The superposition of these two anomaly areas represents prospective areas.

[0041] In this embodiment, based on the above method, Figure 2 and Figure 3 As shown, the Qihe-Yucheng area, Zibo Jinling area, Laiwu Zhangjiawa area, Liaocheng Xuying area and other iron-rich ore prospecting areas can be identified in the deep coverage area of ​​western Shandong.

[0042] S2: Targeting: Based on aeromagnetic anomaly data and Bouguer gravity anomaly data, obtain polar magnetic anomaly maps and residual gravity anomaly maps, and determine key anomaly areas; obtain geological information and determine initial prospecting target areas; lay out gravity and magnetic profiles in key anomaly areas, establish a preliminary inversion model, obtain the best geological information through multiple gravity and magnetic joint inversions, and determine prospecting target areas.

[0043] In step S2, the aeromagnetic anomaly data is polarized to obtain Calculate the polar magnetic anomaly data and generate Figure 4 The pole magnetic anomaly map shown in the figure is used; the sliding average method is used to obtain the regional gravity anomaly data for the Bouguer gravity anomaly data, and the regional gravity anomaly data is subtracted from the Bouguer gravity anomaly data to obtain the residual gravity anomaly data, and the following is generated: Figure 5 The residual gravity anomaly map is shown.

[0044] Since skarn-type iron-rich ores are produced in and near the contact zone between intermediate-acidic intrusions and carbonate rocks, skarns are often seen near the ore bodies. Intermediate-acidic intrusions are magnetic, and obvious magnetic anomalies can be observed, while carbonate rocks are not magnetic. Therefore, the secondary magnetic anomalies superimposed on the transition zone between the calm magnetic field of carbonate rocks and the magnetic field of the intrusions become the hallmark of magnetic surveying for such iron ores. Therefore, key anomaly areas are usually shown on the polarized magnetic anomaly map as transition zones from strong magnetic anomalies to low negative anomalies, i.e., low-slow magnetic anomaly distribution areas. Areas with higher magnetic anomaly values ​​are often where rock masses are located, and areas where multiple magnetic anomaly contour lines bulge out simultaneously are usually target areas for rich iron ores. For example, Figure 4 shown.

[0045] The key anomaly area is shown on the Bouguer gravity anomaly map as the fluctuation and turning of the step belt near the high value area of ​​the contour line, or the side where the gradient of the contour line changes slowly in the same direction. The key anomaly area is shown on the residual gravity anomaly map as the edge of the center of the local high value gravity anomaly. The center of the residual gravity anomaly is usually the location of the rock mass. Figure 5 shown.

[0046] In step S2, the areal aeromagnetic anomaly data and the Bouguer gravity anomaly data are subjected to potential field conversion processing such as polarization, upward continuation, horizontal gradient modulus, horizontal first-order derivative, and vertical second-order derivative, thereby obtaining geological information such as the underground structure, stratum distribution, and rock intrusion in the thick overburden area. Furthermore, the zero value line of the vertical second-order derivative of the gravity and magnetic field and the boundary line between positive and negative anomalies of the residual gravity anomaly are used to determine the range of rock intrusion. The spatial distribution of strata and rock masses is interpreted using upward continuation data at multiple heights. The development of fault structures is inferred using maps such as gravity and magnetic field anomaly morphology, horizontal gradient, and horizontal first-order derivative. Based on the inferred and interpreted geological information, the initial prospecting target area is determined.

[0047] In step S2, a 1:10,000 or 1:5,000 gravity and magnetic profile is laid out in the key anomaly area. The purpose is to use physical property data and known drill holes as constraints to perform 2.5D gravity and magnetic joint inversion and interpretation to obtain relevant information about the deep target geological body, thereby determining the prospecting target area. Specifically, the existing drill hole histograms on the gravity and magnetic profile are first connected and assigned density and magnetic parameters. The Bouguer gravity anomaly is forward calculated based on the density of the geological information in the remaining area, and the contact relationship between the strata and rock bodies is inverted to establish a preliminary inversion model. The preliminary inversion model is then fine-tuned using magnetic parameters, and the polarized magnetic anomaly data is forward calculated. The focus is on adjusting the diorite intrusion range to the location of the iron ore body. The skarn belt is distributed at the contact between the diorite and carbonate rock formations and is associated with magnetite. The preliminary inversion model is then modified by combining the Bouguer gravity anomaly data and the remaining gravity anomaly data. Finally, the optimal geological information is obtained through multiple gravity and magnetic joint inversions, and the prospecting target area is determined.

[0048] According to the above method, a rich iron ore prospecting target area was identified in the thick cover area of ​​Shijiaquan, Laiwu, and drilling verification was carried out. The prospecting effect was good, which proved the effectiveness of large-scale gravity and magnetic measurements in targeting rich iron ore in thick cover areas. Figure 4 、 Figure 5 They are the polarized magnetic anomaly map and the residual gravity anomaly map of Laiwu area. According to the above method, the key anomaly areas are first delineated, and gravity and magnetic profiles are laid out in the key anomaly areas. Figure 6 is the 2.5D gravity and magnetic joint inversion inference interpretation map.

[0049] This profile crosses the known exploration lines of the Shijiaquan Mining Area (50-350 m), the Liuxinggou Mining Area (1200-2160 m), and the Liuwangmiao Mining Area (5120-5360 m). These areas are controlled by known drill holes, and the profile was inverted and interpreted according to the principle of inference from the known to the unknown. The gravity curve gradually rises from west to east, reflecting the gradual thinning of sedimentary strata and the gradual shallowing of rock mass depth. As shown in Figures 6 (a) and (b), the local high-value anomalies in the magnetic curve are the result of the combined effects of diorite undulations and skarn magnetite. The magnetic anomaly in the profile decreases rapidly around 3700 m, inferred to be the diorite intruding into the Ordovician limestone from west to east, where the intrusive diorite was annihilated. The curve reaches its lowest value around 4800 m and then gradually rises, suggesting that the diorite at the base gradually thickens. According to the mineralization principle that "transition zones from high gravity anomalies and strong magnetic anomalies to low negative anomalies (areas with low and slow magnetic anomalies) are favorable locations for searching for iron ore deposits," two favorable mineralization locations exist on this profile. The two planned drill hole locations are shown in Figure 6 (c). Based on the results of 2.5D gravity and magnetic inversion, it is estimated that drill hole ZK1 (2870 m below the profile) will penetrate the Ordovician limestone at an elevation of approximately -500 m and enter the underlying intrusive rock mass, with a planned drilling depth of 700 m. Drill hole ZK2 (750 m below the profile) is expected to penetrate the Ordovician limestone at an elevation of approximately -800 m and enter the underlying intrusive rock mass, with a planned drilling depth of 1000 m. It is speculated that iron ore bodies are likely to exist at the interface between the diorite and limestone in these two drill holes, with ore intersecting depths of 670 m and 970 m, respectively.

[0050] Drilling verification was conducted in borehole ZK1, reaching a final depth of 750m. This borehole revealed altered diorite porphyry at depths of 488.1-501.9m. Both its roof and floor consist of Ordovician limestone, demonstrating the bedding-intrusion of diorite into the Ordovician limestone. Due to the thinness of the intrusive body, no iron ore bodies formed at this depth. Magnetite was observed at depths of 642.1-657.9m, with a thickness of 15.8m. A skarn zone was observed at depths of 654.6-655.9m. The ore body's roof consists of medium- to coarse-grained crystalline limestone, while its floor consists of altered pyroxene diorite. The magnetite layer exhibits a clear intrusive contact with the overlying limestone. The primary mineral compositions are magnetite, calcite, and altered clay minerals. The ore body has an average grade of 52.31% TFe and 46.48% mFe, making it an iron-rich ore. The newly added iron resource (TD) is 1.001 million tons.

[0051] S3: Layer determination: Calibrate the formation velocity value in the prospecting target area, calculate the target layer burial depth data, determine the target layer position and fault, and delineate the geological body stratification boundaries.

[0052] It is known that seismic waves propagate at different speeds in rocks of different lithologies. Generally speaking, the velocity distribution pattern of various rocks is as follows: alluvial clay < sandstone < limestone, dolomite < granite, metamorphic rock. Therefore, in this embodiment, two-dimensional seismic profiles can be used to delineate the boundaries of major geological bodies and interpret the burial depths of the top and bottom plates of major strata, the occurrence morphology and depth of the bedrock interface, the contact relationship, and the spatial distribution characteristics of fault structures.

[0053] The specific method for calibrating formation velocity values ​​is as follows: 2D seismic profiles are laid out in the prospecting target area. Using existing borehole information within the work area, a correspondence is established between the main formation boundaries and the seismic profile reflection events. The formation velocity value is then calculated using the depth of the target layer and the time value of the seismic time profile adjacent to the borehole. Based on the laid-out 2D seismic profiles, the reflection wave time of the target layer is obtained. Combined with the formation velocity value, the target layer burial depth data is obtained using a time-to-depth conversion formula. Finally, the dynamic information of the seismic reflection waves, such as phase characteristics, amplitude characteristics, frequency characteristics, and wave group characteristics, is used for repeated tracking and comparison to determine the target layer position and faults, and to delineate the burial depth and structural morphology of the main target layers in the entire area.

[0054] The basis for inferring fault structure: It is mainly interpreted using the kinematic information of seismic reflection waves, including the misalignment of reflection wave events, bifurcation, merging, distortion, strong phase conversion of reflection events, sudden increase, decrease or disappearance of reflection events, sudden change in wave group interval, sudden change in the occurrence of reflection events, scattered reflections or the appearance of blank zones, the appearance of special waves, etc.

[0055] In this example, the above-mentioned layer determination method is used to interpret the 2D seismic exploration profile of the Duidao area in the Qihe-Yucheng iron ore integrated exploration area. Figure 7 As shown, the burial depth, rock mass burial depth and spatial distribution characteristics of the Quaternary and Cenozoic bottom interfaces were revealed, the preferred target layers for rich iron ore were delineated, and the reliability of the 2D seismic exploration results was verified by drilling.

[0056] S4: Depth determination: Based on the stratification boundaries of the geological body, the wide-area electromagnetic method is used to identify the low-resistance anomaly characteristics, obtain the low-resistance anomaly area, and determine the buried depth of the ore body.

[0057] It is known that the rock-forming and mineralization process of "Yucheng-type" iron-rich deposits can be divided into five stages, from early to late: the early skarnization stage, the magnetite stage, the late skarn stage, the sulfide stage, and the carbonate stage. In the late mineralization stage, as the temperature and oxygen fugacity continue to drop, sulfides such as pyrite, chalcopyrite, and pyrrhotite form. Sulfides are often distributed as disseminated particles within skarns or magnetite ores, and can also be seen as veins or stockwork filling the fissures of magnetite aggregates or skarn fissures.

[0058] In step S4, a wide-area electromagnetic apparent resistivity profile is obtained using the wide-area electromagnetic method. This allows identification of the low-resistance anomaly characteristic of metal sulfides within the high-resistance surrounding rock, providing information on hydrothermal alteration activity associated with deep, concealed rock masses. Metal sulfides typically develop in the hornfels 200-300 m above the iron-rich ore body, extending into the ore body. This characteristic can be used to determine the ore body's depth. Metal sulfide identification is based on the following: igneous and metamorphic rocks have relatively high resistivity values, ranging from 102 to 105 Ω·m. Sedimentary rocks have relatively low resistivity values, such as clay, which has a resistivity of approximately 100-101 Ω·m, sandstone, which has a resistivity of approximately 102-103 Ω·m, and limestone, which is above 103 Ω·m. Metal sulfides have very low resistivity and, regardless of whether they are distributed within diorite, limestone, or sandstone, will exhibit low-resistance anomaly morphology.

[0059] Specific: such as Figure 8 As shown in the wide-area electromagnetic apparent resistivity section, against a high resistivity background, low-resistance anomalies are characterized by U-shaped, V-shaped, or strip-shaped contour lines, reflecting metal sulfides. The high resistivity on either side, combined with geological information, is inferred to be relatively intact limestone, sandstone, or rock mass. Ultimately, based on the low-resistance anomaly characteristics, the low-resistance zone is located 200-300 meters deep, and the burial depth of the ore body is determined.

[0060] In this embodiment, Figure 7 This is a schematic diagram of the wide-area electromagnetic apparent resistivity section of the overlay area within the Qihe-Yucheng Iron Mine integrated exploration zone. U-shaped low-resistivity anomalies appear beneath the Neogene at points 3800-4400, 4700-5000, and 5500-6100, presumably caused by metallic sulfides. Later, drill hole ZK1, drilled at point 3940, verified the low-resistivity anomaly at points 3800-4400. The results revealed a 90-meter-thick iron-rich deposit below the low-resistivity anomaly at an elevation of approximately -1300 meters.

[0061] Example 2

[0062] This embodiment provides a four-point prospecting system for iron-rich ores in thick overburden areas, including the following modules:

[0063] The qualitative module is configured to obtain aeromagnetic anomaly data and Bouguer gravity anomaly data based on the aeromagnetic anomaly map and the Bouguer gravity anomaly map, determine the effective magnetic anomaly range, and delineate the prospecting area based on the effective magnetic anomaly range;

[0064] The targeting module is configured to: obtain polar magnetic anomaly maps and residual gravity anomaly maps based on aeromagnetic anomaly data and Bouguer gravity anomaly data, and identify key anomaly areas in prospecting areas; obtain geological information and determine initial prospecting targets; lay out gravity and magnetic profiles in key anomaly areas, establish a preliminary inversion model, obtain optimal geological information through multiple gravity and magnetic joint inversions, and determine prospecting targets;

[0065] The layer determination module is configured to: calibrate the formation velocity value in the prospecting target area, calculate the target layer burial depth data, determine the target layer position and fault, and delineate the geological body layer boundaries;

[0066] The depth determination module is configured to: based on the geological body stratification boundaries, use the wide-area electromagnetic method to identify the low-resistance anomaly characteristics, obtain the low-resistance anomaly area, and determine the buried depth of the ore body.

[0067] It will be apparent to those skilled in the art that the present invention may be modified and varied in various ways. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A four-point prospecting method for rich iron ore in thick overburden area, characterized in that: include: According to the aeromagnetic anomaly map and Bouguer gravity anomaly map, aeromagnetic anomaly data and Bouguer gravity anomaly data are obtained, and the effective magnetic anomaly range is determined, and the prospecting prospect area is delineated according to the effective magnetic anomaly range; Based on aeromagnetic anomaly data and Bouguer gravity anomaly data, polarization magnetic anomaly maps and residual gravity anomaly maps are obtained, and key anomaly areas are identified in prospecting areas; geological information is obtained to determine the initial prospecting target area; gravity and magnetic profiles are laid out in the key anomaly areas, and a preliminary inversion model is established. The best geological information is obtained through multiple gravity and magnetic joint inversions, and the prospecting target area is determined. Specifically, the area aeromagnetic anomaly data and Bouguer gravity anomaly data are processed by potential field conversion, including polarization, upward continuation, horizontal gradient modulus, horizontal first-order derivative, and vertical second-order derivative to obtain geological information on underground structure, stratum distribution, and rock intrusion in thick cover areas; the zero value line of the vertical second-order derivative of the gravity and magnetic field and the positive and negative anomaly demarcation line of the residual gravity anomaly are used to determine the range of rock intrusion; the upward continuation data at multiple heights are used to interpret the spatial distribution of strata and rock bodies; the anomaly morphology of the gravity and magnetic field, the horizontal gradient, and the horizontal first-order derivative maps are used to infer the development of fault structures; and the initial prospecting target area is determined based on the inferred and interpreted geological information; The drill hole histograms on the gravity and magnetic profiles are connected and assigned density and magnetic parameters. The Bouguer gravity anomaly is forward calculated based on the density of the geological information of the remaining sections, and the contact relationship between the strata and the rock mass is inverted to establish a preliminary inversion model. The preliminary inversion model is fine-tuned using the magnetic parameters, and the polarized magnetic anomaly data is forward calculated. The preliminary inversion model is then modified in combination with the Bouguer gravity anomaly data and the residual gravity anomaly data. Finally, the optimal geological information is obtained through multiple gravity and magnetic joint inversions, and the prospecting target area is determined. Calibrate the formation velocity value in the prospecting target area, calculate the target layer burial depth data, determine the target layer position and fault, and delineate the geological body stratification boundary; Based on the stratification boundaries of geological bodies, the wide-area electromagnetic method is used to identify low-resistance anomaly characteristics, obtain low-resistance anomaly areas, and determine the buried depth of the ore body; among them, the wide-area electromagnetic apparent resistivity section is obtained by the wide-area electromagnetic method. In the wide-area electromagnetic apparent resistivity section, with high resistivity as the background, the low-resistance anomaly characteristics are U-shaped contour lines, V-shaped contour lines or strip shapes.

2. The four-point prospecting method for rich iron ore in thick overburden area according to claim 1, characterized in that: The magnetic anomaly characteristics are obtained based on the aeromagnetic anomaly data, and the effective magnetic anomaly range is determined in combination with the Bouguer gravity anomaly data. According to the effective magnetic anomaly range, the anomaly areas are respectively delineated on the aeromagnetic anomaly map and the Bouguer gravity anomaly map. The superposition of the two anomaly areas is the prospecting prospect area.

3. The four-point prospecting method for rich iron ore in thick overburden area according to claim 1, characterized in that: The aeromagnetic anomaly data are subjected to polarization processing to obtain polarized magnetic anomaly data, and a polarized magnetic anomaly map is generated; the Bouguer gravity anomaly data are subjected to a sliding average method to obtain regional gravity anomaly data, the regional gravity anomaly data are subtracted from the Bouguer gravity anomaly data to obtain residual gravity anomaly data, and a residual gravity anomaly map is generated.

4. The four-point prospecting method for rich iron ore in thick overburden area according to claim 1, characterized in that: A two-dimensional seismic profile is laid out on the prospecting target area, and combined with the drilling information, the correspondence between the main stratum boundaries and the seismic profile reflection phase axis is constructed, and the stratum velocity value is calculated by the target layer depth and the time value of the seismic time profile next to the borehole.

5. The four-point prospecting method for rich iron ore in thick overburden area according to claim 4, characterized in that: According to the laid-out two-dimensional seismic profile, the reflection wave time of the target layer is obtained, and combined with the formation velocity value, the target layer burial depth data is obtained through the time-depth conversion formula.

6. A four-point prospecting system for iron-rich ores in thick overburden areas, characterized by: Includes the following modules: The qualitative module is configured to obtain aeromagnetic anomaly data and Bouguer gravity anomaly data based on the aeromagnetic anomaly map and the Bouguer gravity anomaly map, determine the effective magnetic anomaly range, and delineate the prospecting area based on the effective magnetic anomaly range; The targeting module is configured to: obtain polarization magnetic anomaly maps and residual gravity anomaly maps based on aeromagnetic anomaly data and Bouguer gravity anomaly data, and determine key anomaly areas in prospecting areas; obtain geological information and determine initial prospecting targets; lay out gravity and magnetic profiles in key anomaly areas, establish a preliminary inversion model, obtain optimal geological information through multiple gravity and magnetic joint inversions, and determine prospecting targets. Specifically, it performs potential field conversion processing on areal aeromagnetic anomaly data and Bouguer gravity anomaly data, including polarization, upward extension, horizontal gradient modulus, horizontal first-order derivative, and vertical second-order derivative, to obtain geological information on underground structure, stratum distribution, and rock intrusion in thick cover areas; use the zero value line of the vertical second-order derivative of the gravity and magnetic field and the positive and negative anomaly demarcation line of the residual gravity anomaly to determine the range of rock intrusion; use the upward extension data at multiple heights to interpret the spatial distribution of strata and rock masses; use the gravity and magnetic field anomaly morphology, horizontal gradient, and horizontal first-order derivative maps to infer the development of fault structures; and determine the initial prospecting targets based on the inferred and interpreted geological information. The drill hole histograms on the gravity and magnetic profiles are connected and assigned density and magnetic parameters. The Bouguer gravity anomaly is forward calculated based on the density of the geological information of the remaining sections, and the contact relationship between the strata and the rock mass is inverted to establish a preliminary inversion model. The preliminary inversion model is fine-tuned using the magnetic parameters, and the polarized magnetic anomaly data is forward calculated. The preliminary inversion model is then modified in combination with the Bouguer gravity anomaly data and the residual gravity anomaly data. Finally, the optimal geological information is obtained through multiple gravity and magnetic joint inversions, and the prospecting target area is determined. The layer determination module is configured to: calibrate the formation velocity value in the prospecting target area, calculate the target layer burial depth data, determine the target layer position and fault, and delineate the geological body layer boundaries; The depth determination module is configured as follows: based on the stratification boundaries of the geological body, the wide-area electromagnetic method is used to identify the low-resistance anomaly characteristics, obtain the low-resistance anomaly area, and determine the buried depth of the ore body; wherein, the wide-area electromagnetic apparent resistivity section is obtained by the wide-area electromagnetic method. In the wide-area electromagnetic apparent resistivity section, with high resistivity as the background, the low-resistance anomaly characteristics are U-shaped contour lines, V-shaped contour lines or strip shapes.

7. A computer-readable storage medium having a program stored thereon, characterized in that: When the program is executed by a processor, the steps of the four-point prospecting method for rich iron ore in thick coverage area as described in any one of claims 1 to 5 are implemented.

8. An electronic device comprising a memory, a processor, and a program stored in the memory and executable on the processor, wherein: When the processor executes the program, the steps of the four-determination prospecting method for iron-rich ores in thick coverage areas as described in any one of claims 1 to 5 are implemented.

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