A method for calculating the burial depth of the deep contact zone in uranium-rich granite.

Abstract

This invention belongs to the field of uranium resource exploration technology, specifically relating to a method for calculating the burial depth of the deep contact zone of uranium-rich granite, comprising: Step 1: Conducting stream sedimentary sampling within the granite development area of ​​the study area; Step 2: Statistically analyzing the uranium content of the samples to delineate the uranium-rich granite development area; Step 3: Conducting gravity measurements within the delineated uranium-rich granite development area to obtain Bouguer gravity anomalies and elevation grid data; Step 4: Obtaining residual gravity anomalies and generating a residual gravity anomaly grid file; Step 5: Conducting broadband magnetotelluric profiling measurements and using the inversion results to calibrate the boundary between the deep rock mass and the strata; Step 6: Digitizing each profile boundary and creating a constrained grid file; Step 7: Establishing a model and conducting interface inversion to obtain elevation grid data of the deep contact zone of the granite rock mass; Step 8: Calculating the burial depth of the deep contact zone of the uranium-rich granite. This invention can accurately locate and calculate the burial depth of the deep contact zone of uranium-rich granite.

Description

Technical Field

[0001] This invention belongs to the field of uranium resource exploration technology, specifically relating to a method for calculating the burial depth of the deep contact zone in uranium-rich granite. Background Technology

[0002] Granite-type uranium deposits refer to uranium ore bodies genetically related to granite bodies and occurring within or near them. They are one of the four major uranium deposit types in my country. Since the discovery of the first uranium ore in New China decades ago, several granite-type uranium deposits have been identified. The locations of discovered mineralization are closely related to the rock mass, stratigraphic contact zones, and fault structures. In particular, the contact zones between uranium-rich granite rock masses and deep strata are often more conducive to large-scale mineralization and are more likely to form large and rich deposits.

[0003] However, while the boundaries between exposed granite and other lithologies or stratigraphic units are relatively easy to identify, the contact zones of deep granite bodies are very difficult to locate, especially in southern regions with thick sedimentary strata and well-developed vegetation. Delineating the contact zones and determining their depth is extremely challenging, resulting in a lack of technical support for finding deep contact zone-type uranium deposits. This often leads to overlooking deep exploration opportunities and leaving potential mineralized areas undiscovered. Direct drilling is a highly risky and costly method with very low feasibility.

[0004] Therefore, developing a calculation method capable of determining the location and depth of the deep contact zone in uranium-rich granites is crucial for breaking through the deep granite contact zone type uranium deposits. Summary of the Invention

[0005] The purpose of this invention is to provide a method for calculating the burial depth of the deep contact zone of uranium-rich granite. This method uses stream sediment surveys, large-scale gravity measurements, and magnetotelluric sounding to effectively solve the current problem of being unable to locate and calculate the burial depth of the deep contact zone of uranium-rich granite bodies.

[0006] Technical solution to achieve the purpose of this invention:

[0007] A method for calculating the burial depth of the deep contact zone in uranium-rich granite, the method comprising:

[0008] Step 1: Conduct stream sediment sampling within the granite development area of ​​the study area;

[0009] Step 2: Analyze the uranium content of the samples and delineate the uranium-rich granite development area;

[0010] Step 3: Conduct gravity measurements in the delineated uranium-rich granite development area to obtain Bouguer gravity anomaly and elevation grid data;

[0011] Step 4: Calculate the residual gravity anomaly and generate a residual gravity anomaly mesh file;

[0012] Step 5: Conduct broadband magnetotelluric profiling and use the inversion results to determine the boundary between the deep rock mass and the strata;

[0013] Step 6: Digitize the boundary lines of each section and create a constrained mesh file;

[0014] Step 7: Establish a model and perform interface inversion to obtain elevation grid data of the deep contact zone of the granite mass;

[0015] Step 8: Calculate the burial depth of the deep contact zone of the uranium-rich granite.

[0016] Step 1 includes:

[0017] Step 1.1: Based on the distribution of granite on the geological map of the study area, determine the sampling range of the stream sediments. The range must cover the areas where the granite bodies are exposed.

[0018] Step 1.2: The scale of the sediment sampling work in the water system is 1:50,000. Square grids are divided into sampling units within the study area. The sampling materials are mainly silt and mud, with a particle size of less than 60 mesh. The sample weight is not less than 200 grams.

[0019] Step 2 includes:

[0020] Step 2.1: Analyze the samples collected in Step 1, and calculate the uranium content at each point to obtain uranium content data for each point;

[0021] Step 2.2: Based on the uranium content at each point, calculate the lower limit for delineating uranium anomalies using the following formula:

[0022]

[0023]

[0024] In the formula,

[0025] U(i,j) represents the uranium content data at each point;

[0026] This represents the average uranium content at each point;

[0027] i and j are the east-west and north-south indexes of the sampled square grid nodes, and m and n are the total number of east-west and north-south grids;

[0028] σ represents the standard deviation of the data;

[0029] A(U) represents the lower limit of anomalies in uranium content;

[0030] Step 2.3: Grid the uranium content data U(i,j) at each point using Surfer software to obtain a uranium content contour map. Delineate the planar area where the uranium content value is higher than the lower limit of the uranium content anomaly A(U) as the uranium-rich granite development area.

[0031] Step 3 includes:

[0032] Step 3.1: The gravity working scale is 1:50,000, the survey line spacing is 500 meters, the survey point spacing is 100-500 meters, and the measurement area covers the uranium-rich rock mass development area determined in Step 2.

[0033] Step 3.2: Use a gravimeter and a surveying instrument to conduct measurements, obtain the relative gravity value, latitude and longitude and elevation of each measuring point, and grid the elevation to obtain elevation grid data;

[0034] Step 3.3: Sample the granite and surrounding rock, measure the density of each granite piece and the surrounding rock, and take the average value of all samples as the density value of the granite and surrounding rock in the study area;

[0035] Step 3.4: Calculate the Bouguer gravity anomaly using the following formula.

[0036]

[0037]

[0038] Δg B =g-γ0+δ b +δ 地

[0039] In the above formula, ρ is the latitude of the measuring point; h is the elevation of the measuring point; ρ is the density of the intermediate layer; r is the Earth's radius; Δg B Bouguer gravity anomaly; g is the relative gravity value; γ0 is the normal field correction; δ b δ is the Bouguer correction value. 地 This is the topographic correction value, calculated from digital elevation data collected around the study area.

[0040] Step 4 includes:

[0041] The Bouguer gravity anomaly Δg obtained in step 3 B The remaining gravity anomaly is obtained by processing and calculating using the following method:

[0042]

[0043] Δg 剩余 =Δg B -Δg R

[0044] In the formula, ΔgR The region represents the gravity anomaly at the measuring point; R represents the distance of the calculation window, which must be at least twice the distance of the measuring line; SumΔg B (0,R) represents the sum of Bouguer gravity anomalies at all measuring points within a window distance R used in the calculation; N represents the number of measuring points within this range; Δg 剩余 This indicates a residual gravity anomaly at the measuring point;

[0045] Δg 剩余 The remaining gravity anomaly mesh file is obtained by meshing the data with a grid spacing equal to half the spacing between measurement points.

[0046] Step 5 includes:

[0047] Step 5.1: Broadband magnetotelluric profiles are laid out in a parallel profile manner. The survey lines need to pass through existing boreholes, with a survey line spacing of 1-5 km and a measurement point spacing of 100 or 200 meters. Two electric field components and three magnetic field components are collected simultaneously. The observation time is greater than 24 hours, and the observation frequency range is 10000~0.01HZ to obtain measurement point data.

[0048] Step 5.2: Import the measurement point data obtained in Step 5.1 into the MTPioneer inversion software, set the data threshold error and smoothing coefficient, and select TM mode to perform two-dimensional conjugate gradient inversion calculation to obtain resistivity data;

[0049] Step 5.3: Load the resistivity data of each profile obtained in Step 5.2 into Surfer software to obtain the resistivity profile contour map of each profile;

[0050] Step 5.4: Based on the existing borehole resistivity logging data, and utilizing the numerical characteristics of the resistivity curves of the contact zone between the granite body and the sedimentary strata, the Surfer software is used to divide each resistivity profile contour map obtained in Step 5.3, and to mark the boundary between the deep part of the rock body and the strata.

[0051] Step 6 includes:

[0052] Step 6.1: Digitize the boundary lines marked by each profile in Step 5 to obtain the depth of the boundary line below each measuring point;

[0053] Step 6.2: Calculate the average depth of the boundary line below all measuring points as the average depth of the contact zone, and create a constant grid with this depth value. The grid spacing is completely consistent with the residual gravity anomaly grid file obtained in Step 4. Then, replace the values ​​at the locations of the magnetotelluric measuring points in the constant grid with the depths obtained in Step 6.1 above to form a constrained grid file after electromagnetic calibration.

[0054] Step 7 includes:

[0055] Step 7.1: Use Geosoft software to build a three-layer model. Use the elevation grid file obtained in step 3.3 as the first interface, the constraint grid obtained in step 6 as the second interface, and set the bottom interface to -3km to -10km according to the regional geological conditions.

[0056] Step 7.2: Input the residual gravity anomaly grid obtained in Step 4 as known target data into the model established in Step 7.1, and input the density values ​​of granite and surrounding rock obtained in Step 3.4 into the model;

[0057] Step 7.3: Set the number of inversion iterations and the convergence error, and run the inversion through the interface; when the number of iterations or the convergence error is reached, stop the inversion and obtain the elevation grid data of the deep contact zone of the rock mass.

[0058] Step 8 includes:

[0059] Subtract the elevation grid data obtained in step 7 from the elevation grid data obtained in step 3.3 to obtain the burial depth of the deep contact zone of the uranium-rich granite in the study area.

[0060] The beneficial technical effects of this invention are as follows:

[0061] 1. The present invention provides a method for calculating the burial depth of the deep contact zone of uranium-rich granite, which can quickly calculate the depth of the contact zone between the deep granite body and the surrounding rock, improve exploration efficiency, and locate favorable deep mineral exploration areas.

[0062] 2. The method for calculating the burial depth of the deep contact zone of uranium-rich granite provided by this invention can be widely used in the exploration of granite-type uranium deposits. In particular, after quickly delineating the distribution area of ​​uranium-rich granite through stream sedimentary geochemical methods, geophysical exploration can be carried out to infer the location of the deep contact zone. This method is more operational and reasonable, and can reduce direct geological construction, lower exploration costs and risks.

[0063] 3. The present invention provides a method for calculating the burial depth of the deep contact zone of uranium-rich granite. It uses broadband magnetotelluric inversion and calibration results as constraints, inputs gravity model to perform gravity interface inversion, and uses this method to calculate the depth of the contact zone between the deep granite body and the surrounding rock, which improves the resolution and accuracy. Attached Figure Description

[0064] Figure 1 A flowchart illustrating a method for calculating the burial depth of a deep contact zone in uranium-rich granite, provided by this invention. Detailed Implementation

[0065] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0066] like Figure 1As shown, the present invention provides a method for calculating the burial depth of the deep contact zone of uranium-rich granite, comprising the following steps:

[0067] Step 1: Conduct stream sediment sampling within the granite development area of ​​the study area.

[0068] Step 1.1: Based on the distribution of granite in the 1:50,000 or 1:200,000 geological map of the study area, determine the sampling range of the stream sediments. The range must cover the area where the granite bodies are exposed.

[0069] Step 1.2: The sampling scale for river sediments should be 1:50,000. Within the study area, a square grid of 500 meters on each side should be established, with each small grid measuring 0.25 square kilometers serving as a sampling unit. Sampling locations should be chosen at the bottom of the river or along the riverbank where the water surface meets the surface. If there is no river within the sampling grid, sampling can be conducted at the bottom of a smaller dry ditch. Multiple samples should be taken within a 20-30 meter radius of the initial sampling point, and combined to form a single sample. The sampled material should primarily consist of silt and mud, with a particle size smaller than a 60-mesh sieve. The sample weight should be no less than 200 grams.

[0070] Step 2: Analyze the uranium content of the samples and delineate the uranium-rich granite areas.

[0071] Step 2.1: Analyze the samples collected in Step 1, count the uranium content at each point, and obtain the uranium content data U(i,j) at each point;

[0072] Step 2.2: Based on the uranium content at each point, calculate the lower limit for delineating uranium anomalies using the following formula:

[0073]

[0074]

[0075] In the formula, U(i,j) represents the uranium content data at each point;

[0076] This represents the average uranium content at each point;

[0077] i and j are the east-west and north-south indexes of the sampled square grid nodes, and m and n are the total number of east-west and north-south grids;

[0078] σ represents the standard deviation of the data;

[0079] A(U) represents the lower limit of uranium content anomalies.

[0080] Step 2.3: Grid the uranium content data U(i,j) using Surfer software. The minimum curvature method is selected for gridding to obtain a uranium content contour map. Delineate the planar region where the uranium content value is higher than the lower limit of uranium content anomaly A(U), and denote it as S(U), indicating that this region is a uranium-rich granite development area.

[0081] Step 3: Conduct gravity measurements around the uranium-rich granite development area identified in Step 2 to obtain Bouguer gravity anomalies and elevation grid data.

[0082] Step 3.1: The gravity working scale is 1:50,000, that is, the spacing between survey lines is 500 meters, the spacing between survey points is 100-500 meters, and the measurement area covers the uranium-rich rock mass development area determined in Step 2.

[0083] Step 3.2: Use a gravimeter and a surveying instrument to conduct measurements, obtain the relative gravity value, latitude and longitude and elevation of each measuring point, and grid the elevation to obtain elevation grid data.

[0084] The gravimeter used must have a resolution of 0.001 × 10⁻⁶. -5 m / s 2 The repeatability accuracy is better than 0.005×10⁻⁶. -5 m / s 2 The elevation measurement accuracy of the surveying instrument used is better than 0.1m.

[0085] Step 3.3: Simultaneously sample the granite and surrounding rock, with no fewer than 30 samples. Measure the density of each granite sample and the surrounding rock using a balance and measuring cup, and take the average value of all samples as the density value of the granite and surrounding rock in the study area.

[0086] Step 3.4: Calculate the Bouguer gravity anomaly using the following formula.

[0087]

[0088]

[0089] Δg B =g-γ0+δ b +δ 地

[0090] In the above formula, ρ is the latitude of the measuring point; h is the elevation of the measuring point (m); ρ is the density of the intermediate layer (taken as 2.66 g / cm³). 3 ); r is the Earth's radius; Δg B Bouguer gravity anomaly; g is the relative gravity value; γ0 is the normal field correction; δ b δ is the Bouguer correction value. 地 This is the topographic correction value, calculated from digital elevation data collected around the study area.

[0091] Step 4: Calculate the residual gravity anomaly and generate a residual gravity anomaly mesh file.

[0092] The Bouguer gravity anomaly Δg obtained in step 3 B The remaining gravity anomaly is obtained by processing and calculating using the following method.

[0093]

[0094] Δg 剩余 =Δg B -Δg R

[0095] In the formula, Δg R The region represents the gravity anomaly at the measuring point; R represents the distance of the calculation window, which must be at least twice the distance of the measuring line; SumΔg B (0,R) represents the sum of Bouguer gravity anomalies at all measuring points within a window distance R used in the calculation; N represents the number of measuring points within this range; Δg 剩余 This indicates an anomaly in the residual gravity at the measuring point.

[0096] Δg 剩余 The grid is then created with a grid spacing equal to half the measurement point spacing in step 3.1, resulting in the residual gravity anomaly grid file.

[0097] Step 5: Conduct broadband magnetotelluric profiling and use the inversion results to determine the boundary between the deep rock mass and the strata.

[0098] Step 5.1: Broadband magnetotelluric profiles should be laid out in a parallel profile manner, with the survey lines passing through existing boreholes. The spacing between survey lines should be 1-5 km, and the profiles should uniformly cover the study area. The spacing between measurement points should be 100 or 200 meters. Two electric field components and three magnetic field components should be collected simultaneously, with an observation time of more than 24 hours and an observation frequency range of 10000–0.01 Hz to obtain measurement point data.

[0099] Step 5.2: Import the measurement point data obtained in Step 5.1 into the MTPioneer inversion software, set a data threshold error of 2%, select a smoothness coefficient of 10, and select TM mode to perform two-dimensional conjugate gradient inversion calculation to obtain resistivity data.

[0100] Step 5.3: Load the resistivity data of each profile obtained in Step 5.2 into Surfer software to obtain the resistivity profile contour map of each profile.

[0101] Step 5.4: Mark the location of the surface boundary line on the resistivity contour map of each section.

[0102] Based on existing borehole resistivity logging data, and utilizing the numerical characteristics of the resistivity curves of the contact zone between the granite body and the sedimentary strata, Surfer software was used to divide each resistivity profile contour map obtained in step 5.3, thus marking the boundary between the deep part of the rock body and the strata.

[0103] Step 6: Digitize the boundary lines of each section and create a constrained mesh file.

[0104] Step 6.1: Digitize the boundary lines marked by each profile in Step 5 to obtain the depth of the boundary line below each measuring point.

[0105] Step 6.2: Calculate the average depth of the boundary line below all measuring points as the average depth of the contact zone, and create a constant grid based on this depth value. The grid spacing should be exactly the same as the residual gravity anomaly grid file obtained in Step 4. Then, replace the values ​​at the magnetotelluric measuring point locations in the constant grid with the depths obtained in Step 6.1 above to form the constrained grid file after electromagnetic calibration.

[0106] Step 7: Establish a model to perform interface inversion and obtain elevation grid data of the deep contact zone of the granite rock mass.

[0107] Step 7.1: Use Geosoft software to build a three-layer model. Use the elevation grid file obtained in Step 3.3 as the first interface, the constraint grid obtained in Step 6 as the second interface, and set the bottom interface to -3km to -10km according to the regional geological conditions.

[0108] Step 7.2: Input the residual gravity anomaly grid obtained in Step 4 as known target data into the model established in Step 7.1, and input the density values ​​of granite and surrounding rock obtained in Step 3.4 into the model.

[0109] Step 7.3: Set the inversion iteration count to 20 and the convergence error to 0.05 mgal, then run the inversion through the interface. Stop the inversion when the required number of iterations or the convergence error is reached, and obtain the elevation grid data of the deep contact zone of the rock mass.

[0110] Step 8: Calculate the burial depth of the deep contact zone of the uranium-rich granite.

[0111] Subtracting the elevation grid data obtained in step 7 from the elevation grid data obtained in step 3.3 gives the burial depth of the deep contact zone of the uranium-rich granite in the study area.

[0112] Example

[0113] Taking the granite-type uranium metallogenic belt in northern Zhuguang region as an example, this invention provides a method for calculating the burial depth of the deep contact zone of uranium-rich granite, comprising the following steps:

[0114] Step 1: Conduct stream sediment sampling within the granite development area of ​​the study area.

[0115] Step 1.1: Based on the distribution of granite in the 1:50,000 geological map of the study area, determine the sampling range of the stream sediments, covering the areas where granite bodies are exposed.

[0116] Step 1.2: The sampling scale for river sediments was 1:50,000. The study area was divided into square grids, each 500 meters wide and long, with each grid representing a 0.25 square kilometer area as a sampling unit. Sampling locations were chosen at the bottom of rivers or riverbanks where they met the water surface. If there was no river within the sampling grid, sampling was conducted at the bottom of smaller dry ditches. Multiple samples were taken within a 30-meter radius of each sampling point and combined to form a single sample. The sampled material consisted mainly of silt and mud, with a particle size smaller than a 60-mesh sieve. The sample weight was approximately 250 grams.

[0117] Step 2: Analyze the uranium content of the samples and delineate the uranium-rich granite areas.

[0118] Step 2.1: Analyze the samples collected in Step 1, count the uranium content at each point, and obtain the uranium content data U(i,j) at each point;

[0119] Step 2.2 Calculate the lower limit for uranium anomaly delineation using the following formula:

[0120]

[0121]

[0122] In the formula,

[0123] U(i,j) represents the uranium content data at each point;

[0124] This represents the average uranium content at each point;

[0125] i and j represent the east-west and north-south indexes of the sampled square grid nodes, respectively, and m and n represent the total number of east-west and north-south grids, which are 56 and 40 respectively.

[0126] σ represents the standard deviation of the data;

[0127] A(U) represents the lower limit of uranium content anomalies.

[0128] Step 2.3: Grid the uranium content data U(i,j) using Surfer software. The minimum curvature method is selected for gridding to obtain a uranium content contour map. Delineate the planar region where the uranium content value is higher than the lower limit of uranium content anomaly A(U), and denote it as S(U), indicating that this region is a uranium-rich granite development area.

[0129] Step 3: Conduct gravity measurements around the area determined in Step 2 to obtain Bouguer gravity anomaly and elevation grid data.

[0130] Step 3.1: The gravity working scale is 1:50,000, the survey line spacing is 500 meters, the survey point spacing is 250 meters, and the measurement area covers the uranium-rich rock mass development area determined in Step 2.

[0131] Step 3.2: Use a gravimeter and a surveying instrument to conduct measurements, obtain the relative gravity value, latitude and longitude and elevation of each measuring point, and grid the elevation to obtain elevation grid data.

[0132] The gravimeter used was a CG-5 model with a resolution of 0.001×10⁻⁶. -5 m / s 2 The repeatability accuracy is better than 0.005×10⁻⁶. - 5 m / s 2 The surveying instrument used was a Trimble dual-frequency differential GPS, with an elevation measurement accuracy better than 0.1m.

[0133] Step 3.3: Sample the granite and surrounding rock, with 30 samples collected. Measure the density of each granite sample and the surrounding rock using a balance and measuring cup. Take the average value of all samples as the density value of the granite and surrounding rock in the study area.

[0134] Step 3.4: Calculate the Bouguer gravity anomaly using the following formula.

[0135]

[0136]

[0137] Δg B =g-γ0+δ b +δ 地

[0138] In the above formula, ρ is the latitude of the measuring point; h is the elevation of the measuring point (m); ρ is the density of the intermediate layer (taken as 2.66 g / cm³). 3 ); r is the Earth's radius; Δg B Bouguer gravity anomaly; g is the relative gravity value; γ0 is the normal field correction; δ b δ is the Bouguer correction value. 地 This is the topographic correction value, calculated from digital elevation data collected around the study area.

[0139] Step 4: Calculate the residual gravity anomaly and generate a residual gravity anomaly mesh file.

[0140] The Bouguer gravity anomaly Δg obtained in step 3 BThe remaining gravity anomaly is obtained by processing and calculating using the following method.

[0141]

[0142] Δg 剩余 =Δg B -Δg R

[0143] In the formula,

[0144] Δg R This indicates the regional gravity anomaly at the measuring point; SumΔg B (0,R) represents the sum of Bouguer gravity anomalies at all measuring points within a radius R from the measuring point; N represents the number of measuring points within this radius. R represents the window distance involved in the calculation, which must be at least twice the distance of the measuring line; Δg 剩余 This indicates an anomaly in the residual gravity at the measuring point.

[0145] Δg 剩余 The remaining gravity anomaly mesh file is obtained by meshing the data with a grid spacing equal to half the spacing between measurement points.

[0146] Step 5: Conduct broadband magnetotelluric profiling and use the inversion results to determine the boundary between the deep rock mass and the strata.

[0147] Step 5.1 The broadband magnetotelluric profile is laid out in a parallel profile manner. The survey lines need to pass through existing boreholes, with a spacing of 4 km between lines to uniformly cover the study area. The point spacing is 200 meters. Two electric field components and three magnetic field components are collected simultaneously, with an observation time of more than 24 hours and an observation frequency range of 10000~0.01Hz to obtain the measurement point data.

[0148] Step 5.2: Import the measurement data obtained in Step 5.1 into the MTPioneer inversion software, set a data threshold error of 2%, select a smoothness coefficient of 10, and select TM mode to perform two-dimensional conjugate gradient inversion calculation to obtain resistivity data.

[0149] Step 5.3 Load the resistivity data of each profile obtained in Step 5.2 into Surfer software to obtain the resistivity profile contour map of each profile.

[0150] Step 5.4: Mark the location of the surface boundary line on the resistivity contour map of each section.

[0151] Based on existing borehole resistivity logging data, and utilizing the numerical characteristics of the resistivity curves of the contact zone between the granite body and the sedimentary strata, Surfer software was used to divide each resistivity profile contour map obtained in step 5.3, thus marking the boundary between the deep part of the rock body and the strata.

[0152] Step 6: Digitize the boundary lines of each section and create a constrained mesh file.

[0153] Step 6.1 Digitize the boundary lines marked by each profile in Step 5 to obtain the depth of the boundary line below each measuring point.

[0154] Step 6.2 Calculate the average depth of the boundary line below all measuring points as the average depth of the contact zone, and create a constant grid based on this depth value. The grid spacing is exactly the same as the residual gravity anomaly grid file obtained in Step 4. Then, replace the values ​​at the magnetotelluric measuring point locations in the constant grid with the depths obtained in Step 6.1 above to form the constrained grid file after electromagnetic calibration.

[0155] Step 7: Establish a model to perform interface inversion and obtain elevation grid data of the deep contact zone of the granite rock mass.

[0156] Step 7.1 Use Geosoft software to build a three-layer model. Use the elevation grid file obtained in Step 3.3 as the first interface and the constraint grid obtained in Step 6 as the second interface. Set the depth of the bottom interface to -5km.

[0157] Step 7.2 Input the residual gravity anomaly grid obtained in Step 4 as known target data into the model established in Step 7.1, and input the density values ​​of granite and surrounding rock obtained in Step 3.4 into the model.

[0158] Step 7.3 Set the inversion iteration count to 20 and the convergence error to 0.05 mgal, then run the inversion through the interface. Stop the inversion when the required number of iterations or the convergence error is reached, and obtain the elevation grid data of the deep contact zone of the rock mass.

[0159] Step 8: Calculate the burial depth of the deep contact zone of the uranium-rich granite.

[0160] Subtracting the elevation grid data obtained in step 7 from the elevation grid data obtained in step 3.3 gives the burial depth of the deep contact zone of the uranium-rich granite in the study area.

[0161] The present invention has been described in detail above with reference to the accompanying drawings and embodiments. However, the present invention is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention. All contents not described in detail in the present invention can be derived from existing technologies.

Claims

1. A method for calculating the burial depth of the deep contact zone in uranium-rich granite, characterized in that, The method includes: Step 1: Conduct stream sediment sampling within the granite development area of ​​the study area; Step 2: Analyze the uranium content of the samples and delineate the uranium-rich granite development area; Step 3: Conduct gravity measurements in the delineated uranium-rich granite development area to obtain Bouguer gravity anomaly and elevation grid data; Step 4: Calculate the residual gravity anomaly and generate a residual gravity anomaly mesh file; Step 5: Conduct broadband magnetotelluric profiling and use the inversion results to determine the boundary between the deep rock mass and the strata; Step 6: Digitize the boundary lines of each section and create a constrained mesh file; Step 7: Establish a model and perform interface inversion to obtain elevation grid data of the deep contact zone of the granite mass; Step 8: Calculate the burial depth of the deep contact zone of the uranium-rich granite.

2. The method for calculating the burial depth of the deep contact zone in uranium-rich granite according to claim 1, characterized in that, Step 1 includes: Step 1.1: Based on the distribution of granite on the geological map of the study area, determine the sampling range of the stream sediments. The range must cover the areas where the granite bodies are exposed. Step 1.2: The scale of the sediment sampling work in the water system is 1:50,000. Square grids are divided into sampling units within the study area. The sampling materials are mainly silt and mud, with a particle size of less than 60 mesh. The sample weight is not less than 200 grams.

3. The method for calculating the burial depth of the deep contact zone in uranium-rich granite according to claim 1, characterized in that, Step 2 includes: Step 2.1: Analyze the samples collected in Step 1, and calculate the uranium content at each point to obtain uranium content data for each point; Step 2.2: Based on the uranium content at each point, calculate the lower limit for delineating uranium anomalies using the following formula: In the formula, U(i,j) represents the uranium content data at each point; This represents the average uranium content at each point; i and j are the east-west and north-south indexes of the sampled square grid nodes, and m and n are the total number of east-west and north-south grids; σ represents the standard deviation of the data; A(U) represents the lower limit of anomalies in uranium content; Step 2.3: Grid the uranium content data U(i,j) at each point using Surfer software to obtain a uranium content contour map. Delineate the planar area where the uranium content value is higher than the lower limit of the uranium content anomaly A(U) as the uranium-rich granite development area.

4. The method for calculating the burial depth of the deep contact zone in uranium-rich granite according to claim 1, characterized in that, Step 3 includes: Step 3.1: The gravity working scale is 1:50,000, the survey line spacing is 500 meters, the survey point spacing is 100-500 meters, and the measurement area covers the uranium-rich rock mass development area determined in Step 2. Step 3.2: Use a gravimeter and a surveying instrument to conduct measurements, obtain the relative gravity value, latitude and longitude and elevation of each measuring point, and grid the elevation to obtain elevation grid data; Step 3.3: Sample the granite and surrounding rock, measure the density of each granite piece and the surrounding rock, and take the average value of all samples as the density value of the granite and surrounding rock in the study area; Step 3.4: Calculate the Bouguer gravity anomaly using the following formula. Δg B =g-γ0+δ b +d 地 In the above formula, ρ is the latitude of the measuring point; h is the elevation of the measuring point; ρ is the density of the intermediate layer; r is the Earth's radius; Δg B Bouguer gravity anomaly; g is the relative gravity value; γ0 is the normal field correction; δ b δ is the Bouguer correction value. 地 This is the topographic correction value, calculated from digital elevation data collected around the study area.

5. The method for calculating the burial depth of the deep contact zone of uranium-rich granite according to claim 4, characterized in that, Step 4 includes: The Bouguer gravity anomaly Δg obtained in step 3 B The remaining gravity anomaly is obtained by processing and calculating using the following method: Δg 剩余 =Δg B -Δg R In the formula, Δg R The region represents the gravity anomaly at the measuring point; R represents the distance of the calculation window, which must be at least twice the distance of the measuring line; SumΔg B (0,R) represents the sum of Bouguer gravity anomalies at all measuring points within a window distance R used in the calculation; N represents the number of measuring points within this range; Δg 剩余 This indicates a residual gravity anomaly at the measuring point; Δg 剩余 The remaining gravity anomaly mesh file is obtained by meshing the data with a grid spacing equal to half the spacing between measurement points.

6. The method for calculating the burial depth of the deep contact zone of uranium-rich granite according to claim 5, characterized in that, Step 5 includes: Step 5.1: Broadband magnetotelluric profiles are laid out in a parallel profile manner. The survey lines need to pass through existing boreholes, with a survey line spacing of 1-5 km and a measurement point spacing of 100 or 200 meters. Two electric field components and three magnetic field components are collected simultaneously. The observation time is greater than 24 hours, and the observation frequency range is 10000~0.01HZ to obtain measurement point data. Step 5.2: Import the measurement point data obtained in Step 5.1 into the MTPioneer inversion software, set the data threshold error and smoothing coefficient, and select TM mode to perform two-dimensional conjugate gradient inversion calculation to obtain resistivity data; Step 5.3: Load the resistivity data of each profile obtained in Step 5.2 into Surfer software to obtain the resistivity profile contour map of each profile; Step 5.4: Based on the existing borehole resistivity logging data, and utilizing the numerical characteristics of the resistivity curves of the contact zone between the granite body and the sedimentary strata, the Surfer software is used to divide each resistivity profile contour map obtained in Step 5.3, and to mark the boundary between the deep part of the rock body and the strata.

7. The method for calculating the burial depth of the deep contact zone of uranium-rich granite according to claim 6, characterized in that, Step 6 includes: Step 6.1: Digitize the boundary lines marked by each profile in Step 5 to obtain the depth of the boundary line below each measuring point; Step 6.2: Calculate the average depth of the boundary line below all measuring points as the average depth of the contact zone, and create a constant grid with this depth value. The grid spacing is completely consistent with the residual gravity anomaly grid file obtained in Step 4. Then, replace the values ​​at the locations of the magnetotelluric measuring points in the constant grid with the depths obtained in Step 6.1 above to form a constrained grid file after electromagnetic calibration.

8. The method for calculating the burial depth of the deep contact zone of uranium-rich granite according to claim 7, characterized in that, Step 7 includes: Step 7.1: Use Geosoft software to build a three-layer model. Use the elevation grid data obtained in Step 3.3 as the first interface, the constraint grid file obtained in Step 6 as the second interface, and set the bottom interface to -3km to -10km according to the regional geological conditions. Step 7.2: Input the residual gravity anomaly grid obtained in Step 4 as known target data into the model established in Step 7.1, and input the density values ​​of granite and surrounding rock obtained in Step 3.4 into the model; Step 7.3: Set the number of inversion iterations and the convergence error, and run the inversion through the interface; when the number of iterations or the convergence error is reached, stop the inversion and obtain the elevation grid data of the deep contact zone of the rock mass.

9. The method for calculating the burial depth of the deep contact zone of uranium-rich granite according to claim 8, characterized in that, Step 8 includes: Subtract the elevation grid data obtained in step 7 from the elevation grid data obtained in step 3.3 to obtain the burial depth of the deep contact zone of the uranium-rich granite in the study area.

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