Table of Content

05 March 2020, Volume 34 Issue 01

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Mineralogy and Ore Deposits

Research on Auriferous Pyrite in Hydrothermal Gold Deposits, China

LIU Yihao, XUE Chunji, ZHAO Yun, ZHAO Xiaobo, CHU Haixia, LIU Chengxian, YU Liang, WANG Lu, WU Dehai

2020, 34(01):  1-12.  DOI: 10.19657/j.geoscience.1000-8527.2020.01.01

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Pyrite is the main auriferous mineral in hydrothermal gold deposits. The auriferous properties of pyrite have been researched in many single deposits and some related experiences were accumulated. But it’s rare of the synthetic and quantitative studies and an universal understanding about properties of auriferous pyrite is paid much attention. In this paper, based on mineralogy and chemical compositions of pyrite in various types (including Carlin, orogenic, magmatic-hydrothermal and epithermal gold deposits) of hydrothermal gold deposits in China, the quantitative and comprehensive studies about auriferous properties of different grain sized, various crystalline form and varied As contents pyrite have been conducted. It’s suggested that the auriferous properties of pyrite are mostly negative correlated with its grain size (the correlation coefficients range from -0.049 to -0.783) and idiomorphic degree (correlation coefficients range from -0.049 to -0.989), positive correlated with its As contents (correlation coefficients range from 0.189 to 0.998).The auriferous properties of fine grain, allotriomorphic crystal form and high As contents pyrite are mainly better than that of coarse grain, idiomorphic crystal form and low As contents pyrite. Compared with the coarse and idiomorphic crystal form pyrite, the fine grain and allotriomorphic crystal form pyrite can easily wrap up gold in its lattice defects formed in non-ideal growth conditions. The high As contents pyrite mainly formed through As isomorphism substituting S in pyrite and can easily produce lattice defects, in which the gold hosted, because of the different chemical property of As and S. These may be some reasons for the auriferous properties of pyrite above. The invisible gold in the pyrite may convert into visible one by dissolving, migration and re-precipitation in hydrothermal systems.

Mineral Geochemistry Characteristics and Genesis of the Multicolor Qingtian Stone from Zhejiang Province

SHEN Chonghui, BAI Feng, YANG Xiaoyan, WANG Yukun

2020, 34(01):  13-14.  DOI: 10.19657/j.geoscience.1000-8527.2020.01.02

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Multicolor Qingtian stone is one kind of Qingtian stones from Zhejiang province, shows all kinds of colors and varied textures. In this study, based on the analysis of the petrography, X-ray powder crystal diffraction phase, whole rock major, trace elements and isotope geochemistry for the multicolor Qingtian stone, we have verified the petrologic features, mineral compositions and type divisions, and discussed the ore-forming materials, ore-forming fluids and genesis. Studies have shown that the multicolor Qingtian stone belongs to pyrophyllite-type Qingtian stone and sericite-type Qingtian stone according to the main mineral compositions. The color of the multicolor Qingtian stone is mainly related to the content of colored elements (e.g.Fe, Ti ,Cr and Mn), and has a little of relationship with mineral microcrystalline particles and micro-cracks of hematite (limonite) impregnation of constituent minerals. The ore-forming materials of the multicolor Qingtian stone sourced from medium-acid volcanic rock, and ore-forming fluids sourced from meteoric waters. The multicolor Qingtian stone is mainly composed of filling-genesis pyrophyllite in the early stage and sericite that formed by medium-low temperature hydrothermal alteration on the filling-genesis pyrophyllite in the late stage. It derived from multi-period and multi-stage of hydrothermal alteration metasomatism. Multicolor Qingtian stone often retains high temperature mineral andalusite.

Petrology

Geochronology and Geochemistry Characteristics of Volcanic Rocks from the Daxiyingzi Gold Deposit in Chifeng, Inner Mongolia

LIU Changfeng, ZHAO Shouheng, ZHANG Haoran, LANG Hailong, ZHANG Fengjuan, LIU Wencan

2020, 34(01):  27-39.  DOI: 10.19657/j.geoscience.1000-8527.2020.003

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The Daxiyingzi gold deposit is hosted by Manitu Formation volcanic rocks, and is located at Chifeng, Inner Mongolia. We undertake zircon U-Pb dating and whole-rock geochemical analyses of the volcanic rocks from Daxiyingzi, with the aim to constrain the formation age and tectonic evolution of the volcanic rocks. The volcanic rocks mainly consist of andesite, trachyandesite and trachyte. LA-ICP-MS U-Pb zircon dating of the andesite and trachyandesite yield Late Jurassic (~157 Ma) age. The volcanic rocks are featured by their high alkali and Al₂O₃ contents, and are high-K calc-alkaline to alkaline. The volcanic rocks are also characterized by their moderately-enriched light rare earth element (LREE) patterns and high abundances of Th, U, Zr, and Hf, but negative Nb, Ta, and Ti anomalies. These features indicate that the mafic rocks were likely formed by partial melting of the lithospheric mantle metasomatized by subduction, and the AFC process likely played an important role in the magmatic evolution. Combined with previous studies on the contemporaneous tectono-magmatic activities in the northern North China Craton, we suggest that the volcanic rocks were formed in a post-orogenic extensional setting, possibly related to the closure of Mongol-Okhotsk Ocean.

Zircon U-Pb Age and S-Pb Isotope Features of the Bieluwutu Copper-polymetallic Deposit and Their Geological Significance

GUO Shuo, HE Peng, LIU Yang, TENG Fei, HU Xiaojia, WANG Wenlong, YANG Zeli

2020, 34(01):  40-50.  DOI: 10.19657/j.geoscience.1000-8527.2019.011

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To clarify the metallogenic age and genesis of the Bieluwutu copper-polymetallic deposit, zircon U-Pb age of the ore-related rhyolite and sulfide S-Pb isotopes were analyzed. The weighted mean zircon ²⁰⁶Pb/²³⁸U age of the rhyolite is (271.7±1.6) Ma (MSWD=1.02). This suggests that the ore-related rhyolite and the Bieluwutu copper-polymetallic deposit was formed in the Permian. Sulfur isotope data show that the δ³⁴S_V-CDT variation is small (-0.6‰ to 1.0‰, average 0.49‰), implying that the sulfur may have come from a single source. The sulfide lead isotope compositions are relatively consistent, i.e., ²⁰⁶Pb/²⁰⁴Pb (18.207-18.674), ²⁰⁷Pb/²⁰⁴Pb (15.620-15.699) and ²⁰⁸Pb/²⁰⁴Pb (38.144-38.790), featuring a mixed crust-mantle source. These S-Pb isotopic compositions indicate that the ore-forming materials were principally originated from magmatism. Evidence from regional and local geology, mineralization zonation and sulfur and lead isotopes support that the Bieluwutu copper-polymetallic deposit belongs to VHMS-type and was formed in an intra-arc rift during the Permian.

Zircon U-Pb Ages, Geochemistry and Tectonic Implications of Adamellite in Ophiolite Mélange Belt in South Altyn Tagh

LI Qi, WANG Jiangtao, ZENG Zhongcheng, SHI Wei, LI Hui, GUO Qianyi

2020, 34(01):  51-63.  DOI: 10.19657/j.geoscience.1000-8527.2019.012

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The large Yusupuleke Tagh batholiths intruded the Mangya ophiolite mélange belt in South Altyn Tagh. We carried out detailed geochronologic and geochemical analyses on the adamellite from the Yusupuleke Tagh batholiths. LA-ICP-MS zircon U-Pb dating yielded a Late Ordovician to Early Silurian weighted average age of (443.7±2.3) Ma. Geochemical analysis show that the rocks are characterized by high SiO₂(73.72%-75.08%), low TiO₂(0.11%-0.21%), low CaO (0.63%-1.45%), alkali-rich(N₂O+K₂O=7.19%-8.16%),high K₂O(K₂O/Na₂O=1.32-1.56) and low Mg^#(15.95-28.94) contents and A/CNK=1.11-1.26, suggesting high-K calc-alkaline and peraluminous affinities. REE distribution patterns show negative Eu anomalies, and distinctly high value of LREE/HREE. The chondrite-normalized REE patterns are right-inclined, with a clear V trough. The adamellite is rich in large ion lithophile elements (LILEs, e.g., Cs, K, Pb) as well as Th and Nd and depleted in high field strength elements (HFSEs, e.g., Nb, Ce, Ti) as well as Ba and P. Such geochemical features indicate that the rocks were formed by the partial melting of metamorphic sandstones in the middle-lower crust under a post-collisional setting. Considering the regional geology, the adamellite was likely formed in a compressional to extensional transition tectonic regime, younger than the previously reported ages in South Altyn Tagh. This suggests that the subduction and collision between the Azhong Block and Qaidam Block had occurred, and that the South Altyn Tagh ocean basin had completely closed at about 443 Ma.

Geochemical Characteristics and Geological Significance of Silurian Volcanic Rocks of Balonggongge’er Formation in Southern Qilian Mountain(withdrawal)

CHAI Yun, ZHAO Juan, LI Debiao, MA Zhengting, AN Zhao, WEI Youning, WANG Chengyong

2020, 34(01):  64-73.  DOI: 10.19657/j.geoscience.1000-8527.2019.013

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Volcanic rocks of the Balonggongge’er Formation in the Calete area are composed of calc-alkaline pyroclastic rocks and volcanic lavas. LA-MC-ICP-MS zircon U-Pb dating on the meta-dacite of this formation yielded an age of the Late Silurian according to the weighted average age of (418.7±2.7) Ma, representing the first age reported for this formation. Geochemical data show that the volcanic rocks are featured by their high Al₂O₃ and low TiO₂, relatively high total rare earth element contents (ΣREE), LREE enrichments, distinct LREE/HREE fractionation and negative Eu anomalies. The rocks show marked enrichments in Rb, Th and K, slight enrichments in La, Ce, Ba and Nb, and depletions in Nb, Sr, P and Ti. Comprehensive analysis indicates that the volcanic rocks in this area were formed in a continental arc setting.

Geochemical Features and Genesis of Dolomite in Sinian Dengying Formation of Zigui Area, Hubei Province

MA Jiayi, XIE Shuyun, ZHANG Mohai, JIAO Cunli, HAN Jun, BAO Zhengyu, WU Tie, ZHANG Hai

2020, 34(01):  74-87.  DOI: 10.19657/j.geoscience.1000-8527.2020.004

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Fluid properties of dolomitization and dolomite diagenesis is a hotspot of carbonate diagenesis research in recent years. It is very important to study the genesis of dolomite and to understand the formation mechanism of dolomite reservoirs, which can be used to predict high-quality reservoirs. In this paper, the genesis of dolomites in Dengying Formation in Zigui County has been studied systematically via petrological, mineralogical (X-ray diffraction), and geochemical (trace elements, REEs and carbon-oxygen isotopes) analyses, and possible dolomitization patterns were inferred. According to the trace element characteristics, the Zigui dolomites had not been affected by terrigenous debris, and were formed in an arid, highly-saline seawater and oxidizing environment. The Sr contents show that the dolomites have been completely dolomitized, and the diagenetic environment was likely a high-temperature burial one with no effect of syn-diagenetic leaching. The dolomitized fluids were mainly derived from seawater. Based on the results above, we proposed the evaporite dolomite (Sabuha) and burial dolomitization models to account for the formation of mud microcrystalline dolomite and crystalline dolomite in Zigui area.

Geochemistry

Spatial Distribution Characteristics and Influencing Factors of Soil Cadmium Content in Jieyang of Guangdong Province

WANG Juanheng, WEN Hanhui, CAI Limei, LUO Jie, WANG Shuo, WANG Qiushuang, MU Guizhen, JIANG Huihao

2020, 34(01):  88-96.  DOI: 10.19657/j.geoscience.1000-8527.2020.01.08

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In this paper, 1,330 topsoil (0-20 cm) samples and 331 deep soil (150-200 cm) samples were collected from Jieyang, Guangdong, China. The enrichment characteristics, spatial distribution, structural characteristics and influencing factors of soil cadmium content in the study area were systematically analyzed by the methods of enrichment factor, GIS spatial analysis, semi-variogram fitting and analysis of variance. The results showed that the average cadmium content in the topsoil was 0.09 mg/kg, which was higher than the soil background value of the area, but lower than “Soil Environmental Quality Risk Control Standard for Farmland Soils (Trial)(GB 15618-2018)”. According to the enrichment factor method, the cadmium content in topsoil of the study area was mainly slightly and moderately polluted. From the structural characteristics, the cadmium content in the topsoil of the study area was moderately spatially correlated. The high value areas of cadmium in topsoil of Jieyang City were mainly distributed in the eastern and southern areas where human activities were intensive. Land use types, soil parent materials and soil types were important factors affecting cadmium content in surface soil. Under different land use types, the cadmium content in construction land was the highest; In different parent materials, the cadmium content in the Quaternary sediments was significantly higher than other parent materials; In different soil types, the cadmium content in paddy soil was relatively high.

Geochemical Characteristics and Influencing Factors of Germanium n Surface Soil of Changshan County, Zhejiang Province

LIU Daorong

2020, 34(01):  97-103.  DOI: 10.19657/j.geoscience.1000-8527.2020.01.09

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Through the investigation and study of surface soil in Changshan County, western Zhejiang Province, the characteristics of germanium content in soil have been identified for the first time. The content of germanium in the surface soil of the study area ranges from 0.87 mg/kg to 5.59 mg/kg, with an average of 1.59 mg/kg, which was slightly lower than the value of the Chinese soil(1.70 mg/kg). The average content of germanium in surface soil of different parent materials is slightly different, ranging from 1.50 mg/kg to 1.73 mg/kg. The content of germanium in granite weathering is the highest, quartz sandstone weathering is the lowest, and germanium content in other parent materials is close. The content of germanium in different soil types ranges from 1.45 mg/kg to 1.62 mg/kg, with the highest germanium content in yellow earth and the lowest in fluvo-aquic soil. Germanium content in other types of soils range from 1.51 mg/kg to 1.61 mg/kg. The germanium content of sandstone, siltstone and mudstone with higher argillaceous content is higher, reaching 1.75-1.95 mg/kg, while the germanium content of dolomite and limestone is lower, only 0.12-0.20 mg/kg. The large scale distribution of sandstone, mudstone and siltstone which are high germanium content in Changshan County is the main reason for the relatively high germanium content in soil.

Marine Geology

Archaeal Diversity in Sediments of Core 973-5 from Deep-sea old Seep,Dongsha Area in South China Sea

TENG Tiantian, SU Xin, LIU Haodong, CUI Hongpeng, CHEN Fang, CHENG Sihai, YANG Shengxiong, WANG Hongbin, LIANG Jinqiang, SU Pibo

2020, 34(01):  104-116.  DOI: 10.19657/j.geoscience.1000-8527.2019.009

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Cold seeps are well developed in Dongsha area, South China Sea, but researches on microbes in cold seeps have been inadequate, especially when the high-throughput sequencing technique is used. In this paper, the archaeal diversity of gravity core 973-5 was analyzed based on high-throughput sequencing. The core was 935 cm long and was collected from the deep-sea cold seep area in Dongsha at a depth of approximately 3,000 m. The cell abundance in the sediments collected by core 973-5 varied from 5.3×10⁸ to 34.0×10⁸ cells/g,which increased with depth. The change trend of cell abundance was similar to that of the methane content. Additionally, it was related to the grain size and total organic carbon (TOC) content. The results obtained using high-throughput sequencing revealed that the predominant archaeal groups were MBGB, C3 and ANME-1,which accounted for 39.9%, 15.8% and 12.0% of the total sequences of archaeal communities, respectively, changing with depth. Large amounts of MBGB and ANME-1 along with the rise of pH in the sediments near the sulfate-methane interface (SMI) at approximately 760 cm might indicate the process of methane anaerobic oxidation. At the bottom of the core, considerable amounts of ANME-1 and ANME-2 were detected. This might demonstrate intensive methane-sulfate redox reaction near SMI as well as the decomposition of gas hydrate and upwelling of methane in the lower part of the core, which are possible nutrients for the ANME group. Compared with other sites in Dongsha area, the higher methane flux was observed in core 973-5, but no methanogens were detected. This suggests that the large quantities of methane might have been transported from the shallow and deep fracture system nearby.

Heat Flow Characteristics in Marginal Seas of the Northwestern Pacific Ocean

JIANG Dexin, JIANG Kunpeng, ZHANG He, JIANG Zhenglong

2020, 34(01):  117-129.  DOI: 10.19657/j.geoscience.1000-8527.2019.008

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In this study, we combined the latest collected heat flow data to illustrate the heat flow characteristics of the marginal seas and their corresponding subduction systems in the northwestern Pacific Ocean.We analyzed the relationship between the heat flow distribution and the geological background of the deep tectonic activities, mainly focusing on the thermal structural theory of Northwestern Pacific subduction zone, the theoretical model of the thermal evolution of the marginal oceanic lithosphere, and the controlling factors of the local high anomalous heat flow. We summarized the geological significance of the heat flow in the northwestern Pacific Ocean. The results show that the heat flux is characterized by “low-high-relatively high” from “trench” to “arc” to “marginal sea” of the “Trench-Arc-Sea” system in the northwestern Pacific Ocean, and overall the back-arc region is uniformly hot. Heat flux of the Kuril-Kamchatka, Japan and Ryukyu trenches is about 30.0 mW/m², and their corresponding island arc heat flux value is two to three times above this value. The back-arc heat flow is likely affected by the thermal structure of the subduction zone. The small-scale mantle convection, caused by the changes of upper mantle viscosity because of the subducting slab dehydration, the decrease of seismic velocity and the lithosphere elastic thickness, can explain the uniformly-hot thermal state in the back-arc environment. The spatial-temporal heat flux distribution is also related to the age of the lithosphere. As the age of the lithosphere increases, the surface heat flux decreases. Magnitude and dispersibility of the heat flux in the marginal seas are in general negatively correlated with their formation time. Formation of the Sea of Okhotsk is relatively early (30-65 Ma), and thus the heat flux (86.8 mW/m²) and standard deviation (3.727) are relatively low. In contrast,the Okinawa Trough is still expanding, thus its heat flux (139.0 mW/m²) and standard deviation (7.001) are relatively high.Shallow groundwater circulation, fault, partial melting and magma activity in the deep mantle, small-scale mantle convection and the corner flow likely control the local anomalous heat flow in the back-arc systems.

Geochemical Contrast in Sediments from Active and Inactive hydrothermal Fields on the Southwest Indian Ridge

SONG Bei, SU Xin, LÜ Shihui, NI Jianyu, LIAO Shili, TAO Chunhui, HU Maokang, LI Shiyun, YU Chonghan

2020, 34(01):  130-140.  DOI: 10.19657/j.geoscience.1000-8527.2019.010

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The Longqi and Duanqiao areas are two typical active and inactive hydrothermal fields respectively on the ultra-slow spreading Southwest Indian Ridge (SWIR).For studying the geochemical features between these two regions, 59 seafloor sediments are compared with the material compositions, enrichment factors (EFs) and cluster analysis after major and trace elements test. The results reveal that the two regions show similarities in high contents of biogenic (e.g.Ca, Sr and Ba) and surrounding rock elements (e.g.Fe, Mg, Si and Al),and differences in structure, surrounding rock condition and hydrothermal activities, leading to differential geochemical behaviors of their sediments. We found extra ultramafic rock components in the sediments of Longqi area, where sediments are relatively enrich in hydrothermal elements such as Cu, Zn, Fe and Co. The higher contents of biogenic components in the Duanqiao area, where the hydrothermal related elements are characterized by the obvious enrichment of Pb and W, reflect the biological sedimentation playing dominant roles after hydrothermal activities stopped. Furthermore, the R type cluster analysis gives expression to the extra ultramafic components solely in Longqi area and close connections between hydrothermal activities and mafic base rock in Duanqiao area.

Deposition System and Stratigraphy of Pinghu Formation in Pinghu Tectonic Belt, Xihu Sag

JIANG Yiming, SHAO Longyi, LI Shuai, ZHAO Hong, KANG Shilong, SHEN Wenchao, YI Qi

2020, 34(01):  141-153.  DOI: 10.19657/j.geoscience.1000-8527.2020.002

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In this paper, depositional system and stratigraphy of Pinghu Formation in Pinghu tectonic belt of Xihu Sag were discussed in detail based on the drilling, core logging and seismic data. The paleo-salinity and paleo-water depths were also discussed based on mudstone geochemical compositions. The results show that the bottom of P7 sand group in the middle part of Pinghu Formation is bounded by the fault-depression transition. The fault system controls the distributions of sedimentary facies before the P7 sand group deposited. Above the P7 sand group, however, the influence of fault system on the distribution of sedimentary facies reduced gradually until it disappeared. Paleo-salinity analysis shows that Pinghu Formation is mainly characterized by fresh water deposition, and semi-salt water deposition developed intermittently. Paleo-water depth analysis indicates that the water depth was generally 0-8 m, and reached a maximum in the 3rd member of the Formation (nearly 14 m). Pinghu Formation can be divided into three 3rd order depositional sequences from bottom to top, corresponding to the 5th, 4th to 3rd, and 2nd to 1st member, respectively. The overall depositional setting of tidal flat to deltaic system was developed when Pinghu Formation deposited. During the deposition of sequence I, the sedimentary environment was largely deltaic, and was controlled by the NE-SW-trending fault system. During the deposition of sequence Ⅱ, the faulting influence decreased but the tidal influence increased, and the environment was dominated by tidal flat with local tidal channels. During the deposition of sequence Ⅲ, marine regression occurred gradually, forming tidal flat and tidal-influenced deltaic systems under the background of broad and gentle slope.

Mineral Characteristics, Provenance and Climatic Significance of Wetland Sediments from Dalinghe River Estuary in Liaohe Delta Since Late Pleistocene

GUO Ruoshun, HE Lei, YE Siyuan, ZHAO Lihong

2020, 34(01):  154-165.  DOI: 10.19657/j.geoscience.1000-8527.2020.001

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A total of 58 samples were collected and analyzed for detrital minerals and clay minerals in drillhole ZK3 in the Dalinghe River Estuary. The research reveals that the light minerals account for the majority (average 95.7%) of the sediments, and include mainly plagioclase (43.89%), K-feldspar (28.10%) and quartz (22.45%). Heavy minerals only account for 4.3% of the sediments, and consist mainly of hornblende (38.03%), epidote (27.51%) and authigenic barite (12.01%). Clay minerals comprise mainly illite (50.3%), followed by smectite (24.5%), chlorite (12.7%) and kaolinite (12.6%), constituting an illite-smectite-chlorite-kaolinite assemblage. The sediment provenance of core ZK3 is quite complicated across the geological history. However, except the provenance of the river channel and lacustrine sediments may come from the Dalinghe River, the sediments of other facies were derived mainly from the Liaohe and Daliaohe rivers. Paleoclimatic change, inferred by comprehensive analysis of clay minerals, corresponds well with pollen studies in the Liaohe Delta: in 45~31 ka BP, the smectite/(illite+chlorite) ratios are relatively high, implying a warm and wet climate; in 31~11 ka BP (Lushan inter-glacial stage), the smectite/kaolinite ratios are low, indicating a cold and dry climate during the Dali ice age stage; from 11 ka BP to present (after the end Younger Dryas (YD)), the temperature gradually rises with rising smectite/(illite+chlorite) ratio, which reveals a post-glacial hot and wet climate.

Paleoenvironmental Evolution in the Guadalupian (Permian) Gufeng Formation in Chaohu Area,Anhui

TANG Zhanwen, WEI Hengye

2020, 34(01):  166-176.  DOI: 10.19657/j.geoscience.1000-8527.2020.005

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The Guadalupian (Permian) period was a critical transition of paleo-ocean conditions. The effect of the paleo-ocean and paleo-environmental conditions on the Guadalupian mass extinction of benthic paleo-invertebrates is still a mystery. Here, we analyzed terrestrial detritus input, surface water primary productivity and bottom water redox conditions in the Guadalupian Gufeng Formation via elemental geochemistry. The results show high terrestrial detrital inputs in the Early and Late Guadalupian. The primary marine productivity was the highest in the Early Guadalupian, low in the Middle Guadalupian, and relatively high in the Late Guadalupian. The paleo-water column was mainly anoxic to euxinic in the Guadalupian. The Early Guadalupian was mainly suboxic-anoxic with intermittent euxinic episodes, while the Middle-Late Guadalupian was mainly euxinic with intermittent anoxic episodes. The environmental redox evolution may have controlled mainly by hydrodynamic conditions. The persistent anoxia/euxinia of the deep-water environment in the Guadalupian may have led to persistent suboxia (or even anoxia) of the shallow-platform bottom water, causing vulnerability to the marine ecosystem and eventually biocrisis events.

Hydrogeology

Characteristics and Formation of Salty Springs in Yanyuan County of Sichuan

LI Na, ZHOU Xun, GUO Juan, TA Mingming, XU Yanqiu

2020, 34(01):  177-188.  DOI: 10.19657/j.geoscience.1000-8527.2020.01.16

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Studies of the formation of natural salty springs are helpful in revealing the migration of substance during hydrological circulations in the land. In this paper, hydrogeochemical methods are used to analyze the hydrochemical and isotopic characteristics of nine samples of the springs and brine in Yanyuan County of Sichuan Pro-vince, explore the source of the solutes in the water samples, and summarize the genetic model of the salty springs. The samples include the brine sample with TDS of 311.69 g/L and Cl-Na type, salty springs with TDS of 55.77-89.43 g/L and Cl-Na type,brackish spring with TDS of 1.17 g/L and Cl-Na type and fresh springs with TDS of 0.26-0.56 g/L and mainly HCO₃-Ca and HCO₃·SO₄-Ca·Mg types. The stable hydrogen and oxygen isotopes of the water samples indicate that the springs are of meteoric origin. The characteristic ion ratios show that they are of lixiviation type and have no indications of potash prospecting. The salinity of the springs is mainly derived from the incongruent dissolution of minerals such as halite, gypsum, calcite and dolomite. The formation mechanisms of salty springs are summarized as follows: after receiving infiltration of precipitation in the mountain areas, groundwater undergoes shallow and deep circulations, obtains increasing TDS as a result of the incongruent dissolution of salt-bearing strata or salt mines, and gather in lower topography to emerge to the land surface in the form of springs.

Prediction of Regional Groundwater Quality Evolution Affected by Human Activities: A Case Study of Shijiazhuang Area

SHAN Xiaojie, HE Jiangtao, ZHANG Xiaowen, SUN Jichao

2020, 34(01):  189-198.  DOI: 10.19657/j.geoscience.1000-8527.2020.006

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Prediction of groundwater quality evolution has always been a difficult issue, with its implications largely limited by the sole dependence of historical data for the evaluation. Taking Shijiazhuang area as the stu-dy area, we put forward a method to revise the water quality evolution trend shown by historical data, and predict the water quality change by using the degree of current human activity influence on groundwater as a correction factor. The four major indices of shallow groundwater at Shijiazhuang (i.e., total hardness, TDS, $NO_3^-$ and Fe) were used as prediction indices for the evolution of representative indices in 2025. The results show that the water quality deterioration areas for TDS and total hardness are mainly in the southeastern part of the Lingshou County, Gaocheng District and Wuji County near the Hutuo River. The deterioration areas for Fe are mainly distributed in the central and southeastern parts of Shijiazhuang City, and those for $NO_3^-$ are near the junction of Luquan District and Lingshou County, northwestern Shijiazhuang City and around the Hutuo River in Gaocheng District. The predicted results are in good agreement with the hydrogeological conditions, the man-made pollution sources and groundwater extraction in the study area.

Characteristics and Hydrogeological Significance of Hydrothermal Dissolution in Carbonate Rocks from Laiwu Basin, Shandong Province

LIU Yuanqing, ZHOU Le, LI Wei, WANG Xinfeng, MA Xuemei, LÜ Lin, DENG Qijun, CHEN Chen

2020, 34(01):  199-206.  DOI: 10.19657/j.geoscience.1000-8527.2020.007

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In the Yanshanian period, large-scale magmatic intrusion occurred in the Laiwu Basin. Certain water source areas, karst and water-rich blocks were developed in carbonate rocks around the intrusions. Marbleization often occurs in the carbonate aquifers near the intrusions. Magmatic-hydrothermal fluids, which are rich in acidic components such as CO₂ and H₂S, can cause significant dissolution of carbonate rocks. The mechanism and characteristics of hydrothermal dissolution in the Laiwu Basin were identified via analyzing the chemical composition of rock samples, hydrogeological surveying and data statistical analysis, together with detail observation on the hydrothermal dissolution spots. Consequently, the hydrothermal dissolution model for the region was constructed. The results show that the high-temperature/-pressure magmatic intrusions likely caused the marble metamorphism of carbonate rocks in the contact zone. Hydrothermal fluids migration along permeable faults, fissures and unconformities could cause acidic hydrothermal dissolution and mixed dissolution in the carbonate formation, and formed dissolution cavities of different scales. The cavities constitute the current sites of groundwater enrichment, and provide a new direction of water reserve exploration for towns and cities.

Geothermal Resource Evaluation in Changping New Town, Beijing:Perspective from 3D Geological Modeling

ZHU Zhenzhou, LEI Xiaodong, WU Xiong, XU Nengxiong, JIANG Xingyu

2020, 34(01):  207-214.  DOI: 10.19657/j.geoscience.1000-8527.2020.008

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As a clean renewable energy, geothermal energy has played an important role in improving the atmospheric quality of Beijing. This study evaluates the geothermal resource in the Changping New Town, Beijing, and provides scientific basis for rational utilization of geothermal resource in this area. After analyzing the geological and geothermal conditions in the study area, we built a 3D geological model of the Changping New Town, which is used to calculate the volume of reservoirs,then the geothermal reserve is calculated with the volumetric method, and the geothermal resource distribution is analyzed. 3D geological modeling is used to visualize the local geological structures and calculate the geothermal reserve. The estimated reservoir volume in the study area is 4.88×10¹¹ m³ and the geothermal reserve is 5.42×10¹⁶ kJ. The exploitable volume of geothermal fluid is 6.04×10⁶ m³. The geothermal resource in the study area is likely of great potential, and can support locally green development.