Concealed ore body location prediction method based on parallel dual tunnel transient electromagnetic exploration

Abstract

The present invention discloses a method for locating and predicting a hidden ore body based on parallel dual-tunnel transient electromagnetic exploration, which belongs to applied geophysical exploration technology. The method of the present invention is to locate and predict a hidden ore body with low resistivity around a tunnel in the full spatial domain based on the parallel dual-tunnel transient electromagnetic method, and the implementation of the method mainly includes electrical parameter measurement, tunnel transient electromagnetic observation, apparent resistivity calculation, apparent resistivity anomaly upper limit determination, apparent resistivity anomaly delineation and hidden ore body location prediction. The present method can effectively solve the dual-solution problem of locating hidden ore bodies in the full spatial domain of tunnels.

Description

Technical Field

[0001] The invention relates to a method for locating and predicting a concealed ore body based on parallel double-tunnel transient electromagnetic exploration, and belongs to the field of mineral resource exploration. Background Art

[0002] The basic principle of transient electromagnetic method (TEM) is that the medium will generate eddy currents under the excitation of the primary current pulse field. The eddy currents will not disappear immediately during the pulse interruption period, and a secondary magnetic field that decays with time will be formed in the surrounding space; the law of the decay of the secondary magnetic field with time mainly depends on the conductivity, volume scale and burial depth of the medium (abnormal body), as well as the shape and frequency of the transmitting current. Therefore, the spatial distribution of the abnormal body can be understood by measuring and analyzing the relevant information of the secondary field through the receiving coil or the grounding electrode, so as to achieve the purpose of predicting the underground target body. This method is widely used in the fields of resources, energy, hydrogeology, engineering geology, disaster geology, environmental geological exploration, military exploration, etc., but this method is mainly used for detection in the semi-space domain of the surface, while tunnel detection is currently only used for advance detection of a single tunnel. In the detection of hidden ore bodies, when transient electromagnetic method is measured on the surface, the abnormal source will only be below the surface, while in the full space domain application of the tunnel, the abnormal source may be below the tunnel or above the tunnel, that is, there is a symmetrical double solution, and it is difficult to determine the exact location of the abnormal source. Summary of the invention

[0003] The present invention provides a method for locating and predicting hidden ore bodies based on parallel dual-tunnel transient electromagnetic exploration, which solves the problem that the ore bodies are difficult to accurately locate and predict due to the dual-solution influence of the tunnel transient electromagnetic method, thereby accurately locating and predicting the hidden ore bodies within the entire spatial domain of the tunnel.

[0004] The specific operation steps of the method of the present invention are as follows:

[0005] (1) Electrical parameter measurement

[0006] Measure the electrical parameters of ore and surrounding rocks within the mining area, calculate the geometric mean of resistivity, and determine that the ore body is a low-resistance body.

[0007] (2) Tunnel transient electromagnetic observation

[0008] Define the tunnel's forward direction as the positive X-axis, the vertical X-axis upward direction as the positive Z-axis, and according to the right-hand rule, the vertical X and Z directions are the positive Y-axis. When the two tunnels are parallel, set the distance between the two tunnels to c, specify the first measuring point of the lower tunnel as the origin, and the coordinates are (0, 0, 0); the coordinates of the first measuring point of the upper tunnel are (0, 0, c) ( Figure 1). Where c is between 0 and 500m. The transient electromagnetic measurement points of the tunnel are arranged along the tunnel, with a point spacing of 20m. The measurement points are located using a tape measure and a plan view of the middle section of the tunnel. The coplanar equivalent reverse flux device is used to obtain the voltage V(t), current I and time t data. The number of turns of the transmitting coil is 6, the radius is 0.42m, the power supply current is 100A, the sampling time is 0.17-10ms, the number of superpositions is 30 times, and the detection distance is 500m.

[0009] (3) Calculation of apparent resistivity

[0010] The calculation formula of apparent resistivity is as follows

[0011]

[0012] Where: L is the side length of the transmitting coil, in meters;

[0013] q is the effective area of ​​the receiving coil (single-turn coil area multiplied by the number of turns), in m 2 ;

[0014] V(t) is the observed value of potential, in μV;

[0015] V(t) / I is the normalized potential observation value, in μV / A;

[0016] t is the observation time, in ms;

[0017] ρ τ is the apparent resistivity, unit is Ω.m.

[0018] The apparent depth inversion calculation uses the following formula:

[0019]

[0020] Where: μ0 = 4π × 10 -7 H / m;

[0021] S τ is the longitudinal conductivity, the unit is 1 / Ω;

[0022] V(t) / I is the potential observation value, in μV;

[0023] dV / dt is the derivative of the observed potential, in V / s;

[0024] t is the observation time, in seconds;

[0025] M is the emission magnetic moment, in m 2 A;

[0026] q is the effective area of ​​the receiving coil (single-turn coil area multiplied by the number of turns), in m 2 ;

[0027] h τ is the apparent depth, in meters.

[0028] The apparent resistivity is obtained according to the calculation result of formula (1), and the apparent depth is calculated by applying formulas (2) and (3). The resistivity-apparent depth distribution profile is drawn according to the apparent resistivity and apparent depth.

[0029] (4) Determination of the upper limit of apparent resistivity anomaly

[0030] The median and standard deviation of the apparent resistivity are obtained through the normal distribution statistics of the apparent resistivity measured by tunnel transient electromagnetic. The upper limit of the apparent resistivity anomaly = the median (or average) of the apparent resistivity minus 1-3 times the standard deviation.

[0031] (5) Delineation of apparent resistivity anomaly

[0032] According to the upper limit of the apparent resistivity anomaly determined by (4), the apparent resistivity anomalies of the two tunnels were delineated respectively; there are two areas of apparent resistivity anomaly, which are distributed axially symmetrically with respect to the measuring points.

[0033] (6) Prediction of hidden ore body location

[0034] For the apparent resistivity anomaly circled in step (5), according to the parallel correspondence between the vertical planes of the two tunnels, four apparent resistivity anomaly distribution maps of the two tunnels are made in the XOZ plane. By comparing the overlap of the four apparent resistivity anomalies of the two tunnels in the plane, if the two apparent resistivity anomalies in a certain direction of the two tunnels can overlap, it can be determined that the predicted area is located in the overlapping area; the characteristics are shown in Figure 1 , where is defined as the upper part above the upper tunnel, the lower part below the lower tunnel, and the middle part between the two tunnels. In the XOZ plane, the apparent resistivity anomalies of the two tunnels overlap in the upper part, that is, the predicted area is located in the upper part; the apparent resistivity anomalies of the two tunnels overlap in the lower part, that is, the predicted area is located in the lower part; the apparent resistivity anomalies of the two tunnels overlap in the middle part, that is, the predicted area is located in the middle.

[0035] The advantages and technical effects of the present invention are as follows:

[0036] 1. The method of the present invention has the advantages of being light, fast, efficient, low-cost, and able to overcome the multi-solution problem of tunnel prediction and ore body positioning.

[0037] 2. The method of the present invention has been applied in multiple copper, lead and zinc mining areas and has achieved good prospecting results. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1Schematic diagram of the prediction area for the hidden ore body location prediction method based on parallel double tunnel transient electromagnetic exploration, where (1) is a schematic diagram of the vertical parallel double tunnel coordinate system, (2) is a schematic diagram of the case where the prediction area is located in the middle, (3) is a schematic diagram of the case where the prediction area is located in the upper part, and (4) is a schematic diagram of the case where the prediction area is located in the lower part;

[0039] Figure 2 This is a plan view of the measuring point in the middle section of 670m of a lead-zinc deposit in northeastern Yunnan;

[0040] Figure 3 This is a plan view of the measuring point in the middle section of 610m of a lead-zinc deposit in northeastern Yunnan;

[0041] Figure 4 This is the normal distribution histogram of apparent resistivity in the middle sections of 670m and 610m of a lead-zinc deposit in northeastern Yunnan. The left picture is the middle section of 670m, and the right picture is the middle section of 610m.

[0042] Figure 5 This is a schematic diagram of the positioning of low-resistance ore bodies in the TEM abnormal area of ​​the double tunnel section at 670m and 610m in the middle section of a lead-zinc deposit in northeastern Yunnan; the two figures on the left are the tunnel section at the middle section at 670m, the two figures in the middle are the tunnel section at the middle section at 610m, and the two figures on the right are schematic diagrams of the overlap of the two tunnel section diagrams;

[0043] Figure 6 This is a profile diagram of a hidden ore body predicted by the parallel double-tunnel transient electromagnetic method in a lead-zinc deposit in northeastern Yunnan. DETAILED DESCRIPTION

[0044] The present invention is further described in detail below through examples, but the protection scope of the present invention is not limited to the contents described above, and the methods in the examples are conventional methods unless otherwise specified.

[0045] Example 1: This method for locating and predicting hidden ore bodies based on parallel dual-tunnel transient electromagnetic exploration was applied in a lead-zinc mine tunnel in northeastern Yunnan, and the prospecting effect was good.

[0046] (1) Electrical parameter measurement

[0047] 163 specimens were collected and the identification results were: 85 lead-zinc ores, 25 limestones, and 53 dolomites. The statistical results of resistivity measurement showed that the geometric mean resistivity of lead-zinc ores was 10Ω.m, the geometric mean resistivity of ore-bearing limestone was 30218Ω.m, and the geometric mean resistivity of ore-bearing dolomite was 17403Ω.m. Compared with the surrounding rock, the lead-zinc ore body is a low-resistance body, which meets the electrical property prerequisites for conducting tunnel transient electromagnetic measurement.

[0048] (2) Tunnel transient electromagnetic observation

[0049] This method was applied to two corresponding tunnels in the middle sections of 670m and 610m in a lead-zinc mine in northeastern Yunnan ( Figure 2-3 ), the tunnel transient electromagnetic measuring points are arranged along the tunnel, and the measuring points are positioned using a tape measure combined with the plane map of the middle section of the tunnel, with a point spacing of 20m; a coplanar equivalent reverse flux device is used to measure and obtain voltage V(t), current I and time t data, the number of turns of the transmitting coil is 6, the radius is 0.42m, and the side length of the equivalent transmitting coil square is 0.753m; the power supply current is 100A, the equivalent single-turn power supply current is 600A, the sampling time is 0.17-10ms, and the number of superpositions is 30 times. In order to overcome the interference of iron objects, the receiving coil is placed 100cm above the two tracks and 200cm away from the iron pipe for data collection.

[0050] (3) The apparent resistivity is calculated as follows:

[0051]

[0052] The apparent depth is calculated using the following formula:

[0053]

[0054] The apparent resistivity is obtained by the calculation result of formula (1), and the apparent depth is calculated by formula (2) and (3). The resistivity-apparent depth distribution profile is drawn according to the apparent resistivity and apparent depth ( Figure 5 ).

[0055] (4) Determination of abnormal upper limit

[0056] The normal distribution histogram of apparent resistivity of the 670m middle tunnel using transient electromagnetic method is shown in Figure 4 , it can be seen that the apparent resistivity follows a log-normal distribution. Therefore, the upper limit of the abnormality is determined by the method of subtracting 1-3 times the standard deviation from the median of the apparent resistivity. The median minus 1 times the standard deviation is 307Ω.m, the median minus 2 times the standard deviation is 153Ω.m, and the median minus 3 times the standard deviation is 76Ω.m. Figure 4 Combined with the observed potential anomalies and known ore body anomalies, the upper limit of the apparent resistivity anomaly was determined to be 200Ω.m.

[0057] The normal distribution histogram of apparent resistivity of the 610m middle tunnel using transient electromagnetic method is shown in Figure 4 , it can be seen that the apparent resistivity follows a log-normal distribution. Therefore, the abnormal limit is calculated by the method of the median of the apparent resistivity minus 1-3 times the standard deviation. The median minus 1 times the standard deviation is 327Ω.m, the median minus 2 times the standard deviation is 175Ω.m, and the median minus 3 times the standard deviation is 93Ω.m; Comprehensive Figure 4 Combined with the observed potential anomalies and known ore body anomalies, the upper limit of apparent resistivity anomaly is set at 200Ω.m.

[0058] (5) Delineation of apparent resistivity anomaly

[0059] According to the upper limit of the apparent resistivity anomaly determined by (4), the apparent resistivity anomalies in the cross section and plane of the middle section of the tunnel at 670m and 610m are delineated ( Figure 5 ).

[0060] (6) Prediction of hidden ore body location

[0061] There are two symmetrical apparent resistivity anomalies in the single tunnel; the two symmetrical apparent resistivity anomalies in the middle tunnel of 670m are TEM-670-Q and TEM-670-S, and the two symmetrical apparent resistivity anomalies in the middle tunnel of 610m are TEM-610-Q and TEM-610-S; according to the up-down correspondence between the two tunnels, the apparent resistivity anomalies of the two tunnels are overlapped on the profile, and the overlapping apparent resistivity anomaly range of the low-resistance ore body located below the middle tunnel of 610m is determined as the prediction area, namely TEM-670-S and TEM-610-S ( Figure 5 ); The predicted area is located in the Carboniferous C2w and C1b ore-bearing strata, with the center located in C2w 1-3 In the ore-bearing stratum, 370m to 200m, NW dipping, NE side lying ( Figure 6 ).

[0062] The location of the concealed ore body predicted by this method is generally consistent with the verification results of the drilling project, indicating that this method is feasible.

Claims

1. A method for locating and predicting hidden ore bodies based on parallel dual-tunnel transient electromagnetic exploration, characterized in that: Here are the steps: (1) Measure the electrical parameters of the ore and surrounding rock in the mining area, calculate the geometric mean of the resistivity, and determine that the ore body is a low-resistance body relative to the surrounding rock; (2) Define the tunnel's forward direction as the positive direction of the X-axis, the upward direction perpendicular to the X-axis as the positive direction of the Z-axis, and according to the right-hand rule, the perpendicular direction to the X and Z directions as the positive direction of the Y-axis. When the two tunnels are parallel, set the distance between the two tunnels to be c, and designate the first measuring point of the lower tunnel as the origin O, with coordinates (0, 0, 0); the coordinates of the first measuring point of the upper tunnel are (0, 0, c), where c is between 0 and 500 m; tunnel transient electromagnetic measuring points are arranged along the tunnel, with a point spacing of 20 m; measuring point positioning is carried out using a tape measure and a plan view of the middle section of the tunnel; a coplanar equivalent reverse flux device is used to measure and obtain the potential observation value , Current and time Data, the number of turns of the transmitting coil is 6, the radius is 0.42m, the power supply current is 100A, the sampling time is 0.17-10ms, the number of superpositions is 30 times, and the detection distance is 500m; The calculation formula of apparent resistivity is as follows （1） Where: L is the side length of the transmitting coil, in meters; q The effective area of ​​the receiving coil is m, which is the area of ​​a single-turn coil multiplied by the number of turns. 2 ; is the observed value of potential, in μV; is the normalized potential observation value, in μV / A; is the observation time, in ms; is the apparent resistivity, in Ω.m; The apparent depth inversion calculation formula is as follows: （2） （3） in: ; is the longitudinal conductivity, the unit is 1 / Ω; is the observed value of potential, in μV; is the derivative of the observed potential, in V / s; is the observation time, in ms; M is the emission magnetic moment, in m 2 A; q The effective area of ​​the receiving coil is m, which is the area of ​​a single-turn coil multiplied by the number of turns. 2 ; is the apparent depth, in m; The apparent resistivity is calculated according to formula (1), and the apparent depth is calculated by formulas (2) and (3). The resistivity-apparent depth distribution profile is drawn according to the apparent resistivity and apparent depth. (3) Determination of the upper limit of apparent resistivity anomaly The median and standard deviation of apparent resistivity are obtained by using the normal distribution statistics of apparent resistivity measured by tunnel transient electromagnetic. The upper limit of apparent resistivity anomaly = median of apparent resistivity minus 1-3 times of standard deviation, or the upper limit of apparent resistivity anomaly = average of apparent resistivity minus 1-3 times of standard deviation. (4) Delineation of apparent resistivity anomaly According to the upper limit of the apparent resistivity anomaly determined in step (3), the apparent resistivity anomalies of the two tunnels are delineated respectively; there are two areas of apparent resistivity anomaly, which are distributed axially symmetrically with respect to the measuring points; (5) Prediction of hidden ore body location For the apparent resistivity anomaly circled in step (4), according to the parallel correspondence between the vertical planes of the two tunnels, four apparent resistivity anomaly distribution maps of the two tunnels are made in the XOZ plane, which are defined as the upper part above the upper tunnel, the lower part below the lower tunnel, and the middle part between the two tunnels. By comparing the overlap of the four apparent resistivity anomalies of the two tunnels in the plane, if the two apparent resistivity anomalies in a certain direction of the two tunnels overlap, it can be determined that the prediction area is located in the overlapping area; in the XOZ plane, the apparent resistivity anomalies of the two tunnels overlap in the upper part, that is, the prediction area is located in the upper part; the apparent resistivity anomalies of the two tunnels overlap in the lower part, that is, the prediction area is located in the lower part; the apparent resistivity anomalies of the two tunnels overlap in the middle part, that is, the prediction area is located in the middle.

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