Geoscience

Genetic Mechanism of the “Yucheng-Type” High-Grade Skarn Iron Deposits

ZHANG Zhaochong, WANG Huaihong, XIE Qiuhong, SHEN Lijun, ZHU Yuzhen, LÜ Yunhe, JIN Bowen

2024, 38(01): 1-12. DOI: 10.19657/j.geoscience.1000-8527.2024.003

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The discovery of high-grade skarn iron deposits in the Qihe-Yucheng area of northwestern Shandong Province is a significant breakthrough for iron prospecting in China.It is expected to become another potential important base of high-grade iron ore resource in Shandong Province after Laiwu, Jinling, and Jinan areas.Unlike traditional skarn iron deposits hosted in the contact zone between intrusions and carbonate rocks, the Litun iron orebodies in the Qihe-Yucheng area are hosted in the Carboniferous-Permian coal-bearing strata.The high-grade iron orebodies have a sharp contact with the surrounding rocks, which have been changed to horns in a large range.We attribute the occurrence of the iron orebodies in the Carboniferous-Permian coal-bearing strata far from the contact zone to the extremely low thermal conductivity of the overlying coal rocks, which allow the hydrothermal fluid to maintain a high-temperature state and long-distance migration.The formation of the Litun iron deposit may be ascribed to the rapid precipitation of magnetite due to decreasing temperature and salinity caused by the mixing of high-temperature magmatic fluid and low-temperature meteoric water.In addition, strong albitization commonly occurs near ore bodies, leading to the loss of iron in the dioritic rocks, which lays an important material foundation for the exsolution of iron-rich fluids and the formation of high-grade iron ores.Finally, we propose that the mantle-derived “highly differentiated” diorite and hypabyssal emplacement is favor for the exsolution of magmatic fluids, and is also prerequisites for the formation of the Hanxing-type iron deposit.

Mineral Assemblages of the Mineralized Alteration and Ore-forming Fluid Composition of the Bayan Obo Fe-Nb-REE Deposit, Inner Mongolia

LI Houmin, LI Lixing, LI Yike, KE Changhui, LI Ruiping, LI Xiaosai, WANG Yi

2024, 38(01): 13-24. DOI: 10.19657/j.geoscience.1000-8527.2023.121

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In order to place new constraints to the multiple metallogenic stages and genesis of the footwall dolomite, we carried out detailed petrographic studies on the ore related samples using optical microscope and scanning electron microscope in this study.The following genetic results have been achieved.Firstly, the mineral assemblages associated with the mineralized alteration show similar patterns among carbonatite (dyke), magnetite ore, altered rock, and mineralized dolomite.This pattern is characterized by the presence of magnetite, monazite, fluorine-carbonate rare earth minerals (e.g., bastnasite), calcite, fluorite, apatite, Ba-rich minerals (barite or witherite), biotite, Na-rich minerals (riebeckite and aegirine), and sulfide minerals.This suggests that these rocks were formed in association with a same fluid event that enriches in Fe, Ca, Ba, K, Na, Si, REE, and volatile components, such as CO₂, P₂O₅, F, and S.The textures of the rocks and ores also show distinct one-stage mineralization characterization, supporting that the Bayan Obo deposit is a product of one mineralization event.Secondly, the REE mineralization is not the product of the same fluid event as the footwall dolomite is.Instead, the REE mineralization is related to the fluid activity dominated by carbonate species, which belongs to the type of carbonatitic or magmatic-hydrothermal fluid.The footwall dolomite is REE-mineralized wall rock showing messages of sedimentary origin.The dolomite may represent hydrothermal sedimentary rocks or sedimentary carbonate rocks which have experienced hydrothermal modifications.Thirdly, we conclude that both the magnetite mineralization and the REE mineralization are the products of a same metallogenic event. However, the lack of magnetite in carbonatite raises the question of the relationship between the two sources of iron and REE.

Comparison and Application of Extraction Methods for Aeromagnetic Anomaly Caused by Deep Magnetite: A Case Study of the Qihe-Yucheng Ore Area, Shandong

GAO Xiuhe, YU Changchun, LI Xingsu, GE Tengfei, HE Jingzi

2024, 38(01): 25-34. DOI: 10.19657/j.geoscience.1000-8527.2024.004

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The large depth that the magnetite is buried and the long distance of aeromagnetic survey always leads to a weak signal of magnetic anomaly.In addition, due to that the deep magnetite mostly is formed through contact metasomatism caused by magmatic intrusion, the magnetic anomalies sourced from the source rocks and orebodies are always coupled and interfered with each other.This is challenging to directly delineate the target area for the deep magnetite orebody from the original map of aeromagnetic anomaly.Previous studies show that potential field separation technology is an effective approach to extract ore-caused anomalies.However, there are many potential field separation methods and they are all different, in terms of operation convenience and different results of extraction.In this paper, we systematically compared and analyzed the convenience of six commonly used separation methods, and evaluated the effects of extracting ore-caused anomalies from both the whole and target regions.Consequently, we established the theoretical model and verified the feasibility extracting the deep ore-caused anomalies based on the geologic background of the Qihe area, Shandong.At the end, we recommend using the marker profile line to verify the extraction effect of ore-induced anomalies when the measured data were processed.The ore-caused anomalies extracted agree with the known drilling data, indicating a strong correlation between the extracted and realistic anomalies.This study provides a reference for future delineation of target ore fields and laying-out of drilling locations.

Combined Magnetic and Transient Electromagnetic Methods to Locate and Predict the Dislocated Concealed Orebody at the Deep Edge of Yanqianshan Iron Deposit in Anshan-Benxi Area

YAN Di, FU Jianfei, JIA Sanshi, CHENG Hao, WANG Zhimeng

2024, 38(01): 35-45. DOI: 10.19657/j.geoscience.1000-8527.2024.006

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It’s becoming more and more challenging to find iron ores with economic values since all iron mines on the surface have been explored. The main directions of iron prospecting turn to the concealed orebodies. In particular, locating and identification of the concealed orebodies in deep (or periphery) parts of the existing mines have become the focus and main challenges of current geophysical exploration projects. With this view, we focus our study on locating and identifying the concealed orebodies in deep (or periphery) structural faults of the existing mines by taking the concealed iron orebodies in Yanqianshan, Anshan-Benxi area as a study case. Based on the previous geology and geophysical studies, we conducted the joint detection application studies by using the ground-based high-precision magnetic method and the transient electromagnetic method, which is based on large fixed source central loop devices and multi-turn overlapping loop devices.The research findings indicate that high-precision ground magnetic methods can delineate the planar boundaries of concealed iron ore bodies, thereby narrowing down prospective mining areas. In the eastern and southwestern sectors of the Yanqianshan Mountain iron ore deposit, two mineralization prediction zones have been identified. In the eastern anomaly zone, transient electromagnetic methods were employed to locate and identify the depth and morphology of concealed iron ore bodies. Through drilling verification, a substantial concealed magnetic iron ore body with a depth of 320 to 410 meters was discovered, exhibiting a stable eastward extension and a gradual thickening trend. Based on these findings, it is inferred that the southwestern anomaly zone, exhibiting similar anomalous characteristics, holds significant exploration potential. The multi-turn overlapping loop device of the transient electromagnetic method has higher resolution than the center loop device and is more suitable for detecting and locating concealed metal ore bodies under the cap layer.

Geochronology and Genesis of the Zhaobinggou Fe-P Deposit, Northern Hebei, China

WANG Yi, LI Lixing, LI Houmin, LI Xiaosai, MA Lanjing, XING Yuliang, SUN Xinyu, DAI Yang, WANG Xiaohui

2024, 38(01): 46-55. DOI: 10.19657/j.geoscience.1000-8527.2023.122

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In order to investigate the genesis of the iron-phosphorus (Fe-P) deposits hosted in the Archean metamorphic series in Northern Hebei-Western Liaoning, we carried out petrographic, geochronological, and geochemical studies on the typical Zhaobinggou deposit.Field observations show that the so-called “the banded Fe-P ore” is hosted as veins in the biotite-hornblende-plagioclase gneiss, and is characterized by the gneissic schistosity with cross-cutting Fe-P veins.The formation of the vein folds is associated with the post tectonic deformation.Zircons in the Fe-P-bearing biotite-hornblende-plagioclase gneiss are intergrown with the Fe-Ti oxides and apatite.Cathodoluminescence imaging of these zircon grains shows no or weak zoning or patchy texture, which is typical of mafic magmatic origin.Zircon U-Pb dating using LA-ICP-MS technique obtained a weighted average age at (282±3) Ma (MSWD=0.78), which constrains the Fe-P mineralization to be in the early Permian, rather than Neoarchean as supposed previously.Comprehensive comparison studies show that the geochemical characteristics and the ore-forming age of the Zhaobinggou Fe-P-bearing biotite-hornblende-plagioclase gneiss are similar to those of the regional mafic pyroxenite-hornblendite, which is considered as the parent rock of the Fe-P mineralization.The results indicate that the Zhaobinggou Fe-P deposit is associated with Phanerozoic Alaskan-type mafic-ultramafic magmatism along the Hongshila-Damiao fault zone, but not related to any metamorphism as reported previously.Further investigations are needed for revealing the genesis of other similar deposits.

Study of the Characteristics of Mass Transfer During the Ore-forming Process of High-grade Iron Ore in the Gongchangling Iron Deposit, Liaoning

HOU Tingting, YAO Yuzeng, FU Jianfei, LIU Jing, ZHANG Yongli, GUO Rongrong

2024, 38(01): 56-67. DOI: 10.19657/j.geoscience.1000-8527.2023.120

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As the largest and the only BIF-hosted high-grade magnetite iron orebody with industrial mining value in China, the metallogeny of the Gongchangling iron ore is still controversial.In this study, we collected typical BIF and high-grade ore samples from the No.4 iron ore layer and analyzed their chemical compositions.Consequently, we determined the elemental changes during the formation of high-grade iron ore using mass balance calculations, and therefore the following conclusions are received.For the major elements, Fe₂O₃ is strongly enriched, however, SiO₂ is depleted, accompanying with the migration of alkali and alkaline elements (e.g., Na, K, Ca and Mg), which are more active in geochemical mobilization properties.P₂O₅, BaO, and Cr₂O₃ are relatively less enriched, and this is probably related to the hydrothermal fluids which contributes to the formation of the high-grade iron ore; For trace elements, some high field strength elements (HFSE), such as Nb, Ta, and U are enriched, whereas Ce, Th, and Zr are depleted, and Hf and Ti remain unchanged; In terms of some large ion lithophile elements (LILE), Ba and Cs are enriched, however, Rb and Sr are depleted.This suggests that the Nb-Ta mobilization in both high-grade iron ore and the altered rocks are caused by the same geological event; For rare earth elements (REE), the light REE (e.g., La, Ce, Pr and Nd) are distinctly depleted, whereas, the heavy REE are enriched.In summary, the genesis of the Gongchangling high-grade iron ore is probably related to the granitic magmatic events.

Magnetic Field Anomany Characteristics and Ore Predictions in the Litun Area of Yucheng, Shandong

ZHANG Wenyan, ZHU Yuzhen, LIU Xue, RU Liang, YAN Bing

2024, 38(01): 68-76. DOI: 10.19657/j.geoscience.1000-8527.2024.008

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Recently, significant breakthroughs have been made in the exploration of rich iron deposits in Yucheng, Shandong. However, there are still multiple local magnetic anomalies in the area that have not been verified, which have a promising ore-prospecting potential. However, the Cenozoic Erathem in this area is very thick, about 900-1,100 m, and the magnetite orebody is deeply buried, which leads to weak signals of geophysical anomaly, making it challenging to find the iron ores through surface exploration. In order to systematically summarize the abnormal characteristics of magnetite in this area and provide a basis for drilling deployment, the paper focuses on analyzing the abnormal characteristics of airborne gravity and magnetic plane and the abnormal characteristics of high-precision magnetic survey on the ground in Litun area, Yucheng, and summarizes the main prospecting signs of gravity and magnetic anomalies of skarn type iron ore, which are mainly the anomaly centers of polarized magnetic anomalies, residual magnetic anomalies, vertical derivatives and total gradient modes. Accordingly, two prospecting targets in Diedao Village and Yuzhuang village were delineated. Through the 2.5D gravity and magnetic profile inversion based on the electrical seismic constraints, we delineated two ore target areas, which can further guide the deploying the locations of the verification drilling holes. Significant breakthroughs in ore prospecting have been made in the Litun area of Yucheng City after the drilling verification of stacked-channel anomalies. The results in this study are of great significance and guidance for the future mineral exploration in this area and the search for iron-rich skarn-type ores in other deep ore hidden areas.

Geophysical Characteristics and Prospective Exploration of Vanadium-Titanium-Magnetite Deposit in Taihe Area, Sichuan

YANG Xue, GE Tengfei, FAN Zhengguo, HUANG Xuzhao, HE Jingzi, TIAN Song, LI Jing, YANG Hai, LUO Yao, LI Bing

2024, 38(01): 77-86. DOI: 10.19657/j.geoscience.1000-8527.2024.010

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In this paper, we use regional geological metallogenic characteristics of Taihe area in Sichuan as the research background, the high-precision airborne magnetic data as the research foundation, supplements it with regional gravity data, then combines with the measured physical properties of rocks (minerals), to study and analyze the geophysical characteristics of known iron ores and their surrounding areas. Finally, we select 5 anomalies at M47, M47-1, M47-2, M47-3, and M47-4. These anomalies demonstrate typical geophysical characteristics, signifying potential mineralization. The magnetic anomaly presents as an elliptical local bulge with a positive magnetic anomaly, whereas the vertical second-order gravity derivative field resembles a nasally bulging elliptical positive anomaly. Notably, vanadium-titanium magnetite and gabbro (ore-bearing) exhibit the strongest magnetism and highest density, resulting in significant magnetic anomalies and strong anomalies, as corroborated by geophysical data. Through ground surveying, we established a correlation between the M47 magnetic anomaly and the known orebody, while interpreting M47-1 and M47-2 as concealed ore-bearing basal intrusive rocks. Utilizing 2.5-D inversion with the GeoProbe and GMVPS software, we estimated the M47-1 and M47-2 anomalies to represent an orebody with 469 million tons of resources, highlighting the massive potential for further exploration. The M47-3 and M47-4 anomalies suggest the possible presence of buried magnetic ore bodies at a certain depth, warranting further investigation to explore the potential of vanadium-titanium magnetite associated with mafic intrusive rocks.

Delineation of Sedimentary Metamorphic Rich Iron Ore Bodies Based on Geophysical Techniques: Case Analysis of Qidashan Iron Ore in Anshan, Liaoning

MENG Jiaqi, WANG Zhimeng, JIA Sanshi, FU Jianfei, ZHANG Yansong

2024, 38(01): 87-97. DOI: 10.19657/j.geoscience.1000-8527.2024.005

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Anshan-Benxi Area of Liaoning Province is one of the most important iron resource bases in Northern China. There are various iron-rich orebodies distributed in this area. The studies on the iron-rich ore metallogeny are fruitful for the past decades but the prospecting technology for iron-rich ores is relatively lacking. Based on the discrepancy of physical parameters between the iron-poor and -rich orebodies, we selected surface high-precision magnetic and high-density resistivity methods to perform the comprehensive geophysical exploration of the iron-rich orebodies in the Qidashan iron mine area in Anshan, Liaoning Province. The study results show that the high-precision magnetic method is able to delineate the spatial distribution range of the magnetic anomalies caused by the enriched iron bodies in the magnetic anomaly field with a poor iron grade through limiting the magnetic field intensity at >16,000 nT. The high-density resistivity method can accurately characterize the shape and scale of iron-rich bodies in the high magnetic anomaly field by limiting the resistivity at <2200 Ω·m. This can be considered as a constraint threshold to build a forward and inverse models for the ground magnetic method as to identify and locate the iron-rich bodies in iron-poor ore layers. We also found that the intersection area of the NNW strike and NEE lateral fault in Qidashan iron mine area has a higher potential to form thick and enriched iron orebodies.

Key Ore-controlling Factors of the Skarn Type High-grade Iron Deposits in North China Craton: Constraints from Stratigraphy

ZHANG Baotao, MEI Zhenhua, LI Xiuzhang, JIANG Xiaoping, HU Zhaoguo, WANG Xiaoyu, ZHAO Xiaobo, HU Jiabin, LIU Sen

2024, 38(01): 98-116. DOI: 10.19657/j.geoscience.1000-8527.2024.011

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The key ore-controlling factors of the skarn high-grade iron deposits in North China Craton (NCC) is a challenging topic and largely restrict the ore-prospecting directions in the future and make relevant study breakthroughs impossible.Based on the distribution pattern of typical orebodies in NCC and stratigraphy, we determined the key ore-controlling factors and their restriction mechanism.The large scale of orebodies of typical skarn high-grade iron deposits in NCC are closely related to the surrounding rock series (e.g., karst layers, gypsum beds) and they are mainly distributed in the middle Carboniferous Fengfeng Formation, the lower Majiagou formation, and the upper Majiagou Formation, which are located in the karst stratum above gypsum.The key controlling factors from stratigraphy on the mineralization of skarn type high-grade iron deposits are mainly manifested in four aspects: the vertical distribution of karst stratum restricts the favorable space for the emplacement of iron-rich orebodies; the unconformity surface controls the development of the karst system, affecting the scale of high-grade iron orebodies; the sequence stratigraphy affects the karst stages, constraining the distribution of karst layers and high-grade iron orebodies; the gypsum salt layer indicates the bottom boundary of the strongly phased karstification, limiting the favorable lower bound for hosting the high-grade iron orebodies.Consequently, the ore-prospecting model for the skarn type high-grade iron deposits in NCC was established, and seven potential mineralization spatial segments, including three major ones, were recommended in the study.The key ore-prospecting and research directions were suggested at end of the study.

Apatite U-Pb Geochronology of the Trachy Dacite in Mashan Area, Jiaolai Basin, North China Craton, and Its Geological Significance

ZHU Tuo, HE Dengyang, HUANG Yaqi, QIU Kunfeng

2024, 38(01): 117-127. DOI: 10.19657/j.geoscience.1000-8527.2023.053

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The Wulian-Qingdao-Yantai fault (WQYF) is one of the most important basin-controlling faults in the Jiaolai basin, where the fault dominates the formation and evolution of the basin.This fault is mainly composed of abundant NNE faults, such as Muping-Jimo fault and Taocun fault.The WQYF experienced sinistral strike-slip movement in Late Jurassic, extensional rift in Early Cretaceous, and dextral strike-slip movement during Late Cretaceous-Paleocene.However, the most key question that the duration of the Cenozoic dextral strike-slip movement still remains unclear.Previous studies suggested that temperature of strike-slip movement in this region is about 550-650 ℃, which is higher than the closure temperature, 350-550 ℃, of the apatite U-Pb system.Therefore, in this case apatite can be an ideal candidate to investigate the dextral strike-slip of the WQYF.In this study, we conducted U-Pb dating of apatite from the Early Cretaceous trachy-dacite in the Mashan area and obtained the U-Pb age of 64.1±3.7 Ma.The measured magmatic age of apatite is different from the crystallization age of the Mashan trachy-dacite, indicating that at least there was one geothermal event which reset the apatite U-Pb isotope system in Early Paleocene.Since Early Cretaceous, the collision between the Indian plate and Eurasian plate, and the switch of subduction direction of the paleo-Pacific plate from NWW to NW result in a north-south extension of the Jiaolai basin and the dextral strike-slip of the Muping-Jimo fault.Therefore, we propose that the apatite U-Pb age of the Mashan trachy-dacite documented the dextral strike-slip thermal event of the WQYF, and indicates that the dextral strike-slip may continue until Paleocene.

Genesis and Tectonics of the Sipingshan Gold Deposit in Nadanhada Terrane, Sikhote-Alin Orogen: Constraints from Zircon U-Pb Chronology, Petrological and Fluid Geochemistry

HE Yunlong, ZHANG Guobin, YANG Yanchen, FENG Yue, KONG Jingui, CHEN Xingkai

2024, 38(01): 128-153. DOI: 10.19657/j.geoscience.1000-8527.2023.082

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The Sipingshan gold deposit is located in the east Nadanhada terrane, which is the largest gold deposit in the terrane with a proven gold resource of 5.8 t in Hulin City, Heilongjiang Province.The ore body occurs in the cherts and silicified breccias in Sipingshan Formation, and the rhyolite in Datashanlinchang Formation.In this study, we aim to understand the metallogenic process and diagenetic and metallogenic geodynamics, and further determine the diagenetic and metallogenic ages.We conducted detailed field survey on the Sipingshan gold deposit and sampled the cherts and silicified breccias in Sipingshan Formation and rhyolite in Datashanlinchang Formation.Further, we carried out the zircon U-Pb dating using LA-ICP-MS technique and whole-rock major and trace element geochemistry on the ore-bearing surrounding rocks, and additionally we performed the thermodynamic analysis on the fluid inclusions in the gold-bearing quartz veins.The results indicate that the diagenetic ages of the rhyolite samples SPS-H-002 and SPS-H-009 in Datashanlinchang Formation are (134±1) Ma and (123±1) Ma, respectively.The gold mineralization age is slightly later than the that of the rhyolites, belonging to the late Early Cretaceous.Cherts and silicified breccias have a high SiO₂ content, rich in Cu, Ni, and Ba elements but poor in Co element.Rare earth elements (REE) content is relatively lower in the rocks and the concentration difference between the light and heavy rare earth elements is not significant, with a europium positive anomaly possibly caused by hydrothermal sedimentation.Rhyolite belongs to a type of rock from subalkaline peraluminous calc-alkaline to high potassium calc-alkaline series, with high Si and Al contents but poor in Ti, Mn, P, and Zr contents.Those rocks are enriched in light REE but deficient in heavy REE, with an pronounced Eu negative anomaly but no Ce anomaly.They belong to highly differentiated S-type granite and may be the product of partial melting of young crustal material with depleted mantle accretion.The fluid inclusions in the gold-bearing quartz veins range from 5 to 12 μm in size, and with elliptical and irregular shapes in group or isolated distribution.Fluid inclusion study results in a homogeneous temperature of 119-223 ℃, salinity of 0.40%-8.9%, density of 0.84-0.97 g/cm³, and capture pressure of 21.2-51.4 MPa.The δD value of the gold-bearing quartz ranges from -113.8‰ to -84.0‰ and the δ¹⁸$O_{H_{2}O}$ value ranges from -3.1‰ to 2.2‰. The stable isotopes indicate that the ore-forming fluid has a magmatic origin and shows mixing characteristics of magmatic and meteoric water sources.Combined with the findings from the regional tectonic evolution, it can be concluded that the Sipingshan gold deposit was formed during the post collision and the gold mineralization is closely related to the subduction of the Pale-Pacific plate.

Petrogenesis and Tectonic Setting of the Nanpaotai Granite Porphyry in Inner Mongolia: Constraints from Zircon U-Pb Geochronology, Hf Isotopes, and Whole-rock Geochemistry

LIU Qingzhan, JIANG Xiaojun, WANG Guo, LI Tianyu, LI Dongpeng

2024, 38(01): 154-168. DOI: 10.19657/j.geoscience.1000-8527.2023.080

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Intensive magmatism in early Early Cretaceous is recorded in the Duolun area, which is located in the middle segment of the northern margin of North China Plate.Interpretation of the tectonic setting can aid to resolve the controversy whether the magmatism is controlled by the Mongol-Okhotsk tectonic activities or by the subduction of the Paleo-Pacific Plate.This paper presents the LA-ICP-MS zircon U-Pb geochronology, Hf isotopes, and whole-rock geochemistry of the Nanpaotai granite porphyry in Duolun.Zircons U-Pb dating on the granite porphyry shows a weighted mean age of 136±1 Ma, indicating that it was formed in early Early Cretaceous.The zircon ε_Hf(t) values vary between -8.1 and +1.9, with Hf isotopes crustal model ages ($\mathrm{T}_{\mathrm{DM}}{ }^{\mathrm{C}}$) ranging from 1,044 to 1,680 Ma.The Nanpaotai granite porphyry belongs to slightly peraluminous shoshonite series, enriched in SiO₂ (70.53%-72.72%), total alkali (K₂O+Na₂O=9.09%-9.48%), but poor in MgO (0.19%-0.39%), CaO (0.55%-0.67%), and P₂O₅ (0.19%-0.39%).It is also enriched in LREE and LILEs (e.g., K, Cs and Rb), depleted in HFSEs (e.g., Nb, Ta and Ti), Sr and P elements, with (La/Yb)_N ratio varying between 22.10 and 57.67, and showing a negative Eu anomaly (δEu=0.38-0.52).Comprehensive geochemical evidence indicate that the Nanpaotai granite porphyry was formed in the intraplate anorogenic extensional tectonic environment and belongs to A-type granite.The primary magma mainly derived from the partial melting of the ancient lower crust, and there was mixing of mantle-derived components.Combined with the regional tectonic evolution, it is considered that the early Early Cretaceous magmatism in Duolun is related to an extensional tectonic environment after the closure of Mongol-Okhotsk Ocean.This suggests that the influence of the Mongol-Okhotsk tectonic system along the southeast direction had extended to Southeastern Inner Mongolia in the middle segment of the northern margin of North China Plate.

Petrogenesis and Tectonic Implications of the Zhongpai Fine-grained Granite in Qingshanbao, Gansu: Constraints from Geochemistry and Zircon U-Pb Chronology

CHEN Yaoxin, LIU Wenheng, WANG Kaixing, LIU Xiaodong, SUN Liqiang, YIN Donghua

2024, 38(01): 169-182. DOI: 10.19657/j.geoscience.1000-8527.2023.100

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The Longshoushan uranium mineralization belt is located at the junction of North Qilian Orogenic Belt and Alxa Block.This mineralization belt is controlled by the tectonic activities of Qilian Orogenic Belt during Middle Silurian-Early Devonian and formed in a post-collision extensional environment.However, the ending of the Longshoushan uranium mineralization still lacks constraints from a precise geochronologic method.In this paper, we studied the whole-rock geochemistry, petrography, and zircon U-Pb chronology of the Zhongpai fine-grained granites in Qingshanbao, and discussed their rock types and genesis, and tectonic background.The results show that the diagenetic age of the Zhongpai fine-grained granites is (413.7±3.0) Ma, indicating it was formed from the Early Devonian magmatism in a post-collision extensional environment.The rocks are characterized by a high Si content, alkali, and low contents of CaO, MgO and P₂O₅, and with a A/CNK ratio of ~1.01-1.04.These rocks are enriched in light rare earth elements and Th, U, Nd, K, and depleted in heavy rare earth elements and Ba, Sr, P, Ti, and with a distinct negative Eu anomaly.These comprehensive geochemical data indicate that the Zhongpai fine-grained granites belong to the weakly peraluminous and highly differentiated I-type granite.The result also shows that the magma originated from the lower crust.The main residual mineral facies in the magma is amphibole, and the magma had undergone significant crystal fractionation and differentiation during its evolution.Combined with the previous studies, the magmatism occurred in Early Paleozoic in Longshoushan can be divided into two stages: the Late Ordovician-Early Silurian (~452-438 Ma) and Middle Silurian-Early Devonian (~430-412 Ma), which corresponds to the subduction stage and post-collision stage, respectively.

Trace Element Geochemistry and Its Metallogenic Implications of the Pyrite from the Xiwan Pb-Zn Deposit in Luzong Basin, Anhui

HU Shengping, HAN Shanchu, ZHANG Hongqiu, ZHANG Yong, PAN Jiayong, ZHONG Fujun, LU Jianyan, LI Weixin

2024, 38(01): 183-197. DOI: 10.19657/j.geoscience.1000-8527.2023.094

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Pyrite is the most common metal sulfides formed in lead-zinc (Pb-Zn) deposits, and it accompanies most of the ore-forming process of the Pb-Zn deposits.Pyrite mineralogy and chemical compositions are key information to get insight into the mineralization process and therein the genesis of the ore deposits.The Luzong basin, part of the middle-lower Yangtze river valley metallogenic belt, has recently been found to host a large scale of Xiwan Pb-Zn deposit along its northern margin.Even though the Xiwan Pb-Zn deposit has been intensively investigated, the studies on the correlations between the pyrite geochemistry and the genesis of the ore deposit remain unresolved.This study for the first time employed laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and petrography to investigate the pyrite characteristics from the ore deposit.The aim is to elucidate the trace element geochemistry and substitution mechanisms in pyrite crystals with an aim to understand the genesis of the ore deposit.Our results revealed two stages of pyrite formation based on crystal morphology and mineral associations, namely pre-ore and ore-forming stages.Pre-ore pyrite exhibited a semi-euhedral to anhedral grain structure with the size ranging from 10 to 50 μm and was composed of multiple fine-grained aggregation, characterized by enriched Cu, Ag, As, Pb, and Sb contents.In contrast, the pyrite associated with the Pb-Zn ores displays anhedral to semi-euhedral crystallization with its size > 200 μm.The pyrite occurs within the limestone fractures with vein-like structures and is enriched in Mn, Co, Ni, Zn, Cs, Cd, In, and Sn elements, and mostly associated with the minerals galena and sphalerite.The substitution mechanisms of trace elements in the pyrite primarily involved single-element and multi-element coupled substitutions.Single-element substitutions include Co²⁺↔Fe²⁺, Ni²⁺↔Fe²⁺, and Pb²⁺↔Fe²⁺, and multi-element coupled substitutions comprise As³⁺+Ag⁺↔2Fe²⁺ and (Tl⁺+Cu⁺+Ag⁺) + (Sb³⁺, As³⁺) ↔3Fe²⁺.Additionally, small mineral inclusions such as galena, sphalerite, and arsenopyrite, were observed within the pyrite crystals.The trace elements in pyrite, such as Co, Ni, As, Cu, Mn, Ge, and Ag, exhibited similarities to the skarn-type Pb-Zn deposits.Combining the findings in previous studies, this study classifies the Xiwan Pb-Zn deposit as a distal skarn-type deposit.

Mineralogy, Trace Element Chemistry, and Their Metallogenic Implications of Sphalerites from the Haopinggou Ag-Au-Pb-Zn Polymetallic Deposit, Xiong’ershan Area, Western Henan

LIU Jinbo, ZHANG Dexian, HU Ziqi, CHEN Shaowei, XIE Xiaoyu

2024, 38(01): 198-213. DOI: 10.19657/j.geoscience.1000-8527.2023.093

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The Haopinggou Ag-Au-Pb-Zn deposit is an important Pb-Zn polymetallic deposit in the Xiong’ershan area, Western Henan.The orebodies are identified as mainly occurring in the altered fractures and fault zones, and the metallogenesis of the deposit is associated with magmatic intrusions.Previous studies on this deposit mainly focuses on geochronology and isotopic geochemistry, constraining the ore-forming age and tracing ore-forming materials.Few studies focus on interpreting the mineralization processes from a mineralogy perspective.In this study, we studied the mineralogy, major and trace elements of different types of sphalerite, using EPMA and in situ LA-ICP-MS techniques, with an aim to invert the ore-forming physicochemical conditions and to constrain the genetic types of the deposit.Our study identified two types of sphalerites in this deposit.Sphalerite I contains higher Fe, Mn, Cd, Cu, and In contents, with a dark or light brown color, and is mostly associated with pyrite and chalcopyrite occurrence.Sphalerite II is relatively enriched in Co, Ge, Sn, and Pb contents, with a yellowish or dark brown color, and predominantly coexists with galena, and the fractures of sphalerite II are usually infilled by pyrite and carbonate grains.Sphalerite was investigated to have a considerable Fe, Co, and In contents, and Fe, Mn, Cd, Co, and In basically occur as substitutions in the crystal, but Ag, Sb, Cu, and Pb minerals present as mineral inclusions within the sphalerite.Moreover, the trace elements, element ratios (Zn/Cd, Zn/Fe, and Ga/In), and combined with the geothermometric result indicate a low to medium temperature (229-259 ℃ of the ore-forming fluid) and low sulfur fugacity (lgƒ(S₂)=-12.0--10.1) mineralized environment and the mineralization temperature may have changed significantly from stage II (Sp1) to stage III (Sp2), and the formation temperature of sphalerite grain gradually decreases from the core to the edge based on the elemental mapping analysis.Comparisons with the previous studies on sphalerite from typical Pb-Zn deposits, the low Ga/In and Ge/In ratios, as well as the low Ge content, indicated that this deposit has a close relationship with the magmatic hydrothermalism.Based on those evidence, we propose that the Haopinggou Ag-Au-Pb-Zn polymetallic deposit may belong to the post-magmatic hydrothermal alteration rock type and vein type deposit.

Prospecting Prediction Using Geoelectric Extraction in the Periphery of the No.374 Deposit in Rongshui, Guangxi

ZHANG Jian, WEN Meilan, YE Wu, JIANG Xiaoming, TAN Jiangdong, YANG Hang, LUO Haiyi, LIU Panfeng, JIANG Yuxiong

2024, 38(01): 214-223. DOI: 10.19657/j.geoscience.1000-8527.2023.026

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To ascertain the uranium mineral ore-fields for the purpose of future exploration in the periphery of Guangxi Rongshui No.374 deposit, and further to delineate the target area for future prospecting, we carried out a prospecting study using geoelectric extraction and measurement techniques.At first, a feasibility test of ore prospecting was performed on a known ore profile, and the testing results show that clear anomalies of major ore-forming elements can be detected directly above the known orebodies, showing distinct ore-indicating effect.This test proved that this method is feasible and effective for local ore prospecting.Through the factor and cluster analysis of 13 elements extracted from geoelectricity, four element groups of F1(Pb-Zn-Ce-Eu-La-Nd-Yb), F2(U-Th-As), F3(Sb-W) and F4 (Mo) were obtained, with F2 being the main factor in this study area, and F1 being the secondary factor.The abnormal distributions of those element groups were analyzed through drawing the abnormal scores of F1 and F2 factors, and we found that the abnormal distribution w(U)/w(Th) >1/3 is an important index for uranium prospecting.According to the characteristics of single element, F1 and F2 factor, and w(U)/w(Th) anomaly, and with combination of local geology, we delineated two target areas (I and II), of which target area II has a greater exploration potential for hidden uranium orebodies.

Sedimentary and Paleontological Characteristics of Early Devonian Sequence in the Pali Area in Yadong, South Tibet

WANG Jianhua, ZHU Youan, LI Qiang

2024, 38(01): 224-229. DOI: 10.19657/j.geoscience.1000-8527.2023.095

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In Qinghai-Tibet Plateau, no Paleozoic fish fossils have been found so far due to limited studies.Recently, the second comprehensive scientific expedition to Qinghai-Tibet Plateau-paleontological expedition selected several areas in Southern Tibet with good Devonian exposure to conduct investigations, in which the Pali area in Yadong County of South Tibet is located in the hinterland of the southern Himalayan orogenic belt, and the Devonian sequence was only found in the western and southern parts of Pali Town.Using field paleontological section measurements, fossil sampling, recording and photography, we report a new section of Lower Devonian Liangquan Formation which is enriched in paleontological fossils located in Southwest Pali.We also discussed the sedimentary characteristics during Early Devonian of the study area.The lithology of the lower member of The Lower Devonian Liangquan Formation is interbedded within the coarse-grained and medium-fine grained clastic rocks.The lower part of the middle section is medium-thick bedded limestone, and the upper part is mainly bioclastic limestone.The lithology of the upper strata is mainly clastic rock and marl.From the lower member to the lower part of the middle member in the section, the regressive sedimentary sequence of coarse sands at the bottom and fine at the top reflects a process of seawater deepening in the coastal and shallow sea.The coral-bearing bioclastic limestone in the upper part of the middle member indicates that the seawater begins to be shallower.The clastic rock and marl assemblage in the upper member of Liangquan Formation reflects a coastal sedimentary environment.There are rich paleontological fossils in clastic rocks in the upper member, including cephalopods, aminoids, brachiopods, bivalves, and plant fragments, and bone fragments, and fossils of suspected placodermi are also found.These new data provides a comparative study with the sedimentary characteristics of Early Devonian in the study area.The discovery of the suspected placodermi remains effectively provide a guide to the further work searching for fossil fishes in this area.It also provides potential clues for studying the paleogeographic pattern in the southern Tibet of Paleo-Tethys.

Characteristics and Geological Significance of the Paleogene Microfossil Assemblages in the Liaoxi Sag, Bohai Bay Basin

YAO Yaqin, YANG Jilei, ZHAO Dujing, QI Yumin, WEI Wenyan, CAO Jie, YANG Jiaojiao, LI Guoliang

2024, 38(01): 230-239. DOI: 10.19657/j.geoscience.1000-8527.2024.009

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The deep-water environment in lakes of the middle and late Paleogene in the Liaoxi sag, Bohai Bay Basin, formed a special group of paleontological fossils. In this study, we characterized the microfossil assemblages through investigating the paleontological drilling data in this study area. Five fossil assemblages of pollen algae and five mesomorphic fossil assemblages were established. In the western and northwestern Shahejie Formation, distinct near trapezoidal mesomorph fossils Candona sagmaformis, C. postabscissa, and membrane tube algae fossils Hystrichosphaeridium tubiferidium tubiferi and Membranilarnacia originally formed in deep-water were observed. Moreover, mesomorph fossils Tianjinia fulgida, Bohaicythere sp, Parabohainia elliptica, and others formed in deep-water were widely observed in Dongying Formation. These fossil signatures indicate that the range of sedimentary center in deep water expanded gradually from Shahejie Formation to Dongying Formation, and it connected with the sedimentary centers of the Liaozhong depression in the end. Meanwhile, comparison study of a large number of paleontological fossils and their rock lithology, we concluded that the Liaoxi sag and the low convex zone of Liaoxi sag had a large range of sedimentary breaks when deposited in the second section of Shahejie Formation. Also, the upper subsection of the third section of Shahejie Formation is widely developed. This study provides a strong evidence for the division and comparison of the Paleogene strata in this region, and meanwhile this study enriched the relevant studies on sedimentary environment.

Characteristics of the Lepidodendron Fossils from the Lower Permian Taiyuan Formation in Xishan area of Taiyuan, Shanxi

JIA Gaowen, SHI Jianru, YANG Yongsheng, WANG Jin, HAO Siyu, XUE Peilin, LI Jiarui

2024, 38(01): 240-247. DOI: 10.19657/j.geoscience.1000-8527.2023.092

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The Cathaysia flora is one of the four famous floras in Late Paleozoic, and Lepidodendron is widely distributed in the four major floras.In the Cathaysia flora, Lepidodendron is regarded as the oriental form due to its distinctive characteristics, such as large leaf traces without air passage marks under the leaf.This is different from the Lepidodendron in the Euramerican flora that have air passage mark traces.In this study, three species of Lepidodendron from the Lower Permian Taiyuan Formation in the Xishan area of Taiyuan, Shanxi, are identified and been investigated in detail.According to the fossil records of Lepidodendron in the world and the latest results of the phylogeny, we believe that the Lepidodendron genus may originate in the late of Late Devonian from South China, then it arrived at the Asia Minor of Turkey over sea in the early of Early Carboniferous, and at the end it entered into North America across Western Europe.Another route can be that the genus reached to European Russia from the Asia Minor and then spread to the eastern European and central Asia in the Carboniferous and Permian period.

Lajia Ruins in Qinghai Province Might Be Caused by Seismic-induced Liquefaction Mudflows of Sands and Soils: Implication from the Jishishan Earthquake in Gansu Province on December 18, 2023

LI Junlei, ZHANG Xujiao, YU Hailin, WANG Yifan, ZHANG Xiangge, LI Qiurong, LI Caihong, ZHANG Lilei

2024, 38(01): 248-259. DOI: 10.19657/j.geoscience.1000-8527.2024.012

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The Lajia Ruins, often called the “Pompeii in the East”,situated in Minhe County, Qinghai Province, is well known as an archaeological site documenting a catastrophic event approximately 3,900 years ago. The causation of the disasters responsible for the destruction of the Lajia settlement has been in hot debate for an extended period. Various points of view regarding “flooding causes” has been gained acceptance within the general public. However, is the catastrophic event indeed linked to flooding? The 6.2-magnitude earthquake struck in Jishishan County, Gansu Province on December 18, 2023, with its epicenter located a mere 16 kilometers from the Lajia Ruins. This seismic event not only substantially damaged the Lajia Ruins Museum but also triggered mudflows in Jintian Village and Caotan Village, Zhongchuan Town, Minhe County, just 5 kilometers away from the Lajia Ruins. This catastrophic event led to the direct burial of residential structures and villagers, potentially representing a replication of the formative processes that gave rise to the Lajia Ruins. Consequently, it emerges as a pivotal empirical material for comparative studies investigating the causative factors underlying the genesis of the Lajia Ruins. Through conducting field investigations and comprehensive studies of the seismic disaster, it is conceivable that contemporary insights may shed light on the longstanding enigma surrounding the genesis of the Lajia Ruins. The earthquake has induced an upward surge of groundwater from the ancient riverbed gravel layers beneath the loess, causing the liquefaction of the loess and the rapid downstream flow of mud through gullies. As the mudflow encountered obstacles when passing through Caotan Village and Jintian Village, it overflowed the gullies, destroying some houses and even burying villagers. The distinctive geological stratigraphy and the abundance of groundwater, triggered by seismic activities, resulted in soil’s liquefaction and mudflows’ formation, constituting crucial factors in the genesis of seismic disasters in Zhongchuan Town. Field investigations indicated the tragic burial of a family of five in Caotan Village was not the result of a typical “sand surge”, nor does it exhibit traces of “flooding”. Instead, it is attributed to secondary seismic hazards, specifically mudflows induced by the earthquake. Combined with the preservation status of cultural remains and sedimentary characteristics at the Lajia Ruins, inference suggests that the ancient earthquake 3,900 years ago, along with the resultant liquefaction of soil and the rapid flow of mud, provides a plausible explanation and reconstruction for the instantaneous catastrophe at the Lajia Ruins. The formation of the Lajia Ruins is likely unrelated to the mountainous flash floods induced by heavy rainfall and certainly not caused by the purported megaflood.

Characteristics of the Geoheritage in Xigaze of Tibet and Its Feasibility for Geopark Construction

LI Yuchun, XIAO Shiqi

2024, 38(01): 260-268. DOI: 10.19657/j.geoscience.1000-8527.2024.007

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The diversity, rarity, and its potential scientific value are the most prominent characteristics of the geoheritage resources in Xigaze, Tibet. However, the lack of comprehensive research on their categories, distributions, and origins of these geological heritages restricts the protection and utilization of those resources. Based on the investigations and analysis of previous geological and geographical data, we summarized the categories, distribution, and characteristics of the major geoheritages in the Xigaze area. We divided these geoheritages into three large categories, further eleven basic categories, and twenty-two sub-categories, and identified their spatial distributions of those heritages. Moreover, the SWOT (strength, weakness, opportunity, and threat) method was used to analyze the protection and utilization of geoheritage resources in the area. We therefore put forward the strategies and suggestions for the future geopark construction in Xigaze. This study strengthens the research and evaluation of the geoheritage resources, enhances the scientific cognition of the geoheritages, and constructs a collaborative development ecology for these geoheritage resources and other tourist resources, and for further protections of the environment.

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