US 12,468,060 B1 · Method for positioning and predicting concealed orebody based on parallel double-tunnel transient electromagnetic exploration

Abstract

Provided is a method for positioning and predicting concealed orebody based on parallel double-tunnel transient electromagnetic exploration, and belongs to the applied geophysics exploration technology. The method can locate and predict concealed orebodies with low resistivity around the tunnel in a full spatial domain based on a parallel double-tunnel transient electromagnetic method. The implementation of the method mainly includes measuring an electrical parameter, observing a tunnel transient electromagnet, calculating an apparent resistivity, determining an upper limit of an apparent resistivity abnormity, delineating the apparent resistivity abnormity and positioning and predicting concealed orebodies. The method can effectively solve the double-solution problem of positioning concealed orebodies in the full spatial domain of the tunnel.

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:
ρ
τ
=
0.00632
×
L
4
3
×
q
2
3
×
[
V
⁡
(
t
)
/
I
]
-
2
3
×
t
-
5
3
(
1
)
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:
h
τ
=
4
/
(
μ
0
⁢
S
τ
)
×
(
V
⁡
(
t
)
/
dV
dt
-
t
/
4
)
(
2
)
S
τ
=
16
⁢
π
1
/
3
(
3
⁢
Mq
)
1
/
3
⁢
μ
0
4
/
3
×
(
V
⁡
(
t
)
)
5
/
3
/
(
dV
dt
)
4
/
3
(
3
)
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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Method for positioning and predicting concealed orebody based on parallel double-tunnel transient electromagnetic exploration

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Method for positioning and predicting concealed orebody based on parallel double-tunnel transient electromagnetic exploration

Life of this patent

Abstract

Claims1