Method for calculating burial depth of deep contact zone of uranium-rich granite

Abstract

The invention belongs to the technical field of uranium resource exploration, and particularly relates to a uranium-rich granite deep contact zone burial depth calculation method which comprises the following steps: step 1, carrying out water system deposition sampling in a granite development range of a research area; 2, the uranium element content of the sample is counted, and a uranium-rich granite development area is delineated; 3, gravity measurement is carried out in the delineated uranium-rich granite development area, and Bouguer gravity anomaly and elevation grid data are obtained; 4, solving residual gravity anomaly to form a residual gravity anomaly grid file; 5, broadband magnetotelluric profile measurement is carried out, and a boundary between the deep part of the rock mass and the stratum is calibrated through an inversion result; 6, digitizing each section boundary, and making a constraint grid file; 7, establishing a model to carry out interface inversion, and obtaining elevation grid data of the deep contact zone of the granite rock mass; and 8, calculating the burial depth of the deep contact zone of the uranium-rich granite. According to the method, the deep contact zone burial depth of the uranium-rich granite body can be accurately positioned and calculated.

Description

Technical Field

[0001] The invention belongs to the technical field of uranium resource exploration, and in particular relates to a method for calculating the buried depth of a deep contact zone of uranium-rich granite. Background Art

[0002] Granite-type uranium deposits refer to uranium deposits that are genetically related to granite bodies and are produced in or near the rock body. They are one of the four major types of uranium deposits in my country. Since the discovery of the first uranium ore in New China, several decades have passed, and multiple granite-type uranium deposits have been confirmed. The mineralization locations that have been found are mainly closely related to the rock body, the contact zone of the strata, and the fault structure. In particular, the contact zone between the uranium-rich granite rock body and the deep strata is often more conducive to large-scale mineralization, and it is also easy to form large and rich mines.

[0003] However, the boundary between the exposed granite and other lithologies or strata is relatively easy to find, while the contact zone of the deep granite is difficult to locate, especially in the granite areas in the south where the sedimentary strata are thick and the vegetation is well developed. The division of the contact zone and the determination of the buried depth are very difficult, which makes the current search for deep rock contact zone uranium deposits lack technical support, often miss the deep prospecting space, and cause the potential mineralization area to remain undiscovered. The direct drilling method is blind and costly, and the feasibility is very low.

[0004] Therefore, developing a calculation method that can calculate the position and burial depth of the deep contact zone of uranium-rich granite is the key to breaking through the deep granite lithological contact zone type uranium deposits. Summary of the invention

[0005] The purpose of the present invention is to provide a method for calculating the buried depth of the deep contact zone of uranium-rich granite. The method adopts water system sediment investigation, large-scale gravity measurement and magnetotelluric sounding method to effectively solve the problem that the buried depth of the deep contact zone of uranium-rich granite body cannot be located and calculated at present.

[0006] The technical solution to achieve the purpose of the present invention is:

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

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

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

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

[0011] Step 4: Obtain the residual gravity anomaly and form a residual gravity anomaly grid file;

[0012] Step 5: Conduct broadband magnetotelluric profile measurement and calibrate the boundary between the deep rock mass and the stratum through the inversion results;

[0013] Step 6: Digitize each section boundary line and create a constraint grid file;

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

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

[0016] The step 1 comprises:

[0017] Step 1.1: According to the distribution of granite in the geological map of the study area, determine the sampling range of stream sediments, which must cover the area where granite bodies are exposed;

[0018] Step 1.2: The sampling scale of water system sediment is 1:50,000. A square grid is divided within the study area as the sampling unit. The sampling material is mainly silt and silt, and the particle size is less than 60 mesh. The sample retention weight is not less than 200 grams.

[0019] The step 2 comprises:

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

[0021] Step 2.2: According to the uranium content at each point, calculate the lower limit of uranium anomaly delineation according to the following formula:

[0022]

[0023]

[0024] In the formula,

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

[0026] is the average value of uranium content at each point;

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

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

[0029] A(U) is the lower limit of abnormal uranium content;

[0030] Step 2.3: Use the surfer software to grid the uranium content data U(i,j) at each point to obtain a uranium content contour map, and delineate the plane area where the uranium content value is higher than the lower limit of the uranium content anomaly A(U) as the area where uranium-rich granite is developed.

[0031] The step 3 comprises:

[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 survey area covers the uranium-rich rock development area determined in step 2;

[0033] Step 3.2: Use a gravimeter and a surveying instrument to carry out measurements, obtain the relative gravity value, longitude and latitude, 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 piece of granite and 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, is the latitude of the measuring point; h is the height of the measuring point; ρ is the density of the mesosphere; r is the radius of the earth; Δg B is the Bouguer gravity anomaly; g is the relative gravity value; γ0 is the normal field correction value; δ b is the Bouguer correction value; δ 地 It is the terrain correction value, which is calculated by collecting digital elevation data around the study area.

[0040] The step 4 comprises:

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

[0042]

[0043] Δg 剩余 =Δg B -Δg R

[0044] In the formula, ΔgR Indicates the regional gravity anomaly of the measuring point; R indicates the window distance involved in the calculation, which is at least twice the measuring line distance; SumΔg B (0, R) represents the sum of the Bouguer gravity anomalies of all measuring points within the window distance R involved in the calculation; N represents the number of measuring points within the range; Δg 剩余 Indicates the residual gravity anomaly at the measuring point;

[0045] Δg 剩余 Gridding is performed with a grid spacing of half the measurement point spacing to obtain the residual gravity anomaly grid file.

[0046] The step 5 comprises:

[0047] Step 5.1: The broadband magnetotelluric profile is laid out in parallel profiles. The survey line needs to pass through existing boreholes. The survey line spacing is 1-5km, and the measurement point spacing is 100 or 200 meters. Two electric field components and three magnetic field components are collected at the same time. The observation time is greater than 24 hours, and the observation frequency range is 10000~0.01HZ to obtain the 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 the TM mode to perform two-dimensional conjugate gradient inversion calculation to obtain resistivity data;

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

[0050] Step 5.4: Based on the existing borehole resistivity logging data, using the numerical characteristics of the resistivity curve of the contact zone between the granite body and the sedimentary stratum, use the Surfer software to divide each resistivity profile contour map obtained in step 5.3 and calibrate the boundary between the deep rock mass and the stratum.

[0051] The step 6 comprises:

[0052] Step 6.1: Digitize the boundary lines marked out in each section 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 use this depth value to make a constant grid. The grid spacing is exactly the same as the residual gravity anomaly grid file obtained in step 4; then, replace the value at the magnetotelluric measuring point position in the constant grid with the depth obtained in step 6.1 above to form a constrained grid file after electromagnetic calibration.

[0054] The step 7 comprises:

[0055] Step 7.1: Use Geosoft software to build a three-layer model, using 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 the bottom interface is set 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, convergence error, and run the interface inversion; when the number of iterations or convergence error is reached, stop the inversion and obtain the elevation grid data of the deep contact zone of the rock mass.

[0058] The step 8 comprises:

[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 the present invention are:

[0061] 1. The present invention provides a method for calculating the buried 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 the exploration efficiency, and locate the deep areas that are beneficial for prospecting.

[0062] 2. The method for calculating the buried depth of the deep contact zone of uranium-rich granite provided by the present invention can be widely used in the exploration of granite-type uranium deposits, especially after the distribution area of ​​uranium-rich granite is quickly delineated by the water system sedimentary geochemical method, geophysical exploration is then carried out to infer the position of the deep contact zone. It is more operable and more reasonable, can reduce direct geological construction, and reduce exploration costs and risks.

[0063] 3. The present invention provides a method for calculating the buried depth of the deep contact zone of uranium-rich granite. The method uses broadband magnetotelluric inversion and calibration results as constraints, inputs a 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, thereby improving the resolution and accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 The present invention provides a flow chart of a method for calculating the buried depth of the deep contact zone of uranium-rich granite. DETAILED DESCRIPTION

[0065] The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

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

[0067] Step 1: Carry out stream sediment sampling within the granite development range of the study area.

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

[0069] Step 1.2: The sampling scale of water system sediments is required to be 1:50,000. A square grid with a length and width of 500 meters is divided within the study area, that is, each small grid of 0.25 square kilometers is used as a sampling unit; the sampling location is selected at the bottom of the river or the part where the river bank contacts the water surface. If there is no water system in the sampling grid, sampling can be carried out at the bottom of a smaller dry ditch. Multiple sampling points are carried out within 20-30 meters around the sampling point and combined into a sample. The sampling material is mainly silt and silt, and the particle size is required to be less than the particle size of the 60 mesh sieve; the sample retention weight is not less than 200 grams.

[0070] Step 2: Count the uranium content of the samples and identify 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: According to the uranium content at each point, calculate the lower limit of uranium anomaly delineation according to the following formula:

[0073]

[0074]

[0075] Where, U(i,j) is the uranium content data of each point;

[0076] is the average value of uranium content at each point;

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

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

[0079] A(U) is the lower limit of abnormal uranium content.

[0080] Step 2.3: The uranium content data U(i,j) are gridded using the surfer software. The minimum curvature method is selected as the gridding method to obtain the uranium content contour map. The plane area where the uranium content value is higher than the lower limit of the uranium content anomaly A(U) is circled and recorded as S(U), indicating that the area is a uranium-rich granite development area.

[0081] Step 3: Carry out gravity measurement around the uranium-rich granite development area determined in Step 2 to obtain Bouguer gravity anomaly and elevation grid data.

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

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

[0084] The resolution of the gravimeter used is required to reach 0.001×10 -5 m / s 2 , repeatability is better than 0.005×10 -5 m / s 2 The elevation measurement accuracy of the surveying instrument used is better than 0.1m.

[0085] Step 3.3: Sample granite and surrounding rock at the same time, with the number of samples not less than 30. Use a balance and a measuring cup to measure the density of each piece of granite and surrounding rock, and take the average value of all samples as the density value of 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, is the latitude of the measuring point; h is the height of the measuring point (m); ρ is the density of the middle layer (taken as 2.66g / cm 3 ), r is the radius of the earth, Δg B is the Bouguer gravity anomaly; g is the relative gravity value; γ0 is the normal field correction value; δ b is the Bouguer correction value; δ 地 It is the terrain correction value, which is calculated by collecting digital elevation data around the study area.

[0091] Step 4: Obtain the residual gravity anomaly and form a residual gravity anomaly grid file.

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

[0093]

[0094] Δg 剩余 =Δg B -Δg R

[0095] In the formula, Δg R Indicates the regional gravity anomaly of the measuring point; R indicates the window distance involved in the calculation, which is at least twice the measuring line distance; SumΔg B (0, R) represents the sum of the Bouguer gravity anomalies of all measuring points within the window distance R involved in the calculation; N represents the number of measuring points within the range; Δg 剩余 Indicates the residual gravity anomaly at the measuring point.

[0096] Δg 剩余 Gridding is performed with a grid spacing of half the measurement point spacing in step 3.1 to obtain the residual gravity anomaly grid file.

[0097] Step 5: Conduct broadband magnetotelluric profile measurement and calibrate the boundary between the deep rock mass and the stratum through the inversion results.

[0098] Step 5.1: Broadband magnetotelluric profiles are required to be laid out in parallel profiles. The survey lines need to pass through existing boreholes, with a survey line spacing of 1-5 km and uniform coverage of the study area. The measurement point spacing is 100 or 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 to 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 the data threshold error to 2%, select the smoothing coefficient to 10, and select the TM mode to perform two-dimensional conjugate gradient inversion calculation to obtain the resistivity data.

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

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

[0102] According to the existing borehole resistivity logging data, using the numerical characteristics of the resistivity curve of the contact zone between the granite body and the sedimentary stratum, the Surfer software is used to divide each resistivity profile contour map obtained in step 5.3 to calibrate the boundary between the deep rock mass and the stratum.

[0103] Step 6: Digitize each section boundary line and create a constraint grid file.

[0104] Step 6.1: Digitize the boundary lines marked out in each section 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 use this depth value to make a constant grid, and the grid spacing is exactly the same as the residual gravity anomaly grid file obtained in step 4. Then, replace the value at the magnetotelluric measuring point position in the constant grid with the depth obtained in step 6.1 above to form the constrained grid file after electromagnetic calibration.

[0106] Step 7: Establish a model to carry out interface inversion and obtain the 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, using 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 the bottom interface set to -3km to -10km according to the regional geological conditions.

[0108] Step 7.2: Input the remaining 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 number of inversion iterations to 20, the convergence error to 0.05 mgal, and run the interface inversion. 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.

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

[0111] 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.

[0112] Example

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

[0114] Step 1: Carry out stream sediment sampling within the granite development range of the study area.

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

[0116] Step 1.2: The sampling scale of river sediments is 1:50,000. A square grid with a length and width of 500 meters is divided within the study area, that is, each small grid of 0.25 square kilometers is used as a sampling unit; the sampling location is selected at the bottom of the river or the part where the river bank contacts the water surface. If there is no water system in the sampling grid, sampling is performed at the bottom of a smaller dry ditch. Multiple sampling is performed within 30 meters around the sampling point and combined into a sample. The sampling material is mainly silt and silt, and the particle size is less than the particle size of the 60 mesh sieve; the sample retention weight is about 250 grams.

[0117] Step 2: Count the uranium content of the samples and identify 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 of uranium anomaly delineation according to the following formula:

[0120]

[0121]

[0122] In the formula,

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

[0124] is the average value of uranium content at each point;

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

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

[0127] A(U) is the lower limit of abnormal uranium content.

[0128] Step 2.3: The uranium content data U(i,j) are gridded using the surfer software. The minimum curvature method is selected as the gridding method to obtain the uranium content contour map. The plane area where the uranium content value is higher than the lower limit of the uranium content anomaly A(U) is circled and recorded as S(U), indicating that the area is a uranium-rich granite development area.

[0129] Step 3: Carry out gravity measurement 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 survey area covers the uranium-rich rock development area determined in step 2.

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

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

[0133] Step 3.3: Sample 30 granite and surrounding rocks. Use a balance and a measuring cup to measure the density of each granite and surrounding rock, and 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, is the latitude of the measuring point; h is the height of the measuring point (m); ρ is the density of the middle layer (taken as 2.66g / cm 3 ), r is the radius of the earth, Δg B is the Bouguer gravity anomaly; g is the relative gravity value; γ0 is the normal field correction value; δ b is the Bouguer correction value; δ 地 It is the terrain correction value, which is calculated by collecting digital elevation data around the study area.

[0139] Step 4: Obtain the residual gravity anomaly and form a residual gravity anomaly grid file.

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

[0141]

[0142] Δg 剩余 =Δg B -Δg R

[0143] In the formula,

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

[0145] Δg 剩余 Gridding is performed with a grid spacing of half the measurement point spacing to obtain the residual gravity anomaly grid file.

[0146] Step 5: Conduct broadband magnetotelluric profile measurement and calibrate the boundary between the deep rock mass and the stratum through the inversion results.

[0147] Step 5.1 The broadband magnetotelluric profile is laid out in parallel profiles. The survey line needs to pass through existing boreholes. The survey line spacing is 4 km, evenly covering the study area. The point spacing is 200 meters. Two electric field components and three magnetic field components are collected at the same time. The observation time is greater than 24 hours, and the observation frequency range is 10000~0.01HZ to obtain the measurement point data.

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

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

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

[0151] According to the existing borehole resistivity logging data, using the numerical characteristics of the resistivity curve of the contact zone between the granite body and the sedimentary stratum, the Surfer software is used to divide each resistivity profile contour map obtained in step 5.3 to calibrate the boundary between the deep rock mass and the stratum.

[0152] Step 6: Digitize each section boundary line and create a constraint grid file.

[0153] Step 6.1 digitizes the boundary lines marked out in each section in step 5, that is, obtains the depth of the boundary line below each measuring point.

[0154] Step 6.2 calculates the average depth of the boundary line below all measuring points as the average depth of the contact zone, and uses this depth value to make a constant grid, with the grid spacing being exactly the same as the residual gravity anomaly grid file obtained in step 4. Then, the value at the magnetotelluric measuring point in the constant grid is replaced by the depth obtained in step 6.1 above to form a constrained grid file after electromagnetic calibration.

[0155] Step 7: Establish a model to carry out interface inversion and obtain the 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, the constraint grid obtained in step 6 as the second interface, and set the depth of the bottom interface to -5 km.

[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 sets the inversion iteration number to 20, the convergence error to 0.05 mgal, and runs the interface inversion. When the iteration number or convergence error is reached, the inversion is stopped to 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 uranium-rich granite.

[0160] 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.

[0161] The present invention is described in detail above with reference to the accompanying drawings and embodiments, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge of ordinary technicians in the field without departing from the purpose of the present invention. The contents not described in detail in the present invention can adopt the existing technology.

Claims

1. A method for calculating the buried depth of the deep contact zone of uranium-rich granite, characterized in that: The method comprises: Step 1: Conduct stream sediment sampling within the granite development range of the study area; Step 2: Count the uranium content of the samples and delineate the uranium-rich granite development area; Step 3: Carry out gravity measurement in the delineated uranium-rich granite development area to obtain Bouguer gravity anomaly and elevation grid data; Step 4: Obtain the residual gravity anomaly and form a residual gravity anomaly grid file; Step 5: Conduct broadband magnetotelluric profile measurement and calibrate the boundary between the deep rock mass and the stratum through the inversion results; Step 6: Digitize each section boundary line and create a constraint grid file; Step 7: Establish a model to carry out interface inversion and obtain the elevation grid data of the deep contact zone of the granite rock mass; Step 8: Calculate the burial depth of the deep contact zone of uranium-rich granite.

2. The method for calculating the buried depth of the deep contact zone of uranium-rich granite according to claim 1, characterized in that: The step 1 comprises: Step 1.1: According to the distribution of granite in the geological map of the study area, determine the sampling range of stream sediments, which must cover the area where granite bodies are exposed; Step 1.2: The sampling scale of water system sediment is 1:50,000. A square grid is divided within the study area as the sampling unit. The sampling material is mainly silt and silt, and the particle size is less than 60 mesh. The sample retention weight is not less than 200 grams.

3. The method for calculating the buried depth of the deep contact zone of uranium-rich granite according to claim 1, characterized in that: The step 2 comprises: Step 2.1: Analyze the samples collected in step 1, count the uranium content at each point, and obtain the uranium content data at each point; Step 2.2: According to the uranium content at each point, calculate the lower limit of uranium anomaly delineation according to the following formula: In the formula, U(i,j) is the uranium content data of each point; is the average value of uranium content at each point; i and j are the east-west and north-south numbers of the sampled square grid nodes, and m and n are the total number of east-west and north-south grids; σ is the standard deviation of the data; A(U) is the lower limit of abnormal uranium content; Step 2.3: Use the surfer software to grid the uranium content data U(i,j) at each point to obtain a uranium content contour map, and delineate the plane area where the uranium content value is higher than the lower limit of the uranium content anomaly A(U) as the area where uranium-rich granite is developed.

4. The method for calculating the buried depth of the deep contact zone of uranium-rich granite according to claim 1, characterized in that: The step 3 comprises: 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 survey area covers the uranium-rich rock development area determined in step 2; Step 3.2: Use a gravimeter and a surveying instrument to carry out measurements, obtain the relative gravity value, longitude and latitude, 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 piece of granite and 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, is the latitude of the measuring point; h is the height of the measuring point; ρ is the density of the mesosphere; r is the radius of the earth; Δg B is the Bouguer gravity anomaly; g is the relative gravity value; γ0 is the normal field correction value; δ b is the Bouguer correction value; δ 地 It is the terrain correction value, which is calculated by collecting digital elevation data around the study area.

5. The method for calculating the buried depth of the deep contact zone of uranium-rich granite according to claim 4, characterized in that: The step 4 comprises: The Bouguer gravity anomaly Δg obtained in step 3 B The residual gravity anomaly is obtained by processing and calculating in the following way: Δg 剩余 =Δg B -Δg R In the formula, Δg R Indicates the regional gravity anomaly of the measuring point; R indicates the window distance involved in the calculation, which is at least twice the measuring line distance; SumΔg B (0, R) represents the sum of the Bouguer gravity anomalies of all measuring points within the window distance R involved in the calculation; N represents the number of measuring points within the range; Δg 剩余 Indicates the residual gravity anomaly at the measuring point; Δg 剩余 Gridding is performed with a grid spacing of half the measurement point spacing to obtain the residual gravity anomaly grid file.

6. The method for calculating the buried depth of the deep contact zone of uranium-rich granite according to claim 5, characterized in that: The step 5 comprises: Step 5.1: The broadband magnetotelluric profile is laid out in parallel profiles. The survey line needs to pass through existing boreholes. The survey line spacing is 1-5km, and the measurement point spacing is 100 or 200 meters. Two electric field components and three magnetic field components are collected at the same time. The observation time is greater than 24 hours, and the observation frequency range is 10000~0.01HZ to obtain the 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 the TM mode to perform two-dimensional conjugate gradient inversion calculation to obtain resistivity data; Step 5.3: Load the resistivity data of each section obtained in step 5.2 using Surfer software to obtain the resistivity section contour map of each section; Step 5.4: Based on the existing borehole resistivity logging data, using the numerical characteristics of the resistivity curve of the contact zone between the granite body and the sedimentary stratum, use the Surfer software to divide each resistivity profile contour map obtained in step 5.3 and calibrate the boundary between the deep rock mass and the stratum.

7. The method for calculating the buried depth of the deep contact zone of uranium-rich granite according to claim 6, characterized in that: The step 6 comprises: Step 6.1: Digitize the boundary lines marked out in each section 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 use this depth value to make a constant grid. The grid spacing is exactly the same as the residual gravity anomaly grid file obtained in step 4; then, replace the value at the magnetotelluric measuring point position in the constant grid with the depth obtained in step 6.1 above to form a constrained grid file after electromagnetic calibration.

8. The method for calculating the buried depth of the deep contact zone of uranium-rich granite according to claim 7, characterized in that: The step 7 comprises: Step 7.1: Use Geosoft software to build a three-layer model, using 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 the bottom interface is set 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, convergence error, and run the interface inversion; when the number of iterations or 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 buried depth of the deep contact zone of uranium-rich granite according to claim 8, characterized in that: The step 8 comprises: 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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