| CPC G01V 3/083 (2013.01) [G01V 2003/084 (2013.01); G01V 2003/085 (2013.01); G01V 2003/086 (2013.01)] | 1 Claim |
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1. A method for positioning and predicting concealed orebody based on parallel double-tunnel transient electromagnetic exploration, comprising following steps:
step (1), measuring electrical parameters of ores and ore-hosted rocks in a mining area, calculating a geometric mean of a resistivity, and determining that an orebody is a low-resistance element with respect to a surrounding rock,
step (2), defining a forward direction of a tunnel as a positive direction of an X-axis, an upward direction normal to the X-axis as a positive direction of a Z-axis, and a direction normal to the X-axis and normal to the Z-axis as a positive direction of a Y-axis according to a right-hand rule; when two tunnels are parallel upper tunnel and lower tunnel, assuming that a distance between the two tunnels is c, and specifying a first measuring point of the lower tunnel as the origin O with an coordinate of (0,0,0); specifying a coordinate of a first measuring point of the upper tunnel as (0,0,c), wherein c is between 0 and 500 m; arranging tunnel transient electromagnetic measuring points along the tunnel for measurement, wherein a distance between the measuring points is 20 m; carrying out measurement by using a tape measure and a plan of a middle section of the tunnel for positioning the tunnel transient electromagnetic measuring points; carrying out measurement by using a coplanar equivalent counter-flux device to obtain data about electric potential observation value V(t), current I and time t, wherein a number of turns of a transmitting coil is 6, a radius of the transmitting coil is 0.42 m, power supply current is 100 A, sampling time is 0.17-10 ms, a number of superposition times is 30, and detection distance is 500 m;
calculating an apparent resistivity as follows:
 wherein L is a side length of the transmitting coil in unit of m;
q is an effective area of a receiving coil in unit of m2, and the effective area of the receiving coil is equal to an area of a single-turn coil multiplied by a number of turns;
V(t) is the electric potential observation value in unit of μV;
V(t)/I is a normalized electric potential observation value in unit of μv/A;
t is an observation time in unit of ms;
ρτ is the apparent resistivity in unit of Ω·m;
carrying out an inversion calculation on a visual depth as follows:
 wherein μ0=4π×10−7H/m;
Sτ is a longitudinal conductance in unit of 1/Ω;
V(t) is the electric potential observation value in unit of μV;
dV/dt is a derivative of an observation electric potential in unit of V/s;
t is an observation time in unit of ms;
M is a transmitting magnetic moment in unit of m2A;
q is an effective area of the receiving coil in unit of m2, and the effective area of the receiving coil is equal to the area of the single-turn coil multiplied by the number of turns;
hτ is the visual depth in unit of m;
obtaining the apparent resistivity according to a calculation result of Formula (1), then calculating and obtaining the visual depth according to Formula (2) and Formula (3), and drawing a cross-sectional view of resistivity-visual depth distribution according to the apparent resistivity and the visual depth;
step (3), determining an upper limit of an apparent resistivity abnormity;
through statistics of normal distribution of the apparent resistivity in tunnel transient electromagnetic measurement, obtaining a median and a standard deviation of the apparent resistivity, wherein the upper limit of the apparent resistivity abnormity is equal to the median of the apparent resistivity minus 1 to 3 times the standard deviation, or the upper limit of the apparent resistivity abnormality is equal to an average of the apparent resistivity minus 1 to 3 times the standard deviation;
step (4), delineating the apparent resistivity abnormity;
according to the upper limit of the apparent resistivity abnormity determined in step (3), delineating apparent resistivity abnormities of the two tunnels; wherein there are two areas with the apparent resistivity abnormity, which are axially symmetrically distributed with the tunnel transient electromagnetic measuring points;
step (5), positioning and predicting concealed orebody;
for the apparent resistivity abnormities delineated in step (4), forming a distribution map of four apparent resistivity abnormities of the two tunnels in X-O-Z plane according to a parallel correspondence relationship between vertical planes of the two tunnels, defining a part above the upper tunnel as an upper part, a part below the lower tunnel as a lower part, and a part between the two tunnels as a middle part; comparing coincidences of the four apparent resistivity abnormities of the two tunnels in the plane, and in a case that two apparent resistivity abnormities of the two tunnels overlap in a certain direction, determining that a prediction area is within an overlapping area; wherein in the X-O-Z plane, when the apparent resistivity abnormities of the two tunnels overlap in the upper part, the prediction area is located in the upper part; when the apparent resistivity abnormities of the two tunnels overlap in the lower part, the prediction area is located in the lower part; and when the apparent resistivity abnormities of the two tunnels overlap in the middle part, the prediction area is located in the middle part.
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