Geoscience

Zircon U-Pb Geochronology, Geochemistry Characteristics and Geological Significance of the Solonker Ophiolite, Inner Mongolia

LIU Zhihua, GU Xuexiang, ZHANG Yongmei, WANG Jialin, LIU Tao, WANG Wendong, ZHAO Wei, CHEN Yang

2020, 34(03): 399-417. DOI: 10.19657/j.geoscience.1000-8527.2020.011

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To deepen our understanding on the Late Paleozoic tectonics of the eastern Central Asian Orogenic Belt, a study of the petrology, geochronology and geochemistry of fresh basalts and gabbros in the Solonker ophiolitic mélange belt were reported. Zircon grains from these basalts and gabbros yielded²⁰⁶Pb/²³⁸U ages of (276.7±2.7) Ma and (274.1±3.2) Ma, respectively, indicating an Early Permian emplacement age. Both the basalts and gabbros are tholeiitic, and have low Mg^# values of 41-50 and 62-65, respectively, both below the primary magma value. Meanwhile, the basalt and gabbro samples fall along a fractionation trend in the Harker diagrams, suggesting a dominant role of fractional crystallization in the magma evolution.The Th/La, Th/Ce and Lu/Yb ratios of the two rock types are below those of the average continental crust, but similar to those of typical mantle-derived magmas. Therefore,it is inferred that crustal contamination had little influence on the mafic magmas.Rare earth element (REE) compositions show that the basalts are of the N-MORB-type with light REE (LREE) depletions,probably originated from 5%-10% partial melting of the depleted spinel lherzolite mantle. Gabbros are slightly LREE-depleted with a flat REE distribution pattern, and have clearly lower total REEs (Σ REEs) than N-MORB, probably due to a higher degree of partial melting than the basalts in the source region.In addition, both rock types are highly enriched in large ion lithophile elements (LILEs: Rb, Sr, Ba, Pb) and depleted in high-field-strength elements (HFSEs: Nb, Ta), similar to typical island arc magmas.These features imply that their magmas were affected by subduction-related fluids, or were derived from the melting of subducting sediments.The geochemical characteristics indicate that the Solonker ophiolites belong to the supra-subduction zone (SSZ)-type, and may have formed in an intra-oceanic backarc basin.This indicates that intra-oceanic subduction still persisted till at least the Early Permian in the study area.Comprehensive analyses suggest that the Paleo-Asian Ocean(PAO) was closed in the Late Permian to Early Triassic along the Solonker-Xar Moron suture zone.

Zircon U-Pb Chronology, Geochemistry Characteristics of the Tiezhai Complex in Linqu County of Western Shandong and Their Geological Significance

YU Lidong, YU Xuefeng, LI Dapeng, LIU Qiang, LIU Jiajun, SHU Lei, WEI Pengfei

2020, 34(03): 418-430. DOI: 10.19657/j.geoscience.1000-8527.2020.017

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The Tiezhai complex is located in Linqu County of western Shandong Province, and is mainly composed of grey and light-red quartz monzonite porphyries. To accurately determine the formation age and geochemical characteristics of the complex, we studied the major and trace elements (including REEs), and zircon LA-ICP-MS ages of the grey and light-red quartz monzonite porphyries. Our zircon U-Pb dating reveals that the grey quartz monzonite porphyry was formed in (129.0±1.7) Ma, and contains many Precambrian inherited zircons with ages of (2,520±30) Ma. The light-red quartz monzonite porphyry was formed in similar age at (125.0±1.6) Ma. The rocks are all rich in Si and alkali, but low in Ca and Mg. The grey quartz monzonite porphyry has a higher Mg^# value than its light-red counterpart.Their total REE contents are relatively low, and the LREE/HREE fractionation is high with no Eu anomaly. The rocks have high Sr and Ba contents, and with negative HFSE (high field strength elements,e.g.,Nb, Ta and Ti) anomalies.Geochemical characteristics of the two porphyries indicate that parental magma of the Tiezhai complex may have sourced from partial melting of the enriched mantle and the assimilation of some ancient crustal materials. The difference in Mg^# between the two porphyries was likely resulted from magnetite fractionation. Dehydration of the Pacific subducted slab resided in the mantle-crustal transition zone was likely the cause of the Early Cretaceous lithospheric thinning. Voluminous magmatic rocks were generated in this period, indicating that the lithospheric thinning had peaked during the Early Cretaceous in the North China Craton.

Characteristics and Geological Significance of the Triassic Mungbean Rocks in the Wenquan Town Area, Northern Chongqing

JU Pengcheng, WANG Xunlian, WANG Zhentao, LIU Xifang, ZHONG Jiaai, ZHANG Zaiming

2020, 34(03): 431-449. DOI: 10.19657/j.geoscience.1000-8527.2020.018

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Altered Triassic volcanic ash beds are widely distributed in South China, and is locally called “mungbean rocks”. In the Pinghongcun and Xiejiacao sections in the Wenquan town (northern Chongqing), these “mungbean rocks” were sampled and X-ray diffraction (XRD) analyzed. Our results show these rocks contain mainly quartz and alkali feldspars, together with clay minerals such as illite and montmorillonite.Zircon morphology, Th/U ratio and zircon REE patterns indicate typical magmatic zircon features. However, geological interpretations yielded from zircon geochemistry of different samples are markedly different. Zircon U-Pb dating reveals that the Pinghongcun sample was formed at (247.2±0.59) Ma (MSWD=2.3, n =30), coeval with the T₁/T₂ boundary (247.2 Ma). The zircon geochemical characteristics indicate an intraplate origin, presumably resulted from the intraplate volcanism after the main-stage Emeishan large igneous province (LIP) activity. The Xiejiacao sample was formed at (225.9±1.4) Ma (MSWD=7.1, n=29), and the zircon geochemistry points to a magmatic arc origin. Combined with regional geology, especially the discovery of the coeval volcanic ash beds to the north (southern margin of North China Block) ,we inferred that the Xiejiacao sample was probably the product of the Mian-Lue Ocean closure.

Geochronology, Geochemistry and Sr-Nd-Hf Isotopic Compositions of the Wuhua Gabbros in Langshan, Inner Mongolia: Constraints for Mantle Sources and Petrogenesis

ZHANG Yun, SUN Lixin, ZHANG Tianfu, SUN Yiwei, ZHANG Qi, LI Yanfeng, YANG Zeli, LIU Wengang

2020, 34(03): 450-465. DOI: 10.19657/j.geoscience.1000-8527.2020.010

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Two types of gabbros (i.e., olivine and hornblende gabbros) are exposed in the Wuhua gabbroic intrusions. LA-ICP-MS zircon U-Pb dating indicates that the Wuhua gabbros were emplaced in the late Early Carboniferous ((319.8±1.8) Ma to (325.4±1.6) Ma). The Wuhua gabbros are tholeiitic, with high Mg^# va-lues (mostly 76.70-80.35), high Al₂O₃ (13.55%-25.13%) and low TiO₂ (0.18%-1.35%). The rocks have low total REE contents (∑REE=8.92×10^-6-40.10×10^-6), and are featured by LREE enrichments ((La/Yb)_N=1.74-3.06) and positive Eu anomaly (δEu=1.156-3.86). The Pb and LILE (K, Rb, Ba, Sr) enrichments and HFSE (Nb, Ta, Zr, Hf, Th) depletions, and the relatively low Zr content (4.38×10^-6-26.6×10^-6) and low Zr/Y ratio (1.08-2.35) resemble those of typical subduction-related arc volcanic rocks. The Sr-Nd-Hf isotopic data show that the Wuhua gabbros were derived from an enriched mantle source, and that crustal assimilation was likely insignificant. According to geochemical data and previous regional geological studies, we consider that the Wuhua gabbros may have formed from partial melting of the hydrated and enriched lithospheric mantle wedge. The Wuhua gabbros were likely formed in the incipient subduction phase, when the western section of the northern North China Plate margin started to become an Andean-type continental arc in the late Early Carboniferous. This tectonic phase may have ended before the Early Permian.

Spatial-temporal Distribution of Late Mesozoic Intrusive Rocks in South Daxing’anling Mountains and the Characteristic Contrast of Rocks in the Mid Ridge and the East Slope

WANG Di, ZHAO Guochun, SU Shangguo, LI Hongxing

2020, 34(03): 466-482. DOI: 10.19657/j.geoscience.1000-8527.2020.023

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This work studied the petrology, major and trace element geochemistry, and zircon U-Pb ages of four different granites in the Daxing’anling Mountains (DM), i.e., Malegenba and Chaoyanggou in the DM main ridge,and the Yezhugou and Budunhua in the DM eastern slope,in order to better constrain the magmatic background of the Late Mesozoic DM. LA-ICP-MS zircon U-Pb dating of the Chaoyanggou and Budunhua granites yielded Late Jurassic ages of (154±1) Ma and (154.1±1.6) Ma, respectively, whereas the Malegenba and Yezhugou granites yielded Early Cretaceous ages of (144.62±0.74) Ma and (140.2±2.7) Ma, respectively. According to the petrographic and geochemical characteristics, the DM main-ridge granites are high-K calc-alkaline, metaluminous, and highly-fractionated I-type;whereas those in the DM eastern slope are cal-calkaline to high-K calc-alkaline and metaluminous to peraluminous TTG I-type. The DM main-ridge granites are more depleted in Ba, Nb, Sr, P, Ti, and Eu than their DM eastern-slope counterparts. Combined with the regional geology, the southern DM region was probably co-influenced by the rapid NNW-directed oblique subduction of the Izanagi plate and the Mongolia-Okhotsk Ocean closure during the Late Jurassic to Early Cretaceous. The DM main-ridge granites were probably formed by the partial melting of the lower crust underplated by and mixed with mantle-derived magma, and the granitic magmas were intruded along the fault zones in the DM main ridge. Meanwhile, the DM eastern-slope granites were formed by the collision-related crustal thickening at that time.

Zircon U-Pb Age, Geochemical Characteristics and Tectonic Implications of Granites in the Wulanhaote Area, Central Daxing’an Mountains

ZHANG Haihua, LI Yongfei, ZHANG Jian, SU Fei, ZHENG Yuejuan, BIAN Xiongfei, ZHANG Dejun

2020, 34(03): 483-493. DOI: 10.19657/j.geoscience.1000-8527.2020.009

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Zircon U-Pb geochronological and geochemical data are presented on the granites in Wulanhaote (Inner Mongolia), and we discussed the granite ages, types and regional tectonic evolution.The Wulanhaote granites are monzogranite, and zircon U-Pb dating yielded a weighted mean ²⁰⁶Pb/²³⁸U age of (214.4±2.6) Ma, indicating a Late Triassic granite emplacement. The rocks are characterized by having high SiO₂ and alkali, but low CaO, MgO and TiO₂ contents. Chondrite-normalized REE diagram shows a weak right-inclining, low-MREE pattern with strong negative Eu anomaly. The rocks show enrichments in Rb, Th, Zr, Y and Yb, but depletions in Ba and Sr. They have high Rb/Sr and Rb/Nb values and show features of low-Sr- and high-Yb-type granites. Our results show that the granites were formed under relatively low pressure by partial melting of the delaminated crust. Integrating regional tectonic evolution and tectonic discrimination diagrams, we suggest that the granites were emplaced in a post-orogenic extensional setting. This indicates that the regional tectonics has changed from Middle Triassic collisional orogenic to post-Triassic orogenic extensional, and that the Siberia-North China collision may have lasted till the Middle Triassic.

Zircon U-Pb and Molybdenite Re-Os Ages and Geological Significance of the Chaganhua Molybdenum Deposit, Urad Rear Banner, Inner Mongolia

LI Guangyao, LI Zhidan, WANG Jiaying, LI Xiaoguang, LI Chao, TU Jiarun, XIE Yu, DING Ning

2020, 34(03): 494-503. DOI: 10.19657/j.geoscience.1000-8527.2020.019

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The Chaganhua molybdenum (Mo) polymetallic deposit is a large concealed deposit in the Baoyintu magmatic arc of North China Craton. The Mo orebody is hosted within the exo-contact between the Permian granodiorite and the two-mica quartz schist of the Baoyintu Group. The orebodies are NW-trending, and occur as irregularly-thick layers, veins,or stockworks. The wall-rock alteration styles include potassic, greisen, and chlorite, consistent with the typical porphyry-type deposit. In this study, we separated and LA-ICP-MS U-Pb dated zircons from the Mo-mineralized granodiorite from Chaganhua. Our results yielded a weighted mean ²⁰⁶Pb/²³⁸U age of (257.2±1.3) Ma (n=32, MSWD=1.6),indicating that the Chaganhua granodiorite was formed in the Late Permian.In addition, molybdenite Re-Os dating yielded an isochron age of (238.6±4.4) Ma and a model age of (240.0±1.6) Ma (n=9, MSWD=0.27),which reveals that the Chaganhua Mo mineralization was the product of the Early Indosinian magmatism.Furthermore, the Re content of molybdenite ranges from 64 502×10^-9 to 245 6 21×10^-9, suggesting that the ore-forming material was sourced from a mixture of crust and mantle.

In-situ Monazite U-Pb Geochronology of Highly Fractionated Granites in Shamai Tungsten Deposit, Inner Mongolia and Its Mineralization Significance

MI Kuifeng, YANG Yan, YAN Tingjie, LÜ Zhicheng, LIU Zhenjiang

2020, 34(03): 504-513. DOI: 10.19657/j.geoscience.1000-8527.2020.015

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The Xing’an-Mongolia Orogenic Belt (XMOB) is an important metallogenic belt in northern China, hosting a series of tungsten polymetallic deposits. The Shamai tungsten deposit, located in the eastern part of the Erenhot-Dongwuqi metallogenic belt in the XMOB, is a typical quartz-vein hosted tungsten deposit. In this paper, in-situ LA-ICP-MS monazite U-Pb dating was used to determine the ages of the ore-bearing granites at Shamai, and the metallogenic epoch and geodynamic background of the regional tungsten mineralization were discussed. The monazite from the medium-grained biotite monzogranite and porphyritic biotite monzogranite, yield concordant ages of (141.6±1.1) Ma and (141.4±0.3) Ma, respectively, reflecting their crystallization ages. Tungsten mineralization in the Erenhot-Dongwuqi metallogenic belt occurred in two stages at ca. 300 Ma and ca. 140-130 Ma. The former stage was likely related to the subduction of the Paleo-Asian ocean, while the latter stage was likely co-influenced by the (post)-subduction tectonics of the Mongol-Okhotsk Ocean and the Paleo-Pacific Ocean.

Magmatic Activity and Emplacement of the Devonian Intrusive Rocks in Eastern Altay, Northern Xinjiang

LIN Xinwang, WANG Xing, CHEN Guangting, ZHAO Duanchang, ZHAO Jianglin

2020, 34(03): 514-531. DOI: 10.19657/j.geoscience.1000-8527.2020.03.016

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A large number of magmatic rocks were developed in the eastern Altay, northern Xinjiang. LA-ICP-MS zircon U-Pb dating indicates that the Adeer quartz diorite porphyry and Qiaolakesayi granodiorite were emplaced at (415.7±4.0) Ma and (413.5±3.0) Ma, respectively. These ages revealed that the rocks were emplaced in the Early Devonian. There are significant major-element geochemical differences between the two rock types, but their trace-element (including REE) features are largely similar.The quartz diorite porphyry is medium-low-K calc-alkaline and peraluminous, but the granodiorite is high-K calc-alkaline and metaluminous. The REE distribution patterns reveal that the rocks are LREE-enriched, HREE-depleted, and with strong LREE/HREE fractionation and weakly-moderately negative Eu anomalies. The rocks are enriched in LILEs (Rb, Th, U) and LREEs, and clearly depleted in HFSEs (Nb, Zr, Ti),Sr, and P,demonstrating a subduction-related affinity. Considering also the regional geology, we concluded that magmatism was active in the Early Devonian eastern Altay, and with complex petrogenetic cause and emplacement mode, which formed the various igneous rock assemblages in the region. This plutonism may have been the product of hot mantle and hot crustal structure, and has the potential to generate super-large deposits.

Identification and Geological Significance of Various Types of Muscovite in Jurassic Granite of Bengbu Area on the Southeast Margin of North China Craton

WU Tianhao, XU Lijuan, XIAO Yilin, LIU Sheng’ao

2020, 34(03): 532-544. DOI: 10.19657/j.geoscience.1000-8527.2019.014

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The Triassic subduction of South China continental crust is generally considered to have extended to the Bengbu region (SE margin of the North China craton), yet whether the subduction there had caused ultra-high-pressure (UHP) metamorphism remains controversial. Primary phengite can be used as a geobarometer to estimate the pressure of rock formation. Petrographic observation, electron probe microanalysis (EPMA) and Raman spectral analysis have been performed on the muscovite in the restite, its granite host and the aplite vein from the Jurassic Jingshan granites in the SE margin of the North China Craton. The muscovite in the restite and granite host are coarser, and have higher Si and (Fe+Mg),but lower Al atomic contents than the muscovite in common granites. The muscovite in the restite and granite host also show similar Raman shift (421 cm^-1) and aluminium atom bridge-bond (Al, O(br)), which are lower and higher than that of the white micas, respectively,in the UHP eclogite and non-UHP schist of this study. Therefore, major element contents and Raman shifts of the muscovite suggest that coarse-grained muscovite in the residual and granite are primary metamorphic phengite. Applying geobarometry, the melting pressure of the Jingshan granite is estimated to be 1.0 to 1.3 GPa. The source of the Jingshan granite may have been the subducted South China continental crust. The subducting depth of the South China plate beneath the NE margin of the North China Craton was at least 33 to 45 km, equivalent to the middle and lower crust there.

Geochemical Characteristics of Middle Ordovician in Western Margin of Ordos Basin and Its Implication on Paleoenvironment

JIANG Suyang, HUANG Wenhui, ZHANG Yongsheng

2020, 34(03): 545-553. DOI: 10.19657/j.geoscience.1000-8527.2020.012

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Western margin of the Ordos basin is located at the tectonic junction between Eastern and Western China, and its end Ordovician tectonic architectural change has attracted wide research attention. Middle Ordovician carbonate rocks in the Laoshidan profile are selected as the research target here. Through geochemical analysis, we aim to reconstruct the paleoenvironment and explore the various sedimentary and geochemical features that can serve as tectonic indicators. Our results indicate that: (1) Sandaokan and Zhuozishan formations have δ ¹⁸O=-5.2‰ to -8.9‰ (average -7.0‰) and δ¹³C=1.3‰ to -1.8‰ (average -0.1‰). δ¹⁸O values rise from the bottom upward with a slight drop at the top of Zhuozishan Formation,the same trend is present for the δ ¹³C values; (2) Paleotemperature of seawater likely fluctuated during the early period and then decreased from 32.7 ℃ to 15.7 ℃ gradually, whereas the Z values maintain an increasing trend, indicating deepening seawater and increasing salinity; (3) Geochemical proxies of major and trace elements are well consistent and indicate a transgressive sedimentary setting in the Middle Ordovician. The petrographic features reveal that the content of terrigenous clastic minerals in the carbonates decreases gradually from the Sandaokan Formation to the Zhuozishan Formation, reflecting a transition from the restricted platform to open platform environment. Considering also the regional Mid-Ordovician tectonic background, the western margin of Ordos basin may have already been dominated by a foreland basin tectonic system,with gradually increasing influence from the collisional orogeny between the Alxa Block and North China Block. This results in the paleogeomorphologic highs in the northwest and lows in the southeast of the Ordos basin, leading to the K-rich brine accumulation in the latter. We suggest that the secondary sag in southeast part of salt basin is the key exploration target area for marine potash deposits.

Properties of Ore-forming Fluids and Genesis of the Xiaoxigong Gold Deposit in the Beishan Region, Gansu Province

YUAN Weiheng, GU Xuexiang, ZHANG Yongmei, DU Zezhong, YU Xiaofei, SUN Hairui, LÜ Xin

2020, 34(03): 554-568. DOI: 10.19657/j.geoscience.1000-8527.2020.03.12

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The Xiaoxigong gold deposit is located in the south part of the Beishan orogenic belt. The orebodies are hosted in metamorphic rocks of the Middle Proterozoic Xijianshan Group, and are controlled by the NWW- trending secondary faults. Mineralization process can be divided into three stages, including quartz-pyrite stage (early stage), quartz-polymetallic sulfide stage (main ore stage) and quartz-carbonate stage (late stage). In this paper, fluid inclusions, trace elements and H-O isotopes of the main ore stage are studied in order to determine the properties of the ore-forming fluids and the genesis of the deposit. The quartz of the main ore stage mainly contains H₂O-NaCl, CO₂-H₂O and pure CO₂inclusions. The homogenization temperatures, salinities and densities of H₂O-NaCl and CO₂-H₂O inclusions vary from 194 ℃ to 397 ℃, 2.2% to 8.9% and 0.63 g/cm³ to 0.98 g/cm³, respectively. According to the calculation from CO₂-H₂O three phase inclusions, the trapping pressures in the ore stage are 257 MPa to 395 MPa and the ore-forming depths are 9.5 km to 14.6 km. The results of fluid inclusion microthermometry, laser Raman spectroscopy and quartz trace elements show that the ore-forming fluid is a CO₂-H₂O-NaCl±CH₄ system and somewhat reduced, with medium-high temperature, low salinity and medium-low density. The values of δD_V-SMOW and δ¹⁸ $O H 2 O$ in the ore stage are -100.2‰ to -75.6‰ and +4.15‰ to +8.31‰.The fluid inclusion and H-O isotope characteristics indicate that the ore-forming fluids in the main ore stage were mainly metamorphic water, and the fluid immiscibility is an important mechanism for gold precipitation. Comprehensive analyses show that the Xiaoxigong deposit belongs to a mesozonal to hypozonal orogenic gold deposit.

Sulfur and Lead Isotopic Compositions of Meixian Zinc-lead Polymetallic Deposit, Central of Fujian Province, China and Tracing for the Source of Metals: Examples from the Dingjiashan and Fengyan Zinc-lead Polymetallic Deposits

XIAO Xiaoniu, FEI Lidong, QIN Xinlong, XIAO E, LIU Rongfang

2020, 34(03): 569-578. DOI: 10.19657/j.geoscience.1000-8527.2020.013

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The Meixian lead-zinc polymetallic ore field is located in the central Fujian Province, and occurs in the Mid-Late Proterozoic greenschist-facies metamorphic basement window. Workers still dispute about the ore-forming material source and metallogenic origin of the Pb-Zn deposits in the ore field. Here, we analyzed the sulfur and lead isotope compositions of the main-ore-stage sphalerite and galena from the Dingjiashan and Feng-yan lead-zinc polymetallic deposits in the ore field. Our study shows similar sulfur and lead isotope compositions in these sulfides. The ore sulfides from the Dingjiashan and Fengyan deposits have δ ³⁴S=0.4‰-5.0‰ (average 2.66‰) and 1.8‰-4.2‰ (average 2.88‰),respectively, indicating an identical mantle-derived sulfur source. The ore sulfides from the two deposits have, respectively,²⁰⁶Pb/²⁰⁴Pb=18.326-18.496 (average 18.388) and 18.378-18.646 (average 18.447),²⁰⁶Pb/²⁰⁴Pb=15.658-15.817 (average 15.705) and 15.619-15.746 (average 15.700), and ²⁰⁸Pb/²⁰⁴Pb=38.724-39.257 (average 38.880) and 38.365-39.009 (average 38.823), indicating the same crust-mantle mixed source. The sulfur and lead isotopic characteristics of ore sulfides suggest that the ore-forming materials were mainly from the Yanshanian (porphyritic) granites. Integrating the geological characteristics of deposits and orebody, we suggest that the formation of the Dingjiashan and Fengyan lead-zinc polymetallic deposits was related to the intrusion and contact metasomatism of the Yanshanian (porphyritic) granites.

Sulfur and Lead Isotopic Compositions of Boka Copper Deposit, Central Yunnan, China, and Its Geological Significance

FEI Lidong, XIAO Xiaoniu, XIAO E, LIU Jun, BAI Tao

2020, 34(03): 579-587. DOI: 10.19657/j.geoscience.1000-8527.2019.015

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Boka copper deposit in central Yunnan Province is a representative of the Dongchuan copper depo-sits, but previous studies have different views on its ore-forming material source and the metallogenic origin. In this study, we analyzed the sulfur and lead isotope compositions in typical metal sulfides to reveal the ore-forming material source of this deposit. Metal sulfides from the Renzhanshi copper mine (δ³⁴S=1.6‰ to 10.7‰) indicate that the sulfur was mainly igneous-sourced (volcanic eruptions) with sedimentary input. Lead isotope compositions of metal sulfides from the Renzhanshi, Tianshengtang, Zhuqing’aozi and Baishiyan copper mines indicate that the lead may have had a mantle-crust mixed source. The sulfur and lead isotopic characteristics of metal sulfides from this and previous studies suggest that the ore-forming materials were mainly mantle-sourced with crustal contamination.

Sulfur and Lead Isotopic Compositions of Habilig Uranium Deposit in Northern Margin of North China Block: Implication for Uranium Mineralization

HUANG Zhixin, LI Ziying, CAI Yuqi, ZHU Bin, REN Quan

2020, 34(03): 588-597. DOI: 10.19657/j.geoscience.1000-8527.2020.03.15

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Habilig uranium deposit is located in the middle part of northern margin of North China Block, which is mainly controlled by the Ulanhada-Houershan anticline and regional faults. Uranium mineralization occurs mainly in quartzite of the second member of the Wulashan Group in the Neoarchaean, and has long been consi-dered to be a metamorphic uranium deposit. Based on the study of the geological setting and mineralization cha-racteristics of the deposit, the sulfur and lead isotope compositions of pyrite in ores and surrounding rocks are systematically analyzed. The analysis results show that the sulfur isotope value varies from -4.7‰ to 12.9‰, suggesting that source of ore-forming fluids are mainly from magmatic hydrothermal fluids and are contaminated by stratigraphic materials as well. Lead isotope composition (²⁰⁸Pb/²⁰⁴Pb=36.147-42.968, ²⁰⁷Pb/²⁰⁴Pb=15.919- 34.268, ²⁰⁶Pb/²⁰⁴Pb=19.488-168.032) is much higher than that of single-stage evolution model. ²⁰⁷Pb/²⁰⁴Pb-²⁰⁶Pb/²⁰⁴Pb in different samples have a good linear relationship and represent a typical two-stage lead isotope evolution system, indicating that metamorphic strata provide uranium source for ore-forming fluid. Based on ²⁰⁷Pb/²⁰⁶Pb equation and history of regional magmatic evolution, it is considered that uranium was preliminarily enriched in the Wulashan Group because of the regional metamorphism in Paleoproterozoic (~1 805 Ma). In Late Paleozoic (374 Ma), a large amount of magmatic fluids generated from granodiorite magma, which have activated and extracted uranium from metamorphic strata and contributed to mineralization in favorable structure.

3D Geological Modeling and New Understanding of Ore-controlling Tectonic Evolution of the Hongnipo Copper Deposit in Sichuan Province

YANG Wangdong, GAO Fulei, WANG Gongwen, PANG Zhenshan, SHEN Heming, GONG Lingming, SHEN Hongtao, ZHANG Zhiqiang, LIU Xiaoning

2020, 34(03): 598-608. DOI: 10.19657/j.geoscience.1000-8527.2020.03.16

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The Hongnipo copper deposit is a newly discovered large copper deposit in the Lala region of Sichuan Province, which contains reserves of 642,000 tons Cu with an average grade of 1.31%. Ore bodies are hosted in the Proterozoic fold basement Hekou Group and they have a temporal association with gabbro intrusions, the host rocks have a generally sodic alteration. In this paper, a three-dimensional model of ore bodies and strata is constructed using 224 boreholes and 23 cross sections in the study area. The 3D geological model can delineate fine geological structure of the deposit and explain the regional metallogenesis and tectonic evolution: the early N-S principal stress in the mining area caused the Hekou Group to form a large syncline near E-W direction. On the basis of the reconstruction of the early fold basement, an axial NNE synclinorium superposed on it was formed under the late E-W principal stress. After two-stage major tectonic movements, the area has formed an overlay frame of NNE-SSW and NWW-SEE structures. This study provides new ideas for the research of mineral deposits in the Lala region, and can provide scientific guidance for mineral exploration in the region.

Study on the Genesis and Influencing Factors of Selenium-enriched Soil in the Ailaoshan Area, Xinping County, Yunnan Province

HUANG Zhao, CHEN Zheng, XUE Chuandong, DAO Yan, XU Shengchao, DAI Dalong, WU Song

2020, 34(03): 609-617. DOI: 10.19657/j.geoscience.1000-8527.2020.03.17

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Based on the evaluation results for 1∶50,000 land quality geochemical survey in Zhelong-Jiasa area of Yunnan Province, we analyze the origin of selenium-rich soil and its influencing factors.The results showed that the average of selenium in soil was 0.38 mg/kg, which was higher than national soil selenium average concentration (0.29 mg/kg).In addition, the area of the delineated selenium-enriched land accounted for 26.74% on the basis of division principle for 0.4 mg/kg<Se≤3 mg/kg.The selenium in the study area is mainly derived from the primary content of selenium in rocks and the secondary enrichment of selenium in soil, and the latter as the main reason for the widespread distribution of selenium-rich soil.Selenium content in soil is obviously affected by soil parent material, soil type, land use pattern, topography, pH value and soil organic matter.

The Analysis of Geochemical Characteristics and Genesis of Selenium-rich Soil in Western Suburb of Tianjin

HOU Jiayu, YANG Yaodong, XIE Wei, LIU Jincheng, LI Guocheng

2020, 34(03): 618-625. DOI: 10.19657/j.geoscience.1000-8527.2020.03.18

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In order to find out the geochemical characteristics and genesis of selenium-rich soil in western suburb of Tianjin, we carried out soil-water-atmosphere-plant investigations and subsequent study. The results show: the average value of soil selenium in the study area is 0.66 mg/kg, which is 2.87 times of the background value, 83% soil samples from the study area are selenium-rich soil. Selenium in soil is mainly immobilized and absorbed by particulate organic matter, and accumulated in surface soil. Selenium in surface soil has significant positive correlations with coarse sand, fine sand, Pb, Zn, Cd, Cu, Hg, N, P; and has significant negative correlations with silt, clay, Na, K, Mg, As, CEC, pH. The extensive use of organic fertilizers is the major cause of selenium accumulation in the study area, which occupies 86.55% of total input influx, atmospheric deposition is the secondary factor, occupies 13.35% of total. Selenium concentration in soil of the study area increases 2.77% which is 0.019 mg/kg annually.

Research and Application on Optimal Evaluation Scale Determination Method in the Mine Geological Environment Evaluation

CHEN Yujia, TIAN Shufang

2020, 34(03): 626-634. DOI: 10.19657/j.geoscience.1000-8527.2020.03.19

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The geological environmental evaluation of mine is significant for the development and utilization of mineral resources, as well as the conservation and restoration of mine environment. Proper optimal evaluation scale improves the accuracy and uniformity of the result of evaluation. This article presents a new method on determining the optimal evaluation scale based on mine geological environment. Under different scales, the evaluation area is firstly divided into grids according to its boundary, and then the scale effect performance (heterogeneity, consistency, information content and fragmentation) of each scale are quantified in order to calculate the fitting function changed with the evaluation scale. Secondly, with these fitting functions the optimal evaluation scale function is established. Finally, the range of suitable evaluation scales and the optimal scale can be obtained. This method was applied to evaluate mine geological environment in Xinluo District of Longyan City and Datian County of Sanming City,Fujian Province. The results are as following: the optimal range of suitable evaluation scales of Xinluo District and Datian County are [997.8 m, 1 194 m] and [955.5 m, 1 297.8 m], with the optimal evaluation scale 1 049.6 m and 1 182.1 m, respectively. In these scale ranges, the obtained evaluation results are basically consistent. The evaluation results of optimal evaluation scales have the best effect, thus proving the feasibility of the method. The research shows that the optimal evaluation scale function is comprehensively affected by factors such as the size of the study area, the distribution of the evaluating contents, and the geographical surroundings. This study can provide theoretical support for the determination of evaluation scale in the work of mine geological environment.

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