Geoscience

Stable Isotopic Geochemistry of the Bainaimiao Copper Deposit in Inner Mongolia and Its Geological Significance

ZHAO Yun，WANG Jian-ping，YANG Zeng-hai，LIAO Dong-jiu，LIAN Chun-yu

2014, 28(6): 1103-1111.

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The Bainaimiao copper deposit in Inner Mongolia is located in the Ondor Sum Caledonian copper polymetallic zone of the Central Asian Orogenic Belt. Copper mineralization in Bainaimiao is comprised of the northern and southern zones. The host rock of the southern zone is greenschist of the Bainaimiao Formation, while orebodies in the northern zone mainly occur in the Caledonian granodiorite porphyry. The metallogenic processes can be divided into early, middle, and late stage, which is characterized by mineral assemblages of quartz-pyrite, quartz-chalcopyrite±molybdenite, and quartz±calcite±galena-sphalerite, respectively. The δ¹⁸O_H2Oand δD values of fluid inclusions in quartz range from -3.2 ‰ to 5.5 ‰ and from -94.2 ‰ to -69 ‰, respectively. The δD values are relatively constant, whereas the δ¹⁸O_H2O values decrease gradually from early to late stage. In addition, the δ¹³C_PDB and δ¹⁸O_SMOW values of hydrothermal carbonate minerals range from -5.4 ‰ to -2.4 ‰ and from -3.1 ‰ to 10.9 ‰, respectively. The δ¹³C_PDB values keep steady, and the δ¹⁸O_SMOW values reduce gradually during the mineralization processes. The δ³⁴S values of the sulfides range from -0.6 ‰ to -6 ‰ and are typical of mantle source. The C-H-O-S isotopic compositions of the southern and northern zones show that ore-forming fluids of different stage are mainly derived from magma system, and there are no obvious differences between these two zones. However, the fluids in the southern zone exhibit closer affinity to meteoric water and crustal substances. Combined with geological features of the deposit, it is concluded that the Bainaimiao deposit was produced by granodioritic magma that formed by anatexis under subduction environment, and the magma arose along fissures up to the shallow crust. These processes gave rise to the activation and enrichment of ore metals from source beds of the Bainaimiao strata, and the formation of the Bainaimiao porphyry copper deposit.

Geological Characteristics and Genesis of the Dongjun Pb-Zn-Ag Deposit in Inner Mongolia

LIANG Yu-wei，ZHANG Bin，TIAN Jing，LI Jin-wen，SHE Hong-quan，YANG Yun-cheng

2014, 28(6): 1112-1121.

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Based on the studies of the geological and geochemical characteristics, the genesis of the Dongjun lead-zinc-silver deposit in Inner Mongolia was discussed in this paper.Geochemical studies showed that the magmatic rocks belong to the calc-alkaline series, and their light rare earth and large ion lithophile elements are both relative enrichment.REE distribution modes are similar between ore and magmatic rocks, the content of K, Th, U and Rb elements showed obviously positive anomalies among the ore, altered rock, volcanic rocks and monzonite porphyry.On the contrary, the content of elements Ta and Nb showed negative anomalies.These indicated all kinds of rocks, have the same provenance in the deposit, were derived from the enriched mantle enriching large ion lithophile elements with a contamination of a little crustal material.Pb and S isotope studies of the metal sulfides showed the oreforming materials were derived from magma system.According to the studies of the geological and geochemical characteristics, the Dongjun Pb-Zn-Ag deposit was considered to be a hydrothermal vein type deposit related to volcanic-subvolcanic magmatism.The mineralization is closely related to Mesozoic volcanic magmatism.The NW and NE trending fractures are the ore-bearing and ore-controlling structures.

Geochemistry of Granitoid Rocks of Weilasituo Deposit, Inner Mongolia and Its Tectonic Significance

HUANG Ding-ling, ZHU Luo-ting, HOU Qing-ye, WANG Jin, LIU Jin-bao

2014, 28(6): 1122-1137.

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Weilasituo Cu polymetal deposit is located in the west of middle-southern metallogenic belts in Great Xing’an Mountains of Inner Mongolia. In order to constrain the forming tectonic setting of the deposit, this paper analyses the major and trace elements and Sr-Nd-Pb isotopic compositions of the granitoid rocks. The granitoid rocks are composed of granites, monzonitic granites and diorites, and these granitoid rocks are calc-alkali rocks. The granites and monzonitic granites are rich in SiO₂, and characterized by high REE, middle negative Eu, relatively lower partition of HREE, strongly enriched in LILE, and depleted in HFSE. The (⁸⁷Sr/⁸⁶Sr)t (0.705 93-0.710 75) and ε_Nd(t) (-4.45--0.63) values suggest that the rocks are highly fractionated I-type granites. The primary magma for granitic rocks could be mainly derived from partial melting of the deep crust, which may be related to Xilingele complex. The diorites are rich in Mg，Cr，Ni, slightly negative Eu, with geochemical features of analogous to sanukite. The results indicated that the magma was derived from enriched mantle metasomatized by slab-derived fluids or melts. By combining with comprehensively analyses of the tectonic settings, we suggest that the Weilasituo granitoid rocks were formed in a post-collisional tectonics

Geochemical Characteristics and Metallogenic Significance of Quart Porphyry in Liaotun Gold Deposit, Bama County, Guangxi

LI Yuan-qiang, PANG Bao-cheng, YANG Feng, ZHANG Dong-wei,ZENG Qing-feng

2014, 28(6): 1138-1150.

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The Liaotun gold deposit, located in northwestern Guangxi, is the only gold deposit spatially closely related to quartz porphyry. The metallogenic significance study for quartz porphyry will be helpful in the recognition of the genesis of Carlin type gold deposit in this district, and will provide more basis on further prospecting. Based on the geological characteristics of the deposit and geochemical characteristics of quartz porphyry, the paper regards that the quartz porphyry rocks belong to acid rocks and calc-alkaline series, which have a feature of rich K and full Al，and belong to the remelting magmatite. The ore-forming materials may mainly derive from clastic rocks of Middle Triassic series, but we can not exclude the probability that the ore-forming materials derive from quartz porphyry. The geological characteristics of the field and the analysis data of geochemical indicate that there are at least two stages of mineralization in the ore field, and that the mineralization occurs before or after the diagenesis of quartz porphyry. Fracture zone were formed by structural shearing. The later ore thermal fluid transport, unload, and mineralize along the fracture zone; the alteration and the metallization occurs in quartz porphyry around the fracture zone, forming the mineralized quartz porphyry. Both in our country and abroad, there is growing evidence that the formation of Carlin type gold deposits are associated with the activities of the magma. In this district, the mineralization is probably related to the invasion of quartz porphyry in Yan-shanian; and it provides the ore-forming material, fluid, or heat source. These questions need further study and discussion.

REE Geochemical Characteristics of Xiaoqinling Gold Deposits and Their Geological Significance

FENG Jian-zhi，ZHANG Deng-tang，ZHANG Wei-min，WANG Xing-cun，CUI Xie-xiang，LIU Zon

2014, 28(6): 1151-1160.

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The Xiaoqinling gold deposits are located in the Neoproterozoic Taihua Group, of which the secondary detachment faults are the major ore bearing structure. In order to figure out geochemical characteristics and genesis of ore deposit, we collected 100 samples from the Taihua Group , magmatic rocks and gold ores of main geological body in the study area, respectively. The main characteristics of rare earth elements are as following: the ΣREEs of Taihua Group are from 30.81×10^-6 to 188.66×10^-6, and the δEu values are from 0.62 to 1.24; ΣREEs of granite and dike rocks are from 58.22×10^-6 to 365.98×10^-6, and the δEu values are from 0.90 to 1.10;ΣREE of gold ores are mainly concentrated in 76.74×10^-6-358.22×10^-6,δEu values are mainly concentrated in 0.74-1.14. The results show that the ΣREE from the three kinds of geologic body are similar, and there is no Eu anomaly or there are only weakly positive and negative europium anomaly. The rare earth distribution of ores is similar to that of the Taihua Group, and is different from that of Wenyu granite. It proves that the ore-forming materials come from the Taihua Group instead of granite.

U-Pb Age of Yemaquan Deep Variscan Granodiorite in Qimantage Area, Eastern Kunlun and Its Significance

SONG Zhong-bao, ZHANG Yu-lian, JIA Qun-zi, CHEN Xiang-yang, JIANG Lei, LI D

2014, 28(6): 1161-1169.

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Yemaquan large-scale deposit, found in recent years in the Qimantage area, Eastern Kunlun, is related to intrusive rock and is skarn type iron copper polymetallic deposit. Using zircon LA-ICP-MS U-Pb method, the authors measured the Yemaquan granodiorite formation age for (392.4±2.2) Ma, which belongs to the Variscan Stage. Previous use of molybdenite Re-Os method obtained isochron age of skarn type copper-molybdenum polymetallic ores and skarn type molybdenum ores which are (225.0±4.0) Ma (n=7,MSWD=0.24) and (230.1±4.7) Ma (n=5, MSWD=0.12). In the stage of hydrothermal superimposition, in mineralization periods, early metallogenic hydrothermal is likely to be provided by Yemaquan granodiorite (392.4±2.2 Ma). Since there are much acidic rocks in this area, the intermediate-acid rock mass may be the main source for iron-copper polymetallic deposit; therefore, the intrusive body formation age, in the search for skarn type iron-copper polymetallic deposit, not only has important theoretical significance, but also has important practical significance.

U-Pb Dating and Hf Isotopic Composition of Detrital Zircons in the Sediments from the Lancang River and Its Geological Significance

CHEN Xue，CHEN Yue-long，BAO Chuang，LI Guang-qi ，YAN Jia-pan ，LI Da-peng

2014, 28(6): 1170-1182.

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In order to study the source of sediments from Lancang River and the crustal growth history of adjacent block，Lancang River’s detrital zircons were measured for U-Pb ages and Hf isotopic composition by LA-MC-ICP-MS. The detrital zircon U-Pb ages show 5 populations including＜177 Ma，201-418 Ma，428-544 Ma，581-1,189 Ma and 1,406-2,533 Ma.The peak ages are 260 Ma，788 Ma，1,827 Ma and 2,474Ma.The detrital zircon U-Pb age distribution of sediments from the Lancang River is consistent with those of the North Qiangtang Block，which indicates dominant contribution of material from the North Qiangtang Block to the Lancang River. The detrital zircon U-Pb ages and Hf isotopic composition of the Lancang River’s sediments may reflect the formation and evolution history of the North Qiangtang Block. The period from Neoarchean to Mesoproterozoic is the continuous stage of crustal growth from the depleted mantle in the North Qiangtang Block，which accounts for more than 78% of the whole crust; until 0.64 Ga，the crustal growth of North Qiangtang block have mainly completed.

Behavior of Major and Trace Elements in Soil and Its Insoluble Matter from Saline and Acid Solution Developed over Granodiorite in the Southwest of Beijing, China: A Case Study on Indicator Elements of Hydrothermal Mineralization

JIANG Yong, GONG Qing-jie, HAN Dong-yu, LIU Ning-qiang,DING Peng-bo, FAN Tian-qi

2014, 28(6): 1183-1193.

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Stream sediment is the main medium sampled in the Regional Geochemistry-National Reconnaissance (RGNR) project in China, and soil is the main source of stream sediments. Behaviors of major and trace elements during the weathering from soil to stream sediment have played an important role in delineating and interpreting the geochemical anomalies. The soil developed over granodiorite in the southwest of Beijing was selected and its insoluble matter from 0.5 mol/L NaCl solution and then from 0.1 mol/L HCl solution was removed sequentially to simulate the geochemical process from soil to stream sediment. According to the particle size of soil, seven size fractions were meshed from 5 mm to less than 0.154 mm for two soil samples, then its insoluble matter from each size fraction was extracted sequentially from saline to acid solution. The results indicate that the sample mass ratio of soil insoluble matter from saline and acid solution respectively to its soil are all less than 13% and their values of WIG (weathering index of granite) are decreasing clearly from soil to saline insoluble matter and then to acid insoluble matter. This shows WIG is a good geochemical index to describe the sample’s weathering degree during the process from soil to stream sediment (represented by the insoluble matter). Soil and its insoluble matter (or stream sediment) developed over granodiorite have more extensive degrees of weathering with finer particle size. Contents of most indicator elements of hydrothermal mineralization are also increasing with finer particle size. Samples with particle size of 80-100 mesh (or 0.2 mm to 0.154 mm) are suggested as the best medium sampled for the geochemical exploration in this region. With respect to the difference of element contents in samples with different particle size, contents of indicator elements of hydrothermal mineralization in each size fraction vary unclearly in soil and its insoluble matter. This provides an example to verify the feasibility of collecting different medium (soil or stream sediment) with same size fraction to recognize element anomalies in geochemical exploration.

A Study on Cr(Ⅵ) Migration and Locking in Biochar-amended Soil

JING Ming, LI Ye, CHEN Ying-yu, CHEN Jia-wei

2014, 28(6): 1194-1201.

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Biochar-amended soil is under investigation as an approach to carbon sequestration to produce and improve soil fertility and increase agricultural productivity and quality. Previous studies showed absorptive effects of biochar on heavy metals including Cu, Cd, etc. However, Cr(Ⅵ) has got few attention to study in biocharamended soil. Herein, soil column leaching experiments are designed for Cr(Ⅵ) migration behaviors in soils before and after adding biochar. In particular, simulated acid rain leaching is for understanding the locking effect of Cr(Ⅵ) in biochar/soil. The results showed that 1% of biochar added in soil can fix much more Cr(Ⅵ). Furthermore, small particles of biochar showed a stronger adsorption capacity and they could lock Cr(Ⅵ) as three times as large particles, while Cr(Ⅵ) was not easy to release again under acid rain leaching. It confirms that biochar effectively mitigate Cr(Ⅵ) migration in soils and it has locking effect on Cr(Ⅵ), which provides an important means and basis for development of farmland soils.

Age of Upper Jinghe River Terraces at the Eastern Piedmont of Liupanshan and Its Significance for Neotectonic Movement

ZHAO Qiu-chen,ZHANG Xu-jiao,HE Ze-xin,HE Xiang-li,WANG Jian-yong,FU Lian-zhen,JI

2014, 28(6): 1202-1212.

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Liupanshan is the key region to research the uplift and tectonic deformation of the northeastern Tibetan Plateau. Jinghe River terraces at the eastern piedmont are geomorphology carriers to record tectonic uplift process of Liupanshan since the Quaternary.The detailed study of profiles of the upper Jinghe River terraces shows that Jinghe River mainly developed 5 river terraces, i.e.T5-T1. Terraces of T5, T4 and T3 in Liu-shugou are accumulation terraces，and T2 and T1 are pedestal terraces; terraces in Gaojiashan are erosional terraces or pedestal terraces. Trough dating results of OSL and ESR and combined with loess-paleosol sequences the ages of 5 level terraces were defined as 541 ka B.P., 477 ka B.P., 279 ka B.P., 60 ka B.P. and 8 ka B.P.,respectively.The morphological types of terraces and the relationship between age of terraces and climate change indicate that the upper Jinghe River terraces are mainly driven by tectonic uplift while the effects of climate change are complementary. During 541 ka B.P.to 279 ka B.P., Liushugou region is accumulation area and the accumulation rate is 0.31m/ka, correspondingly, the incision rate of Jinghe River in Gaojiashan is averaged as 0.37 m/ka, which is located in tectonic uplift region, and the accumulation rate is almost equal to the incision rate, indicating the thick gravel layers in T5, T4 and T3 related to Liupanshan rapid uplift. In 279 ka B.P., Liushugou transforms to an erosion area under sustained uplift in Liupanshan, resulting the incision rate in T1 and T2 increasing to be 1.13 m/ka, indicating eastward extrusion uplifting under the background of expansive uplift of the northeastern Tibetan Plateau. The study provides a new evidence for the cognition that the Tibetan Plateau expands in a way of area and volume.

Differentiation of Anomalous Cretaceous Post-Rift Subsidence in the Southern Songliao Basin

LI Chao, LIU Shao-feng , BAI Yu

2014, 28(6): 1213-1224.

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To understand the dynamic mechanisms of post-rift subsidence in Songliao Basin, the backstripping and strain rate inversion methods are used to study the stratigraphic sections and boreholes in Changling sag and Shiwu sag on the southern edge of Songliao Basin by analyzing the relevant data. The post-rift anomalous subsidence is computed as the discrepancy between observed and predicted post-rift subsidence based on modeling exponential thermal cooling following earlier lithospheric thinning events. The modeling results of 13 wells show clearly that the anomalous subsidence during the post-rift stage is between 160 m and 800 m in the study area. With averagely maximium subsidence rate reaching 16 m/Ma and strain rate reaching 6 Ga-1, the rapid subsidence periods in the study area occurred at 99.6-91.4 Ma(Quantou Formation) and 84.7-79.1 Ma(Nenjiang Formation). The Cretaceous anomalous post-rift subsidence in the southern Songliao Basin was primarily induced by downdrag pressure of subducting in western Pacific slab and deep mantle flow under Songliao Basin. The basement faulting in Songliao Basin during Early Cretaceous and normal faulting in the post-rift stage also make contribution to anomalous post-rift subsidence.

Discussion on Faults, Tungsten-tin Anomaly and Ore-controlling Factors of Chaling Area, Southeastern Hunan

WANG Dong-sheng, ZHANG Hong-yuan

2014, 28(6): 1225-1233.

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The Chaling area is located at the southeastern Hunan Province, which is a major ore concentration area in south China metallogenic belt. In this region, there are complicated faults in the plutons (Dengfuxian, Xitian), wall rocks and cap rocks. What’s more, the distribution patterns of the element-associating geochemical anomaly are also complex. In this paper, through methods of fault-grade classifications, field survey and anomaly comparison, the relationship between the fault and the anomaly is discussed in order to obtain the distribution regularity of tungsten and tin. The conclusions can be drawn as follows: (1)Many second-class NE-striking faults develop along the first-class Laoshanao fault; these faults and the Laoshanao fault form in the same stress field; the second-class NE-striking faults are parallel to each other and many third-class joints develop between them with different directions; the second-class NE-striking faults and the joints constitute the riedel shear system. (2)In the plutons, there are obvious concentration focuses of tungsten-tin anomalies developing in joints of the second-class NE-striking faults and the third-class faults. (3)In the Cretaceous, the geochemical anomaly is controlled by the second-class faults and the Quaternary. (4)The anomaly is also related to the contact zone. The relationship between the fault and element geochemical anomaly, which is always helpful to reveal the ore-forming dome, can be a reference to deep mineral exploration.
Key words:southeastern Hunan; Chaling; fault; element geochemical anomaly

Quaternary Magnetostratigraphic Time Framework Constraints on Activity Characteristics of the Shunyi Fault，Beijing Plain

BAI Ling-yan,ZHANG Lei,CAI Xiang-min,WANG Ji-ming,YANG Tian-shui

2014, 28(6): 1234-1242.

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Shunyi fault is one of Quaternary active faults in northeastern Beijing plain. Its activity is regarded as one of potential geological disasters to the urban security. In order to reveal the activity history of Shunyi fault,the magnetostratigraphy research was conducted on borehole ZK12-1 at the footwall of fault. The detailed stepwise thermal demagnetization isolated two components，and the characteristic remanent magnetization (ChRM) with moderate downward or upward inclinations was identified after removing a low-stability drilling-induced remanence with steep downward inclinations.Combined with the lithologic association of the core，a magnetostratigraphic frame of borehole ZK12-1 was established. Based on the magnetostratigraphic framework of borehole ZK12-1 at footwall and borehole ZK12-2 at the hanging wall and the distance of the vertical movement，the vertical activity rates between the hanging wall and footwall of Shunyi fault were computed to be 0.023 mm/a in the Early Pleistocene，0.001,7 mm/a in the Middle Pleistocene，0.033 mm/a in the Late Pleistocene and 0.051 mm/a in the Holocene. These results indicate Shunyi fault activated strongly in the Early Pleistocene and activated weakly in the Middle Pleistocene. In the Late Pleistocene，this fault became much more active，and in the Holocene it experienced the strongest activity.

Application of DEM Extracted from IRS-P5 Stereo Images on Paleo-Earthquake Study of Daqingshan Piedmont Fault

HE Zhong-tai，HOU Jian-jun，SU Yuan-yuan

2014, 28(6): 1243-1251.

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A case DEM was extracted from IRS-P5 stereo images of middle three segments(Tuyou, Tuzuo and Bikeqi)in Daqingshan piedmont fault, and this DEMs vertical accuracy was tested to meet hilly-area and mountainous-region requirement of 1:10,000 topographic maps. Twenty-five gullies across the fault on the footwall have been extracted from this DEM, and the knickpoints caused by fault activities in Holocene have further been extracted from profiles of gullies, and the six-, five-and three-ranks of knickpoints are identified in the gullies from west to east. The newest rank knickpoints in the Tuyou and Tuzuo segments are regarded as those caused by the A.D.849 earthquake to get their retreat rates. The retreat rate of the newest knickpoint in each gully is also considered as that of other points in the same gully; the average retreat-rate value of the newest rank knickpoints in the Tuyou and Tuzuo segments is considered as that of the knickpoints in the Bikeqi segment; then the formation time of the six-, five- and three-ranks of knickpoints in the three segments is computed combining with the retreat distances of knickpoints on the gullies, thus the paleo-earthquake series in the study area in Holocene have been obtained. These paleo-earthquake series are close to the results that are derived from trench techniques and Holocene paleosols in paleo-alluvial-pluvial fans in previous studies.

Numerical Simulation Study on the Site Speed Response of Yanqing New City Planning Region in Beijing

FENG Jun, ZHANG Bin, HUANG Xiao, SUN Jin-zhong, BAI Yong-liang, HUO Dong-ping

2014, 28(6): 1252-1259.

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In the earthquake prone inland environment of China, the evaluation of site stability has drawn more and more attention.For the study of large site dynamic response characteristics of Yanqing new city planning region, this paper firstly found out the Quaternary overburden layer and the spatial distribution of fractures in Yanqing new city planning region; secondly, it established a 3D simulation model for planning region using FLAC3D based on numerical simulation; thirdly, it made a simulation of the site dynamic response in planning region; and lastly, it described the characteristics of site dynamic response by defining the coefficient of site speed response. The results reveal the following aspects: in the typical sites of soil-rock composite,different thicknesses of the Quaternary overburden layer could lead to different levels of site speed response under the low-frequency shear-wave excitation, and while the Quaternary overburden layer gets thicker,the coefficient of site speed response gets greater and the degree of dynamic amplification gets higher; in the complex site of underlying fracture, the shear wave propagation path becomes very complicated,and the fracture has an amplification effect to the coefficient of surface speed response,while the amplification level is related with the distribution form and development scale of fractures.

Transfer Zone Characteristics of the Yudong 3 Fault Zone in Yubei Area of the Tarim Basin

ZHAO Bin-bin，TANG Liang-jie，YU Teng-xiao，CHEN Gang ，YUE Yong

2014, 28(6): 1260-1265.

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Based on the interpretation of the latest 3D seismic profiles, this study discussed the characteristic and evolution of the transfer zone in Yudong 3 fault belt in Tarim Basin according to the analysis of displacement-distance method. The Yubei area mainly consists of a number of faults striking northwest. From the northeast section to the southwest section, the direction of the main fault gradually changed from southeast to northwest. According to the combination and intersection relations of fault structures in this area, the transfer zone in transform section was interpreted as convergent-overlap type based on the classification of Morley. The transfer zone between the two sections has transferred their displacements and keeps the conservation of fault displacements in Yudong 3 fault zone. The evolution of this transfer zone can be divided into three stages, i.e. the formation of isolated reverse fault, formation of transfer-zone and complication of transfer zone.

Age Assignment and Suggestion on Stratal Code Alteration of Upper Ganchaigou Formation, Qaidam Basin

MA Xin-min，LIU Chi-yang，LUO Jin-hai，ZENG Fang-ming，CHEN Da-you1，ZHANG

2014, 28(6): 1266-1274.

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Reservoir Fracture Numerical Simulation of Keshen-2 Block in Tarim Basin

ZHAO Ji-long, WANG Jun-peng, LIU Chun, ZENG Qing-lu, DAI Jun-sheng

2014, 28(6): 1275-1283.

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Quantitative prediction of reservoir fracture is an important guarantee of development in later period of Keshen-2 Block in Kelasu Structural Belt of Tarim Basin.Based on the description of single well fracture character and the confirmation of paleo- and current crustal stress by structural analysis and inversion matching, mechanical model of research area is built, and numerical simulation of reservoir fracture in Bashijiqike Formation of Keshen-2 Block is carried out combining with the quantitative relationship between crustal stress and fracture parameters.The result shows that fault belts are high value area of fracture parameters, and the top of anticline has low linear density and high aperture, porosity and permeability of fracture while the wing is on the contrary.The reason is that near fault zone the fracture where has high linear density, and the fracture communicate the single sand body.while the high position of anticline where has low linear density,high aperture,weak filling and high effectiveness.The results of numerical simulation has a better matching with single well core fracture and imaging fracture interpretation results.The prediction of fracture permeability of development well is as high as 75%, which provides a basis for the natural gas exploration and development of Keshen-2 Block in Kelasu Structural Belt of Tarim Basin.

Delta Sedimentary Simulating Experiment on Saline Basin

GOU Ying-chun，CAO Zheng-lin，ZHANG Xiao-jun，WAN Chuan-zhi，WANG Pu，SU

2014, 28(6): 1284-1288.

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In order to guide the exploration of saline basin from Palaeogene to Neogene in western Qaidam Basin, models of sands control and enrichment in saline basin were constructed, combining with field study of modern saline basin sedimentary characteristics of Qinghai lake. Delta sedimentary simulating experiment in salt water medium was carried out. The research results of delta sedimentary simulating experiment in salt water medium indicated that the sedimentary facies of saline basin delta is mainly composed by plain facies, accounting for over 80% of the entire delta area, and mouth bar microfacies in the delta front sub-facies is the most developed. The results show that the saline water medium controls the distance of transportation of various granularities, contrasting with water medium which less saline, fine-grained sediments in saline water were rapidly deposited in the mouth of river, and the coarse sediments transported farther, the sedimentary range were also more larger. The results indicate that saline basin delta sediment developed sand body architecture of river-over-bar sand body, on the longitudinal. Delta sedimentary simulating experiment defines the distribution characteristic of reservoir, enlarges the range of reservoir, and provides a technical support on oil-gas exploration in western Qaidam Basin.

Apply Various Methods to Comprehensively Explore the Deep-water Sedimentary Lithological Traps’ Boundary in Baiyun Depression

2014, 28(6): 1289-1296.

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To reduce the risk of exploration in deep water，and accurately identify the lithologic traps’boundary in the deep zone of Baiyun depression，this paper adopted the method of combining multiple technologies to study the sedimentary lithologic traps’ boundary in deep-water. In the sequence stratigraphic framework and under the control of sedimentary system，the favorable area is targeted, in which lithological traps can form; The forward model is built, which can describe various kinds of sedimentary reservoir faces about the gravity flow in deep water; Making use of the analytical technology of seismic waveform，the reservoirs and non-reservoirs are indentified，and the characterization of channel deposition and filling，the sedimentary fan body inside structure，sand body packing mode of microstructure are finely described; Combination of reservoir inversion and a variety of seismic attributes，the lithological traps’ boundary is further comprehensively identified. The study result summarized the recognizable characters of sand rock lithological traps’boundary about the slope gravity flow channel sand，slope fan，floor fan sandstone in Baiyun deep-water,and it is applied to the exploration practice，then the good exploration results are obtained.

Genetic Analysis of Natural Gas in No.2 Structural Belt of Nanpu Depression

CHEN Xiang-fei,LI Su-mei, WANG Zheng-jun, XU Man, MENG Xiang-bing

2014, 28(6): 1297-1306.

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The origin of natural gas in No.2 structural belt of Nanpu depression is still unclear. Geological and geochemical approaches are utilized to reveal the characteristics and genetic mechanisms of deep and shallow natural gas. The results show that the components of natural gas in No.2 structural belt are dominated by hydrocarbon gas with non-hydrocarbon mainly composed of CO₂, N₂ and H₂S, which are mainly found in buried hill reservoirs. The dry coefficient of natural gas varies from 0.68 to 0.94, indicating mainly a wet gas. Carbon isotopes of natural gas are relatively heavy, showing a tendency of normal order, but some samples display a partially reversed isotopic order with δ¹³C₃>δ¹³C₄. There are three types of natural gas in No.2 structural belt with the analysis of organic matter type and maturity: the mixture gas generated during early phase of mature stage (gas within Ed₁ and Ng), the mixture gas generated during late phase of mature stage (gas within LPN1 fault block) and coal-based pyrolysis gas generated during high mature stage (gas within NP280 fault block). The comprehensive analysis indicates that the natural gas within Ed₁ and Ng formations of Tertiary is mainly generated from Ed₃ and E_s1 source rocks, while natural gas within buried hill is mainly derived from humic type organic matter in E_s3 Member. Faults and unconformities are the main paths for hydrocarbon migration. This research should be helpful to further exploration of deep and shallow natural gas in Nanpu depression.

Fracture Rupture Point Optimization for Staged Fracturing of Perforated Horizontal Well

YIN Jian，GUO Jian-chun，ZHAO Zhi-hong，WANG Xing-zhun，BAO Wen-hui

2014, 28(6): 1307-1314.

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To determine the location of fracture rupture point for horizontal wells and to guide the choice of preferred perforation location，a horizontal well fracturing stress field model has been established，which takes induced stress interference caused by open cracks and fitting the actual characteristics of horizontal well fracturing into account. On this basis，a rupture point optimization methods has be established combined with rock fracture criterion from an angle of lowering fracture pressure. The results show that the induced stress interference caused by cracks makes stress field around the horizontal wellbore more complex，so studying on the problem of fracture initiation this factor must be considered. This method was applied to staged fracturing for horizontal wells in western Sichuan. According to the result，the actual fracture gradient is lower than those of adjacent wells，which greatly reduced the construction risk. The breaking point optimization method has some guiding significance for the design of horizontal well fracturing.

Experimental Study on Profile-Controlling Mechanisms of Air Foam Flooding in Tight Oil Reservoirs

WU Yong-bin，ZHANG Yun-jun，DUAN Wen-biao

2014, 28(6): 1315-1321.

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Based on the coring samples, injection water and formation water, optimized air foam, etc, from a typical tight oil block in Changqing oilfield, the 1D long core flooding system is utilized to carry out the experiments of injection capacity of pure foaming liquid, air and air foam into the core matrix and fracture. The experimental results indicate that under the real formation conditions, the air foam is not able to be injected into the tight core matrix directly, but because some of the foaming surfactant is absorbed by the reservoir rock, the defoamed liquid and air are able to flow into the tight core matrix and realized the stable displacement. According to the actual formation characteristics, three-core parallel flooding experiment is designed which include two matrix cores with permeability difference of 10 and one fractured core and the profile-controlling mechanisms by air foam are analyzed and determined. The air foam majorly flows into the fractured core and plugs the fractures, a part of defoamed liquid and air flow into the matrix cores to displace the waterflooded residual oil.Finally, the residual oil saturation of air foam flooding is 21.12% lower than that of waterflooding, and the oil displacement efficiency is 32.89% higher, which indicates encouraging performance following waterflooding. In order to avoid the inefficient production phase of ultra high watercut, it is recommended to convert to air flooding as early as possible before the water cut reaches 90%, so as to enhance oil rate and economic performance.

Using the ³H and ¹⁴C Dating Methods to Calculate the Groundwater Age in Nuomuhong,Qaidam Basin

LIU Feng，CUI Ya-li， ZHANG Ge，GENG Fu-qiang，LIU Jie

2014, 28(6): 1322-1328.

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By utilizing the ³H and ¹⁴C dating methods, this paper calculated the distribution of groundwater age and then analyzed the groundwater renewability in the study area of Nuomuhong in Qaidam basin. The results show that: (1) in areas from the mountain to the middle part of the alluvial-proluvial fan, the groundwater age varies slightly (15-18 a), indicating that the groundwater is recharged after 1952 with a strong renewability; (2) the groundwater age, in the leading edge of the alluvial-proluvial fan, is less than 2 ka, indicating that the groundwater is a mixture of the modern groundwater with the fossil groundwater and has a poor renewability; (3) in areas from overflow zone to the center of the basin, the groundwater age gets older rapidly from 5 ka to 28 ka, indicating that the hidden fault underlaid the overflow zone has the property of water blocking, and that groundwater in this area can be considered as unrenewable resources

Hydrochemical Characteristics and Influencing Factors of Shallow Groundwater in Siyang Area，Jiangsu Province

WANG Ming-peng

2014, 28(6): 1329-1336.

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Based on experimental data of the shallow groundwater samples, the hydrogeological characteristics in Siyang area and spatial distributions of the chemical components were studied,meanwhile, the formation characteristics and influencing factors were discussed. The results showed that the hydrochemical type of shallow groundwater in Siyang area presented some horizontal zoning regularity. In the southwest of the Grand Canal, HCO^-₃ is the predominant anion of the shallow groundwater; total dissolved solids (TDS) is less than 1 g/L; total hardness is less than 450 mg/L, and the water quality is generally good. While in the northeast of the Grand Canal, the predominant anions of shallow groundwater areHCO^-₃,Cl^-and SO^2-₄; TDS usually is within 1-3 g/L; total hardness is more than 450 mg/L; the water is brackish and the quality is bad. In addition, the ammonium nitrogen and nitrate nitrogen contaminations of the shallow groundwater are obvious in Siyang area, and the spatial distributions there have significantly uneven regional differences, ammonium nitrogen and nitrate nitrogen concentrations are high at both sides of the Grand Canal and near the Siyang farm.NH⁺₄-N high-concentration in shallow groundwater is less than that in 18 meters in the vertical, while NO^-₃-N highconcentration in shallow groundwater is within 8-20 meters. The spatial variations of hydrochemical characteristics of shallow ground-water in Siyang area are affected by the interactive marine and terrestrial deposit, the chemical constituents of the supply source, supply and runoff flow conditions of aquifer medium and human activities.

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