Ore finding method by utilizing ground high-precision gravity measurement
阅读说明：本技术 一种利用地面高精度重力测量的找矿方法 (Ore finding method by utilizing ground high-precision gravity measurement ) 是由 聂逢君 王彦国 邓居智 严兆彬 李满根 夏菲 何剑锋 张成勇 封志兵 于 2019-10-25 设计创作，主要内容包括：一种利用地面高精度重力测量的找矿方法,主要包括六个方法,分别为位场高阶导数的波数域迭代法、基于迭代滤波法的位场分离方法、识别地质体边界的TASD法、位场数据处理的欧拉反褶积法、位场异常互相关成像技术方法和重力人机交互剖面正演模拟方法。本发明的优点是：利用地面高精度重力测量的找矿方法,对多条重力剖面的数据处理和解释,解释方法涵盖波数域导数迭代法、场分离的迭代滤波法,以及基于剩余异常的互相关成像技术应用于重力数据中,取得了较好的处理结果。(An ore-finding method by utilizing ground high-precision gravity measurement mainly comprises six methods, namely a wave number domain iteration method of a high-order derivative of a potential field, a potential field separation method based on an iterative filtering method, a TASD method for identifying geologic body boundaries, an Euler deconvolution method for processing potential field data, a potential field abnormal cross-correlation imaging technical method and a gravity man-machine interaction profile forward modeling method. The invention has the advantages that: the mining method of ground high-precision gravity measurement is utilized to process and explain data of a plurality of gravity profiles, and the explaining method covers a wave number domain derivative iteration method, a field separation iteration filtering method and a cross-correlation imaging technology based on residual anomaly applied to gravity data, so that a better processing result is obtained.)
1. An ore prospecting method by utilizing ground high-precision gravity measurement is characterized by comprising the following steps: the method mainly comprises six methods, namely a wavenumber domain iteration method of a high-order derivative of a potential field, a potential field separation method based on an iterative filtering method, a TASD method for identifying the boundary of a geologic body, an Euler deconvolution method for processing potential field data, a potential field abnormal cross-correlation imaging technical method and a gravity man-machine interaction profile forward modeling method.
2. The method for prospecting by using ground high-precision gravity measurement according to claim 1, characterized in that: a wave number domain iteration method of the high-order derivative of the potential field; the specific method comprises the following steps:
in the wavenumber domain, the arbitrary-order arbitrary-direction derivative spectrum of the bit field data can be expressed as:
wherein S(m,p,q)(u, v) and S (u, v) are the derivative spectrum and the original anomaly spectrum, respectively;respectively an x-direction m-order derivative operator, a y-direction p-order derivative operator and a z-direction q-order derivative operator; u and v are wave numbers in x and y directions respectively; m, p and q are real numbers which are more than or equal to zero;
from the above formula, the derivative order l and the theoretical derivative operator
l＝m+p+q，
will be provided with
to S(m,p,q)Multiplying by an operator comprising the derivative order l and the derivative
α≥1，β＞0，
will be provided withSubstituting the formula to obtain a first order approximation of S:
reuse of S and S(1)Is paired with
repeating the above steps to obtain S(m,p,q)Approximation of order n:
and has the following components:
then, the following steps are obtained:
order to
3. The method for prospecting by using ground high-precision gravity measurement according to claim 1, characterized in that: the bit field separation method based on the iterative filtering method; the specific method comprises the following steps:
let the spectrum of the superposition anomaly U (x, y) be U (U, v), and assuming that the operator H (U, v, α) is a low-pass filter and satisfies 0 ≦ H ≦ 1, then applying H (U, v, α) to U (U, v) can achieve the purpose of field separation, namely:
Ureg(u,v,α)＝U(u,v)·H(u,v,α)
where u and v are the wavenumbers in the x and y directions, respectively, and α is the filter parameter of operator H;
the field separation can be divided into the following three cases according to the selection of the filter parameter α:
① the filter parameters α are selected so that the separated region field u is not properly selectedregContaining local field formationIn which u isreg＝F-1[Ureg],F-1Is Fourier inverse transformation;
② filtering parameters α are properly selected to enable the separation of the superposition anomaly u to be thorough;
③ the filter parameters α are selected so that the separated local field u is not well definedred＝u-uregThe composition contains area field components;
in practical applications, the first or third situation is easy to occur in the field separation due to the fact that the filtering parameter α is not easy to determine, and the bit-field separation effect is not ideal;
for the first case, the improvement is proposed that the filter parameters α are fixed such that the region field u isregContaining more local field components, then H is applied again to UregTo further lift off local anomalies, i.e.Provided that a
only by selecting proper action times n, local field components in the area field can be better stripped;
for the third case, the improvement is that the parameters α are fixed such that the local field u isredContains a large number of local field components, it is necessary to strip out the local field components in the local anomalous spectrum and "return" the local field components to the local field, i.e.
At this time, the local abnormal spectrum becomes:
in the second improved scheme, the processes of local field stripping and 'returning' are consistent with the thought mode of iterative filtering, and the improved scheme is an iterative filtering method of a separation field;
in a second refinement, the low-pass filter H is given by:
in order to satisfy the conditions of the second kind of situation, α is set to be larger than or equal to 1, h is larger than or equal to 50 delta d, β is set to be larger than or equal to 1, and the selection scheme of the iteration times, namely the stripping return times adopts the difference of the cross correlation coefficients.
4. The method for prospecting by using ground high-precision gravity measurement according to claim 1, characterized in that: the TASD method for identifying the geologic body boundary; the specific method comprises the following steps:
identification of field source boundaries is performed in the form of a normalization of the derivative standard deviation in the form of
The method has the defects of poor continuity and high susceptibility to noise interference of geologic body boundaries, and an inclination angle method of a derivative standard deviation is provided and is in the form of:
wherein the transformation factor m is more than or equal to 1.
5. The method for prospecting by using ground high-precision gravity measurement according to claim 1, characterized in that: an Euler deconvolution method of the bit field data processing; the specific method comprises the following steps:
the Euler homogeneous equation is as follows:
wherein f (x, y, z) is a bit field anomaly;
6. The method for prospecting by using ground high-precision gravity measurement according to claim 1, characterized in that: the potential field abnormal cross-correlation imaging technical method; the specific method comprises the following steps:
in the survey area of relief, the (x, y) plane of the Cartesian coordinates is on the reference plane, and z is taken vertically positive, falseSetting underground arbitrary coordinates of a measuring area as (x)q,yq,zq) Volume v ofqHas a residual density of Δ σ of the q-th point mass ofqIts gravity anomaly Δ g at any point (x, y, z) on the survey areaq(x, y, z) can be represented as
Wherein the gravitational constant G is 6.67 × 10-11m3/(kg·s2)；
Defining the normalized cross correlation between the measured gravity anomaly on the measuring area and the gravity anomaly on the measuring area of the q point mass as follows:
wherein (x)i,yi,zi) For the coordinates of the ith observation point of the survey area, Δ g (x)i,yi,zi) Δ g being the measured gravity anomaly at the observation pointq(xi,yi,zi) And N is the total number of observation points of the survey area.
7. The method for prospecting by using ground high-precision gravity measurement according to claim 1, characterized in that: the gravity man-machine interaction profile forward modeling method; the specific method comprises the following steps:
(1) inputting results obtained by the gravity anomaly processing and conversion method and prior information obtained by other geological and geophysical methods into the model to form an initial model;
(2) according to the difference between the calculation result and the actual gravity anomaly, the model is conveniently modified at any time, and the forward and backward course is intuitively supervised and guided;
(3) and continuously correcting the model by comparing the gravity effect calculated by the initial model with the residual gravity anomaly on the measuring line until the difference between the calculated gravity effect and the residual gravity anomaly on the measuring line meets the preset precision.
Technical Field
The invention relates to an ore searching technology, in particular to an ore searching method by utilizing ground high-precision gravity measurement.
Background
The diagenetic geological background and conditions of the sandstone-type uranium ore in northern China are greatly different from those of foreign countries, so that the exploration of an ore finding method has different ideas.
The middle Asia region is a region which is rich in interlayer infiltration oxidized zone sandstone-type uranium ores, and an ore forming model of the interlayer oxidized zone ore deposit mainly comes from the region, and the ore forming theory and the ore searching method of the sandstone-type uranium ores introduced at the end of 1980 of the Chinese nuclear industry mainly refer to the successful experience of the former Soviet Union in the middle Asia. However, the special mineralogical conditions of the middle Asia are not available in China, for example, the deposition environment of the target layer mainly containing minerals of the middle Asia is a sea-land transition environment, and the stability of sand bodies in the lateral direction is self-evident. Also like the wyoming basin in the midwest of the united states, the basin belongs to an extruded intermodal basin, but the target layer in the basin is close to the ancient uranium-rich granite in the uplifted region, and the uranium source in the eroded source region is very sufficient. The conditions in the north of China are completely different, and the target layer mostly belongs to the terrestrial basin deposition environment, and is characterized by near material source, large phase, fast accumulation, poor lateral continuity, and inferior stability than the medium-Asia. In addition, the uranium-producing basins in the north of China are distributed on two sides or the middle of a middle Asia mountain-making zone, and although the raised basin area contains more granites, most uranium is not high in content, and the weathering degree is not as good as that of the wyoming in the west of the United states.
The complex variability of the ore-forming environment of the northern sandstone-type uranium ores in China determines that the ore-finding thought of the northern sandstone-type uranium ores has to be innovated on the basis of the theory of the middle-sublevel oxidation zone and the theory of the American coiled sandstone-type uranium ores. The method for finding the ore in the middle Asia region of the former Soviet Union is mainly based on the theory of 'secondary mountain making', and utilizes the drilling technology and a part of post-alteration geochemical zonation method. The sand body distribution rule formed in the sea-land transitional phase environment is easy to master, so that the success rate of drilling is high.
In the late 1980 s to early 1990 s, China mainly introduces the theory of ore formation and the method of finding ore in Zhongya, and once a large amount of drilling work is deployed in many areas in northwest and northeast China, the effect is very little, and the main reason is that the background condition characteristics of the ore formation in China cannot be fully considered. In late 1990 to early 2000, researches on mineralogical conditions, particularly researches on a target layer deposition system and a sand body distribution rule are strengthened, and good effects are achieved in a jungle basin, a Kailu basin and a Bartonegobi basin by matching with a drilling technology.
The ancient river sandstone type is the most important type of a two-basin-connected land, and for uranium mineralization development in the ancient river sand, research groups initiatively utilize a ground high-precision gravity measurement and inversion method to prepare and position the position and depth of a river, and simultaneously invert the development conditions of the sand and nearby faults, so that bases are provided for finding uranium ore bodies in the river and explaining formation of uranium mineralization.
Disclosure of Invention
The invention aims to provide an ore searching method by utilizing ground high-precision gravity measurement, which is used for preparing and positioning the position and the depth of a river channel, and simultaneously reversing the development conditions of sand bodies and nearby fault layers, thereby providing a basis for searching uranium ore bodies in the river channel and explaining the formation of uranium mineralization.
The technical scheme adopted by the invention is as follows: an ore-finding method by utilizing ground high-precision gravity measurement mainly comprises six methods, namely a wave number domain iteration method of a high-order derivative of a potential field, a potential field separation method based on an iterative filtering method, a TASD method for identifying geologic body boundaries, an Euler deconvolution method for processing potential field data, a potential field abnormal cross-correlation imaging technical method and a gravity man-machine interaction profile forward modeling method.
Further, a wave number domain iteration method of the high-order derivative of the potential field; the method is characterized in that:
the basic principle is as follows: in the wavenumber domain, the arbitrary-order arbitrary-direction derivative spectrum of the bit field data can be expressed as:
wherein S(m,p,q)(u, v) and S (u, v) are the derivative spectrum and the original anomaly spectrum, respectively;
From the above formula, the derivative order l and the theoretical derivative operator
will be provided with
in general, the larger the derivative order/the derivative operator
α is more than or equal to 1, β is more than 0 (generally, α is equal to 1, β is equal to 1),
will be provided with
reuse of S and S(1)Is paired with
repeating the above steps to obtain S(m,p,q)Approximation of order n:
and has the following components:
then, the following steps are obtained:
order to
The model test is as follows: and (4) carrying out numerical inspection by adopting the superposition abnormality of the two-degree vertical cylinders. As shown in fig. 7 b: the model body is 1km long, the upper top burial depth is 2km, the lower bottom burial depth is 2.5km, and the central coordinates of the upper top surface are 11km and 2 km; 2km long model body, 2.5km buried depth of upper top, 3.5km buried depth of lower bottom, and central coordinates (14km, 2.5km) of upper top; the residual densities of both models were 1.0g/cm3. The gravity anomaly generated by the combined model is shown in FIG. 7 a.
Fig. 8 and 9 show the results of comparing the vertical second and third derivatives obtained by the conventional method (without upward extension and with a certain height of upward extension) and the iterative method. As can be seen from the figure: compared with theoretical values, the abnormal values (figures 8a and 9a) obtained by conversion of derivatives which are not extended upwards have obvious volatility in addition to obvious boundary effect, and particularly effective abnormality cannot be identified by the vertical third-order derivatives (figure 9 a); although the vertical second derivative extending upward by 0.5 times the dot pitch (fig. 8b) and the vertical third derivative extending upward by 1 times the dot pitch (fig. 9b) are better improved in terms of the outliers compared to fig. 8a and 9a, respectively, the fluctuation of the data is still obvious; to further suppress the high frequency oscillations, the vertical direction
Compared with the derivatives calculated by the conventional method (fig. 8a, b and c and fig. 9a, b and c), the vertical second-order and third-order derivatives (fig. 8d and fig. 9d) obtained by the derivative conversion based on the iterative method have better fitting with theoretical values except that the limited data on the edge generate more obvious boundary effect.
The model test result shows that the stability of the calculation result of the derivative conversion without upward continuation is poor, and the higher the derivative order is, the stronger the data fluctuation is, which is caused by the amplification of the high-frequency component by the theoretical derivative operator; although the abnormal stability of the derivative extending upwards by a certain height is improved, the obvious amplitude unreserving property exists, which is caused by the reduction of the low-frequency component by the filter operator extending upwards by a certain height; the iteration method not only has strong stability of the calculation result, but also has strong amplitude-keeping capability, and is a result that a derivative operator of the iteration method can approach a theoretical derivative factor in a low frequency band and can effectively suppress high-frequency components.
Incidentally, as the derivative order of an anomaly increases, the boundary features of the geologic body reflected by the anomaly become more apparent. This effect is fully illustrated in figure 8 and figure 9 at the location of the geobody boundary indicated by the dashed line.
Further, the bit field separation method based on the iterative filtering method; the method is characterized in that:
the basic principle is as follows: let the spectrum of the superimposed anomaly U (x, y) be U (U),v), assuming operator H (U, v, α) is a low pass filter and satisfies 0 ≦ H ≦ 1, then H (U, v, α) is applied to U (U),v) the purpose of field separation can be achieved, namely:
Ureg(u,v,α)＝U(u,v)·H(u,v,α)
where u and v are the wavenumbers in the x and y directions, respectively, and α is the filter parameter for operator HThe wave parameters α can be selected to separate the field separation into three types, ① filter parameters α are selected improperly to separate out the region field ureg(ureg＝F-1[Ureg],F-1Is Fourier inverse transform), ② filtering parameter α is selected properly to separate the superposition anomaly u thoroughly, ③ filtering parameter α is selected improperly to separate the local field ured＝u-uregContains the region field component.
In practical applications, the first or third case is easy to occur in the field separation due to the filtering parameter α not being easily determined, so that the bit-field separation effect is not ideal.
For the first case, an improvement is proposed in that the filter parameters α are fixed such that the region field u isregContaining more local field components, then H is applied again to UregTo further lift off local anomalies, i.e.
by selecting the appropriate number of actions n, the local field components in the area field can be better stripped out.
For the third case, the improvement is that the parameters α are fixed such that the local field u isredContains a large number of local field components, it is necessary to strip out the local field components in the local anomalous spectrum and "return" the local field components to the local field, i.e.
At this time, the local abnormal spectrum becomes:if the local field still has the regional field information, the local field is stripped and returned to the regional field, and the process is continued until the stripping and returning are carried out for n times, and the process is terminated when no or almost no regional field component exists in the local field, and at the moment, the regional abnormal spectrum
obviously, in the second modification, the local field stripping and "returning" process is consistent with the idea mode of iterative filtering, so that the modification can be referred to as an iterative filtering method of separating fields. The principle of the method is as follows: the region in the local field is gradually stripped off along with the increase of the iteration times to be returned to the region field, when the iteration reaches a certain number of times, the local field can be considered to contain no (or a small amount of) region field components, the iteration times are optimal at this time, and along with the continuous increase of the iteration times, the local field components are stripped too much to cause that the region field contains local field information.
For the first type of improvement, analysis and simulation are temporarily omitted, but the solution has its own physical meaning, for example, given H ═ exp (-r (u, v) · Δ d) (r is the number of circles and Δ d is the distance between grid points; it can be generally considered to include in an outlier extending 1 point distance upwardsContaining more local field information), the area field spectrum of H action n times is
The second improvement is considered here, where the low-pass filtering H is given in the form:
to satisfy the conditions of the second case, α ≧ 1, h ≧ 50 Δ d, β ≧ 1, and the selection scheme of the number of iterations (i.e., the number of peel "returns") uses the difference of the cross-correlation coefficient of the document [14] (reflecting the change of the isolated field and local field with the number of iterations.) the parameters α ═ β ═ 1, and h ═ 100 Δ d were selected in the model test.
And (3) model test: in order to verify the correctness of field separation by the iterative filtering method, a two-dimensional superposition anomaly test is carried out, and the calculation result and the conventional upward continuation are subjected to binary analysis. The selected area field source is a sphere, and the parameters are as follows: the gravity anomaly of the generated area at the point position of the centroid plane with the burial depth of 10km and the radius of 3km is shown in figure 10. The selected local field source is the superposition of two spheres, and the parameters of the
Taking the extension height corresponding to the minimum mean square error of the upward extension value and the theoretical regional anomaly (fig. 13) as the optimal height (0.7km), and the extension value corresponding to the extension height as shown in fig. 14a, it can be seen that the regional anomaly (26a) obtained by upward extension is greatly affected by the local field, and the regional field above the
To further eliminate the effect of local fields on regional anomalies, the upward extension height is raised to 1.2km, and the resulting extension values (i.e., regional anomalies) and residual anomalies are shown in fig. 15a and 15b, respectively. It can be seen that the regional anomaly with an extension height of 1.2km is less affected by the local anomaly than the extension anomaly extending 0.7km upwards, and the remaining anomalies isolated are also significantly closer to the theoretical values, above the
Fig. 17a and 17b show the region anomaly and the remaining anomaly obtained when the optimal iteration number (n is 17) is selected based on the relationship between the differential cross-correlation coefficient and the iteration number (fig. 16). It can be seen that the regional anomalies separated by iterative filtering are similar to the theoretical anomalies in morphology and are not much different in numerical value, and the maximum error is 0.526mGal (6.62%), which is less than the error extending upwards by 0.7km and 1.2 km; the obtained outliers of the residual field above the
The model test contrastive analysis shows that the phenomenon that the regional abnormality and the residual abnormality which are obtained by the upward continuation method have mutual influence exists. The influence of the local field on the regional field obtained by the iterative filtering method is small, the superposition abnormality can be well separated, and the field separation precision is improved.
Further, the TASD method for identifying the geologic body boundary; the method is characterized in that:
the basic principle is as follows: in 2008, Cooper and Cowan develop a new path, the field source boundary is identified by utilizing the normalization form of the derivative standard deviation to obtain better application effect, and the normalization form is
However, this method has the disadvantage of identifying the geologic body boundary with poor continuity and susceptibility to noise, and for this reason, the inventor proposes a Tilt of standard deviation of derivative (in the form:
wherein the transformation factor m is more than or equal to 1.
And (3) testing the model: three cubes with side lengths of 1km and with top interface burial depths of 0.1km, 0.5km and 1km are combined into a test model, and the residual densities of the three models are set to be 1.0g/cm3The model body plane positions respectively correspond to three dotted lines in a theoretical gravity anomaly map (fig. 18), and the theoretical gravity anomaly is correspondingly processed by adopting an improved identification method and a conventional method, and the calculation result is subjected to comparative analysis.
As can be readily seen from FIG. 18, the normalized standard deviation method (FIG. 18b) more clearly reflects the boundary of the shallow geologic body, and the identified boundary position fits well with the reality; but affected by the interference, the boundary of the
Further, the Euler deconvolution method of the bit field data processing; the method is characterized in that:
the principle of the method is as follows: thompson gives the Euler homogeneous equation as follows:
wherein f (x, y, z) is a bit field anomaly;
And (3) model verification: the test was conducted by taking as an example a vertical column having an upper top and a lower bottom of 1km and 2km, respectively, and a residual density of 1.0g/
Further, the potential field abnormal cross-correlation imaging technology method; the method is characterized in that:
the principle of the method is as follows: in the survey area of relief, in Cartesian coordinates (x),y) plane is on the reference plane, z is taken to be vertically downward as positive, and the underground arbitrary coordinate of the measuring area is assumed to be (x)q,yq,zq) Volume v ofqHas a residual density of Δ σ of the q-th point mass ofqIts gravity anomaly Δ g at any point (x, y, z) on the survey areaq(x, y, z) can be represented as
Wherein the gravitational constant G is 6.67 × 10-11m3/(kg·s2)。
By using the normalized cross-correlation formula of the adjacent least square residual abnormality of Abdelrahman and the like, the normalized cross-correlation between the actually measured gravity abnormality on the measuring area and the gravity abnormality of the q point mass on the measuring area is defined as
Wherein (x)i,yi,zi) For the coordinates of the ith observation point of the survey area, Δ g (x)i,yi,zi) Δ g being the measured gravity anomaly at the observation pointq(xi,yi,zi) And N is the total number of observation points of the survey area.
And (3) model verification: the cross-correlation probability imaging method was examined with the gravity anomaly (fig. 20a) of a square upright column with 1km side length to which random interference was added as a test object. As can be seen from the imaging graph 20b, the method is not only strong in calculation stability, but also the inversion result can better identify the centroid position of the geologic body. This shows that it is effective to invert geologic body occurrence states by using a cross-correlation probability imaging method.
Further, the gravity man-machine interaction profile forward modeling method; the technology has the advantage that the results obtained by the processing and conversion method of the gravity anomaly and the prior information obtained by other geological and geophysical methods are conveniently input into the model to form the initial model. And according to the difference between the calculation result and the actual gravity anomaly, the model is conveniently modified at any time, and the forward and backward process is intuitively supervised and guided.
The forward simulation process of the gravity man-machine interaction profile is shown in fig. 21. The gravity man-machine interaction forward and backward technology is characterized in that: the gravity man-machine interaction forward and backward modeling technology is mainly realized by a two-degree body gravity anomaly calculation method with a polygonal cross section. And continuously correcting the model by comparing the gravity effect calculated by the initial model with the residual gravity anomaly on the measuring line until the difference between the calculated gravity effect and the residual gravity anomaly on the measuring line meets the preset precision.
The invention has the advantages that: the mining method of ground high-precision gravity measurement is utilized to process and explain data of a plurality of gravity profiles, and the explanation method covers a wave number domain derivative iteration method, a field separation iteration filtering method and a cross-correlation imaging technology based on residual anomaly applied to gravity data, so that a better processing result is obtained. Meanwhile, according to the results of gravity anomaly derivative analysis, TASD and Euler deconvolution inversion, the fracture positions and the fracture shapes of the gravity profiles are inverted, and 5 fractures on the NL profile, 6 fractures on the MD profile, 9 fractures on the E400 line and 4 fractures on the SH line are obtained. In addition, a geological-geophysical model with a plurality of sections is established by taking gravity data as a basis and combining geological data, drilling data and electrical data of a research area; the division of the secondary construction units is carried out, and the situation that the Tureler-Aoshi secondary recess of the NL section and the MD section both show obvious river sedimentation characteristics is pointed out, so that geophysical evidence is provided for the existence of ancient river channels.
Drawings
FIG. 1 is a NL line elevation measurement chart of the present invention.
FIG. 2 is a graph of MD line elevation measurements of the present invention.
FIG. 3 is a graph of E400 line elevation measurements in accordance with the present invention.
FIG. 4 is a graph of SH line elevation measurements in accordance with the present invention.
Fig. 5 is a graph of static change of the CG-5 gravimeter of the present invention.
FIG. 6 is a graph of the dynamic zero displacement of the various points of the gravimeter of the present invention.
FIG. 7 is a schematic diagram of a model gravity anomaly and a model according to the present invention, wherein a is a model body gravity anomaly and b is a model body schematic diagram.
FIG. 8 is a vertical second derivative model inspection chart of the present invention, wherein a is no upward continuation; b is upward continuation 0.5 times of point distance; c is
FIG. 9 is a vertical third derivative model test chart of the present invention, wherein a is no upward continuation; b is
Fig. 10 is a regional gravity anomaly map of a two-dimensional stacking anomaly test in the iterative filtering method of the present invention.
FIG. 11 is a theoretical local anomaly map of a two-dimensional superimposed anomaly test in the iterative filtering method of the present invention.
Fig. 12 is a superimposed gravity anomaly graph of a two-dimensional superimposed anomaly test in the iterative filtering method of the present invention.
FIG. 13 is a graph of the relationship between upward continuation value and theoretical regional anomaly error and continuation height of the present invention.
FIG. 14 is a graph of regional anomalies and residual anomalies from upward continuation of 0.7km of the present invention; wherein (a) the region is abnormal; (b) an exception remains.
FIG. 15 is a graph of regional anomalies and residual anomalies from upward continuation of 1.2km of the present invention; wherein (a) the region is abnormal; (b) an exception remains.
FIG. 16 is a graph of the differential cross-correlation coefficient versus the number of iterations of the present invention.
FIG. 17 is a graph of regional anomalies and residual anomalies obtained from 17 iterations of the iterative filtering method of the present invention; wherein (a) the region is abnormal; (b) an exception remains.
FIG. 18 is a graph of the results of identifying field source boundaries by the TASD method and the NSTD method of the present invention, wherein (a) gravity anomaly; (b) NSTD; (c) TASD.
FIG. 19 is a graph of the results of the Euler deconvolution inversion of the present invention.
FIG. 20 is a cross-correlation probability plot of gravity anomaly with random noise according to the present invention, wherein (a) gravity anomaly with 30% noise; (b) and (5) cross-correlating the imaging results.
FIG. 21 is a flowchart of the gravity human-computer interaction forward modeling of the present invention.
FIG. 22 is a graph of NL line vs. Bragg gravity anomaly for the present invention.
FIG. 23 is a graph of MD line vs. Bragg gravity anomaly in accordance with the present invention.
FIG. 24 is a graph of the E400 line versus a Booth gravity anomaly of the present invention.
FIG. 25 is a graph showing SH line vs. Bruger force anomaly according to the present invention.
FIG. 26 is a diagram of the results of NL line first derivative processing according to the present invention.
FIG. 27 is a graph of the first derivative MD processing results.
FIG. 28 is a graph of the results of the E400 line first derivative processing of the present invention.
FIG. 29 is a graph showing the results of SH line first derivative processing according to the present invention.
FIG. 30 shows the result of the NL line gravity anomaly TASD according to the present invention.
FIG. 31 is a graph of the result of MD line gravity anomaly TASD of the present invention.
FIG. 32 is a graph of the result of the E400 line gravity anomaly TASD of the present invention.
FIG. 33 is a graph showing the result of SH line gravity anomaly TASD according to the present invention.
FIG. 34 is a diagram of the NL line Euler deconvolution inversion results of the present invention.
FIG. 35 is a graph of the results of the MD wire Euler deconvolution inversion of the present invention.
FIG. 36 is a graph of the E400 line Euler deconvolution inversion results of the present invention.
FIG. 37 is a graph of the SH line Euler deconvolution inversion results of the present invention.
FIG. 38 is a diagram showing a comprehensive analysis of the results of NL line breaking treatment according to the present invention.
FIG. 39 is a graph showing the results of the MD line breaking treatment of the present invention.
FIG. 40 is a graph showing the results of the E400 line breakage treatment of the present invention.
FIG. 41 is a graph showing the results of the SH line-breaking treatment of the present invention.
FIG. 42 is a view showing the results of gravity-induced abnormal separation of NL lines according to the present invention.
FIG. 43 is a graph showing the result of abnormal separation by MD line gravity according to the present invention.
FIG. 44 is a graph showing the result of abnormal separation by gravity on line E400 according to the present invention.
FIG. 45 is a graph showing the results of gravity-induced abnormal separation of SH lines according to the present invention.
FIG. 46 is a NL line residual gravity anomaly probability imaging result chart of the present invention.
FIG. 47 is a graph of the MD line residual gravity anomaly probability imaging results of the present invention.
FIG. 48 is a graph of the residual gravitational anomaly probability imaging (a) and the MT electrical inversion result (b) of the present invention for E400 line.
FIG. 49 is a graph showing the SH line residual gravity anomaly probability imaging result of the present invention.
FIG. 50 is a graph of the relationship between residual gravity anomaly and building blocks of the NL line of FIGS. 4-31 according to the present invention.
FIG. 51 is a graph of the relationship of the present invention to the inversion of the fracture versus the structural unit of the NL line of FIGS. 4-32.
FIG. 52 is a diagram of the geological-geophysical comprehensive model of the line NL of FIGS. 4-33 of the present invention.
FIG. 53 is a graph of the relationship between residual gravity anomaly and building blocks of the MD lines of FIGS. 4-34 in accordance with the present invention.
FIG. 54 is a graph of the present invention showing the relationship between the MD lines of FIGS. 4-35 for the inversion of fracture and structural elements.
FIG. 55 is a geological-geophysical integral model of FIG. 4-36MD of the present invention.
FIG. 56 is a graph of the relationship between residual gravity anomaly and building blocks of the line 400 of FIGS. 4-37E in accordance with the present invention.
FIG. 57 is a graph of E400 line inversion fracture versus structural unit in accordance with the present invention.
FIG. 58 is a diagram of an E400 section geological-geophysical integral model of the present invention.
FIG. 59 is a graph showing the relationship between the residual gravitational field and the structural units of SH line.
FIG. 60 is a graph of the SH line inversion fragmentation and building block relationship of the present invention.
FIG. 61 is a SH section geological-geophysical synthetic model diagram of the present invention.
Detailed Description
The invention is attached to the implementation of the technology from the early preparation to the achievement of the project.
Firstly, field gravity exploration work; firstly, the GPS geodesic and gravity measurement group of the project completes the rapid static GPS positioning measurement and gravity measurement of four cutting lines, wherein the rapid static GPS positioning measurement and gravity measurement comprises the data supplementary measurement work of two cutting lines. Field workload-data acquisition of 685 gravity measurement points which are designed according to a plan is completed, and the completion rate reaches 154.60%. Four gravity profiles are completed for NL, MD, E400 and SH lines. The total length of the section is 105.4km, and the total number of physical points is 1172.
Secondly, working progress and data arrangement; and carrying out gravity measurement work between the Sunit right flag and the Erlianhaote according to the design requirements of the project. Since the accuracy of the point positions (longitude, latitude and elevation) directly influences the precision of the (relative) grid gravity anomaly, the GPS geodetic work is completely carried out according to the requirements of the Global Positioning System (GPS) measurement Specification (GB/T18314-2001). The gravity measurement was performed as required by the Large Scale gravity survey Specification (DZ/T0171-1997).
1. Fast static GPS geodesic, survey area range and natural geography general;
1.1 measuring area range; the measuring area is located between the inner Mongolia Xiongate union Sunit right flag and Erythao City. The measuring area range is as follows: e111 DEG 48.25 '-112 DEG 24.36' and N42 DEG 55.31 '-43 DEG 19.56'.
Measuring area coordinate system: WGS84 coordinate system. The measurement zone is within six degrees of 1 19 bands, with the central meridian at 111 degrees.
1.2 measuring the natural geographic conditions of the area; erlianhaote City is located in the middle of Mongolian autonomous region in the north China, and is hopeful to separate from Zamen Ude city of Mongolia. The terrain of Erlianhaote is flat, slowly inclines from southwest to northeast, and the average altitude is 932.2 m.
The Sunit right flag is positioned in the middle of an inner Mongolia autonomous region, the west part of the Xilinguo union is the west gate of the Xilinkui union, and the east-adjacent Sunit left flag and the yellow flag are inlaid; the south-leaning Wulan Chongbu city Chonghar Right rear flag, Shandu county; west grafting of the four-seed king flag of Wulan scotch; the northeast is bordered by the city of Erlianhaote Union. The Sunit right flag belongs to the ancient lake basin and rises to form a denuded plateau, and the average altitude is 1000 m-1400 m. The main road of the survey area is a national road 208, and other auxiliary roads are grassland gravel roads.
2. Observing a scheme and acquiring data;
2.1 observing a benchmark, wherein a coordinate system of data acquisition is a WGS-84 coordinate system, and geometric parameters of reference ellipsoids are that a is 6378137m as a long radius, b is 6356752.3142m as a short radius, and α is 1/298.257223563 as a flat rate.
2.2, an observation mode and data acquisition are carried out, wherein the rapid static observation mode is adopted, the sampling rate is 1s, a GPS receiver is not turned off in the observation process, observation is carried out on a measurement point position for 3-5 minutes, then the receiver is directly moved to the next measurement point, and in order to control the resolving precision, encryption observation is carried out for 15 minutes every 10 measurement points; in order to avoid that data segmentation caused by time difference cannot be solved, encryption observation is required to be carried out at 8 am every day; meanwhile, the measurement points after the batteries are replaced are also encrypted for 15 minutes for observation, and the receiver is turned off after the measurement work of a working day is finished. In order to avoid the influence of a high-power launching tower, a high-voltage wire and the like, geodetic personnel appropriately avoid the high-voltage wire, and if the geodetic personnel cannot avoid or meet the launching tower, the observation time of the measuring point is also prolonged.
And 2.3, observing a check point, wherein in order to check the observation precision of the common measuring points, repeated observation is carried out on a part of measuring points every day, and the check point is not less than 5% of the workload of the day.
3. GPS internal calculation; after the field observation is finished, the data is downloaded from the receiver on the same day, and the mapping professional software is used for converting the format data of the receiver into a standard format. And the software is used for carrying out necessary modification on the generated file, such as antenna height, antenna similarity, initial coordinates, receiver and other information. And after the modification is finished, performing quality check on the data, and performing rough single-point positioning calculation, thereby ensuring that the collected data has no problem.
GPS data processing flow:
(1) sorting original observation data: converting the original observation data into standard RINEX, checking the data quality by using software and editing and perfecting RINEX header file information.
(2) Obtaining high-precision existing products of IGS: and acquiring precise satellite orbits, precise satellite clock correction, satellite masking information, time, polar motion, rotation, polar axis direction and other data of the earth on the corresponding observation days on an IGS website.
(3) Selecting a processing strategy: the method comprises the steps of fixing JPL precise satellite orbit and clock difference by adopting a high-efficiency precise point-to-point protocol (PPP) mode, estimating receiver clock bias (white noise) and estimating troposphere zenith gradient delay every 5 minutes, wherein the troposphere model adopts GMF (Gaussian mixture model), the height cut-off angle is 15 degrees, the satellite and receiver antenna adopt an absolute phase center change and offset model, and the ocean tide load model adopts FES 2004.
4. The finished workload and precision are evaluated; the total length of a GPS measuring lead is 105.4km, 1058 effective physical points, 1165 actual measuring physical points and 107 check points.
The accuracy evaluation adopts a formula
5. Measuring gravity;
1 gravimeter performance, according to the requirements of the industry standard of the Ministry of geological and mineral products of the people's republic of China, namely the Standard of gravity exploration with large scale, various performance indexes of the gravimeter are tested before field data acquisition. The experiment includes static test and dynamic test.
1.1 static test, the static test place is the geoscience building of east China university of science of Nanchang city of Jiangxi, and a reinforced cement pier is specially arranged in the test room to avoid the interference of floor vibration to the instrument. The observation time exceeds the specified 24 hours; the gravimeter is observed once every 100 seconds, the gravimeter is provided with solid tide correction software, and a static drift curve of the gravimeter is drawn according to corrected data as shown in figure 5. As can be seen from the figure, the curve measured by the instrument is approximately linearly changed, and the lattice loss coefficient K is about-0.016 mGal/h.
1.2 dynamic test, the test sites are selected from 9 points with different heights, the observation is repeated for 13 times, when the continuous observation time is about 4 hours, the gravity difference between the test points is more than 0.5 multiplied by 10-5/s2And the one-way observation time between the two points is less than 20 minutes. Because the instrument is internally provided with solid tide correction, a dynamic zero
The instrument dynamic grid-dropping coefficient formula is as follows:
Wherein: Δ giThe difference between observed values before and after the ith point is taken as the difference; Δ tiIs the difference between the observation times before and after the ith point, and has the unit: the method comprises the following steps of (1) taking minutes; n is the number of repeated observations. And calculating the dynamic zero displacement rate k of the gravimeter to be-0.0004 mGal/min according to dynamic observation data and the above formula.
And counting the dynamic observation precision, and calculating the continuous observation increment of the instrument between 9 different height points according to an independent increment form. The evaluation formula of the instrument dynamic observation precision is as follows:
Wherein: viThe difference between a single independent increment and an average increment between the ith two adjacent points; m is the total increment number; n is the number of edges in the joint measurement. The mean square error of the dynamic test of the gravimeter is calculated to be 0.0066mGal by the experiment of m being 104 and n being 8.
As can be seen from the static test and dynamic test results of the CG-5 type gravimeter, the gravimeter adopted by the field gravity exploration completely meets the high-precision measurement requirement.
2, collecting and arranging gravity data;
2.1, the sampling interval of the current gravity measurement work is 0.1km, and the lengths of four measuring lines are all less than 100km (the longest measuring line is 39.9km), so that the relative gravity measurement mode can be adopted for operation. Two gravity base points are set up in the field, the two base points are selected beside a road which is convenient to transport and obvious in sign, and a reinforcing steel bar with the length of about 1m is vertically arranged underground so as to be easy to store. In order to ensure the precision of the base point, the early base and the late base in the measurement are carried out in a mode of 'base-auxiliary-base', and the error of the measurement on the base point twice is not more than 0.005 mGal.
2.2 observing the common point and the check point; the common point gravity measurement in the research area adopts a single observation mode, and the observation time of each point is 60s (the instrument automatically observes data once per second). The operator of the gravimeter needs to observe the data change within 60s, and if the data change is too large (generally, the change of five continuous data is considered to be more than 0.01mGal), the operator needs to observe again to ensure the data accuracy of the measuring point.
In order to evaluate the accuracy and precision of the measurement, a certain proportion of inspection measurement needs to be carried out on the measured common points. The number of the inspection points of the four outdoor gravity exploration lines meets the requirement of 5% -10%, the number of the inspection points of the shorter survey line is more than 10%, and the inspection points are basically and uniformly distributed on the whole survey line.
3, sorting gravity data; because the research area belongs to a plateau area with flat terrain, the influence of the terrain on the gravity value can be ignored, and a terrain correction value mode is estimated by eyes in an area with slightly large local terrain variation. Therefore, the gravity data arrangement in the work area mainly comprises three items of normal field correction (latitude correction), middle layer correction and height correction.
3.1 correction and precision of normal field, in China, the calculation of normal field adopts 1901-year Hull ink normal gravity formula:
The normal field corrected mean square error is calculated by:
The average latitude of the measuring point is 43.1 degrees and epsilonD. + -. 0.001km (from the measurement data), calculated as εDThe standard is +/-0.0008 mGal, and the requirement of 0.01mGal specified by the industry standard of the geological mineral department of the people's republic of China, namely the large-scale gravity exploration standard is completely met.
3.2 Booth correction and precision, the following formula is adopted for the height correction:(unit: mGal) in which
The middle layer correction was calculated as follows: Δ gσ＝-0.0419{σ}g/cm 3{h}m(unit: mGal); wherein sigma is the density of the middle layer, and sigma is 2.65g/cm according to the rock density data in the research area3。
The bragg correction error (not considering the intermediate layer density error) is calculated using the following equation:
in the formula ofhFor the mean square error of elevation of the survey point (provided by the survey,. epsilon.)h0.14m), calculated as: epsilonb＝±0.030mGal。
3.3 calculating relative to the Brookfield force abnormal value, the Brookfield force abnormal value is calculated by adopting the following formula:
3.4, evaluating the gravity measurement quality; according to the requirements of the technical regulation of gravity exploration, the quality inspection and evaluation are carried out by adopting a method of equal precision and repeated observation. The field measurement totally completes 115 check points, which account for 10.9% of the total number of the check points. The evaluation formula of the repeated observation precision of the measuring points is as follows:
wherein: diThe difference between observed values before and after the ith point is taken as the difference; n is the number of repeated observation points; calculated to obtain epsilong0.014mGal, 0.03mGal which also meets the specification requirements.
The accuracy evaluation of the obtained Bragg gravity anomaly needs to take observation errors, Bragg correction errors and normal gravity field correction errors into consideration. Therefore, the accuracy of the Bragg gravity anomaly is evaluated according to the following formula:
the foregoing has given εg＝±0.014mGal；εb＝±0.030mGal；
4, the precision evaluation of the workload condition and the observation point of the gravity measurement is completed, the gravity measurement result has no jump point, and the mirror image relationship between the data change characteristic and the elevation of the measurement point is obvious, so that the fast static GPS geodesic measurement and the gravity measurement result are mutually verified to be accurate. Relative gravity anomaly obtained through normal field correction and grid correction has no obvious correlation between the anomaly form and the measuring point elevation relative to the relative gravity value, and the gravity data arrangement is correct; meanwhile, the abnormal curve is more smooth and concise, and the reflected characteristics of high gravity and low gravity are more obvious.
And thirdly, the adopted method technology is the content of the specification.
Fourthly, processing gravity profile data and interpreting data;
firstly, the method comprises the following steps: the gravity field characteristics of the four gravity sectioning lines;
1.1NL line gravity section, NL line section main body goes to EW, the section mainly lies in the Grayler's Aho recess, only in the section end (east) on the east red protrusion. As can be seen from the NL line versus the bulgy gravity anomaly (fig. 22), the gravity anomaly is characterized by "west low east high", and in the west of the section, the gravity anomaly changes smoothly and appears as a relatively weak negative anomaly; the anomaly is obviously ascending at 10-19km, the anomaly gradient can reach 1.48mGal per kilometer, and the boundaries of the concave Grailea and the convex Oriental red are exactly in the anomaly gradient band.
1.2MD line gravity section, the main body of the MD line section is in NE direction, the main body of the section is positioned on the east red projection, and the NE section is positioned in the GrailerAodu recess. As can be seen from the relative buerger gravity anomaly (fig. 23), the gravity anomaly is characterized by high in the southwest, low in the middle, high in the northeast, high in 2 gravity and low in 1 gravity, and the height of the gravity anomaly is closely related to the protrusion and the depression which are passed by the section.
1.3 line E400 gravity section, line E400 trend is ES, section northwest section is on the red arch of east, the middle section is in the depression of the Qihari grid diagram, the southeast section is on the suniting of Sunint. As can be seen from the gravity anomaly map (FIG. 24), the line anomaly varies from-1.43 to 20.71mGal, and the anomaly amplitude varies greatly; the gravity anomaly can be divided into 3 gravity high parts and 2 gravity low parts on the whole, wherein the gravity high of the northwest section is probably caused by the east red bulge; the gravity height at the southeast end is related to the suniting of suniting; while a high gravity between two low gravities in the middle part may indicate that a local secondary protrusion is present in the depressed middle part of the cheohttes diagram.
1.4SH line gravity section, SH line trend is 135 degrees, and E400 line parallel. It can be seen from fig. 25 that the cross-section is located in the depression of the root of the brain, but it can be seen from the relative gravity anomaly that the gravity at the two ends of the cross-section is low, the gravity at the middle section is high, and the feature of high gravity is presented on the whole. This indicates that there is also a next level of relief in the nakai root depression.
Secondly, the method comprises the following steps: and (3) processing gravity anomaly data of four broken line fracture structure identifications:
2.1, analyzing a first derivative, and determining the horizontal position of the fault by using an extreme point of the gravity abnormal horizontal derivative and a gradient band (or a zero point) of the vertical derivative. The horizontal and vertical first derivatives of the gravity anomaly of the 4 profiles are calculated by adopting the wave number domain iteration method, and the results are shown in FIGS. 26-41. It can be seen that the derivative calculations significantly improved the lateral resolution of the anomaly relative to the original gravity anomaly (FIGS. 22-37), while the results showed greater computational stability, indicating that an iterative approach to derivative conversion of the actual data is feasible.
2.2 the method of the derivative standard deviation Tilt Angle (TASD), which is an outcome of the doctor stage of the writer, and the method identifies the boundary of the geologic body by calculating the maximum value of the result, not only has certain calculation stability, but also can identify the boundary of different depth field sources. The TASD results for the four gravity profiles are shown in FIGS. 30-45.
2.3 fracture inversion based on Euler deconvolution, which is an inversion method based on the theory that the derivative of the field position and the position satisfies the Euler homogeneous equation. The method can automatically or semi-automatically invert geometric parameters such as field source centroid position, boundary position, field source depth and the like under the condition of less prior information; the method has stronger flexibility and practicability, and is a common data processing inversion method and a gravity and magnetic data interpretation tool for geophysical workers at present. FIGS. 34-49 are Euler deconvolution inversion results based on iterative derivation in the wavenumber domain. It can be seen that the euler inversion points can better identify the location of the fracture and invert the occurrence of the fracture.
And 2.44 comprehensive analysis of fault processing results of the sections, and in order to further analyze the accuracy of fault break points and occurrence reflected by the results processed by various methods, the derivative analysis result, the TASD processing result and the Euler deconvolution inversion result are superposed together, so that the comprehensive analysis results of 4 sections can be obtained (see fig. 38-53). As can be seen in the figure, the fault breakpoint positions reflected by different methods have better consistency. Because the Euler inversion points are least square inversion solutions under a sliding window, and the positions with more inversion point distributions can be regarded as the trend positions of fractures, a writer considers that when the three methods have differences in fault breakpoint and trend judgment, the Euler deconvolution inversion result is used as a standard.
Through the first derivative analysis of the gravity anomaly, the TASD method of fracture identification and the comprehensive analysis of the inversion result of Euler deconvolution, 5 fractures can be divided on an NL gravity section, 6 fractures can be divided on an MD section, 9 fractures with different scales can be divided on an E400 section, and 4 fractures can be divided on an SH line section.
Thirdly, the gravity field separation of the 4 sections can be known from the geological and geophysical significance of the rag gravity anomaly, and the rag gravity anomaly obtained after various corrections are carried out on the gravity value measured on the ground is the superposition of various anomalies caused by the density difference between longitudinal and transverse geologic bodies and surrounding rocks. That is, the anomaly of the bulgy force has certain complexity, and the separation of the anomaly is a more complex problem.
If the sedimentary stratum distribution problem needs to be researched, a certain filtering method needs to be adopted to obtain the gravity anomaly of the part of the geologic body caused by the density difference. The separation of the gravity field is performed here for four sections using an iterative filtering method, as a result of which fig. 42-57 are shown. It can be seen that the regional gravity anomaly reflects the overall variation trend of the original gravity anomaly, indicating that the separated regional field is reasonable; the positive anomaly and the negative anomaly of the local (residual) gravity field appear alternately, the amplitude of the positive anomaly is equivalent to that of the negative anomaly, and meanwhile, the sum of the positive anomaly and the negative anomaly tends to be zero, which proves that the local gravity anomaly separated by using the iterative filtering method is generated by the shallow geologic body.
And fourthly, 4 pieces of cutting line residual gravity anomaly related probability imaging, wherein the related imaging of gravity data is developed according to the concept of probability imaging, and the test of a model and actual data of predecessors proves that the method can draw out the field source distribution of gravity and magnetic anomaly to a certain extent, and has the characteristics of high calculation efficiency, stable calculation process, easiness in implementation and the like.
To reveal the occurrence of 4 sections of subsurface geologic bodies, the remaining gravity data of 4 sections were subjected to normalized cross-correlation probability imaging processing, the results of which are shown in FIGS. 46-61. As can be seen in the figure, the NL line presents a 'biconvex-biconcave' characteristic, and the 'sunken zone' is approximately 10km wide, and the probability imaging inversion result of the NL section line can be proved to be reasonable according to EZK1248-1903# (industrial uranium mine, not to the base) and EZK1420-2031# (no mine, to the base); the MD line has a characteristic of two convex and two concave parts, a left concave area is positioned at the edge part of the west section of the line, the range of a middle convex area reaches 16km, the width of a middle concave area is about 10km, and the probability imaging inversion result of the MD section line is also proved to be reasonable according to two drilling data of EZK1376-1903# (mineralized well, not reaching the base) and EZK1420-2031# (reaching the base); the E400 line probability imaging result presents the characteristic of three convex and two concave, although the writer of the section can not collect the drilling data of the corresponding area, the reliability of the inversion result can be verified from the electrical data; the SH line body is positioned on a convex, two sides of the SH line body show signs of depression, and the data of DHZK-1# (without a mine and to the base) shows the validity of the gravity data inversion result.
And establishing and comprehensively explaining the geological-geophysical model of the fifth and fourth gravity profiles, wherein related contents such as rock density data, cross survey line drilling data, geological data and other geophysical data of a research area need to be collected before the man-machine interaction inversion of the gravity profiles is carried out. Through communication with other units, four-hole drilling data and E400 line CSAMT electrical data, the important data provides favorable guarantee for the reliability of the gravity forward modeling. Dividing the forward modeling into four layers according to the related data, wherein the four layers are a quaternary stratum, a tertiary stratum, an ancient-middle-age stratum and a substrate, and the average density is 2.05g/cm3、 2.15g/cm3、2.45g/cm3、2.75g/cm3And taking the average density of rocks as 2.65g/cm3. During the forward modeling process, the thickness variation of the stratum distribution is mainly related to the residual gravity anomalyAnd (5) imaging results. The geologic-geophysical model of the four gravity profiles is shown in figures 52, 55, 58 and figure 61, respectively.
Sixth, the NL profile geological-geophysical synthesis interpretation, the line laid in the Grayler-AoDo recess, the survey line passed EZK1248-1903 industrial uranium mines and EZK1420-2031 unmine. The purpose of laying the profile is to verify whether gravity exploration can be used for searching ancient watercourses and to research the secondary structure and sedimentation characteristics of the greenelo-and-odon recess by utilizing gravity data.
The NL section line was divided into gridler-die recessed middle secondary projections, gridler-die recessed east secondary recesses, and east red projections in order from west to east, in conjunction with the residual gravity anomaly (fig. 50), fracture distribution (fig. 51), and constructed geo-geophysical model (fig. 52).
6.1.1 NL section gravity field and fracture structure relationship, FIG. 51 is 5 fractures of different scales sketched according to the results of gravity anomaly derivative analysis, TASD and Euler deconvolution inversion. Wherein F1The fracture in the secondary protrusion of the Gray-Aore recess is not obviously reflected in the (residual) gravity field, and is only characterized by the sudden change of the gravity step band, but the fracture is obviously reflected by the derivative analysis, TASD and Euler deconvolution inversion results (figure 16); f2The boundary between the middle secondary projection and the east secondary projection of the gridlike-and-die recess is broken, and the broken boundary shows obvious step belt characteristics in a gravity field; f3In the east secondary recess of the Graylordica recess, the strip shows slowly-changing step band characteristics in the gravity field, namely, the strip has small fracture dip angle (which is consistent with the inversion result); f4Also in the east secondary recess of the gridlike-and-die recess, there is no apparent indication in the gravity field, but three fracture identification methods also indicate that the fracture is present, it being noted that during the operation in the field of gravity, the strip of fracture is found to be exposed to the surface due to careful observation by the members of the project team; f5The fracture is a boundary fracture of the gridlike and Aori recesses and the eastern red protrusions, which appears as a large gravity abnormal step band in the gravity field, and the contact band fracture has been demonstrated by EZK1420-2031 drilling.
6.1.2 distribution relation of NL section gravity field and sedimentary earth layer; FIG. 52 is a plot of stratigraphic distribution using forward modeling based on the residual gravity anomaly cross-correlation imaging results (FIG. 46). As can be seen from the geological map of the study area, the section shows that the stratum exposed to the surface is a tertiary system without a quaternary stratum. From the geology-geophysical model it can be seen that: the third stratum has limited thickness, the thickness is larger on the middle secondary bulge and the east red bulge which are dented in the Grailera overall, the distribution positions of the stratums in different ages are matched, and the maximum interpretable depth of the third stratum is 200m and is positioned at the 14.5km position of the cutting line; the stratums in the period are mainly distributed in the secondary recess at the east part of the recess of the Grilera and Aha, have certain thickness and scale, and the distribution has obvious river channel sedimentation characteristic, and can be inferred that the width of a 'river channel' is about 10km, and the average depth of a bottom interface is about 730 m; the substrate of the section has the characteristics of shallow burying depth at the east and west sides and large burying depth at the middle part, and the shallowest depth of the simulated substrate is only 230m and is positioned at the tail end of a measuring line.
6.2 geological-geophysical comprehensive explanation of MD section, the line is laid on the red east, the Griylora recess and the red east in turn from the southwest to the northeast, and the measuring line passes through EZK1376-1903 mineralized wells and EZK1420-2031 non-mineralized wells. The purpose of the layout of this section is the same as the NL line.
The MD sections were divided into east red projections, gridlike-jodo-recess east secondary recesses and east red projections in order from southwest to northeast according to the residual gravity field anomaly morphology (fig. 53), fracture spread characteristics (fig. 34) and the constructed geo-geophysical model (fig. 55).
6.2.1 MD section gravitational field and fracture structure relationship, FIG. 54 is 6 fractures of different scales sketched according to the results of gravity anomaly derivative analysis, TASD and Euler deconvolution inversion. Wherein F1The fracture is located in the eastern red bulgeThe characteristic of the obvious abnormal step band is shown in the gravity field; f2、F3The magnetic field is also positioned in the east red bulge and is also characterized by abnormal step bands in the gravity field, and the abnormal gradient is different in size; f4The fracture is a boundary fracture between the eastern red bulge and the Gray-Aore recess, and the fracture also has the characteristic of abnormal gradient change in a gravity field; f5In the gridler and hollow, there is no obvious display in the gravity field; f6Also the limit between the eastern red protrusion and the gridley-die recess breaks off, showing as abnormal step bands in the gravitational field.
6.2.2 MD section gravity field and stratum distribution, and FIG. 55 is a stratum distribution diagram obtained by forward modeling according to the residual gravity anomaly cross-correlation imaging result (FIG. 47). As can be seen from the geological map of the study area, the section reveals that the strata exposed to the surface are tertiary, and there is no quaternary strata. The third-stage stratum has limited deposition thickness and uniform overall distribution, the average thickness is about 130m, the deposition on the oriental red bulge is thicker, and the maximum interpretable thickness is 190 m; under the new-generation stratum, there is also a middle-generation stratum distributed in a certain scale (the ancient stratum has low possibility, the reason is the same with NL section), the stratum of this time has little distribution thickness variation in eastern red bulge, the average thickness is about 210m, the thickness is larger in the secondary depression of eastern part of the greenle and the Aha, and has a certain scale, the distribution also has river channel sedimentation characteristic, it can be inferred that the width of the 'river channel' is also 10km, and the average thickness of the bottom interface is 700 m; the substrate of the section has the characteristics of shallow burying depth at the two sides of the southwest and the northeast and large burying depth at the middle part, and the shallowest depth of the simulated substrate is only 260m and is positioned at the tail end of a measuring line. The present profile has a distinct contrast in rock distribution characteristics due to its geographical close proximity to the NL profile.
6.3E 400 line geological-geophysical complex interpretation, the line is laid on the eastern red bumps, the Oldham recesses and the suniting bumps in sequence from northwest to southeast. The position of the cross section layout is completely coincided with the position of the wire E400 by the electrical method in 2012. The purpose of the profile layout is to investigate whether inversion results of gravity and an electrical method have consistency or similarity, and perform heavy-electrical combined inversion to improve the reliability of a geological model.
According to the Ulandiacon depression geological map, the E400 section line is divided into a red-square red bulge, a Qiharangg chart depression (secondary structures are a western secondary depression, a middle secondary bulge and an east secondary depression in sequence) and a sunitin bulge from the northwest to the southeast by combining the residual gravity field abnormal feature (figure 56), the fracture spread (figure 57) and the constructed geological-geospheric physical model (figure 58).
6.3.1E 400 section gravity field and fracture structure relationship, FIG. 57 is 9 fractures of different scales sketched according to the results of gravity anomaly derivative analysis, TASD, Euler deconvolution inversion. Wherein F1The boundary fracture of the east red bulge and the zihari lattice diagram depression is characterized by large abnormal step belts in a (residual) gravity field; f2One of the secondary depressions in the east part of the depressions of the quash-hague diagram is broken, and no obvious reflection is caused in a gravitational field; but all three fracture identification methods (derivative analysis, TASD and Euler deconvolution) have obvious inversion results, and the fracture can be a contact zone between sedimentary formations or a position where formation change is obvious; f3The boundary between the east secondary depression and the middle secondary projection of the depressions of the Qihari grid diagram is represented by an obvious step band in a gravity field; f4The boundary fracture of the secondary bulge in the middle of the depression of the Qihari grid diagram and the secondary depression in the east part is realized, and the obvious abnormal step band is also used as the reflection in the gravity field; f5The fracture is a fracture in the secondary depression at the east part of the depression of the parallel-Hardgroved plot, the fracture is reflected by an abnormal step band in a gravity field, and the step band has a wider range, so that the fracture has a certain trend and scale; f6And F8Respectively in the depressions of the Qihakuri diagram and the suniting bumps, and no obvious reflection is generated in a gravity field; f7The boundary of the depressions of the Qihari lattice diagram and the suniting elevation is broken, and the fracture appears as a large abnormal step band in a gravity field; f9Is a small break in the sunite ridge but also exhibits a distinct abnormal step band in gravity anomaly.
6.3.2E 400 profile gravity field and sedimentary earth layer distribution relation, FIG. 58 is a stratigraphic distribution diagram obtained by forward modeling according to the residual gravity anomaly cross-correlation imaging result and the MT apparent resistivity inversion result (FIG. 47). As can be seen from the geological map of the study area, the sections reveal the third and fourth families of strata exposed to the surface. From the geology-geophysical model it can be seen that: the quaternary stratum is limited in distribution and small in thickness, is only distributed between 3.5-11.2 km, has an average thickness of 65m and a maximum thickness of 150m, and is mainly distributed in secondary recesses in west parts of recesses of the Quahygur pattern; the third-stage stratum is still approximately horizontally layered and uniformly distributed, and the average thickness is 75 m; ancient strata and middle-aged strata distributed on a certain scale are arranged below the new-aged strata (the south side of the survey line has local early-second-aged strata which is exposed, so the ancient strata can exist below the section), the ancient strata and the middle-aged strata are mainly distributed in secondary depressions at the west part and the east part of the depressions of the Qihahara chart, have equivalent thickness and scale, and the interpretable depth of the sedimentary strata of the two secondary depressions is more than 1000 m; the profile base has obvious fluctuation characteristics, the positions with shallow burial depths are positioned on the east red bulge, the secondary bulge in the middle of the ziharpag graph depression and the suniting bulge, and the shallowest depths of the three positions are 80m, 170m and 150m respectively.
6.4 geological-geophysical comprehensive explanation of SH section, the survey line is a gravity section temporarily added in the field working process of project groups, the section is arranged in the Chinese azalea root pit, the arrangement purpose of the section is mainly to verify whether an ancient river channel exists in the pit, and meanwhile, the section is also used for researching the underground rock distribution characteristics of the Chinese azalea root pit.
According to the Wulan exploration depression geological map, the SH sectioning lines are divided into a west secondary depression, a middle secondary protrusion and an east secondary depression of the Chinese rhododendron root depression from the northwest to the southeast in sequence by combining the residual gravity field abnormal feature (figure 59), the fracture spread (figure 60) and the constructed geological-geospheric physical model (figure 61).
6.4.1 SH section gravity field and fracture structure relationship, and FIG. 60 is 4 fractures outlined according to the results of gravity anomaly derivative analysis, TASD, Euler deconvolution inversion. Wherein F1 and F2 are positioned in the west secondary recess of the rhododendron molle recess, show as slowly-changing abnormal step bands in a gravity field, and are obviously reflected in derivative analysis, TASD and Euler deconvolution; f3 is the break of the boundary between the west secondary recess and the middle secondary projection of the Chinese azalea root recess, and the abnormal step band is displayed in the gravity field; f4 is the boundary between the central secondary bulge and the east secondary bulge of the nakai root depression, and is characterized by a distinct abnormal step band in the gravity field.
6.4.2 SH section gravity field and rock distribution relation; FIG. 61 is a forward simulation of a rock distribution diagram of 0-1500 m from the residual gravity anomaly cross-correlation imaging results (FIG. 48). As can be seen from the geological map of the study area, the section reveals that the stratum exposed to the surface is a third line. From the geological-geophysical model it can be seen that: the third stratum is similarly distributed approximately horizontally and uniformly in a layered mode, and the average thickness is 80 m; under the new generation stratum, a middle generation stratum with the average thickness of 420m is arranged (the old generation stratum has low possibility of existing and has the reason about the same as the NL section), the stratum in the time does not have obvious fluctuation like other three sections, the stratum bottom interface is embedded deeply in the east secondary recess of the Chinese azalea root recess, the deepest part is 760m, the embedded depth is shallow in the middle secondary recess of the Chinese azalea root recess, and the shallowest part is 370 m; the relief variation of the substrate is not obvious, but there is a certain raised feature in the secondary projection in the middle of the recess of the Chinese azalea root.
The gravity anomaly generated by the geological-geophysical model established based on the residual gravity anomaly related imaging is better fitted with the known residual gravity anomaly, and the simulated stratigraphic distribution is matched with the known geological data and drilling data. This indicates that: the constructed geological model has certain credibility, and provides a powerful basis for researching important geological information such as the distribution of the sedimentary strata of the two-link basin, the position of the ancient river channel, the hidden uplift and the like.
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