2021 Vol. 46, No. 12
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2021, 46(12): 4197-4229.
doi: 10.3799/dqkx.2021.221
Abstract:
Metasomatized lithospheric mantle has been considered to play a key control on the formation of giant gold (Au) deposits. Investigating the extent of Au enrichment in the metasomatized lithospheric mantle source and Au contents of mantle-derived magmas, as well as the mechanisms that promote the transportation and enrichment of Au from mantle source to large Au mineralization, could help us to understand the major controls responsible for the formation of giant hydrothermal Au deposits. Gold is one of the highly chalcophile elements and is also mobile in fluids. The behavior of Au in many processes such as mantle melting/metasomatism, magmatic-hydrothermal evolution, and mineralization is complicated. In this study, it compiles Au contents of mantle rocks and their derivative mafic magmas, and attempts to clarify key factors that control the behavior of Au from mantle, magmatic-hydrothermal processes to gold mineralization. It suggests that the metasomatized lithospheric mantle is an important source for giant hydrothermal Au deposits, but the remarkable Au enrichment of such mantle source is not necessarily required. Metasomatic components, especially volatiles, enable efficient release of Au from the mantle source to hydrous magmas and promote subsequent transportation and enrichment during magmatic-hydrothermal processes through trans-lithospheric fault systems. It thus emphasizes the main role of the metasomatized lithospheric mantle as the source of giant Au deposits and highlight the importance of metasomatic volatiles and related magmatic-hydrothermal processes in Au enrichment rather than anomalously pre-enriched sources or primary magmas. Therefore, understanding the behavior of Au in mantle metasomatism and magmatic-hydrothermal processes during the long-term evolution of the lithospheric mantle is the key to decode the genesis of giant hydrothermal Au deposits.
Metasomatized lithospheric mantle has been considered to play a key control on the formation of giant gold (Au) deposits. Investigating the extent of Au enrichment in the metasomatized lithospheric mantle source and Au contents of mantle-derived magmas, as well as the mechanisms that promote the transportation and enrichment of Au from mantle source to large Au mineralization, could help us to understand the major controls responsible for the formation of giant hydrothermal Au deposits. Gold is one of the highly chalcophile elements and is also mobile in fluids. The behavior of Au in many processes such as mantle melting/metasomatism, magmatic-hydrothermal evolution, and mineralization is complicated. In this study, it compiles Au contents of mantle rocks and their derivative mafic magmas, and attempts to clarify key factors that control the behavior of Au from mantle, magmatic-hydrothermal processes to gold mineralization. It suggests that the metasomatized lithospheric mantle is an important source for giant hydrothermal Au deposits, but the remarkable Au enrichment of such mantle source is not necessarily required. Metasomatic components, especially volatiles, enable efficient release of Au from the mantle source to hydrous magmas and promote subsequent transportation and enrichment during magmatic-hydrothermal processes through trans-lithospheric fault systems. It thus emphasizes the main role of the metasomatized lithospheric mantle as the source of giant Au deposits and highlight the importance of metasomatic volatiles and related magmatic-hydrothermal processes in Au enrichment rather than anomalously pre-enriched sources or primary magmas. Therefore, understanding the behavior of Au in mantle metasomatism and magmatic-hydrothermal processes during the long-term evolution of the lithospheric mantle is the key to decode the genesis of giant hydrothermal Au deposits.
2021, 46(12): 4230-4246.
doi: 10.3799/dqkx.2021.062
Abstract:
E-MORB-like mafic dykes are exposed in Southwest Fujian Province and record key information of tectonic-magmatism in Southeast China during Late Cenozoic. A comprehensive research of petrology, zircon U-Pb dating, elemental geochemistry and isotope geochemistry was carried out. Mafic dykes are composed of dolerite and hornblende gabbro dolerite, and possess middle-low potassic features, with the Mg# values range from 55.80 to 66.38. Zircon U-Pb dating yield an age of 117.4±3.8 Ma, indicating that mafic dykes were emplaced at end of Early Cretaceous. Dykes enrich in Rb, Ba, U, K and LREE, without obvious depletion of Nb, Ta and Ti, which is consist with the E-MORB geochemical affinities. Samples have positive εNd(t) (-0.9 to 4.0), and (87Sr/86Sr)i values range from 0.706 50 to 0.710 19. Geochemical compositions show that the olivine and clinopyroxene fractionation have occurred and crustal contamination did not played an important role during the emplacement. We propose a slab window model to interpret the formation of mafic dykes. Subduction speed of Pacific plate beneath Nanling area was decreased by the overlying thickened lithosphere, which lead to the subduction velocity of the plate to be different from that of the adjacent area, and resulted in the formation of slab windows. Asthenospheric material could rise through slab windows, and carried and interacted with oceanic sediments, forming the E-MORB-like mantle rocks. With the upwelling of asthenosphere, E-MORB-like mantle materials will undergo partially melt and the resulting melts will emplace to form mafic dykes with a continental extensional-intracontinental rift setting at end of Early Cretaceous.
E-MORB-like mafic dykes are exposed in Southwest Fujian Province and record key information of tectonic-magmatism in Southeast China during Late Cenozoic. A comprehensive research of petrology, zircon U-Pb dating, elemental geochemistry and isotope geochemistry was carried out. Mafic dykes are composed of dolerite and hornblende gabbro dolerite, and possess middle-low potassic features, with the Mg# values range from 55.80 to 66.38. Zircon U-Pb dating yield an age of 117.4±3.8 Ma, indicating that mafic dykes were emplaced at end of Early Cretaceous. Dykes enrich in Rb, Ba, U, K and LREE, without obvious depletion of Nb, Ta and Ti, which is consist with the E-MORB geochemical affinities. Samples have positive εNd(t) (-0.9 to 4.0), and (87Sr/86Sr)i values range from 0.706 50 to 0.710 19. Geochemical compositions show that the olivine and clinopyroxene fractionation have occurred and crustal contamination did not played an important role during the emplacement. We propose a slab window model to interpret the formation of mafic dykes. Subduction speed of Pacific plate beneath Nanling area was decreased by the overlying thickened lithosphere, which lead to the subduction velocity of the plate to be different from that of the adjacent area, and resulted in the formation of slab windows. Asthenospheric material could rise through slab windows, and carried and interacted with oceanic sediments, forming the E-MORB-like mantle rocks. With the upwelling of asthenosphere, E-MORB-like mantle materials will undergo partially melt and the resulting melts will emplace to form mafic dykes with a continental extensional-intracontinental rift setting at end of Early Cretaceous.
2021, 46(12): 4247-4259.
doi: 10.3799/dqkx.2021.085
Abstract:
Due to the low mineralization temperature, no suitable dating minerals have been found in the MVT type lead-zinc deposit at present. In addition, due to the superposition of multi-stage mineralization and the existence of multiple mixing of ore-forming materials, it seriously restricted the study on mineralization chronology of this type of deposit. Some achievements have been made on the genesis, material source and metallogenic conditions of the super-large MVT lead-zinc deposit in Jinding, Yunnan. However, the age of deposit formation is still uncertain. On the basis of summarizing a large number of previous study results and combining the Re-Os isotopic dating results of fresh bitumen samples taken from Paomaping and Jiayashan ore sections, it shows that the ancient oil reservoirs was formed at 59.1 Ma, and the formation age of Jinding lead-zinc deposit might be 27.7 Ma. Ancient reservoirs are of greatly important condition on formation of lead-zinc mine, the tectonic domes provided storage space for metal mineralization. On account of the structure and hydrothermal process in damage, cracking of oil and gas meantime release large amounts of reducing substances, which provides important carrier for Pb, zinc and other ore-forming materials migration, enrichment and precipitation, thus formed the Jinding super-large Pb-Zn deposit. The results confirm that asphalt Re-Os isotope can not only provide an effective technical way to determine the metallogenic age of MVT type lead-zinc deposit, but also provide a favorable basis for the generation and destruction age of the oil and gas reservoirs.
Due to the low mineralization temperature, no suitable dating minerals have been found in the MVT type lead-zinc deposit at present. In addition, due to the superposition of multi-stage mineralization and the existence of multiple mixing of ore-forming materials, it seriously restricted the study on mineralization chronology of this type of deposit. Some achievements have been made on the genesis, material source and metallogenic conditions of the super-large MVT lead-zinc deposit in Jinding, Yunnan. However, the age of deposit formation is still uncertain. On the basis of summarizing a large number of previous study results and combining the Re-Os isotopic dating results of fresh bitumen samples taken from Paomaping and Jiayashan ore sections, it shows that the ancient oil reservoirs was formed at 59.1 Ma, and the formation age of Jinding lead-zinc deposit might be 27.7 Ma. Ancient reservoirs are of greatly important condition on formation of lead-zinc mine, the tectonic domes provided storage space for metal mineralization. On account of the structure and hydrothermal process in damage, cracking of oil and gas meantime release large amounts of reducing substances, which provides important carrier for Pb, zinc and other ore-forming materials migration, enrichment and precipitation, thus formed the Jinding super-large Pb-Zn deposit. The results confirm that asphalt Re-Os isotope can not only provide an effective technical way to determine the metallogenic age of MVT type lead-zinc deposit, but also provide a favorable basis for the generation and destruction age of the oil and gas reservoirs.
2021, 46(12): 4260-4273.
doi: 10.3799/dqkx.2021.178
Abstract:
The Boka gold deposit is located in the middle-south section of "Kangdian axis" in the western margin of Yangtze River. It is quite different from the "Dongchuan type" copper mineralization in the Yinmin-Tangdan area of Dongchuan. The rich wall rock of the deposit is black carbonate clastic rock stratum of Dongchuan group. Au occurs in quartz dolomite sulfide vein. It has obvious alteration characteristics of diabase magma extraction type Au deposit, which is different from ductile shear zone type Au deposit.In this paper, the Au-bearing pyrite and the wall rock carbonaceous slate in the Xinshan-Majiagou ore block were selected for Re-Os isotopic and trace element studies respectively. The results show that the Re-Os isochron age of pyrite is 779±14 Ma (MSWD=11.1), indicating that the Boka gold deposit was formed in Neoproterozoic. The initial Os ratio of pyrite is 3.03±0.42, indicating that the ore-forming materials of Boka gold deposit were mainly derived from the crust (wall rock strata) rather than diabase magma. The contents of Au (402.50×10-9and 44.98×10-9on average) and Cu (1 733.00×10-6 and 46.07×10-6 on average) in pyrite and carbonaceous slate are much higher than Clark values (about 4×10-9 and 60×10-6), which further confirms that the ore-forming materials were derived from the carbonaceous slate of the surrounding rock strata. The diagenetic age of Boka gold deposit in Dongchuan is basically consistent with the Neoproterozoic magmatic rock related hydrothermal transformation events, which indicates that the metallogenic background is the ore-forming response of Neoproterozoic magmatic/hydrothermal transformation in the area. During this period, the magmatic rock is in thermal contact with the ore rich wall rock, and the favorable ore-forming elements were extracted from the wall rock strata, The Boka gold deposit in Dongchuan was formed in a good metallogenic space.
The Boka gold deposit is located in the middle-south section of "Kangdian axis" in the western margin of Yangtze River. It is quite different from the "Dongchuan type" copper mineralization in the Yinmin-Tangdan area of Dongchuan. The rich wall rock of the deposit is black carbonate clastic rock stratum of Dongchuan group. Au occurs in quartz dolomite sulfide vein. It has obvious alteration characteristics of diabase magma extraction type Au deposit, which is different from ductile shear zone type Au deposit.In this paper, the Au-bearing pyrite and the wall rock carbonaceous slate in the Xinshan-Majiagou ore block were selected for Re-Os isotopic and trace element studies respectively. The results show that the Re-Os isochron age of pyrite is 779±14 Ma (MSWD=11.1), indicating that the Boka gold deposit was formed in Neoproterozoic. The initial Os ratio of pyrite is 3.03±0.42, indicating that the ore-forming materials of Boka gold deposit were mainly derived from the crust (wall rock strata) rather than diabase magma. The contents of Au (402.50×10-9and 44.98×10-9on average) and Cu (1 733.00×10-6 and 46.07×10-6 on average) in pyrite and carbonaceous slate are much higher than Clark values (about 4×10-9 and 60×10-6), which further confirms that the ore-forming materials were derived from the carbonaceous slate of the surrounding rock strata. The diagenetic age of Boka gold deposit in Dongchuan is basically consistent with the Neoproterozoic magmatic rock related hydrothermal transformation events, which indicates that the metallogenic background is the ore-forming response of Neoproterozoic magmatic/hydrothermal transformation in the area. During this period, the magmatic rock is in thermal contact with the ore rich wall rock, and the favorable ore-forming elements were extracted from the wall rock strata, The Boka gold deposit in Dongchuan was formed in a good metallogenic space.
2021, 46(12): 4274-4290.
doi: 10.3799/dqkx.2021.101
Abstract:
The Weiningbeishan area is the most promising polymetallic ore target area in Ningxia, where numerous Au, Ag, Cu, Pb, Zn, Fe, Co, and other ore occurrences have been found. The Jinchangzi gold deposit is the largest gold deposit found in the area, and the ore bodies are mainly hosted in the intra-layer fault fractures, with an east-west distribution and near-uniform with the bedding. Magmatism is weak in this district, with several diorite porphyrite having been identified in exposures adjacent to the gold veins. In order to explore the nature, source and genesis of the ore-forming fluid of the Jinchangzi gold deposit, the fluid inclusions and C-H-O isotopes in the study area were studied. The ore-forming hydrothermal period of the deposit can be divided into 4 metallogenic stages, from early to late, they are sericite-pyrite-quartz stage (Ⅰ), pyrite-barite-quartz stage (Ⅱ), polymetallic sulfide-carbonate-quartz stage (Ⅲ) and pyrite-carbonatite stage (Ⅳ), of which stage Ⅲ is the main metallogenic stage. There are four types of fluid inclusions in the mineralization stage, which are aqueous solution inclusions, pure CO2 inclusions, CO2-H2O inclusions and multiphase inclusions containing daughter crystals. The completely homogenous temperature of the ore-forming fluids is between 171-396℃, the salinity is between 1.30%-10.99% NaCl equiv, and the density is 0.24-0.78 g/cm3, which are CO2-H2O-NaCl systems with medium-low temperature, low salinity, low density, CO2 rich, and a small amount of N2. The δD value of hydrothermal quartz is -66.0‰ to -32.0‰, and the δ18OV-SMOW value is (+19.7‰)-(+22.6‰), indicating that the ore-forming fluid is metamorphic and the magmatism is not obvious. The C isotope shows that the δ13C of calcite and siderite in the late stage (stage Ⅳ) is between -2.540‰ and -0.736‰, indicating that C in the ore-forming fluid has the characteristics of mixed sources. The fluids formed by the metamorphic dehydration of Ordovician-Carboniferous terrigenous clastic rocks and carbonate rocks may be the main source of gold ore-forming fluids. During the ore-forming process, the fluids had an obvious immiscibility phenomenon, which was an important factor causing gold precipitation. The genetic type of the deposit is an orogenic gold deposit.
The Weiningbeishan area is the most promising polymetallic ore target area in Ningxia, where numerous Au, Ag, Cu, Pb, Zn, Fe, Co, and other ore occurrences have been found. The Jinchangzi gold deposit is the largest gold deposit found in the area, and the ore bodies are mainly hosted in the intra-layer fault fractures, with an east-west distribution and near-uniform with the bedding. Magmatism is weak in this district, with several diorite porphyrite having been identified in exposures adjacent to the gold veins. In order to explore the nature, source and genesis of the ore-forming fluid of the Jinchangzi gold deposit, the fluid inclusions and C-H-O isotopes in the study area were studied. The ore-forming hydrothermal period of the deposit can be divided into 4 metallogenic stages, from early to late, they are sericite-pyrite-quartz stage (Ⅰ), pyrite-barite-quartz stage (Ⅱ), polymetallic sulfide-carbonate-quartz stage (Ⅲ) and pyrite-carbonatite stage (Ⅳ), of which stage Ⅲ is the main metallogenic stage. There are four types of fluid inclusions in the mineralization stage, which are aqueous solution inclusions, pure CO2 inclusions, CO2-H2O inclusions and multiphase inclusions containing daughter crystals. The completely homogenous temperature of the ore-forming fluids is between 171-396℃, the salinity is between 1.30%-10.99% NaCl equiv, and the density is 0.24-0.78 g/cm3, which are CO2-H2O-NaCl systems with medium-low temperature, low salinity, low density, CO2 rich, and a small amount of N2. The δD value of hydrothermal quartz is -66.0‰ to -32.0‰, and the δ18OV-SMOW value is (+19.7‰)-(+22.6‰), indicating that the ore-forming fluid is metamorphic and the magmatism is not obvious. The C isotope shows that the δ13C of calcite and siderite in the late stage (stage Ⅳ) is between -2.540‰ and -0.736‰, indicating that C in the ore-forming fluid has the characteristics of mixed sources. The fluids formed by the metamorphic dehydration of Ordovician-Carboniferous terrigenous clastic rocks and carbonate rocks may be the main source of gold ore-forming fluids. During the ore-forming process, the fluids had an obvious immiscibility phenomenon, which was an important factor causing gold precipitation. The genetic type of the deposit is an orogenic gold deposit.
2021, 46(12): 4291-4315.
doi: 10.3799/dqkx.2021.018
Abstract:
Jienagepu gold deposit is a newly discovered Miocene hydrothermal gold deposit in the Zhaxikang ore concentration area, eastern Tethyan Himalayas, but its genesis is rather vague. The ore body is stratified or approximately stratified, strictly controlled by extensional fault structure. In this study, two types of ores were recognized, namely altered rock type and quartz vein type, with extensive hydrothermal alternation, including silicification, pyritization, sericization and calcite. Samples were systematically taken from the altered rock type ore in orebody No. Ⅱ and No. Ⅲ, and the composition characteristics of He-Ar and in-situ S isotope of pyrite were analyzed to determine the genesis of the deposit. The results show that the content of 4He and 3He/4He ratio in pyrite ranged widely from 0.038×10-7 cm3 STP/g to 0.446×10-7 cm3 STP/g, 0.08 Ra to 0.09 Ra, with an average of 0.200×10-7 cm3 STP/g and 0.08 Ra. The content of 40Ar and 40Ar/36Ar ratio vary from 0.049×10-7 cm3 STP/g to 0.132×10-7 cm3 STP/g, 308.0 to 386.3, with an average of 0.084×10-7 cm3 STP/g and 347.1, indicating that the ore-forming fluid mainly originated from the crustal metamorphic fluid. The δ34S value of pyrite is concentrated, and the overall variation is between 1‰ and 3‰, with an average of 2.98‰, showing that the ore-forming material is from crustal-mantle homogenized deep source. Combined with previous research results, in this paper it holds that Jienagepu gold deposit is an orogenic type gold deposit, and the determination of genesis is of great significance to enrich and perfect the mineralization theory of continental collisional orogeny and to guide the exploration of regional ore deposits.
Jienagepu gold deposit is a newly discovered Miocene hydrothermal gold deposit in the Zhaxikang ore concentration area, eastern Tethyan Himalayas, but its genesis is rather vague. The ore body is stratified or approximately stratified, strictly controlled by extensional fault structure. In this study, two types of ores were recognized, namely altered rock type and quartz vein type, with extensive hydrothermal alternation, including silicification, pyritization, sericization and calcite. Samples were systematically taken from the altered rock type ore in orebody No. Ⅱ and No. Ⅲ, and the composition characteristics of He-Ar and in-situ S isotope of pyrite were analyzed to determine the genesis of the deposit. The results show that the content of 4He and 3He/4He ratio in pyrite ranged widely from 0.038×10-7 cm3 STP/g to 0.446×10-7 cm3 STP/g, 0.08 Ra to 0.09 Ra, with an average of 0.200×10-7 cm3 STP/g and 0.08 Ra. The content of 40Ar and 40Ar/36Ar ratio vary from 0.049×10-7 cm3 STP/g to 0.132×10-7 cm3 STP/g, 308.0 to 386.3, with an average of 0.084×10-7 cm3 STP/g and 347.1, indicating that the ore-forming fluid mainly originated from the crustal metamorphic fluid. The δ34S value of pyrite is concentrated, and the overall variation is between 1‰ and 3‰, with an average of 2.98‰, showing that the ore-forming material is from crustal-mantle homogenized deep source. Combined with previous research results, in this paper it holds that Jienagepu gold deposit is an orogenic type gold deposit, and the determination of genesis is of great significance to enrich and perfect the mineralization theory of continental collisional orogeny and to guide the exploration of regional ore deposits.
2021, 46(12): 4316-4333.
doi: 10.3799/dqkx.2021.068
Abstract:
The Zimudang gold deposit, part of the Southwest Guizhou Au metallogenic province, is an important large-size Carlin-type Au deposit. However, the sources of ore-forming materials of this deposit are still unclear. In this study, it systematically evaluated the S, C, O, Pb, and Sr isotopic compositions for various orebodies and host rocks of this deposit. δ34S values of sulfides from orebodies range from -13.49‰ to 17.91‰, with peaks ranging from -0.99‰ to 3.58‰, while those of host rocks range from -26.23‰ to -19.63‰, which indicates that the sulfur in the ore-forming period mainly derived from magma and partially from pre-mineralization pyrites in the host-strata. δ13C and δ18O values of hydrothermal calcites range from -9.10‰ to 0.59‰ and 15.65‰ to 23.82‰, respectively, which are different from those of host rocks and regional strata, suggesting that the C and O in ore-forming fluids were partially from carbonate rocks (via dissolution) and might be partially from magma. Pb isotopic ratios of 206Pb/204Pb, 207Pb/204Pb and208Pb/204Pb for sulfide minerals from orebodies are 18.064 to 18.973, 15.585 to 15.670 and 38.219 to 39.054, respectively, and those for host rocks are 18.136 to 18.650, 15.574 to 15.656 and 38.423 to 38.812, respectively. These Pb isotopic ratios show that the Pb in orebodies was not from a single source, but might be a combination source of host-strata and magma. Initial 87Sr/86Sr of quartzes and carbonates from orebodies and the host rocks are in ranges of 0.707 26-0.708 11 and 0.707 28-0.707 31, respectively, which illustrate that the Sr in ore-forming fluids was mainly from host-strata. These S, C, O, Pb, and Sr isotopic studies for the Zimudang Au deposit demonstrate that the ore-forming materials have a mantle-crust mixed origin-a main source of deep concealed mantle magma with a minor input from the Permian-Triassic host-strata.
The Zimudang gold deposit, part of the Southwest Guizhou Au metallogenic province, is an important large-size Carlin-type Au deposit. However, the sources of ore-forming materials of this deposit are still unclear. In this study, it systematically evaluated the S, C, O, Pb, and Sr isotopic compositions for various orebodies and host rocks of this deposit. δ34S values of sulfides from orebodies range from -13.49‰ to 17.91‰, with peaks ranging from -0.99‰ to 3.58‰, while those of host rocks range from -26.23‰ to -19.63‰, which indicates that the sulfur in the ore-forming period mainly derived from magma and partially from pre-mineralization pyrites in the host-strata. δ13C and δ18O values of hydrothermal calcites range from -9.10‰ to 0.59‰ and 15.65‰ to 23.82‰, respectively, which are different from those of host rocks and regional strata, suggesting that the C and O in ore-forming fluids were partially from carbonate rocks (via dissolution) and might be partially from magma. Pb isotopic ratios of 206Pb/204Pb, 207Pb/204Pb and208Pb/204Pb for sulfide minerals from orebodies are 18.064 to 18.973, 15.585 to 15.670 and 38.219 to 39.054, respectively, and those for host rocks are 18.136 to 18.650, 15.574 to 15.656 and 38.423 to 38.812, respectively. These Pb isotopic ratios show that the Pb in orebodies was not from a single source, but might be a combination source of host-strata and magma. Initial 87Sr/86Sr of quartzes and carbonates from orebodies and the host rocks are in ranges of 0.707 26-0.708 11 and 0.707 28-0.707 31, respectively, which illustrate that the Sr in ore-forming fluids was mainly from host-strata. These S, C, O, Pb, and Sr isotopic studies for the Zimudang Au deposit demonstrate that the ore-forming materials have a mantle-crust mixed origin-a main source of deep concealed mantle magma with a minor input from the Permian-Triassic host-strata.
2021, 46(12): 4334-4345.
doi: 10.3799/dqkx.2021.111
Abstract:
In-situ Li isotope geochemistry has been better utilized to trace many complex processes including fractional crystallization, crust contamination and melt/fluid-mineral reaction during the petrogenesis and mineralization of mafic-ultramafic rocks. This study summarizes the major progresses in Li isotope geochemistry during petrogenesis and mineralization of mafic-ultramafic intrusions based on case studies. Firstly, the Li isotope study of Yellow Hill Alaskan-type intrusion reveal Li isotope fractionation during magma differentiation. Secondly, the studies on ophiolites from Turkey and Tibet indicate that Li isotope systematics have potential to constrain genesis of ophiolitic mantle section and evolution of chromitites. Thirdly, the Li isotope study of the ultramafic zone of the Stillwater complex demonstrates that hydrous fluids constrained mineral composition and acted as a critical medium of chemical exchange between minerals in the chromitites. Finally, Li isotope fractionation behavior in the formation of magmatic Ni-Cu sulfide deposits has been investigated.
In-situ Li isotope geochemistry has been better utilized to trace many complex processes including fractional crystallization, crust contamination and melt/fluid-mineral reaction during the petrogenesis and mineralization of mafic-ultramafic rocks. This study summarizes the major progresses in Li isotope geochemistry during petrogenesis and mineralization of mafic-ultramafic intrusions based on case studies. Firstly, the Li isotope study of Yellow Hill Alaskan-type intrusion reveal Li isotope fractionation during magma differentiation. Secondly, the studies on ophiolites from Turkey and Tibet indicate that Li isotope systematics have potential to constrain genesis of ophiolitic mantle section and evolution of chromitites. Thirdly, the Li isotope study of the ultramafic zone of the Stillwater complex demonstrates that hydrous fluids constrained mineral composition and acted as a critical medium of chemical exchange between minerals in the chromitites. Finally, Li isotope fractionation behavior in the formation of magmatic Ni-Cu sulfide deposits has been investigated.
2021, 46(12): 4346-4365.
doi: 10.3799/dqkx.2020.390
Abstract:
The formation of ore deposits is subject to varieties of complex geological processes, including plate tectonics, magmatic activities, metamorphic sedimentary transformations and other processes on global scale, and is generally accompanied by a series of geological and geochemical processes such as hydrothermal activities, fluid migration, fluid-rock interaction, elemental differentiation and isotopic fractionation. Over the past decades, studies of geochemical methods have focused on major, trace elements and traditional stable isotopes, that have addressed the genesis of ore deposits. However, there are still some difficulties and multi solutions. For instance, portions of ore deposits in the mineralization, alteration zoning, and metal mineral assemblage have many similarities, so the conventional geochemical indicators are difficult to be distinguished. With the improvement of analysis and the integrity of natural reservoir composition, Li isotope has become a new stable isotope system in recent years. The Li isotopic fractionation of up to 80‰ in the natural process enhances the identification ability of Li isotope, as well as in direct or indirect indicator function. Thus, Li isotopic systematics has the potential to be a good tracer to study various complex metallogenic processes. Here, this paper summarizes the studies and applications of Li isotopes on ore deposit in recent years, mainly in subduction zone mineralization, the geochemical behavior and characteristics of Li isotopes in porphyry-hydrothermal deposits, pegmatite deposits and sedimentary deposits, then it explores an application prospect of new Li isotopic method for ore deposits. Based on the applications of Li isotopic system in various ore deposits, it proposes that Li isotopic system will provide more indicative information for ore deposit study in the future.
The formation of ore deposits is subject to varieties of complex geological processes, including plate tectonics, magmatic activities, metamorphic sedimentary transformations and other processes on global scale, and is generally accompanied by a series of geological and geochemical processes such as hydrothermal activities, fluid migration, fluid-rock interaction, elemental differentiation and isotopic fractionation. Over the past decades, studies of geochemical methods have focused on major, trace elements and traditional stable isotopes, that have addressed the genesis of ore deposits. However, there are still some difficulties and multi solutions. For instance, portions of ore deposits in the mineralization, alteration zoning, and metal mineral assemblage have many similarities, so the conventional geochemical indicators are difficult to be distinguished. With the improvement of analysis and the integrity of natural reservoir composition, Li isotope has become a new stable isotope system in recent years. The Li isotopic fractionation of up to 80‰ in the natural process enhances the identification ability of Li isotope, as well as in direct or indirect indicator function. Thus, Li isotopic systematics has the potential to be a good tracer to study various complex metallogenic processes. Here, this paper summarizes the studies and applications of Li isotopes on ore deposit in recent years, mainly in subduction zone mineralization, the geochemical behavior and characteristics of Li isotopes in porphyry-hydrothermal deposits, pegmatite deposits and sedimentary deposits, then it explores an application prospect of new Li isotopic method for ore deposits. Based on the applications of Li isotopic system in various ore deposits, it proposes that Li isotopic system will provide more indicative information for ore deposit study in the future.
2021, 46(12): 4366-4389.
doi: 10.3799/dqkx.2021.140
Abstract:
There are three magnesium (Mg) isotopes, 24Mg, 25Mg and 26Mg, among which the relative mass difference of 26Mg and 24Mg is large, up to 8.33%. Such a large relative mass difference can cause significant mass dependent fractionation of Mg isotopes due to the changes of chemical and physical conditions during crustal activities or other geological processes. Variations of δ26Mg in nature are mainly from -5.60‰ to 0.92‰, spanning a limited range of 6.5‰. Mg isotope is a potential geochemical index and tracer for geological processes because Mg fractionates significantly in low-temperature geochemical processes, but not in high-temperature environments. Mg isotopes have made important progress in the fields of low-temperature weathering, high-temperature partial melting and magmatic crystallization differentiation, metamorphism, plate subduction, crust-mantle material recycling, hydrothermal alteration and genesis of deposits. In this paper, the analysis methods of Mg isotopes are briefly introduced firstly. Secondly, the composition and distribution characteristics of Mg isotopes in various reservoirs of the earth and the fractionation mechanism of Mg isotopes in geological processes are systematically summarized. And then, the application of magnesium isotopes in the study of carbonatites in recent years is emphatically introduced. Finally, it discusses the origin of low δ26Mg in mantle-derived rocks (related to carbonate rocks of subduction and recycling, oceanic crust materials or mineral separation crystallization) and trace the petrogenesis of magmatic carbonatites by the combination of Li, Mg and Ca isotopes. At the end of this paper, the advantages of the dual-path collision cell-capable multiple-collector inductively coupled plasma mass spectrometer (Nu Sapphire MC-ICP-MS) and the application of Li-Mg-Ca and other metal isotopes in the enrichment mechanisms of rare earth elements are prospected.
There are three magnesium (Mg) isotopes, 24Mg, 25Mg and 26Mg, among which the relative mass difference of 26Mg and 24Mg is large, up to 8.33%. Such a large relative mass difference can cause significant mass dependent fractionation of Mg isotopes due to the changes of chemical and physical conditions during crustal activities or other geological processes. Variations of δ26Mg in nature are mainly from -5.60‰ to 0.92‰, spanning a limited range of 6.5‰. Mg isotope is a potential geochemical index and tracer for geological processes because Mg fractionates significantly in low-temperature geochemical processes, but not in high-temperature environments. Mg isotopes have made important progress in the fields of low-temperature weathering, high-temperature partial melting and magmatic crystallization differentiation, metamorphism, plate subduction, crust-mantle material recycling, hydrothermal alteration and genesis of deposits. In this paper, the analysis methods of Mg isotopes are briefly introduced firstly. Secondly, the composition and distribution characteristics of Mg isotopes in various reservoirs of the earth and the fractionation mechanism of Mg isotopes in geological processes are systematically summarized. And then, the application of magnesium isotopes in the study of carbonatites in recent years is emphatically introduced. Finally, it discusses the origin of low δ26Mg in mantle-derived rocks (related to carbonate rocks of subduction and recycling, oceanic crust materials or mineral separation crystallization) and trace the petrogenesis of magmatic carbonatites by the combination of Li, Mg and Ca isotopes. At the end of this paper, the advantages of the dual-path collision cell-capable multiple-collector inductively coupled plasma mass spectrometer (Nu Sapphire MC-ICP-MS) and the application of Li-Mg-Ca and other metal isotopes in the enrichment mechanisms of rare earth elements are prospected.
2021, 46(12): 4390-4404.
doi: 10.3799/dqkx.2021.080
Abstract:
The progresses of the radioactive Pd-Ag system in planetary sciences and the stable silver isotope in environmental sciences and ore-deposits are systematically reviewed in this paper. In the formation of solar nebula and planetary nucleus, 107Ag can be produced by 107Pd through β decay, and the dissipation of volatile elements will cause the early Pd/Ag differentiation, which makes the Pd-Ag system applicable to investigate various activities of the early solar system, such as defining the formation of planetary nucleus and the age of planetary formation. In the stable silver isotope system, it has been proved that the wide variation range of δ109Ag is -1.0‰ to +2.3‰ in terrestrial materials. Stable silver isotope has characteristics similar to "fingerprint" in environmental materials, which makes it possible to effectively determine pollutants sources and to track migration paths of pollutants. Much wider variations of δ109Ag in metallic ore-deposits have been observed, showing a great potential of silver isotope in studying the genesis and evolution mode of Au-Ag deposits. However, there are still many concerns remained to be resolved, such as the precise definition of 107Pd/108Pd ratio in the early solar system of radioactive Pd-Ag system, and the quantification of silver isotope fractionation in physiochemical processes (e.g., boiling/phase separation, multistage ore paragenesis, precipitation, redox, adsorption and remobilization etc.) involved in silver migration and deposition in environmental and ore-forming processes.
The progresses of the radioactive Pd-Ag system in planetary sciences and the stable silver isotope in environmental sciences and ore-deposits are systematically reviewed in this paper. In the formation of solar nebula and planetary nucleus, 107Ag can be produced by 107Pd through β decay, and the dissipation of volatile elements will cause the early Pd/Ag differentiation, which makes the Pd-Ag system applicable to investigate various activities of the early solar system, such as defining the formation of planetary nucleus and the age of planetary formation. In the stable silver isotope system, it has been proved that the wide variation range of δ109Ag is -1.0‰ to +2.3‰ in terrestrial materials. Stable silver isotope has characteristics similar to "fingerprint" in environmental materials, which makes it possible to effectively determine pollutants sources and to track migration paths of pollutants. Much wider variations of δ109Ag in metallic ore-deposits have been observed, showing a great potential of silver isotope in studying the genesis and evolution mode of Au-Ag deposits. However, there are still many concerns remained to be resolved, such as the precise definition of 107Pd/108Pd ratio in the early solar system of radioactive Pd-Ag system, and the quantification of silver isotope fractionation in physiochemical processes (e.g., boiling/phase separation, multistage ore paragenesis, precipitation, redox, adsorption and remobilization etc.) involved in silver migration and deposition in environmental and ore-forming processes.
2021, 46(12): 4405-4426.
doi: 10.3799/dqkx.2021.091
Abstract:
Uranium isotope (238U/235U, usually expressed as δ238U) has been the research hotspot in the field of non-traditional stable isotopes. In the last century, it was thought that uranium isotope fractionation did not exist, so the development of uranium isotope research was very slow. However, with the development of the analytical technology, it has been found that there exists significant fractionation between238U and 235U in nature, which makes uranium isotopes an ideal tracer in Earth science. Indeed, overwhelming amounts of studies of uranium isotopes as a paleo-redox proxy have been published so far, most of which use uranium isotope to track the evolution of oxygen levels of Earth's subaerial environments through time and, furthermore, the potential relationship between the several big mass extinctions and the redox conditions of the oceans. Although researches on uranium isotope have achieved progresses in the co-evolution of the hydrosphere and biosphere, some problems still remain some unsolved. For example, the effects of microcosmic pathways of biological and abiotic reduction reactions on uranium isotope fractionation, and how the 238U/235U can trace the source of uranium ore deposits. Here, in this paper, it provides an overview of the uranium and its isotope geochemistry over the last decades, aiming at promoting applications of uranium isotopes in the genesis of uranium polymetallic deposits and high-temperature geochemistry in the future.
Uranium isotope (238U/235U, usually expressed as δ238U) has been the research hotspot in the field of non-traditional stable isotopes. In the last century, it was thought that uranium isotope fractionation did not exist, so the development of uranium isotope research was very slow. However, with the development of the analytical technology, it has been found that there exists significant fractionation between238U and 235U in nature, which makes uranium isotopes an ideal tracer in Earth science. Indeed, overwhelming amounts of studies of uranium isotopes as a paleo-redox proxy have been published so far, most of which use uranium isotope to track the evolution of oxygen levels of Earth's subaerial environments through time and, furthermore, the potential relationship between the several big mass extinctions and the redox conditions of the oceans. Although researches on uranium isotope have achieved progresses in the co-evolution of the hydrosphere and biosphere, some problems still remain some unsolved. For example, the effects of microcosmic pathways of biological and abiotic reduction reactions on uranium isotope fractionation, and how the 238U/235U can trace the source of uranium ore deposits. Here, in this paper, it provides an overview of the uranium and its isotope geochemistry over the last decades, aiming at promoting applications of uranium isotopes in the genesis of uranium polymetallic deposits and high-temperature geochemistry in the future.
2021, 46(12): 4427-4451.
doi: 10.3799/dqkx.2021.088
Abstract:
How early anoxic earth evolved to modern oxic Earth is the key to understand the formation and evolution of Earth's habitability. However, reconstructions of atmospheric and oceanic oxygen levels over Earth's history are still significant challenges. The high precision analysis of redox sensitive metal stable isotopes provides a powerful means to trace Earth's oxygenation history. In this review, it takes Mo, U, Tl, Cr isotopes as example to introduce the geochemical behaviors and fractionation mechanism of redox sensitive metal stable isotope systems. On this basis, it systematically reviews the advances of metal stable isotopes in important research issues including the onset of oxygenic photosynthesis, Great Oxidation Event (GOE), the redox state of atmosphere and ocean in the Mesoproterozoic, Neoproterozoic Oxidation Event (NOE). Metal stable isotopes have great application prospects in reconstructing the oxidation processes of Earth's surface. Furthermore, metal stable isotopes have profound significance in understanding the evolution of Earth's habitability and exploring its development in the future.
How early anoxic earth evolved to modern oxic Earth is the key to understand the formation and evolution of Earth's habitability. However, reconstructions of atmospheric and oceanic oxygen levels over Earth's history are still significant challenges. The high precision analysis of redox sensitive metal stable isotopes provides a powerful means to trace Earth's oxygenation history. In this review, it takes Mo, U, Tl, Cr isotopes as example to introduce the geochemical behaviors and fractionation mechanism of redox sensitive metal stable isotope systems. On this basis, it systematically reviews the advances of metal stable isotopes in important research issues including the onset of oxygenic photosynthesis, Great Oxidation Event (GOE), the redox state of atmosphere and ocean in the Mesoproterozoic, Neoproterozoic Oxidation Event (NOE). Metal stable isotopes have great application prospects in reconstructing the oxidation processes of Earth's surface. Furthermore, metal stable isotopes have profound significance in understanding the evolution of Earth's habitability and exploring its development in the future.
2021, 46(12): 4452-4469.
doi: 10.3799/dqkx.2021.117
Abstract:
Halogen in geological materials is the key tracer for the fluid/volatile related geological processes. Due to low concentration of halogens and high volatility, it is a challenge for the analysis of halogens in geological materials. Many studies on sample preparation for the analysis of halogens in geological materials have been reported in the last decade. Pyrohydrolysis, alkali fusion, acid digestion and alkali extraction are suitable for the high concentrations of halogens in soils, sediments and most of rocks. Only neutron activation analysis and noble gas technique can be utilized to analyze the low concentrations of halogens in geological materials. With the development of earth science and the analytical geochemistry, the future analysis of halogens will be more effective, more convenients and with higher sensitivity and precision are the future of the analysis of halogens. In this study, we reviewed the development of analysis techniques for halogens and compares the advantages and drawbacks between different methods. Finally, a perspective of the development of analytical method for halogens in geological materials are given.
Halogen in geological materials is the key tracer for the fluid/volatile related geological processes. Due to low concentration of halogens and high volatility, it is a challenge for the analysis of halogens in geological materials. Many studies on sample preparation for the analysis of halogens in geological materials have been reported in the last decade. Pyrohydrolysis, alkali fusion, acid digestion and alkali extraction are suitable for the high concentrations of halogens in soils, sediments and most of rocks. Only neutron activation analysis and noble gas technique can be utilized to analyze the low concentrations of halogens in geological materials. With the development of earth science and the analytical geochemistry, the future analysis of halogens will be more effective, more convenients and with higher sensitivity and precision are the future of the analysis of halogens. In this study, we reviewed the development of analysis techniques for halogens and compares the advantages and drawbacks between different methods. Finally, a perspective of the development of analytical method for halogens in geological materials are given.
2021, 46(12): 4470-4479.
doi: 10.3799/dqkx.2021.052
Abstract:
Reaction temperature and reaction time are key factors for the determination of oxygen isotopic composition of oxides and silicate minerals by BrF5 method. This work aims to study the effect of the higher temperature (550-800℃) on the oxygen isotopic composition analysis by BrF5 method. The national standard sample GBW04409 for oxygen isotopic composition were prepared and analyzed at high reaction temperatures. The results show that sufficient yields of O2 could be achieved when sample was reacted with BrF5 at 550-675℃, under which condition the δ18O value fell in the range of 10.4‰-11.8‰ with high accuracy. However, when the reaction temperature was higher than 700℃, the yields of O2 were low, and the δ18O values were in the range of 10.8‰-26.8‰, which had a significant positive deviation to the given δ18O values. To solve the problem due to effect of the higher temperature, fractional fluorination was conducted. The results of oxygen isotopic composition obtained were consistent with the recommended value when the oxygen liberated after each time fluorination was all collected. The consumption of BrF5 by the nickel reactor at higher temperature results in the insufficient amount of BrF5 reacted with the sample, which causes the low yield of O2, thus the fractionation of oxygen isotope.
Reaction temperature and reaction time are key factors for the determination of oxygen isotopic composition of oxides and silicate minerals by BrF5 method. This work aims to study the effect of the higher temperature (550-800℃) on the oxygen isotopic composition analysis by BrF5 method. The national standard sample GBW04409 for oxygen isotopic composition were prepared and analyzed at high reaction temperatures. The results show that sufficient yields of O2 could be achieved when sample was reacted with BrF5 at 550-675℃, under which condition the δ18O value fell in the range of 10.4‰-11.8‰ with high accuracy. However, when the reaction temperature was higher than 700℃, the yields of O2 were low, and the δ18O values were in the range of 10.8‰-26.8‰, which had a significant positive deviation to the given δ18O values. To solve the problem due to effect of the higher temperature, fractional fluorination was conducted. The results of oxygen isotopic composition obtained were consistent with the recommended value when the oxygen liberated after each time fluorination was all collected. The consumption of BrF5 by the nickel reactor at higher temperature results in the insufficient amount of BrF5 reacted with the sample, which causes the low yield of O2, thus the fractionation of oxygen isotope.
2021, 46(12): 4480-4491.
doi: 10.3799/dqkx.2021.090
Abstract:
In order to understand the dominant hydro-biogeochemical processes affecting the migration and transformation of iodine in groundwater system, in this study it analyzed the chemistry and carbon/sulfur isotope signatures of groundwater samples from typical high iodine area in Datong basin. Results show that the iodine concentrations of groundwater range from 14.40 to 1 030.00 μg/L and high iodine groundwater (I>100 μg/L) is mainly distributed in the discharge area near the center of the basin. The δ34SSO4 and δ13CDIC signatures of groundwater have the ranges of (-12.11‰)-(-9.79‰) and 4.04‰-16.63‰, respectively. The positive correlation between the δ13CDIC values and DOC concentrations in groundwater suggests that microbial degradation of organic matter is one of the important sources of DIC in the Datong basin. The correlation between the low δ13CDIC values and the high δ34SSO4 values indicates that groundwater SO42- serves as one of the electron accepters during the biodegradation of organic matter, and groundwater environment was dominant by the weak reducing conditions. High iodine groundwater is characterized by lower δ13CDIC and higher δ34SSO4, indicating that microbial degradation of organic matter, which acts as a dominate host of sediment iodine, promotes the release of iodine into groundwater. Moreover, the transformation among iodine species, for instance, from organic iodine/iodate to iodide, also favors the enrichment of groundwater iodine under the reducing conditions.
In order to understand the dominant hydro-biogeochemical processes affecting the migration and transformation of iodine in groundwater system, in this study it analyzed the chemistry and carbon/sulfur isotope signatures of groundwater samples from typical high iodine area in Datong basin. Results show that the iodine concentrations of groundwater range from 14.40 to 1 030.00 μg/L and high iodine groundwater (I>100 μg/L) is mainly distributed in the discharge area near the center of the basin. The δ34SSO4 and δ13CDIC signatures of groundwater have the ranges of (-12.11‰)-(-9.79‰) and 4.04‰-16.63‰, respectively. The positive correlation between the δ13CDIC values and DOC concentrations in groundwater suggests that microbial degradation of organic matter is one of the important sources of DIC in the Datong basin. The correlation between the low δ13CDIC values and the high δ34SSO4 values indicates that groundwater SO42- serves as one of the electron accepters during the biodegradation of organic matter, and groundwater environment was dominant by the weak reducing conditions. High iodine groundwater is characterized by lower δ13CDIC and higher δ34SSO4, indicating that microbial degradation of organic matter, which acts as a dominate host of sediment iodine, promotes the release of iodine into groundwater. Moreover, the transformation among iodine species, for instance, from organic iodine/iodate to iodide, also favors the enrichment of groundwater iodine under the reducing conditions.
2021, 46(12): 4492-4502.
doi: 10.3799/dqkx.2021.054
Abstract:
In recent years, it has been reported that high arsenic groundwater is widely distributed in the the middle Yangtze River lacustrine plain. The Poyang Lake plain (PYP) and the Jiangbei plain (ancient Pengli Lake, JBP) are typical lacustrine plains rich in groundwater resources on the northern and southern sides of the middle reach of the Yangtze River. However, the spatial distribution of groundwater arsenic in these regions has not been clearly studied, which posed potential risks to regional water supply security. In this study, 98 shallow groundwater samples and 8 surface water samples were collected in these two regions. The spatial heterogeneity of arsenic in groundwater and its controlling factors were identified by hydrochemistry and stable isotope analysis. The arsenic contents of shallow groundwater in JBP range from 0.65 to 956.72 μg/L (average 210.78 μg/L), and the high arsenic groundwater is mainly distributed in the ancient Yangtze River channel. The arsenic contents of shallow groundwater in PYP range from 0.09 to 267.45 μg/L (average 11.85 μg/L), and the high arsenic groundwater is only distributed in parts of Ganjiang River delta. Stable water isotope composition (δD and δ18O) of groundwater samples from the JBP is more negative and significantly different from surface water relative to the PYP. Multivariate statistical results of groundwater chemistry data indicate that the differences of provenance and aquifer structure are the key factors affecting arsenic spatial heterogeneity in shallow groundwater in PYP and JBP, the microbially mediated reductive dissolution of arsenic-bearing iron minerals leads to arsenic release in groundwater. Groundwater arsenic in the Jiangbei plain is supposed to be originated from the sediments from ancient Pengli area of Yangtze River provenance. The stable isotopic signatures of hydrogen and oxygen in groundwater indicate that the aquifer environment in JBP is closer and the groundwater circulation and alternation speed is slower compared with the PYP, which is more conducive to arsenic release and enrichment in the groundwater.
In recent years, it has been reported that high arsenic groundwater is widely distributed in the the middle Yangtze River lacustrine plain. The Poyang Lake plain (PYP) and the Jiangbei plain (ancient Pengli Lake, JBP) are typical lacustrine plains rich in groundwater resources on the northern and southern sides of the middle reach of the Yangtze River. However, the spatial distribution of groundwater arsenic in these regions has not been clearly studied, which posed potential risks to regional water supply security. In this study, 98 shallow groundwater samples and 8 surface water samples were collected in these two regions. The spatial heterogeneity of arsenic in groundwater and its controlling factors were identified by hydrochemistry and stable isotope analysis. The arsenic contents of shallow groundwater in JBP range from 0.65 to 956.72 μg/L (average 210.78 μg/L), and the high arsenic groundwater is mainly distributed in the ancient Yangtze River channel. The arsenic contents of shallow groundwater in PYP range from 0.09 to 267.45 μg/L (average 11.85 μg/L), and the high arsenic groundwater is only distributed in parts of Ganjiang River delta. Stable water isotope composition (δD and δ18O) of groundwater samples from the JBP is more negative and significantly different from surface water relative to the PYP. Multivariate statistical results of groundwater chemistry data indicate that the differences of provenance and aquifer structure are the key factors affecting arsenic spatial heterogeneity in shallow groundwater in PYP and JBP, the microbially mediated reductive dissolution of arsenic-bearing iron minerals leads to arsenic release in groundwater. Groundwater arsenic in the Jiangbei plain is supposed to be originated from the sediments from ancient Pengli area of Yangtze River provenance. The stable isotopic signatures of hydrogen and oxygen in groundwater indicate that the aquifer environment in JBP is closer and the groundwater circulation and alternation speed is slower compared with the PYP, which is more conducive to arsenic release and enrichment in the groundwater.
2021, 46(12): 4503-4516.
doi: 10.3799/dqkx.2021.120
Abstract:
In order to investigate the temporal and spatial changes of the offshore sedimentary processes such as terrestrial material input and sedimentation rate in the context of human activities during the past 100 years, the radionuclides 238U, 226Ra, 232Th, 210Pb, 40K and 137Cs in surface and column sediments in the Bohai Sea region were analyzed using γ energy spectrometry. The horizontal and vertical distribution characteristics of radionuclides in the sediments of the Bohai Sea were obvious, and the radionuclides 238U, 226Ra and 210Pb in the uranium decay series were unbalanced. 232Th and 210Pb were significantly affected by sediment grain size and organic carbon. The correlation between 238U and 226Ra, 232Th, 40K was obvious. There were significant temporal and spatial differences in the ratios of 226Ra/238U, 232Th/238U and 40K/238U. The influence of terrestrial input of Bohai Sea sediments extends from southwest to northeast. Affected by rivers, the sediments in the northern and southern Bohai Sea material input were unstable and fluctuated significantly in recent decades. The sedimentation rate calculated by the 210Pbex and 137Cs dating methods in the Bohai Sea in the past 100 years was within the background value of the sedimentation rate research in the offshore China. Spatially, the sedimentation rate was at the same level in the northern part, central part and southern part, among which it was relatively high in the northern part. Temporally speaking, the sedimentation rate of the Bohai Sea fluctuated with time in the past 100 years and showed an overall increasing trend, especially since 1980, under the influence of human activities, the increase was significant, corresponding to the changes in sediment input.
In order to investigate the temporal and spatial changes of the offshore sedimentary processes such as terrestrial material input and sedimentation rate in the context of human activities during the past 100 years, the radionuclides 238U, 226Ra, 232Th, 210Pb, 40K and 137Cs in surface and column sediments in the Bohai Sea region were analyzed using γ energy spectrometry. The horizontal and vertical distribution characteristics of radionuclides in the sediments of the Bohai Sea were obvious, and the radionuclides 238U, 226Ra and 210Pb in the uranium decay series were unbalanced. 232Th and 210Pb were significantly affected by sediment grain size and organic carbon. The correlation between 238U and 226Ra, 232Th, 40K was obvious. There were significant temporal and spatial differences in the ratios of 226Ra/238U, 232Th/238U and 40K/238U. The influence of terrestrial input of Bohai Sea sediments extends from southwest to northeast. Affected by rivers, the sediments in the northern and southern Bohai Sea material input were unstable and fluctuated significantly in recent decades. The sedimentation rate calculated by the 210Pbex and 137Cs dating methods in the Bohai Sea in the past 100 years was within the background value of the sedimentation rate research in the offshore China. Spatially, the sedimentation rate was at the same level in the northern part, central part and southern part, among which it was relatively high in the northern part. Temporally speaking, the sedimentation rate of the Bohai Sea fluctuated with time in the past 100 years and showed an overall increasing trend, especially since 1980, under the influence of human activities, the increase was significant, corresponding to the changes in sediment input.
2021, 46(12): 4517-4532.
doi: 10.3799/dqkx.2021.065
Abstract:
Several Early Cretaceous rare metal pegmatite deposits have been discovered within and around the Late Jurassic-Early Cretaceous Mufushan complex granitic batholith in the Jiangnan metallogenic belt. It is still controversial whether the pegmatites were originated from the highly evolved Mufushan granite in this region. Tourmaline-, garnet-, and muscovite-bearing monzogranites in the Maishi and other areas have zircon LA-ICP-MS U-Pb ages between 130 and 135 Ma, similar to ages of the pegmatites within the errors. Compared with the early porphyritic biotite monzogranite and muscovite monzogranite (151-143 Ma), the late tourmaline-, garnet-, and muscovite-bearing monzogranites have zircon with high Hf, Ta, Nb, Th, U contents and low Th/U and Eu/Eu* ratios, indicating a highly evolved nature. This is also consistent with mineral assemblages and zircon crystallization temperatures of the granites. Ages and trace elements from zircon indicate that rare metal pegmatites may be the fractionated product of Early Cretaceous evolved granitic magmas in the Mufushan batholith.
Several Early Cretaceous rare metal pegmatite deposits have been discovered within and around the Late Jurassic-Early Cretaceous Mufushan complex granitic batholith in the Jiangnan metallogenic belt. It is still controversial whether the pegmatites were originated from the highly evolved Mufushan granite in this region. Tourmaline-, garnet-, and muscovite-bearing monzogranites in the Maishi and other areas have zircon LA-ICP-MS U-Pb ages between 130 and 135 Ma, similar to ages of the pegmatites within the errors. Compared with the early porphyritic biotite monzogranite and muscovite monzogranite (151-143 Ma), the late tourmaline-, garnet-, and muscovite-bearing monzogranites have zircon with high Hf, Ta, Nb, Th, U contents and low Th/U and Eu/Eu* ratios, indicating a highly evolved nature. This is also consistent with mineral assemblages and zircon crystallization temperatures of the granites. Ages and trace elements from zircon indicate that rare metal pegmatites may be the fractionated product of Early Cretaceous evolved granitic magmas in the Mufushan batholith.
2021, 46(12): 4533-4545.
doi: 10.3799/dqkx.2021.106
Abstract:
To reveal the tectonic evolution of the eastern Himalayan syntaxis and its surrounding areas, in this paper it reports 10 40Ar/39Ar ages of biotite from Motuo Section of the Yarlung Tsangpo River. It quantitatively interprets the rock's uplift and exhumation rates represented by these ages, using a modeling code "Pecube". Biotite 40Ar/39Ar ages in this paper are in the range of 11.25-24.04 Ma. Corresponding exhumation rates are in the range of 0.25-0.51 km/Ma. The rock exhumation rates in Motuo Section of the Yarlung Tsangpo River have obvious differences between northern and southern, which is characterized by the northern exhumation rates about 0.2 km/Ma higher than the southern. The ages and simulation results show that relative to the inside of the eastern Himalayan syntaxis, the exhumation rates in Motuo Section of the Yarlung Tsangpo River are lower. And the NW/NWW-trending thrust fault zones which were resulted by the collision between Himalayan terrane and Lhasa terrane, not only located in the inside of the eastern Himalayan syntaxis, but also probably located in Motuo Section of the Yarlung Tsangpo River.
To reveal the tectonic evolution of the eastern Himalayan syntaxis and its surrounding areas, in this paper it reports 10 40Ar/39Ar ages of biotite from Motuo Section of the Yarlung Tsangpo River. It quantitatively interprets the rock's uplift and exhumation rates represented by these ages, using a modeling code "Pecube". Biotite 40Ar/39Ar ages in this paper are in the range of 11.25-24.04 Ma. Corresponding exhumation rates are in the range of 0.25-0.51 km/Ma. The rock exhumation rates in Motuo Section of the Yarlung Tsangpo River have obvious differences between northern and southern, which is characterized by the northern exhumation rates about 0.2 km/Ma higher than the southern. The ages and simulation results show that relative to the inside of the eastern Himalayan syntaxis, the exhumation rates in Motuo Section of the Yarlung Tsangpo River are lower. And the NW/NWW-trending thrust fault zones which were resulted by the collision between Himalayan terrane and Lhasa terrane, not only located in the inside of the eastern Himalayan syntaxis, but also probably located in Motuo Section of the Yarlung Tsangpo River.
2021, 46(12): 4546-4561.
doi: 10.3799/dqkx.2020.181
Abstract:
Porphyroclastic rhyolites of Ehuling and Daguding formations were taken as the research objects in this paper, which was sampled from the boreholes in the midwestern parts of Xiangshan uranium orefield. A comparative study of porphyroclastic rhyolite from these two formations were carried out by means of petromineralogy, lithogeochemistry, U-Pb geochronology and Hf isotopes. The results illustrate that the mineralogical composition and lithogeochemical characteristics of porphyroclastic rhyolite from Ehuling and Daguding formations are relatively semblable, the rock enriching Si and K2O, low Na2O and MgO. Chondrite normalized REE curves are generally consistent, showing right-inclined type with enriched LREE. The samples from the Ehuling Formation demonstrate more intensive Eu negative anormaly, indicating that a high degree of crystallizational fractionation of plagioclase was occured, or more plagioclase residued in source area. While the high fractional degree of LREE and HREE of Daguding porphyroclastic rhyolite is likely related to the high contents of secondary minerals, such as titanite, epidoite and monazite. Primitive mantle-normalized spider diagram shows depletion of lithophile elements (K, Ba, Sr) and high field strength elements (Nb, Ti, P), and enrichment of Rb, Th, Nd. These similar petrogeochemical characteristics suggest a certain homology between Ehuling and Daguding porphyroclastic rhyolite. Zircon U-Pb dating results indicate that the age of porphyroclastic rhyolite from Ehuling Formation and Daguding Formation are 132.4±0.7 Ma and 131.9±0.8 Ma respectively. The εHf(t) of porphyroclastic rhyolite of Ehuling Formation is (-9.5)-(-4.5), and the two-stage Hf model age is 1 470-1 787 Ma; while the εHf(t) of porphyroclastic rhyolite of Daguding Formation is (-14.2)-(-8.1), and the two-stage Hf model age is 1 704-2 087 Ma. The above petromineralogy, lithogeochemistry, zircon U-Pb age and Hf isotope characteristics show that the porphyroclastic rhyolite of Ehuling Formation and the Daguding Formation have certain similarities, but at the same time, some differences exist. Combined with previous research data, a conclusion can be drawn, the formation of two sets of porphyroclastic rhyolite maybe homologous, both of them are derived from the partial melting of Paleoproterozoic-Mesoproterozoic metamorphic rock basement under the background of Early Cretaceous regional extensional environment, and may be accompanied by the merging of mantle material in a certain degree.
Porphyroclastic rhyolites of Ehuling and Daguding formations were taken as the research objects in this paper, which was sampled from the boreholes in the midwestern parts of Xiangshan uranium orefield. A comparative study of porphyroclastic rhyolite from these two formations were carried out by means of petromineralogy, lithogeochemistry, U-Pb geochronology and Hf isotopes. The results illustrate that the mineralogical composition and lithogeochemical characteristics of porphyroclastic rhyolite from Ehuling and Daguding formations are relatively semblable, the rock enriching Si and K2O, low Na2O and MgO. Chondrite normalized REE curves are generally consistent, showing right-inclined type with enriched LREE. The samples from the Ehuling Formation demonstrate more intensive Eu negative anormaly, indicating that a high degree of crystallizational fractionation of plagioclase was occured, or more plagioclase residued in source area. While the high fractional degree of LREE and HREE of Daguding porphyroclastic rhyolite is likely related to the high contents of secondary minerals, such as titanite, epidoite and monazite. Primitive mantle-normalized spider diagram shows depletion of lithophile elements (K, Ba, Sr) and high field strength elements (Nb, Ti, P), and enrichment of Rb, Th, Nd. These similar petrogeochemical characteristics suggest a certain homology between Ehuling and Daguding porphyroclastic rhyolite. Zircon U-Pb dating results indicate that the age of porphyroclastic rhyolite from Ehuling Formation and Daguding Formation are 132.4±0.7 Ma and 131.9±0.8 Ma respectively. The εHf(t) of porphyroclastic rhyolite of Ehuling Formation is (-9.5)-(-4.5), and the two-stage Hf model age is 1 470-1 787 Ma; while the εHf(t) of porphyroclastic rhyolite of Daguding Formation is (-14.2)-(-8.1), and the two-stage Hf model age is 1 704-2 087 Ma. The above petromineralogy, lithogeochemistry, zircon U-Pb age and Hf isotope characteristics show that the porphyroclastic rhyolite of Ehuling Formation and the Daguding Formation have certain similarities, but at the same time, some differences exist. Combined with previous research data, a conclusion can be drawn, the formation of two sets of porphyroclastic rhyolite maybe homologous, both of them are derived from the partial melting of Paleoproterozoic-Mesoproterozoic metamorphic rock basement under the background of Early Cretaceous regional extensional environment, and may be accompanied by the merging of mantle material in a certain degree.
2021, 46(12): 4562-4572.
doi: 10.3799/dqkx.2021.086
Abstract:
The East Lake, located in the downtown of Wuhan city, Hubei Province, is the largest city lake in China or even in Asia. It is one of the first batches of national key scenic spots and 5A tourist attractions, and has been an important water source area for industrial, agricultural production and aquatic base in Wuhan. Nowadays, in Wuhan it building the ecological green heart of East Lake, therefore there is great significance for resources, environment, ecology and humanity. However, the formation cause of the East Lake has long been disputed. This study is the first one to analyze the origin of the East Lake from many aspects, including geology, geomorphology and sedimentation, further to discuss the relationship between the East Lake and the Yangtze River. The main conclusions are as follow: (1) The geomorphological characteristics of the lake: branching, meandering coastline and headlands and bays, this is generally developed on the hillock of Middle-Late Pleistocene. (2) The thickness of lacustrine sediments in East Lake is various, showing thin in the south and thick in the north, thin in the margin and thick in the middle. The underlying strata are mainly the Late Pleistocene Xiashu loess, and the Late Pleistocene slope layer is locally distributed near the southern margin of the bedrock residual mound. There is an obvious unconformable relationship between lacustrine sediments and Xiashu loess. (3) The basin of East Lake was formed in the last glacial maximum (LGM) about 20 ka ago. In this time, the sea level of the East China Sea has dropped sharply, and induced the riverbed of the Yangtze River incised. The Luojia, Nanwang and Yujia mountains on the south bank of the Yangtze River were deeply incised landscape when it flowed into the Yangtze River due to low erosion baseline of the LGM, resulting in a series of gullies. After that, the Holocene global warming and high sea-level, the water surface of the Yangtze River rose rapidly, and the natural dikes along its banks developed and expanded with resultant in filling of the incised gullies, accounted for the formation of lake. Based on the above analyses, the East Lake was a gully choked lake. (4) According to the characteristics of geology and geomorphology, the East Lake and Shahu Lake are two independent lakes with different formation processes. The Yangtze River does not flow through the East Lake, however, the formation of the East Lake is related to the Yangtze River, which is the result of the complex feedback of the East China Sea-Yangtze River-East Lake, this process was driven by global climate change.(5)The worth of the East Lake lies in nature. Protecting its natural characteristics and conforming its natural laws is principles of protection and utilization of the East Lake. As a whole, for the scientific concept of mountain-water-forest-paddy-lake-grass community, it is necessary to regard lake shore and landform as a whole and regard catchment and basin as a whole to protect and manage the East Lake in a holistic and systematic way.
The East Lake, located in the downtown of Wuhan city, Hubei Province, is the largest city lake in China or even in Asia. It is one of the first batches of national key scenic spots and 5A tourist attractions, and has been an important water source area for industrial, agricultural production and aquatic base in Wuhan. Nowadays, in Wuhan it building the ecological green heart of East Lake, therefore there is great significance for resources, environment, ecology and humanity. However, the formation cause of the East Lake has long been disputed. This study is the first one to analyze the origin of the East Lake from many aspects, including geology, geomorphology and sedimentation, further to discuss the relationship between the East Lake and the Yangtze River. The main conclusions are as follow: (1) The geomorphological characteristics of the lake: branching, meandering coastline and headlands and bays, this is generally developed on the hillock of Middle-Late Pleistocene. (2) The thickness of lacustrine sediments in East Lake is various, showing thin in the south and thick in the north, thin in the margin and thick in the middle. The underlying strata are mainly the Late Pleistocene Xiashu loess, and the Late Pleistocene slope layer is locally distributed near the southern margin of the bedrock residual mound. There is an obvious unconformable relationship between lacustrine sediments and Xiashu loess. (3) The basin of East Lake was formed in the last glacial maximum (LGM) about 20 ka ago. In this time, the sea level of the East China Sea has dropped sharply, and induced the riverbed of the Yangtze River incised. The Luojia, Nanwang and Yujia mountains on the south bank of the Yangtze River were deeply incised landscape when it flowed into the Yangtze River due to low erosion baseline of the LGM, resulting in a series of gullies. After that, the Holocene global warming and high sea-level, the water surface of the Yangtze River rose rapidly, and the natural dikes along its banks developed and expanded with resultant in filling of the incised gullies, accounted for the formation of lake. Based on the above analyses, the East Lake was a gully choked lake. (4) According to the characteristics of geology and geomorphology, the East Lake and Shahu Lake are two independent lakes with different formation processes. The Yangtze River does not flow through the East Lake, however, the formation of the East Lake is related to the Yangtze River, which is the result of the complex feedback of the East China Sea-Yangtze River-East Lake, this process was driven by global climate change.(5)The worth of the East Lake lies in nature. Protecting its natural characteristics and conforming its natural laws is principles of protection and utilization of the East Lake. As a whole, for the scientific concept of mountain-water-forest-paddy-lake-grass community, it is necessary to regard lake shore and landform as a whole and regard catchment and basin as a whole to protect and manage the East Lake in a holistic and systematic way.
