The Feature And Evolution Of Nappe Structure And Coal Prospect Area Predication Of Hunjiang Coalfield

Hunjiang Coalfield is located in the southern part of Jinlin Provence, which falls under the jurisdiction of Tonghua and Baishan cities, its range from Tiechang Zhen west Erdaojiang urban area of Baishan city via Baishan city, Zhazi, Wangou to Songshu Zhen the east of Baishan city. The overall length of Hunjiang Coalfield is 130km, 15km in width and has an area of about 1950km~2. In recent years, with the coal resource developing intensity increases, most of coal mines had to shut down because the coal resources are exhausted. The production coal mines include Zhazi, Babao and Songshu greatly restricted the economic growth of local areas for the continued coal resources becoming less and less. At the same time, the structure is very complex and the nappe structure develop in Hunjiang Coalfield, and the research on the structure coal-controlling theory, especial the nappe structure coal-controlling theory is relative laggard, which extremely add to the difficulties to the coal exploration and production.So,the research on the characteristic and evolution of the nappe structure and structure coal-controlling law, not only has active realistic significance ,but also has profound historic significance. It is very necessary to find the further exploration potential coal resource region and expand new coal areas.Based on the information collecting, the regional structures, the characteristic, formation and evolution of nappe structure, the structure characteristic and evolution history, the coal collecting law and structure coal-controlling styles have been studied in detail, The main results obtained are as follows:1. The study concludes that the NE orientation fault zones of Hunjiang to Wangou and the EW orientation fault zones of Xinhuan to Baitoushantianchi,are main regional structures to affect the formation and development of Hunjiang Coalfield, whose formation and evolution is essential for the structure formation and evolution of Hunjiang Coalfield. 2. The nappe structure geometric significance of Hunjiang Coalfield was studied in detail, the belts of nappe structure was divided, the style kinds of nappe structure was determined and the nappe structure combined type was divided into six patterns, complex duplex structure pattern, thrust-nappe structure pattern, face to face thrust structure pattern, top thrusting cut-off and duplex structure pattern, bedding slipping fold structure pattern and bedding cutting fold structure pattern.3. Through the study of kinematics characteristics of nappe structure, The exactly forming era of nappe structures was proposed for the first time, and the sliding structures forming time can be divided into two main periods (the early stage was at the end of Triassic, the late stage was at middle Jurassic); the thrust nappe structures forming time was at middle Jurassic. It is believed that the overall movement direction of thrust faults and nappes was from southeast to northwest and the sliding distance was at least 12km.The forming and developing of thrust nappe structures were controlled and affected by gravitational sliding structures.4. The mechanism of gravitational sliding structures of Hunjiang Coalfield was expatiated for the first time. It is believed that the Hunjiang to Wangou and Xinghua to Baitoushantianchi fault zones provided very good dynamics conditions for the nappe structures forming; The alternate mudstone, clay rock, shale and coal seam of hard and soft in the research area, were the best interfaces for nappe structures formation; and the abundant limestone aquifers developing in the late Paleozoic coal measures, provided material conditions for high pore fluid pressure, which is the precondition for gravitational nappe to slide.5. According to the different evolution characteristics, the nappe structure evolution history of Hunjiang Coalfield was divided four main periods. It is believed that the Indo-Chinese period is Paleozoic cover fold and the early gravitational nappe forming time; the early Yanshan period is the forming time of late gravitational nappe and nappe structure; the late Yanshan period is the time of gravitational sliding structure activation; the Himalayan period is the weathering time of gravitational sliding structure. The nappe structure model map of Hunjiang Coalfield was drawn.6. The structure characteristic of Hunjiang Coalfield was mainly discussed, and it was considered that the NE orientation fault zones of Hunjiang to Wangou and the EW orientation fault zones of Xinghua to Baitoushantianchi are the bases for structure area dividing from the east to the west and zone dividing from south to the north. The folds are mainly synclines, which have the characteristic of complex folds. In the west area, the synclines distribute in NE, which can be divided into two complex synclines, Tiechang to Badaojiang and Toudaogou to Laofangzi to Weitang. In the east area, the synclines distribute in EW, which include Shiren and Songshu synclines. The bigger numbers of structure are nappe structures, the smaller number of structure are NW and NE direction tensional fault's. The faults have the characteristic of more forms, more times and more direction.7.Through the analysis and study, the structure formation and evolution history was divided into coal measure basement forming stage before coal forming, synsedimentary structure stage during coal forming and structural movement stage after coal forming and the Hunjiang Coalfield mainly experienced Indo-Chinese period, the early Yanshan period, the late Yanshan period and Himalayan period structural movement.8. The coal-accumulation process of Hunjiang Coalfield was mainly controlled by regional structure before coal forming, synsedimentary structure during coal forming and structural movement after coal forming. Liaoning-Jilin rift systems and Hunjiang rift affected to the formation of coal-basin very much; the fault zones of Hunjiang to Wangou and Xinghua to Baitoushantianchi played an important role in sedimentary environment and structure evolution of Hunjiang Coalfield; after coal formation, the Dataishan fault (one branch fault of the Hunjiang to Wangou in the south) divided Hunjiang Coalfield into east and west parts, in which the belts structure is very clear. There have big differences on the control to coal measures, the west area, the coal measures controlled mainly by faults and the east area by folds.9. The thrust nappe structure and gravitational sliding structure are the main coal control structure patterns were proposed for the first time. The thrust nappe structure coal control patterns include complex duplex structure pattern, thrust-nappe structure pattern, face to face thrust structure pattern, top thrusting cut-off and duplex structure pattern, which controlled the coal seams mainly through thrust faults, not only brought the carboniferous and Permian systems to reverse ,but also made them repeat in the vertical direction. At the same time, by the combining control of thrust and sliding faults, at certain depth under the nappes existe coal-bearing formation, which is general law in Hunjiang Coalfield. The gravitational sliding coal control patterns include bedding slipping fold structure pattern and bedding cutting fold structure pattern. Through the gravitational sliding nappes bed cutting or bedding movement in hard or soft strata, under the sliding nappes existe coal-bearing formation.10.Based on the study results above, combining the coal resource prospecting and developing present situation, three forecasting areas with exploration potential were determined(forecasting area in north of Toudagou Mine, Qujiayingzi forecasting area and Shajingou forecasting area). The total forecasting area is 46.8km~2 and the amount resources is 1553.4 thousand ton.In a word, in this paper, the structure forming mechanism and evolution of Hunjiang Coalfield was fully discussed, the characteristics and forming mechanism of nappe structure and its evolution were studied in detail, and based on the nappe structure coal control theory, forecasted the exploration potential areas. The study of nappe structures and the determination of forecasting areas will play an instruction role in the coal resource prospecting and developing in Hunjiang Coalfield and have important practical use and application value.