Four-determination prospecting method and system for rich iron ore in thick coverage area

Abstract

The invention discloses a four-determination prospecting method and system for a thick coverage area rich iron ore, and relates to the technical field of deep prospecting of geological exploration, and the method comprises the steps: delineating a prospecting prospecting area according to an aeromagnetic anomaly graph and a Bouguer gravity anomaly graph; based on the aeromagnetic anomaly data and the Bouguer gravity anomaly data, obtaining a chemical pole magnetic anomaly graph and a residual gravity anomaly graph, and determining a key anomaly region; a gravity-magnetic section is arranged in the key abnormal area, a preliminary inversion model is established, optimal geological information is obtained through multiple times of gravity-magnetic combined inversion, and a prospecting target area is determined; determining a target layer position and a fault in the prospecting target area, and delimiting a geologic body layering boundary; and identifying low-resistance abnormal characteristics by using a wide-area electromagnetic method to obtain a low-resistance abnormal region, and determining the position of the buried depth of the ore body. The method has the characteristics of accurate information identification, high positioning precision, large detection depth and the like, and effectively solves the technical problem of thick coverage area rich iron ore prospecting.

Description

Technical Field

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

[0002] Iron accounts for a very high proportion in metal consumption, reaching about 95% of the total metal consumption. And iron and steel products are widely used in all aspects of modern life. It is an important pillar of social development and a key metal material for modern industry. However, the supply of iron ore resources is tight, and the supply of iron ore has long been unable to meet the demand of steel production. Although there is still great potential for iron ore prospecting in the deep part of the main ore - forming belts, due to the large burial depth of the ore deposits and weak information shown on the surface, the actual prospecting difficulty is very great. There is an urgent need for accurate and efficient technical methods in this field to identify hidden iron ore deposits in thick - covered areas.

[0003] The existing prospecting methods generally use geophysical prospecting methods, mainly including regional gravity and magnetic measurement method, large - scale gravity and magnetic measurement method, two - dimensional seismic method, and wide - area electromagnetic method. Among them, the regional gravity and magnetic measurement method can only delineate the general prospecting range by observing and analyzing the gravity and magnetic anomalies caused by the density and magnetic differences of rocks (ores), and cannot accurately locate the ore body; the large - scale gravity and magnetic measurement method uses potential - field conversion processing and forward and inverse calculations to extract geological information and determine the prospecting target area. However, 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 the prospecting target area; the two - dimensional seismic method delimits the boundaries of the main geological bodies based on the velocity distribution law of seismic waves in rocks with different lithologies. However, in actual applications, the propagation of seismic waves is interfered by various factors, such as the heterogeneity of underground media and terrain undulation, resulting in ineffective identification of some geological bodies; the wide - area electromagnetic method identifies the low - resistance anomaly characteristics of metal sulfides from high - resistance surrounding rocks, obtains information on hydrothermal alteration activities related to deep - buried hidden rock masses, and then determines the burial depth of the ore body. However, since this method cannot delineate the general prospecting range and target area and cannot comprehensively understand the geological body situation, it will affect the accuracy of prospecting.

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

[0005] Aiming at the deficiencies existing in the prior art, the present invention provides a four - fixed prospecting method and system for rich iron ore in thick - covered areas. The present invention uses four comprehensive geophysical exploration methods, namely gravity, magnetism, electricity, and seismic, to search for skarn - type rich iron ore in thick - covered areas, with the characteristics of high positioning accuracy, large detection depth, and good prospecting effect.

[0006] To achieve the above - mentioned purpose, the present invention adopts the following technical solutions: In the first aspect, the present invention provides a four - fixed prospecting method for rich iron ore in thick - covered areas, including: According to the aeromagnetic anomaly map and Bouguer gravity anomaly map, obtain aeromagnetic anomaly data and Bouguer gravity anomaly data, and determine the effective magnetic anomaly range. According to the effective magnetic anomaly range, delineate the prospecting prospective area. Based on the aeromagnetic anomaly data and Bouguer gravity anomaly data, obtain the reduced - pole magnetic anomaly map and residual gravity anomaly map, and determine the key anomaly area on the prospecting prospective area; obtain geological information and determine the initial prospecting target area; deploy gravity - magnetic profiles in the key anomaly area, establish a preliminary inversion model, and through multiple gravity - magnetic joint inversions, obtain the best geological information and determine the prospecting target area. Calibrate the formation velocity value in the prospecting target area, calculate the buried depth data of the target layer, determine the target layer horizon and faults, and delimit the stratigraphic boundary of the geological body. Based on the stratigraphic boundary of the geological body, use the wide - area electromagnetic method to identify the low - resistivity anomaly characteristics, obtain the low - resistivity anomaly area, and determine the buried position of the ore body.

[0007] As a further technical solution, obtain the magnetic anomaly characteristic performance according to the aeromagnetic anomaly data, combine with the Bouguer gravity anomaly data to determine the effective magnetic anomaly range, delineate the anomaly areas on the aeromagnetic anomaly map and Bouguer gravity anomaly map respectively according to the effective magnetic anomaly range, and the superposition of the two anomaly areas is the prospecting prospective area.

[0008] As a further technical solution, perform reduced - pole processing on the aeromagnetic anomaly data to obtain reduced - pole magnetic anomaly data and generate a reduced - pole magnetic anomaly map; use the moving average method to obtain the regional gravity anomaly data for the Bouguer gravity anomaly data, subtract the regional gravity anomaly data from the Bouguer gravity anomaly data to obtain the residual gravity anomaly data, and generate a residual gravity anomaly map.

[0009] As a further technical solution, connect the borehole columnar diagrams on the gravity - magnetic profiles, assign density and magnetic parameters, perform forward calculation on the Bouguer gravity anomaly according to the density of the geological information in other areas, and then invert the contact relationship between the strata and rock masses to establish a preliminary inversion model; use the magnetic parameters to fine - tune the preliminary inversion model, perform forward calculation on the reduced - pole magnetic anomaly data, and then modify the preliminary inversion model in combination with the Bouguer gravity anomaly data and the residual gravity anomaly data. Finally, through multiple gravity - magnetic joint inversions, obtain the best geological information and determine the prospecting target area.

[0010] As a further technical solution, a two-dimensional seismic profile is arranged on the ore prospecting target area, and combined with borehole information, the corresponding relationship between the main formation boundary and the seismic profile reflection isochron is constructed, and the formation velocity value is calculated through the depth of the target layer and the time value of the seismic time profile beside the borehole.

[0011] As a further technical solution, according to the arranged two-dimensional seismic profile, the reflection wave time of the target layer is obtained, and combined with the formation velocity value, the buried depth data of the target layer is obtained through the time-depth conversion formula.

[0012] 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 in the shape of an isoline U, an isoline V or a strip.

[0013] In a second aspect, the present invention provides a four-determination ore prospecting system for rich iron ore in a thick overburden area, including the following modules: A qualitative module, configured to: obtain aeromagnetic anomaly data and Bouguer gravity anomaly data according to the aeromagnetic anomaly map and the Bouguer gravity anomaly map, and determine the effective magnetic anomaly range, and delineate the ore prospecting area according to the effective magnetic anomaly range; A target determination module, configured to: obtain a reduced-to-pole magnetic anomaly map and a residual gravity anomaly map based on the aeromagnetic anomaly data and the Bouguer gravity anomaly data, and determine the key anomaly area on the ore prospecting area; obtain geological information to determine the initial ore prospecting target area; arrange gravity and magnetic profiles in the key anomaly area, establish a preliminary inversion model, obtain the best geological information through multiple gravity and magnetic joint inversions, and determine the ore prospecting target area; A layer determination module, configured to: calibrate the formation velocity value in the ore prospecting target area, calculate the buried depth data of the target layer, determine the target layer horizon and faults, and delimit the geological body stratification boundary; A depth determination module, configured to: based on the geological body stratification boundary, use the wide-area electromagnetic method to identify the low-resistance anomaly features, obtain the low-resistance anomaly area, and determine the buried depth position of the ore body.

[0014] One or more technical solutions of the present invention have the following beneficial effects: Based on four geophysical exploration methods of gravity, magnetics, electricity, and seismic, the present invention effectively combines the four physical exploration methods by qualitatively delineating the prospective ore areas, targeting the ore targets, stratifying the main geological bodies, and determining the depth of rich iron ore, realizing ore prospecting in a way that organically combines geology, geophysical exploration, and drilling, and solving the problem that various existing geophysical exploration methods are difficult to effectively combine. Moreover, the four-step ore prospecting method provided by the present invention has the characteristics of accurate information recognition, high positioning accuracy, large detection depth, etc. on the one hand, effectively solving the technical problems of rich iron ore prospecting in thickly covered areas. On the other hand, it can solve the limitations of existing geophysical exploration methods during use and meet the ore prospecting requirements under complex geological conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings forming a part of this specification are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0016] Figure 1 is a flowchart of the four-step ore prospecting method of the present invention; Figure 2 is a 1:50,000 aeromagnetic anomaly map of the Qihe-Yucheng area of the present invention; Figure 3 is a 1:50,000 local Bouguer gravity anomaly map of the Qihe-Yucheng area of the present invention; Figure 4 is a reduced-to-pole magnetic anomaly map of the Laiwu area of the present invention; Figure 5 is a residual gravity anomaly map of the Laiwu area of the present invention; FIG. 6 is an inferred map of 2.5D joint inversion of gravity and magnetics profiles of the present invention. Among them, (a) is the magnetic survey curve of the profile; (b) is the gravity curve of the profile; (c) is the inferred geological interpretation profile of 2.5D joint inversion of gravity and magnetics.

[0017] Figure 7 is a schematic diagram of a two-dimensional seismic depth profile of the present invention; Figure 8 is a schematic diagram of a wide-area electromagnetic apparent resistivity section of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS 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 of ordinary skill in the technical field to which the present invention belongs.

[0018] Example 1 As Figure 1 shown, in this embodiment, a four-step ore prospecting method for rich iron ore in thickly covered areas is provided, and ore prospecting is achieved through four steps: qualitative analysis, target determination, stratification, and depth determination. The specific steps of the method are as follows: S1: Qualitative analysis: Based on the aeromagnetic anomaly map and Bouguer gravity anomaly map, obtain the aeromagnetic anomaly data and Bouguer gravity anomaly data, and determine the effective magnetic anomaly range. Then, delineate the prospective ore areas according to the effective magnetic anomaly range.

[0019] According to geological data, skarn-type rich iron ores in western Shandong are mainly produced at the contact between Mesozoic Yanshanian intermediate-basic intrusive rocks and surrounding rocks. The intermediate-basic intrusive rocks are mainly gabbro diorite, biotite diorite, diopside diorite, etc., and the surrounding rocks are the limestone of the Majiagou Group. The occurrence forms of the ore-forming related rock masses are laccoliths and sills. The plunging parts of the rock masses are often the best for mineralization. At the contact between the captured wall rocks and the rock masses, it is often a favorable place for the occurrence of iron ore bodies. Especially, the locally convex parts and the abrupt changes of convex and concave of the stratoid intrusions are important ore-controlling parts.

[0020] In step S1, as Figure 2 and Figure 3 shown, according to the 1:50,000 aeromagnetic anomaly map and 1:50,000 Bouguer gravity anomaly map, delineate the prospective ore areas. Specifically: According to the aeromagnetic anomaly data on the aeromagnetic anomaly map, the characteristics of the magnetic anomalies are as follows: Sedimentary strata are non-(weakly) magnetic, and the induced magnetic anomalies can be ignored; Mesozoic diorite has medium-high magnetic characteristics, with the magnetic susceptibility κ varying between (100 - 5000) × 10-64π SI and the remanent magnetization intensity Jr varying in the range of (10 - 1000) × 10-3 A / m; Magnetite has strong magnetism, with the average value of its magnetic susceptibility κ being 160000 × 10-64π SI and the average value of the remanent magnetization intensity Jr being 180000 × 10-3 A / m; The magnetic parameters of the above geological bodies determine that rich iron ores show high magnetic anomalies on the aeromagnetic anomaly map. Due to the different thicknesses of the overlying strata, the intensities of the induced magnetic anomalies are also different, and it is impossible to determine the quantitative magnetic anomaly index. Therefore, in this embodiment, the effective magnetic anomaly range is determined by combining the Bouguer gravity anomaly data.

[0021] According to the Bouguer gravity anomaly data on the Bouguer gravity anomaly map, the characteristics of the gravity anomalies are as follows: There are density differences between different geological bodies underground (generally speaking, the density values are Quaternary < sandstone < limestone < diorite < magnetite), which causes the reflection of rich iron ores on the Bouguer gravity anomaly map to be high gravity value areas. From the analysis of the magnetic and density parameters of the rocks (ores), the areas with coincident high gravity and high magnetism have the potential for rich iron ore mineralization (effective magnetic anomaly range). According to the effective magnetic anomaly range, delineate the anomaly areas on the aeromagnetic anomaly map and Bouguer gravity anomaly map respectively, and the superposition of the two anomaly areas is the prospective ore area.

[0022] In this embodiment, based on the above method, as Figure 2 and Figure 3 shown, prospective ore areas for rich iron ores such as the Qihe-Yucheng area, Zibo Jinling area, Laiwu Zhangjiawa area, and Liaocheng Xuying area can be determined in the deep-covered area of western Shandong.

[0023] S2: Target Setting: Based on the aeromagnetic anomaly data and Bouguer gravity anomaly data, obtain the reduced-to-pole magnetic anomaly map and the residual gravity anomaly map, and determine the key anomaly areas; acquire geological information to determine the initial prospecting target areas; deploy gravity and magnetic profiles in the key anomaly areas, establish a preliminary inversion model, and obtain the optimal geological information through multiple gravity and magnetic joint inversions to determine the prospecting target areas.

[0024] In step S2, perform reduced-to-pole processing on the aeromagnetic anomaly data to obtain reduced-to-pole magnetic anomaly data, and generate a reduced-to-pole magnetic anomaly map as shown in Figure 4 Figure [specific figure number]; use the moving average method for the Bouguer gravity anomaly data to obtain the regional gravity anomaly data, subtract the regional gravity anomaly data from the Bouguer gravity anomaly data to obtain the residual gravity anomaly data, and generate a residual gravity anomaly map as shown in Figure 5 Figure [specific figure number].

[0025] Since skarn-type iron-rich deposits occur in the contact zone between intermediate-acid intrusions and carbonate rocks and their vicinity, skarn can often be seen near the ore bodies; intermediate-acid intrusions are magnetic, and obvious magnetic anomalies can be observed, while carbonate rocks are non-magnetic. Therefore, the secondary magnetic anomalies superimposed on the transition zone between the quiet magnetic field of carbonate rocks and the magnetic field of intrusions become the markers for magnetic prospecting for such iron ores. Thus, the key anomaly areas usually appear as the transition zone from strong magnetic anomalies to low negative anomalies, i.e., the area of low and gentle magnetic anomalies, on the reduced-to-pole magnetic anomaly map. Areas with higher magnetic anomaly values are often the locations where the rock masses occur. The areas where multiple magnetic anomaly isoclines bulge out synchronously are usually the target areas for rich iron ores, as shown in Figure 4 Figure [specific figure number].

[0026] The key anomaly areas appear as the fluctuations and turns of the step zones near the high-value areas of the isoclines, or on the side with a relatively gentle gradient change where the isoclines bend in the same direction, on the Bouguer gravity anomaly map. The key anomaly areas appear as the edges of the local gravity high-value anomaly centers on the residual gravity anomaly map. The residual gravity anomaly centers are usually the locations where the rock masses occur, as shown in Figure 5 Figure [specific figure number].

[0027] In step S2, perform potential field transformation processing such as reduced-to-pole, upward continuation, horizontal gradient modulus, horizontal first derivative, and vertical second derivative on the areal aeromagnetic anomaly data and Bouguer gravity anomaly data to obtain geological information such as the underground structure, stratigraphic distribution, and rock mass intrusion in the thickly covered area. And use the zero-value lines of the vertical second derivative of the gravity and magnetic fields and the boundary coils of the positive and negative anomalies of the residual gravity anomaly to delineate the intrusion range of the rock mass, use the upward continuation data at multiple heights to interpret the spatial distribution of the strata and the rock mass, use the maps of the gravity and magnetic anomaly shapes, horizontal gradients, horizontal first derivatives, etc. to infer the development of fault structures, and determine the initial prospecting target areas based on the inferred and interpreted geological information.

[0028] 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 boreholes as constraint conditions to conduct 2.5D gravity and magnetic joint inversion and interpretation, so as to obtain relevant information of deep target geological bodies, and then obtain the prospecting target area. Specifically: First, connect the existing borehole histograms on the gravity and magnetic profiles and assign density and magnetic parameters. Forward calculate the Bouguer gravity anomaly according to the density of geological information in other areas, and then invert the contact relationship between strata and rock masses to establish a preliminary inversion model; then use magnetic parameters to fine-tune the preliminary inversion model, forward calculate the reduced-to-pole magnetic anomaly data, and focus on adjusting the intrusion range of diorite rock mass to the occurrence position of iron ore bodies. The skarn zone is distributed at the contact part between the diorite rock mass and carbonate rock strata and is associated with magnetite; then combine the Bouguer gravity anomaly data and the residual gravity anomaly data to modify the preliminary inversion model again. Finally, obtain the best geological information through multiple gravity and magnetic joint inversions and determine the prospecting target area.

[0029] According to the above method, a prospecting target area for rich iron ore is determined in the thickly covered Shijiaquan area in Laiwu, and borehole verification is carried out on it. The prospecting effect is good, which proves the effectiveness of large-scale gravity and magnetic measurement in targeting rich iron ore in thickly covered areas. Figure 4 、 Figure 5 They are respectively the reduced-to-pole magnetic anomaly map and the residual gravity anomaly map of the Laiwu area. According to the above method, first delineate the key anomaly area and lay out gravity and magnetic profiles in the key anomaly area. Figure 6 is the inferred interpretation map of 2.5D gravity and magnetic joint inversion.

[0030] This section crosses the exploration lines of the known Shijiaquan mining area (section 50 - 350 m), the Liuxinggou mining area (section 1200 - 2160 m), and the Liuwangmiao mining area (section 5120 - 5360 m). These areas are controlled by known drill holes, and the section is inversely inferred and interpreted according to the principle of inferring from the known to the unknown. The gravity curve gradually rises from west to east, reflecting the law that the sedimentary strata gradually thin and the buried depth of the rock mass gradually becomes shallower; as shown in Figures 6 (a) and (b), the locally high-value abnormal parts of the magnetic survey curve are the result of the combined action of the diorite rock mass undulation and skarn-type magnetite. The downward trend of the magnetic anomaly on the section increases rapidly near 3700 m, and it is speculated that the diorite intrudes into the Ordovician limestone along the bedding from west to east and is annihilated here. The curve gradually rises after reaching the lowest value near 4800 m, and it is speculated that the bottom diorite gradually thickens. According to the metallogenic law that "the transition zone from high gravity anomaly and strong magnetic anomaly to low negative anomaly (low and gentle magnetic anomaly distribution area) is a favorable area for finding iron deposits", there are 2 favorable metallogenic areas on this section, and the positions of 2 drill holes are designed as shown in Figure 6 (c). According to the results of 2.5D gravity and magnetic joint inversion inference, it is expected that the ZK1 drill hole (at 2870 m of the section) will penetrate the Ordovician limestone and enter the lower intrusive rock mass at an elevation of about -500 m, and the designed drill hole depth can be 700 m; it is expected that the ZK2 drill hole (at 750 m of the section) will penetrate the Ordovician limestone and enter the lower intrusive rock mass at an elevation of about -800 m, and the designed drill hole depth can be 1000 m. It is speculated that there is probably an iron ore body at the contact part of the diorite rock mass and the limestone in the above two drill holes, and the ore-seeing depths are 670 m and 970 m respectively.

[0031] Drilling verification was carried out on the ZK1 drill hole, and the final hole depth was 750 m. The drill hole revealed altered diorite porphyrite at a depth of 488.1 - 501.9 m, and its roof and floor are both Ordovician limestone, which proves that the diorite intrudes along the bedding into the Ordovician limestone. Since the intrusive rock mass is thin, no iron ore body is formed at this depth. Magnetite was seen at 642.1 - 657.9 m, with a thickness of 15.8 m. Among them, a skarn zone was seen at 654.6 - 655.9 m. The roof of the ore body is medium- to coarse-grained crystalline limestone, and the floor is altered pyroxene diorite. The magnetite ore layer has an obvious intrusive contact relationship with the upper limestone. The main mineral components are magnetite, calcite, and altered clay minerals. The average grade of the ore body is TFe 52.31% and mFe 46.48%, which is a rich iron ore, and the newly added iron resource amount (TD) is 1.001 million tons.

[0032] S3: Layer determination: Calibrate the formation velocity value in the prospecting target area, calculate the buried depth data of the target layer, determine the target layer position and faults, and delimit the stratification boundaries of geological bodies.

[0033] It is known that seismic waves have different propagation speeds in rocks of different lithologies. Generally speaking, the velocity distribution law of various types of rocks is alluvial clay < sandstone < limestone, dolomite < granite, metamorphic rock. Therefore, in this embodiment, the two-dimensional seismic profile can be used to delineate the boundaries of major geological bodies, interpret the burial depths of the top and bottom plates of major strata, the occurrence form and burial depth of the bedrock interface, the contact relationship and the spatial distribution characteristics of the fault structure.

[0034] The specific method for calibrating the formation velocity value is: lay out a two-dimensional seismic profile on the prospecting target area, use the existing borehole information in the work area, construct the corresponding relationship between the main formation boundary and the seismic profile reflection phase axis, and calculate the formation velocity value through the target layer depth and the seismic time profile time value next to the borehole. 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; finally, the dynamic information of the seismic reflection wave, such as phase characteristics, amplitude characteristics, frequency characteristics and wave group characteristics, is used to repeatedly track and compare, determine the target layer position and fault, and delineate the burial depth and structural morphology of the main target layer in the entire area.

[0035] 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, sudden increase, decrease or disappearance of reflection events, sudden change in wave group interval, sudden change in the occurrence of reflection events, disordered reflection or the appearance of blank zones, the appearance of special waves, etc.

[0036] In this embodiment, the above-mentioned layer determination method is used to interpret the two-dimensional seismic exploration profile of the Duidao area in the Qihe-Yucheng Iron Mine integrated exploration area, such as Figure 7 As shown, the burial depth of the Quaternary and Cenozoic bottom interfaces, the burial depth of the rock mass and the spatial distribution characteristics were revealed, the preferred target strata for rich iron ore were delineated, and the reliability of the two-dimensional seismic exploration results was verified by drilling.

[0037] 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.

[0038] It is known that the rock-forming and mineralization process of the "Yucheng-style" iron-rich ore can be divided into five stages from early to late, namely the early skarn stage, the magnetite stage, the late skarn stage, the sulfide stage, and the carbonate stage. In the late stage of mineralization, with the continued decrease in temperature and oxygen fugacity, pyrite, chalcopyrite, pyrrhotite and other sulfides are formed. Sulfides are often distributed in skarn or magnetite in the form of dissemination, and can also be seen in veins or stockwork filling the cracks of magnetite aggregates or skarn cracks.

[0039] In step S4, the wide-area electromagnetic apparent resistivity section is obtained by the wide-area electromagnetic method, and the low-resistance anomaly characteristics of metal sulfides can be identified from the high-resistance surrounding rocks, and the hydrothermal alteration activity information related to the deep concealed rock mass can be obtained. Generally, metal sulfides are developed in the hornfels 200 to 300 meters above the rich iron ore until the ore body, and the burial depth of the ore body can be determined based on this characteristic mark. The identification method of metal sulfides is as follows: the resistivity values of igneous rocks and metamorphic rocks are relatively high, varying in the range of 102 to 105Ω·m, and the resistivity values of sedimentary rocks are relatively low, such as clay resistivity of about 100 to 101Ω·m, sandstone resistivity of about 102 to 103Ω·m, and limestone resistivity of more than 103Ω·m. The resistivity of metal sulfides is very low, and no matter whether they are distributed in diorite, limestone or sandstone, they will show low-resistance anomaly morphological characteristics.

[0040] Specific: such as Figure 8 As shown in the figure, in the wide-area electromagnetic apparent resistivity section, with high resistivity as the background, the low-resistance anomaly features U-shaped contour lines, V-shaped contour lines or strip-shaped contour lines, which are the reflections of metal sulfides. The high resistance on both sides is combined with geological information to infer that it is a relatively complete limestone, sandstone or rock mass. Finally, according to the low-resistance anomaly characteristics, the location of the low-resistance area is determined to extend 200 to 300 meters deep, and the burial depth of the ore body is determined.

[0041] In this embodiment, Figure 7 This is a schematic diagram of the wide-area electromagnetic apparent resistivity section of the overlay area in the Qihe-Yucheng iron ore integrated exploration area. The three sections of points 3800-4400, 4700-5000, and 5500-6100 have "U"-shaped low-resistance anomalies in the apparent resistivity below the Neogene, which is speculated to be caused by metal sulfides. Later, at the location of point 3940, the drill hole ZK1 was laid to verify the low-resistance anomaly of points 3800-4400. The result showed that there was a 90m thick rich iron ore at an elevation of -1300m below the low-resistance anomaly.

[0042] Embodiment 2 This embodiment provides a four-point prospecting system for rich iron ore in thick coverage areas, including the following modules: The qualitative module is configured to: obtain aeromagnetic anomaly data and Bouguer gravity anomaly data according to the aeromagnetic anomaly map and the Bouguer gravity anomaly map, determine the effective magnetic anomaly range, and delineate the prospecting prospect area according to the effective magnetic anomaly range; The targeting module is configured to: obtain the polar magnetic anomaly map and the residual gravity anomaly map based on the aeromagnetic anomaly data and the Bouguer gravity anomaly data, and determine the key anomaly area in the prospecting area; obtain geological information and determine the initial prospecting target area; lay out the gravity and magnetic profile in the key anomaly area, establish a preliminary inversion model, obtain the best geological information through multiple gravity and magnetic joint inversions, and determine the prospecting target area; The layer determination module is configured to: calibrate the formation velocity value within the ore prospecting target area, calculate the buried depth data of the target layer, determine the target layer horizon and faults, and delimit the geological body stratification boundary; The depth determination module is configured to: based on the geological body stratification boundary, use the wide - area electromagnetic method to identify the low - resistance anomaly characteristics, obtain the low - resistance anomaly area, and determine the buried depth position of the ore body.

[0043] For those skilled in the art, various modifications and variations can be made to the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A four - determination prospecting method for rich iron ore in thick - covered areas, characterized in that, Including: Based on the aeromagnetic anomaly map and Bouguer gravity anomaly map, obtain aeromagnetic anomaly data and Bouguer gravity anomaly data, determine the effective magnetic anomaly range, and delineate the prospecting far - reaching area according to the effective magnetic anomaly range; Based on the aeromagnetic anomaly data and Bouguer gravity anomaly data, obtain the reduced - pole magnetic anomaly map and residual gravity anomaly map, and determine the key anomaly areas on the prospecting far - reaching area; obtain geological information to determine the initial prospecting target area; deploy gravity - magnetic profiles in the key anomaly areas, establish a preliminary inversion model, and obtain the best geological information through multiple gravity - magnetic joint inversions to determine the prospecting target area; Calibrate the formation velocity value within the prospecting target area, calculate the buried depth data of the target layer, determine the target layer horizon and faults, and delimit the stratigraphic boundaries of geological bodies; Based on the stratigraphic boundaries of geological bodies, use the wide - area electromagnetic method to identify the low - resistivity anomaly characteristics, obtain the low - resistivity anomaly area, and determine the buried depth position of the ore body.

2. The four-fixed prospecting method for thick-covered area rich iron ore according to claim 1, wherein, Obtain the magnetic anomaly characteristic manifestations according to the aeromagnetic anomaly data, determine the effective magnetic anomaly range in combination with the Bouguer gravity anomaly data, delimit the anomaly areas on the aeromagnetic anomaly map and Bouguer gravity anomaly map respectively according to the effective magnetic anomaly range, and the superposition of the two anomaly areas is the prospecting far - reaching area.

3. The four-fixed prospecting method for thick-covered area rich iron ore as described in claim 1, characterized in that, Perform reduced - pole processing on the aeromagnetic anomaly data to obtain reduced - pole magnetic anomaly data and generate a reduced - pole magnetic anomaly map; use the moving average method for the Bouguer gravity anomaly data to obtain regional gravity anomaly data, subtract the regional gravity anomaly data from the Bouguer gravity anomaly data to obtain residual gravity anomaly data, and generate a residual gravity anomaly map.

4. The four-fixed prospecting method for thick-covered area rich iron ore as described in claim 1, characterized in that, Connect the borehole columnar diagrams on the gravity - magnetic profiles, assign density and magnetic parameters, perform forward calculation on the Bouguer gravity anomaly according to the density of geological information in other sections, and then invert the contact relationship between strata and rock masses to establish a preliminary inversion model; fine - tune the preliminary inversion model using magnetic parameters, perform forward calculation on the reduced - pole magnetic anomaly data, and then modify the preliminary inversion model in combination with the Bouguer gravity anomaly data and residual gravity anomaly data. Finally, obtain the best geological information through multiple gravity - magnetic joint inversions to determine the prospecting target area.

5. The four-fixed prospecting method for thick-covered area rich iron ore according to claim 1, characterized in that, Deploy a two - dimensional seismic profile on the prospecting target area, and in combination with borehole information, construct the corresponding relationship between the main stratigraphic boundaries and the seismic profile reflection isochrones, and calculate the formation velocity value through the target layer depth and the time value of the seismic time profile beside the borehole.

6. The four-fixed prospecting method for rich iron ore in thick coverage areas as described in claim 5, characterized in that, According to the deployed two - dimensional seismic profile, obtain the reflection wave time of the target layer, and in combination with the formation velocity value, obtain the buried depth data of the target layer through the time - depth conversion formula.

7. The four-fixed prospecting method for thick-covered high-grade iron ore as described in claim 1, characterized in that, Obtain the wide - area electromagnetic apparent resistivity section through the wide - area electromagnetic method. In the wide - area electromagnetic apparent resistivity section, with high resistivity as the background, the low - resistivity anomaly characteristics are U - shaped isopleths, V - shaped isopleths or strip - shaped.

8. A four - determination prospecting system for rich iron ore in thick - covered areas, characterized in that, Including the following modules: A qualitative module, configured to: based on the aeromagnetic anomaly map and Bouguer gravity anomaly map, obtain aeromagnetic anomaly data and Bouguer gravity anomaly data, determine the effective magnetic anomaly range, and delineate the prospecting far - reaching area according to the effective magnetic anomaly range; The fixed target module is configured to: obtain a reduced pole magnetic anomaly map and a residual gravity anomaly map based on aeromagnetic anomaly data and Bouguer gravity anomaly data, and determine key anomaly areas in the prospecting prospective area; obtain geological information and determine the initial prospecting target area; deploy gravity and magnetic profiles in the key anomaly areas, establish a preliminary inversion model, obtain the best geological information through multiple gravity and magnetic joint inversions, and determine the prospecting target area; The horizon determination module is configured to: calibrate the formation velocity value in the prospecting target area, calculate the buried depth data of the target layer, determine the target layer horizon and faults, and delimit the geological body stratification boundary; The depth determination module is configured to: based on the geological body stratification boundary, use the wide area electromagnetic method to identify the low resistivity anomaly characteristics, obtain the low resistivity anomaly area, and determine the buried depth position of the ore body.

9. A computer-readable storage medium having a program stored thereon, characterized in that, When the program is executed by the processor, it implements the steps in a four - determination prospecting method for rich iron ore in thick - covered areas as described in any one of claims 1 - 7.

10. An electronic device, comprising a memory, a processor, and a program stored on the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the steps in a four - determination prospecting method for rich iron ore in thick - covered areas as described in any one of claims 1 - 7.

Images