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10 August 2024, Volume 38 Issue 04

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Theories and Methods of Tectono-physicochemistry

Theoretical Outline and Application Prospects of Tectonophysicochemistry

LÜ Guxian, ZHANG Baolin, HU Baoqun, ZHOU Yongsheng, WANG Zongxiu, WANG Hongcai, CAO Daiyong, FANG Weixuan, HAN Runsheng, XU Deru, YANG Xingke, JIAO Jiangang, WANG Cuizhi, LÜ Chengxun

2024, 38(04):  837-852.  DOI: 10.19657/j.geoscience.1000-8527.2024.081

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Tectonophysicochemistry is an emerging study direction in geomechanics within the field of “structure-combined construction”. It has developed into an interdisciplinary field that studies the correlation between the physical and chemical changes of rocks during tectonic activities. In addressing the challenging problem in earth sciences, namely “whether tectonic force can affect chemical equilibrium”, the author conducted in-depth research on the geological structures of ore fields and explored the influence of tectonic force on pressure. The tectonic stress field can be divided into two parts: one is the stress difference, which causes the deformation of rocks; and the other is the average stress, which is the positive pressure stress state of equal directions that changes the volume of rocks. The latter is called “structural additional hydrostatic pressure”. The “tectonic additional hydrostatic pressure” is superimposed on the pressure caused by its geological processes, altering the pressure at a given point and affecting other physical and chemical conditions, thus controlling the diagenetic and geochemical processes of diagenesis and mineralization.Tectonophysicochemistry is the study of “how tectonic forces change the physicochemical conditions and then affect the chemical process”. It focuses on structural additional pressure, temperature, and other physicochemical conditions caused by tectonism and their control over physicochemical processes. The prediction of “second enrichment zone” deep in Jiaodong gold deposit, using theories and methods such as tectonophysicochemistry and “structural correction of metallogenic depth” has been confirmed. This provides theoretical and methodological support for Jiaodong, the third-largest gold region in the world. After more than 30 years of scientific research and prospecting practices, tectonophysicochemistry has gained extensive academic influence. The Geomechanics Committee of the Geological Society of China established the “Professional Group of Tectonophysicochemistry” in 1996, and the Chinese Geophysical Society approved the establishment of the “Professional Committee of Tectonophysicochemistry” in 2018. The problems in tectonophysicochemistry that need further study are: additional hydrostatic pressure, tectonism affecting temperature, tectonism changing physical properties of rock, tectonism affecting geological PT phase diagram, and developing methods for observing and studying structural deformation lithofacies. Tectonophysicochemistry has made significant progress in various areas, including the expansion and application of abnormal crustal pressure and deep crustal pressure states, tectonic driving and trapping of oil and gas, tectonic correction calculation of diagenetic and metallogenic depth and prediction of hidden ore deposits, “crustal genesis of tectonic pressurization” in ultra-high-pressure metamorphic belt, physicochemical conditions of coal deformation and metamorphism, thermodynamic analysis of critical mineralization, tectonophysicochemical constraints of earthquake disaster fluid on rock system, and geophysical exploration based on tectonic deformation lithofacies belts. There is a broad prospect for the development of tectonophysicochemistry.

Multi-order Characteristics of the “Tectonic Uplift-Detachment Depression” in Blocks of the Neocathaysian Tectonic System: A Study of the Greater Khinganling Orogenic Belt

LÜ Guxian, ZHANG Baolin, JIAO Jiangang, WANG Cuizhi, BI Minfeng, FU Xu, LÜ Chengxun, MA Licheng

2024, 38(04):  853-864.  DOI: 10.19657/j.geoscience.1000-8527.2024.082

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Block morphology can be divided into two categories: tectonic belt and tectonic block.The “tectonic belt” refers to an extension belt within a block characterized by strong rock deformation and complex geological processes, and often manifests itself as an uplift orogenic belt.The regions with weak rock deformation, primarily characterized by sedimentary processes and similar length and width, are termed tectonic blocks.Most of them are depression basins controlled by detachment structures.In the tectonic system, the block feature of “uplift and detachment” holds universal significance.This paper reveals the hierarchical characteristics of block distribution.Tectonic blocks at a certain level may be considered tectonic belts on a larger scale or at a higher level.Conversely, on a smaller scale or at a lower level, they may be represented as a combination of lower-level tectonic belts and tectonic blocks.Taking the Greater Khinganling orogenic belt as an example, this paper describes a five-order “uplift and disassembly depression” tectonic features of blocks.The first order of the Neocathaysian tectonic system is the Eastern Asian tectonic assemblage, characterized by an anticlockwise compressional shear dynamic relationship between the oceanic and continental plates.In the Neocathaysian tectonic system of Eastern China, the NNE-trending giant uplift tectonic belt and the giant detachment sedimentary basin belt represent the second order.The Greater Khinganling orogenic belt is the third-order structure, with alternating uplifted tectonic belts and subsidence depression belts.The southern section of the Greater Khinganling Mountains, known as the “magmatic core complex uplift-detachment basin depression belt” in the Chifeng area, belongs to the fourth order of the Neocathaysian tectonic system.At the fifth order, the “Mesozoic granite-complex core uplift belt-volcanic depression belt” in the Chaihulanzi gold field is crucial for orefield prospecting.The characteristics of the five-order “tectonic uplift-detachment depression belts” within the Neocathaysian tectonic system can guide the determination of metallogenic regionalization units, as well as the study of metallogenic patterns and prospecting work.In particular, the distribution of blocks within the orefield, part of the fifth order tectonic system, has fundamental and guiding significance for achieving breakthrough in ore prospecting within the key mining belt.

Analysis of Crustal Stress in Tectonic Ore-forming Processes: Research Status and Thought

FAN Taoyuan, LÜ Chengxun, LÜ Guxian

2024, 38(04):  865-872.  DOI: 10.19657/j.geoscience.1000-8527.2024.086

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The “lithostatic pressure” model of underground rocks posits that the primary source of lithostatic stress in underground rocks is the gravitational force exerted by the overlying rocks.This model assumes that the rock mass is internally static and that no shear stress is present.The premise of the “lithostatic pressure” model is that rocks are in a relatively stable environment over a long period.However, the Earth is a dynamic and non-steady system, with different tectonic environments controlling the formation and evolution of rocks and subjecting them to various dynamic mechanisms.The application of the “lithostatic pressure” model is limited, especially in compressional tectonic environments where horizontal tectonic stress can cause deviations from “lithostatic pressure”.The stress in underground rocks can be composed of two parts: gravitational stress and tectonic stress.The formation and evolution of deep underground minerals are controlled by the temperature and pressure of the formation environment.Tectonic dynamics is the main factor controlling the internal pressure of solid minerals, while also being influenced by the plasticity, viscosity, and strength of the solid rocks, as well as the pressure of fluids in the pores and cracks within the rocks.The process of ore formation is influenced by the tectonic environment and constrained by temperature and pressure conditions.Therefore, the ore-forming process needs to be analyzed in conjunction with the specific tectonic environment.The internal pore fluid in the rocks undergoes corresponding changes with the evolution of tectonic activity.When the permeability of the rock pores and cracks is impeded during tectonic the evolution, a certain degree of pore fluid overpressure will develop.The pore fluid overpressure and differential stress at the same depth vary under different tectonic environments, with overpressure in compressive tectonic environments being higher than in extensional environments.“Tectonic additional lithostatic pressure” plays an important role in the study of deep geological structure, the tectonic control of rocks and ores, and deep engineering geology.

Migration and Emplacement of Ore-forming Fluids and Their Structural Controlling Mechanisms: An Example from Jiaojia Gold Belt in Jiaodong Peninsula

ZHANG Longxiao, YANG Liqiang, YANG Wei, XIE Dong

2024, 38(04):  873-891.  DOI: 10.19657/j.geoscience.1000-8527.2024.092

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Hydrothermal ore-forming system can be controlled by the migration and placement of ore-forming fluids induced by tectonic movement.Structure is the primary ore-controlling factor, and the migration and placement of ore-forming fluids are the core theory of tectonic ore-controlling.Multiple or single dominant factors, such as fluid pressure differences, integrated hydraulic gradients, and heat conduction, drive fluid migration within transport channels formed by faults, cracks, and pores in the surrounding rocks.Chemical reactions of fluids in structural cracks or pores, fluid mixing and immiscibility, and fluid boiling lead to changes in the physical and chemical properties of the fluids, resulting in the precipitation of ore-forming materials.Fluid migration patterns affect the form of mineralization.Fluid migrating through macroscopic faults and fractures, resembling pipeline flow, primarily forms large vein ore bodies with high mineralization.However, permeation flow, which widely develops in micron-scale cracks and pores of surrounding rock, mostly forms fine veins and disseminated ore bodies with stable mineralization grade and medium scale.The dynamic coupling between tectonic deformation, fluid pressure, and stress state leads to the temporal and spatial occurrence of the ore body.The fault valve-pumping mechanism is the most representative tectonic-fluid coupling model to explain orogenic gold mineralization.The formation and distribution of deposits in the Jiaojia gold belt are controlled by three-order fault structures.The compression-shear Jiaojia fault is a first-order ore-controlling structure, which governs the extensive hydrothermal alteration dominated by sericitization and the placement of altered rock type gold ore bodies within fracture zones.The Wangershan fault, a tensile shear structure in its footwall, serves as a secondary ore-controlling structure, where hydrothermal alteration is relatively weaker, resulting in the development transitional gold ore-body.The third-order ore-controlling structure consists of dozens of tensile-shear faults and joint systems dominated by the Baoli fault, which exhibits the weakest degree of alteration and mineralization.This structure mainly controls the occurrence of quartz vein-type gold orebodies.The study of the three-dimensional geometry of the ore-body in Sizhuang gold deposit shows that the morphological flatness of the ore-body group increase from No.I ore body to No.Ⅲ ore body.This indicates the spatial evolution of ore-forming fluid transport from infiltration to pipeline flow, and the differences in ore-body occurrence reflect changes in ore-forming fluid migration directions.Further research needs to integrate results from multidisciplinary studies, especially conducting in-depth analysis of the coupling relationship between micro-ultra-microscopic deformation fabric and ore-forming fluid behaviors.This includes constructing a multi-scale structure-fluid coupling ore-forming model that closely mimics reality and reveals the intricate processes and mechanisms of hydrothermal ore-forming system.

Advancements in Experimental Studies on the Tectonic Physical-chemical Mechanisms of Coal Metamorphism

DONG Bo, CAO Daiyong, WEI Yingchun, WANG Anmin, LI Xin, ZHANG Yun

2024, 38(04):  892-909.  DOI: 10.19657/j.geoscience.1000-8527.2024.091

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Coal is an organic rock that is highly sensitive to geological conditions such as temperature and pressure.Various tectono-thermal events during geological evolution inevitably result in a series of changes in the physics, chemistry, texture, and structure of coal.Physical simulation experiments are essential to reveal the mechanisms of coal metamorphism.Based on previous thermal simulation experiments and high-temperature, high-pressure simulation studies of coal metamorphism, this paper reviews the previous research on the metamorphism processes, evolutionary stages, applications, and simulation experiments of coal.Coal metamorphism includes coalification and graphitization, which manifest as multi-scale and multi-stage physical and chemical structural evolution.Its basic characteristics involve a progressive simplification of chemical constituents and structural ordering.Temperature is the dominant factor in coal metamorphism, while the mode of force also influences coal metamorphism.The thermal simulation experiment is based on the “time-temperature compensation principle” and utilizes various experimental systems, such as open, semi-open, and closed, to simulate the pyrolysis process under different temperature and pressure conditions, and tectono-thermal environments.According to the principle of similarity, high-temperature and high-pressure experiments include pressure as a variable in addition to thermal simulation.These experiments were conducted under varying temperature and pressure conditions, and stress-strain conditions to comprehensively simulate the physical and chemical changes of coal across different physicochemical environments.The mechanism, influencing factors, and evolutionary pathway of coal metamorphism under different coupling conditions of temperature and pressure have been investigated.Thermal simulation and high-temperature, high-pressure experiments of coal metamorphism have been widely used in various fields such as oil and gas generation, coal reservoir evaluation, coal-forming graphitization, and strategic migration of metal elements in coal.In the future, these experiments will evolve towards multidisciplinary cross-integration and multi-field coupling simulation, aiming to more accurately simulate the complex geological conditions influenced by stratigraphic structure.It provides a more effective technical means for the in-depth exploration of the tectonic-physicochemical mechanisms of coal metamorphism.

Discussion on the Method for Calculating Diagenetic and Metallogenic Depths in the Jiaodong Gold Deposit

LÜ Chengxun, WANG Jianping, CHEN Xiaolong

2024, 38(04):  910-921.  DOI: 10.19657/j.geoscience.1000-8527.2024.089

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The reserves and production of the Jiaodong gold deposit account for one-quarter and one-third of China’s totals, respectively.The gold mineralization theory in the Jiaodong area is continuously evolving through ongoing research, discussion, development, and innovation, driven by advances in geological science and technology.The Xincheng gold deposit in Northwestern Jiaodong is a representative example of altered-rock type gold deposits and is also one of the key production mines.With the state’s increasing attention to mineral resource safety, there is an urgent need for deep exploration and resource storage in the Jiaodong area.In the mineral exploration, particularly for deep prospecting, the estimation of diagenetic depth, metallogenic depth, and denudation depth is an important prospecting method and geological theory.Therefore, this study selects the Xincheng gold mine as a case study to discuss the methods and applications for measuring or calculating the depths of diagenesis, mineralization, and denudation.Using the Xincheng gold deposit as an example, the average diagenetic depth of the Guojialing granodiorite, the ore-host rock mass, is estimated to be 3 km based on calculated mineral formation pressure.The average depth of erosion and transformation of the Xincheng gold deposit is estimated to be 2 km using the correction method for metallogenic depth.Fission track analysis indicates that the post-mineralization denudation depth of the Xincheng gold deposit is approximately 2.5 km.Based on the above calculation results, we discuss the metallogenic patterns and predictions for gold deposit depths in the Jiaodong area.The production and exploration work in the study area has confirmed that the metal-logenic depths calculated in this study are consistent with the principles of mineralization formed in depth, providing important reference value for deep ore prospecting in the Jiaodong gold deposit and other types of hydrothermal metal deposits.

Constraints from Periodic Replenishment of Mafic Magma on Porphyry Mineralization in the Pulang Porphyry Cu-Au Deposit, Yunnan Province: Energy-constrained Thermodynamic Modeling

ZHANG Shaoying, HE Wenyan, XIAO Yiwu

2024, 38(04):  922-933.  DOI: 10.19657/j.geoscience.1000-8527.2024.093

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Periodic replenishment of mafic magma into silicic magma chambers is a critical factor in the formation of large-scale porphyry deposits.Using the Pulang giant porphyry copper-gold deposit as an example, this study aims to quantitatively assess the significance of the formation of process porphyry deposits by constructing an energy-constrained thermodynamic model.Mafic microgranular enclaves (MMEs)are widely developed in both the pre-ore coarse-grained quartz diorite porphyry (CQD)and the syn-ore quartz monzonite porphyry (QMP)in the Pulang deposit.Petrological characteristics with rhythmic zoning and resorption textures of amphibole and biotite, and the presence of elongated apatife, both indicate the replenishment of mafic magma.Compared to the fractional crystallization model (FC), the multi-stage replenishment-fractional model (R₃FC) indicates that the replenishment of mafic magma would suppress the crystallization of feldspar, and promote the formation of multiple types of amphiboles and significantly advance the crystallization time of magmatic biotite.Using the correlation between the molar fraction variations of siliceous magma materials and volatiles as a reference, the results indicate that the replenishment of mafic magma would increase the H₂O content of the residual melt in the early stages and decrease it in the late stage of magma evolution (0.16%, 0.04%, and -0.30%).It will continuously increase the SCSS (sulfur concentration at sulfide saturation in silicate melt; 78.74×10^-6, 94.44×10^-6 and 137.88×10^-6), and Cl solubility (0.04%, 0.10% and 0.20%), but the effect on Cu solubility is limited.The results indicated that the R₃FC and FC models under the energy-constrained system can not only explain the petrological characteristics of the Pulang porphyry intrusions but also quantitatively verify the contribution of mafic magma replenishment to the abnormally high H₂O, S, and Cl contents in the ore-forming rocks.

Ore-controlling Mechanism and Exploration Applications of Tectono-physicochemistry

Interpretations of Geochemical Exploration Data in Overburden Area Based on Tectonic Deformation Lithofacies Belt and Their Applications: A Case Study of the Jinxiu Nickel-Cobalt Polymetallic Ore Field in Guangxi,China

ZHANG Baolin, LÜ Guxian, SHEN Xiaoli, ZHANG Zhuang, CAO Mingjian, HUANG Xinshuo, SU Yanping, JIA Wenchen

2024, 38(04):  934-946.  DOI: 10.19657/j.geoscience.1000-8527.2024.085

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The geochemical exploration data in covered areas are complicated and challenging to interpret,therefore,calling for strengthened constraints on structural ore-controlling factors.The outcroping extent of tectonic traces in various types of overlying areas varies,making it essential to extract distribution information of ore-bearing tectonic deformation lithofacies belts from multiple levels of the tectonic systems.Based on the evolutionary characteristics of the geomechanical tectonic system,a novel approach is proposed to identify favorable ore-bearing structure trends in overlying area,and to interpret metallogeny from geochemical exploration data,and to delineate prospecting more efficiently target areas.Firstly,the structural traces of ore field and the metallogeny of hydrothermal deposits are interpreted using known geological,remote sensing,and geophysical data.Secondly,the direction of principal stress can be determined based on the characteristics of the tectonic stress field during the mineralization period.Thirdly,the tensional-shear and tensional-tectonic deformation lithofacies belts can be identified as favorable ore-bearing structures.Finally,based on the data processing results,the anomalous area for ore prospecting is identified.This method has been applied to the Jinxiu nickel-cobalt polymetallic ore field in Guangxi,identifying two main ore-bearing structural directions.The NWW-EW-NEE and NW-NNW trending fractures were formed in different periods.These fractures controlled nickel-cobalt polymetallic veins enriched in arsenide and sulfide,respectively.This method and prospecting approach can be further promoted in mineral exploration in covered areas.

Control of Sulfide Saturation on the Formation of Porphyry Cu-Au Deposits During Magmatic Evolution

CHEN Haoyu, HE Wenyan

2024, 38(04):  947-958.  DOI: 10.19657/j.geoscience.1000-8527.2024.090

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Porphyry deposits are important sources of global copper, gold, silver, molybdenum, and other strategic minerals/metals, and they are mainly distributed along convergent plate margins.Previous studies have revealed that large porphyry deposits generally originate from arc magmatism due to plate subduction, and the mineralization mostly take place at near-surface (~3-5 km).Magmatic sulfides can strongly concentrate chalcophile elements, which play important roles in metal enrichment during magmatism.Studying the enrichment and activation processes of chalcophile elements in sulfides is key to understanding the metallogenic mechanism of porphyry deposits.In this paper, we systematically summarize previous studies on magmatic sulfides in porphyry deposits, investigate the controlling factors and differentiation processes of sulfide saturation, and compare and analyze the controls of magmatic sulfide saturation processes on metal enrichment in porphyry deposits.Magmatic sulfide saturation can be controlled by various factors such as temperature, pressure, and oxygen fugacity, with oxygen fugacity being the key to sulfide saturation.Sulfide saturation will promote the efficient concentration of metals such as Cu, Au, and PGE.Particularly, PGE and Au are extremely sensitive to sulfide saturation, and slight sulfide saturation will lead to the aggregation of a large amount of PGE and Au metals.The influence of magmatic sulfide saturation on porphyry mineralization potential is controversial.Some studies conclude that sulfide saturation is the key step in porphyry mineralization because saturated sulfide promotes the concentration of metals Cu and Au.When new magma is injected or when the oxygen or sulfur fugacity of magma changes, sulfide will dissolved again, causing ore-forming metals to become enriched in the silicate melt once more.Other studies conclude that sulfide saturation does not hinder porphyry mineralization during magmatic evolution because a small amount of sulfide saturation and precipitation in the early stage will not reduce the abundance of ore-forming elements in the remaining magma, and therefore will not affect the mineralization potential.Sulfide saturation in thick crust generally occurs in the early stage, while sulfide saturation in thin crust usually occurs in the late stage.

Petrogenesis and Geological Significance of the Caledonian Heavy Rare Earth Ore Parent Rock in Southern Jiangxi Province

ZHANG Defu, WANG Xianguang, HE Tao, CAO Mingxuan, LÜ Tingting, GONG Liangxin, XU Jin

2024, 38(04):  959-976.  DOI: 10.19657/j.geoscience.1000-8527.2024.0959

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Many studies have been conducted to investigate the Yanshanian heavy rare earth ore-bearing parent rocks, however only a few reports concern the Caledonian ore-bearing parent rocks.In this study, we analyzed the geochemistry, zircon U-Pb geochronology, Lu-Hf and Sr-Nd isotopes of the biotite monzonitic granites in the Caledonian Sunwu pluton in Southern Jiangxi Province.The rock samples show a SiO₂ content of 69.7%-73.0%, a K₂O/Na₂O ratio of 1.38-2.20, and an A/CNK ratio of 1.20-1.67, belonging to the high-silicon and high-potassium-calcium alkaline-potassium basaltic S-type granite.The rock samples are relatively enriched in light rare earths ((La/Yb)_N=6.78-10.38) and show moderate negative europium anomalies (δEu=0.43-0.63).The weighted average ages of zircon ²⁰⁶Pb/²³⁸U in the two granites are (451±3.8) Ma and (461±5.6) Ma, respectively, belonging to the Middle Ordovician Epoch.The crustal model age ( {T_{DM}}^C) for Hf isotope of zircon is 1918-1496 Ma, and for the whole rock is 1.79-1.76 Ga.The magma source area is mainly composed of Mesoproterozoic lower crust granulite facies source rocks, and the rock mass is intraplate granite formed during the Early Caledonian intracontinental orogeny in South China.The weathering of rare earth element-bearing minerals in the Sunwu pluton can form ion-adsorption heavy rare earth deposits.The Caledonian granite should be given sufficient attention in future exploration work for heavy rare earth elements.The research results provide a reference for the exploration of ion-adsorbed rare earth deposits in the weathering crust of Caledonian granite.

Geochemical Characteristics and Geological Significance of Pyrite and Calcite in the Puke Gold Prospect Area, Guizhou Province

LIU Xu, JI Xingzhong, CHEN Qiang, LI Yuanhong

2024, 38(04):  977-990.  DOI: 10.19657/j.geoscience.1000-8527.2024.094

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The Puke gold prospecting area is located 3 km southwest of the famous Nibao gold deposit, sharing the same regional geological background, similar stratigraphic characteristics, tectonic style, and ideal geolo-gical conditions for gold mineralization.Based on field observations of the calcite veins (limonitization) deve-loped on the surface and in drill holes, we conducted mineralogical analysis of calcite and pyrite, rare earth element (REE) analysis of calcite, electron probe micro-analysis (EPMA), and LA-ICP-MS analysis of pyrite to constrain the origin of the ore-forming fluids and materials in the Puke gold prospecting area.The results show that most of the calcite veins in the Puke gold prospect area have similar characteristics to those in the Nibao gold deposit; however, the latter does not contain ore-bearing calcite veins.Most calcite veins in the Puke gold prospect area exhibit REE patterns similar to those of the Nibao gold deposit, and a few calcite samples show positive Eu anomalies, similar to the calcite from the mineralization period of Carlin-type gold deposits in Southeastern Guizhou.However, the Au content of pyrite in these calcite veins is several orders of magnitude higher than that of the average crustal abundance and sedimentary pyrite, with Au existing in pyrite in the form of Au⁺.This suggests that these pyrite veins are of hydrothermal origin.The gold-bearing calcite exhibits an enrichment pattern of medium REE and positive Eu anomalies.This suggests that the gold-forming fluids are reducing, possibly controlled by acidic ore-forming fluids as in the case of the Nibao gold deposit.There are fewer calcite veins exposed on the surface in the Puke gold prospect area, possibly because the favorable ore-forming strata of the Puke gold are deeper.There is less ore-forming hydrothermal fluid transported to the pre-sent-day surface strata, implying that ideal gold mineralization developed at deeper levels.

Formation Age and Magmatic Source of the Wulantaolegai Cu-Ni Deposit in Central Inner Mongolia

WANG Jiaxin, JIAO Jiangang, MA Yunfei, LI Feng, GAO Chao

2024, 38(04):  991-1012.  DOI: 10.19657/j.geoscience.1000-8527.2024.088

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The newly discovered medium-scale Wulantaolegai copper-nickel sulfide deposit marks a significant breakthrough in nickel prospecting in central Inner Mongolia.Central Inner Mongolia hosts several important mafic and ultramafic metallogenic belts.The Wulantaolegai Cu-Ni deposit formed within the Huanghuatan and Xiaonanshan mineralization belt.To understand the formation age and tectonic setting of the deposit and its correlations with the metallogenic zone,we conducted LA-ICP-MS zircon U-Pb dating and Hf isotope analysis,whole-rock major and trace element geochemistry,and Sr-Nd isotope analyses of gabbro and lamprophyre in the mining area.The results show that the U-Pb age of the gabbro is 270.8±3.2 Ma,and U-Pb ages of the lamprophyre are approximately 251.5-250.9 Ma.They recorded two stages of magmatic activity during the extension following the collision between the Siberian Craton and the North China Craton.The gabbro shows a sub-alkaline tholeiite series with a SiO₂ content of approximately 47.3%-51.5% and a Na₂O+K₂O content of approximately 1.0%-3.1%.The high (⁸⁷Sr/⁸⁶Sr)_i value of approximately 0.7199-0.7239 and low ε_Nd(t) value of approximately -12.18 to -9.55 suggest that the source of the magma may be EM Ⅱ-type enriched lithospheric mantle.A low SiO₂ content of approximately 47.72%-52.15% and Na₂O+K₂O content of approximately 4.47%-9.43% indicates that the lamprophyre belongs to the calc-alkaline potassium series.The peralkalic lamprophyre,enriched in LILE and LREE but depleted in HFSE (such as Nb,Ta and Ti),as well as its negative ε_Hf(t) of approximately -20.0--2.9,indicates an enriched lithospheric mantle metasomatized by subduction fluids.These research achievements provide valuable insights for ore prospecting in the regional mafic and ultramafic rock bodies.

Alteration Fractural System and Orebody Locating in the Linglong Gold Field

SHEN Yuke, GUO Tao, HAN Fengbin, XIAO Changhao, YAN Shaohua, LI Kang, LIU Weimin

2024, 38(04):  1013-1025.  DOI: 10.19657/j.geoscience.1000-8527.2024.096

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The Linglong granite occurs over a large area in the Linglong gold field, and its deformation at different crustal depths varies during metallogenesis.The rocks occurring in the shallow crust mainly show characteristics of brittle deformation.The fracture network within the main fault zone formed a tectonic system that controls the migration, precipitation, enrichment, and distribution of minerals.Meanwhile, the center of the tectonic system served as the main space for storing gold ore bodies.The deformation of rocks farther from the fault center gradually weakens, transitioning from fractured rocks to those with fewer reticulated fissures.These problems result in resource shortages in the gold mine.In this study, to accurately and effectively predict the positions of hidden gold orebodies in the Linglong gold field, we analyzed the correlations between the width of the typical alteration fracture network vein zone and the spatial positioning of the orebody.This analysis is based on dissecting the rock deformation mechanism and the corresponding relationship between rock deformation and tectonic development.Structural and statistical analyses of alteration fractures indicate that the density parameters of these fractures in the Linglong gold field can generally be used to determine the structural position of the observed rocks within the tectonic zones.This allows for the reference of deformation characteristics of rocks in hidden areas and the establishment of a spatial distribution model ore bodies and an alteration fracture system during mineralization.Moreover, this study can estimate the intensity of mineralization, as well as the size and occurrence of the ore body.Therefore, the degree of development of tectonic alteration fractures is a key indicator of geological information for deep prospecting and spatial positioning of orebodies.In addition, measuring and analyzing the density of alteration fractures in the structural mineralization zone, as well as understanding the distribution patterns of this density, can effectively locate the position of hidden ore bodies.Furthermore, this study enables estimates of the development degree and location of ore bodies, thereby achieving the goals of positioning and predicting these ore bodies.

Observation and Analysis of Diagenesis and Mineralization Structures of the Jinchuan Cu-Ni Sulfide Deposit in Gansu

JIAO Jiangang, TAN Fu, LI Linna, LIU Jian, YANG Xingke, GAO Dong

2024, 38(04):  1026-1042.  DOI: 10.19657/j.geoscience.1000-8527.2024.087

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The Jinchuan giant Cu-Ni sulfide deposit in Gansu formed during the Neoproterozoic.From the initial emplacement of its parent magma to subsequent tectonic superposition, this deposit has undergone a complex geological evolution.Despite the fact that many previous studies have been conducted, significant controversy regarding the tectonics of the deposits still remains.Furthermore, it is of great significance to clarify the rock- and ore-controlling structures for magma intrusion and its emplacement processes, as well as to prospect for ore deposits at depths.In this study, we analyzed the stress field based on the classification, correlation, cross-cutting relationships, and chronological sequence of structures in the deposit area, using nodal production statistics.In the end, we determined three primary compressive stress directions: N-S, NE-SW, and NNE-SSW.Finally, by integrating regional and mining tectonics, we concluded that there are six stages of tectonic evolution in the Longshoushan area: Lüliang, Jinning, Caledonian, Hercynian, Yanshan, and Himalayan.We also established a model of tectonic evolution for the Jinchuan Cu-Ni sulfide deposit, including the pre-, syn-, and post-mineralization stages.The model for the tectonic evolution of the Jinchuan Cu-Ni sulfide deposit illustrates the emplacement of parental magma to form the deposit, providing new insights into mineral prospecting in both within the deposit and in its periphery.

Metallogenic Characteristics in the Abrupt Change Zone of Tectono-physicochemical Parameters in the Dayin’gezhuang Gold Orefield,Jiaodong Peninsula

WANG Zongyong, LÜ Guxian, ZHANG Baolin, LI Yongwu, MA Shengming, HAN Xin, ZHANG Liangliang, YUAN Yuelei, LIU Zhifang, HE Changcheng

2024, 38(04):  1043-1053.  DOI: 10.19657/j.geoscience.1000-8527.2024.083

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In the study of orefields with endogenetic metallogenesis,tectono-deformation lithofacies can not only reflect the characteristics of tectonic stress field during the formation of the deposit but also reveal their geoche-mical features and physicochemical conditions.The Jiaodong gold-concentration area has a unique characteristic among global gold deposits,with its scale of gold reserves ranking third in the world.It is noteworthy that the Dayin’gezhuang orefield is one of the super-large gold fields in this region.Based on previous research on tectonic alteration lithofacies,it is particularly necessary to clarify the relationship among the tectono-physicoche-mistry parameters and to delve into how tectonic processes can drive gold mineralization by influencing the physicochemical conditions of ore formation.This study selected tectono-physicochemical parameters representing the composition,temperature and pressure,properties of ore-forming fluids,and conditions of ore-forming structures in order to analyze tectonic diagenesis and mineralization.The results show that the tectono-physicochemistry conditions represented by fluid inclusion components such as CO₂/H₂O,pH,oxygen fugacity (lg$f_{0_{2}}$),tectonic additional hydrostatic pressure (P_s),homogenization temperature of fluid inclusion,minimum pressure of fluid inclusion (P_min),and other parameters have a significant influence on ore formation.The effect of the ore-forming fluid’s composition,properties,temperature and pressure conditions,and the tectonic process represented by CO₂/H₂O,lg$f_{0_{2}}$,P_s,homogenization temperature,and P_min are positively correlated,while the effect of pH shows a negative correlation; additionally,in the pyrite-sericite zone,the pyritic-sericitic granitic cataclastic zone,and the strong potassic feldspar granite belt of the ore field,the tectonic additional hydrostatic pressure (P_s),fluid inclusion component CO₂/H₂O,oxygen fugacity (lg$f_{0_{2}}$),minimum pressure of fluid inclusion (P_min),and homogenization temperature of fluid inclusions exhibit a trend of initially increasing and then decreasing.The ore-forming physical and chemical conditions represented by fluid inclusion component Na⁺/K⁺ and F^-/Cl^- have a negative correlation with ore formation.In the pyrite-sericite zone,pyritic-sericitic granitic cataclastic zone,and strong potassic feldspar granite belt,F^-/Cl^-demonstrate a gradually downward trend,while Na⁺/K⁺ exhibits the opposite trend.Tectonic additional hydrostatic pressure (P_s) can drive ore-forming fluids to migrate from areas with higher P_s to lower P_s,leading to ore precipitation.There is a tectono-physicochemistry interface between the high and low values of tectono-physicochemical parameters,with gold deposits primarily located in stress relaxation zones at this interface.

Application of Comprehensive Geophysical Exploration in the Lizichong Mining Area, Ailaoshan Tectonic Belt, Southwest Yunnan Province

YU Huimin, SHEN Xiaoli, SU Huhu, JIA Wenchen, ZHANG Baolin, SU Jie

2024, 38(04):  1054-1066.  DOI: 10.19657/j.geoscience.1000-8527.2024.084

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The Lizichong iron-copper deposit is located in the southern section of the Ailaoshan tectonic belt, between the Yangtze Plate and the Indian Plate in Yunnan Province. A large number of iron-copper deposits have been found in the periphery of this area, making it an important iron-copper mineral base in Yunnan Province. However, this study area is covered by alpine vegetation and has large topographic variations, complex geological structures, intense magmatic activities, making ore exploration challenging. To overcome the limitations of a single exploration method, we used high-precision magnetic method, dual-frequency IP methods, and EH4 electromagnetic sounding methods to conduct a comprehensive geophysical exploration in the mining area. Combined with a geological survey, the deep extension of the structure, buried magmatic rock and mineralized body in the mining area were interpreted, and the prospecting information was summarized. Comprehensive geophysical results show that the mineralized bodies are mainly hosted in the metamorphic rock series in the Ailaoshan Group and are closely related to the basic intrusive rocks and the granodiorite porphyry rock with various types of mineralization. The iron-mineralized area shows high magnetism, low apparent resistivity and high apparent amplitude frequency, while the copper-mineralized area is characterized by low magnetism, low apparent resistivity and high apparent amplitude frequency. According to the magnetic anomalies of abrupt or bending deformation of magnetic field lines, IP anomalies of low apparent resistivity and the measurement and interpretation results of EH4 profiles, there may be earlier-formed NW-trending tensile faults and subsequently-formed NE-trending shear faults. The NW-trending fault is conducive to mineralization, while the NE-trending fault is destructive to the ore body. In the mining area, the positions with a good combination of IP anomalies and magnetic anomalies, and deep ore-forming potential revealed by EH4 electromagnetic sounding have been verified by engineering operations. The results show that the ore body, to some extent, extends into the deep, and that the NW-trending fault and its secondary structure are the main ore-bearing area. There may be new iron-copper mineralization bodies in the deeper locations with relatively low and gentle magnetic anomalies, which have the potential to expand the reserve. This has significance for further geological exploration.

Ore-controlling Structural Characteristics of the Bankangmu Copper-Gold Deposit in Laos: Magmatic Core Complex Uplift-Detachment Zone

ZHAO Junhong, YANG Renyi, LÜ Guxian, ZHAO Yanpeng, KANG Tiesuo, CHEN Xiaofeng

2024, 38(04):  1067-1075.  DOI: 10.19657/j.geoscience.1000-8527.2024.097

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The Bankangmu copper-gold deposit, located in the tectonically active zone at the southern margin of the Simao-Phetchabun block in Southeast Asia, is a large copper-gold deposit associated with Mesozoic magmatism.Despite the significant resource potential of this area, some key geological questions remain unresolved, such as those related to ore-forming models and evolutionary processes.This paper investigates the distributions of ore-forming intrusions, fault structure deformation features, and ore-forming characteristics within the detachment zone to reveal the uplift features of the magmatic core complex and the structural characteristics of the deposit in this zone.This study posits that the Bankangmu deposit is controlled by the structure of the “magmatic core complex” and its boundaries within the uplift-detachment zone, categorizing it as a hydrothermal copper-gold deposit formed in this magmatic core complex uplift-detachment zone.The magmatic core complex structure of the Bankangmu deposit consists of three parts: the magmatic complex core, the detachment zone structure, and the volcanic-sedimentary rocks.The magmatic complex core is mainly composed of granodiorite.At the contact zone between the granodiorite-andesite and limestone in the footwall, a gneiss-like texture has developed.The foliation, centered on the core granodiorite, exhibits an outward dip and is inferred to have formed under regional compressive shear stress during the magmatic intrusion processes.Magnetic and induced polarization measurements reveal the relationship between the mineralized zone and the magmatic core complex in the Bangkangmu deposit.Combined with geological survey data on the distribution of intrusions, we suggest that there is a concealed intrusion deeper whithin the structure.The detachment zone structure, developed between the footwall granodiorite and the hanging wall volcanic-sedimentary rocks, is the focal area for copper-gold mineralization.The formation age of the mineralized alteration rocks in the detachment zone (244-251 Ma) is younger than the emplacement age of the complex (264±10 Ma).Observations and analyses of the detachment zone structure and small-scale structures on both sides indicate that the detachment zone exhibits a shovel-shaped morphology in cross-section.It is characterized by distinct early ductile deformation followed by later brittle deformation, with the main movement direction of the hanging wall being NWW.Consequently, this paper suggests that the southeastern part of the Bankangmu copper-gold deposit also exhibits characteristics of the magmatic core complex uplift-detachment zone ore-forming pattern, making it a potential target for exploration.

Remote Sensing Geological Interpretation, Alteration Information Extraction, and Mineral Prospecting Prediction in the Chaihulanzi Gold Field, Chifeng, Inner Mongolia

HAN Yaohui, WANG Cuizhi, WU Zhijie, LÜ Guxian, ZHANG Baolin, ZHANG Qipeng

2024, 38(04):  1076-1091.  DOI: 10.19657/j.geoscience.1000-8527.2023.112

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The Chaihulanzi gold field, situated at the northwesternmost end of the Chifeng-Chaoyang gold metallogenic belt, is an significant gold-producing region in China.However, this region faces harsh natural conditions and has seen limited geological studies using remote sensing.Research on the distribution characteristics of key ore-controlling factors (e.g., strata, structures, and igneous rocks) and alterations of host rocks related to gold mineralization remains relatively scarce.Therefore, utilizing remote sensing technology for prospecting in this ore field is of great significance.This paper uses Landsat 8 and GF-2 remote sensing images, along with the “Principal Component Analysis+Optimal Index Factor” method, to perform remote sensing geological interpretation of the Chaihulanzi gold ore field in Songshan District, Chifeng City, Inner Mongolia.Based on the spectral characteristics of altered minerals, a scheme was developed to extract alteration information from Landsat 8 and Sentinel-2A remote sensing images.The scheme involves removing interference information, extracting anomaly information, grading anomalies, and processing anomaly data.Three prospecting target areas were delineated based on previous regional geological and mining studies, integrating characteristics of alteration information with geological interpretation results.This study shows that using multi-source remote sensing satellite images for geological interpretation and extracting alteration information in the study area generally meets the requirements for medium-scale prospecting prediction and comprehensive geological surveys, significantly enhancing prospecting efficiency.The research results provide crucial fundamental guidance for future prospecting and exploration in the Chaihulanzi gold ore field.

Mesozoic and Cenozoic Deformation Sequences and Their Dynamic Background in the Danyishan Area, Southern Hunan

CHEN Zhiyou, ZENG Guangqian, BAI Daoyuan, YAO Zeyu, WANG Lingjue, WEN Chunhua, CHEN Xu, WANG Yong, LI Bin, HUANG Leqing, CHEN Jianfeng, LIANG Enyun, XU Ruochao, MA Huiying, XIANG Ke

2024, 38(04):  1092-1108.  DOI: 10.19657/j.geoscience.1000-8527.2024.063

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The Dayishan area is located at the junction of the Nanling tectonic belt and the Qinhang tectonic belt.It has developed multi-directional and different types of structural systems since the Early Mesozoic.Studying the deformation sequences is essential for better understanding of the tectonic evolution along and adjacent to South Hunan.However, detailed analysis of the deformation characteristics and evolution of the stress field remains unsolved.This study employs structural analysis to correlate structural elements such as shear fractures and folds in the bedrock of the Dayishan area.The paleo-stress field of shear fractures is reconstructed using the lower hemisphere stereographic projection method.Combining the regional tectonic evolution history of South China in the Mesozoic and Cenozoic, this study defines five deformation events based on their dynamic backgrounds.The first phase (D₁) of NEE-SWW compression, occurring during the early stages of the Indosinian Movement (late Middle Triassic), resulted from the oblique intraplate under-thrusting of the Yangtze Craton beneath the Cathaysia Block in a multi-plate confining setting.The difference in local and regional shortening directions may be related to the E-W compressional stress field derived from the NW-trending Shao-yang-Chenzhou fault and the sinistral drag caused by strike-slip motion.The second phase (D₂) of S-N compression formed during the late stage of the Indosinian Movement (Late Triassic to Early Jurassic).This phase may be related to the southward compression of the North China Craton and northward compression of the Simao-Indochina Block.The third phase (D₃) of NWW-SEE compression occurred during the Early Yanshanian Movement (latest Middle Jurassic).This phase was driven by the westward subduction of the Palaeo-Pacific Plate, or the Izanazaki Plate, beneath the South China Block.The fourth phase (D₄) of magmatism-related deformation includes folding, tectonic foliations, pinch-and-swell structures, and tension-shear fractures.These structures are possibly related to episodic upward invasion and lateral flow of Late Jurassic granitic magmas along variously orientated basement faults during the post-orogenic stage of the Early Yanshanian Movement.The fifth phase (D₅) of N(N)E-S(S)W compression occurred during the Middle and Late Paleogene.This phase may be related to the local compressive stress field derived from dextral strike-slip motion along previous NNE-trending fault zones.Its dynamic mechanism may be the eastward escape of the Tibetan Plateau caused by the collision between the Indian and Eurasian plates.Further analysis suggests that the strongest strike-slip motion of the Shaoyang-Chenzhou fault zone might have occurred in the early stage of the Indosinian Movement, thereby establishing the tectonic framework of the Mesozoic and Cenozoic in the surrounding area of this fault zone.

Ore-controlling Factors of the Sandstone-type Uranium Mineralization in the Xinjiang Basin of South China

ZHANG Wanliang, LI Yuliang

2024, 38(04):  1109-1120.  DOI: 10.19657/j.geoscience.1000-8527.2024.017

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Sandstone uranium deposits in the basins of South China are integral to China’s sandstone-type uranium deposits. Significant progress has been made in genetic research on sandstone-type uranium deposits in North China, while research on sandstone-type uranium deposits in South China remains predominantly descriptive, representing a critical gap in uranium genesis studies. The Xinjiang Basin in Jiangxi is a representative uranium-rich basin in South China, where Xiaojia sandstone-type and multiple sandstone-type uranium mineralization have been discovered. This study takes Xinjiang Basin as an example to investigate the ore-forming characteristics and controlling factors of sandstone-type uranium deposits in South China. It aims to perform comparative studies on ore-forming mechanisms and provide a theoretical basis for understanding sandstone-type uranium mineralization in China through literature review, field surveys, microscopic observations, and trace element analysis. The results indicate that uranium mineralization in the Xinjiang Basin primarily occurs in the grey layers sandwiched between the red layers of the Upper Cretaceous Maodian, Zhoutian, Hekou, and Tang-bian Formations. The ore-bearing rocks include grey, grey-white, grey-green, bluish-grey conglomerates, sandstone conglomerates, sandstones, silty sandstones, and silty mudstones. The selectivity of mineralization based on stratigraphic and lithological characteristics is not significant. Spatially, sandstone uranium mineralization is primarily located at the central and western ends of the Xinjiang Basin, near the deep-seated source rock of the Lower Cretaceous Lengshuiwu Formation or its periphery. The intensity of mineralization correlates with the organic matter content in the rocks. It is concluded that sandstone uranium mineralization is controlled by multiple factors: (1) Rocks in basin depression areas control the sources of ore-forming materials; (2) Grey layers sandwiched between red layers determine the extent of uranium mineralization; (3) Anticline structures’ axes concentrate uranium body formation; (4) Neotectonic fault structure activity governs mineral deposit localization. The mineralization involves the activation of uranium and other elements in deep source rocks due to fault activity, migrating along fault channel to rock layers or tensile fractures (fracture belts) near shallow anticline axes. When uranium-bearing deep reducing fluids enter shallow, more oxidized environments, uranyl organic complexes dissociate. Elements such as uranium precipitate due to these reducing agents, forming uranium mineralization or deposits.

Origin of the Gravel Layer and Evolution of the Qingyi River in Front of the Southern Longmen Shan Foreland Basin:Insights from the Burial Age of Cosmogenic Nuclides ²⁶Al/¹⁰Be

ZHOU You, LI Bin, WU Zhonghai, ZUO Jiameng, ZOU Renzhou, ZHENG Liping

2024, 38(04):  1121-1133.  DOI: 10.19657/j.geoscience.1000-8527.2023.106

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Since the Miocene, strong thrust uplift has occurred in the Longmen Shan nappe tectonic belt, resulting in the formation of a steep topographic gradient zone.In the foreland region, ancient alluvial fans composed of gravels have been widely developed, primarily including the Mingshan-Qionglai (MQ)and Danling-Simeng (DS)gravel layers.These layers, deposited by the ancient Qingyi River, are ideal for exploring the river’s evolution and the paleoenvironmental changes in this region.We conducted field investigation in the Longmen Shan Foreland region and performed cosmogenic nuclide ²⁶Al/¹⁰Be dating analysis on the MQ and DS gravel layers.The analysis indicates that the burial age of the MQ gravel layer is 0.608,9±0.018,7 Ma, and the burial age of the DS gravel layer is 0.218,0±0.094,1 Ma.Therefore, we conclude that the MQ gravel layer formed in the late Early Pleistocene to early Middle Pleistocene ( Q_1^3- Q_2^1), and the DS gravel layer formed in the Middle Pleistocene ( Q_2^2).Combing previous research results, the two gravel layers correspond to the δ¹⁸O curve of deep-sea ice core and the sequence curve of Chinese loess, indicating they formed during a warm interglacial period.Based on statistical analysis of gravel composition, size, orientation, and paleoflow directions in the region, three major diversion events have been identified in the Qingyi River system.In the early stage, the Qingyi River flowed from Ya’an in a north-northeast direction towards Jianshan.With the uplift of the Xiongpo anticline and the continued uplift of the Mingshan Qionglai terraces, the Qingyi River, which initially flowed from the southwest-north to the northeast, was forced to cut through the Xiongpo anticline and divert southeast at Caoba.

Grain-sizeCharacteristics and Sedimentary Environment Analysis of the Lower Member of the Anju’an Formation, A Copper-bearing Rock Series at the Shalu Copper Deposit, Wuhe, Xinjiang

LIU Kunfeng, FENG Changrong, XU Lei, Qi Xiaopeng, CAI Zhenfeng, XIE Jin, ZHAI Liming, LEI Hao

2024, 38(04):  1134-1146.  DOI: 10.19657/j.geoscience.1000-8527.2023.088

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The Wuhe Shalu copper deposit is located at the northern margin of the Wuqia foreland basin in the Tianshan Mountains, Southwest Xinjiang.Large sets of Meso-Cenozoic continental sand bodies are deposited in this basin, forming important ore-bearing rock series of lead, zinc, copper, uranium, and other sandstone-type deposits.The lack of sedimentological studies on this deposit has long restricted the understanding of regional metallogeny and hindered mineral exploration.Therefore, this paper uses the Wuhe Shalu copper deposit as a case study, focusing on the clastic sedimentary rocks of the Neogene Miocene Anju’an Formation containing copper.This study primarily uses methods from sedimentology, sequence stratigraphy, lithofacies paleogeography, and clastic petrology.Samples for grain-size analysis of the lower member of Anju’an Formation in the mining area were systematically collected.Grain-size analysis and analytical methods of clastic rock were used to conduct in-depth research on the sediments in the mining area.The results show that the sedimentary facies type of Anju’an Formation is consistent with that of braided river delta.We identified two sedimentary subfacies: braided river delta plain and braided river delta front.In addition, we recognized six sedimentary microfacies in each lithologic segment: distributary channel sand bar, natural embankment on land, underwater distributary channel, interdistributary bay, estuarine sand bar, and far sand bar.The lower part of the Anju’an Formation is the main copper-rich horizon in the study area.The microfacies of the underwater distributary channel and the distributary channel sand bar are key targets for copper exploration in the Wuhe Shalu area.The sudy results provide a prospecting strategy for resource prediction on both sides and the periphery of the Wuhe Shalu copper deposit, and also serve as an important reference for searching for sandstone copper deposits in this area.

Discovery of the Mesozoic Volcanic Rocks in Lahegen Area of the Eastern North Qaidam Tectonic Belt, and Its Geological Implications: Evidence from Geochemistry and Zircon Geochronology

ZHENG Ying, HAN Jie, ZHANG Xiaoyong, GOU Mingliang, WANG Ming, YUAN Bowu

2024, 38(04):  1147-1161.  DOI: 10.19657/j.geoscience.1000-8527.2023.074

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The stratigraphic attribution of volcanic rocks in the eastern area of the northern margin of the Qaidam Basin is difficult to determine due to a lack of geochronological data.These rocks are located between the Wahongshan-Wenquan Fault and the southern margin of the Zongwulong Mountain Fault.This also leads to significant disputes over the division of geotectonic units in this area, as no Mesozoic volcanic rocks have been found here before.In this study, a set of Mesozoic volcanic rocks consisting of rhyolite, intermediate-acid brecciate lava and dacite was newly confirmed in the Lahegen area.Zircon U-Pb dating was performed on the rhyolite samples using the LA-ICP-MS technique with weighted mean age of 248.3±1.2 Ma, indicating an Early Triassic age.The geochemical data show that the volcanic rock is a metaluminous high-potassium calc-alkaline rock with clear fractionation of light rare earth elements, enrichment of light rare earth elements and depletion of heavy rare earth elements.The mean δEu value is 0.63, indicating a weak negative anomaly.The rocks are relatively enriched in large ion lithophile elements (e.g., Rb and Ba) and high field strength elements (e.g.,Th, U, Pb, and Zr), and are significantly depleted in Sr, Ta, and Nb.These are typical geochemical characteristics of continental island arc volcanic rocks.Zircon Hf isotope compositions show ε_Hf(t) values of~-19.62 to-3.07 and t_{D{M}_2 }values of~1,639 Ma to 2,421 Ma, indicating that the volcanic rocks are derived from the partial melting of Paleoproterozoic crustal materials.Based on geochronology and geochemical characteristics, the volcanic rocks are attributed to the anatexis of crustal materials (the Darken Daban Group) caused by the northward subduction of the Anemaqen Ocean to the East Kunlun block in the Early Triassic.The volcanic rocks of the Hongshuichuan Formation are similar to those in the magma arc of Olashan, according to the regional correlation.Therefore, these rocks are identified as Early Triassic Hongshuichuan Formation volcanic rocks.The confirmation of the studied volcanic rocks indicates that the Lahegen area has a close tectonic affinity with the Olashan magmatic arc of the East Kunlun orogenic belt.This study provides new evidence for the tectonic division of the eastern area of the northern margin of Qaidam Basin.

Genesis and Tectonic Significance of Volcanic Rocks from the Lancang Group in the Lincang Terrane, Sanjiang Region, Southwest China

ZHANG Binhui, WANG Hong, NIU Haobin, YU Yuanshan, CHEN Minhua

2024, 38(04):  1162-1176.  DOI: 10.19657/j.geoscience.1000-8527.2024.032

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Studying the Lincang terrane is essential to understand the tectonic evolution of the Proto-Tethys in the Sanjiang region of Southwest China.However, there have been ongoing debates about its tectonic characte-ristics.This study focuses on the Lancang Group, which serves as the basement of the terrane.Our study presents zircon U-Pb chronology and whole-rock elemental composition of altered metavolcanic rocks in the area.The zircon U-Pb dating results indicate that these rocks formed during the Late Ordovician period, specifically at (457±2) Ma and (455±2) Ma.The protoliths of the 22 chlorite schists are from the low-potassium tholeiite series, while the protoliths of the six albite chlorite schists are basaltic-andesites from the high-potassium calc-alkaline-potassium basalt series.These rocks share similar characteristics with typical arc volcanic features, such as strong enrichment of light rare earth elements (LREEs), large-ion lithophile elements (LILEs), and negative anomalies of high field strength elements (HFSE).This evidence supports the idea that the Huimin magmatism was formed through the subduction of the Proto-Tethys Ocean to the Simao Block during the Ordovician-Silurian period.Therefore, we propose that the Lincang terrane may not be a distinct block with Precambrian basement, but rather a continental arc that formed through the subduction of the Proto- and Paleo-Tethys at the margin of the Simao Block.

Characteristics of Fluid Inclusions and Mineralization Indications of the Yechangping Mo Deposit,East Qinling

DING Gaoming, YAN Guolong, WANG Kunming, XU Yongzhong, TANG Yi’ang, LIU Jiyang

2024, 38(04):  1177-1191.  DOI: 10.19657/j.geoscience.1000-8527.2024.018

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The Yechangping molybdenum (Mo) deposit is located in the middle East Qinling molybdenum orogenic belt.Its metallogenic type mainly belongs to the skarn type in the early stage,followed by the porphyry type.In the East Qinling molybdenum mineralization belt,there are relatively fewer studies focusing on the fluid inclusions of the skarn-porphyry composite molybdenum deposits,particularly their fluid evolution characteristics and the metallogenetic mechanisms,which are essential to understanding ore genesis.This study classifies the hydrothermal mineralization stages of the Yechangping Mo deposit from early to late as follows: early silica and late silica quartz-potassic stage (stage I: quartz),quartz-pyroxene stage (stage II: quartz,main mineralization stage),quartz-polymetallic sulfide stage (stage III: quartz),and quartz-carbonate stage (stage IV: quartz).Based on this preliminary study,inclusion samples were collected from stages Ⅰ to Ⅳ quartz and analyzed using microscopy,micro-thermometry,and laser Raman microprobe.The results show that the types of fluid inclusions within the quartz are NaCl-H₂O gas-rich type (WG type),NaCl-H₂O liquid-rich type (WL type),CO₂ type (C type),and daughter mineral-bearing type (S type).From the early to the late stage of mineralization,the homogeneous temperatures of fluid inclusions are concentrated at 380-437 ℃,331-370 ℃,312-320 ℃ and 257-350 ℃,corresponding to average salinity (NaCl_eqv.) of 10.83%,9.29%,7.16%,and 4.51%,respectively.The mineralizing fluids gradually evolved from a high-temperature,medium-high salinity,and CO₂-rich NaCl-H₂O-CO₂ system at the early stage to a low-temperature,low-salinity,and CO₂-poor NaCl-H₂O system at the late stage.The fluid mixing effect leads to a decrease in fluid temperature and salinity,and the fluid transforms from an oxidized state to a reduced state.This results in a drastic decrease in the solubility of the Mo element in the fluid,and the rapid unloading and precipitation of Mo.Consequently,we constructed a mineralization model on the scale of mining area based on the “magma-fluid-construction” mineralization system.

Tourism Geology

Evaluation of Geotourism Resources in Longyan UNESCO Global Geopark and Its Development Strategy

WEI Chonghui, ZHENG Yuan, SUN Wenyan, WANG Min, LIU Gang, ZHANG Zhiguang

2024, 38(04):  1192-1204.  DOI: 10.19657/j.geoscience.1000-8527.2024.080

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The Longyan UNESCO Global Geopark is located in Longyan City,in the west of Fujian Province.With its unique geological background,rich biodiversity,and long-standing Hakka cultural heritage,this area boasts numerous significant geotourism resources.The integrated development and comprehensive utilization of geotourism resources within the Longyan UNESCO Global Geopark are still in the preliminary stage.This study analyzes the characteristics of geotourism resources in the Longyan UNESCO Global Geopark through field investigation and data collection.In accordance with the “Specification for geoheritage investigation” (DZ/T0303-2017) and “Classification,investigation,and evaluation of tourism resources” (GB/T18972-2017),the geotourism resources included can be categorized into three categories,ten classes,and nineteen subclasses.We used the Analytic Hierarchy Process (AHP) to construct a geotourism resource evaluation system and conducted a quantitative analysis of the geotourism resources.The study results in a comprehensive score of 89.90 for the Longyan UNESCO Global Geopark’s geotourism resources,classifying it as first-rate with significant development potential.Furthermore,this study has planned six geotourism routes for the Longyan UNESCO Glo-bal Geopark and proposed an initial geotourism development model based on the practices of establishing the Longyan UNESCO Global Geopark.The research results also provide a reference for geotourism development in other similar regions.

Earth-Science Lectures

Classification and Nomenclature for Plutonic Rocks

ZHANG Zhaochong

2024, 38(04):  1205-1208.  DOI: 10.19657/j.geoscience.1000-8527.2024.102

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