Application of aerial remote sensing technology in geological prospecting in western Junggar

Yang Qinghua Guo Hongzhou Zhang Yong Zhang Xueqin Zhao Fuyue

(Aerogeophysical Remote Sensing Center, Beijing 100083)

Aerial color infrared remote sensing images are widely used in agriculture, forestry, water conservancy, geoscience, environment and other departments because of their rich information and bright colors, and have important practical value in geological prospecting, environmental management, land and resources investigation and so on. This study takes this as the main source of information.

The study area is located in the northwest of Xinjiang, bordering Kazakhstan, with a geographical location of 83636 ′ ~ 87 25 ′ east longitude and 46 07 ′ ~ 47 04 ′ north latitude. The large terrain difference, sparse population and inconvenient transportation in this area bring difficulties to the development of conventional geological work. Remote sensing technology can play an important role in the rapid exploration and evaluation of minerals in this area.

In order to obtain high-quality aerial remote sensing data, we carried out 1:60000 color infrared aerial photography in this area, and the obtained aerial remote sensing data can meet the needs of geological prospecting.

I. Characteristics of Regional Geological Remote Sensing

(1) stratum

The exposed strata in this area are mainly Ordovician, Silurian tuffaceous sandstone, siltstone, limestone and shale in Lower Paleozoic. Basic volcanic sedimentary rocks, tuffaceous sandstone, fine sandstone and limestone in Devonian, Carboniferous and Permian of Upper Paleozoic; Mesozoic Triassic, Jurassic and Cretaceous continental clastic rocks; Cenozoic tertiary conglomerate, sandstone, siltstone and shale, quaternary clayey silty sand and gravel layer.

(2) Intrusive rocks

The intrusive rocks in this area are mainly Caledonian ultrabasic rocks and basic intrusive rocks. The ultrabasic rock belt is mainly distributed in the southern margin of Hobuxel Valley, with a length of 120km, and the surface is an altered ophiolite suite. The basic rocks are mainly distributed in the fault zone in the Hoboksar-Bahqila region, and the surface is altered diabase. There were two magmatic intrusions in the middle of Variscan, the first one was mainly gabbro, diabase and diorite, and the second one was mainly diorite and granite. The intrusive rocks in this period are mainly distributed in the southern foot of Sawur Mountain, Xiemistai Mountain and Urkash Mountain. The late Variscan intrusive bodies are granite and granite porphyry, which are distributed in the exposed zone of magmatic rocks in the middle Variscan.

(3) Structure

The structures in this area mainly include fold structure, fault structure and ring structure.

1. Fold structure

Fold structures are developed in this area, among which the major ones are Sawuer Mountain syncline, Tuohujiliao Mountain Pass anticline, Talbahatai syncline and Barluk-Shemistai anticline.

2. Fault structure

The fault structure in this area is very developed. According to the scale and nature of fault structures and their relationship with gold and copper deposits, it is considered that the main faults in this area are Laofengkou-Hefeng Forest Farm Fault (F 1), Talbahatai-Hongguleleng Fault (F2), the southern foot of Talbahatai Mountain Fault (F3) and Bussel-Bahelala Fault (F4).

Figure 1 Schematic Diagram of Regional Structure in West Junggar Region

F 1- Laofengkou-Hefeng Forest Farm Fault; F2- Talbahatai-Hongguleleng fault; F3 —— the great fault at the southern foot of Talbahatai Mountain; F4- and Bussel-Bahekela faults; F5- Bayinbuluke Bath Fault; F6- Dalbet fault

3. Ring structure

A total of 22 ring structures were interpreted from remote sensing images, which can be divided into three types according to their genesis: concealed rock mass (5), volcanic mechanism (2) and structural ring (20). Most of these annular images are closely related to geochemical anomalies and the spatial distribution characteristics of mineralization points.

The second is the analysis of remote sensing image characteristics of typical ore deposits.

The typical metal minerals in the study area are mainly gold and copper. Known remote sensing characteristics of Zhahe Hallgeir Tu gold mine and Suri Delgantek copper mine are described as follows.

(1) Zhahe gold-soil mine in Hargil

The gold mine is located in the north of Hefeng Forest Farm in Hebukesaier Mongolian Autonomous County, that is, at the southern foot of Sawuer Mountain. The strata distributed in the mining area are mainly Heishantou Formation of Lower Carboniferous (C 1h), and the lithology is coarse tuffaceous sandstone, carbonaceous siltstone, silty mudstone, gravelly Shi Ying sandstone and limestone lens. The intrusive rocks in the mining area are mainly rocky diorite, which is grayish white in aerial color infrared remote sensing image and distributed in east-west direction, with a length of 1.5km and a width of 400 ~ 600 m. According to the image analysis, it is considered that diorite body has three intrusive lithofacies. Through field investigation, it is found that the main body is medium-coarse diorite, and the latter two are medium-fine diorite.

It is known that gold ore bodies occur in diorite passing through the NNW fault zone. The fracture zone in diorite profile is 1000m in length and 800m m in width. The rocks in the zone are obviously sericitized, epidote, chloritization, pyritized and limonite, and the honeycomb limonite iron cap can be seen, and the remote sensing image is pale yellow. There are sericitization, silicification, carbonation and iron oxide staining in tuffaceous sandstone on the south side of the fault zone.

Gold ore bodies exist in the distribution area of diorite bodies passing through the fault zone in the form of gold-bearing diorite porphyrite veins. Two gold-bearing veins are delineated in the fault zone, with a length of 350~450m and a width of 1 1 ~ 14m. The cut-off grade of gold is greater than 1.28g/t, and the highest grade is 5.

At present, gold deposits are found in the southern foot of Sawuer Mountain, and gold mineralization points are mainly distributed in Xiemistai Mountain and Wuer Cacheur Mountain.

(2) Suridelgantke copper mine

The copper mine is located in the western corner of Shaerbuti Mountain in Hebukesaier Mongolian Autonomous County, structurally in the mechanism of volcanic fragmentation, and the exposed rocks are mainly tuff and andesite, followed by breccia tuff, breccia and agglomerate. On the aerial color infrared remote sensing image, there are two groups of annular images along the east-west direction, and each group of annular images has multiple annular structures nested together. These phenomena reflect that the volcanic mechanism has two eruption centers and multiple eruption cycles.

The linear images on the north and south sides of the above two groups of ring images have clear characteristics, and there are white linear images at the intersection of lines and rings. Through field investigation, it is found that these white linear bodies are the reflection of copper-bearing time pulses in the fracture zone. The andesite and tuff thin slices in the fracture zone have strong physical and chemical properties, mainly manifested as disseminated ignimbrite and andesite. In the fracture zone, the phenomenon of disseminated copper mineralization is more obvious, and the copper-bearing time pulse can be seen Mineralization is closely related to andesite porphyrite and diorite porphyrite, and its surrounding rocks are often accompanied by peridotite and carbonization.

There are seven copper ore bodies on the surface of the mining area. The ore body is 70 ~ 350m long and 2 ~ 5m wide. The main ore mineral is malachite (mass fraction is more than 90%), followed by azurite and chalcocite, and the mass fraction of copper is 0.04% ~ 0.48%. Known copper mines are mainly distributed in the southern foothills of Sawur Mountain and the area around Xiemistai Mountain.

3. Research on prospecting method of aerial color infrared remote sensing technology.

In the study, using the rich information of aerial color infrared remote sensing images, several different remote sensing prospecting methods, mainly gold and copper, have been established, which have achieved good results in narrowing the prospecting scope and delineating favorable prospecting areas.

(A) fault structure analysis method

Fault structure analysis is an indirect prospecting method. Based on the analysis of ore-controlling structure, ore-guiding structure and ore-storing structure in the area, the ore-controlling and ore-forming fault structures are interpreted by using remote sensing images, and it is considered that the ore-forming conditions at the intersection of structures and its vicinity are superior.

(2) Analysis method of rock mass ore control.

Rock mass ore-controlling analysis method is also an indirect prospecting method. Using remote sensing images, the boundary and distribution range of rock mass can be effectively delineated. Through the further analysis of the main ore-controlling and ore-bearing rocks in the area, the rock mass related to mineralization and its alteration zone can be found.

(3) analogy method

Analogy is a common remote sensing prospecting method. Through the remote sensing interpretation and analysis of known ore deposits and mineralization points, the abnormal information related to mineralization is extracted as prospecting indicators, and compared with surrounding areas to find new mineralization targets.

(4) Remote sensing and multivariate prospecting and sorting methods.

This method firstly takes the extracted effective ore-controlling and metallogenic factors as variables, and then carries out assignment and weighted analysis according to the role of these variables in mineralization in different regions to determine the method of prospecting favorable areas. This is a semi-quantitative method. The main variables are anomalies in remote sensing images of mineralization alteration, geochemical anomalies (including anomaly scale, anomaly concentration zoning, anomaly coincidence degree and element anomaly combination), geophysical anomalies, ore-controlling strata, intrusive rocks, ore deposits and mineralization characteristics, linear and annular structures.

(5) Remote sensing prospecting model method.

Remote sensing prospecting model method is a comprehensive prospecting method. By analyzing the metallogenic regularity and image characteristics of known deposits and mineralization points in the area, a remote sensing prospecting model is established to predict favorable metallogenic belts.

Fourthly, remote sensing prospecting information extraction.

The geological background of the study area is very favorable for the formation of gold and copper deposits. In order to scientifically define favorable prospecting areas, the image characteristics of strata, rock mass, structure and mineralization alteration related to mineralization in the study area on remote sensing images are analyzed and studied, so as to extract the above information directly from remote sensing images.

(A) strata ore-controlling information

The strata related to gold and copper deposits and mineralization points in the study area are mainly Silurian, Devonian and Carboniferous. Gold deposits are mainly concentrated in Sawuer Mountain Formation of Middle Devonian and Heishantou Formation of Lower Carboniferous, which are light red in remote sensing images due to strong silicification. In the above-mentioned strata fault zone development area, due to strong jarosite and limonite, it is yellow-brown or brown in remote sensing image; Copper deposits are mainly distributed in SILURIAN intermediate-basic volcanic rocks or volcanic institutions, which are closely related to quartz porphyry and albite porphyry in volcanic institutions, and the remote sensing images are light gray or light yellow.

(2) Ore-controlling information of intrusive rocks

Intrusive rocks are well developed in the study area, and their exposed area accounts for about 30% of the total area. Mainly neutral, acidic and alkaline intrusive rocks. There are few basic and ultrabasic rocks, which are mainly distributed regularly along the large fault zone.

The extensive development of intrusive rocks provides favorable conditions for the formation of endogenetic metal minerals such as gold and copper. Gold deposits in the study area are closely related to basic intrusive rocks, while copper deposits are related to ultrabasic rocks. This shows that the gold and copper deposits in the study area are intrinsically related to magma intrusion in the deep crust.

(III) Structural ore-controlling information

The crustal movement in the study area is strong and the fault structure is developed. There are many groups of fault structures in remote sensing images, which shows that regional fault structures are extremely obvious and generally have multi-stage activity, and control strata, intrusive rocks, volcanic eruptions and mineral distribution. Minerals are generally accompanied by secondary faults parallel to regional large faults or intersecting with their micro-angles. The gold deposit on the south side of Sawuer Mountain and the Sha 'erburtishan copper deposit are located on the NW-trending Hongguleleng large fault line, and the ore-controlling fault is a secondary fault in NWW direction, which is associated with the large fault. The Dalbet giant fault is distributed in the northeast, and the chrome ore and many gold mines on the north side of it are located in the secondary fault zone parallel to it. It can be seen that the ore-guiding structure in the area is a big fault (NWW or NE), while the ore-hosting structure is a secondary fault (nearly EW) derived from the big fault.

The ring structure in the study area is also closely related to mineralization. For example, Zhahehaer gold mine and Songshugou gold mine are located at the intersection of ring structure and NW-trending fault structure in concealed rock mass.

(4) remote sensing image information of mineralization and alteration

The mineralization and alteration of rocks in Xiemitaishan and Heishantou areas in the study area have obvious image characteristics in remote sensing images, in which silicification is mostly white and gray; The mineralization of limonite is brownish yellow and brownish red, and it is regularly distributed in dense veins. The jarosite is mostly distributed in yellowish flakes. Mineralization and alteration information is directly extracted from remote sensing images, which provides important information and clear targets for prospecting.

Five, remote sensing prospecting favorable area prediction

On the basis of extracting remote sensing prospecting information and combining with geochemical data, the above information is further analyzed and studied. According to the comprehensive evaluation of geochemical anomaly area, concentration, concentration zoning, element combination and conformity, the following three favorable prospecting areas are finally determined through field verification and sampling analysis.

(1) Hefeng Forest Farm-Heishantou Gold Mine Prospecting Favorable Area

This section is located in the Sawuer Mountain in the north of the study area, with an east-west zonal distribution and an area of 9735km2. Geologically, it is located in the back arc area of early Paleozoic island arc and the island arc area of late Paleozoic. According to the theoretical analysis of plate tectonics, it is considered that this area is the most promising area for gold and copper deposits.

The exposed strata in this area are mainly marine pyroclastic rocks of Devonian Sawuer Mountain Formation and Carboniferous Heishantou Formation. According to geochemical data, gold mainly occurs in Heishantou Formation, followed by Sawuer Mountain Formation. The intrusive rocks include the first intrusive ultrabasic rocks and hornblende gabbro, the second intrusive adamellite and granite, and the third intrusive granite and potash granite.

Through remote sensing interpretation, it is found that linear and annular structures are developed in the area, and the Hongguleleng regional large fault is exposed in the south of this section. The fault gradually changes from west to east and from northwest to northeast, showing an arc protruding to the south. The regional mylonite belt has obvious characteristics, and its associated secondary fault structures are extremely developed. The northeast regional fault of Laofengkou-Hefeng Forest Farm is exposed in the middle of this section, and the secondary faults parallel to it in the west are well developed. There are four ring structures. According to the analysis of geophysical data, it is considered that there are concealed intermediate-basic intrusive rocks.

Through field investigation, it is confirmed that the four gold deposits being mined are all located in the fracture zone, and the ore-bearing strata are Heishantou Formation of Lower Carboniferous. At the same time, a gold-bearing fractured alteration zone, with a length of 150m and a width of 20m, was newly discovered on the regional fault in Hongguleleng, which was distributed along the direction of NWW(285), with obvious alteration phenomena such as jarosite, sericitization, pyritization, silicification and carbonation.

The strata in this prediction area have good ore-bearing property and frequent magmatic intrusion activities, especially the basic intrusive rocks are developed, the ore-controlling structural conditions are superior, there are known gold mineralization points, and the geochemical exploration of gold elements is abnormal, which indicates that this prediction area is the most favorable gold prospecting area.

(2) emin county Youshalasu gold and copper prospecting area.

The favorable prospecting area is located in the west of Urkash Mountain, belonging to the Xiemistai gold, copper and silver polymetallic metallogenic belt. Structurally, it is located in the late Paleozoic magmatic island arc zone, where intrusive rocks and volcanic rocks are developed. The exposed strata are mainly marine pyroclastic rocks of Silurian, Devonian and Carboniferous. The intrusive rocks are mainly rock-like gabbro in middle Caledonian, rock-like diorite in middle Variscan and granite, adamellite and granite porphyry in late Variscan.

The interpretation of remote sensing images shows that the structure in this area is complex and the linear and annular structures are well developed. There is a large-scale regional fault in Bayinbulukbas in the south of this section, and the secondary faults near the east-west direction develop and control the extension direction of intrusive rock branches. Moreover, the buke sair-Bahe quela regional large fault is exposed in the east of this section, showing the characteristics of repeated activities, and the secondary faults parallel to it develop in the northeast. The intrusive rocks at the intersection of the above two regional large faults are extremely developed, and the characteristics of alteration zone and four-ring structure are obvious in remote sensing images.

The geochemical anomalies of gold and copper elements in this area are concentrated, and the anomalies are mainly distributed along large faults, with favorable metallogenic conditions and good prospecting prospects.

During the field investigation and verification in Jeler Yemen, many nearly east-west fault mineralization alteration zones were found, among which silicification, chloritization, epidotization and limonitization alteration were stronger. Two gold-bearing quartz veins, 20m long and 0.2 ~ 0.5m wide, with gold grade of 0.3 ~ 5.73g/t and copper grade of 1.09% ~ 4. 15%, were also found in the fractured alteration zone. This section can be used as a prospecting target area for further work.

(3) The Xiemistaishan-Heshituogai gold deposit is favorable for prospecting.

The favorable prospecting area is located in the central and eastern part of Xiemitai Mountain, with an east-west zonal distribution, covering an area of about 8586km2. Structurally, it belongs to the late Paleozoic magmatic island arc belt, and intermediate-acid volcanic rocks and intrusive rocks are well developed. The intrusive rocks mainly include middle Caledonian ultrabasic rocks, middle Variscan olivine gabbro and diorite, late Variscan granite, granite porphyry and syenite. The exposed strata are mainly middle Devonian Sawuer Mountain Formation, middle Devonian Tarbahatai Formation, Lower Carboniferous Bukehe Formation and Lower Permian Kalagang Formation. The geochemical anomalies of gold elements in this area are distributed in sheets, and the abnormal concentration is obviously banded.

Through remote sensing interpretation, it is found that the fault structure in this area is very developed and the image information is obvious. Among them, the eastern section of Bayinbuluke-Mongbulak fault is exposed in the eastern part of this area, which obviously controls the shape and distribution direction of intrusive rock mass. Moreover, the secondary fault structures in the east-west, northeast and northwest directions are also relatively developed, and the diamond-shaped characteristics are obvious in remote sensing images.

A mineralized fault alteration zone with a length of 70 meters, a width of 50 meters and a strike of NE (60) was found during field verification in the western part of the favorable exploration area. The main alterations are silicification, pyritization, jarosite, chloritization and epidotization. The geochemical anomaly area of gold element in this area is large, which is in good agreement with the abnormal shape of copper element. There are white veins distributed intermittently in remote sensing images.

In the field verification of Salekentanwu III in the eastern part of the favorable prospecting area, it is found that the rock fracture in the outer contact zone between the late Variscan granite and the middle Devonian Sawushan Formation is obviously mineralized, which is 200 meters long and 50 meters wide, and the main alteration is limonitization, silicification and malachite fossilization. There are pyritization and keratinization alteration zones with a length of 10m and a width of 2m near the rock mass, in which pyrite particles are 0.5mm and distributed in veinlets. The results of chemical analysis show that the mass fraction of gold in the fracture zone is 220× 10-9.

Conclusion and suggestion of intransitive verbs

The application of aerial color infrared remote sensing technology in geological prospecting in western Junggar has achieved the following main understandings.

1. On the basis of previous research results, by analyzing the characteristics of remote sensing images of known ore deposits or mineralization points in the area, and using the comprehensive analysis method of geological, geophysical and geochemical exploration and remote sensing multi-source information, a variety of prospecting information, mainly gold and copper, is put forward.

(1) The volcanic rocks of Middle Devonian and Lower Carboniferous are gold-bearing strata, while copper deposits are mostly found in Silurian basic pyroclastic rocks.

(2) Gold deposits are closely related to intermediate-basic intrusive rocks, while copper deposits are mostly related to ultrabasic rocks.

(3) The regional large fault is the main ore-guiding structure in the area, and the intersection of secondary fault structures derived from it contains many gold, copper and polymetallic ores. Ring structure is also one of the important signs for searching for gold and copper deposits.

(4) The elements such as gold, silver, arsenic, copper, lead and zinc in the geochemical field are unusually large in scale, high in strength, good in element combination and obvious in concentration zoning, which can be used as a direct indicator for searching for gold, copper and polymetallic deposits.

(5) In the gradient zone of geophysical gravity anomaly, the areas where the magnetic anomaly changes sharply are often accompanied by gold and copper deposits.

2. Based on the interpretation of aerial remote sensing images, a remote sensing image model of mineralization and alteration is established, in which the time pulse of gold-copper mineralization is mainly white and grayish white; Limonite and jarosite are brownish red and brownish red. Using the above-mentioned image marks, two gold-bearing and copper-bearing time pulses and a minute time pulse group with a length of1000m and a width of 2m were found in the northeast fracture zone of Jiele Yemen, in which the highest grade of gold is 5.7g/t and the mass fraction of copper is 4. 15%. Another pulse group with a length of 2000m and a width of 10 ~ 15 m has a maximum gold grade of 0.98 g/t and a copper mass fraction of 1.09%.

3. Using remote sensing images to explore the regional geological structure, divide the spatial distribution range of island arc area, front arc area and back arc area, and analyze the corresponding sedimentary formation, structural evolution law and metallogenic characteristics.

4. Using remote sensing image analysis to study the metallogenic regularity in western Junggar area, and some breakthroughs have been made. It is considered that the study area has mineralization in both the evolution stage of the active continental margin and the volcanism stage. The island arc zone is dominated by gold and copper deposits, and the back arc zone is dominated by copper, lead and zinc polymetallic deposits. Using the above laws, a large-scale gold-copper mineralization body was discovered for the first time.

5. In view of the low level of work in the study area, the advantages of aerial color infrared remote sensing technology are emphatically applied in the prospecting method, and obvious prospecting results have been achieved.

refer to

1. Xinjiang Bureau of Geology and Mineral Resources. Geological map of Xinjiang Uygur Autonomous Region1∶ 20,000 and its description. 1993

2. Xinjiang Bureau of Geology and Mineral Resources. Geological and mineral map and explanation of1∶ 200,000 in western Junggar area. 196 1

Application of aerial remote sensing technology in mineral exploration in western Junggar, Xinjiang

Yang Qinghua, Guo Hongzhou, Zhang Yong, Zhang Xueqin, Zhao Fuyue

(Aerogeophysical Remote Sensing Center, Beijing 100083)

abstract

Using aerial color infrared images, Landsat TM data and geophysical and geochemical data in western Junggar, Xinjiang, the remote sensing prospecting is studied. Firstly, by analyzing the characteristics of remote sensing images of some famous mineral deposits, the remote sensing information of strata, structures, rocks and mineral alteration related to copper and gold deposits is extracted. Secondly, based on the study of metallogenic regularity, some geological, remote sensing, geophysical and geochemical factors that directly or indirectly indicate the existence of the deposit are selected. Thirdly, the mineral anomalies in this area are classified and screened by using these screened factors. Finally, some far-sighted areas and target areas are delineated. The sample analysis in one area shows that the gold grade is as high as 5.73g/ton, and the copper content is about 4.65438 0.5%. The research shows that aerial remote sensing technology is very effective in searching for gold and copper deposits in this area.