Table of Content

10 October 2018, Volume 32 Issue 05

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Petrology and Ore Deposits

Discovery of the Early Indosinian Granite in Lujing Area, Hunan and Jiangxi Border and Its Geological Significance

ZHANG Wanliang, GAO Mengqi, LÜ Chuan, HUANG Chao, HUANG Di, XIE Zhicong

2018, 32(05):  863-873.  DOI: 10.19657/j.geoscience.1000-8527.2018.05.01

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Indosinian granites are widely distributed in Southern China. Previous studies indicate that the Indosinian granites mainly concentrated in the Middle-Late Triassic are attributed to post-collisional granite type. In this paper, we reported a Jiaoyelong concealed granite from Lujing area, the border of the Hunan and Jiangxi provinces. The results show that this granite with medium-coarse grained granitic texture and muscovite is chara-cterized by high contents of silicon (SiO₂=73.97%-76.92%), aluminum (Al₂O₃=12.56%-13.86%), potassium (K₂O=4.02%-5.13%), and K₂O>Na₂O, and belongs to high potassium calcalkaline series. The A/CNK ranges from 1.17 to 1.30,suggesting a peraluminous series. It is rich in large ion lithophile elements (Rb, K, etc.) and high field intensity elements (Th, U, Ta, Nb, Zr, Hf, etc). The contents of U range from 3.24 × 10^-6 to 15.40×10^-6, with the average content of 8.31 × 10^-6. The ratio of Th/U is 1.21-1.98, indicating a rich uranium pluton property. This granite enriched in LREE has a relatively high fractionation between LREE and HREE. LA-ICP-MS zircon U-Pb dating of the granite yields a mean age of (247±2.2) Ma, belonging to the early Indosinian intrusion. Furthermore, the aluminum saturation index and Rb/30-Hf-3Ta diagram show that the pluton formed in the collisional continental margin tectonic background, suggesting that a tectonic transition from compression to extension took place in Southern China during the Early-Middle Triassic.

Characteristics and Significance of Skarn Minerals of Mengya’a Pb-Zn Deposit in Tibet

WU Qiumin, CHEN Cuihua, TU Zonglin, ZHANG Yan, SONG Zhijiao, LAI Xiang

2018, 32(05):  874-886.  DOI: 10.19657/j.geoscience.1000-8527.2018.05.02

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Mengya’a lead-zinc deposit in Tibet is an important stratified or stratoid skarn deposit in the northern margin of Gangdise. Laigu Formation, the main ore-hosting strata, provides the main metallogenic material. The main skarn minerals consist mainly of wollastonite, pyroxene, garnet, hopfnerite, actinolite, epidote, chlorite etc.According to the association combination and replacement relationship of minerals, the authors infer that Mengya’a lead-zinc deposit experienced four stages, i.e., early-skarn stage, late-skarn stage, quartz-sulfide stage and carbonation stage. Combining with mineral hand specimens and microscopic observation and the electron microprobe analysis, the authors analyzed the mineralogical characteristics of garnet, pyroxene and wollastonite. The results of electron microprobe analysis show that Mengya’a lead-zinc deposit in Tibet belongs to calcareous skarn deposit; the composition of garnet and pyroxene changed greatly, which respectively were And_59.9-94.72 Gro_0-37.87(Pyr+Spe+Alm)_0.87-6.78 and Di_18.85-94.44 Hd_3.39-70.58 Jo_0.09-11.14; the mineral composition of wollastonite is Wo_99.00-99.44Fs_0.37-0.78En_0.07-0.23. The garnets are mainly andradite-grossuthe, and the garnets always develop zoning structure. The pyroxene is diopside-hedenbergite series, and the wollastonite is pure. The skarn of Mengya’a deposit in Tibet is calcareous skarn. Its ore deposit experienced multi-stage and multi-order evolution of hydrothermal fluid during its formation, and the forming environment of the deposit also is not a stable close system. The mineral composition characteristics of skarn indicate that the metallogenic environment of Mengya’a Pb-Zn deposit was a low acid and oxidation-weak oxidation environment.

Characteristics of Ore-forming Fluids of the Nanmingshui Gold Deposit in the East Junggar, Xinjiang: Evidences from Fluid Inclusions and H-O Isotopes

GE Zhanlin, ZHANG Yongmei, GU Xuexiang, CHEN Weizhi, XU Jinchi, WU Ruochen, HUANG Gang

2018, 32(05):  887-901.  DOI: 10.19657/j.geoscience.1000-8527.2018.05.03

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The Nanmingshui gold deposit is located in the eastern part of the Kalamaili metallogenic belt. Its ore-bodies, controlled by the NW—NWW trending ductile-brittle faults, are hosted in epimetamorphic marine volcaniclastic sedimentary rocks of the Lower Carboniferous Jiangbasitao Formation. Based on the studies of fluid inclusions and hydrogen and oxygen isotopic geochemistry, the properties, source and evolution of ore-forming fluids are discussed in this paper. The ore-forming process can be divided into three metallogenic stages including the early, middle and late stages. Three types of fluid inclusions that include CO₂-H₂O, H₂O-NaCl and pure CO₂ inclusions are identified in the quartz of the Nanmingshui gold deposit. The early-stage quartz mainly contains CO₂-H₂O and pure CO₂ inclusions with homogenization temperatures and salinities ranging from 257 ℃ to 339 ℃ and 0.4% to 2.2%. All three types of inclusions are trapped in the middle(main)-stage quartz. The homogenization temperatures and salinities of CO₂-H₂O and H₂O-NaCl inclusions vary from 196 ℃ to 361 ℃ and 0.4% to 6.0%. Only H₂O-NaCl inclusions are found in the late stage quartz with relatively lower homogenization temperatures clustering at 174 ℃ to 252 ℃. Meanwhile, the salinities of H₂O-NaCl inclusions vary from 1.4% to 3.2%. According to the estimation from CO₂-H₂O inclusions, the minimum trapping pressures for early and middle stages are 214 MPa to 371 MPa and 236 MPa to 397 MPa, respectively, corresponding to the metallogenic depths of 8.1 km to 14.0 km and 8.9 km to 15.0 km, respectively. The studies of fluid inclusions in different metallogenic stages indicate that the metallogenetic temperatures and fluid densities show a decreasing trend, as the ore-forming fluids are evolved from CO₂-H₂O-NaCl±CH₄ system in the early and middle stages to H₂O-NaCl system in the late stage. Fluid inclusions and hydrogen and oxygen isotopic studies show that the ore-forming fluids of the main metallogenic stage were dominantly originated from metamorphic water. The immiscibility of CO₂-H₂O-NaCl fluids is an important mechanism that leads to the gold precipitation and enrichment. The genesis of the Nanmingshui gold deposit is a mesozonal to hypozonal orogenic gold deposit.

Characteristics of Ore-forming Fluids of the Changpai Uranium Deposit in Guangdong Province

XU Hao, ZHANG Chuang, PANG Yaqing, CAO Haojie, LIU Jialin, LIU Wenquan

2018, 32(05):  902-912.  DOI: 10.19657/j.geoscience.1000-8527.2018.05.04

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The Changpai uranium deposit is located in the Changjiang ore field in northern Guangdong Pro-vince. The uranium orebodies are controlled by the NNW trending silicified fracture zones and hosted within both the fracture zones and adjacent altered granites. Microthermometric measurements and Laser Raman Spectrum analysis indicate that the ore-forming fluids of the Changpai uranium deposit are of medium-low temperature, medium-low salinity and contain volatiles including CO₂, CH₄ and H₂. The homogenization temperatures of the ore-forming fluids range from 120 to 250 ℃ while the salinities range from 0.4% to 10.2%. Hydrogen and oxygen isotopic systems of quartz indicate that the ore-forming fluids are mainly derived from magmatic water in the early stage but mixed with meteoric water in the late stage. The δ¹³C values of calcite from the mineralization stage are mostly from -9.1‰ to -8.2‰,signifying deep-sourced carbon in this deposit. On the basis of the aforementioned analyses, it is suggested that the Changpai uranium deposit is a medium-low temperature hydrothermal vein type uranium deposit. Fluid boiling of the ore-forming fluids and consequent escape of the volatile (e.g., CO₂) components resulted in the precipitation of pitchblende and other uranium minerals.

Petroleum Geology

Division of Base-level Cycles and Superimposition of Sandbodies in Marine Braided Delta Reservoir:A Case Study of Zhujiang Formation in Xijiang W Oilfield, Pearl River Estuary Basin

LIANG Xu, FAN Ting’en, HU Guangyi, CHEN Fei, WANG Haifeng, FAN Hongjun

2018, 32(05):  913-923.  DOI: 10.19657/j.geoscience.1000-8527.2018.05.05

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Reservoirs in the Zhujiang Formation of the Xijiang W Oilfield are composed of marine braided river delta front deposits. They are characterized by complex internal architecture and contain different microfacies. In this study, high-resolution sequence stratigraphic framework is established via comprehensive analysis of core, wireline logs, spectrum and high-resolution sequence stratigraphy theory. The results show the presence of five long-term and eighteen medium-term base-level cycles within the Zhujiang Formation.The sandbody architecture comprises four types (i.e., the isolated-,lateral superposition-, two-way migration-and amalgamated type) within the Zhujiang Formation stratigraphic framework, as revealed by statistical analysis of geometric parameters and sandbody distributions. The results indicate that long-term base-level changes play an important role in controlling the sandbody architecture and evolution. During the early-stage rising or late-stage falling in the base-level cycle,the sandbody architecture is dominated by the amalgamated type and lateral superposition type, yet it is dominated by the two-way migration type and isolated type in the opposite case. Analysis of sandbody architecture provides an effective tool for discovering residual oil and assists decision-making process in offshore hydrocarbon exploration.

High-resolution Stratigraphic Division and Formation Model of the Callovian-Oxfordian Sequences in the Central Part of Block B in the Right Bank of Amu Darya Basin, Turkmenistan

WU Chongyang, YU Bingsong, WANG Hongjun, RUAN Zhuang, CHENG Chuanjie, GUO Tongcui, ZHANG Liangjie, CHENG Muwei

2018, 32(05):  924-937.  DOI: 10.19657/j.geoscience.1000-8527.2018.05.06

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The Amu Darya Basin in Turkmenistan is a large petroliferous sedimentary basin, yet its Callovian-Oxfordian stratigraphic division and correlation are still disputed. We analyzed the Callovian-Oxfordian sequences in Block B of the Amu Darya right bank area (based on Vail’s classic sequence stratigraphy and relevant sedimentology theories), integrating drill core, logging, seismic, thin section petrographic, and geochemical data. We found that the Callovian-Oxfordian sequences can be divided into five 3^rd order sequences and 15 4^th order sequences. Stratigraphy framework for the study area is newly established based on these high-resolution sequence divisions. Two carbonate platform models were developed: (i) Callovian, the region was likely a ramp platform with topographic highs in the west and lows in the east, and a gradual slope gradient with spatially consistent sedimentation rate; (ii) Oxfordian, the region was likely evolved into a rimmed platform system, with highly disparate sedimentation rates (low in the east) that were sensitive to sea level change, and a starkly different sedimentary landform that was high in the west and low in the east.

Composition of Lipid Compounds in the Peat Deposit in Mildred Bog from the Athabasca Region, Canada

HE Dashuang, HUANG Haiping, HOU Dujie, ZHANG Penghui

2018, 32(05):  938-952.  DOI: 10.19657/j.geoscience.1000-8527.2018.05.07

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A total of 37 peat samples from Mildred bog in the Athabasca Region, Canada, were analyzed with GC-MS to reveal the compositional characteristics and origins of peat lipids. The results show that long-chain components predominate in the n-alkanes, n-alkan-2-ones, n-alkanals, n-alkanols, n-fatty acids and fatty acid methyl esters, with strong odd or even carbon predominance. Polar compounds of steroids and terpenoids are also present in relatively high abundances. According to molecular geochemistry of the peat samples, the organic matter in Mildred peat profile was mainly derived from the in situ vascular plants, and also from Sphagnum and aquatic plants. Woody plants of conifer, woody debris and Ericaceae, herbaceous plants of Cyperaceous, and Sphagnum are the main peat-forming plants. Among polar compounds, γ-lactone is considered to be a self-oxidation product of tocopherols. A series of sesquiterpene, pentacyclic triterpenoid ketones, pentacyclic triterpenoid alcohols and pentacyclic triterpenes are abundant in the top interval,and their formation are associated with Sphagnum or higher plants. Most steroids are not origin-specific, and the distributions of C₂₈, C₂₉ and C₃₀ steroids are assigned to a higher plant source. γ-Sitosterol, campesterol and stigmastan-3,5,22-triene are effective biomarkers for terrigenous higher plants.

Evolution Model for the Gas Reservoirs in the Shaximiao Formation, Eastern Slope of the Western Sichuan Depression

XU Min, LIU Jian, LIN Xiaoyun, XIONG Shan, NIU Binli

2018, 32(05):  953-962.  DOI: 10.19657/j.geoscience.1000-8527.2018.05.08

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The Shaximiao Formation is the main gas-producing sequence in the eastern slope of the Western Sichuan Depression, and its trap type is dominantly tectonic-lithologic trap.Most of the gas reservoirs are composed of tight sandstones with well-developed faults and fractures, which effectively improved the physical properties of reservoirs. The coupling patterns of fault and sandstone and their tectonic evolution are of great importance to the hydrocarbon accumulation.Our analyses on the dynamic evolution,gas-water distribution characteristics and hydrocarbon formation sequence of the gas reservoirs in the Shaximiao Formation (and the integration with regional tectonic evolution and hydrocarbon accumulation periods) concluded that gas accumulation in the Shaximiao Formation was influenced by tectonic uplifts, fault-sandstone configurations,physical properties of reservoir and tectonic evolution.This formed the reservoiring evolution patterns that are of tectonic orientation-controlled, fault-reservoir migrating-controlled,reservoir accumulation-controlled and evolution modification-controlled.The control of paleostructures in the Gaomiaozi region is more pronounced, while the Zhongjiang region is dominated by lithologic-control.Gas reservoirs in the Shaximiao Formation are featured by the three Yanshanian episodic reservoiring, and the subsequent Himalayan modification.The multi-phase tectonic evolution and strong reservoir heterogeneity have influenced the gas saturation,leading to the widely different gas distributions and reservoir productivity in the Shaximiao Formation.

Coalfield Geology

Geological Controlling Factors of Coal Pore System and Its Significance in CBM Development

LIU Na, KANG Yongshang, LI Zhe, WANG Jin, SUN Liangzhong, JIANG Shanyu

2018, 32(05):  963-974.  DOI: 10.19657/j.geoscience.1000-8527.2018.05.09

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To systematically analyze the key geological controlling factors of coal pore system and the significance for coalbed methane development, we present new statistical data for the mining area of 37 major CBM blocks/mercury, and use the trend analysis method to clarify the coal rank, coal body structure vitrinite and ash effect coal porosity, and the significance of porosity research for coalbed methane development. Our results suggest that R_o,max is an important parameter for reservoir property evaluation, and that coal porosity in low rank area is most sensitive to R_o,max. Besides, the average porosity shows successive peaks and troughs with increasing coal maturity. The range of porosity in the same coalbed methane block/mining area of low rank is wider than that of high rank. Complex coal body structure has a destructive effect on the coal reservoir properties, whereas the high coal rank region and complex coal structures are beneficial to the properties; Vitrinite content is negatively correlated with porosity, and no obvious correlation is found between ash content and porosity. In the low coal rank region, vitrinite and ash content have obvious negative correlation with porosity, whereas the effect on the porosity is negligible in the high coal rank region. The proportion of meso/macro-pores and average permeability increase with increasing average porosity and porosity size. In particular, the changes of porosity with the coal rank in different areas have important guiding significance for the coalbed methane development.

Petrography and Quality Characteristics of Lower-Middle Jurassic Coal Seam in the Southeastern Tarim Basin

WANG Di, TIAN Jijun, FENG Shuo, LU Xingyu

2018, 32(05):  975-984.  DOI: 10.19657/j.geoscience.1000-8527.2018.05.10

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Petrology and quality of the Lower-Middle Jurassic coal seams in the southeastern margin of the Tarim basin (distributed intermittently along the Altyn Tagh) are very different from the Jurassic coal seams in northwestern China. To characterize these coal seams, various experiments including coal petrography, coal quality identification and coalification index have been conducted on a large amount of coal samples collected from the Hetian Buya, Yutian Pulu and Qiemo Hongliugou coal mines. The results reveal that the main mining layer consists mainly of clarain and semi-bright coal, followed by durain and semi-dull coal. The macerals are mainly characterized by vitrinite, with minor exinite and middle-high V/I. In addition, the total sulfur content in the coal increases with the vitrinite content, due to the lower degree of coal-forming swamp that promotes the formation of inorganic sulfur. Moreover, it is obvious that the content of coal seam sulfur decreases with the ash content. Similarly, the volatile content of coal seam affected by various sulfur contents is significantly different. The analyses also show that the main component of sulfur in the medium-high sulfur coal of the Minfeng sag is inorganic sulfur, and that the volatile fraction increases with increasing sulfur content. However, the productivity of volatile influence of organic sulfur is not obvious in the medium-low sulfur coal in the Washixia sag. It is found that the ash composition index in the coal seam of the Minfeng sag is higher than that of the Washixia sag, which suggests that the water table of the coal-forming swamp of the latter is much higher. Our results confirm that the change of coal petrology and coal quality diversity in the southeastern Tarim basin are controlled by the faulted lacustrine basin and the local water depth in the reducing swamp environment, which led to the medium-high volatility, medium-low ash, medium-low sulfur, and the rich vitrinite-poor inertinite coal features there.

Study of Natural Gas Hydrates

Geological Characteristics of Carboniferous-Jurassic Potential Source Rocks for Natural Gas Hydrates in Muli Depression, South Qilian Basin

FAN Dongwen, LU Zhenquan, XIAO Rui, NIU Suoan, QI Lajia, WEI Yi, ZHANG Yong’an, FEI Deliang, DANG Xiaofeng

2018, 32(05):  985-994.  DOI: 10.19657/j.geoscience.1000-8527.2018.05.11

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Through field geological survey and lab-based analyses on the Carboniferous to Jurassic sedimentary sequences along five geological sections in the Muli depression of south Qilian basin, we clarify the regional lithological characteristics, sedimentary facies and sedimentary evolution. The Carboniferous-Permian sedimentation system is characterized by medium-thick sandstone with thin mudstone interbeds, and comprises shallow marine continental shelf, littoral and delta facies. The fault development likely reduced the partial strata thickness and the mudstone sequence is mostly lost, making it an unlikely potential source rock of gas hydrates. The Upper Triassic sedimentation system is characterized by the development of medium-thick sandstone with medium-thin mudstone interbeds, and comprises tidal flat, lacustrine and fluvial facies. The mudstone sequence is thick, making it the main potential source rock of gas hydrates. The Middle Jurassic sedimentation system is mainly characterized by thick mudstone with sandstone, and comprises braided river, delta and lacustrine facies, making it a potential source rock of gas hydrates. Our finding provides important implications on gas hydrate source rocks in the Muli depression.

Geochemical Characteristics and Implications of Helium and Neon in Natural Gas Hydrates Deposits in the Muli Permafrost, Qilian Mountains

ZHOU Yalong, SUN Zhongjun, YANG Zhibin, ZHANG Fugui, ZHANG Shunyao

2018, 32(05):  995-1002.  DOI: 10.19657/j.geoscience.1000-8527.2018.05.12

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The noble-gas helium(He)and neon(Ne)are rare components of natural gas hydrates, and their concentration changes are almost unaffected by complex chemical reactions and near-surface microorganism activities. Discussion of rare-gas geochemical exploration can not only eliminate the strong interference of microorganisms, but can also improve the intensity of the near-surface gas geochemical anomalies including natural gas hydrates. In this paper, natural gas hydrates mining area in the Muli permafrost region of Qilian mountains was investigated, where the average headspace He and Ne contents is 7.99×10^-6 and 20.8×10^-6, respectively, both higher than the average atmospheric concentrations. It is found that He and Ne have strong penetrative power, and show clear geochemical anomaly halos above the known hydrate deposits/prospects. Drilling-hole profiles show that there is obvious upper gas anomaly above the hydrate accumulation horizon, and the noble-gas differentiation and vertical percolation occur during the rare gas hydrate formation in Qilian, while the noble-gas He and Ne carry migrates vertically in the form of “gas-like” geogas current. Our study demonstrates that He-Ne anomaly has a good indication of the gas hydrate deposits, and He-Ne exploration technology is an effective supplement for hydrate exploration in permafrost regions.

Geochemical Investigation and Prospective Evaluation of Natural Gas Hydrates in the Permafrost of Mohe Basin

ZHANG Fugui, TANG Ruiling, YANG Zhibin, ZHU Jinghua, ZHOU Yalong, SUN Zhongjun

2018, 32(05):  1003-1011.  DOI: 10.19657/j.geoscience.1000-8527.2018.05.13

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The Mohe basin is a major permafrost region in China.Gas hydrate reservoir system is well deve-loped in the basin, and the basin shows good accumulation conditions for gas hydrates. The 1∶50k scale regional gas hydrate geochemical survey was conducted in the Mohe basin to delineate prospecting gas hydrate target areas, and to recognize oil and gas traps and identify the hydrocarbon source. Our results show that: (1) In the forest bog region, headspace gas and fluorescence spectra are the main indices of gas hydrate exploration. Considering the AMT and geology materials, and the previous gas hydrate geochemical work in the Muli permafrost of Qinghai, we consider the Yuanbao depression as the gas hydrate target. (2) Methane carbon isotope analysis on core samples shows that the primary hydrocarbon gas is multi-genetic, and only a few adsorbed gases are from bacterial and hydrocarbon pyrolysis. (3) Multiple classification-GIS technique employed in this study can exclude the interference factors and precisely delineate the boundary of geochemical anomalies, and can thus be applied in the geochemical exploration of gas hydrates.

Climatic, Environmental and Biological Impacts of Gas Hydrate Decomposition in Arctic Svalbard and its Surrounding Areas

NIE Yunfeng, YU Jing, CHEN Hongwen, WAN Ling, FAN Guanghui, FANG Qiang, WU Huaichun

2018, 32(05):  1012-1024.  DOI: 10.19657/j.geoscience.1000-8527.2018.05.14

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As a potential huge energy reservoir, natural gas hydrate has a significant impact on climate and marine environment due to its decomposition and release of methane. However, the influence of gas hydrates on environment and biological community has not been thoroughly known. There are a huge amount of methane reservoirs in the seafloor and permafrost in Svalbard and its adjacent areas in Arctic,which is very sensitive to the climate changes, well known as one of the best natural laboratories to study climatic, environmental and biological effects of the gas hydrate decomposition. This paper systematically summarized the relationship between the hydrate decomposition process in Svalbard and its adjacent areas and its effects on climate, marine environment and biology. The results are shown as follows: (1) The current annual emissions of CH₄ linked to the decomposition of gas hydrates in the study area cannot reach a level which is detectable against the background emissions, so the effects of CH₄ on climate might be limited; (2) Gas hydrate dissociation is often considered as a precursor or triggering factor for submarine slope failures, but not a main cause; (3) The emissions of CH₄ can break existing chemical equilibrium, the distributions and transfer pathways of productivity, biological coupling, the connectivity among habitats and the final benthic community. These results might provide references for studying the possible impacts of natural gas hydrate exploration and production on ecological environment and its prevention and control measures.

Discussion on the Distribution and Main Controlling Factors of Mud Volcanoes in Makran Accretionary Wedge,Northern Indian Ocean

GONG Jianming, LIAO Jing, ZHANG Li, HE Yongjun, ZHAI Bin, MENG Ming, CHENG Haiyan

2018, 32(05):  1025-1030.  DOI: 10.19657/j.geoscience.1000-8527.2018.05.15

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In order to study the distribution and main controlling factors of mud volcanoes in the active continental margin in low angle subduction background, a large amount of data on sedimentary strata, fault structures, mud volcanoes or mud diapir have been collected in the Makran accretionary wedge of northern Indian Ocean. The comprehensive analysis results show that the sedimentary strata in the study area are mainly composed of the upper and lower parts, among which the lower hemipelagic muddy strata have the characteristics of “east thick and west thin”, while the upper coarse Makran sand strata have the characteristics of high speed deposition. The characteristics of density inversion and high sedimentary rate provide the material basis for the formation of mud diapir or mud volcano. In Makran accretionary wedge, the convergence rate between Arabian plate and Eurasian plate is characterized by “east fast and west slow”, moreover, the strike-slip faults and mud-volcanoes developed on both sides of the east and west. Considering the convergence rate of the Mediterranean Sea Ridge with the same low subduction angle and the distribution characteristics of mud volcanoes, it is considered that the mud volcanoes on both sides of the east and west are mainly controlled by strike-slip faults, while the mud volcanoes in the accretionary wedge are mainly controlled by the convergence rate, thrust faults and density inversion, showing the characteristics of “the East mud volcanoes are more than the West”.

Applied Geochemistry

Quantitative Description of the Geochemical Background Value of Selenium During Weathering Based on the Certified Reference Materials in China

LI Jinzhe, GONG Qingjie, LIU Yaxuan, YAN Taotao, LI Ruikun

2018, 32(05):  1031-1041.  DOI: 10.19657/j.geoscience.1000-8527.2018.002

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The behavior of selenium, an important trace element for human and animal in environmental geochemistry, is described quantitatively based on the components of 58 certified reference materials collected as rocks, soils or stream sediments in China. The description equation on the relationship between the selenium contents and the corresponding chemical weathering indices is fitted as lgc=0.822×(1.2-WIG/100)-1.061×lg(K₂O/SiO₂)-2.704, where c is the content of selenium in μg/g, the value of WIG varies from 4.3 to 111.6, and the value of K₂O/SiO₂ varies from 0.020 to 0.137. This equation can be used to describe the geo-chemical background values of selenium resulted from different weathering degrees in rocks, soils, and stream sediments. Samples with strong weathering degrees have higher values of the selenium geochemical backgrounds commonly. The equation is applied to two districts of Hetai and Nankunshan in Guangdong Province, China. The results tell us that the areas with strong weathered geological bodies can be viewed as the candidates to find the areas with plentiful or rich selenium contents. The areas with plentiful or strong weathered geological bodies can be found feasibly based on the data of the Regional Geochemistry-National Reconnaissance (RGNR) project. In the soil evaluation on environmental quality, the plentiful or rich selenium areas can be assessed by the analyzed values of selenium. Furthermore,residual values which are the deduction results of geochemical background values from their analyzed values can be used to determine the plentiful or rich selenium geological bodies underlying the weathered materials. In other words, the geological bodies with plentiful or rich selenium which are underlying the weathered soils can be determined feasibly based on the data of the Multi-Purpose Regional Geochemical Survey project. The case study on the Nankunshan district indicates that the middle and west part of the Nankunshan pluton must be plentiful or rich in selenium.

Regional Geochemical Characteristics of Metallogenic Elements in Northwest China

ZHANG Jing, YANG Bo, LI Baoqiang, LI Huiying

2018, 32(05):  1042-1052.  DOI: 10.19657/j.geoscience.1000-8527.2018.05.17

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Based on 322,000 regional geochemical data of Shaanxi, Gansu, Ningxia, Qinghai and Xinjiang in Northwest China, a series of geochemical maps have been compiled and geochemical anomaly genealogy in Northwest China has also been established by statistical analysis, spatial analysis and expert analysis. The enrichment degree of W, Sn, Mo, Cu, Pb, Zn, Au, Ag and Ni in each geochemical region have been calculated, by which the geochemical region have been sorted, then the anomalous significance of W, Sn, Mo, Cu, Pb, Zn, Au, Ag and Ni in each geochemical region and sub-region have been calculated. Based on the result of calculation,the geochemical region and sub-regions has been sorted. The results show that Qinling geochemical region and Xiaoqinling geochemical sub-region are the geochemical regions and sub-regions with the highest anomaly significance, respectively. In Xiaoqinling geochemical sub-region, the anomaly significance index of Mo is the highest and the anomaly scale is the biggest; the anomaly significance index of Au is the second.

Ecological and Environmental Effects of Raw Coal and Coal Combustion Pollution in Xuanhua, Hebei Province

LIU Yu, XIANG Wu, ZHANG Yanxi, XING Xudong, ZHU Jie, YANG Weilin

2018, 32(05):  1053-1062.  DOI: 10.19657/j.geoscience.1000-8527.2018.05.18

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Geochemical distribution characteristics of 16 PAHs and 13 kinds of heavy metal elements,including Hg, Cd, V, Zn, Mn, Cr, Mo, U,etc., were investigated in the topsoil and near surface dust of the raw coal and coal combustion polluted area in Xuanhua, Hebei Province. The results showed that Hg and Cd are the dominant pollutant within about 100 meters in raw coal polluted area. While, Hg,V, and Cd were the dominant pollutants within 2, 000 meters in coal combustion area, where being downwind from coal burning enterprises. And the accumulation of Hg, Cd, Zn, Mo, U, PAHs in topsoil of the raw coal polluted area and Hg, V, Mo, U, Mn, Cr,PAHs of the coal combustion polluted area were mainly from atmospheric deposition. Enzyme activities of the urease, alkaline phosphatase and β-glucosidase in the soil were all restrained to varying degrees with the greatest of β-glucosidase in polluted areas. In addition, the inhibition of soil enzyme activities by coal combustion polluted is more significant than that of raw coal, implying the negative effect of coal pollution on soil carbon cycling.

Regional Geochemistry of Niobium and Tantalum Across the Boundary of China and Mongolia in the Altay Metallogenic Belt

LIU Hanliang, WANG Xueqiu, NIE Lanshi, WANG Wei, CHI Qinghua, LIU Dongsheng

2018, 32(05):  1063-1073.  DOI: 10.19657/j.geoscience.1000-8527.2018.05.19

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Niobium and tantalum are indispensable rare metal materials for high technology, and Altay is an important rare metal metallogenic belt, so it is crucial to carry out the potential prospect areas of niobium and tantalum resources in this area. This paper discussed the background values of niobium and tantalum in different tectonic belts and the regional geochemical anomalies based on the 1∶1,000,000 geochemical data across the boundary of China and Mongolia in the Altay metallogenic belt. The median and average values of niobium in the whole area are 13.80×10^-6 and 14.93×10^-6, and the two values in China side (12.19×10^-6 and 13.31×10^-6) are lower than those in Mongolia side (14.90×10^-6 and 16.39×10^-6). The median and average values of tantalum in the whole area are 1.11×10^-6 and 1.31×10^-6, and the two values in China side (1.02×10^-6 and 1.20×10^-6) are also lower than those in Mongolia side (1.20×10^-6 and 1.41×10^-6). The median and average values of the arc basin system in the Gobi Altay, the arc basin system in the southern margin of Altay and the Altay tectonic belt are higher than other tectonic belts, showing that niobium and tantalum are enriched in those area. The total of 13 niobium and 13 tantalum geochemical anomalies have been delineated respectively based on the 85% cumulative percentage, and 7 niobium and 10 tantalum geochemical provinces have been selected. The work fills the gap in the niobium and tantalum geochemical distribution and provides important data for the comparison of deposits in the study area.

Significance of the Correction Parameters of Variation Coefficient in Regional Geological Evaluation

LIU Mingyi, ZHANG Jing, MENG Guanglu, HU Li

2018, 32(05):  1074-1079.  DOI: 10.19657/j.geoscience.1000-8527.2018.05.20

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By summarizing and studying the data of geochemical divisions in the west Tianshan of Xinjiang,China, the enrichment coefficients of 12 common ore-forming elements are calculated;the correction coefficients formula is put forward, and variation coefficients are reasonably corrected and sorted.Combining with the case deposit and mineralized points,the validity and applicability of correction coefficients is confirmed and the restrictive relationship between enrichment coefficients and variation coefficients in ore-forming process is summarized. By this way, it is possible to compare the ore conditions among different ore-forming elements and the applicability of geochemical parameters is broadened.Besides,the study improves the accuracy of geochemical evaluation methods in low exploration degree areas and provides scientific basis for geochemical evaluation.

Thermoluminescence:An New Tool for Natural Gas Hydrate Exploration

ZHANG Fugui, WANG Chengwen, ZHANG Shunyao, ZHOU Yalong, TANG Ruiling

2018, 32(05):  1080-1088.  DOI: 10.19657/j.geoscience.1000-8527.2018.05.21

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The development of geochemical exploration technologies unaffected by marsh microorganisms is necessary to improve the prediction of wells and to explore natural gas hydrates in mid-latitude permafrost areas. The potential of thermoluminescence as a new tool for the investigation of gas hydrates in permafrost areas was studied in this paper. The study area, 150 km² in size, is located in the alpine-arctic swamp landscape of the Qilian Mountains. The sampling density and depth were 2 points/km² and 60 cm, respectively. In total, 300 soil samples were collected and the Thermoluminescent Dosimeter (TLD) was used in measurement of soil natural thermoluminescence. The results indicated that thermoluminescence anomalies were identified in the gas hydrate deposits. A comprehensive interpretation was conducted based on geological and geochemical survey results. The relationship between the hydrocarbon of gas hydrates anomalies and thermoluminescence anomalies was further explored. We proposed a geogas migration mechanism of soil thermoluminescence in the soil above the natural gas hydrate deposits. The soil thermoluminescence anomalies near the ground surface of the Muli Coalfield in the Qilian Mountains, derived from the deep hydrate deposits and fault structure, are not affected by marsh microorganisms; they are effective tools for natural gas hydrate exploration in permafrost areas.

Research on the Methane Emission and Carbon Isotope of Permafrost Wetland in Qinghai-Tibet Plateau

ZHANG Shunyao, YANG Fan, ZHANG Fugui, SHI Zeming, YANG Zhibin, ZHOU Yalong, WANG Huiyan

2018, 32(05):  1089-1096.  DOI: 10.19657/j.geoscience.1000-8527.2018.05.22

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As one of the most important wetland area component, carbon cycle in Qinghai-Tibet Plateau plays a critical role in the terrestrial ecosystem. For systematically studying the methane emission of permafrost wetland in Qinghai-Tibet Plateau, by using the chamber method, we made a field measurement on the methane carbon isotope. Furthermore, combining with the adsorbed gas chromatography result, we conducted the gas source discrimination. The results show that the soil methane emission is the highest and mainly on biogenic source in spring. In summer, methane of soil emission is mainly on mixed-genetic source. In autumn, the soil methane emission is the lowest and mainly on thermo genic gas. The biological action is the main influence factor of methane emission. Meanwhile, the gas escaped from the natural gas hydrate underground also influenced the atmospheric methane content to some extent.

Investigation of the Village Ponds and Environmental Quality Assessment in Dongshan Karst Area, Mengzi,Yunnan Province

LIAO Hongwei, LI Shehong, YAN Song, SU Yangyang, LI Yujing, FU Song

2018, 32(05):  1097-1102.  DOI: 10.19657/j.geoscience.1000-8527.2018.05.23

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There are 22 village ponds in the Dongshan karst area for investigation in Mengzi, Yunnan Pro-vince. Based on pH analysis, the village ponds is belong to the neutral-alkaline water quality. The average concentrations of ammonia-nitrogen and TP in ponds are 1.66 and 0.68 times as those of the class Ⅴ on the surface water. The average concentrations of TN and SO₄^2- in ponds are 3.37 and 16.24 times as those of the class Ⅴ on the surface water. On the other side, the average concentrations of Mn, Cu, Zn, Cd and Pb in ponds are 651.54, 3.77, 21.74, 5.90 and 4.10 times as those of class Ⅴ on the surface water. These reservoirs were polluted heavily by heavy metals. The village ponds pollution was widespread and serious in Dongshan karst area, and the water is class Ⅴ. The concentration of Zn and Cd in Baigu village reservoir is 446.1 and 86.5 times as class Ⅴ water. The local population and the government should pay more attention to these situation.

Geochemical Characteristics of Soil Nutrients in Xinmin-Lierbao Area of Minhe County, Qinghai Province

FU Song, DING Yujin, ZHANG Xinyuan, WANG Wei, LI Shehong

2018, 32(05):  1103-1108.  DOI: 10.19657/j.geoscience.1000-8527.2018.05.24

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Based on the soil geochemical survey in Xinmin-Lierbao area, we collected 574 soil samples for geochemical analysis and testing. The pH values and nutrient indicators,such as organic matter, nitrogen (N), phosphorus (P), potassium (K), sulfur (S),water soluble calcium (Ca) and magnesium (Mg), were discussed. The study area mainly belongs to alkaline-strong alkaline, rich K, medium rich P, poor N soil, S exceeding in some areas. In the comprehensively researched evaluation, there are first and second rich levels accounting for 31.99%, the middle rich levels accounting for 43.8%, the low-middle rich levels accounting for 24.07% and the poor levels accounting for 0.15% in the study area. The results provide reference for soil improvement and high efficiency in the study area.