(1) regional geological survey
The comprehensive geological survey in this area is mainly the geological survey of1∶ 250,000 blank area from 2000 to 2006. Since 2006, a small amount of1∶ 50,000 regional geological survey has been carried out in this area around important metallogenic belts and major geological problems, but it is still in its infancy. At present, the1∶ 50,000 regional geological survey and mineral prospect survey projects are mainly deployed in Geji-Gaize Cu-Fe-Cr-Au metallogenic prospect area in the western section of Bannu belt, and a few are deployed in Bango Cu-Pb-Zn-Cr planning area and Yanshiping-Amdo Fe-Cu planning area. In the middle and east of Bannu belt, there are few geological survey projects.
The most important of the above work is the regional geological survey of1∶ 250,000, which comprehensively and systematically investigates and studies the stratigraphic framework, magmatic activity, tectonic evolution and other aspects of the Bannu Belt and its adjacent areas. The petroleum geological survey of Qiangtang basin and the strategic selection of oil and gas resources in Qinghai-Tibet Plateau organized by the Ministry of Petroleum and China Geological Survey mainly study the petroleum geology, basin pattern and structural evolution of the central uplift zone in Qiangtang.
This project systematically collected1∶ 250,000 regional geological survey results, special research results, published papers and monographs, and at the same time tracked the progress and phased results of the project under study at any time. This book makes full use of the above information.
(2) Investigation of mineral resources
In 20001and 2002, the investigation and evaluation, geophysical exploration, geochemical exploration and remote sensing of mineral resources were carried out in Shuanghu-Naqu area in the east of this area, in the north of Gaize county in 2003, and in Shiquanhe, Ritu and Gaize areas in 2005, and a large number of new discoveries, achievements and new understandings were obtained. In addition, in the oil and gas geological work in Qiangtang, 199 1 By 2006, the Chengdu Institute of Geology and Mineral Resources had carried out the major basic project of "great basin Analysis in Western China"; From 200/KLOC-0 to 2004, the project "Potential Analysis of Oil and Gas Resources in Key Sedimentary Basins of Qinghai-Tibet Plateau" was launched. From May 2004 to April 2008, the special plan of "Investigation and Evaluation of National Oil and Gas Resources Strategic Constituency" was launched.
From 2007 to 2009, China Geological Survey carried out geological prospecting for porphyry copper and iron ore in Ritu-Gaize area in the western section of Bangonghu-Nujiang metallogenic belt, and made remarkable progress, and found large gold-rich porphyry copper deposits in Duo Long, Ye Fu and Caimafu magnetite. It is considered that Dobuza mining area is a super-large porphyry copper-gold mine. Great progress has also been made in the study of Zhongyan gold deposits in Bannu belt. However, compared with Gangdise metallogenic belt, the geological prospecting and scientific research level of Bannu metallogenic belt is still very low. In 20 10, China Geological Survey deployed five mineral prospect investigation projects and 1 comprehensive mineral research projects in the western section of Bannu Belt. On 20 1 1 year, China Geological Survey once again deployed the 1 1 mineral prospect survey project in this area. Mineral projects are mainly deployed in "Geji-Gaize Cu-Fe-Cr-Au Survey Planning Area", "Bango Cu-Pb-Zn-Cr Planning Area" and "Yanshiping-Amdo Fe-Cu Planning Area" in Bannu area, aiming at finding out the metallogenic geological background and conditions of these important metallogenic areas, finding out the prospecting clues and providing prospecting targets for the subsequent mineral survey.
(3) Regional geochemical exploration
The geochemical exploration of Bangonghu-Nujiang metallogenic belt is very weak. 1999 and 200 1,1∶ 200,000 and1∶ 500,000 regional geochemical exploration are arranged in the south of Karakorum in the northwest of this area, but this area is not involved. In 2002, a lot of geochemical exploration work was carried out around this area, and only 6 geochemical explorations were carried out around Shuanghu Lake in the east, and most areas were still blank. In 2006, China Geological Survey arranged 6 regional geochemical surveys1∶ 200,000 (covering an area of 43320km2) in the favorable metallogenic area (Qusong-Geji). Since 2006, the1∶ 50,000 mineral prospect survey project in the western part of this area has all involved1∶ 50,000 geochemical exploration, but it was too late to adopt this project. In 2009 and 20 10, China Geological Survey deployed1:200,000 regional geochemical exploration (2009 ~ 20 1 1) in Brou. 1:250,000 Songxi sheet, Tuzegang daily sheet, Ritu county sheet, Qiang multi-regional geochemical exploration (20 10 ~ 20 12),1:250,000 Bangguo multi-regional geochemical exploration (2010 ~)
(4) regional geophysics and geophysical exploration
Geophysical and geophysical exploration work in this area was mainly carried out after 1999. Before 1980,1∶ 500,000 aerial geophysical prospecting only involved Naqu and Nima areas, excluding Bannu area and Qiangtang area. 110,000 aeromagnetic surveys were conducted in western Tibet in 1999, covering the Bannu Belt and most areas of Qiangtang. In 2003, a 1∶ 1 10,000 gravity geological survey was carried out in Bannu belt and Qiangtang area, and the Ministry of Petroleum carried out a1∶ 200,000 gravity geological survey in Qiangtang central uplift belt. In 200 1 and 16, an aerial remote sensing geological survey was arranged in western Tibet, covering Shuanghu, gaize and shiquanhe areas. In addition, some special work has been done in geophysics, from Yadong-Golmud geoscience section of the Ministry of Geology and Mineral Resources 1986 to1990; 199 1 ~ 1992, the State Seismological Bureau organized Sino-US cooperation, and used 1 1 stations to form a seismic network to record natural earthquakes and study the crust and upper mantle. 1998 ~ 2000, in-depth cooperation between China and the United States-Qiangtang plot project, etc. These results provide deep data for the basement and basin edge of Qiangtang basin. Remote sensing data of gravity, aeromagnetism and ETM satellites in the study area 1 ∶ 1 10,000 are collected in this project. In this project, the gravity and aeromagnetic anomaly maps of the whole research area and ETM remote sensing anomaly maps of key areas in Japan and Tibet have been compiled. In 20 10, China Geological Survey conducted a comprehensive remote sensing survey of mineral resources in the central and western parts of Bangong Lake-Nujiang metallogenic belt in Tibet, and conducted a mineral survey in the western part of Bangong Lake-Nujiang metallogenic belt using high-resolution data. In 20 10, China Geological Survey deployed1:250,000 regional gravity surveys in Rebuka and Shenzha counties,1:250,000 regional gravity surveys in Tuotuo River, Hoh Xil Lake, Wulanlula Lake and Bukadaban Peak in Qinghai, and in Chibu Zhangcuo, Wenquan Military Station and Qinghai. In 20 1 1 year, China Geological Survey established regional gravity surveys in Dangxiong County, Menba District, Tibet1:250,000 and Bango County, Naqu County, Tibet1:250,000.
(5) Several important geological problems in Bangong Lake-Nujiang belt.
The structural properties of 1. Bannu belt
As a plate suture zone, Bangong Lake-Nujiang ophiolite melange zone separates Lhasa terrane in the south from Qiangtang terrane in the north, which has been recognized (Guo et al.,1991; Ren Jishun and Xiao Liwei, 2004). Some scholars believe that the Ban-Anger belt represents the Tethys Ocean from Paleozoic to Mesozoic, which separates the Eurasian plate from Gondwana plate (Hsü et al.,1995; Pan Guitang et al., 1997). Ophiolite did exist in the area of Dingqing and Bitu in the east of Bannu Belt from Paleozoic to Triassic, so this area was opened as an ocean basin in Carboniferous, which lasted until the early Triassic (Yin Guanghou, Hou, 1998) and began to subduct and close in the middle and late Triassic (,et al., 2002). However, some people think that the Paleo-Tethys ocean basin in eastern Tibet is connected with Changning-Menglian suture zone in western Yunnan to the south and Shuanghu-Longmucuo suture zone in the northwest, forming a multi-island ocean main basin opened by the Paleo-Tethys (Wu Genyao, 2006), while the Bannu belt is an ocean basin opened only in Mesozoic, and its age and attributes are similar to those of the Yarlung Zangbo River basin. In the area of Lanagou, Baila Township, Bange County, the upper Triassic Chahala Group is in angular unconformity contact with the underlying rock series, indicating that there may be Paleozoic ophiolite, and the Mesozoic ocean basin may be inherited and developed on the basis of the Paleozoic ocean basin (Chen et al., 2005).
Most scholars agree that Bannu Belt is only a branch of Mesozoic Tethys Ocean, and the northern boundary of Gondwana Plate is located in Shuanghu-Longmucuo suture zone (Cai Li et al.,1995; Bao Peisheng et al.,1999; Cai Li et al., 2006). According to the deep geophysical evidence, it is considered that the Bannu zone may not be a suture zone in a strict sense, but an ancient back-arc extension zone (Zhao et al., 2004). Based on the detailed study of the petrochemistry of Bangongcuo ophiolite, it is considered that there are two types of ophiolite, ocean ridge type and subduction type, which were formed in two tectonic environments (stages) above the mid-ocean ridge and late subduction zone, but they are only considered as the block boundaries (rocks, etc.) within Gondwana continent. , 2008). According to the occurrence and petrochemical comprehensive characteristics of porphyry, Bannu ophiolite is of type, not formed in marine environment (Qiu et al., 2004; Shi Rendeng et al., 2005; Sheng et al., 2004; Liu Wenbin et al., 2002; Qiu et al, 2007).
It can be seen that the tectonic attribute and age of Ban-Nuhai basin and its temporal-spatial relationship with Tethys evolution are still controversial. There is still a lack of in-depth study on its evolution process, magmatic rock response and its temporal and spatial relationship with mineralization.
2. The subduction polarity and its age of the Bannu belt ocean basin.
Ophiolite isotope chronology shows that the Bannu Tethys Ocean existed in Jurassic, but the closed age is still controversial. Shrimp u-Pb age of gabbro zircon in Bangongcuo ophiolite is (162.5 8.6) ~ (177.1.5438+0.4) Ma, and the weighted average age is (167.0/kloc-). The Sm-Nd isochron age of Shemalagou layered gabbro is (19 1 22) Ma, and the K-Ar age is (140 4.07) Ma and (152.3 3.6) Ma, so it is considered as ocean basin age. Zircon SHRIMPU—Pb dating of gabbro in Dongqiao ophiolite was carried out, and the age of (187.8 3.7) Ma was obtained (Xia Bin et al., 2008).
Ophiolite and Mugangangli Group in the western part of Bannu belt are unconformity, covered by Shamro Formation, and have continental sedimentary characteristics, indicating that the late Jurassic ocean basin closed and began to uplift (Cappato). , 2003; Chen Guorong et al., 2004). According to the geological survey in Naqujueweng area, it is considered that ophiolite existed in the early Cretaceous in Bannu belt and was unconformity covered by Jingzhushan Formation in the late Cretaceous, so the final closing age of Tethys Ocean in Bannu belt was the late Cretaceous (Chen et al., 2006). The age of Shrimpu-Pb is (132 3) ma, and the age of 40Ar/39Ar of the whole basalt is (137.4 2.7) ma and (140.9 2.8) ma (Bao Peisheng et al.). In addition, the discovery of the early Cretaceous oceanic island basalt in Tarenben indicates that the Bangong Lake-Nujiang Tethys Ocean did not completely disappear in the early Cretaceous (Wang Zhongheng et al., 2005; Zhu Dicheng et al., 2006). These evidences show that the western section of Bannu belt was still in the ocean basin environment in the early Cretaceous and closed in the late Cretaceous.
The subduction age and polarity of the Tethys Ocean in the Bancroft belt are also controversial. There are northward subduction (Qu Xiaoming et al., 2009) and southward subduction (Geng Quanru et al., 2005; 2006) and two-way diving in stages (Liao Liugen et al., 2005; Cao Shenghua et al., 2006). The subduction time is generally considered to have occurred from the Middle Jurassic to the Early Cretaceous. However, the formation of the Permian initial island arc in the Gangdise belt may also be related to the southward subduction of the Paleo-Tethys oceanic crust. , 2009).
3. Yanshanian magmatic arc and mineralization on the north side of Bangonghu-Nujiang suture zone
Jurassic and Cretaceous magmatic rocks in the northern margin of Bannu belt are considered as magmatic arcs, which is an important progress in the geological and mineral survey of Qinghai-Tibet Plateau. Duo Long porphyry copper deposit and Ye Fu-Caima large magnetite deposit discovered in recent years are the most remarkable achievements of geological and mineral investigation in this area, which may be the third porphyry copper belt in Qinghai-Tibet Plateau after Yulong and Gangdise (Qu Xiaoming et al., 200 1).
Jurassic granitoids are distributed in Japan, Qiangduo and Duo Long (regional data1∶ 250,000 Japanese soil sheet, Qiangduo sheet and Uma sheet). 40Ar—39Ar geochronology of volcanic rocks and biotite granite in the east of Labuke, 20 kilometers north of Zhengzhou, was studied. Their ages are (1 1 1 2) Ma and (145 1) Ma (Kapp et al. , 2000) mA. Gabbro walls with the age of 159Ma were found in northern Japan, which have the characteristics of magmatic arc composition (Qu Xiaoming et al., 2009). Zircon SHRIMP age of Gaerqiong copper-bearing porphyry in the east of Shiquanhe belt is 1 12.0Ma (Qu Xiaoming, Xin Hongbo, 2006). However, whether the granite in Shiquanhe area is related to the subduction of Bannu Belt needs further study.
Previous isotope tests have found that the age of magmatic rocks related to mineralization in Duo Long and Ritu areas is mainly early Cretaceous. The magmatic arc related to regional mineralization was formed in the early Cretaceous (Zhang, 2007, doctoral thesis of China Academy of Sciences; Li Jinxiang, 2008, doctoral thesis of China Academy of Sciences; She Hongquan et al., 2009). The ore-bearing porphyry of Duobuzha large porphyry copper deposit belongs to K-high K-calc-alkaline series (Qu Xiaoming, Xin Hongbo, 2006). Early Cretaceous intrusive rocks in Ritu area, Geze Duo Long area and volcanic rocks in Kana area may represent Yanshanian magmatic arc belt in the north of Ban-Nu belt, and the age of magmatic activity is supported by isotopic chronology (Jiangxi Geological Survey and Research Institute, 2004; Sichuan Geological Survey Institute, 2006; Xizang Autonomous Region Geological Survey Institute, 2006). The 40Ar—39Ar age of amphibole and whole rock about 5km north of the country is changed to11116ma (kappetal. , 2003). In the past, the geochronology test of Japanese soil-Ye Fu magmatic arc was still weak.
At present, the large-scale porphyry copper deposit related to Bannu belt is only confirmed in Dobuza in the west, and Garqiong porphyry copper deposit is located in Gangdise belt. Whether it is related to the magma arc in Bannu belt is still uncertain. However, the belt extends westward, forming famous porphyry copper deposits such as Shi Mei (Iranian) and Shengdake (Pakistani) in Salce (Rui Zongyao et al., 2004). Another type of deposit found in the western part of Bannu belt is skarn magnetite, which is distributed in Qiangduo and Ritu areas. The early Cretaceous isotopic age of rocks related to mineralization was preliminarily measured, but the Jurassic age of granitic rocks in this area was also obtained. Preliminary research shows that these deposits are related to the magmatic arc formed by the northward subduction of the Tethys oceanic crust in Bannu belt (Liao Liugen et al., 2005; Li Guangming et al., 2006; Bao Peisheng et al., 2007; Feng et al., 2007; Li Jinxiang et al., 2008). However, did the nature of magmatic arc represent continental margin arc or island arc in this period? The existence of continental crust or pre-arc accretionary wedge basement in magmatic arc, the temporal and spatial relationship of its mineralization, the structural attributes of the southern margin of the South Qiangtang plate at that time and the existence of back-arc basin have not been studied. It is necessary to study the stratigraphic correlation, magmatic petrology and structural evolution characteristics.
(6) Analysis of major geological and mineral problems.
Previous geological and mineral work has accumulated a lot of data, including basic geological, mineral and geophysical, geochemical and remote sensing data. Bannu belt and Shuanghu-Longmucuo ophiolite belt have been basically determined, and the main metallogenic types are porphyry copper ore, contact metasomatism-hydrothermal filling iron ore, ultramafic magmatic separation chromium ore and so on. However, some important basic geological problems have not been solved, such as the subduction polarity of Tethys in Bannu belt, the temporal and spatial distribution of magmatic arc (sedimentary basin), the basement of Qiangtang basin and the evolution of Tethys. It is also necessary to study the regional metallogenic background (the tectonic background of copper, gold and iron formation and its relationship with Yanshanian magmatism). Is mineralization related to the magmatic arc in Bannu belt? Time, period, distribution, etc. The main geological and mineral problems are as follows.
1. The spatial framework needs to be further clarified and improved in regional stratigraphic division and structure.
Regional geological survey has made important progress in stratigraphic division and correlation, spatial pattern of magmatic activity and so on. However, due to the lack of comprehensive correlation and division, stratigraphic division is very chaotic. ① Precambrian basement and its spatial distribution in Qiangtang area; ② Distribution of Lower Paleozoic in Qiangtang Basin and its representative sedimentary environment; ③ Whether there is Late Paleozoic granite in Qiangtang area and its tectonic significance, and the temporal and spatial distribution of granite activities in Qiangtang and Bannu belt; (4) As a structural mixed zone, the Bannu zone has a chaotic stratigraphic division, which needs further clarification and correlation; ⑤ On the basis of detailed comparison and division, the temporal and spatial structure of strata, magmatic activities and tectonic activities in this area should be determined.
2. Major basic geological problems have not been solved.
With the development of regional geological survey and related scientific research, the basic geological data of Bannu belt and Qiangtang basin are becoming more and more abundant, which needs regional summary and comparison, and some key problems have not been fundamentally solved.
(1) Longmuco-Shuanghu-Lancang ophiolite melange and the northern margin of Gondwana continent
The evolution of Tethys in the Qinghai-Tibet Plateau and the study of the boundary between Gondwana and Eurasia have been continuous research hotspots for decades. Whether the Longmucuo-Shuanghu-Lancang suture zone can be used as the boundary between the two continents is still controversial.
On the basis of a large number of regional geological survey data, China scholars put forward the models of "multi-island arc-basin system", "one Tethys ocean, two continental margins" and accretion orogeny (Pan Guitang et al., 20 10). Under the new theoretical model, how to understand the boundary between Gondwana and Pan-Cathaysia is a subject to be studied in the future.
(2) Qiangtang basin basement.
Whether there is Precambrian basement in Qiangtang basin is an important geological problem that has been debated for a long time. According to field observation and isotopic dating, it is considered that the basement of Qiangtang basin is Proterozoic metamorphic rock series, and even Archean continental core (Huang, 2001; Wang Guozhi and Wang Chengshan, 20065438+0; Lu Bing, 20065438+0; Yuan Shoucheng et al., 2007; Tan Wenfu et al., 2009). Another diametrically opposite view is that there is no reliable evidence of crystalline basement in Qiangtang basin, and the zircon age of basement obtained is clastic zircon age, which cannot represent the original rock and metamorphic age (Cai Li et al., 2000; 200 1; 2003)。
Through field and indoor research, felsic gneiss and sericite quartz schist containing kyanite and sillimanite have been discovered in Shuanghu-Longmucuo fault zone and parts of northern Qiangtang (Malgochaka, Okumai, Bensongcuo and Gacuo), representing a set of negative metamorphic rock assemblages (regional scale is 65,438+0 ∶ 250,000, A Mu Yan Gang Formation, Qidragon five Ruyan Formation and Gacuo Formation). Whether this set of schists and gneisses occasionally exposed represent the Precambrian crystalline basement of Qiangtang basin needs further study. Interestingly, similar gneiss and schist outcrops have not been found in the South Qiangtang Basin. Does it mean that the Paleozoic and Mesozoic sedimentary basins in South Qiangtang were built on different types of basement? It is necessary to study this problem deeply with the help of geological and geophysical data.
(3) The tectonic attributes of Qiangtang Basin in Paleozoic and Mesozoic.
Qiangtang basin is the largest marine basin on the plateau, with an area of over 654.38+800,000 km2. It has good conditions for source, reservoir and cap rocks and good oil and gas prospects. However, there are still great differences in understanding the nature, tectonic background and evolution process of the basin, which directly affects the guiding ideology of finding oil and gas resources. This problem involves the regional stratigraphic correlation between Paleozoic and Mesozoic in Qiangtang Basin. Does the Paleozoic Qiangtang basin represent the passive continental margin? Does South Qiangtang represent Mesozoic (Jurassic) pre-arc accretionary wedge? Solving the structural evolution and basin nature of Qiangtang basin is not only a major basic geological problem, but also of great significance to the study of mineral resources and oil and gas geology.
3. It is necessary to divide the metallogenic belt in detail and summarize the regional metallogenic background and laws.
Due to the lack of mineral geological investigation and special research on Bannu belt and its adjacent areas, the research on metallogenic geological background and metallogenic belt division in this belt is very weak. The investigation of regional harmonic minerals has found a large number of deposits, occurrences and metallogenic clues, which need to be comprehensively and deeply studied from the aspects of regional metallogenic background, metallogenic belt and metallogenic mechanism. At present, a good porphyry copper deposit has been found in Dobuza-Tiegelong in the western part of Bannu Belt. Gold deposits are widely distributed in the whole region; Important discoveries of chromium and precious metals have been made in Amdo-Naqu area in the middle part of Bannu belt, and the metallogenic prospect is good. There are still differences in the understanding of regional metallogenic characteristics and laws, and there is still a lack of in-depth discussion on regional metallogenic laws and their internal reasons.
4. The foundation of regional geophysical exploration, geochemical exploration and remote sensing geological survey is weak.
At present, there are only 1∶ 1 10,000-weight and aeromagnetic data in this area, but there are no medium and large-scale regional geophysical and geophysical survey data and1∶ 200,000 regional geochemical data, so the existing geochemical achievements have not been fully utilized. The comprehensive utilization and research of regional geophysical and geochemical remote sensing data is of great significance not only to the temporal and spatial division of regional structures, but also to the regional metallogenic regularity and mineral prediction.
In the past, important progress has been made in the geological and mineral work in Bannu Belt and Qiangtang Block, and important basic geological problems have also been discovered. Geological and mineral surveys in this area are still in progress. It is necessary to systematically summarize the actual data of strata, structure, magmatic chronology and geochemistry, and deepen the understanding of metallogenic geological background and prospecting direction.