The Jinyinshan-Huangdi′nao Li deposit (12,000 t Li_(2)O @ 0.60%) was recently discovered in southern Hubei Province, South China. This deposit is divided into two ore sections, namely, Jinyinshan (0.24–1.32 wt.% Li2...The Jinyinshan-Huangdi′nao Li deposit (12,000 t Li_(2)O @ 0.60%) was recently discovered in southern Hubei Province, South China. This deposit is divided into two ore sections, namely, Jinyinshan (0.24–1.32 wt.% Li2O) and Huangdi′nao (0.20–0.47 wt.% Li_(2)O). The dominant Li-bearing phase and mechanism for Li enrichment remain unclear. Herein, a comprehensive study of ore geology, mineralogy and geochemistry is conducted. Field and petrographic investigations revealed that Li mineralization in the deposit was fault-controlled and that the altered metasedimentary rocks and hydrothermal veins with intensive Li mineralization contained high abundances of Li-rich clay minerals. Whole-rock XRD and in situ analyses of SEM-EDS, EMPA and LA-ICP-MS of clay minerals reveal that cookeite (0.99–2.80 wt.% Li_(2)O) is the dominant Li-bearing phase, with subordinate illite (0.02–0.57 wt.% Li_(2)O). The widespread replacement of Li-enriched illite by cookeite combined with the compositional continuum suggests that cookeite was likely formed by the hydrothermal replacement of illite at a temperature of 240–270 ℃, as constrained by chlorite geothermometry (with average temperatures of 254 ± 2℃ in Jinyinshan and 259 ± 2 ℃ in Huangdi′nao). Since metasedimentary rocks of the Neoproterozoic Lengjiaxi Group in the deposit with variable Li anomalies host abundant Li-rich illite, Li mineralization was inferred to have occurred via hydrothermal metasomatism of these clay-rich clastic rocks. The hydrothermal fluids may have been driven by a deep magmatic heat source, as evidenced by previously reported U-Pb dating of apatite from the clay-Li ore, similar to the age of the Mufushan granitic batholith in the south, both of which are Early Cretaceous. The deep-sourced hydrothermal fluids caused the mobilization, migration and reprecipitation of Li as Li-rich clays along the fault zones. This mechanism of Li mineralization is different from existing models for clay-Li deposits worldwide, and this deposit can be classified as a new type, namely, fault-controlled hydrothermal metasomatic clay-Li deposit. Similar deposits are highly prospective both regionally and worldwide.展开更多
To understand climate changes recorded in the Luochuan loess-palaeosols, Shaanxi province, northwes- tern China, clay mineralogy was studied using X-ray diffraction （XRD）, high-resolution transmission electron micro...To understand climate changes recorded in the Luochuan loess-palaeosols, Shaanxi province, northwes- tern China, clay mineralogy was studied using X-ray diffraction （XRD）, high-resolution transmission electron microscopy （HRTEM）, and scanning electron microscopy （SEM） methods. XRD results show that clay mineral compositions in the Luochuan loess-palaeosols are dom- inantly illite, with minor chlorite, kaolinite, smectite, and illite-smectite mixed-layer clays （US）. Illite is the most abundant species in the sediments, with a content of 61%- 83%. The content of chlorite ranges from 5%-22%, and the content of kaolinite ranges from 5%-19%. Smectite （or US） occurs discontinuously along the loess profile, with a content of 0-8%. The Kfibler index of illite （IC） ranges from 0.255°-0.491°, and the illite chemical index （ICI） ranges from 0.294-0.394. The CIA values of the loess- palaeosols are 61.9-69.02, and the R3＋/（R3＋ ＋ R2＋ ＋ M＋） values are 0.508-0.589. HRTEM observations show that transformation of illite to illite-smectite has occurred in both the loess and palaeosol, suggesting that the Luochuan loess-palaeosols have experienced a certain degree of chemical weathering. The Luochuan loess-palaeosols have the same clay mineral assemblage along the profile. However, the relative contents of clay mineral species, CIA, ICI, and IC values fluctuate frequently along the profile, and all these parameters display a similar trend. Moreover, climate changes suggested by the clay index are consistent with variations in the deep-sea 6180 records and the magnetic susceptibility value, and thus, climate changes in the Luochuan region have been controlled by global climate change.展开更多
Crystallinity,polytype,and morphology of clay minerals in the Luochuan loess-palaeosols in Shaanxi Province,northwest China were studied in order to have an insight into their origin using X-ray diffraction(XRD)analys...Crystallinity,polytype,and morphology of clay minerals in the Luochuan loess-palaeosols in Shaanxi Province,northwest China were studied in order to have an insight into their origin using X-ray diffraction(XRD)analysis and scanning electron microscopy(SEM)methods.The SEM observations showed that the morphology of some illites seems to be lath-shaped crystals.An analysis of illite crystallinity(IC)on the Luochuan section indicated that the origin of illite was related to the rocks of an anchizone.Most illite in the Luochuan loess-palaeosol section were of 2M1 polytype,but some were of 1M polytype formed by weathering of feldspar in the process of pedogenesis.Illite in the Luochuan section has undergone both physical and chemical weathering.These results revealed that most illite were of detrital origin related to the source area of an anchizone,but parts of the illite were of an authigenic origin formed during pedogenesis after sedimentation.Chlorites in the samples of the Luochuan section were mainly composed of irregular flaky grains and their crystallinity was good.These showed that chlorite had the detrital origin formed by physical weathering.Kaolinite crystallinity was relatively good.The value of CIA on the Luochuan section ranges from 61.9 to 69,and therefore kaolinite could not be formed during weathering and pedogenesis.These results indicated that the kaolinite had a detrital origin.Morphology of smectite seems to be capillaceous.The XRD patterns of all samples contained diffraction peaks at 1.5218Å(nontronite)and 1.5052Å(montmorillonite),thus indicating an intermediate composition between trioctahedral and dioctahedral smectite.The smectite crystallinity was very poor.These results revealed that smectite in the study area was authigenic rather than detrital origin.展开更多
The alteration pathways of volcanic ashes depend on the physicochemical conditions of the watermass in which they are deposited.Different conditions in terrestrial,paralic,and marine facies may impart recognizable che...The alteration pathways of volcanic ashes depend on the physicochemical conditions of the watermass in which they are deposited.Different conditions in terrestrial,paralic,and marine facies may impart recognizable chemical signatures on altered ash beds(i.e.,K-bentonites)that are potentially useful for distinguishing depositional facies in ancient ash-bearing stratigraphic successions.Western Guizhou Province in South China contains widespread Permian-Triassic transition strata from terrestrial lacustrine to shallowmarine shelf facies.In this study,factors influencing the mineralogy and geochemistry of K-bentonites accumulating across a spectrum of freshwater facies in Permian-Triassic transition strata of south-western China were comparatively investigated using mineralogical and geochemical data.Our results show that K-bentonites preserve diagnostic information regarding their depositional environment.The clay mineral assemblages of these K-bentonites are facies-dependent,with dominance of mixed-layer illite/smectite(I/S)clays in freshwater lacustrine facies,kaolinite and I/S in lagoonal facies,mixed-layer kaolinite/smectite(K/S)in mixed marine-terrestrial facies,and smectite and I/S in littoralneritic facies.The lagoonal Chinahe(CNH)K-bentonites exhibit clay mineral compositions dominated by kaolinite(both highly and poorly crystalline forms)and R1 and R3 I/S clays;the CNH-16 K-bentonite additionally contains minor chlorite.The abundance of kaolinite and absence of smectite in the CNH K-bentonites resulted from strong chemical weathering in an organic acid-rich and oxidizing environment characterized by low porewater pH.The littoral Langdai(LD)K-bentonites contain mainly R1 and R3 mixed-layer illite/smectite(I/S)and smectite,with minor poorly crystalline kaolinite,suggesting a higher pH in seawater-derived pore fluids.The littoral LD Kbentonites and their host sediments have Sr/Ba ratios of 0.34−0.49,consistent with deposition in brackish coastal facies,whereas the higher Sr/Ba ratios of the CNH Kbentonites(0.67−1.07)indicate deposition in a marine to slightly hypersaline lagoonal facies linked to warm,arid climate conditions.展开更多
基金financially supported by projects from the National Natural Science Foundation of China (Nos. 92162323, 42321001)the National Key R&D Program of China (No. 2017YFC0602405)a project from the Hubei Geological Bureau ([2019]09).
文摘The Jinyinshan-Huangdi′nao Li deposit (12,000 t Li_(2)O @ 0.60%) was recently discovered in southern Hubei Province, South China. This deposit is divided into two ore sections, namely, Jinyinshan (0.24–1.32 wt.% Li2O) and Huangdi′nao (0.20–0.47 wt.% Li_(2)O). The dominant Li-bearing phase and mechanism for Li enrichment remain unclear. Herein, a comprehensive study of ore geology, mineralogy and geochemistry is conducted. Field and petrographic investigations revealed that Li mineralization in the deposit was fault-controlled and that the altered metasedimentary rocks and hydrothermal veins with intensive Li mineralization contained high abundances of Li-rich clay minerals. Whole-rock XRD and in situ analyses of SEM-EDS, EMPA and LA-ICP-MS of clay minerals reveal that cookeite (0.99–2.80 wt.% Li_(2)O) is the dominant Li-bearing phase, with subordinate illite (0.02–0.57 wt.% Li_(2)O). The widespread replacement of Li-enriched illite by cookeite combined with the compositional continuum suggests that cookeite was likely formed by the hydrothermal replacement of illite at a temperature of 240–270 ℃, as constrained by chlorite geothermometry (with average temperatures of 254 ± 2℃ in Jinyinshan and 259 ± 2 ℃ in Huangdi′nao). Since metasedimentary rocks of the Neoproterozoic Lengjiaxi Group in the deposit with variable Li anomalies host abundant Li-rich illite, Li mineralization was inferred to have occurred via hydrothermal metasomatism of these clay-rich clastic rocks. The hydrothermal fluids may have been driven by a deep magmatic heat source, as evidenced by previously reported U-Pb dating of apatite from the clay-Li ore, similar to the age of the Mufushan granitic batholith in the south, both of which are Early Cretaceous. The deep-sourced hydrothermal fluids caused the mobilization, migration and reprecipitation of Li as Li-rich clays along the fault zones. This mechanism of Li mineralization is different from existing models for clay-Li deposits worldwide, and this deposit can be classified as a new type, namely, fault-controlled hydrothermal metasomatic clay-Li deposit. Similar deposits are highly prospective both regionally and worldwide.
基金This work was supported by the National Natural Science Foundation of China （Grant Nos. 41272053 and 41472041）. C.W. acknowledges a postdoctoral science foundation of China （2015M582301）, Fundamental Research Funds for the Central Universities, China University of Geosciences （Wuhan）, and National Natural Science Youth Foundation of China （Grant No. 41602037）. The authors wish to thank Dr. Yu J. S. for XRD analysis, Dr. Liu X. W, for HRTEM analysis and Dr. Yang H. and Dr. Yang Q. for SEM analysis.
文摘To understand climate changes recorded in the Luochuan loess-palaeosols, Shaanxi province, northwes- tern China, clay mineralogy was studied using X-ray diffraction （XRD）, high-resolution transmission electron microscopy （HRTEM）, and scanning electron microscopy （SEM） methods. XRD results show that clay mineral compositions in the Luochuan loess-palaeosols are dom- inantly illite, with minor chlorite, kaolinite, smectite, and illite-smectite mixed-layer clays （US）. Illite is the most abundant species in the sediments, with a content of 61%- 83%. The content of chlorite ranges from 5%-22%, and the content of kaolinite ranges from 5%-19%. Smectite （or US） occurs discontinuously along the loess profile, with a content of 0-8%. The Kfibler index of illite （IC） ranges from 0.255°-0.491°, and the illite chemical index （ICI） ranges from 0.294-0.394. The CIA values of the loess- palaeosols are 61.9-69.02, and the R3＋/（R3＋ ＋ R2＋ ＋ M＋） values are 0.508-0.589. HRTEM observations show that transformation of illite to illite-smectite has occurred in both the loess and palaeosol, suggesting that the Luochuan loess-palaeosols have experienced a certain degree of chemical weathering. The Luochuan loess-palaeosols have the same clay mineral assemblage along the profile. However, the relative contents of clay mineral species, CIA, ICI, and IC values fluctuate frequently along the profile, and all these parameters display a similar trend. Moreover, climate changes suggested by the clay index are consistent with variations in the deep-sea 6180 records and the magnetic susceptibility value, and thus, climate changes in the Luochuan region have been controlled by global climate change.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.41272053 and 41472041).
文摘Crystallinity,polytype,and morphology of clay minerals in the Luochuan loess-palaeosols in Shaanxi Province,northwest China were studied in order to have an insight into their origin using X-ray diffraction(XRD)analysis and scanning electron microscopy(SEM)methods.The SEM observations showed that the morphology of some illites seems to be lath-shaped crystals.An analysis of illite crystallinity(IC)on the Luochuan section indicated that the origin of illite was related to the rocks of an anchizone.Most illite in the Luochuan loess-palaeosol section were of 2M1 polytype,but some were of 1M polytype formed by weathering of feldspar in the process of pedogenesis.Illite in the Luochuan section has undergone both physical and chemical weathering.These results revealed that most illite were of detrital origin related to the source area of an anchizone,but parts of the illite were of an authigenic origin formed during pedogenesis after sedimentation.Chlorites in the samples of the Luochuan section were mainly composed of irregular flaky grains and their crystallinity was good.These showed that chlorite had the detrital origin formed by physical weathering.Kaolinite crystallinity was relatively good.The value of CIA on the Luochuan section ranges from 61.9 to 69,and therefore kaolinite could not be formed during weathering and pedogenesis.These results indicated that the kaolinite had a detrital origin.Morphology of smectite seems to be capillaceous.The XRD patterns of all samples contained diffraction peaks at 1.5218Å(nontronite)and 1.5052Å(montmorillonite),thus indicating an intermediate composition between trioctahedral and dioctahedral smectite.The smectite crystallinity was very poor.These results revealed that smectite in the study area was authigenic rather than detrital origin.
基金supported by the National Natural Science Foundation of China(Grant Nos.42472064 and 42172045).
文摘The alteration pathways of volcanic ashes depend on the physicochemical conditions of the watermass in which they are deposited.Different conditions in terrestrial,paralic,and marine facies may impart recognizable chemical signatures on altered ash beds(i.e.,K-bentonites)that are potentially useful for distinguishing depositional facies in ancient ash-bearing stratigraphic successions.Western Guizhou Province in South China contains widespread Permian-Triassic transition strata from terrestrial lacustrine to shallowmarine shelf facies.In this study,factors influencing the mineralogy and geochemistry of K-bentonites accumulating across a spectrum of freshwater facies in Permian-Triassic transition strata of south-western China were comparatively investigated using mineralogical and geochemical data.Our results show that K-bentonites preserve diagnostic information regarding their depositional environment.The clay mineral assemblages of these K-bentonites are facies-dependent,with dominance of mixed-layer illite/smectite(I/S)clays in freshwater lacustrine facies,kaolinite and I/S in lagoonal facies,mixed-layer kaolinite/smectite(K/S)in mixed marine-terrestrial facies,and smectite and I/S in littoralneritic facies.The lagoonal Chinahe(CNH)K-bentonites exhibit clay mineral compositions dominated by kaolinite(both highly and poorly crystalline forms)and R1 and R3 I/S clays;the CNH-16 K-bentonite additionally contains minor chlorite.The abundance of kaolinite and absence of smectite in the CNH K-bentonites resulted from strong chemical weathering in an organic acid-rich and oxidizing environment characterized by low porewater pH.The littoral Langdai(LD)K-bentonites contain mainly R1 and R3 mixed-layer illite/smectite(I/S)and smectite,with minor poorly crystalline kaolinite,suggesting a higher pH in seawater-derived pore fluids.The littoral LD Kbentonites and their host sediments have Sr/Ba ratios of 0.34−0.49,consistent with deposition in brackish coastal facies,whereas the higher Sr/Ba ratios of the CNH Kbentonites(0.67−1.07)indicate deposition in a marine to slightly hypersaline lagoonal facies linked to warm,arid climate conditions.
