Guangxi Debao copper-tin mine

The working area is located around Qinjia copper-tin mine in Debao County, Baise City, Guangxi Zhuang Autonomous Region, outside the contact zone of Qinjiahuagang rock mass, with an area of about 300km2.

I. Geological background of the deposit

The Qinjia copper-tin mine area in Debao County, Guangxi Province is located in the southeast of Jingxi block of Youjiang Paleozoic rift basin in the south China active zone of South China plate, specifically at the intersection of Longguang anticline and Heishuihe fault in the NW-trending fault zone, and in the contact zone with Qinjia granite in the north (Figure 3-6- 1).

Figure 3-6- 1 Brief Table of Regional Geological and Mineral Resources of Debao Copper Mine (according to Guangxi Geological Second Team, 1972)

The exposed strata are Cambrian and Lower Devonian Lianhuashan Formation, Nagaoling Formation, Yujiang Formation and Tang Ding Formation. The Cambrian in the mining area experienced different degrees of metamorphism due to granite intrusion. The main lithology is shallow metamorphic sandstone, amphibole, marble and skarn.

The fault structures are mainly mineralized first, strike northwest, and are large in scale, and often form fault zones. The development of fractured rock mass in the fault zones is a favorable factor for ore guiding and controlling. After mineralization, the faults are NE-trending and NW-trending, which is an unfavorable factor to destroy the continuity of ore bodies.

The structure in this area controls magmatic activity, and the ore-bearing solution comes from granite magma, which precipitates after magmatic period and migrates along faults, and favorable strata are selected for metasomatism to form skarn-type deposits. Skarn has become an indirect prospecting indicator. Generally speaking, "CAMBRIAN argillaceous limestone+Caledonian S-type granite+dome and related faults (superimposed rock contact zone)" is a favorable combination of metallogenic factors.

Qinjia copper-tin deposit has a large distribution area, and the ore bodies are mostly layered or lenticular. The exploration area is about 5 square kilometers, and there are one, two, three, four, six and eight ore sections. The ore bodies are numbered according to the sequence of Cambrian strata from bottom to top, and the ore bodies in layers 3, 4, 5, 7 and 9 are numbered as 1, 2, 3, 4 and 5 respectively. Among them, No.3 ore body and No.4 ore body are layered, widely distributed, large in area, stable in shape and high in ore grade. The reserves of copper and tin account for 96. 17% and 95. 1% of the total reserves in the mining area respectively. At present, the main production sections of this mine are ⅵ and ⅷ sections. The main industrial ore bodies are No.3 ore body (produced in the fifth layer of middle-upper Cambrian) and No.4 ore body (produced in the middle-lower part of the seventh layer). 1, No.2 and No.5 ore bodies are only distributed sporadically in local sections, 1 ore body is located in the third floor, No.2 ore body is located in the fourth floor and No.5 ore body is located in the ninth floor.

Second, geophysical characteristics

(1) Physical parameters and abnormal characteristics of rocks and ores

According to previous magnetic data, the magnetic field value in this area is -50 ~ 150 nt. All granite bodies are slightly negative anomalies, and the anomaly range is -50 to -80 nt. Among the surrounding rocks, the Cambrian rocks have the strongest magnetism, abnormal disorder and steep gradient. They are serrated in profile, and the anomalies of ore bodies are 2 ~ 4 times higher than those of surrounding rocks. The abnormal gradient of shallow-buried ore body is steep; Deep is a slow form. Generally, it is 60 ~ 100 nt, with good regularity, regular shape and positive and negative symmetry.

See table 3-6- 1 for the magnetic parameters of representative rocks and ores in the area.

Table 3-6- 1 Table of Magnetic Parameters of Mining Area and Surrounding Rock Ore

The magnetoelectric parameters of 185 rock samples were collected and measured in this physical property work. Lithology includes copper-iron ore, granite, amphibole, marble, dolomite limestone and argillaceous sandstone. The magnetic properties of ore bodies, granites, hornfels, marbles, arsenopyrite veins, skarns and other outcrops were measured on 63 outcrops in the middle section of No.8 and No.6 ore blocks. The determination results are listed in Table 3-6-2. It can be seen from Table 3-6-2 that the copper-iron ore has high magnetic susceptibility [(1.31~ 847.0) ×10-5Si], high polarization (2.33% ~ 53.6%) and low resistivity (0./kloc).

Table 3-6-2 Electromagnetic Parameter Table of Rock and Ore Samples and Outcrop Determination

It can be seen from table 3-6- 1 and table 3-6-2 that magnetite, skarn copper-tin ore, skarn, pyrrhotite and magnetite breccia are the main causes of electromagnetic anomalies in the mining area. The first three are CAMBRIAN rocks and minerals, and their abnormal shapes are regular. The latter is the rock at the bottom of Devonian, and the anomalies caused by it are serrated, irregular and changeable. According to statistics, in the geomagnetic survey results of 1∶25000, all anomalies with chaotic magnetic anomaly curves and large gradient are mostly caused by bare or shallow buried mineralized geological bodies; The anomalies with regular curves and gentle slopes are mostly caused by concealed mineralized geological bodies. The magnetic anomaly of 100 ~ 300 nt has been found in all concealed ore bodies in the area, which is due to the great difference in magnetic strength between copper-tin ore and magnetite or skarn body with more magnetic minerals. Therefore, the prediction area has the premise of using magnetic exploration.

As can be seen from Table 3-6-2, the copper-iron ore body has the characteristics of low resistance and high polarization; While amphibole, granite and marble are characterized by high resistance and weak polarization. The argillaceous sandstone has medium-high resistivity and non-polar effect. Therefore, the intensity and distribution of IP anomalies indicate that it is closely related to copper-iron mineralization, and the distribution area of high polarization and low resistance anomalies will indicate the existence of copper-iron ore bodies.

(2) Geological-geophysical exploration model

According to the geological and metallogenic laws summarized by predecessors, the ore bodies in this area mainly occur in the 3rd to 9th layers of Cambrian, mainly in the 5th and 7th layers. The lithology is amphibole, skarn amphibole, rocks containing skarn and magnetite, copper-tin ore and pyrrhotite, and the ore body is obviously controlled by lithology. According to the geophysical characteristics of the deposit, there are obvious magnetic differences between copper and tin mineralized bodies and surrounding rocks. The ideal model of magnetic exploration in mining area is constructed with high-precision magnetic survey of 1∶ 10000, as shown in Figure 3-6-2.

Fig. 3-6-2 Ideal Profile of Prospecting Model of Debao Copper Mine (Qinjia 28 Line Profile)

Third, the application of geophysical methods and techniques.

(1) Objectives, tasks and work arrangements

In this geophysical exploration, high-precision magnetic survey area combined with comprehensive geological engineering exploration such as geology and drilling is used to delineate the plane distribution characteristics of magnetic bodies in the survey area, and electrical sounding is used to study anomalies, so as to further understand the distribution, scale, deep structure and changes of copper-tin ore bodies in the work area, delineate favorable metallogenic areas and evaluate the metallogenic prospect of ore bodies (mineralized zones) in this area. Combined with the geographical and metallogenic geological conditions of the prediction area, we deploy 1∶ 10000 high-precision magnetic survey and induced polarization sounding to study, infer and reveal favorable metallogenic areas, and provide targets for the next prospecting and exploration. Its main task is to carry out fine magnetic survey in the west of No.1 mining area. In the ⅷ section of the northern contact zone and the western contact zone of Qinjia rock mass, the best IP sounding profile is selected, the favorable prospecting areas for skarn copper deposits are delineated, and suggestions for drilling verification are put forward.

According to the requirements of mineral prediction, geophysical exploration is carried out to provide a basis for the deployment of mineral prediction projects. The main physical workload of geophysical exploration in 2008 is: 1∶ 10000 high-precision magnetic survey 9km2, IP sounding 100 physical point (AB=2000m).

(2) Working methods, techniques and tools used

1.1:10000 high-precision magnetic survey

The scale of magnetic survey is 1: 10000, and the grid is 100m×20m, and 46 sections are arranged.

The instruments and equipment used in this magnetic survey are CZM-3 microcomputer proton precession magnetometer produced by Beijing Dior Detection Instrument Company, and its main performance parameters are shown in Table 3-6-3.

Table 3-6-3 Performance Parameter Table of Proton Precession Magnetometer

The whole process of magnetic measuring instrument calibration, noise level and consistency test, base point setting, daily variation station setting, daily variation observation and field network observation. Completely in accordance with the relevant regulations, the relevant parameters meet the design requirements.

2.IP detection

It is used to study magnetic anomalies. Seven sections are respectively arranged on the lines 140, 160, 2 10, 320, 400, 440 and 560, with a total of 100 physical points, with an interval of 40m.

Because it is very difficult to arrange in karst area, IP sounding adopts three-pole device, and the infinite pole is arranged perpendicular to the survey section, about 3km away from the section. Three receivers with one power supply simultaneously collect the potential and polarizability parameters of three measuring points with different polar distances.

The feeder poles AO are 40m, 60m, 80m, 100m, 120m, 140m, 160m, 180m, 200m, 240m, 320m and 320m respectively. The polar distance of MN/2 is 20 ~120 m. the polar distance of ao is less than 400m, and the polar distance of power supply at each measuring point is basically the same. When AO is greater than 400m, the distance between power supply poles at each measuring point is slightly different, with a difference of about 20 ~ 80 m.

The instruments and equipment used are medium and high power IP system (DWJ-2A) produced by Beijing Geological Instrument Factory, and its main technical indicators are shown in Table 3-6-4.

Table 3-6-4 List of Main Technical Indicators 3-6-4 DWJ-2A IP Instrument System

(3) anomaly interpretation and inversion methods and techniques

1. Identify ore and non-ore anomalies.

Magnetic anomalies 17 were found in the whole survey area, numbered as C 1, C2...C 16 and C 17, as shown in figure 3-6-3. Through the exploration and inspection of anomalies, it is preliminarily judged that C 12, C 13, C 14, C 15, C 16 and C8 are non-mineral anomalies. Among them, four anomalies, C 12, C 13, C 14 and C 15, are located around Debao copper mine, all of which are anomalies with large gradient changes and are chaotic and irregular. Due to the existence of strong interference sources such as iron pipes, wires, buildings and smelters. In the Ministry of Mines, after investigation, it was determined that it was abnormal interference. The anomaly of C 16 is located on the tailings pond, which is obviously the interference anomaly caused by tailings sand. The C8 anomaly is located between 470 and 490 points on the 330-380 line on the east side of the C7 anomaly, and it is an anomaly with great gradient change, so it is speculated that the anomaly is buried shallowly. According to the distribution position of C8 anomaly, it is considered that this anomaly is related to C7 anomaly. Because there are obvious interferences in the positive and abnormal parts-rails and wires, and the surface is not mineralized, it is preliminarily judged that the anomaly is also a disturbance anomaly.

Except for the above six kinds of magnetic anomalies, other anomalies are preliminarily judged as meaningful anomalies. Among them, the anomaly of C 1 is located in the known no. ⅵ and no. ⅷ ore block, which is ore-induced anomaly; The C2 anomaly is located at. No.8 ore block is to the north of No.2 ore block. Number three and number three. IV ore block, which is a kind of ore-induced anomaly. C5 anomaly is located in the old mining area, which is disturbed by wires and rails. It is preliminarily considered that the anomaly is caused by the superposition of mine anomaly and interference anomaly.

C3 and C4 anomalies are located in the northern margin of blocks ⅵ and ⅷ, C6 anomaly is located in the northwestern margin of block I, C9 anomaly is located in the western margin of block ⅷ, and C7 anomaly has mineralized outcrops. These anomalies are of great prospecting significance.

2. Calculation of magnetic data field

After obtaining the δ t value of the scalar anomaly of the total magnetic field, the anomaly is separated by using the magnetic data correlation processing software (AgsmGIS).

A. Extend upward

The magnetic anomaly extends upward, and the grid spacing is 20m×20m. The purpose of continuation treatment is to suppress the interference of shallow magnetic bodies and highlight the meaningful anomalies produced by deep magnetic bodies.

B. digital spectrum filtering anomaly separation

The δ T magnetic anomaly data in the survey area are separated into various component data expressed by the following formula, so as to extract various effective geological information components from the original data and analyze and study various target geological bodies in the survey area. After data processing, the scalar anomaly δ t of the total magnetic field satisfies the following equation:

δT =δTq+δTj+δT b+δTx

Where: Δ TB is the background abnormal component (i.e. low frequency component); Δ TQ is the regional abnormal component (i.e. intermediate frequency component); Δ TJ is a local abnormal component (i.e. high frequency component); δ tx is a random high frequency interference component.

Figure 3-6-3 High-precision magnetic δ T contour map of Debao copper mine exploration area

C. Forward calculation

Copper-tin ore bodies in this area mainly occur in the 3rd to 9th layers of Cambrian, with the 5th and 7th layers as the main ones. The lithology is amphibole, skarnized amphibole and skarn (mainly located at the edge of granite), containing magnetite and pyrrhotite that can cause magnetic anomalies. Ore bodies are obviously controlled by lithology and distributed in layers.

Forward modeling is mainly inclined magnetized thin plates, and some models are spheres or semi-infinite steps.

3. Two-dimensional inversion of IP sounding data

The software for 2D inversion calculation is "resistivity/polarizability 2D inversion software system" compiled by Guilin Institute of Technology and "electrical prospecting workstation software system" compiled by Institute of Geophysical and Geochemical Exploration of Chinese Academy of Geological Sciences.

The inversion algorithm of "resistivity/polarizability two-dimensional inversion software system" is a 2.5-dimensional finite element forward simulation based on resistivity/polarizability data and a least square inversion algorithm based on smooth model constraints, which is suitable for inversion interpretation of dual-frequency instrument measurement data (apparent resistivity and apparent polarizability) in different devices of high-density electrical method and conventional electrical method at present, and also suitable for data interpretation under horizontal terrain and undulating terrain, without correcting topographic influence. Triangular element division is adopted in forward calculation, which can simulate the undulating terrain well, and the electrical parameters in the element are set to change continuously. In order to reduce the multiplicity of the solution, prior information such as the simplest model and background field are added to the objective function of inversion.

The software system of electrical prospecting workstation has the functions of human-computer interaction and forward modeling, which can carry out one-dimensional forward modeling of human-computer interaction and two-dimensional forward modeling of undulating terrain, lock known parameters and reduce the multiplicity of forward modeling.

4. Comprehensive analysis and interpretation

Copper-tin ore bodies mainly occur in granite contact zone or skarn and amphibole zone, and occur in layers. Granite, skarn and amphibole have high resistivity, but the resistivity of ore-bearing amphibole and skarn will decrease. The resistivity of overlying Devonian argillaceous sandstone is equivalent to 1/3 ~ 1/4 of the above high resistivity rocks. According to the types of sounding curves and known data, the interface between Cambrian and Devonian strata and the local low resistance area in the deep high resistance area of Cambrian can be roughly divided. Copper-tin ore bodies can cause comprehensive anomalies of high magnetic force, high polarizability and low resistivity. Therefore, we regard the blocks with overlapping positions of low resistivity and high polarization anomalies and magnetic anomalies in IP sounding as important prospecting targets.

Taking the comprehensive result of C3 anomaly on 160 line as an example, the comprehensive anomaly is explained and inferred.

Three groups of positive and negative magnetic anomalies were found at 5 10 ~ 526, 532 ~ 582 and 588 ~ 650. The forward calculation results show that the magnetic anomaly at 5 10 ~ 526 is narrow, which is caused by the shallow magnetic body with the roof buried about 60 m. The magnetic anomalies at 532 ~ 582 are supposed to be two magnetic bodies with a buried depth of about 150 ~ 200 m, and the magnetic anomalies at 588 ~ 650 are composed of two adjacent magnetic anomalies (Figure 3-6-4). The forward simulation results show that the average depth of the left magnetic anomaly roof is about 225 meters (similar to the ore body that controls the northeast inclined end of No.1 ore body). VIII ore section), the depth of the right magnetic anomaly roof is about 2 15m.

In order to study the anomaly at the northwest end of C3, IP sounding profiles of 594 ~ 650 were arranged on C3 anomaly. The apparent resistivity curve type diagram of IP sounding (Figure 3-6-4) shows that the sounding type curves on both sides of the section are completely inconsistent with the boundary of 622 points: there are more than five electrical layers in the section from 594 to 622 points, and the high resistivity anomaly of AB/2≥ 1200m section may be granite; From 622 to 650, there are only three layers of electricity, and there is also a high resistance reaction in the deep.

Apparent resistivity sounding profile: bounded by 622 points, the south and west sides of the profile are dominated by low resistivity, and the resistivity value is about100 ~ 300 Ω m; The north-east side is dominated by medium resistance, and the resistivity value is about 300 ~1500 Ω m. It is speculated that there is a group of faults with steep dip from south to west at 622.

Apparent polarization sounding profile. The high IP anomalies are mainly distributed in the shallow part of 594 ~ 638 (AO≤300m) and the middle-deep part of 6 10 ~ 634. In the middle and deep part of the profile (AO = 700 ~ 1400 m), a layered medium and high polarization anomaly was found. IP anomalies at 594 ~ 6 10 correspond to C 1 negative anomalies and weak anomalies of C3 left arm, and IP anomalies at 6 16 ~ 640 correspond to C3 anomalies, with an average depth of about 220m m m. ..

Two-dimensional inversion profile. The apparent resistivity inversion profile shows that there are obvious low resistivity areas at 600 ~ 300 m and 622 ~ 650, and the relatively high resistivity body in the deep part may be granite. The apparent polarization inversion profile shows that there is a highly polarized body in the shallow part (above 700 meters above sea level), which is presumed to be a lithologic unconformity surface, and the IP anomaly in the deep part is not obvious.

According to the above interpretation results, it is considered that there are anomalies in the southwest section of C3 anomaly at 588-600 points and the main anomaly section of C3 (between 604-624 points), and the magnetic and electrical conjectures are basically the same, and it is inferred that it is a copper-tin mineralized body with a center depth of 245 meters and 230 meters respectively. In addition, according to the polarization sounding profile, there is a high polarization anomaly at the depth of 630 ~ 644 (AB/2 = 800 ~ 1200m), and the top depth of the polarization anomaly is about 235m, which should be a sub-anomaly of C3 anomaly extending northeast, but there is no corresponding magnetic anomaly.

IV. Verification results

Initially, two abnormal verification holes were designed, but due to financial problems, only the workload of building one hole was approved. After many field investigations and studies, the relevant technicians and supervision experts from the prediction unit, geological exploration unit and geophysical exploration unit finally chose to verify the C3 magnetic anomaly. The verification hole ZK 160 1 is located near 160 geophysical prospecting line (geological number ZK90 1, 103 exploration line) 6 14, and the IP sounding of 160 line is in ao. The drilling verification results show that the final hole depth is 283.45 meters, and the ore is found at 2 17. 18 ~ 223.95 meters. The apparent thickness of the ore body is 6.77 meters, the real thickness is 5. 18 meters, and the copper grade is 0.43% ~1.40. Gold is 0.47g/ton, tin is 0. 1 1%, iron 16.32% and silver10.8g/ton. The hole is drilled with granite 15m, and the copper deposit is a skarn copper-tin deposit.

The verification results show that the Cambrian skarn body has great prospecting potential, which provides a basis for further prospecting in this area.

(Contributed by: Li Hailong, Lu Huaicheng, Huang Qixun)

Figure 3-6-4 Comprehensive Interpretation Profile of Debao Copper Mine 160 Line Magnetic Survey and IP Sounding