Table of Content

28 October 2020, Volume 34 Issue 05

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Geochemistry

Construction and Test of Geochemical Genes: Case Studies in China

GONG Qingjie, WU Xuan, YAN Taotao, LIU Ningqiang, LI Xiaolei, LI Ruikun, LIU Mengxiang

2020, 34(05):  865-882.  DOI: 10.19657/j.geoscience.1000-8527.2020.049

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Geochemical gene is a new technique presented recently. According to the construction steps of a geochemical gene, a new lithogene called LG01 was presented and the early presented lithogene was named as LG02. Meanwhile, two rare earth element (REE) geochemical genes were also presented labeled as REEG01 and REEG02. These geochemical genes were tested on four weathering profiles which are LY18D06 profile developed over the Lianyang granite intrusion located in Guangdong Province, TT profile formed on the Fogang granite intrusion also in Guangdong Province, HK06 profile formed on the Neogene basalt in Hainan Province, and ZKD2 profile developed over a granodiorite intrusion in Beijing, China. The results indicate that lithogenes and REE genes are stable or have subtle differences in the weathered products. Furthermore, LG01 gene is more stable than LG02 gene and REEG01 gene is more stable than REEG02 gene in these weathering profiles. The sample’s gene similarity relative to the acidic rock in China (a virtual sample with the elemental abundance of acidic rocks in China) is called acidic similarity. According to the acidic similarities of LG01 gene, samples can be classified into three groups as acidic-like composition, intermediate-like composition, and basic-like composition (or two groups as intermediate-acidic-like composition and intermediate-basic-like composition). The acidic similarity of LG01 gene can be used as a tool to recognize the provenance of soils or weathered products tested on samples from the four weathered profiles. Based on the regional geochemical survey database and the geochemical gene techniques, (forensic) geological samples may be traced or located.

Research Progresses on Applied Geochemistry from 2011 to 2020 in China: Eco-geochemistry

XIA Xueqi, GONG Qingjie, XU Changyan

2020, 34(05):  883-896.  DOI: 10.19657/j.geoscience.1000-8527.2020.05.071

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Based on geochemical survey,eco-geochemistry assessment focuses on the circling of the elements in the ecosystems. And also,it investigates the input and output fluxes of soil elements,compounds,and other geochemical variables in order to predict the trend of their circling and make early-warning of risks. During the recent decade,the theoretical frame and the related techniques are under development with the emergence of a lot of technical standards,published articles and books. Furthermore,social and economic benefits have been produced in the aspects of pollution control,management of land resources,development of distinctive agricultural products,and even soil carbon sequestration and global warming prevention. Theoretical and practical requirements have pushed forward the development of eco-geochemistry and its branches have been developed in the areas of soil carbon sequestration,soil heavy metal from “high background”,geochemical assessment of land quality,development of soil beneficial element,and soil pollution control and remediation. This paper aims to summarize the progress of eco-geochemistry in China during the past decade.

Geochemical Characteristics of Stream Sediments and Prospecting Implications in Shangri-La Wengshui Area, NW Yunnan

HUANG Yonggao, XIONG Changli, LUO Gai, ZHANG Tong, JIA Xiaochuan, YANG Xuejun, YE Chunlin, WANG Yi

2020, 34(05):  897-907.  DOI: 10.19657/j.geoscience.1000-8527.2020.58

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The Wengshui area is located in the southern Yidun Arc (NW Yunnan) and belongs to the Shangri-La arc-type porphyry Cu-Mo-W metallogenic belt. This area has good prospecting potential for polymetallic deposits such as Mo, W, Pb and Zn, where the large Xiuwacu Mo-W deposit and many other ore deposits/occurrences have been discovered. The 1∶50,000 stream sediment survey shows that the contents of Cu, W, Pb, Zn, Sn, As, Sb, Bi, Co and Ni at Wengshui are significantly higher than those in the average Sanjiang metallogenic belt, SW China. The element anomalies are clearly controlled by structure and lithology. Gold is mainly enriched in T₃lm ³; W, Mo and Bi are enriched in monzonitic granite pluton; and Pb, Zn are enriched in T₃t ². According to the spatial distributions of element anomalies and metallogenic conditions, we have delineated 29 integrated geochemical anomalies, and two prospecting targets including the Xiuwacu Mo-W Grade-A target and the Momoya Pb-Zn-Ag Grade-B target. This provides direction and important reference for further prospecting work.

Indium Distribution and Enrichment Characteristics in Gejiu Sn-Polymetallic Orefield Area in Yunnan Province

GUO Zhijuan, SONG Yuntao, XU Renting, WANG Chengwen, YANG Fan, WANG Qiaolin, HAN Wei, LIU Huazhong, KONG Mu

2020, 34(05):  908-916.  DOI: 10.19657/j.geoscience.1000-8527.2020.048

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Different types of rocks from the Gejiu Sn-polymetallic orefield in Yunnan province were studied for the indium (In) distribution features in the granite, sedimentary and metamorphic rocks.The In enrichmentregularity in ore minerals was also analyzed via plasma mass spectrometry, petrographic identification and high-precision electron probe microanalysis (EPMA). Our results show that In content in the granites has clear relation with Sn, which plays an important role in the In enrichment.Indium is distributed in the source of ore-forming materials in the intrusion, and the In enrichment coefficient is higher in porphyritic biotite granite. The indium is mainly concentrated in the skarn of Gejiu Group limestone ore host, and there is no distinct In enrichment in metamorphic rocks. The indium is highly concentrated in the interlayer oxide ore but only weakly enriched in the primary sulfide ore, and In has positive correlation with Sn and Zn in the two types of ores. Indium is detected by EMPA in sphalerite but not in cassiterite, which indicates that In enters sphalerite and other sulfide minerals rather than cassiterite during ore precipitation.

Ecological Risk Assessment of Heavy Metals in Farmland System from an Area with High Background of Heavy Metals, Southwestern China

TANG Ruiling, WANG Huiyan, LÜ Xupeng, XU Jinli, XU Renting, ZHANG Fugui

2020, 34(05):  917-927.  DOI: 10.19657/j.geoscience.1000-8527.2020.068

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Southwestern China contains high metals (HMs) background, and ecological risk assessment on HMs is important to ensure food security.A total of 242 soil samples (0-20 cm) and 74 sets of rhizosphere soil and crop samples were collected from high-HM background area in Yunnan Province. We analyzed the concentrations of Cd, Hg, Pb, As, Cu, Zn, Ni and Cr in the soil and crop samples, as well as the chemical forms of heavy metals in soil. The results show that most soil samples are acidic (low pH) and low organic matter (OM) content, and the mean Cd, Cr, Cu, Hg, Ni, and Zn contents in the topsoil all exceed the soil background value in Yunnan Province. The average Cd, Cu, and Ni contents are remarkably higher than the screening value specified in the soil contamination risk in agricultural land (GB 15618-2018). Speciation analysis indicates that the HMs (Cr, As, Pb, Cu, Zn, and Ni) mainly exist in the residual form, with low bioavailability and source from the background geology. Cd has a high bioavailability ratio. Distribution of geo-accumulation index (I_geo) of Cd shows that Cd is affected by the superposition of anthropogenic pollution and background geology, and represents the highest pollution risk in the study area. Mercury has a complex source with a low volume and low pollution risk. The HMs concentrations of the staple crops in the study area do not exceed the standard, and the bioconcentration factor (BCF) is below 0.03, thus the food crops are safe for consumption and ecological risks are low. The Cd concentration in tobacco far exceeds the preliminary safety limit standard, and the BCF is 3.13, indicating that tobacco can concentrate much Cd, and affect human health and pose ecological risks. The potential ecological risk index (RI) shows that the descending order of Cd>Hg>Cu>Ni>As>Cr>Pb>Zn, with the contribution ratios of 40.33%, 31.41%, 13.81%, 4.79%, 4.04%, 2.27%, 2.21%, and 1.13%, respectively. Mercury and Cd are the main source of risk because of their high toxicity coefficient.Both Hg and Cd present moderate risk, and the strong risk area is small. The overall ecological risk is low and the risk is controllable in the study area.

Heavy Metal Contents, Spatial Distributions and Their Relationships with the Grain Size of Surficial Sediments in Dingziwan, Shandong

TANG Shikai, ZHANG Jie, YU Xiaojing, TAO Zhibin, LI Jinpeng

2020, 34(05):  928-935.  DOI: 10.19657/j.geoscience.1000-8527.2020.059

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To elucidate the regularity of heavy metal content and grain size, 126 surficial sediment samples were collected from Dingziwan in Shandong Province. The sediment types and spatial distributions of heavy metal contents were summarized. Accordingly, the heavy metal contents, spatial distributions, and their relations with grain size were analyzed. The results show that sediment types are fan-shaped and grain size decreases offshore.Contents of Cr, Pb, Cd, and Hg increase, while the As content first decreases and then increases.The relations between heavy metal contents and grain size vary in different sediments.In sand, sandy silt and silt, clear positive correlation is present between Cr content and the average grain size.There is negative correlation between As content and the average grain size for sand, and positive correlation between As content and the average grain size for silt.The positive correlation between Hg content and the average grain size for sandy silt is the same as silt.There is no discernible correlation between other heavy metal contents and sediment average grain size.

Interaction of Heavy Metals and Other Elements in Soil-wheat System in Anqiu Area, Shandong Province

ZHAO Xiufang, WANG Yixuan, ZHANG Yongshuai, WANG Yanyan

2020, 34(05):  936-944.  DOI: 10.19657/j.geoscience.1000-8527.2020.063

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To study the interactions between heavy metals and other elements in the soil-wheat system, we perform correlation analysis and discuss the relations between 40 sets of wheat seed and their root soil elements. The results show that: (1) Enrichment coefficients of Cd, Hg, Pb, As, Ni, Cu and Zn in the wheat seed are negatively correlated with the soil pH, CEC and clay contents, whereas positive correlation exists between pH and Cr enrichment coefficient; (2) Enrichment coefficients of heavy metals and other elements in the wheat seed are mostly positively correlated; (3) In the wheat seeds, the Pb and Cu contents are positively correlated with the soil As and Pb contents, respectively, while the Cu and Zn contents in the wheat seeds are positively correlated with the Cd and Pb contents in the soil, respectively. Except that the Cr content in the wheat seeds is markedly positively correlated with the Mg content in the soil, there is no major relation between other heavy metals in the wheat seeds and Ca and Mg in the soil. The contents of some heavy metals (such as Cd, Pb and As) in the wheat seeds are positively correlated to the contents of trace elements (such as Mn, Mo and F) in the soil, but most of them are not highly correlated; (4) Contents of most heavy metals (such as Cd, Hg, Pb and As) in the wheat seeds show significant positive correlation with the contents of Ca, Mg, Mn and Mo in the wheat seeds. The above results indicate synergistic or antagonistic effects among heavy metals and other elements in the soil-wheat system, yet the actual mechanism would require further investigation.

Bimodal Mixing Model on the Dolomite Alteration Geochemistry in the Yangshudixia Gold Deposit in Huairou, Beijing

YAO Ning, GONG Qingjie, WANG Xuyang, CHAO Yuede, PENG Cheng, WU Yuan, LIU Ningqiang

2020, 34(05):  945-956.  DOI: 10.19657/j.geoscience.1000-8527.2020.062

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Altered rocks are important objects in the study of hydrothermal mineralization. The alteration belt is clear at the Yangshudixia gold deposit in the Huairou district of Beijing (China). A lateral surficial alteration profile on dolomite was selected to investigate the alteration geochemistry. Two dolomite samples were collected from each end of the profile, 2 altered samples with different alteration intensity were collected from the quartz vein in the profile, and 2 samples were collected from the quartz vein. Eleven major element oxides and 39 trace elements were analyzed on the 6 samples. The results indicate that the 2 dolomite and the 2 quartz vein samples have similar geochemical contents, while those of the 2 altered rocks are clearly different. Using the bimodal mixing model, two end-members of dolomite and quartz vein were first determined geochemically. Subsequently, the proportional function method and the plateau method were adopted to calculate the mixing ratios of the 2 altered samples based on the 11 major components. The calculation results show the technical defect of the proportional function method, in which the fitting results are much affected by the maximum value and the feasibility of the plateau method, and the median values were used to overcome the defect. According to the mixing ratios of the 2 altered samples calculated on 11 major components with the plateau method, the contents of other 39 trace elements were calculated on the bimodal mixing model for the 2 altered samples. Within the error of 0.3 log interval, the calculated values are similar to the analytical results. This indicates that the bimodal mixing model can well be used to explain the geochemical components of the altered dolomite at Yangshudixia. Our findings can help to reveal the formation mechanism of the dolomite alteration zone in the area.

Ecological Effect of A Typical Sulfide Deposit in Carbonate Area —Xijikeng Lead-Zinc Mine in Guigang, Guangxi

LI Bo, YANG Zhongfang, JI Wenbing, YU Tao, HOU Qingye, HE Haiyun, ZHANG Qizuan, WU Tiansheng, QIN Jianxun

2020, 34(05):  957-969.  DOI: 10.19657/j.geoscience.1000-8527.2020.05.09

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The environmental pollution effect of sulfide deposit mining is closely related to the surrounding rock properties. To a certain extent, the surrounding rock of carbonate can neutralize the acid mine drainage (AMD) produced by sulfide mining, so as to reduce the harm of AMD and heavy metals. In this paper, Xijikeng sulfide mining area in Guigang, Guangxi is selected as the research area. In order to study the ecological effects of mining of sulfide deposits in carbonate areas, the samples of ores, tailings, wastewater, surface water, suspended solids, deposits and groundwater were collected systematically in the study area, and they were measured physical and chemical indicators such as heavy metals content and pH. It is expected to provide a scientific basis for ecological hazard assessment and environmental protection of mining of sulfide deposits in similar carbonate areas. The conclusions are as follows: (1) The content such as Cd, Pb and other heavy metals in tailings and wastewater samples are relatively high, which has a great potential risk to the surface water and groundwater in the mining area; (2) For the sulfide deposit in carbonate rocks, the release of heavy metals in the mining process has a significant impact on the surface water in the mining area. But due to the neutralization of the carbonate rocks, the dissolved, suspended and deposited content of heavy metals will decrease rapidly after the surface water flows out of the mining area, and the potential risk of heavy metals is at a slight level; (3)The deep pit water in the mining area is rich in heavy metals. During the infiltration process, due to the buffering effect of a large number of Ca²⁺, $CO_{3}^{2-}$,$HCO_{3}^{-}$ in the carbonate area, the groundwater environment quality of Xijikeng mining area is good. In addition to a small number of samples near the tailings pond and mine pit ponding in the mining area do not meet the standard, the groundwater quality of surrounding villages and towns is not affected by the mining area. It is shown that carbonate rock is the natural geochemical barrier of the migration of heavy metals, which can effectively reduce the environmental pollution risk of sulfide deposits mining.

Distribution Characteristics and Source Identification of Heavy Metals in Topsoils and Subsoils of Hainan Island

ZHANG Xianyi, PANG Chengbao, WANG Anting, YUAN Guoli, SANG Xuezhen, LI Yuanzhong, YANG Yi

2020, 34(05):  970-978.  DOI: 10.19657/j.geoscience.1000-8527.2020.05.10

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Geo-statistical and multivariate analyses are effective methods to determine the source and impact factors on heavy metals in the soil. The comparative analysis of contents and spatial distribution of heavy metals in topsoils and subsoils of different lithologic regions on a regional scale can also provide valuable information for distinguishing the sources of heavy metals. In our study, concentrations of 8 heavy metals were respectively measured in 8,713 topsoil samples and 2,197 subsoil samples collected from Hainan Island. The mean concentrations of As, Co, Cr, Cu, Pb, Zn, Cd, Hg in topsoils and subsoils were 5.29 mg/kg, 11.95 mg/kg, 60.79 mg/kg, 17.24 mg/kg, 26.18 mg/kg, 51.22 mg/kg, 0.081 mg/kg,0.043 mg/kg and 5.53 mg/kg, 12.89 mg/kg, 65.24 mg/kg, 19.97 mg/kg, 29.15 mg/kg, 58.87 mg/kg, 0.065 mg/kg, 0.029 mg/kg, respectively. The dominant impact factors including lithology of soil parent material, pedogenesis and human activities were figured out for heavy metals both in topsoils and subsoils by using Pearson correlation analysis and multivariate compositional analysis. The result shows that As, Co, Cr, Cu, Pb and Zn mainly come from the inheritance of soil parent material and influence of the pedogenesis, while Cd and Hg are greatly affected by the input of human activities.

Geochemical Characteristics and Risk Assessment of Lead in the Soils of Jiucheng—Jiemao District in Yingjiang, Yunnan

ZONG Qingxia, XIAO Gaoqiang, XIANG Longzhou, XU Yongqiang

2020, 34(05):  979-986.  DOI: 10.19657/j.geoscience.1000-8527.2020.05.11

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Based on 4,706 topsoil samples and 9 vertical soil profiles of Jiucheng—Jiemao district in Yingjiang County, Yunnan Province, the geochemical characteristics of lead in soils were studied and human health risk assessment was performed in combination with the Second National Land Survey Patch. The results showed that the average concentration of Pb in the topsoils was 43.40 mg/kg, while the background concentration of Pb was 1.55 times of that in A horizon of National Soil Survey. The ratio of the samples exceeding the national standard(GB 15618—2018) was 3.10%. A significant difference occurred in the spatial distribution of Pb in soils which was affected by both soil parent materials and anthropogenic activities. The Pb content characteristics in the residual soil profiles had more inherited the characteristics of their parent material, showing a lightly enrichment from the top layer to the deep layer. The characteristics of the Pb content in the soils developed by different parent materials were as follows: granite>slate>gneiss, metagranite>clastic rock. Obviously, the human activities were superimposed in the alluvial soil profile so that the Pb content showed an enrichment from deep to top. The possibility of human health risks caused by soil Pb in the study area was relatively small. And the soil could be utilized safely under current land pattern.

Petrology

Zircon U-Pb Geochronology, Geochemistry and Geological Significance of Granitoids in the Yazigou,Qimantage Area of East Kunlun Mountains

WANG Panxi, GUO Feng, WANG Zhenning

2020, 34(05):  987-1000.  DOI: 10.19657/j.geoscience.1000-8527.2020.026

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To enhance our understanding on the regional tectonic evolution and metallogenic regularity in the east Kunlun mountains, The authors report a synthesis of the petrology, geochronology and geochemistry of grani-toids in Yazigou area, Qimantage, and discuss the petrogenesis, tectonic setting and its metallogenic relations. Zircon grains from the monzodiorite with biotite and quartz yielded ²⁰⁶Pb/ ²³⁸U age of (415.5±2.6) Ma, indicating that the rock was formed in the earliest Devonian. Comparing syenite and adamellite with diorite, they all have similarly high SiO₂, K₂O, and total alkali, and low CaO, MgO, FeO_T, and TiO₂. They have similar Al₂O₃ content. The K₂O content is lower than Na₂O in diorite, but higher Na₂O in the other rock types. The rocks are meta-aluminous to weakly peraluminous, and are either subalkalic or alkaline. They have average total ∑REE content of 305×10 ^-6, and mostly negative Eu anomaly (δEu = 0.26-1.03, average 0.61). The chondrite-normalized REE patterns are right-inclining with LREE enrichments and LREE/HREE fractionation. The rocks have significant enrichments in large ion lithophile elements (LILEs, e.g.Cs, Rb, K, U, and Th), LREEs and Pb, but depletions in high field strength elements (HFSEs, e.g.Nb, Ta, Zr, P, and Ti), Ba, and Sr. The Yazigou granitoids may have derived mainly from a mantle source with little crustal material input, belonging to a crust-mantle mixed origin. The rocks were likely formed by upward ascent of mantle-derived materials along continental margin rift under the Caledonian post-orogenic setting. Considering the structural features and regional geological setting, it is inferred that the intrusive body was formed in a post-collisional extension environment, and closely related to Pb-Zn mineralization, Attention should be paid to the Early Variscan granitoids in future mineral exploration.

Petrogenesis of the Guluo and Wangjiangchong Shoshonite-gabbro in Southeastern Guangxi Province: Constraints from Petrochemistry, Zircon U-Pb Age and Hf Isotope

NONG Junnian, GUO Shangyu, SUN Minghang, TANG Juanhong, QIN Ruicai, ZHOU Qiue

2020, 34(05):  1001-1014.  DOI: 10.19657/j.geoscience.1000-8527.2019.032

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The Guluo and Wangjiangchong plutons are located in the southwestern section of the suture between the Yangtze and Cathaysia blocks. They are important in revealing the tectonic evolution of South China. The plutons are composed dominantly of gabbro with minor diorite. The zircon U-Pb ages of the Guluo and Wangjiangchong plutons are (163 ± 1) Ma and (158 ± 1) Ma, respectively. The rocks show no negative Nb-Ta anomalies and intraplate potassic basalt affinity. The zircon ε_Hf(t) values (0.7-8.3) and T_DM2 (672-1,168 Ma) are indicative of a Neoproterozoic lithospheric mantle source. Integrating the regional geology, whole-rock geochemistry and zircon Hf isotopes studies, we suggest that the Guluo and Wangjiangchong plutons were formed in an intraplate extensional setting, via mixing between materials from the depleted asthenospheric mantle and the enriched lithospheric mantle, and contaminated by crustal materials during the magma ascent.

Geochronological, Geochemical and Geological Significance of Huilong Gabbroic Pluton in Southeastern Guangxi

LI Daixian, KANG Zhiqiang, LIU Di, CHEN Huan, CAO Yan, WEI Naishao, WEI Tianwei, WANG Rui, LIU Dongmei, ZHOU Tong, LAN Haiyang

2020, 34(05):  1015-1027.  DOI: 10.19657/j.geoscience.1000-8527.2020.033

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Early Mesozoic tectonics of South China has been disputed for decades. There are two prevailing view points for tectonic attributes: oceanic-continental subduction/collision or intracontinental tectonics. Previous studies mainly focus on the granitic rocks, causing multiple interpretations on its tectonic setting. The LA-ICP-MS zircon U-Pb age of Huilong gabbros is (245.8±1.7) Ma, showing that Huilong pluton was formed in the Early Triassic. The Huilong gabbros have relatively low contents of SiO₂ (47.42%-48.80 %) and MgO (2.24%-2.62 %), and relatively high contents of TFe₂O₃ (18.24%-21.49 %), P₂O₅ (0.38%-0.88%) and TiO₂ (1.66%-2.04%). The rocks are enriched in large ion lithophile elements (LILEs, such as Ba, Rb, and U) and depleted in high field strength elements (HFSEs, such as Nb, Ta, Zr, Hf, and Ti, (La/Yb)_N=3.85-5.99), showing a significant positive Eu anomaly (δEu=1.04-1.48). Sr-Nd isotope characteristics, including ( ⁸⁷Sr/ ⁸⁶Sr)_i=0.717,658 - 0.718,405 and ε_Nd(t)=-10.30 to -10.71, demonstrate affinity to the EM II enriched mantle, and imply an enriched mantle source formed under the influence of ancient subduction events at Yunkai. Based on previous studies, the Huilong pluton was probably generated from the partial melting of an enriched mantle source under the backarc spreading of paleo-Pacific subduction beneath South China, with fractionation of mafic minerals.

Volcanic Characteristics, LA-ICP-MS Zircon U-Pb Ages of Claystone at the Permian-Triassic Boundary, Guanba Area in Guizhou Province, South China and the Geological Implications

HE Bi, ZHANG Xiangwen, ZHAO Fei, JIN Canhai, REN Guangming, WANG Ningzu, ZHANG Wenbin, ZHANG Zhixi, SUN Pingyuan

2020, 34(05):  1028-1042.  DOI: 10.19657/j.geoscience.1000-8527.2020.042

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Three Permian-Triassic claystone are outcropped at Guanba (Qianxi County) in Guizhou Province, geologically in the southwestern South China block. One sample for zircon U-Pb dating and 7 samples for geochemical analysis were collected from the base of the claystone. LA-ICP-MS zircon U-Pb analysis shows that the zircons have 60.26×10 ^-6-297.90×10 ^-6 U and 46.14×10 ^-6-244.26×10 ^-6 Th, with Th/U value of 0.76-1.55, resembling typical igneous zircons. Zircon U-Pb dating yielded a ²⁰⁶Pb/ ²³⁸U weighted mean age of (252.6±1.4) Ma, and the concordant age of (252.7±0.6) Ma. Geochemical analysis shows that the tuff contains calc-alkaline volcanic materials with high Si-Al-K-Mg contents and low Fe-Ti contents. Additionally, the claystone has relatively high total REE contents, with elevated LREE enrichments and REE fractionation. Negative Eu anomaly is obvious (δEu=0.19-0.45). Geochemical characteristics indicate that the Permian-Triassic boundary at Guanba is comparable to the marine-facies Permian-Triassic boundary at Changhsing (GSSP, southeastern South China block).

Origin and Magmatic Evolution of the Neoproterozoic Dengganping Granite in Western Sichuan: Mineralogical Evidence from Plagioclase and Biotite

LIU Hang, ZOU Hao, LI Yang, LI Xinyu, JIANG Xiuwei, ZHANG Qiang, LI Die

2020, 34(05):  1043-1057.  DOI: 10.19657/j.geoscience.1000-8527.2020.022

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The Neoproterozoic Dengganping granite is located in the middle part of the Longmenshan orogenic belt, which is in the transition zone between the eastern margin of the Qinghai-Tibet Plateau and the western margin of the Yangtze block. It is a typical area for studying the tectonic-magmatic evolution of the western margin of the Yangtze block. In this paper, field geological, petrographic and electron microprobe analyses were carried out on the Neoproterozoic Dengganping intrusion. We discuss the genetic features of plagioclase structure, compositional characteristics of biotite, and the magmatic evolution of the granite. The results show that the plagioclase in the Dengganping monzonitic granite has a simple “anti-ring” texture, mainly for the oligoclase (An_12.51Ab_47.43Or_40.06), In the syenogranite, the corrosive texture is clear, and alkaline feldspar predominates, most of which is sanidine (An_7.46Ab_42.39Or_50.16). Biotite in the granite is characterized by being Al-rich, Fe-rich, low-Mg and low-K, and belongs to iron biotite. Meanwhile, the I_Fe value is 0.47-0.50, indicating that the biotite was subjected to late fluid modification. Geochemical features of the biotite show that the Dengganping intrusion belongs to the peraluminous granite, whose formation was related to a crustal source. The crystallization pressure and depth are 1.81×10 ⁵-2.23×10 ⁵ Pa, 6.58-8.11 km, and the biotite crystallization temperature is 750-786 ℃. The granitic magma may have had high oxygen fugacity, belonging to the medium-deep formation phase. The results provide new evidence for the 800-740 Ma strongly-extensional magmatism in the Neoproterozoic western margin of the Yangtze block.

Geochemistry and Hydrogen-Oxygen Isotope Compositions of Jiajik Two-mica Granite, Sichuan Province, and Their Geological Significance

HOU Jianglong, LI Jiankang, WANG Denghong, DAI Hongzhang, LIU Lijun

2020, 34(05):  1058-1066.  DOI: 10.19657/j.geoscience.1000-8527.2019.031

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Jiajika is a superlarge lithium deposit in Sichuan Province. The two-mica granite in the southern Jiajika orefield is closely related to rare metal pegmatites in space, time and origin. In this study, geochemical and hydrogen-oxygen isotope analyses of the granite were carried out to understand the rare metal metallogenic process. The results show that the Jiajika two-mica granite is S-type with high SiO₂, high-K calc-alkaline and peraluminous. The total rare earth composition of the granite is very low. The magma source of the granite may have been partial melting of the Triassic Xikang Group sandy-mudstone, and the fluid source may have been a mixture of magmatic and metamorphic water. R cluster analysis of trace elements shows that Li, Rb, Ti, W and Mn are closely related to rare metal metallogeny. Changes in the rare element contents suggest that ore-forming efficiency in the north was higher than in the south. Therefore, future prospecting work should focus on the northern part of the granite. Results of geochemistry, hydrogen-oxygen isotopes and previous studies reveal immiscibility in the diapirism of granitic magma. Pegmatitic magma segregated from the granitic magma may have concentrated the rare metals, and eventually formed the pegmatitic rare metal deposit.

Geochemistry Characteristics and Tectonic Environment Analysis of Middle Jurassic A-type Granites in Zhangjiawan Area, Heilongjiang Province

REN Yongjian, CHENG Shuo, ZHANG Mingming, CAO Guangyuan, YU Wang, ZHAO Han, LIANG Heng, WANG Fuqiang, QI Caiji

2020, 34(05):  1067-1076.  DOI: 10.19657/j.geoscience.1000-8527.2020.038

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Through comprehensive petrographic and geochemical analyses of the Middle Jurassic syenite and alkali feldspar granite in Zhangjiawan area (Heilongjiang Province), we explore the regional granitic magmatism, genetic type and tectonic environment. The results show that the syenite granite and alkali feldspar granite have high SiO₂(73.12%-77.82%), and are alkali-rich (K₂O+Na₂O = 6.36%-8.56%), Fe-rich and Mg-poor (FeO ^T/MgO = 6.67-25.43). The rocks have aluminum saturation index (A/CNK value) mostly above 1.1, distinct negative Eu anomalies (δEu = 0.01-0.74), enrichments in Th, U, K and Rb, and depletions in Ba, Sr, P and Ti. Zircon saturation temperatures are calculated to be 757-900 ℃, with an average of 816 ℃. The granites are A-type, and likely evolved from highly-fractionated granite to peraluminous A-type granite. REE features indicate that the magma was sourced from a mixture of mantle and lower crustal materials. The mid-Jurassic syenite granite-alkaline granite is A2-type, and was likely formed in a post-orogenic lithospheric extension setting. The above-mentioned lithogeochemical characteristics indicate that the Middle Jurassic regional tectonics was influenced by the west-dipping Paleo-Pacific subduction and post-collisional orogeny. The Zhangjiawan area was in a post-orogenic extension environment, and the lithosphere tectonic regime changed from compressive to extensional. The mantle upwelling accompanied by magma intrusion may have triggered the melting of crustal materials, which formed the syenite and alkali feldspar granite in the area.

Ore Deposits

The Source of Ore-forming Material in the Longtougou Gold Metallogenic Belt of South Qinling: Evidence from Element and Sulfur Isotopic Composition

XUE Yushan, CUN Xiaoni, LIU Xinwei, HU Xishun

2020, 34(05):  1077-1091.  DOI: 10.19657/j.geoscience.1000-8527.2020.05.19

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The Longtougou gold metallogenic belt is located in Shanyang County, Shaanxi Province. Four gold deposits have been discovered in this belt since 21st century, containing at least 20 t Au. The orebodies are hosted in the middle Devonian Dafenggou Formation and occur as pyrite-quartz veins. In order to find out the ore-forming process, two typical orebodies were chosen for careful study in this paper. Mineralization process can be divided into three stages, including silicification stage(early stage),quartz-sulfides stage(main ore-forming stage) and carbonation stage(late stage). In the main ore-forming stage, pyritohedron pyrite is the major gold carrier mineral. Furthermore, it is found that Au is unhomogeneous and local enrichment in broken gold-bearing pyrite during the later tectonic activation stage. The trace element compositions of gold-bearing pyrite and sulfur isotope studies revealed that the Neo-proterozonic Yaolinghe Formation is mostly likely the dominant source of gold based on their similar REE patterns and sulfur composition. Besides, Yaolinghe Formation has higher Au concentration than any other geologic bodies in the Longtougou metallogenic belt. The Co/Ni ratios of the pyrite range from 1.14 to 1.83, indicating a deep magmatic origin for the mineralization. Ore-forming fluid is characterized by higher oxygen fugacity since the δEu positive anomalies preserves not only in ores but also in pyrite grain. The geologic thermometer of sulfur isotope shows that the temperature of mineralization is 200-260 ℃. Thus, we proposed that the gold deposits in this belt are possibly related to magmatic activity beneath the Longtougou anticline at late Indo-Chinese epoch. Hydrothermal fluid, which exsolved from the magma, extracted gold from Yaolinghe Formation and then migrated upward and precipitated in secondary fractures of Longtougou fault later.

Geochemistry, Zircon U-Pb Dating and Tectonic Setting of the Granitoid Related with the Dayangshan Molybdenum Deposit, Daxinganling

YANG Yuanjiang, LI Chenglu, DENG Changzhou, LI Wenlong, ZHANG Li, ZHAO Zhonghai, ZHAO Handong

2020, 34(05):  1092-1102.  DOI: 10.19657/j.geoscience.1000-8527.2020.05.20

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The Dayangshan molybdenum deposit is a newly discovered small deposit in the Huzhong area, northeast of Daxinganling. The ore is mainly hosted by the quartz-monzonite porphyry and hanging wall rock, and its occurrence is controlled by the quartz-monzonite porphyry. U-Pb dating of the quartz-monzonite porphyry using LA-ICP-MS yielded an age of (119.83±0.87) Ma, indicating that the mineralization in the Dayangshan molybdenum deposit occurred in the Early Cretaceous. The geochemical data of the quartz-monzonite porphyry show that the rock is relatively enriched in Al(Al₂O₃=15.04%-15.31%) and K(K₂O/Na₂O=1.15-1.21) and depleted in Ti(TiO₂=0.36%-0.39%). These characteristics show that the quartz-monzonite porphyry is a potassic basaltic rock, which is normally formed in orogenic belt settings, and magmatic melts which produce these rocks do not interact with mantle. In addition, the rock is relatively enriched in LILEs (e.g., Rb and K), and depleted in HFSEs(e.g.,Nb, Ta, P, Ti and HREE), depleted in mantlephilic elements, enriched in LREE ((La/Sm)_N=4.62-4.64), and with medium Eu value (δEu=0.46-0.48), suggesting that it was crystallized from a magma originated from continental crust. Based on the regional geological data, we argue that the source of ore-forming material was derived from the remelted crust related to the subduction and closure of the Mongolia-Okhotsk Ocean, and the mineralization occurred in the extensional tectonic setting. The study supplemented the data of regional metallogenic regularity and provided basis for regional metallogenic prediction.