Gejiu tin polymetallic deposit, Yunnan Province

Gejiu tin polymetallic deposit is located in Gejiu City, southeast of Yunnan Province, with an area of about 2000km2. Gejiu tin mine has a history of mining and geological exploration for nearly a hundred years. Before 1949, dozens of geologists had done geological surveys in the mining area. Systematic geological exploration began in the 1950s. 1950, the investigation department of Yunnan Tin Industry Company (1952 was changed to the Geological Department) and the second geological survey team of Gejiu Tin Mine Survey Team of Southwest Geological Bureau (1953 was changed to Team 224 of Southwest Geological Bureau) started the geological survey together, and Team 50/kloc-0 of Southwest Geological Bureau conducted the geological survey in 65434. In the 265438+20th century, the deep geological prospecting in the mining area was jointly conducted by Yunnan Tin Company, Team 308 of Yunnan Nonferrous Geology Bureau, Institute of Geology, Geophysics and Exploration of Yunnan Nonferrous Geology Bureau and other geological prospecting units and scientific research institutions.

From 1954 to 1956, the 30 1 team of Geophysical Exploration Bureau of the Ministry of Geology conducted prospecting in the mining area by means of self-electricity, electric sounding, magnetic method, gravity and soil survey. Due to the limitation of deep oxidation depth and great interference, the prospecting effect is not good. 1957 to the early 1960s, the No.5 Team and No.1 Team of the Geophysical Exploration Corps of the Ministry of Metallurgy conducted geophysical and geochemical exploration in this area, and completed1∶ 50,000 magnetic survey, 4 10km2 self-electrical survey and 584 electrical sounding points (AB/2 = 2000 m). The work results delineate the distribution range and undulating form of concealed granite between Shuangzhu (bamboo forest and bamboo leaves) and Malage ore field, which provides an important basis for finding "contact zone deposits with domes (or anticlines) at the top and granite plants protruding at the bottom", and works closely with Team 308 to find a number of deposits, opening up the situation of indirect prospecting.

From the mid-1960s to the mid-1970s, the Geophysical Exploration Team of Yunnan Metallurgical Geological Exploration Company, the Department of Mathematics of Yunnan University and the Department of Geology of Central South University of Technology jointly tackled key problems and carried out the research and practice of comprehensive geophysical and geochemical exploration methods. During the period of 1962 ~ 1965, the geophysicists scanned the surface with the scale of 1∶5000 by using the combined section method with different polar distances. After eliminating all kinds of interference, six ore-bearing faults in Yindong were delineated, with tin and gold content 18000t and1. During this period, electric sounding with large polar distance (AB= 10000m) was carried out in the whole region, and 195 points were completed. After excluding the influence of lateral low (high) resistivity rock series, the large-scale tin polymetallic ore field in Gaosong was found by combining electrical sounding data with rock survey anomalies and geological indicators, and the depth was1000 m.

Gejiu tin mine has five large ore fields from north to south, namely Malage, Songshujiao, Gaosong, Laochang and Kafang. The mining area is dominated by tin, as well as copper, tungsten, bismuth, lead, zinc, silver and other metals. After nearly 60 years of exploration, five kinds of non-ferrous and rare metals 15 have been found, and the metal reserves are nearly 8 million tons.

I. Geological background of the deposit

Gejiu mining area is located at the intersection of the Pacific Rim Giant Metallogenic Belt and the Mediterranean-Himalayan Giant Metallogenic Belt. Located at the location where Eurasian plate was subducted and collided by Pacific plate and Indian plate, it belongs to the southwest corner of fault fold bundle in Nanpanjiang depression of Youjiang continental margin basin on the southwest edge of China microplate, and the southwest corner of Youjiang geosyncline fold belt of South China fold system where Yangtze paraplatform, South China fold system and Tanggula-Changdu-Lanping-Simao fold system converge. Due to the interaction between Eurasia, Pacific Ocean and India, the evolution of Youjiang geosyncline is complex, the tectonic magmatism is strong and the metallogenic conditions are superior.

The mining area is located in the western edge of the southern Yunnan fold belt of the Caledonian fold system in South China, with the southwest cut by the Red River fault and the northwest limited by the southwest extension fault after the intersection of Xiaojiang fault and Mile-Shizong fault. Gejiu fault extending in the north-south direction divides the mining area into east and west areas. The eastern part is Wuzishan anticlinorium, which is composed of Gejiu carbonate rocks in the Middle Triassic, and there are concealed granites under it, including tin polymetallic sulfide deposits. There are five large ore fields in Gejiu mining area from north to south, namely Malage, Songshujiao, Gaosong, Laochang and Kafang, where the main tin ore bodies are concentrated.

The exposed strata in the mining area are mainly Triassic, which are divided into Triassic six groups (Figure 6-2- 1), Upper Triassic Huobachong Formation (T3h) and Niaoge Formation (T3n). Middle Triassic Falang Formation (T2f) and Gejiu Formation (T2G); Yongningzhen formation (T 1y) and feixianguan formation (T 1f) of lower Triassic. It is mainly composed of sandstone, shale and argillaceous limestone. The Middle Triassic is the main ore-bearing bed in the mining area. The Shangfalang Formation (T2f) is composed of siltstone, shale, argillaceous limestone, intermediate-acid tuff and basic lava, with some mineralization of iron, copper, tin and lead. The next old formation (T2g) is divided into Upper Bainidong section (T2g3), which is dominated by limestone with irregular dolomite and tin-lead mineralization. The middle Malage member (T2g2) is dominated by dolomite with irregular limestone, with tin and lead mineralization; The Lower Kafang Member (T2g 1) is interbedded with limestone and calcareous dolomite, and the bottom metamorphic basalt is multi-layered, with tin, copper, lead and gold mineralization.

Fig. 6-2- 1 Geological Schematic Diagram of Gejiu Mining Area

The fault structures in the area are criss-crossed and well developed, forming a structural framework that looks like a "checkerboard" format. There are two groups of faults which are obviously related to mineralization, northeast (northeast) and nearly east-west (northwest), and they are the main rock-controlling and ore-controlling structures in the area.

Magmatic rocks in the area mainly include Yanshanian granite and Indosinian alkaline basalt, which are buried deeply and not exposed to the surface.

The deposits in this area are post-magmatic tin-copper polymetallic sulfide deposits related to Yanshanian granite intrusion, and some of them have been oxidized into oxide deposits, belonging to post-magmatic gas-generated hydrothermal deposits.

Gejiu tin polymetallic deposit includes placer and primary ore. Most placer deposits are formed by eluvial deposit, slope deposit and artificial accumulation, which are mainly distributed in karst basins, hillsides and erosion terraces near primary deposits. The scale is huge, and the proven reserves account for 45% of the total tin in the region. There are five types of primary deposits: tin-bearing greisen type, tourmaline veinlet type, cassiterite-skarn sulfide type (interlayer oxidation deposit, skarn sulfide deposit), tin-bearing dolomite tin deposit and volcanic massive sulfide copper-tin deposit.

At present, there are 300 ore bodies 1300 (including 328 placer mines) in Gejiu East Mining Area, 4 existing and planned large-scale mining areas 10, and 4 medium-sized mining areas10, and the accumulated proven non-ferrous metal reserves are about 8 million tons. Gejiu mining area is not only a super-large tin mining area, but also a medium-large copper, lead, zinc, tungsten and silver mining area, accompanied by a variety of rare metal minerals.

Middle and Upper Triassic argillaceous limestone and sand shale are exposed in the west of Gejiu tin polymetallic mine. The main structure is the northeast Jiasha River syncline, and its axis is produced by Yanshanian granite. There are Niushipo large-scale placer-tin deposits and dozens of small and medium-sized tin-lead deposits (spots). At present, the degree of geological work is low.

Second, geophysical characteristics

Characteristics of electrical and magnetic parameters of (1) rock (ore)

According to the previous geophysical prospecting results in Gejiu area and the determination results of various rocks (ores) in the mining area (Table 6-2- 1), rocks (ores) have the following electrical and magnetic properties.

Table 6-2- 1 Rock (Ore) Electromagnetic Parameter Table in Gejiu Mining Area

1) Granite has only weak magnetism or even no magnetism, so it is impossible to study the undulating shape of concealed granite by magnetic method; There is a certain magnetic difference between sulfide ore and surrounding rock, which provides a certain physical premise for high-precision magnetic survey.

2) marble, dolomite and basalt have high resistivity; Secondly, granite and mineralized basalt, skarn, pyrite-bearing granite and oxide ore have low resistivity; The resistivity of mineralized skarn and sulfide ore is the lowest, which is several times to several times different from that of surrounding rock, which provides a good physical premise for transient electromagnetic method to predict granite uplift in this area and find sulfide ore in contact zone. The resistivity of oxidized ore is also obviously different from that of surrounding rock, and there is also a good physical premise for finding oxidized ore bodies with a certain depth by transient electromagnetic method.

3) Sulfide ore, ore-bearing skarn, mineralized basalt and pyrite-bearing granite in the mining area have high polarizability, which is obviously different from surrounding rocks by several times to ten times, providing good physical conditions for induced polarization method and charging method for prospecting.

On the basis of the above ores, there are obvious differences in IP and conductivity between mineralized skarn, mineralized granite and the surrounding rocks of the deposit, and at the same time, due to the high resistivity of rocks in this area, the electromagnetic exploration depth is increased (from the verification of exploration results, the exploration depth in some areas can reach 1000m). Therefore, electrical exploration has become the preferred exploration method in Gejiu area.

(2) Abnormal characteristics of ore bodies

According to the measured TEM results of section 254 (Figure 6-2-2), the multi-channel normalized secondary potential profile curve of TEM has obvious abnormal reflection of high value at the measuring point 195. It is verified that the borehole ZK06-2540 1, ZK06-25402 and ZK06-25403, which are arranged in the middle section of 1785, reveal the corresponding abnormal positions of tin mineralized bodies, which shows that the transient electromagnetic method is effective.

Third, the application of integrated geophysical methods and techniques.

(1) Work deployment and working methods

1999 From 2008 to 2008, the Institute of Geology, Geophysics and Chemistry of Yunnan Nonferrous Geology Bureau successively carried out surface transient electromagnetic and induced polarization prospecting in Axizhai, Daqingdong-Tuofengshan, Chibeishan and Dabaiyan sections of Gejiu mining area. Among them, the ground transient electromagnetism in Axizhai and Daqingdong-Tuofengshan ore sections is carried out to cooperate with the deep prospecting work of Yunxi Company, and the working grid is 200m× 100m or 200m×50m m. SD- 1 transient electromagnetic instrument produced by Central South University is used, and 200m×200m overlapping loop device is selected to work. At the same time, in order to cooperate with tunnel exploration, some induced polarization (charging) methods are carried out in tunnels and boreholes, and underground geophysical exploration is used for prospecting. In Beishan and Dabaiyan ore sections, in order to cooperate with the exploration of replacement resources of crisis mines in China, surface transient electromagnetic exploration was carried out. Tem-57 transient electromagnetic system produced by Geonics Company in Canada is used, and the central loop device with a side length of 200m is selected to work. The purpose is to find out the deep geological structure and search for deep tin polymetallic deposits.

Figure 6-2-2 Geological-TEM Normalized Secondary Potential Model

(ii) Work results

1. Searching for sulfide metal deposits in the contact zone controlled by granite uplift by transient electromagnetic method.

During the period of 1999, three transient electromagnetic profile tests were carried out in the known mining areas in Gao Fengshan, among which the transient electromagnetic results of lines C and D showed (Figure 6-2-3) that the excitation potentials of 3-6 measuring points in the southeast section of lines C and D showed weak and high value anomalies in the later period, reflecting the existence of low-resistivity bodies underground, and it was presumed that it was a sulfide mine in the limestone contact zone of Kafang section of Gejiu Formation, which was controlled by granite uplift. According to the previous electrical sounding data and some drilling holes, there is a hidden granite bulge in the deep part of this section, and the elevation is about 1750m, which is consistent with the TEM anomaly inference result.

2. The application of transient electromagnetic method in deep prospecting.

From 2001to 2002, the transient electromagnetic method (TEM) work with a working grid of 200 m× (50 ~ 100) m was carried out in Daqing East-Tuofengshan section, with an area of 6. 15km2. A total of 7 low resistance anomalies are obtained (Figure 6-2-4). As can be seen from the figure, TEM anomaly zone I and TEM anomaly zone V are nearly east-west, while TEM anomaly zones II, III, IV, VI and VII are northwest, and the distribution directions of these anomalies are basically consistent with the nearby fault zones. Except for the ⅶ anomaly, the other six anomalies are inferred as anomalies with prospecting potential.

According to the results of transient electromagnetic method, the designed tunnel and borehole are explored and verified. Many tin mineralized bodies (in tunnels) were found in the transient electromagnetic 1 anomaly area, and multi-layer ore bodies were exposed in the underground tunnel (in the middle section of 1820) and in the holes CK6, CK 1 and CK3 of the exploration line 2 13. Ore body thickness 1 ~ 5m, tin grade is about 2%.

Fig. 6-2-5 shows the TEM anomalies of 16 and 17 sections. The abnormal profile reflects three obvious low-resistivity anomalies, all of which well reflect ore bodies or fault structures.

According to the exploration and verification results of 1 and No.6 anomaly pits, it is speculated that No.2, No.3, No.4 and No.5 anomalies have good prospecting prospects. It provides a prospecting target for deep geological engineering exploration and expands tin polymetallic prospecting resources.

In 2005-2006, Beishan ore section, with a grid of 200m× 100mTEM and an area of 10km2, has a total length of 45.6km and 474 physical points. TEM work obtained a- 1, a-2, a-3, a-4, b- 1 and b-26 TEM anomalies (fig. 6-2-6).

Figure 6-2-3 Comprehensive Geological and Transient Electromagnetic Profile of Line C and Line D in Gaosong Mining Area

Combined with the analysis of geological conditions, it is speculated that the anomaly of A- 1 is caused by Laoxiongdong fault and concealed tin mineralization (which may be the anomaly of skarn sulfide ore in contact zone). It is inferred that A-2 anomaly is a mineralized body and a fault anomaly, which is affected by human interference. The section west of highway no.10. 15 may be a skarn sulfide anomaly in a contact zone. 15 may be a fault and interlayer mineral anomaly. A-3 anomaly is presumed to be an interlayer ore anomaly. It is speculated that A-4 anomaly is mainly fault anomaly, and the possibility of interlayer ore anomaly cannot be ruled out. There is artificial interference in the area near the tailings pond. B- 1 anomaly is presumed to be an anomaly of human interference, and the possibility of concealed tin ore (mineralized body) is not ruled out. It is speculated that B-2 anomaly is caused by tailings filling cracks.

In 2006-2008, the transient electromagnetic method was used in Dabaiyan ore section, with a grid of 200m× 100m, an area of 4.32km2, a total section length of 2 1.3km and 223 physical points. A total of 1 1 TEM anomalies were obtained (Figure 6-2-7).

Figure 6-2-4 See Figure 6-2- 1 for the symbols of the comprehensive map of geological-geophysical (TEM) anomalies in the Tuofengshan section of Gaosong mining area.

Geophysical anomaly 1, which is presumed to be the coexistence of Class I (known ore body anomaly) and Class II (abnormal prospecting potential); There are 7 geophysical anomalies (anomalies with prospecting prospects), which are presumed to be secondary geophysical anomalies. According to the layout of mine engineering, pyritization and copper mineralization were found in the borehole near the tems- 1 anomaly on the edge of the survey area. The profile contour relief shape drawn by TEM according to longitudinal conductance is consistent with that of concealed granite, which provides reliable information for delineating deep concealed geological bodies.

IV. Verification results

According to the interpretation and inference of anomalies, the normalized secondary potential is used to determine the drilling plane position, and the abnormal elevation of resistivity profile is inverted to determine the hole depth. In Beishan ore block, it is suggested to carry out drilling verification for the anomalies of lines B- 1 and A- 1 of 250 ~ 254 (Figure 6-2-6). From June 2006 10 to June 2008 10 in the old factory and mine of Yunnan Tin Industry Group (Holdings) Co., Ltd., according to the suggestions of the Institute of Geology and Geophysical Exploration of Yunnan Nonferrous Geology Bureau and the TEM measurement results, in the middle pit of exploration work area 1785, the B-/KLOC-of line 250 ~ 254 was surveyed.

According to the information provided by Yunnan Tin Industry Group (Holdings) Co., Ltd. through the exploration and prospecting work in recent 10 years, "from 2003 to 2009, the amount of non-ferrous metals in Gejiu mining area increased by 13 16600 t, including 443 1000 t of tin and 6000t of copper. Especially in 2005, 2006 and 2007, the amount of metals such as tin, copper, lead and tungsten detected each year exceeded 240,000 t, which increased by 226,900 t in 2008 and 98,500 t in 2009. Create a new record of new reserves for geological prospecting in Yunxi, which is more than three times the production and consumption reserves of that year, and reverse the situation that the reserves of retained resources have been declining for many years. "

Verb (abbreviation of verb) conclusion

1) tin polymetallic deposits in Gejiu mining area are deeply buried, most of which are more than 500m above the ground. Therefore, surface geophysical exploration must adopt technical methods with relatively deep detection depth, such as transient electromagnetic method (TEM) and electromagnetic sounding method (EH-4).

2) The surface lithology of Gejiu mining area is mostly carbonate rocks with high resistivity, which is obviously different from tin polymetallic ore bodies (mineralized bodies) and mineralized granite. The depth of electrical exploration is obviously increased compared with other areas, and it is more favorable to use electromagnetic method for deep exploration.

3) According to the verification results, the application of transient electromagnetic method and other methods in deep prospecting in Gejiu mining area is successful and the prospecting effect is remarkable. Geophysical prospecting methods have played an important role in deep prospecting in Gejiu mining area.

Reference: Yunnan Tin Industry Group (Holding) Co., Ltd. in 2009. Study on deep and peripheral geological prospecting of Gejiu tin deposit in Yunnan Province

(Contributed by Feng Kaiping, Xindu, Chen Mingwei)

Fig. 6-2-5 Comprehensive Geological (TEM) Profile of Gaosong Mining Area 16 and 17 Lines.

Figure 6-2-6 TEM anomaly distribution map of ore field period in Beishan survey area of Gejiu Laochang

Figure 6-2-7 See Figure 6-2- 1 for symbols of abnormal diagram of transient electromagnetic measurement in Gejiu Dabaiyan copper-tin mine.