Geoscience

Formation and Metamorphic Ages of the Banded Iron Formation in Fangmayu of Miyun, Beijing: Zircon SHRIMP U-Pb Dating

SHI Zhiqiang, SHI Yuruo

2017, 31(01): 1-10.

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This paper reports zircon SHRIMP U-Pb ages for magnetite-garnet-plagioclase gneiss from host rocks in the Fangmayu iron deposit, Miyun of Beijing. Zircon ²⁰⁷Pb/²⁰⁶Pb ages of the gneiss we mainly obtained are (1 817±13) Ma and (2 456±6) Ma, respectively. Based on the cathodoluminescence images of zircons, together with the petrography of rocks, the ages represent two stages of metamorphism of the banded magnetic quartzite, corresponding to similar ages of two large-scale metamorphic events (namely ca. 2.44 Ga and ca. 1.82 Ga) reported from the eastern block of North China Craton. Then, we also found some owning oscillatory zoning zircons with ²⁰⁷Pb/²⁰⁶Pb age of (2 529±8) Ma, which represent the age of the detrital zircon from the magnetite-garnet-plagioclase gneiss. It also indirectly constrains that the banded iron formation was formed between (2 456±6) to (2 529±8) Ma, most likely at the end of Neoarchean by combining previous research data. The results also provide further detailed information for research of early tectonic evolution of North China Craton and iron deposits (BIF) in China.

Geological Characteristics, Zircon LA-MC-ICP-MS U-Pb Age of Kailekesaiyi Iron Deposit in Altay, Xinjiang, and Their Geological Implications

GUO Xuji, LI Yan, YANG Chengdong

2017, 31(01): 11-19.

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Kailekesaiyi iron deposit, the unique small specularite deposit in Altay, Xinjiang, occurs in a sequence of metamorphic volcanic-sedimentary rocks. The wall-rock is muscovite quartz schist, and the orebodies are stratiform and in accordance with the stratigraphic occurrence. The ores occur as massive, banded, and striped structures. Ore minerals are dominated by specularite (TFeO=87.349%-88.988%,TiO₂=0-1.042%,Al₂O₃=0.036%-0.256%) with sedimentary characteristics. Zircons from the specularite muscovite-quartz schist yield a LA-MC-ICP-MS U-Pb concordant age of (375.6 ± 0.6) Ma, and constrained the ore forming age to the Middle Devonian (ca.376 Ma), suggesting that this deposit is one product of the few Middle Devonian mineralization in Altay. Meanwhile, the ore-bearing metamorphic volcanic-sedimentary rocks are dated to the Middle-Late Devonian Altay Formation, rather than the Early Devonian Kangbutiebao Formation which is considered by the previous scholars.

Geochemistry and Zircon U-Pb Dating of Granites in Early Cretaceous in Eastern Xilin Hot, Inner Mongolia and Its Geological Implications

YUAN Jianguo, GU Yuchao, XIAO Rongge, QU Yunyan, DUAN Kaibo, HAN Yue

2017, 31(01): 20-32.

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In this paper, a series of analyses including SHRIMP zircon U-Pb isotopic dating, major elements and trace elements, have been performed on the granite in Early Cretaceous in eastern Xilin Hot in order to make the discussion of tectonic environment in the study area. The results of the SHRIMP zircon U-Pb dating are (139.1±1.7) Ma for syenogranite(DS214) and (134.7±1.7) Ma for granite(DS220), which suggests that the granite formed in the early period of Early Cretaceous. The geochemical feature of major elements in the granites is found containing high SiO₂ and K₂O +Na₂O contents, low Al₂O₃ content relatively. The average A/CNK value is 1.06, which belongs to weak peraluminous series. The trace element geochemistry shows evident enrichment of LILE(Th, U and K), deficit of HFSE (Nb, Ba, Sr, P and Ti). The REE patterns are the richment type of LREE/HREE value (5.71-14.36) with high total REE contents(122.90×10^-6-368.77×10^-6) and strong negative Eu anomalies(0.10-0.50), which implies that the samples are A-type granites. The K₂O-Na₂O diagram for tectonic environments also shows that they are A-type granite. The Y/Nb-Ce/Nb diagram of A-type granites of different tectonic environments displays the feature of A2-type granite. These geochemical characteristics of the granites reveal that the granites formed in the extending phase of the post-orogenic by the evolution of crustal magma with mantle mixing. The cause of the granite may be related to the procession from the extruding to extending environment which is the result of the lithosphere thinning after the plates collision (including Mongolia-Okhotsk ocean) with the close of Paleo-Asian Ocean during the Late Paleozoic to the Early Mesozoic. It was also effected by the westward subduction of the Paleo-Pacific Ocean.

Genesis Study on Mafic Microgranular Enclave from Early Jurassic Granites in the Southern Zhangguangcai Mountains in Heilongjiang Province

REN Yongjian, CHENG Shuo, ZHU Jingbin, WANG Bo, ZHANG Mingming, ZHANG Xu, YU Wang, HAN Yue

2017, 31(01): 33-45.

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Early Jurassic granites in the Southern Zhangguangcai Mountains show magma-mixing characteristics. In the granite mafic microgranular enclaves are well developed. They are mostly fine-grained dioritic magmatic enclaves. The enclaves highly vary in shape and size and have clear-cut, vague or transitional relationships with host rocks. It is evident that the mineral assemblage of enclaves is not in balance. For example, mineral has the characteristic of directional arrangement; the plagioclase has developed from the epicyclic zone and has the presence of both the old and the new generations,and there also appears acicular apatite. Research on geochemistry shows that enclaves and their host granite are closely related both in the REE and trace elements,which also shows a significant geochemical affinity. It indicates that Early Jurassic granitic rocks are of crust-mantle mixing, and that dark enclaves are formed by relatively basic mantle magma into the host magma, quenching and crystallizing. Granitic magma sources are mainly from newborn crust substance in the Southern Zhangguangcai Mountains.

Recent Tectonic Stress Field at the Shallow Earth’s Crust near the Tan-Lu Fault Zone

FENG Chengjun, ZHANG Peng, QI Bangshen, MENG Jing, TAN Chengxuan, HU Daogong

2017, 31(01): 46-70.

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Tan-Lu fault belt is a deep fractured zone in east China, as well as the largest Quaternary active tectonic belt and seismic belt. The recent tectonic stress field obviously controls the motion mode of the fault, the activity intensity, and the seismicity of the fault belt. Therefore, it is of important scientific significance to make further research on the tectonic stress field near the Tan-Lu fault zone and the adjacent region. Based on the previous research results, the paper preliminarily reveals the distribution of the shallow crustal in situ stress, and analyzes the discrepancy of different tectonic positions on the basis of the in-situ stress measuring results at 6 boreholes with the depth of 600-1,000 m near Shandong-Bohai-Liaoning segments of the Tan-Lu fault zone and the vicinities. Then, the recent tectonic stress field in the vicinity of the Tan-Lu fault zone is exhibited combined with other basic stress data, such as focal mechanism solutions, borehole breakouts, stress relief data, and fault slip vector inversion results. Furthermore, the influence of tectonic stress field on the fault active mode is also analyzed. The preliminary results reveal that: (1) In terms of tectonic stress accumulations,the horizontal tectonic stress accumulation in the southern tip of Shandong segment of the Tan-Lu fault zone is the strongest, and that in the Liaodong Peninsula on the eastern and western sides of the Bohai segment takes the second place, and the horizontal tectonic stress accumulation in Benxi region at the northern tip of Liaoning segment is slightly lower than that in the Bohai segment, while it is the lowest in Pingdu region at the northern tip of Shandong segment and Changli of Hebei Province. (2) The stress regimes of the southern and northern tips of Shandong segment of the Tan-Lu fault zone are of thrust and normal faulting states, and are normal faulting and strike-slip faulting in the Bohai and the northeastern tip of Liaoning segments. The stress regime of each segment of the Tan-Lu fault zone can correspond to the active characteristics of the fault belt since the Quaternary. (3) The orientations of principal compressive stress in the tectonic stress field are N70°E, N68°E and N72°E in the vinicinity of Shandong, Bohai and Liaoning segments of the Tan-Lu fault zone, respectively. Under such stress background, the activity of the Tan-Lu fault zone is liable to be right-lateral strike sliping.

Characteristics of Structural Geomorphology and Segmentation of Sertengshan Piedmont Fault from Dahoudian to Wayaotan

LONG Jianyu, HE Zhongtai, ZHANG Hao, MA Baoqi

2017, 31(01): 71-80.

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Sertengshan piedmont fault is located in the middle-west segment of Yingshan Mountain, controlling the north boundary of Linhe basin with a strong movement since the Late Quaternary. Based on the field investigation and measurements of Sertengshan piedmont fault from Dahoudian to Wayaotan, it is revealed the segment is not a single arcual fault in the NE direction but two secondary segments which are the east-trending Hongqicun segment (Dahoudian-Wubulangkou) and the southeast-trending Kuluebulong segment (Wubulangkou-Wayaotan). There are four terraces along the fault. The age of T₃ terrace is 50-70 ka in which lacustrine deposits are from Hetao lake. The age of T₂ terrace is 20-30 ka. The terrace scale and landscape between Hongqicun segment and Kuluebulong segment are different. The average height of the Holocene T₁ terrace is 5.37 m in the Hongqicun segment and 8.1 m in Kuluebulong segment. The ages of them are respectively 6.23 ka and 12.36 ka. T₁ terrace in the two segments is composed by fluvial deposits. The average vertical slip rate is 0.86 mm/a and 0.65 mm/a, respectively. The characteristics of geometrical distribution, structural landscape, kinematics of the fault are completely different. So the two segments are independent from each other. There is a T-shaped junction between the two segments.

Stratigraphic Subdivision and Sedimentary Facies of Quaternary Sediments in Xinxiang of Henan Province

ZHENG Jianbin, CHEN Jianqiang

2017, 31(01): 81-91.

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Xinxiang is located between the mountainous region of northwest Henan and the plain of east Henan. Both the evolution of Yellow River alluvial fan and the Neotectonic movement have significant effect on the sedimentary process of the study area in Quaternary. This research dated core samples’ age and compared sedimentary facies of the stratigraphy in the study area according to the description of the core. The result implies that both the evolution of the Yellow River alluvial fan and the movement of the river channel from north to south play an important role in the sedimentation of the study area in Quaternary. Fluvial facies are the main sedimentary facies in this area. And all the drillholes reveal that the thickness of Holocene series is 10 m with the average age of about 9.5 ka, and the thickness of the Upper Pleistocene series is 69 m with the average age of 129 ka, and the thickness of the Middle Pleistocene series is 55 m with the average age less than 829 ka. This study didn’t find the bottom interface of the Lower Pleistocene series. In Early Quaternary, the Yellow River alluvial fan located at the west of the study area, and the river channel’s evolution had little effect on Xinxiang. The main sediments were of fine grained flood plain. As with the movement of the Yellow River from southwest to northeast, the main sediments were of the fluvial facies, and the sand became more than ever. In the Late Quaternary, the river channel moved to the south, thus the Yellow River alluvial fan had less impact on the study area than in the middle period of Quaternary, and the sand content decreased. In addition, this research suggests that the hiatus of the northeast of the study area and the differential subsidence in some region are the result of the Neotectonic movement in Early Quaternary. And the terrain in the northeast of the study area is higher than that in the southwest.

Evolution Characteristics of Cambrian Stromatolites in Western Henan and the Coupling Relationship with Metazoan

CHANG Yuguang, BAI Wanbei, WANG Min

2017, 31(01): 92-101.

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As the construction of microbial mats, stromatolites recorded a large number of palaeoclimate and palaeogeographic information. Eighteen layers of stromatolites are found in the Cambrian settings in western Henan. Based on macro and micro characteristics, the Cambrian stromatolites can be divided into 6 types of assemblages according to the abundance(thickness) and the diversity(morphological types). The episodic evolution is discussed as microbiolite-stromatolites and microbolite-limestone evolution scene according to the micro laminations, microbial fossils and microbial mats, combined with the characteristics of sedimentology and biological fossil of stromatolites in each type assemblages. According to the density relationship between the microbolites and trace fossils in Middle Cambrian limestone, the relationship between the stromatolite-microbolite evolution and metazoan is not simple waxing and waning but dynamic-balance coupling in the whole Cambrian.

Tectonic-depositional Environment and Proto-type Basin Evolution of the Cambrian in the Tarim Basin

GAO Huahua, HE Dengfa, TONG Xiaoguang, WEN Zhixin, WANG Zhaoming

2017, 31(01): 102-118.

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The Cambrian carbonate is the objective exploration strata in the Tarim Basin recently, and the restoration of the proto-type basins is the foundation for the research of the tectonic evolution and petroleum exploration. Based on the newest data of drillings, seismic profiles and outcrops, with the analysis of sedimentary facies and the combination of basins and orogenic belts, this paper reconstructed the Cambrian tectonic-depositional environment of the Tarim Basin and established the models of basin fill processes, by employing the method of “point→line→face”. The Cambrian of the Tarim Basin underwent a complete transgressive-regressive cycle which consisted of two secondary cycles which are the rapid transgression in the early of the Early Cambrian→the regression in the Middle Cambrian and the slow transgression in the Late Cambrian→the regression at the end of the Cambrian. The two secondary cycles responded to the two stages of sedimentary evolution, respectively: the Taxi intra-cratonic depression experienced the evolution from the clastic onshore facies-open shelf facies in the Early Cambrian→the restricted platform facies in the Early Cambrian→the evaporative platform facies in the Middle Cambrian and the restricted platform facies in the Late Cambrian→the exposed unconformity at the end of the Cambrian;the Tadong cratonic margin depression developed the basin facies and underwent the lithofacies evolution from the siliceous mudstone→the limestone thinly interbedded with clay-silt rock→the carbonate rock. The characteristics and evolution of the Cambrian proto-type basins of the Tarim Basin were controlled by the extension of the Rodinia supercontinent and the tectonic-depositional pattern of the Tarim Basin experienced the transition from the pattern of the end of the Sinian which was differentiated from north to south to the pattern of the Middle-Late Cambrian which was differentiated from west to east.

Formation and Distribution of Tight Oil of Permian Lucaogou Formation in the Jimsar Sag of Junggar Basin, Northwestern China

QU Jiangxiu, AIRETI Wufuer, ZHA Ming, CHEN Hong, DING Xiujian, GAO Changhai, SU Yang, LIAN Huan, LAI Ren

2017, 31(01): 119-128.

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Based on the data sets of geology, oil production test, logging, rock thin section and geochemistry of Permian Lucaogou Formation (LCG) in the Jimsar Sag of Junggar Basin, we studied the formation and distribution of tight oil. LCG source rocks are excellent level with high total organic carbon and Ⅰ, Ⅱ type kerogens, containing low mature to mature organic matter. The sweet spot sections are large in total thickness, good in continuity, with a variety of lithology. The source rocks and tight reservoirs are widely distributed and form an optimal source-reservoir-caprock combination through space and time, which are beneficial to tight oil accumulation. The abnormal overpressure in LCG provided a drive force for tight oil migration and charging. The excellent level source rocks, reservoirs, optimal source-reservoir-caprock combination, and abnormal overpressure are key factors to tight oil formation. There is oil show in the whole LCG and the tight oil is mainly accumulated in reservoirs related to excellent level source rocks in vertical. The tight oil is mainly distributed in the areas with thick source rocks (>200 m), high TOC (>3.5%) and thick reservoirs (>15 m), and controlled by source rocks and reservoirs in plane.

Characteristics of the Basement Weathering Crust in Dongping Area, Qaidam Basin

WU Jin, GAO Xianzhi, MA Dade, ZHANG Yongshu, ZHOU Wei, NIU Huapeng, KONG Hongxi, WANG Bo

2017, 31(01): 129-141.

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Large-scale distributed gas fields are discovered in frontal slope of the Altun Mountain in Qaidam Basin and the role of the basement weathering crust becomes the concerns. Basing on element analysis, X-ray diffraction analysis, cores and slices observation, conventional logging and image logging, structures of the basement weathering crust are identified and each structure owns different reservoir properties. The result shows that the structure of the basement weathering crust of Dongping area in Qaidam Basin can be divided into three layers, soil layer, completely weathered layer and semi-weathered layer which can be further divided into two zones, dissolution weathered zone and fracture weathered zone. The thickness of soil layer is 0-2 m. The thickness of completely weathered layer is 4-15 m. The thickness of dissolution weathered zone is 36.5-164 m. The thickness of fracture weathered zone is 300-1,000 m. The semi-weathered layer is the reservoir of the basement weathering crust. The reservoir property of the dissolution weathered zone is better than that of fracture weathered zone. The dissolution weathered zone with porosity range from 2%-16% develops dissolved pores and map fractures with high degree of dissolution, and the fracture weathered zone with porosity range from 2%-8% develops tectonic fractures and joint fractures with low degree of dissolution. Large-scale development of the basement weathering crust in Dongping area provides the basis for finding hydrocarbon in the slope area of Qaidam Bain far from the source rock.

Distribution Prediction of Lower Jurassic Shell Limestone Reservoir in Yuanba Area of Sichuan Basin

HE Zhiyong, LIU Haitao, XIAO Wei, DU Hongquan

2017, 31(01): 142-149.

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The shell limestone in the first submember of the Da’anzhai member (D1sm) of the Lower Jurassic Ziliujing Formation is an important natural gas reservoir in Yuanba area, Sichuan Basin. In this paper, we conducted an integrated study based on cores, thin sections, porosity and permeability data, oil test data, well logging data, and seismic data in order to predict the distribution of the shell-shoal limestone reservoir in the D1sm. The D1sm are composed of mainly shelly limestones and argillaceous shelly limestones. The shelly limestones have an average of porosity of 2.36% and an average of permeability of 0.02×10^-3 μm², while the argillaceous shelly limestones have an average of porosity of 4.59% and an average of permeability of 0.21×10^-3 μm². The shelly limestones in the D1sm comprise the high-energy shoal microfacies that developed in the shallow lake subfacies, and the argillaceous shelly limestones are interpreted as moderate-energy or subhigh-energy shoal microfacies. The classification of seismic waveform shows that the reflection characteristics of the high-energy shoal microfacies are well continuity, low frequency, moderate to large amplitudes, and wave troughs in the seismic profiles, and that the reflection characteristics of the moderate-energy shoal microfacies are well continuity, low frequency, moderate to small amplitudes, and wave troughs. These two types of waveforms distributed from southwest to northeast along the central part of the study area. The natural gamma data cube of the shelly limestones and argillaceous shelly limestones was constructed after rejecting the mudstones and muddy siltstones by giving the threshold value of 46 API. The distribution of shelly limestones (high-energy shoal microfacies) and argillaceous shelly limestones (moderate-energy shoal microfacies) was precisely mapped; the result shows that the favorable exploration area of natural gas has enlarged by about 518 km². The conclusions of this study provide a solid foundation for the increase of the natural gas reserves and production of the Da’anzhai member in Yuanba aera.

Study on Desorption Properties of Shale Gas

YUE Changtao, LI Shuyuan, LI Linyue, WEN Hailong

2017, 31(01): 150-157.

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Shale gas is an unconventional natural gas reservoir that exists as adsorption, free and dissolved states. Adsorption is the main occurrence state of shale gas. It is very important to study the properties of shale gas adsorption and desorption for exploiting shale gas reservoir. Shale samples were selected from marine shale region in Jingmen, Hubei Province and Sichuan Province. A series of analyses are conducted to obtain the basic properties of shale, and the results indicate that the high degree of organic carbon content and organic matter maturity of the shale samples. MSB magnetic suspension balance adsorption instrument is used to proceed isothermal desorption experiments. The results show that the volume of desorption is low and nearly keeps no change under pressure of 33 MPa to 10 MPa. It increases rapidly when the pressure falls to the range of 10 MPa. The pressure range of 10 MPa to 0.5 MPa is the main period for desorbing the adsorption methane. Adsorption potential theory can be used to estimate the desorption status and desorption strength of shale samples. The larger adsorption potential leads to the more difficult desorption.

Temperature Monitoring Results for Gas Hydrate Borehole DK-9 and Thickness of Gas Hydrate Stability Zone in the Qilian Mountains Permafrost

WANG Chaoqun, DING Yingying, HU Daogong, QI Bangshen, ZHANG Yaoling, TAO Tao, WU Huanhuan

2017, 31(01): 158-166.

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Gas hydrate was discovered in 2008 in the Sanlutian coalfield, Qilian Mountain permafrost, Northwest China. This discovery was first successfully sampled by drilling in mid-low-latitudes mountain permafrost, and was a breakthrough in gas hydrate exploration in onshore regions of China. Temperature monitoring for gas hydrate scientific borehole DK-9, one of boreholes in the Sanlutian coalfield in which gas hydrate was discovered, yielded steady ground temperature data for both in and beneath permafrost layer for one year. The results suggest that the thickness of permafrost in the Sanlutian coalfield is about 160 m and that the geothermal gradient is 1.38 ℃/100 m in the permafrost layer and 4.85 ℃/100 m below the permafrost layer. Analysis of the gas hydrate stability conditions indicate that the permafrost conditions and gas components are favorable for gas hydrate formation, and the maximum depth of the gas hydrate stability zone(GHSZ)in the Sanlutian coalfield is 510-617 m.

The Study and Application of Land Quality Geochemical Evaluation Method: Illustrated by the Case of Hongsheng Town, Heilongjiang Province

LIU Guodong, CUI Yujun, LIU Lifen, WANG Enbao

2017, 31(01): 167-176.

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In order to strengthen the application of achievements of land quality geochemical evaluation, the work took polygons of current land use as the evaluation unit, arranged soil samples in grid by 400×400 meters whose the depth is between 0 to 20 centimeters. Sixteen elements were analyzed, including N, P, K, As, Se, etc. The geochemical quality of cultivated land in Hongsheng Town in Heilongjiang was evaluated referring to the Determination of Land Quality Geochemical Evaluation. The results show that the geochemical comprehensive grade of cultivated land soil quality in Hongsheng Town is “premium”. 99.30 percent of the study area reaches the first grade of environmental quality and more than 94.03 percent reaches the abundant grade of comprehensive nutrients quality. Furthermore, precious selenium-rich land resources of 81.05 km² were found, whose concentration of Se ranges from 0.4 to 1.01 mg/kg.

The Concentration Distribution Characteristics of Pb in Inhalable Particulate Matters in Beijing

BAI Mengmeng, FENG Haiyan, JING Huimin

2017, 31(01): 177-183.

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Based on the concentration distribution characteristics of inhalable particulate matters during heating period and after heating period of Beijing, the comparison of the concentration of PM₁₀, PM_2.5 and concentration characteristics of Pb in the urban and rural areas of Beijing, as well as the different functional areas in the urban was focused. It was found that the concentration of the inhalable particulate matters was much higher during heating period. It was 1.74 to 2.56 times in the smog weather than the non-smog weather. During heating period, the concentration of Pb was much higher in the PM₁₀ than that in the PM_2.5 and its concentration in the urban areas was higher than the rural areas, especially the concentration of inhalable particulate matters in the building materials factory area was the highest among the functional areas, and the second was the commercial area. After heating period, there was little difference of the concentration of Pb in PM₁₀ and PM_2.5. Although the concentration of Pb in the building materials factory area was still the highest, the concentration in the urban and rural areas has little difference as a whole. It can be estimated that the concentration of Pb in PM₁₀and in PM_2.5has grown at a rate of 9.78% and 11.45% every year separately by comparing the data of the year of 2007 with 2013’s. Therefore, more attention should be paid to the concentration increase of the Pb in the inhalable particulate matters of Beijing by relevant departments.

Heavy Metal Concentration and Assessment of Environmental Quality in Atmospheric Dust near Ground of Tangshan City

CUI Xingtao, LIU Wei

2017, 31(01): 184-190.

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The 161 atmospheric dust samples gathered near the ground of Tangshan City were studied for the concentration and environmental quality of heavy metals. The atmospheric dust near the ground of Tangshan City was assessed for the environmental quality of heavy metals with single-factor contaminant index and Nemerow multi-factor index method and was interpolated to a distribution map by using the spatial analysis module of ARCGIS. The results had shown that the actual content of all the heavy metals in the atmospheric dust near the ground of Tangshan City was over their original background level. The variance indices of Zn,Cd,Pb,Cu,Hg,Cr,Ni and As in the atmospheric dust near the ground of Tangshan City were 43.23%,213.99%,113.21%,29.56%,70.83%,51.80%,29.21%,32.67%, respectively. Cd and Pb were the strong variance elements. The results of the environmental quality of heavy metals with single-factor contaminant index had shown that Cd and Zn were the serious pollution level and Cr,Hg,Pb,Cu,Ni were the potential pollution level, As was the clean level. The results showed that the elements, according to the environmental quality of heavy metals with single-factor contaminant index,were followed by Cd>Zn>Cu>Cr>Pb>Hg>Ni>As. The results of the environmental quality of heavy metals with Nemerow multi-factor index had shown the heavy metal pollution in the atmospheric dust near the ground of Tangshan city was serious. Considering synthetically the pollution level of heavy metals, the percentage of clean, potential pollution, light pollution, heavy pollution and severe pollution were 0,3.72%,52.19%,38.51%,5.58%,respectively. The sum of proportion of heavy pollution and severe pollution reached 44.09%. High concentration of heavy metals in atmospheric dust was coincided with the distribution of industrial and developed transportation area. The heavy metal pollution may be associated with the use of coal and the traffic and other sources of pollution.

Study on the Salinization Mechanism of Shallow Groundwater along the Upstream Qingshui River in Ningxia

WANG Yushan, LI Shu, MENG Ying, CHENG Xuxue

2017, 31(01): 191-199.

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Research on salinization mechanism of groundwater in arid areas is of great significance for water resources management. Fifty-two groundwater samples and eight rock samples were taken from the upstream Qingshui river plain in Ningxia. Hydrogeochemical processes controlling groundwater salinization were studied and their contribution ratios to salinity were calculated using element mass balance method. The results show that the salinization extent increased along groundwater flow path. The salinization processes mainly depended on rock weathering and had a spatial variation. Carbonate weathering played a dominant role in recharge area and sulfate weathering in strong runoff area. In slow runoff area, 68-93 percents of total salt were supplied by sulfate and halite weathering. The contribution ratios of evaporite increased with groundwater TDS, while carbonate and silicate had an opposite trend, which indicated that evaporite weathering controlled groundwater salinization.

Hydrogeochemical Characteristics of Groundwater in the Xide Geothermal Field, Southwest Sichuan, China

YUAN Jianfei, DENG Guoshi, XU Fen, TANG Yeqi, LI Pengyue

2017, 31(01): 200-208.

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The formation and chemical characteristics of thermal groundwater are commonly influenced by the fault structures and the strata lithology of geothermal reservoirs, such as Xide geothermal field. It is located in north shore of the Sunshui River of Xide town, Liangshan Prefecture, Sichuan Province, and belongs to low-medium temperature convective geothermal fluid system in carbonate aquifer. The hydrogeochemical characteristics of cold spring and thermal waters in this area are mainly affected by faults. The cold spring water derived from the shallow circulation clastic rock pore-fracture water or karstic fracture water, which was controlled by the main fault. The thermal water originated from deep cycle fissure water, which was significantly influenced by the secondary fault. In addition, the main reservoir of thermal water is carbonate rocks. Based on the local geological structure, hydrochemistry analysis of thermal and cold spring waters were incorporated with water-rock interaction simulation to analyze the hydrogeochemical characteristics of groundwater in this area. The results were shown as followings. Thermal and cold spring waters originated from meteoric water and the recharge elevation are of 2,874-3,092 m and 2,584-2,818 m, respectively. The hydrochemical type and chemical components are distinctive between thermal and cold spring waters due to reservoir temperature, aquifer types, and water-rock interactions. The thermal waters is of HCO₃·SO₄-Ca·Mg type, while the cold spring waters is of HCO₃-Ca·Mg type. The main cause for those differences is that the dissolution and precipitation of carbonate and gypsum, and cation ion exchange. In addition, the reservoir temperature and circulation depth calculated by silica geothermometer are 56-90 ℃ and 1,422-2,558 m, respectively. The results provide important insights into the genesis of the Xide geothermal field, and are instructive for further management and sustainable utilization of geothermal resource for local government.

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