2024 Vol. 30, No. 1

Cover Page
Cover Page
2024, 30(1): .
Abstract (134) PDF (1354KB)(36)
Abstract:
Contents
Contents
2024, 30(1): .
Abstract (108) HTML (44) PDF (465KB)(23)
Abstract:
Guest Chief Editor's Speech
Guest Chief Editor's Speech
2024, 30(1): 1-2. doi: 10.12090/j.issn.1006-6616.20243001
Abstract (276) HTML (99) PDF (352KB)(57)
Abstract:
Ore Field Structural Theory
Generalized fracturing activation criteria
TONG Hengmao, ZHANG Hongxiang, HOU Quanlin, CHEN Zhengle, HOU Guiting
2024, 30(1): 3-14. doi: 10.12090/j.issn.1006-6616.2023180
Abstract (322) HTML (92) PDF (1156KB)(76)
Abstract:
  Objective  Rock fracturing and its subsequent activations are the most basic tectonic deformation modes. However, the classical fracturing criteria (Coulomb-Mohr criterion, Griffith criterion, and Byerlee sliding-friction law) have different limitations in practical applications.   Methods  Based on the classical fracturing criteria and the analysis of the physical nature of fracturing generation (extensional fracturing and shear fracturing), combined with the generalized shear activation criterion and long-term research practice, a "generalized fracturing activation criterion" is proposed through theoretical analysis in this paper.   Conclusion  This criterion can be used to quantitatively determine the possibility and types of fracturing of any medium, under any triaxial stress state, and at any orientation interface (including pre-existing weak surface and non-weakness surface). It unifies the Coulomb-Mohr criterion, Byerlee's law, and Griffith's criterion, and extends fracturing to fracturing activation.   Significance  The proposed criterion has broad application prospects in the fracturing activation-related resource (such as shale gas and hot, dry rock) exploration and development and prediction and prevention of natural disasters (such as earthquakes and landslides).
Characteristics of hydraulic ore-bearing structure: A case study of hydrothermal tungsten and uranium deposits in South China
CHEN Bailin
2024, 30(1): 15-37. doi: 10.12090/j.issn.1006-6616.2023127
Abstract (276) HTML (61) PDF (24499KB)(64)
Abstract:
  Objective  Hydraulic fracturing is a vital deformation and fracture mode in the whole crust-lithosphere range. The related structures are also critical ore-bearing structures of some hydrothermal deposits. Clarifying the main characteristics and identification marks of hydraulic fracturing ore-bearing structures aids in conducting detailed structural analyses of ore fields.  Methods  The article introduces the formation mechanism of hydraulic fracturing structures and classifies the hydraulic ore-bearing structures into two types, namely, hydraulic fracturing and hydraulic spreading. Taking typical hydrothermal tungsten and uranium deposits in South China as examples, the study, based on detailed field investigations, analyzes the essential characteristics of hydraulic fracturing ore-bearing structures, including the Shimensi tungsten deposit, Xingluokeng tungsten deposit and Zoujiashan uranium deposit.  Results  The study suggests that hydraulic fracturing ore-bearing structures are characterized by complex shapes (arc-shaped, branched, radial, chrysanthemum-shaped, etc.), relatively small scale, predominantly tensional macro-mechanical properties, variable trends and dips, indistinct directionality with dominant orientations in only local areas, and often accompanied by hydrothermal crypto-explosive breccia. Meanwhile, five typical marks of the hydraulically fractured ore-bearing structures have been identified, including arc bifurcation or irregular shape, overall small scale, multi-directional occurrence, uneven distribution, and associated hydrothermal crypto-explosive breccia.  Conclusion  After comparing and analyzing the similarities and differences between hydraulic fracturing ore-bearing structures and stress-induced ore-bearing fracturing, the study concludes that hydraulic fracturing ore-bearing structures are relatively limited in development. In contrast, hydraulic spreading fracturing ore-bearing structures are relatively common. There is no apparent correlation between the hydrothermal alteration zoning and whether the ore-bearing structure is due to hydraulic fracturing or stress-induced fracturing. Tensional structural features exhibited by compressional genesis structures during the mineralization period are attributed to overpressure from mineralizing fluids rather than changes in regional tectonic stress fields. Although the ore-bearing structures of compressive origin show tensional macro-mechanical properties during the metallogenic period, some result from the overpressure of ore-forming fluids rather than the change in the regional tectonic stress field. [ Significance ] As an important ore-bearing structure type, hydraulic fracturing enriches the connotation of ore field structure. The coupling effect between the extensional fracturing of fracture ends caused by hydraulic fracturing and ore-forming fluids is an essential mechanism of structural control of the ore-forming end effect, which will enhance the theory of structural ore control and contribute to breakthroughs in prospecting strategies.
The spatial and temporal evolution of thermal stress after granite emplacement and its influencing factors
ZHAO Yuda, ZHANG Wengao, LIU Hao, LIU Xiangchong
2024, 30(1): 38-56. doi: 10.12090/j.issn.1006-6616.2023157
Abstract (446) HTML (63) PDF (4451KB)(61)
Abstract:
  Objective  Granitic magmas are genetically associated with magmatic-hydrothermal deposits and oil and gas reservoirs. The emplacement of granitic magmas into cooler rocks produced thermal anomaly and thermal stress, yet systematic studies on the spatial and temporal evolution of thermal stress still need to be completed. Previous numerical modeling often used rocks' linear thermal expansion coefficient at room temperature, but this parameter is highly temperature-dependent and reaches much higher levels at high temperatures. Therefore, the magnitude of the thermal stress caused by magma emplacement needs to be re-examined. A series of numerical experiments were carried out to investigate how the surrounding rock's lithology (granite or carbonate rocks), Young's modulus, thermal parameters, and the depth of magma emplacement affect the thermal stress generated by the magma in the overlying surrounding rocks.  Methods  Because the magma cools and eventually reaches thermal equilibrium with the surrounding strata, numerical simulation is one of the common methods to examine the thermal stress after magma emplacement quantitatively. This article used FLAC3D software to simulate the thermal stress caused by the emplacement of granitic magma into the upper crust. The differential equations we solved include the thermal conduction and linear thermoelasticity equations. The models' thermal field influences the stress field through temperature difference and the linear thermal expansion coefficient. However, changes in the stress field do not affect the thermal field, i.e., one-way coupling between the thermal field and the stress field.  Results   (1) Heat transfer is quicker on wallrocks with high thermal conductivity, causing a faster change in thermal stress. Compared to the high-thermal-conductivity case, the same thermal stress can be produced on wallrocks with a lower thermal conductivity after a more extended period of magma cooling. (2) The thermal stress produced by the surrounding rock's Young's modulus of 80 GPa is higher than the surrounding rock's Young's modulus of 60 GPa and 40 GPa. (3)The thermal stress simulated in the article is an order of magnitude larger than those generated using the linear coefficient of thermal expansion at room temperature. The thermal stress induced by granite surrounding rocks is nearly 30 MPa higher than that induced by carbonate rocks. (4) The thermal stress decreases with increasing distance from magma, approaching the initial stresses at nearly 2 km. (5) When the emplacement depth is shallow, both initial temperature and initial stress are lower than those in deeper emplacements; The magma room cools faster at shallow depths. Because the initial temperature of magma is the same, shallow emplacements will produce higher thermal stresses on overlying surrounding rocks.  Conclusion  The modeling results indicate that the thermal conductivity of surrounding rocks influences the change rate of thermal stress through the heat transfer rate. The thermal stress increases with the surrounding rock's Young's modulus. Since the average Young's modulus of granites is greater than that of carbonate rocks, the thermal stress on granite is greater than that on carbonate rocks. Either granites or carbonate rocks at high temperatures have a thermal expansion coefficient about one order of magnitude greater than that at room temperature, resulting in thermal stress of up to 100 MPa. The temperature of the surrounding rock gradually increases after the granite magma emplacement, corresponding to the increasing thermal stress. The thermal stress decreases with increasing distance from magma, exerting no influence on the initial stress of host rocks above 2 km of the granitic magma. When the magma emplacement is shallow, the combination of high thermal stress and low initial stress is more conducive to the formation and expansion of fractures in overlying surrounding rock.  Significance  The results of numerical simulations reveal that the thermal stresses generated by magma emplacement can affect the stress field 2 km above the magma. These localized and short-lived thermal stresses may fracture the overlying rocks, providing transport channels or ore-bearing spaces for later hydrothermal fluids.
Ore Field Structural Analysis and Exploration Techniques
Research on weak information extraction methods in the exploration of hidden Carlin-type gold deposits in southwestern Guizhou, China
TAN Lijin, LIU Jianzhong, TAN Qinping, LI Songtao, SONG Weifang, LI Junhai, WANG Zepeng, XU Liangyi, ZHANG Bingqiang, LIU Ping, MENG Minghua
2024, 30(1): 57-71. doi: 10.12090/j.issn.1006-6616.2023115
Abstract (168) HTML (62) PDF (5260KB)(65)
Abstract:
  Objective  The southwestern Guizhou region is a concentrated distribution area of Carlin-type gold deposits in China, with superior geological conditions for gold mineralization and enormous potential for mineral exploration. However, the shallow gold resources in the region have been largely exhausted, and the exploration work has entered the stage of "exploration in deep and blind areas". Due to the deep burial depth of the ore body, the mineralization information on the surface of hidden gold mines is inevitably very weak or may not even be displayed, making it challenging to obtain deep mineralization information. How to accurately identify and obtain geochemical information related to deep mineralization has become a key factor restricting exploration breakthroughs.  Methods  Conventional geochemical prospecting methods are susceptible to the influence of surrounding rocks or cover materials, making it difficult to acquire information related to deep mineralization. The formation and emplacement of Carlin-type gold deposits in southwestern Guizhou are mainly controlled by anticlines and fault structures, and the distribution, differentiation, and mineralization of elemental geochemistry are also influenced by tectonic stress. Based on the theory of tectonic geochemistry, this study conducts an in-depth analysis of the geological conditions for gold mineralization and the migration and enrichment patterns of corresponding element combinations in the southwestern Guizhou region. The sampling principles, sampling media, and data selection of weak information extraction in tectonic geochemistry are restricted to a certain extent. Various high permeability conductive shallow structural rock samples are collected to test their ore-forming indicator elements. This method can identify and extract weak information on the formation of deep-hidden ore bodies on the surface.  Results   Deep mineralization information is related to the shallow and surface through faults and fractures, and the geochemical anomalies in the shallow structural rocks can somewhat reflect the deep mining-induced anomalies. The sampling object for weak information extraction in tectonic geochemistry is tectonic altered rocks, which highlights information related to mineralization and weakens other interference information, thus enabling the extraction of weak geochemical anomalies formed by deep-hidden mineralization on the surface. In the formation process of hydrothermal deposits, the structure is not only a good channel for the migration of ore-forming fluids but also a favorable space for mineral precipitation and enrichment of ore-forming. The element geochemical anomalies obtained from collecting structural rock samples can indicate the ore-forming properties of the corresponding structure, indirectly indicating the ore-forming center and providing a scientific basis for the preliminary positioning prediction and engineering verification of hidden deposits. The weak information extraction method of structural geochemistry has been proven effective in the exploration of hidden Carlin-type gold deposits in southwestern Guizhou. This method can be extended to more exploration practices of hidden deposits in hydrothermal deposits, showing broad application prospects.  Conclusion  The weak information extraction technology of structural geochemistry is applicable to the exploration of hydrothermal deposits, which can effectively extract weak mineralization information of deep-hidden deposits, help invert the structural control type, infer the approximate occurrence of hidden deposits, select key exploration target areas, and conduct preliminary positioning and prediction of hidden deposits.  Significance  The research results on identifying and extracting weak geochemical information have specific academic value for enriching the ore-forming theory of Carlin-type gold deposits in southwestern Guizhou. At the same time, this method can effectively delineate and optimize the exploration target areas for hidden hydrothermal mineral deposits, which has positive practical significance for implementing a new round of breakthrough strategic action tasks in mineral exploration.
Quartz deformation characteristics, deformation temperature, and their constraints on pegmatites of the 509 Daobanxi lithium deposit in the West Kunlun area, Xinjiang
HUO Hailong, CHEN Zhengle, ZHANG Qing, WANG Yong, MA Huadong, WANG Wei, ZHANG Wengao, LI Yong, HAN Fengbin, DU Xiaofei, MIN Zhuang, MENG Xiangpeng
2024, 30(1): 72-87. doi: 10.12090/j.issn.1006-6616.2023078
Abstract (270) HTML (111) PDF (16591KB)(51)
Abstract:
  Objective   The 509 Daobanxi deposit in the West Kunlun orogenic belt is a newly discovered large pegmatite-type lithium-polymetallic deposit in northwestern China. As a typical granite pegmatite lithium deposit in the region, the metallogenic characteristics and pegmatite evolution of the 509 Daobanxi deposits are of great significance for understanding the entire lithium-polymetallic mineralization process of the West Kunlun metallogenic belt. The granite pegmatites contain assemblages of plagioclase, spodumene, quartz, muscovite, etc., exhibiting strong mylonization and forming typical ductile deformation characteristics in the 509 Daobanxi deposit. Quartz, an essential mineral in granite pegmatite, is ideal for tracking pegmatite's mineralization process and studying the deformation behavior of continental rocks in long-term geological history.  Methods  To study the late-stage emplacement process of pegmatite evolution, comprehensive analyses were conducted on the quartz deformation structures measurements, fluid inclusion temperature, and quartz trace elements for the 509 Daobanxi granite pegmatites. Cathodoluminescence (CL) analysis of quartz in deformed granite pegmatite samples was performed to reveal the compositional zoning of Ti in quartz. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was used to analyze 64 points from samples Zk2707-9 and Zk1107-2.  Results  The minerals of spodumene and plagioclase in deformed pegmatites primarily show brittle fracturing characteristics, with the features of rigid body deformation and the muscovite presence of mica-fish. Meanwhile, the conspicuous feature is that quartz grains mainly develop dynamic recrystallization and contain subgranis. According to the microstructural characteristics of spodumene, plagioclase, and quartz, the deformation temperature of mylonitized granite pegmatite is 300~400℃. The CL images of quartz bands in the granite pegmatite samples have no apparent zoning, indicating that the Ti content reaches a relative equilibrium state in the quartz deformation stage. The LA-ICP-MS analysis shows quartz from the 509 Daobanxi granite pegmatites contains a lower concentration of Ti (1.03 ×10−6 to 7.67×10−6 and 1.04 ×10−6 to 6.75×10−6), suggesting relatively lower deformation temperatures. The Ti-in-quartz thermobarometry indicates quartz deformation temperatures ranging from 371 to 398°C and 351 to 377°C, respectively. The thermometric measurement shows that homogenization temperatures of the quartz fluid inclusions in pegmatite varied from 260℃ to 283℃, likely recording the temperature of the late stage of pegmatite evolution.  Conclusion  Comprehensive analysis shows that the 509 Daobanxi granite pegmatites underwent a period of intense ductile deformation during the emplacement process, with low temperature and high strain rate. The emplacement of pegmatite is a product of the rapid cooling process, and the grain size reduction caused by dynamic recrystallization (GBM) under high-stress and low-temperature conditions profoundly changed the rheological properties of pegmatite. The supercooling process from ~400℃ to ~260℃ (ΔT=140℃±), resulting in less rapid mineral crystalline new nuclei in pegmatites, is more conducive to the formation of coarse quartz and other mineral particles, forming the significant characteristics of granite pegmatites. [ Significance ]In fact, the emplacement process of granitic pegmatites remains a puzzle, and high-quality, accurate systematic work is needed to understand the evolution process and behavior of granite pegmatite. By studying the 509 Daobanxi granite pegmatites, we proposed that the pegmatite emplacement was a product of the rapid cooling process, and supercooling plays an essential role in pegmatite emplacement. Similar deformation characteristics are widely developed in the Tugeman lithium deposit in the Altyn Tagh area and the Jiajika lithium deposit in the western Sichuan. Although the current work is preliminary, our study provides some clues for exploring the emplacement process of granitic pegmatites.
Theoretical innovation and applications of ore-field tectonic lithofacies mapping
FANG Weixuan, GUO Yuqian, LI Tiancheng, JIA Runxing, MA Zhenfei
2024, 30(1): 88-106. doi: 10.12090/j.issn.1006-6616.2023143
Abstract (138) HTML (54) PDF (2949KB)(82)
Abstract:
  Objective   In the matter of material architecture, the diagenetic-metallogenic system may be classified into lithofacies of root-feeders (metallogenic material feeders), lithofacies of structural channel (migration of diagenetic-metallogenic material), lithofacies of closed-reservoir space (unloading-enriching room of diagenetic-metallogenic material), and lithofacies of surrounding rock alteration (water–fluid–rock system of diagenetic-metallogenic material). Ore-field tectonic lithofacies mapping and detailed analysis of the formation mechanism of different types of tectonic lithofacies aid in identifying and delineating in-situ diagenetic-metallogenic systems at the scale of ore clusters and ore fields. These approaches also reveal the formation mechanisms of resources, energy, and minerals, marking it as an innovative direction in ore-field structure and prospecting prediction. In order to promote and deepen the research and understanding of tectonic lithofacies and prospecting prediction in ore fields, this article focused on the lithofacies establishment and modeling predictions on the mineralization-alteration-tectonics-lithofacies, discussing and exploring eight important types of mineralization-alteration-tectonics-lithofacies models and their formation mechanisms domestically and internationally.  Methods  The article carried out ore field tectonic lithofacies mapping and detailed analysis of the formation mechanism of different types of tectonic lithofacies in order to recognize and delineate in situ diagenetic-metallogenic systems at the scale of ore clusters and ore fields.  Results  Eight models and formation mechanisms for the mineralization-alteration-tectonics-lithofacies at the scale of ore-field tectonic lithofacies were discussed in this study. The IOCG-type ore field in the Copiapo area of Chile is controlled by the main arc belt, arc-related basins, magmatic superimposing and basin–deformation style. However, the SSC-type Cu deposit and the IOCG-type ore field in the Dongchuan area of Yunnan in southwestern China are located at the marginal rift basin with different styles of basin deformation and reworked by the magmatic superimposing tectonic system. The Jia–Cha epithermal Au-Ag-Pb-Zn ore-field in Inner Mongolia of northern China is dominated by volcanic lake-basin, volcanic dome structure, facies-type of volcanic rocks, and volcanic hydrothermal crypto-explosive breccias, whereas porphyry Cu-Mo-Au and epithermal Au-Cu ore-fields in the South Gebi area of Mongolia are formed in the Devonian–Carboniferous plutonic magmatic arc. The Sedex-type Ag-Cu-Pb-Zn-Ba-Fe ore-field in the Qinling orogeny of central China is shaped by the three-order sub-basin, syngenesis fault, and facies of hydrothermal sedimentary rock in the marginal pull-apart basin. However, gold and Au-Mo-polymetallic ore fields are dominated by different scales of the brittle-ductile shear zones in the orogenic belt. Migrations of the ore-reservoir-forming matters for metallic ore field and gas field are derived from the Jurassic coal-measure hydrocarbon-metal-bearing source rocks in the western Tarim of basin-mountain-plateau mosaic structure in western China. The Wulagen glutenite-type celesite-Pb-Zn ore field located at the piedmont compression to extension conversion basin is coupled by the pneumatogenic plume and superimposed by the piedmont thrust-fold belt. The Sareke glutenite-type Cu-polymetallic ore-field hosted at irony glutenite of the dry-fan facies in the tail-end lake basin is reworked by the hedging-style, base-type thrust fold belt and superimposed by mantle-derived hydrothermal plume.   Conclusion  Eight models and formation mechanisms for the mineralization-alteration-tectonics-lithofacies at the scale of ore field tectonic lithofacies were discussed in this study based on a review of ore-field tectonics. The tourmaline-rich plume tectonics, magmatic gasbag structure, and compound karsting tectonic lithofacies are three new types of mineralization-alteration-tectonics-lithofacies. Ore-field tectonic paleogeographic unit and formation mechanism of important ore-field tectonic lithofacies, new classification methods and principles of the mineralization-alteration-tectonics-lithofacies and 12 different types of deformational tectonic lithofacies were established in this essay.   Significance  All achievements in this study have established a new foundation for tectonic lithofacies mapping and ore prediction.
Mineral Deposit Geochemistry and Mineralization Characteristics
Variation patterns of boron and lithium isotopes in salt lakes on the Qinghai–Tibetan Plateau and their application in evaluating resources in the Damxung Co salt lake
LYU Yuanyuan
2024, 30(1): 107-128. doi: 10.12090/j.issn.1006-6616.2023135
Abstract (204) HTML (66) PDF (2567KB)(40)
Abstract:
  Objective  The Qinghai–Tibet Plateau is rich in salt lake resources, known particularly for the concentration of elements such as boron and lithium, forming many distinctive resource-type salt lakes. Compared with ordinary salt lakes, a notable characteristic of resource-type salt lakes is the abundant supply of elements such as boron and lithium. Consequently, these elements' sources and accumulation patterns are key scientific issues for understanding the genesis and mineralization patterns of resource-type salt lakes. Boron and lithium isotopes, characterized by significant mass differences and variations in natural isotope ratios, serve as effective tracers for studying the material sources of boron and lithium in salt lakes. However, the application of boron and lithium isotopes in salt lake systems faces the following three challenges: (1) There is insufficient understanding of how boron and lithium isotopes respond to the fundamental geochemical processes of salt lakes. The salt dissolution process that occurs when supply water flows into lake basins is the main reason for drastic changes in geochemical parameters. Inadequate recognition of salt dissolution processes can lead to an overinterpretation of boron and lithium isotope fractionation changes, weakening their tracking capabilities. (2) Isotope fractionation degree is conflated with changes in isotope composition. In salt lake research, discussions of the solid phase's influence on boron and brine's lithium isotopes are often based solely on fractionation factors between the solid and liquid phases, without considering the ratios of boron and lithium amounts involved in the fractionation process. (3) Discrepancies still exist in understanding the fractionation patterns of boron and lithium isotopes during salt crystallization.  Methods  In light of these problems, our study systematically reviews and analyzes the mechanisms of boron and lithium isotopic fractionation in salt lake systems and summarizes some essential understandings.  Conclusion  (1) Only salt crystallizations have specific impacts on B and Li isotopes in salt lakes. Since there is a genetic association between salt assemblages and specific salt lake hydrochemical types, the salt lakes with the same hydrochemical type exhibit consistent patterns of B and Li isotope changes during their evolutionary processes. Until halite precipitation, the B and Li isotopic compositions in sulfate- and chloride-type salt lakes are in accord with δ11B and δ7Li values of their sources instead of being controlled by their salt deposits. In contrast, the paths of B and Li isotopic changes of carbonate-type salt lakes are complex and are divided into two branches: calcite subtype and hydromagnesite subtype. After calcite precipitation, the δ11B value of the salt lake increases, and its δ7Li value is marginally above source characteristics (less than 2‰). After hydromagnesite precipitation, the δ11B value of the salt lake is also marginally above source characteristics (less than 2‰). After the stage of halite precipitation, the B and Li isotopic compositions of salt lakes in all types show an increasing trend. (2) Based on the evolutionary processes of B, Li, and K during seawater evaporation, the amounts of B, Li, and K in the current salt lake represent most of the corresponding resources in the lake if the salt lake never experienced complete dryness such as playa. For the salt-dissolving lake, most of the B, Li, and K resources are preserved in salt deposits and interstitial brine at the bottom of the lake. It is optimal for the resource potential of a carbonate-type salt lake in the salt-dissolving lake. (3) The B sources of the current Damxung Co salt lake located in the Tibetan Plateau are from clay carbonates exposed to the lake shore and highly soluble salts and interstitial brine at the bottom of the lake. The geothermal waters produced during early hydrothermal activity are the original B source of the Damxung Co salt lake. Based on mass balance equations, it is estimated that the B resource at the bottom of the Damxung Co salt lake is at least 9.1×106t (B2O3), and the lithium resource is at least 8.6 ×106t (LiCl).
Characteristics of chlorites from the Haopinggou Ag–Au polymetallic deposit in the Xiong’ershan ore concentration area and its exploration implications
LIU Songyan, ZHANG Da, YANG Mingjian, ZHANG Xinming, WEI Guodong, NIE Shengqiang, WANG Xuan, FENG Yanping, LI Wenjie, CHEN Guilan
2024, 30(1): 129-146. doi: 10.12090/j.issn.1006-6616.2023121
Abstract (228) HTML (57) PDF (8092KB)(29)
Abstract:
  Objective  The Haopinggou Ag-Au polymetallic deposit is a typical intermediate-sulfidation epithermal deposit in the Xiong'ershan ore concentration area. Ag-Pb-Zn mineralization mainly occurs in steeply dipping veins and breccia matrix. The relationship between large-scale Pb-Zn mineralization and widely developed alteration minerals remains unclear.   Methods  In order to discuss chlorite's significance related to Pb-Zn mineralization, chlorite composition in the Haopinggou Ag-Au polymetallic deposit has been analyzed by field geological observation and electron microprobe analysis (EMPA) in this paper.  Results  Three types of chlorite were observed in the deposit, occurring in altered wall rocks (Type I), in(with) Pb-Zn sulfides (Type II), and in(with) the breccia matrix (Type III). All three types of chlorite are prochlorites and fall within the compositional range of Fe-rich chlorite, indicating that they could be formed in a partially reducing acidic environment. Fe2+ for Mg2+ is the primary substitution in chlorite lattice, suggesting a close association between chlorite formation and mafic wall rocks. Based on the corrected chlorite geothermometer, these chlorites formed under aluminum-saturated conditions in the medium to low-temperature range of 196-239℃. The temperatures of chlorites associated with mineralization (Types II and III) are higher than those in chlorites around quartz veins (Type I). It is believed that during the mineralization process, the hydrothermal fluids evolved from acidic to nearly neutral conditions as the temperature gradually decreased. The initial acidic environment facilitated interaction between water and rocks, promoting the dissolution of surrounding rocks and providing space for the further precipitation of metal sulfides. The evolution of ore fluid properties also corresponds to the deposition process of Ag-Pb-Zn. The genesis of chlorite in the deposit is well-correlated with the ore-forming and holds significant prospecting value. (1) Type I chlorites mainly develop on both sides of quartz veins, formed by the dissolution and metasomatism of basic wall rocks by ore-bearing hydrothermal fluids. Type I chlorite's Fe and Mg components are mostly derived from the wall rocks. Although this type does not contain mineralization, it can be used to trace veins. (2) Type III chlorites reflect the migration process of ore-bearing hydrothermal fluids carrying dissolved minerals (biotite/clinopyroxene), which precipitate with changes in the physicochemical environment. Type III chlorite's Fe and Mg components are mainly introduced by ore-bearing hydrothermal fluids. This type of chlorite fills the intergranular pore spaces between minerals and easily replaces minerals such as biotite and hornblende, exhibiting apparent mineral alteration features in hand specimens, which is beneficial for prospecting.(3) The formation mechanism of Type II chlorites includes the possibilities mentioned above. This type of chlorite is formed by complete dissolution and metasomatism of cement in ore-bearing hydrothermal fluids, forming fine-grained cryptocrystalline chlorite fillings in breccia rocks. Ore-bearing hydrothermal fluids and wall rocks both contribute Fe and Mg in the chlorites. Hand specimens of Type II chlorite are dark green, disseminated and filled in the matrix, making it easy to distinguish. The chemical characteristics of Type II chlorites are similar to those of chemical characteristics of granite-related deposits, implying the contribution of magmatic fluids to ore-forming fluids.  Conclusion  The Haopinggou Ag-Au polymetallic deposit contains three types of chlorites. Their chemical characteristics all reflect an acidic and reducing metallogenic environment. In cation exchange, the primary substitution is Fe for Mg, and other substitutions are insignificant. The effect of Fe/(Fe+Mg) must be eliminated in order to calculate the temperature of such deposits using chlorite geothermometers. The formation mechanism of the three chlorites is closely related to mafic wall rock, and their chemical properties suggest the involvement of magmatic fluids in ore-forming fluids.  Significance  These three types of chlorite are well-matched with intense Ag-Pb-Zn mineralization and can serve as key indicators for locating Pb-Zn veins.
Spatial and temporal distribution, geochemical characteristics of carbonatites and their relationship with U–REE mineralization in the Xiaoqinling area, Shaanxi Province
KANG Qingqing, CHEN Zhengle, PAN Jiayong, LI Peng, LIU Yulong, LI Lei, JIANG Hongjun, GAO Cheng
2024, 30(1): 147-167. doi: 10.12090/j.issn.1006-6616.2023106
Abstract (182) HTML (37) PDF (6833KB)(50)
Abstract:
[ Objective ] Carbonatites, as magmatic-origin rocks, are crucial source rocks for uranium, rare earth, and other minerals. They are widely distributed in the Xiaoqinling region of Shaanxi, giving rise to numerous large to super-large carbonatite deposits of uranium, molybdenum, and rare earth, represented by Huayangchuan and Dashigou, attracting attention from scholars in recent years. Previous studies on carbonatite deposits in the area focused on petrology, mineralogy, genesis, and mineralization chronology. However, they were often limited to individual deposits, needing more regional cross-sectional comparative studies. [ Methods ] This study employs field geological surveys, petrographic analysis, and geochemical characterization of typical rocks and ores to reclassify different types and stages of Xiaoqinling carbonatites. It analyzes the geochemical characteristics of various carbonatite types and explores the mineralization processes of uranium and rare earth elements associated with carbonatites. [ Results ] Xiaoqinling carbonatites exhibit a large vein, vein group, and vein network morphology, intruding into the Archean metamorphic basement, Xiong'er Group volcanic sedimentary rocks of the Changchengian System, and Gaoshanhe Group clastic rocks of the Jixianian System along fault structures. Based on field crosscutting relationships and primary mineral assemblage characteristics, Xiaoqinling carbonate rocks can be re-divided into five stages from old to new: aegirine syenite stage (I), aegirine carbonatite stage (II), potassium feldspar carbonatite stage (III), quartz carbonatite stage (IV) and zeolite-bearing carbonatite stage (V). Spatially, the division is roughly along the nearly EW-striking Xiaohe Fault, with northern carbonatite veins dominated by aegirine syenite and aegirine carbonatite, rich in aegirine, biotite and other dark minerals, distributed in the Archean gneiss basement. The southern part is mainly composed of light-colored potassic feldspar carbonatites and quartz carbonatites, almost devoid of dark minerals, with surrounding rocks consisting of Xiong'er Group volcanic sedimentary rocks and Gaoshanhe group clastic rocks. Zeolite-bearing carbonatites are distributed throughout the region. Temporally, the carbonatites formed in the Late Triassic, but distinct temporal differences exist among different sections. Previous data indicate a possible 30 Ma gap in the formation times of various carbonatite types in the Xiaoqinling area. The geochemical characteristics of Xiaoqinling carbonatites reveal an average SiO2 content of 30.43%, significantly higher than the global average for carbonatites. CaO is relatively low, with an average content of 28.71%, exhibiting a clear negative correlation with SiO2 content. Total alkali (Na2O+K2O) content is relatively high, averaging 2.25%, with a maximum value of 10.23%. The total alkali content decreases gradually from early to late stages, strongly correlating with CaO and Al2O3 content. The potassium-sodium ratio (w(K2O)/w(Na2O)) is exceptionally high, with an average of 4.625 and a maximum value of 36.55. Ferromagnesian content (TFe2O3+MgO) varies significantly, with early-stage carbonatites (Stages I, II, III) having higher ferromagnesian content (average 8.29%), while late-stage carbonatites (Stages IV, V) generally have lower ferromagnesian content (average 1.92%). Ferromagnesian content correlates positively with TiO2 content. MnO has an average content of 1.22%, reaching up to 4.49%, notably enriched in late-stage quartz carbonatites. REE content averages 0.26%, with a maximum value of 0.96%, exhibiting a positive correlation with MgO content. The ∑LREE/∑HREE ratio ranges from 0.47 to 27.72, with early-stage carbonatites (Stages I, II, III) showing strong heavy REE depletion. Late-stage quartz carbonatites have an average ∑LREE/∑HREE ratio of 2.15, indicating relatively heavy REE enrichment, especially in Tm, Yb, Lu, and Y. Heavy REE content correlates linearly with MnO content. The overall REE distribution pattern of carbonatites is a steep-left and gentle-right, relatively flat-right-trending model, showing continuous variations in REE distribution patterns throughout different stages. Ore-related element content characteristics of various carbonatite types reveal significant U and Nb enrichment in aegirine syenite, aegirine carbonatite, and potassium feldspar carbonatite. Mo-mineralization is closely associated with potassium feldspar carbonatite and quartz carbonatite, while Pb and Ba-Sr mineralization is evident in all carbonatite stages. [ Conclusions ] (1) Xiaoqinling carbonatites are categorized into aegirine syenites, aegirine carbonatites, potassium feldspar carbonatites, quartz carbonatites, and zeolite-bearing carbonatites in chronological order. (2) Xiaoqinling carbonatites exhibit notably high SiO2 and total alkali content, low MgO content, and exceptionally high potassium-sodium ratio. There is a gradual decrease in CaO, TiO2, Al2O3, ferromagnesian, and total alkali content from early to late stages, while MnO content shows an opposite trend. Carbonatites evolve from early ferrocarbonatite to late calciocarbonatite. (3) Different types of carbonatites show distinct ore-related characteristics, with early stages (aegirine syenite, aegirine carbonatite, and potassium feldspar carbonatite) mainly enriched in U (Nb), and Potassic Feldspar Carbonate additionally enriched in Mo. Late-stage quartz carbonatites are characterized by Mo and HREE enrichment. [ Significance ] The findings of this study provide valuable information for the exploration and research of carbonatite-type uranium, rare earth, and polymetallic deposits in the Xiaoqinling area, holding significant practical importance.
ZHOU Jiyuan, CHEN Shizhong, XIAO Fan
2024, 30(1): 168-180. doi: 10.12090/j.issn.1006-6616.2022140
Abstract (158) HTML (95) PDF (1996KB)(35)
Abstract:
Inside Front Cover
Inside Front Cover
2024, 30(1): .
Abstract (97) PDF (944KB)(18)
Abstract:
Inside Back Cover
Inside Back Cover
2024, 30(1): .
Abstract (116) PDF (931KB)(9)
Abstract: