2014 Vol. 20, No. 2

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PAN-AFRICAN CENTRAL AFRICAN FOLD BELT, WITH EMPHASIS ON BEDROCKS AND HEAVY MINERAL ANALYSIS OF RIVER ALLUVIUM IN THE NORTHERN CAMEROON
YE Hao, , ZHAO Yue, LIU Jian
2014, 20(2): 103-113.
Abstract (365) HTML (386) PDF (10400KB)(22)
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The assembly of Gondwanaland and Pan-African orogeny were briefly presented. Then, the lithological units and their tectonic settings in the northern Cameroon and southwestern Chad were dissected based on previous research. On this basis, heavy mineral analysis was carried out for river alluvium collected from northern Cameroon. The analysis results (species and contents of heavy mineral) were consistent with the basement rocks of the Mayo Kebbi magmatic arc belt and the Rey Bouba greenstone belt from Western Cameroon Domain (WCD). Gold in the alluvium may come from Rey Bouba greenstone belt, and the analysis results may give a prospect for alluvial gold exploit in northern Cameroon.
RESEARCH ON CLASSIFICATION OF WATER-SOLUBLE GAS IN WEIHE BASIN
ZHANG Xue, LIU Jian-chao, LI Rong-xi, WANG Xing-yun, WENG Kai
2014, 20(2): 114-122.
Abstract (163) HTML (105) PDF (1308KB)(15)
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The reserve of water-soluble gas is rich but the composition and origin is complex in Weihe basin. In order to guide the comprehensive utilization and development in the further, it is necessary for researching the characteristics of water-soluble gas in this area and presenting an appropriate classification scheme for late development. The samples of water-soluble gas are from geothermal wells which in different tectonic units and different completion depths. This research collects the gas through the drainage method and sends the samples to analyze the composition and origin. The methane and helium of water-soluble gas have the most industrial value in the Weihe basin, whose content are maximally about 98.370% and 4.140%. Isotope analysis of carbon indicates that the geneses of the methane are various including inorganic and organic gas from biogas to pyrolysis gas. Isotope analysis of the helium gas from the water-soluble gas shows that it is mainly crust-derived helium. Through summarizing the classification of water-soluble gas and combined with the characteristics of composition, origin and distribution, analogy and contrast, the research shows that the helium gas accumulation layer is located under Zhang Jiapo Formation and suggests that improve former classification scheme and replace formation (Zhang Jiapo Formation) with depth. Finally, the water-soluble gas in the Weihe basin can be divided into two type, they are shallow combustible gas and deep rich helium gas.
ROCK COLLAPSE MECHANISM ON HIGH-STEEP SLOPE FAILURE IN SUB-HORIZONTAL THICK-BEDDED MOUNTAINS
FENG Zhen, LI Bin, HE Kai
2014, 20(2): 123-131.
Abstract (213) HTML (93) PDF (3146KB)(22)
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Sub-horizontal thick bedding slope shows a gentle dip of approximately 0~10°and strata structure of hard on soft, or hard interbedded with soft. It forms a high and steep terrain and is prone to rock collapse. Reviewing a lot of references, failure process and initiation mechanism, as well as failure modes of high-steep slope in sub-horizontal thick bedding mountains are analyzed in terms of rock mass failure mechanism. Six geomechanic models are summarized such as slipe-tensile, creep-tensile, slipe-shear, shear-rupture, shear-slipe and split-bulk. Corresponding to the reconginition features of geological structure are also presented.
DEVELOPMENT CHARACTERISTICS AND PREVENTION SUGGESTIONS OF THE LEPA DEBRIS FLOW IN THE ANNING RIVER FAULT ZONE
ZHANG Rui-duan, GUO Chang-bao, ZHANG Yong-shuang, FU Xiao-xiao
2014, 20(2): 132-139.
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The paper gives careful calculations of the maximum debris flow in the Lepa gully in June 17th, 2011, the extraordinarily serious debris flow calamities in the last fifty years. By calculation, the mean velocity of the debris flow was 2.03 m/s with a peak discharge of 200.11 m3/s. The unstable slopes in the front edge of the upper Lepa gully's river bank together with those gravels overlapped on its riverbed proved to be the main solid substance source of the Lepa debris flow. The diameter of the clastics' particle in the upper branch was small, so they are prone to be swept away by floods in the gully rather than resulting in the formation of barrier lakes or extraordinarily serious debris flow calamities. Currently, Lepa gully still has possibility of debris flow's breakout, suggestions lie in planting trees in the upper and middle reaches of the gully, cleaning riverbed in the lower reaches, setting up monitoring and warning system, to prevent the debris flow.
COMPUTATION COMPARISON BETWEEN THE EARTHQUAKE FORCE OF SAFETY RELATED SLOPE AND THAT OF COMMON SLOPE
CHEN Li-wei
2014, 20(2): 140-148.
Abstract (224) HTML (116) PDF (912KB)(18)
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On the basis of theoretic model and deduced formulas, the earthquake forces difference between the safety related slope and that of common slope were compared, and some deficiencies of the specification on the earthquake force computation in the current standard for seismic design of nuclear power plant were stated briefly. Then some recommendations were presented, which could be reference for the revise of the standard.
ANALYSIS OF INFLUENCING FACTORS FOR GROUND STRESS IN CHANNEL SANDSTONE
ZU Ke-wei, ZENG Lian-bo, LIU Xi-zhong, ZHANG Jun-hui, ZHAO Xiang-yuan, LIU Guo-ping
2014, 20(2): 149-158.
Abstract (227) HTML (86) PDF (3152KB)(16)
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With the further geological exploration, it is showed that different values and directions of in-situ stress are appeared in the adjacent sedimentary facies by a mass of production test data. By changing different boundary conditions(including the elasticity modulus and Poisson's ratio of channel and surrounding rock, the inclined angle between channel direction and the orientation of the regional principal stress and boundary stress ratio), the influence factors of the geostress in the channel sandstone are analyzed in finite element method. It is showed that the stress values and directions of the channel sandstone change seriously under the influences of different boundary conditions, compared with the in-situ stress characteristics in the surrounding rocks and region. The influence factors on the present stress of the channel sandstone are mainly the elastic modular ratio of channel to the surrounding rocks, the inclined angle between channel direction and the orientation of the regional principal stress and boundary stress ratio. The result could provide references for artificial fracturing and well network deployment in different sedimentary microfacies.
AUTOMATIC FINITE STRAIN DETERMINATION OF QUARTZ SANDSTONE IN WEAK STRUCTURAL DEFORMATION REGION
CUI Min, CAI Jia
2014, 20(2): 159-164.
Abstract (176) HTML (88) PDF (2475KB)(10)
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Finite strain determination is an important research for deformation characteristics of rocks. In order to improve the precision and the velocity, and ameliorate the status which is laborious and time consuming methods availability for manual finite strain determination, we take automatic method of finite strain determination by MICASRG algorithm, which is short for Multiply Images Constrained Automated Seeded Region Growing, and set the quartz sandstone of Daqing Mountain as an example. Based on multiply images and information of color, the MICASRG can recognize the grain without the necessity for the special equipment. In addition, this method enhances the contrast gradient between the inner and the boundary of the grain by the Canny operator. The results of automatic identified and handcrafted have the great comparability on centroid, area, major axis, minor axis and finite strain determination, and reflect the feasibility of this method. We also give a satisfied explanation about the poor correlation on orientation of the major axis between auto-identified and handcrafted.
ON THE ENVIRONMENTAL CHANGES SINCE 15 ka BP IN THE ORDOS PLATEAU
JIANG Fu-chu, WANG Shu-bing, FU Jian-li, LI Chao-zhu, Cai Yao
2014, 20(2): 165-173.
Abstract (209) HTML (122) PDF (1005KB)(13)
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In this paper, the climatic and environmental evolution since past nearly 15 kaBP were revealed by the comprehensive analysis of grain size, magnetic susceptibility and chrominance from lacustrine deposits in the Shejialiang Lake Area, central Ordos Plateau. It's revealed that during 14.3~11.9 kaBP, at depth of 235~205 cm, depositional environment are dry and cold relatively. 11.9~4.0 kaBP, at depth of 205~85 cm, sediment proxies reflect that abundant rainfall, enlarging lake, and the lake has developed into a stable deep-water condition, wetter climate possibly due to increase monsoon activity. 4.0~0 kaBP, at depth of 85~0 cm, showed that the climatic characteristics were fluctuated by a large margin, that was period of alternate cool dry and warm wet, and the water level of Shejialiang Lake has been fluctuate. That frequency and intensity of sandstorms have strengthened, Including of 1.2~1.4 kaBP, at depth of 25~30 cm, It was one of the driest period, the strong dust storm are frequent, and that deposited coarse sandy layer.
THE FEATURES AND AGES OF LAKE BEACH ROCK AROUND SAYRAM LAKE IN WESTERN TIAN SHAN AND ITS SIGNIFICANCE ON LAKE LEVEL FLUCTUATION DURING THE LAST INTERGLACIAL EPOCH MIS3
CHEN Ming-yong, XU Sheng-li, WU Zhong-hai, LI Yue-hua, ZHAO Xi-tao, ZHANG Ke-qi, MA Zhi-bang, MA Dan, TIAN Ting-ting
2014, 20(2): 174-184.
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Lake beach rock is one of the products which can reflect the land and sea interactions, of great significance for studying the ancient lake level fluctuations, lakeshore zone evolution and paleoclimatic change. On the basis of Quaternary geological survey and 1 :50000 scale geological mapping for Sayram Lake Basin in western Tianshan, we found lake beach rocks on the different shore terraces, indicating lake level fluctuations. The levelling result showed that the concentration distribution of typical lake beach rock was mainly on the fluvial terraces above the lake level 7.1~9.4 m and 33.4~39.7 m. The Petrologic and mineralogical study further showed that the lake beach rocks were mainly composed of intraclast, algal briquette, terrigenous clastic, cement and filler content, etc., and the cement mainly for the sparry calcite with a small amount of aragonite, which proved that the Sayram Lake beach rocks were typical calcite cementation sand gravel chip rocks. According to the U series dating results of lake beach rock samples, the lake beach rocks on the fluvial terraces were formed from 24.8±1.5 ka to 27.6±1.5 ka and 55.4±3.8 ka, late of the late Pleistocene, roughly corresponding to the relatively warm climate stage of early and late in last glacial interglacial epoch MIS3 stage.The lake beach rocks and dating results indicated that the recent highest level of Sayram Lake appeared in the distance of about 55.4 ka, early in the last interglacial epoch. Due to the subsequent drying climate, the lake level was overall in the process of decline gradually. During the relatively warm moist period, the lake level underwent multiple relatively stable periods, and resulted in lake beach rock formed.
DEVELOPMENT SITUATION IN GEOMECHANICAL FIELD IN RECENT YEARS AND THE RELATED COUNTERMEASURE ANALYSIS
FENG Hui, ZHANG Xue-ke, SONG Li-cai, WU Zhong-hai
2014, 20(2): 185-198.
Abstract (264) HTML (202) PDF (2976KB)(13)
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Geomechanics theory is a systematic earth science theory system. For more than fifty years, both talent team and discipline of geomechanics have been growing and perfecting, great achievements famous at home and abroad have been made in each field, making great contribution to Chinese economic and social construction and development. For a comprehensive understanding of recent progresses and problems of geomechanics, after systematic collection and analysis of the talent team construction, structural establishment and disciplinary arrangement, research fund inputs, etc. since 2006, the authors figured out problems about talent team, disciplinary arrangement and development and fund inputs in geomechanics development, providing essential basic support for strategic study of geomechanics, supplying decision-making basis for medium and long-term development plan, and achieve the leapfrog development of geomechanics, and provide better service for national economic and social development.
ACHIEVEMENTS OF NATIONAL SURVEY OF MINERAL RESOURCES AND ITS APPLICATION
ZHANG Qi, WANG Gao-shang
2014, 20(2): 199-204.
Abstract (147) HTML (61) PDF (828KB)(4)
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The paper outlines the objectives and tasks of the reserves survey, and summarizes the main achievements obtained from projects. The application of the survey results to strengthen the mineral resources management, promote economic and social development, and ensure resource security and so on is stated briefly. The survey results not only contribute to helping us to know the status of mineral resources reserve and their utilization, but also make the application of the results to the actual management.

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