The composition of gases trapped in olivine, orthopyroxene and clinopyroxene in Iherzolite xenoliths collected from different locations in eastern China has been measured by the vacuum stepped-heating mass spectrometr...The composition of gases trapped in olivine, orthopyroxene and clinopyroxene in Iherzolite xenoliths collected from different locations in eastern China has been measured by the vacuum stepped-heating mass spectrometry. These xenoliths are hosted in alkali basalts and considered as residues of partial melting of the upper mantle, and may contain evidence of mantle evolution. The results show that various kinds of fluid inclusions in Iherzolite xenoliths have been released at distinct times, which could be related to different stages of mantle evolution. In general, primitive fluids of the upper mantle (PFUM) beneath eastern China are dominated by H2, CO2 and CO, and are characterized by high contents of H2 and reduced gases. The compositions of PFUM are highly variable and related to tectonic settings. CO, CO2 and H2 are the main components of the PFUM beneath cratons; the PFUM in the mantle enriched in potassic metasomatism in the northern part of northeastern China has a high content of H2, while CO2 and SO2 are the dominant components of the PFUM in the Su-Lu-Wan (Jiangsu-Shandong-Anhui) region, where recycled crustal fluids were mixed with deeper mantle components. There are several fluids with distinct compositions beneath eastern China, such as primitive fluids of upper mantle (CO, CO2 and H2), partial melting fluids (CO2 and CO) and metasomatic fluids mixed with recycled crustal fluids (CO2, N2, SO2 and CH4) etc. Fluids of the upper mantle beneath the North China craton are different from that of the South China craton in total gases and chemical compositions: the contents of the reduced gases of the PFUM in the NCC are higher than those in the SCC.展开更多
Based on petrological studies of the wall rocks, mineralizing rocks, ores and veins from the Laowangzhai gold deposit, it is discovered that along with the development of silication, carbonation and sulfidation, a kin...Based on petrological studies of the wall rocks, mineralizing rocks, ores and veins from the Laowangzhai gold deposit, it is discovered that along with the development of silication, carbonation and sulfidation, a kind of black opaque ultra-microlite material runs through the spaces between grains, fissures and cleavages. Under observations of the electron microprobe, scanning electronic microscopy and energy spectrum, this kind of ultra-microlite material is confirmed to consist of ultra microcrystalline quartz, silicate, sulfides and carbonates, as well as rutile, scheelite and specularite （magnetite）, showing characters of liquation by the analyses of SEM and energy spectrum. The coexistence of immiscibility and precipitating co-crystallization strongly suggests that the mineralizing fluid changed from the melt to the hydrothermal fluid. Combined with the element geochemical researches, it is realized that the ultra-microlite aggregate is the direct relics of the mantle fluid behaving like a melt and supercritical fluid, which goes along with the mantle-derived magma and will escape from the magma body at a proper time. During the alteration process, the nature of the mantle fluid changed and it is mixed with the crustal fluid, which are favorable for mineralization in the Loawangzhai gold deposit.展开更多
Based on studies of petrography, mineralogy and mineral chemistry, deep mantle fluids and their products in kimberlites and diamonds can be assorted into the ultradeep fluid-transmitted minerals with an oxygen-free fe...Based on studies of petrography, mineralogy and mineral chemistry, deep mantle fluids and their products in kimberlites and diamonds can be assorted into the ultradeep fluid-transmitted minerals with an oxygen-free feature, the deep fluid metasomatized-minerals characterized by enrichment in TiO2, K2O, BaO, REE and Fe3+, and the deep fluid-reformed minerals. The three types show a successive descent in fluid origin depth and metasomatism strength, and they have brought forth a series of corresponding metasomatic products.展开更多
This special issue of Geoscience Frontiers is a tribute volume honoring the life and career of Jacques Touret. A set of research papers has been assembled, which broadly reflect his research interests over his 50 plus...This special issue of Geoscience Frontiers is a tribute volume honoring the life and career of Jacques Touret. A set of research papers has been assembled, which broadly reflect his research interests over his 50 plus year career. These papers Focus on the role that fluids play during the Formation and evolution of the Earth＇s crust. Below I provide a brief summary of the life of Jacques Touret, along with a select bibliography of his more important papers. This is then followed by a brief introduction to the papers assembled for this special issue.展开更多
: Minerals of various mantle-derived xenoliths from the Hannuoba basalt in Hebei Province have been studied by means of IR spectroscopy. The results show that all xenoliths from the mantle at depths <75 km contain ...: Minerals of various mantle-derived xenoliths from the Hannuoba basalt in Hebei Province have been studied by means of IR spectroscopy. The results show that all xenoliths from the mantle at depths <75 km contain trace amounts of water (0.45%–11.6×10?2% H2O). The data of about 0.1% H2O contained in primary pyrolite estimated by earlier studies may be on the high side. The water might enter the frameworks of olivine, pyroxene and garnet earlier than it entered those of amphibole and phlogopite. The presence of water in amphibole and phlogopite may be a local phenomenon of water enrichment, which is related to relatively small-scale magmatic or metasomatic events although they can contain a hundred times more water than pyroxene contains. There is a little more water (1.11%–3.01×10?2% of H2O mostly) in xenoliths from the Hannuoba basalt than in those from mid-ocean ridge basalt and kimberlites of South Africa (less than 1×10?2% of H2O mostly). This indicates the heterogeneity of water in time and space in the upper mantle. The presence of trace amounts of water in mantle-derived anhydrous silicate minerals provides basic data for us to understand the distribution of water in the upper mantle and the role of water in the mantle dynamic and geochemical processes.展开更多
The finite element method was used to solve fluid dynamic interaction problems between the crust and mantle of the Earth. To consider different mechanical behaviours, the lithosphere consisting of the crust and upper ...The finite element method was used to solve fluid dynamic interaction problems between the crust and mantle of the Earth. To consider different mechanical behaviours, the lithosphere consisting of the crust and upper mantle was simulated as fluid-saturated porous rocks, while the upper aesthenospheric part of the mantle was simulated as viscous fluids. Since the whole lithosphere was computationally simulated, the dynamic interaction between the crust and the upper mantle was appropriately considered. In particular, the mixing of mantle fluids and crustal fluids was simulated in the corresponding computational model. The related computational simulation results from an example problem demonstrate that the mantle fluids can flow into the crust and mix with the crustal fluids due to the resulting convective flows in the crust-mantle system. Likewise, the crustal fluids can also flow into the upper mantle and mix with the mantle fluids. This kind of fluids mixing and exchange is very important to the better understanding of the governing processes that control the ore body formation and mineralization in the upper crust of the Earth.展开更多
Using the secondary spinel standard, the authors have precisely measured theFe^(3+)/SIGMA Fe values of spinels in mantle xenoliths from Cenozoic basalts in eastern China, andestimated the oxygen fugacities recorded by...Using the secondary spinel standard, the authors have precisely measured theFe^(3+)/SIGMA Fe values of spinels in mantle xenoliths from Cenozoic basalts in eastern China, andestimated the oxygen fugacities recorded by 63 mantle xenoliths through olivine-orthopyroxene-spineloxygen barometry. The results indicate that the oxygen fugacities of the lithospheric mantle ineastern China are higher in the south than in the north. Among them, the oxygen fugacity of theNorth China craton lithospheric mantle is the lowest, similar to that of the oceanic mantle, whilethat of Northeast and South China are the same as that of the global continental mantle. Thevariations of mantle redox state in eastern China are mainly controlled by the C-O-H fluids derivedfrom the asthenospheric mantle. According to the mantle oxidation state, it can be concluded thatthe C-O-H fluids in the lithospheric mantle of eastern China consist mainly of CO_2 and minor H_2O,but CH_4-rich fluids should come from the asthenosphere where the oxidation state is lower.展开更多
Three special types of xenoliths have recently been found in an aegirine-augite syenite porphyry in Liuhe, Yunnan, China. Petrographical, petrochemical, electron microprobe, and scanning electron microscopy studies in...Three special types of xenoliths have recently been found in an aegirine-augite syenite porphyry in Liuhe, Yunnan, China. Petrographical, petrochemical, electron microprobe, and scanning electron microscopy studies indicate that pure calcite xenocrysts and quartz-bearing topaz pegmatite xenoliths result from the degassing of mantle fluids during their migration, and that black microcrystalline iron-rich silicate-melt xenoliths are the product of the extraction of mantle fluids accompanying degassing and are composed dominantly of quartz, chlorite, and iron-rich columnar and sheet silicate minerals with characteristic minerals, such as native iron, apatite, and zircon. According to the bulk-rock chemical and mineral compositions and crystallization states, the microcrystalline melt xenoliths are not the product of conventional magmatism, and especially the existence of native iron further proves that the xenoliths were mantle fluid materials under reduction or anoxic conditions. The study of the special xenoliths furnishes an important deep-process geochemical background of polymetallic mineralization in different rocks and strata in the study area.展开更多
Based on previous studies of kimberlite xenoliths and diamond inclusions in this region, macrocrystai garnet was analyzed with the electric microprobe technique （EPMA）. The garnet is collected from the Shengli No.1 ...Based on previous studies of kimberlite xenoliths and diamond inclusions in this region, macrocrystai garnet was analyzed with the electric microprobe technique （EPMA）. The garnet is collected from the Shengli No.1 kimberlite pipe in the Mengyin area of Shandong Province, China. The results indicate that the garnet contains two kinds of multiphase inclusions： one is K-, B-, and CI- bearing oxygen-free phase, K- and Cl-bearing oxygen-free phase, and volatile-bearing garnet inclusions （in1 and in3）; and the other is chlorite, phlogopite, apatite and calcite （in2）. It is suggested that the formation of garnet and its inclusions is associated with strongly reduced mantle fluid. Such a fluid was transformed from ultra-deep high-reduction oxygen-free fluid into low-reduction alkaline fluid, and finally into oxidized fluid with low oxygen fugacity. This result confirms that the Mengyin area underwent metamorphism of slightly active deep fluid, and provides evidence for searching diamond by means of indicative minerals.展开更多
The genesis of giant gold provinces is an international scientific frontier,in which the source of a huge amount of gold and the drive for mineralization are key challenges.The mineralization intensity of the Jiaodong...The genesis of giant gold provinces is an international scientific frontier,in which the source of a huge amount of gold and the drive for mineralization are key challenges.The mineralization intensity of the Jiaodong gold province in eastern China is a rare occasion in the world,because it owns gold reserves of~5500 tons within an area of less than 10,000 km^(2).The Jiaodong gold province formed in the superimposed domain of diverse tectonic regimes in an intracontinental setting.Paleoproterozoic regional peak metamorphism and Triassic continental collision are followed by the tectonic transition and gold mineralization at ca.120 Ma with time intervals of 1.9 billion years and about 100 million years,respectively.The Jiaodong gold deposits are different from orogenic and intrusion-related gold deposits in terms of the tectonic background,types of host rocks,and oreforming mechanism.These gold deposits show close spatial-temporal and genetic relationships to mafic igneous rocks,implying the derivation of ore-forming fluids from the metasomatic mantle domains.Mafic dykes in Jiaodong have negativeε_(Hf)(t)values of-29.9 to-9.1,Os content of 0.002-0.16 ppb,heavyδ^(18)O up to 8.23‰,and high initial^(187)Os/^(188)Os ratios of 0.1352-0.8858.These indicate that the lithospheric mantle was metasomatized by ancient crust-derived components.The lithospheric mantle in the western Jiaodong shows generally more enriched isotope features than that in the eastern part,which is explained to be an important reason for its huge gold resources.The mafic dykes show lighter Mg isotope characteristics(averageδ^(26)Mg of-0.33‰,n=50)and high Ca O content(overall greater than 6.5 wt%),indicating that the lithospheric mantle would also record the metasomatism by the carbonate rocks from the subducting oceanic slab.Under the background of the rollback of the subducting paleo-Pacific slab and the destruction of the North China Craton,partial melting of the lower crust would produce granitic magmas that led to the enrichment of gold in the residual crust.The syn-mineralization asthenosphere upwelling would promote the recycling of the lower crust and the partial melting of the metasomatic mantle domains.Basic magmas,produced by the partial melting,and the mantle itself would degas to form ore fluids.The ore fluids would further leach gold in the lower crust to increase its fertility.The auriferous fluids were transported to the middle to upper crust along the detachment and strike-slip faults.Water-rock interaction and fluid immiscibility,which occurred in and above the ductile-brittle transition zone to induce gold precipitation,formed the Jiaodong gold deposits.Given the unique geological features and genetic model of the Jiaodong gold deposits,they can be defined as“Jiaodong-type”gold deposits.展开更多
The source of rare earth elements (REE) ore-forming substances is identified to be extremely distinct from that of iron ores.The Bayan Obo Fe-REE ore deposits were generated by a composite process of both crustal and ...The source of rare earth elements (REE) ore-forming substances is identified to be extremely distinct from that of iron ores.The Bayan Obo Fe-REE ore deposits were generated by a composite process of both crustal and mantle source mineralization.The original iron bodies are of a sedimentary deposit from supergenesis,while the REE ores have been formed by mantle fluid metasomatism superimposed upon the pre-existing iron bodies.It is believed that the REE ore deposit would be controlled by intracontinental hot spot.The H_8 dolomite in mine regions belongs to normal sedimentary carbonate rock,its C and O isotopic composition rules out the possibility comparable with magrnatic carbonatite.The Sm-Nd isochrons of separated REE minerals have shown two REE peak mineralization periods:early-middle Proterozoic (1 700 Ma±480 Ma) and Caledonia (424-402 Ma).展开更多
基金the Natural Science Foundation of China(grant 40273009).
文摘The composition of gases trapped in olivine, orthopyroxene and clinopyroxene in Iherzolite xenoliths collected from different locations in eastern China has been measured by the vacuum stepped-heating mass spectrometry. These xenoliths are hosted in alkali basalts and considered as residues of partial melting of the upper mantle, and may contain evidence of mantle evolution. The results show that various kinds of fluid inclusions in Iherzolite xenoliths have been released at distinct times, which could be related to different stages of mantle evolution. In general, primitive fluids of the upper mantle (PFUM) beneath eastern China are dominated by H2, CO2 and CO, and are characterized by high contents of H2 and reduced gases. The compositions of PFUM are highly variable and related to tectonic settings. CO, CO2 and H2 are the main components of the PFUM beneath cratons; the PFUM in the mantle enriched in potassic metasomatism in the northern part of northeastern China has a high content of H2, while CO2 and SO2 are the dominant components of the PFUM in the Su-Lu-Wan (Jiangsu-Shandong-Anhui) region, where recycled crustal fluids were mixed with deeper mantle components. There are several fluids with distinct compositions beneath eastern China, such as primitive fluids of upper mantle (CO, CO2 and H2), partial melting fluids (CO2 and CO) and metasomatic fluids mixed with recycled crustal fluids (CO2, N2, SO2 and CH4) etc. Fluids of the upper mantle beneath the North China craton are different from that of the South China craton in total gases and chemical compositions: the contents of the reduced gases of the PFUM in the NCC are higher than those in the SCC.
基金supported by the National Natural Science Foundation of China (Grants No. 40473027 and 40773031)the Foundation of Doctoral Supported by the Ministry of Education (20105122110010 and 20115122110005)+1 种基金the Foundation of Open Subjects of State Key Laboratory for Mineral Deposits Research,Nanjing University (14-08-3)the Project of the State Key(Preparation Support) Disciplines of Mineralogy,Petrology and Mineral Deposit Geology of Sichuan Province (SZD0407)
文摘Based on petrological studies of the wall rocks, mineralizing rocks, ores and veins from the Laowangzhai gold deposit, it is discovered that along with the development of silication, carbonation and sulfidation, a kind of black opaque ultra-microlite material runs through the spaces between grains, fissures and cleavages. Under observations of the electron microprobe, scanning electronic microscopy and energy spectrum, this kind of ultra-microlite material is confirmed to consist of ultra microcrystalline quartz, silicate, sulfides and carbonates, as well as rutile, scheelite and specularite （magnetite）, showing characters of liquation by the analyses of SEM and energy spectrum. The coexistence of immiscibility and precipitating co-crystallization strongly suggests that the mineralizing fluid changed from the melt to the hydrothermal fluid. Combined with the element geochemical researches, it is realized that the ultra-microlite aggregate is the direct relics of the mantle fluid behaving like a melt and supercritical fluid, which goes along with the mantle-derived magma and will escape from the magma body at a proper time. During the alteration process, the nature of the mantle fluid changed and it is mixed with the crustal fluid, which are favorable for mineralization in the Loawangzhai gold deposit.
基金the National Natural Foundation of China grants 40273016 , 49973013
文摘Based on studies of petrography, mineralogy and mineral chemistry, deep mantle fluids and their products in kimberlites and diamonds can be assorted into the ultradeep fluid-transmitted minerals with an oxygen-free feature, the deep fluid metasomatized-minerals characterized by enrichment in TiO2, K2O, BaO, REE and Fe3+, and the deep fluid-reformed minerals. The three types show a successive descent in fluid origin depth and metasomatism strength, and they have brought forth a series of corresponding metasomatic products.
文摘This special issue of Geoscience Frontiers is a tribute volume honoring the life and career of Jacques Touret. A set of research papers has been assembled, which broadly reflect his research interests over his 50 plus year career. These papers Focus on the role that fluids play during the Formation and evolution of the Earth＇s crust. Below I provide a brief summary of the life of Jacques Touret, along with a select bibliography of his more important papers. This is then followed by a brief introduction to the papers assembled for this special issue.
基金The study was supported by the National Natural Science Foundation of China grant 49373168.
文摘: Minerals of various mantle-derived xenoliths from the Hannuoba basalt in Hebei Province have been studied by means of IR spectroscopy. The results show that all xenoliths from the mantle at depths <75 km contain trace amounts of water (0.45%–11.6×10?2% H2O). The data of about 0.1% H2O contained in primary pyrolite estimated by earlier studies may be on the high side. The water might enter the frameworks of olivine, pyroxene and garnet earlier than it entered those of amphibole and phlogopite. The presence of water in amphibole and phlogopite may be a local phenomenon of water enrichment, which is related to relatively small-scale magmatic or metasomatic events although they can contain a hundred times more water than pyroxene contains. There is a little more water (1.11%–3.01×10?2% of H2O mostly) in xenoliths from the Hannuoba basalt than in those from mid-ocean ridge basalt and kimberlites of South Africa (less than 1×10?2% of H2O mostly). This indicates the heterogeneity of water in time and space in the upper mantle. The presence of trace amounts of water in mantle-derived anhydrous silicate minerals provides basic data for us to understand the distribution of water in the upper mantle and the role of water in the mantle dynamic and geochemical processes.
基金Project(10872219) supported by the National Natural Science Foundation of China
文摘The finite element method was used to solve fluid dynamic interaction problems between the crust and mantle of the Earth. To consider different mechanical behaviours, the lithosphere consisting of the crust and upper mantle was simulated as fluid-saturated porous rocks, while the upper aesthenospheric part of the mantle was simulated as viscous fluids. Since the whole lithosphere was computationally simulated, the dynamic interaction between the crust and the upper mantle was appropriately considered. In particular, the mixing of mantle fluids and crustal fluids was simulated in the corresponding computational model. The related computational simulation results from an example problem demonstrate that the mantle fluids can flow into the crust and mix with the crustal fluids due to the resulting convective flows in the crust-mantle system. Likewise, the crustal fluids can also flow into the upper mantle and mix with the mantle fluids. This kind of fluids mixing and exchange is very important to the better understanding of the governing processes that control the ore body formation and mineralization in the upper crust of the Earth.
基金the Nationa1 Natural Science Foundation(Grant No.49673185)the Ministry of Science and Technology of China(Grant No.95-Pre-39).
文摘Using the secondary spinel standard, the authors have precisely measured theFe^(3+)/SIGMA Fe values of spinels in mantle xenoliths from Cenozoic basalts in eastern China, andestimated the oxygen fugacities recorded by 63 mantle xenoliths through olivine-orthopyroxene-spineloxygen barometry. The results indicate that the oxygen fugacities of the lithospheric mantle ineastern China are higher in the south than in the north. Among them, the oxygen fugacity of theNorth China craton lithospheric mantle is the lowest, similar to that of the oceanic mantle, whilethat of Northeast and South China are the same as that of the global continental mantle. Thevariations of mantle redox state in eastern China are mainly controlled by the C-O-H fluids derivedfrom the asthenospheric mantle. According to the mantle oxidation state, it can be concluded thatthe C-O-H fluids in the lithospheric mantle of eastern China consist mainly of CO_2 and minor H_2O,but CH_4-rich fluids should come from the asthenosphere where the oxidation state is lower.
基金supported by National Natural Science Foundation of China grant 40473027 and 40773031Foundation of Open Subjects of the State Key Laboratory of Geological Processes and Mineral Resources of the China University of Geosciences grant GPMR0509 and GPMR200705the Project of the State Key(Preparation Support)Disciplines of Mineralogy,Petrology and Mineral Deposit Geology of Sichuan Province.
文摘Three special types of xenoliths have recently been found in an aegirine-augite syenite porphyry in Liuhe, Yunnan, China. Petrographical, petrochemical, electron microprobe, and scanning electron microscopy studies indicate that pure calcite xenocrysts and quartz-bearing topaz pegmatite xenoliths result from the degassing of mantle fluids during their migration, and that black microcrystalline iron-rich silicate-melt xenoliths are the product of the extraction of mantle fluids accompanying degassing and are composed dominantly of quartz, chlorite, and iron-rich columnar and sheet silicate minerals with characteristic minerals, such as native iron, apatite, and zircon. According to the bulk-rock chemical and mineral compositions and crystallization states, the microcrystalline melt xenoliths are not the product of conventional magmatism, and especially the existence of native iron further proves that the xenoliths were mantle fluid materials under reduction or anoxic conditions. The study of the special xenoliths furnishes an important deep-process geochemical background of polymetallic mineralization in different rocks and strata in the study area.
基金supported by the National Natural Science Foundation of China (Grant No. 4027301)the National Geological Survey Project (Grant No.003201)
文摘Based on previous studies of kimberlite xenoliths and diamond inclusions in this region, macrocrystai garnet was analyzed with the electric microprobe technique （EPMA）. The garnet is collected from the Shengli No.1 kimberlite pipe in the Mengyin area of Shandong Province, China. The results indicate that the garnet contains two kinds of multiphase inclusions： one is K-, B-, and CI- bearing oxygen-free phase, K- and Cl-bearing oxygen-free phase, and volatile-bearing garnet inclusions （in1 and in3）; and the other is chlorite, phlogopite, apatite and calcite （in2）. It is suggested that the formation of garnet and its inclusions is associated with strongly reduced mantle fluid. Such a fluid was transformed from ultra-deep high-reduction oxygen-free fluid into low-reduction alkaline fluid, and finally into oxidized fluid with low oxygen fugacity. This result confirms that the Mengyin area underwent metamorphism of slightly active deep fluid, and provides evidence for searching diamond by means of indicative minerals.
基金supported by the National Natural Science Foundation of China(Grant Nos.42130801,42125203,42261134535,41230311,42272071)the National Key Research and Development Program(Grant No.2019YFA0708603)+1 种基金the 111 Project of the Ministry of Science and Technology(Grant No.BP0719021)the Fundamental Research Funds for the Central Universities(Grant Nos.2652023001,3-7-8-2023-09)。
文摘The genesis of giant gold provinces is an international scientific frontier,in which the source of a huge amount of gold and the drive for mineralization are key challenges.The mineralization intensity of the Jiaodong gold province in eastern China is a rare occasion in the world,because it owns gold reserves of~5500 tons within an area of less than 10,000 km^(2).The Jiaodong gold province formed in the superimposed domain of diverse tectonic regimes in an intracontinental setting.Paleoproterozoic regional peak metamorphism and Triassic continental collision are followed by the tectonic transition and gold mineralization at ca.120 Ma with time intervals of 1.9 billion years and about 100 million years,respectively.The Jiaodong gold deposits are different from orogenic and intrusion-related gold deposits in terms of the tectonic background,types of host rocks,and oreforming mechanism.These gold deposits show close spatial-temporal and genetic relationships to mafic igneous rocks,implying the derivation of ore-forming fluids from the metasomatic mantle domains.Mafic dykes in Jiaodong have negativeε_(Hf)(t)values of-29.9 to-9.1,Os content of 0.002-0.16 ppb,heavyδ^(18)O up to 8.23‰,and high initial^(187)Os/^(188)Os ratios of 0.1352-0.8858.These indicate that the lithospheric mantle was metasomatized by ancient crust-derived components.The lithospheric mantle in the western Jiaodong shows generally more enriched isotope features than that in the eastern part,which is explained to be an important reason for its huge gold resources.The mafic dykes show lighter Mg isotope characteristics(averageδ^(26)Mg of-0.33‰,n=50)and high Ca O content(overall greater than 6.5 wt%),indicating that the lithospheric mantle would also record the metasomatism by the carbonate rocks from the subducting oceanic slab.Under the background of the rollback of the subducting paleo-Pacific slab and the destruction of the North China Craton,partial melting of the lower crust would produce granitic magmas that led to the enrichment of gold in the residual crust.The syn-mineralization asthenosphere upwelling would promote the recycling of the lower crust and the partial melting of the metasomatic mantle domains.Basic magmas,produced by the partial melting,and the mantle itself would degas to form ore fluids.The ore fluids would further leach gold in the lower crust to increase its fertility.The auriferous fluids were transported to the middle to upper crust along the detachment and strike-slip faults.Water-rock interaction and fluid immiscibility,which occurred in and above the ductile-brittle transition zone to induce gold precipitation,formed the Jiaodong gold deposits.Given the unique geological features and genetic model of the Jiaodong gold deposits,they can be defined as“Jiaodong-type”gold deposits.
基金the National Natural Science Foundation of China
文摘The source of rare earth elements (REE) ore-forming substances is identified to be extremely distinct from that of iron ores.The Bayan Obo Fe-REE ore deposits were generated by a composite process of both crustal and mantle source mineralization.The original iron bodies are of a sedimentary deposit from supergenesis,while the REE ores have been formed by mantle fluid metasomatism superimposed upon the pre-existing iron bodies.It is believed that the REE ore deposit would be controlled by intracontinental hot spot.The H_8 dolomite in mine regions belongs to normal sedimentary carbonate rock,its C and O isotopic composition rules out the possibility comparable with magrnatic carbonatite.The Sm-Nd isochrons of separated REE minerals have shown two REE peak mineralization periods:early-middle Proterozoic (1 700 Ma±480 Ma) and Caledonia (424-402 Ma).
