2016 Vol. 41, No. 1
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2016, 41(1): 1-16.
doi: 10.3799/dqkx.2016.001
Abstract:
The fine-grained syenogranite in the Dong'an goldfield is the early Yanshanian granite body in the Lesser Xing'an Mountains, it is one of the granite bodys of the granite belt which is related to porphyry and skarn-type molybdenum-polymetallic deposits in the east Jilin-Heilongjiang Province. In order to understand regional magmatic evolution in the early Yanshanian and cosmical molybdenum-polymetallic hydrothermal mineralization, thus further promote the research degree of the metallogenic background in the Dong'an goldfield. This paper presents geochemisty, zircon U-Pb geochronology, and Hf-isotopic data of these rocks, their petrogenesis, sources and tectonic implications have been investigated. The granitic rocks yield an average zircon LA-ICP-MS U-Pb age of 184±2 Ma (MSWD=1.2), i.e., the Early Jurassic. The granites have high SiO2 (75.39%-78.84%) and K2O (K2O/Na2O: 1.46~1.81), low CaO, MgO and Mg# (12.79-23.52), with A/CNK values of 1.05-1.14, indicating high potassium calc-alkaline, weakly peraluminous granites. The granites are enriched in large ion lithosphile elements (Rb, K) and incompatibale elements (Th, U), and depleted in high field-strength element (Nb, Ti). They have strong fractionation between LREE and HREE, as well as slightly negative Eu anomalies (Eu/Eu*=0.76-0.92). It was shown that these granitic rocks belong to highly fractionated I-type granites according to lithogeochemical constituents, Harker plots, the discrimination diagrams of Ce vs. SiO2 and (K2O+Na2O)/CaO vs. Zr+Nb+Ce+Y. All zircons in the granites have 176Hf/177Hf ratios ranging from 0.282 588 to 0.282 775, εHf(t) values ranging from -2.35 to +3.94, and two-stage Hf model ages (TDM2) ranging from 973 to 1 386 Ma. It was indicated that the magma was originated from the partial melting of Meso-Neoproterozoic juvenile accreted lower crust that was derived from the depleted mantle, with addition of ancient sialic crustal materials. The results show that the granites were generated from the extensional and lithospheric thinning environment due to the subduction of the Paleo-Pacific plate, and underplating of the mantle-derived magma provided the thermodynamic power for the partial melting of the crust. The small scale hypabyssal-middle high potassium calc-alkaline granitic intrusive bodies that were generated in the continental arc extension setting in the early Yanshanian are main targets for the prospecting of porphyry and skarn-type molybdenum-polymetallic deposits in the east Jilin-Heilongjiang Province.
The fine-grained syenogranite in the Dong'an goldfield is the early Yanshanian granite body in the Lesser Xing'an Mountains, it is one of the granite bodys of the granite belt which is related to porphyry and skarn-type molybdenum-polymetallic deposits in the east Jilin-Heilongjiang Province. In order to understand regional magmatic evolution in the early Yanshanian and cosmical molybdenum-polymetallic hydrothermal mineralization, thus further promote the research degree of the metallogenic background in the Dong'an goldfield. This paper presents geochemisty, zircon U-Pb geochronology, and Hf-isotopic data of these rocks, their petrogenesis, sources and tectonic implications have been investigated. The granitic rocks yield an average zircon LA-ICP-MS U-Pb age of 184±2 Ma (MSWD=1.2), i.e., the Early Jurassic. The granites have high SiO2 (75.39%-78.84%) and K2O (K2O/Na2O: 1.46~1.81), low CaO, MgO and Mg# (12.79-23.52), with A/CNK values of 1.05-1.14, indicating high potassium calc-alkaline, weakly peraluminous granites. The granites are enriched in large ion lithosphile elements (Rb, K) and incompatibale elements (Th, U), and depleted in high field-strength element (Nb, Ti). They have strong fractionation between LREE and HREE, as well as slightly negative Eu anomalies (Eu/Eu*=0.76-0.92). It was shown that these granitic rocks belong to highly fractionated I-type granites according to lithogeochemical constituents, Harker plots, the discrimination diagrams of Ce vs. SiO2 and (K2O+Na2O)/CaO vs. Zr+Nb+Ce+Y. All zircons in the granites have 176Hf/177Hf ratios ranging from 0.282 588 to 0.282 775, εHf(t) values ranging from -2.35 to +3.94, and two-stage Hf model ages (TDM2) ranging from 973 to 1 386 Ma. It was indicated that the magma was originated from the partial melting of Meso-Neoproterozoic juvenile accreted lower crust that was derived from the depleted mantle, with addition of ancient sialic crustal materials. The results show that the granites were generated from the extensional and lithospheric thinning environment due to the subduction of the Paleo-Pacific plate, and underplating of the mantle-derived magma provided the thermodynamic power for the partial melting of the crust. The small scale hypabyssal-middle high potassium calc-alkaline granitic intrusive bodies that were generated in the continental arc extension setting in the early Yanshanian are main targets for the prospecting of porphyry and skarn-type molybdenum-polymetallic deposits in the east Jilin-Heilongjiang Province.
2016, 41(1): 17-34.
doi: 10.3799/dqkx.2016.002
Abstract:
The early Yanshanian geology of southeastern China is characterized by widespread igneous rocks, especially granites. However, the petrogenesis and tectonic implication of these granites in South China remain highly controversial. The A-type granites are the important carrier for better understanding the tectonic evolution of the South China block since the formation is commonly related to extensional tectonic setting. In this study, a set of new zircon U-Pb geochronological, elemental and Sr-Nd-Hf isotopic data is presented for the Wengong A-type granite in eastern Nanling range in northern Guangdong Province. Laser zircon U-Pb dating for the Wengong granitic sample give a weighted mean age of 196.9±4.4 Ma and in-situ zircon εHf(t) values ranging from +2.1 to +7.7. Their whole rock εNd(t) values range from -2.7 to -0.5. The Wengong granites are enriched in SiO2 (69.22%-76.33%) and total alkalis (7.77%-8.35%). They are metaluminous-peraluminous with A/CNK values ranging from 0.95 to 1.10. These samples have high rare earth element contents, FeOt/MgO (4.40-9.75) and 10 000×Ga/Al ratios (2.9-3.3), as well as significant Sr, Ti and Eu negative anomalies. Based on these geochemical data, it is proposed that the Wengong granites originated from mafic lower crust in response to the earliest Jurassic extensional setting. In combination with available data, it is inferred that the A-type granites in the Nanling range predominantly formed at 196-156 Ma, suggesting an early Yanshanian extensional event in SE China. These A-type granites probably formed in intra-plated extensional environment, indicating the transformation from Paleotethyan to Paleopacific domain after earliest Jurassic.
The early Yanshanian geology of southeastern China is characterized by widespread igneous rocks, especially granites. However, the petrogenesis and tectonic implication of these granites in South China remain highly controversial. The A-type granites are the important carrier for better understanding the tectonic evolution of the South China block since the formation is commonly related to extensional tectonic setting. In this study, a set of new zircon U-Pb geochronological, elemental and Sr-Nd-Hf isotopic data is presented for the Wengong A-type granite in eastern Nanling range in northern Guangdong Province. Laser zircon U-Pb dating for the Wengong granitic sample give a weighted mean age of 196.9±4.4 Ma and in-situ zircon εHf(t) values ranging from +2.1 to +7.7. Their whole rock εNd(t) values range from -2.7 to -0.5. The Wengong granites are enriched in SiO2 (69.22%-76.33%) and total alkalis (7.77%-8.35%). They are metaluminous-peraluminous with A/CNK values ranging from 0.95 to 1.10. These samples have high rare earth element contents, FeOt/MgO (4.40-9.75) and 10 000×Ga/Al ratios (2.9-3.3), as well as significant Sr, Ti and Eu negative anomalies. Based on these geochemical data, it is proposed that the Wengong granites originated from mafic lower crust in response to the earliest Jurassic extensional setting. In combination with available data, it is inferred that the A-type granites in the Nanling range predominantly formed at 196-156 Ma, suggesting an early Yanshanian extensional event in SE China. These A-type granites probably formed in intra-plated extensional environment, indicating the transformation from Paleotethyan to Paleopacific domain after earliest Jurassic.
2016, 41(1): 35-54.
doi: 10.3799/dqkx.2016.003
Abstract:
Caledonian peraluminous granites (420.5 to 424.0 Ma), is closely related with the development and evolution of the crust. In order to study their composition features and formation mechchanism, petrographical and geochemical investigations were carried out. It consist of biotite tonalite, biotite granodiorite, biotite granite, two-mica granite and muscovite granite in Heihai region. The rock types are of calc-alkali series and high-K calc-alkaline series (SiO2=65.32%-75.87%, K2O/Na2O=0.47-1.52, δ=1.09-3.00), and belong to peraluminous granites or strongly peraluminous granites (A/CNK=1.02-1.31). REE display relatively LREE-enriched and HREE-depleted characteristics, with moderate Eu negative abnormality. LILE are of relatively selective enrichment and HFS elements are of relatively depletion. The melting materials of source are metagreywacke and metapelite. Based on regional geology, this paper suggests that Heihai peraluminous granites were formed by partial melting of the alumina-silica crust, which was caused by mantle underplating and extension of the southern subduction accretionary complex.
Caledonian peraluminous granites (420.5 to 424.0 Ma), is closely related with the development and evolution of the crust. In order to study their composition features and formation mechchanism, petrographical and geochemical investigations were carried out. It consist of biotite tonalite, biotite granodiorite, biotite granite, two-mica granite and muscovite granite in Heihai region. The rock types are of calc-alkali series and high-K calc-alkaline series (SiO2=65.32%-75.87%, K2O/Na2O=0.47-1.52, δ=1.09-3.00), and belong to peraluminous granites or strongly peraluminous granites (A/CNK=1.02-1.31). REE display relatively LREE-enriched and HREE-depleted characteristics, with moderate Eu negative abnormality. LILE are of relatively selective enrichment and HFS elements are of relatively depletion. The melting materials of source are metagreywacke and metapelite. Based on regional geology, this paper suggests that Heihai peraluminous granites were formed by partial melting of the alumina-silica crust, which was caused by mantle underplating and extension of the southern subduction accretionary complex.
2016, 41(1): 55-66.
doi: 10.3799/dqkx.2016.004
Abstract:
LA-ICP-MS zircon U-Pb dating and geochemical data of the Nankouqian granitic intrusion were studied to determine its formation time and tectonic background. The zircon U-Pb dating results indicate that the granitic pluton was formed in the Late Triassic (224±1 Ma). The granite shows calc-alkaline and metaluminous to weakly peraluminous affinities, with A/CNK ratio ranging from 0.98 to 1.07. The granitic pluton has features similar to adakitic rock with high Sr (394×10-6-545×10-6) and low Yb (0.61×10-6-0.93×10-6). The in situ zircon εHf(t) value varies from -13.2 to -6.9, and a two-stage model age (TDM2) varies from 1 669 to 1 825 Ma. These characteristics suggest that the primary magma was derived from partial melting of primarily Proterozoic lower crustal materials. Considering the regional tectonic evolution, we suggest the granites formed in the post-orogenic extension setting which could be related to the closure of the Paleo-Asian Ocean.
LA-ICP-MS zircon U-Pb dating and geochemical data of the Nankouqian granitic intrusion were studied to determine its formation time and tectonic background. The zircon U-Pb dating results indicate that the granitic pluton was formed in the Late Triassic (224±1 Ma). The granite shows calc-alkaline and metaluminous to weakly peraluminous affinities, with A/CNK ratio ranging from 0.98 to 1.07. The granitic pluton has features similar to adakitic rock with high Sr (394×10-6-545×10-6) and low Yb (0.61×10-6-0.93×10-6). The in situ zircon εHf(t) value varies from -13.2 to -6.9, and a two-stage model age (TDM2) varies from 1 669 to 1 825 Ma. These characteristics suggest that the primary magma was derived from partial melting of primarily Proterozoic lower crustal materials. Considering the regional tectonic evolution, we suggest the granites formed in the post-orogenic extension setting which could be related to the closure of the Paleo-Asian Ocean.
2016, 41(1): 67-83.
doi: 10.3799/dqkx.2016.005
Abstract:
In order to study the chronological and geochemical characteristics of the Mesozoic granite and granodiorite from Fanshan area and their relationship with the regional mineralization, the LA-MC-ICPMS zircons U-Pb dating method was employed to assess the ages and Hf isotope composition, preceded by their petrological and geochemical studies. In addition, the authors aim to provide more evidences that will facilitate the next phase of prospecting by making a comparison with Zijinshan copper-gold ore field. The metaluminous-peraluminous high-K calcalkaline granite series and granodiorite are characterized by high contents of K2O, SiO2, and low TiO2. These samples are enriched in light rare earth element (LREE) and large ionic lithophile elements (LILE, e.g. K, Rb, Sr, Cs), but depleted in high strength elements (HFSE, e.g. Nb, Ta, Zr, Ti), and have negative Eu anomalies. The geochemical properties of granite and granodiorite are similar to those of the magmatic arc rocks, which suggest a backarc spreading setting. The zircon U-Pb dating of two representative samples yield an emplaced age of 110 Ma, in Early Cretaceous. Zircon grains from the granites have lower Hf-isotpe compositions with εHf(t)=-3.1-1.6 and younger Hf model ages (TDM2)=1 066-1 366 Ma. In comparison with the metamorphic basement near the study area, we suggest that the granitic rocks are probably derived from a Mesoproterozoic crust, but the granodiorite may have originated from a Mesoproterozoic crust-mixed with a fraction of mantle materials. Based on the comparative study with Zijinishan Orefield, it is concluded that there are similar structural, lithogeneous and metallogenic features between the two areas, and there is huge prospecting potential to find "Zijinshan style" copper-gold polymetallic deposits in Fanshan area.
In order to study the chronological and geochemical characteristics of the Mesozoic granite and granodiorite from Fanshan area and their relationship with the regional mineralization, the LA-MC-ICPMS zircons U-Pb dating method was employed to assess the ages and Hf isotope composition, preceded by their petrological and geochemical studies. In addition, the authors aim to provide more evidences that will facilitate the next phase of prospecting by making a comparison with Zijinshan copper-gold ore field. The metaluminous-peraluminous high-K calcalkaline granite series and granodiorite are characterized by high contents of K2O, SiO2, and low TiO2. These samples are enriched in light rare earth element (LREE) and large ionic lithophile elements (LILE, e.g. K, Rb, Sr, Cs), but depleted in high strength elements (HFSE, e.g. Nb, Ta, Zr, Ti), and have negative Eu anomalies. The geochemical properties of granite and granodiorite are similar to those of the magmatic arc rocks, which suggest a backarc spreading setting. The zircon U-Pb dating of two representative samples yield an emplaced age of 110 Ma, in Early Cretaceous. Zircon grains from the granites have lower Hf-isotpe compositions with εHf(t)=-3.1-1.6 and younger Hf model ages (TDM2)=1 066-1 366 Ma. In comparison with the metamorphic basement near the study area, we suggest that the granitic rocks are probably derived from a Mesoproterozoic crust, but the granodiorite may have originated from a Mesoproterozoic crust-mixed with a fraction of mantle materials. Based on the comparative study with Zijinishan Orefield, it is concluded that there are similar structural, lithogeneous and metallogenic features between the two areas, and there is huge prospecting potential to find "Zijinshan style" copper-gold polymetallic deposits in Fanshan area.
2016, 41(1): 84-96.
doi: 10.3799/dqkx.2016.006
Abstract:
The harzburgites and basalts from northeastern Jiangxi ophiolite belt have been investigated in the present study, with the aim to review Neoproterozoic tectonic environment. The results show that harzburgites are characterized by low TiO2 (0.02%-0.37%), K2O (0-0.02%) and Na2O (0.02%-0.10%), along with high MgO (40.81%-44.58%) and ignition loss (10.09%-13.47%), suggesting that the harzburgites suffered intensive alteration. The Chondrite-normalized REE patterns and primitive-normalized spider diagrams indicate that the harzburgites are sourced from a depleted mantle source suffered metasomatism in subduction zones. The data suggest that the meta-basalts are mostly characterized by high SiO2 (52.63%-52.63%), Al2O3 (13.07%-15.27%), Na2O (3.42%-5.03%) and low MgO (3.66%-6.46%), with medium TiO2 (1.14%-2.66%) contents, indicating that they are of andesitic basalt rocks. In a Chondrite-normalized REE plots, andesitic basalt rocks are rich in LREE((La/Yb)N=1.84-2.61) with smoothly right declined trend. The trace elements are characterized by enrichment in LILE such as Th, Ba, U and Pb and depletion in HFSE like Nb and Ti, indicating that andesitic basalts are derived from partial melting of enriched mantle wedge metasomatized by slab fluid in subduction belt, and the TNT (Ta, Nb, Ti) negative anomalies also imply those rocks may be contaminated by crustal materials. These geochemical characteristics indicate that the northeastern Jiangxi ophiolitic may have experienced multi-stage tectonic evolution. Harzburgites with LREE enrichments result from fluid metasomatism under intraoceanic subduction process in ancient Huanan ocean. Subsequently, island-arc tholeiite basalts and MORB-like basalts formed in the stage of back-arc basin evolution and those andesitic basalts contaminated with crustal materials, show strong enrichment of LREE, and with high Pb and low Ti.
The harzburgites and basalts from northeastern Jiangxi ophiolite belt have been investigated in the present study, with the aim to review Neoproterozoic tectonic environment. The results show that harzburgites are characterized by low TiO2 (0.02%-0.37%), K2O (0-0.02%) and Na2O (0.02%-0.10%), along with high MgO (40.81%-44.58%) and ignition loss (10.09%-13.47%), suggesting that the harzburgites suffered intensive alteration. The Chondrite-normalized REE patterns and primitive-normalized spider diagrams indicate that the harzburgites are sourced from a depleted mantle source suffered metasomatism in subduction zones. The data suggest that the meta-basalts are mostly characterized by high SiO2 (52.63%-52.63%), Al2O3 (13.07%-15.27%), Na2O (3.42%-5.03%) and low MgO (3.66%-6.46%), with medium TiO2 (1.14%-2.66%) contents, indicating that they are of andesitic basalt rocks. In a Chondrite-normalized REE plots, andesitic basalt rocks are rich in LREE((La/Yb)N=1.84-2.61) with smoothly right declined trend. The trace elements are characterized by enrichment in LILE such as Th, Ba, U and Pb and depletion in HFSE like Nb and Ti, indicating that andesitic basalts are derived from partial melting of enriched mantle wedge metasomatized by slab fluid in subduction belt, and the TNT (Ta, Nb, Ti) negative anomalies also imply those rocks may be contaminated by crustal materials. These geochemical characteristics indicate that the northeastern Jiangxi ophiolitic may have experienced multi-stage tectonic evolution. Harzburgites with LREE enrichments result from fluid metasomatism under intraoceanic subduction process in ancient Huanan ocean. Subsequently, island-arc tholeiite basalts and MORB-like basalts formed in the stage of back-arc basin evolution and those andesitic basalts contaminated with crustal materials, show strong enrichment of LREE, and with high Pb and low Ti.
2016, 41(1): 97-104.
doi: 10.3799/dqkx.2016.007
Abstract:
Tephra layers with unknown ages are usually identified and fingerprinted by their glass compositions. But, such correlations may be problematic when they own heterogeneous glass compositions. Lake Sihailongwan locates in the Longgang volcanic field and its varved lacustrine sediments can preserve the volcanic products from surrounding areas. Additionally, its varve-chronology can provide an advantage chronological framework for recent geological events which are difficult to date by other dating methods. A core drilled from Lake Sihailongwan (core 2008) shows that there is a tephra layer at 78-79 cm and an age of AD 308 was assigned to it by varve-chronology. The volcanic glass exhibits a heterogeneous composition, ranging from basaltic trachyandesite to tephriphonolite. Such a heterogeneous characteristic of glass shards from this tephra layer can be clearly revealed by the biplots of FeO, TiO2 and Al2O3 vs. MgO. For the applications to the tephrostratigraphy, whole rock analysis of tephra may be wrong and could not reflect the heterougeneous of primary magma while composition of glass is a better choice.
Tephra layers with unknown ages are usually identified and fingerprinted by their glass compositions. But, such correlations may be problematic when they own heterogeneous glass compositions. Lake Sihailongwan locates in the Longgang volcanic field and its varved lacustrine sediments can preserve the volcanic products from surrounding areas. Additionally, its varve-chronology can provide an advantage chronological framework for recent geological events which are difficult to date by other dating methods. A core drilled from Lake Sihailongwan (core 2008) shows that there is a tephra layer at 78-79 cm and an age of AD 308 was assigned to it by varve-chronology. The volcanic glass exhibits a heterogeneous composition, ranging from basaltic trachyandesite to tephriphonolite. Such a heterogeneous characteristic of glass shards from this tephra layer can be clearly revealed by the biplots of FeO, TiO2 and Al2O3 vs. MgO. For the applications to the tephrostratigraphy, whole rock analysis of tephra may be wrong and could not reflect the heterougeneous of primary magma while composition of glass is a better choice.
2016, 41(1): 105-120.
doi: 10.3799/dqkx.2016.008
Abstract:
The Wusihe lead-zinc deposit, hosted in the Dengying Formation, is a large lead-zinc deposit in the Sichuan Province, China. The previous research noted the Wusihe deposit was classified as a sediment-hosted stratiform lead-zinc deposit. However, our field survey result suggests that hydrothermal ore-forming processes are crucial to lead-zinc mineralization. In this paper, we present a detailed petrographic, microthermometric and laser Raman spectroscopy study of fluid inclusions from the Wusihe deposit reveals the characteristics of ore-forming fluids and mineralization mechanism. Primary fluid inclusions (FIs) in dolomite, quartz, calcite, fluorite and sphalerite are mainly two phases (L+V type). Microthermometric data show the homogenization temperatures range from 120 ℃ to 260 ℃, and the average of salinity is 10.0% NaCl eqv. The estimated trapping pressures are 32 MPa to 68 MPa. The laser Raman spectroscopy shows that the gas components have a certain amount of CH4, H2S, C2H6, C2H2, N2 and NH3. The mixed ore-forming fluids offer heat, SO42-, and Mg2+ to provoke the thermochemical sulfate reduction (TSR). The TSR could be a key factor for sulfur source and H+. The change of pH value leads to the precipitation of metallogenic elements.
The Wusihe lead-zinc deposit, hosted in the Dengying Formation, is a large lead-zinc deposit in the Sichuan Province, China. The previous research noted the Wusihe deposit was classified as a sediment-hosted stratiform lead-zinc deposit. However, our field survey result suggests that hydrothermal ore-forming processes are crucial to lead-zinc mineralization. In this paper, we present a detailed petrographic, microthermometric and laser Raman spectroscopy study of fluid inclusions from the Wusihe deposit reveals the characteristics of ore-forming fluids and mineralization mechanism. Primary fluid inclusions (FIs) in dolomite, quartz, calcite, fluorite and sphalerite are mainly two phases (L+V type). Microthermometric data show the homogenization temperatures range from 120 ℃ to 260 ℃, and the average of salinity is 10.0% NaCl eqv. The estimated trapping pressures are 32 MPa to 68 MPa. The laser Raman spectroscopy shows that the gas components have a certain amount of CH4, H2S, C2H6, C2H2, N2 and NH3. The mixed ore-forming fluids offer heat, SO42-, and Mg2+ to provoke the thermochemical sulfate reduction (TSR). The TSR could be a key factor for sulfur source and H+. The change of pH value leads to the precipitation of metallogenic elements.
2016, 41(1): 121-130.
doi: 10.3799/dqkx.2016.009
Abstract:
Occurred in Zhenzhumen Formation of Laoling Group of Proterozoic Era and controlled by ductile shear belt, the Huanggoushan gold deposit is one of the most representative deposits in Laoling gold-polymetallic metallogenic belt in southern Jilin Province. Based on the geological characteristics, mineral assemblage and the crosscutting relationship between different kinds of veins, the hydrothermal mineralization processes can be divided into two main stages, namely, stageⅠpyrite arsenopyrite quartz and stageⅡ later stibnite-milky quartz. Systematic study on petrography and microthermometry of fluid inclusions shows that quartz of Stage Ⅰcontains three types of primary fluid inclusions, which are CO2 bearing three phases, carbonic and aqueous two phases inclusions respectively, and the ore forming fluid is of medium to low temperature and low salinity NaCl-H2O-CO2 kind of solutions and immiscibility happened in the ore forming process, which led to the enrichment of gold etc; in quartz of Stage Ⅱ, there are aqueous two phases fluids only and ore forming fluid is of homogeneous NaCl-H2O kind of solutions. Isotopic studies of carbon, hydrogen and oxygen show that the ore forming fluids of mineralization Stage Ⅰ mainly derived from magmatic solutions, whereas fluids of mineralization stage Ⅱ mainly came from meteoric water in addition to the relicts of stage Ⅰ ore forming solutions. The values of δD and δ13CV-PDB reveal that the ore forming fluids of both mineralization Stage Ⅰ and Ⅱ all experienced strong rock water reaction. The genesis of the gold deposit is medium temperature magmatic hydrothermal deposit.
Occurred in Zhenzhumen Formation of Laoling Group of Proterozoic Era and controlled by ductile shear belt, the Huanggoushan gold deposit is one of the most representative deposits in Laoling gold-polymetallic metallogenic belt in southern Jilin Province. Based on the geological characteristics, mineral assemblage and the crosscutting relationship between different kinds of veins, the hydrothermal mineralization processes can be divided into two main stages, namely, stageⅠpyrite arsenopyrite quartz and stageⅡ later stibnite-milky quartz. Systematic study on petrography and microthermometry of fluid inclusions shows that quartz of Stage Ⅰcontains three types of primary fluid inclusions, which are CO2 bearing three phases, carbonic and aqueous two phases inclusions respectively, and the ore forming fluid is of medium to low temperature and low salinity NaCl-H2O-CO2 kind of solutions and immiscibility happened in the ore forming process, which led to the enrichment of gold etc; in quartz of Stage Ⅱ, there are aqueous two phases fluids only and ore forming fluid is of homogeneous NaCl-H2O kind of solutions. Isotopic studies of carbon, hydrogen and oxygen show that the ore forming fluids of mineralization Stage Ⅰ mainly derived from magmatic solutions, whereas fluids of mineralization stage Ⅱ mainly came from meteoric water in addition to the relicts of stage Ⅰ ore forming solutions. The values of δD and δ13CV-PDB reveal that the ore forming fluids of both mineralization Stage Ⅰ and Ⅱ all experienced strong rock water reaction. The genesis of the gold deposit is medium temperature magmatic hydrothermal deposit.
2016, 41(1): 131-138.
doi: 10.3799/dqkx.2016.010
Abstract:
Late Quaternary loess deposit is widely distributed in the Qinghai Lake region and adjacent area. The loess deposit independently recorded the environmental and climatic changes during the late Quaternary in the Qinghai Lake region, northeastern Qinghai-Tibetan Plateau. Nearly all studies are focused on reconstructing the environmental and climatic changes recorded by loess deposit in the Qinghai Lake region. However, up to now, the provenance of the loess deposit in the Qinghai Lake region is still poorly understood. Here we present the elemental concentration of the silicate fraction of the eolian deposit ( < 75 μm) from the ZYC section in the Qinghai Lake region and LT section at Lintao County on the western Chinese Loess Plateau, loess deposits at Guanjiaoshan Mountain, Chaka town and Wulan County, eolian sands at western and eastern shore of the Qinghai Lake, and fluvial deposits from the Buhahe river and lacustrine deposits at Erlangjian site in the Qinghai Lake region. The results show that: (1) K2O/Al2O3 (molar ratio) and Zr/Ti, Zr/Nb ratios indicate that the eolian deposits in the Qinghai Lake region and adjacent area can be distinguished clearly from the local deposits represented by river deposits at Buhahe river and lacustrine deposits at Erlangjian in the drainage basin of Qinghai Lake; (2) There is similarity of the elemental ratios (K2O/Al2O3 and Zr/Ti, Zr/Nb) between the eolian deposits in the Qinghai Lake region and loess deposits at Lintao County. Thus, the eolian deposits in the Qinghai Lake region and Lintao County may have the same source region; (3) Late Quaternary loess deposit in the Qinghai Lake region is probably sourced from the Qaidam basin.
Late Quaternary loess deposit is widely distributed in the Qinghai Lake region and adjacent area. The loess deposit independently recorded the environmental and climatic changes during the late Quaternary in the Qinghai Lake region, northeastern Qinghai-Tibetan Plateau. Nearly all studies are focused on reconstructing the environmental and climatic changes recorded by loess deposit in the Qinghai Lake region. However, up to now, the provenance of the loess deposit in the Qinghai Lake region is still poorly understood. Here we present the elemental concentration of the silicate fraction of the eolian deposit ( < 75 μm) from the ZYC section in the Qinghai Lake region and LT section at Lintao County on the western Chinese Loess Plateau, loess deposits at Guanjiaoshan Mountain, Chaka town and Wulan County, eolian sands at western and eastern shore of the Qinghai Lake, and fluvial deposits from the Buhahe river and lacustrine deposits at Erlangjian site in the Qinghai Lake region. The results show that: (1) K2O/Al2O3 (molar ratio) and Zr/Ti, Zr/Nb ratios indicate that the eolian deposits in the Qinghai Lake region and adjacent area can be distinguished clearly from the local deposits represented by river deposits at Buhahe river and lacustrine deposits at Erlangjian in the drainage basin of Qinghai Lake; (2) There is similarity of the elemental ratios (K2O/Al2O3 and Zr/Ti, Zr/Nb) between the eolian deposits in the Qinghai Lake region and loess deposits at Lintao County. Thus, the eolian deposits in the Qinghai Lake region and Lintao County may have the same source region; (3) Late Quaternary loess deposit in the Qinghai Lake region is probably sourced from the Qaidam basin.
2016, 41(1): 139-152.
doi: 10.3799/dqkx.2016.011
Abstract:
This study investigates the characteristics of the fluid and its mineralization potential in magmatic-hydrothermal phase by the inclusions study of the Shanshenfu granite located in the Hongyan area, Inner Mongolia. The study shows that the inclusions of the Shanshenfu granite can be divideddevided into three types includingof melt inclusions, melt-fluid inclusions and fluid inclusions. The presence of melt-fluid inclusions indicates that granitic magma has experiencedgot through magmatic-hydrothermal transition stage, which is confirmed by the large changes in homogenization temperatures (from 281 ℃ to > 550 ℃) and the salinities(from 1.1% NaCl eqv to > 66.8% NaCl eqv) from rock center lithofaciesphase to edge lithofaciesphase. We use inclusion isochors of different homogenization temperatures and salinitiesy together with water-saturated solidus of granitic magma to estimate the temperatures and pressures of exsolved fluids. Considering that the three-phase inclusions containing CO2 have a good limitation to the smallest emplacement pressure, we estimate that the smallest emplacement depth of Shanshenfu granite of range 7.6-9.5 km, exsolution temperature and depth of range 580-700 ℃ and 6.0-14.9 km, respectively. Laser-Raman characteristics of inclusions show that the solid phases of melt-fluid inclusions contain strong oxidation substances such as barite, azurite and hematite, which indicates the strong oxidation in magmatic-hydrothermal system that is very beneficial for Cu enriched in the exsolved fluids under the conditions of high-pressure, high-temperature and high-salinity. Combined with the wild in situ mineralized alteration characteristics, we conclude that the Shanshenfu area has good mineralization potential to form magmatic-hydrothermal deposit of Cu.
This study investigates the characteristics of the fluid and its mineralization potential in magmatic-hydrothermal phase by the inclusions study of the Shanshenfu granite located in the Hongyan area, Inner Mongolia. The study shows that the inclusions of the Shanshenfu granite can be divideddevided into three types includingof melt inclusions, melt-fluid inclusions and fluid inclusions. The presence of melt-fluid inclusions indicates that granitic magma has experiencedgot through magmatic-hydrothermal transition stage, which is confirmed by the large changes in homogenization temperatures (from 281 ℃ to > 550 ℃) and the salinities(from 1.1% NaCl eqv to > 66.8% NaCl eqv) from rock center lithofaciesphase to edge lithofaciesphase. We use inclusion isochors of different homogenization temperatures and salinitiesy together with water-saturated solidus of granitic magma to estimate the temperatures and pressures of exsolved fluids. Considering that the three-phase inclusions containing CO2 have a good limitation to the smallest emplacement pressure, we estimate that the smallest emplacement depth of Shanshenfu granite of range 7.6-9.5 km, exsolution temperature and depth of range 580-700 ℃ and 6.0-14.9 km, respectively. Laser-Raman characteristics of inclusions show that the solid phases of melt-fluid inclusions contain strong oxidation substances such as barite, azurite and hematite, which indicates the strong oxidation in magmatic-hydrothermal system that is very beneficial for Cu enriched in the exsolved fluids under the conditions of high-pressure, high-temperature and high-salinity. Combined with the wild in situ mineralized alteration characteristics, we conclude that the Shanshenfu area has good mineralization potential to form magmatic-hydrothermal deposit of Cu.
2016, 41(1): 153-166.
doi: 10.3799/dqkx.2016.012
Abstract:
There are many controversies about the metallogenic mechanism for the Qianjiadian uranium deposit in the southern Songliao basin. Using a series of tests including micropolariscope, SEM and XRD, the epigenetic alteration of the Qianjiadian uranium deposit have been described. It has been shown that this deposit contains six types of alteration: Haematization, ferritization, pyritization (gelatinous pyrite, framboidal pyrite and granular pyrite), argillation (hydromicazation, kaolinization and illitization), carbonatation (calcilization, ankeritization and sideritization) and uranium mineralization. Haematization, ferritization, hydromicazation, kaolinization, illitization and calcilization frequently occur in the red sandstones and yellow sandstones, and the extent of haematization, ferritization and hydromicazation is lower in the yellow sandstones than that in the red sandstones. Weak haematization, pyritization, kaolinization, illitization, ankeritization and sideritization can often be seen in the non-mineralized grey sandstones. Pyritization, kaolinization, illitization, ankeritization, uranium metallization and sideritization are primarily formed in the mineralized grey sandstones. Pyritization and sideritization often occur in the primary grey sandstones. The Qianjiadian uranium deposit has undergone neutral-alkalescent environment during the diagenetic period, acidic environment during the early metallogenic period, alkalescent-alkalic environment during the late metallogenic period, and alkali environment during the postmineralization. The neutral-alkalescent environment during the diagenetic period is characterized by formation of siderite. The acidic environment during the early metallogenic period is characterized by formation of hematite, allcharite, pyrite, gyulekhite and kaolinite. The alkalescent-alkalic environment during the late metallogenic period is characterized by formation of ankerite. The alkali environment during the postmineralization is characterized by formation of calcite.
There are many controversies about the metallogenic mechanism for the Qianjiadian uranium deposit in the southern Songliao basin. Using a series of tests including micropolariscope, SEM and XRD, the epigenetic alteration of the Qianjiadian uranium deposit have been described. It has been shown that this deposit contains six types of alteration: Haematization, ferritization, pyritization (gelatinous pyrite, framboidal pyrite and granular pyrite), argillation (hydromicazation, kaolinization and illitization), carbonatation (calcilization, ankeritization and sideritization) and uranium mineralization. Haematization, ferritization, hydromicazation, kaolinization, illitization and calcilization frequently occur in the red sandstones and yellow sandstones, and the extent of haematization, ferritization and hydromicazation is lower in the yellow sandstones than that in the red sandstones. Weak haematization, pyritization, kaolinization, illitization, ankeritization and sideritization can often be seen in the non-mineralized grey sandstones. Pyritization, kaolinization, illitization, ankeritization, uranium metallization and sideritization are primarily formed in the mineralized grey sandstones. Pyritization and sideritization often occur in the primary grey sandstones. The Qianjiadian uranium deposit has undergone neutral-alkalescent environment during the diagenetic period, acidic environment during the early metallogenic period, alkalescent-alkalic environment during the late metallogenic period, and alkali environment during the postmineralization. The neutral-alkalescent environment during the diagenetic period is characterized by formation of siderite. The acidic environment during the early metallogenic period is characterized by formation of hematite, allcharite, pyrite, gyulekhite and kaolinite. The alkalescent-alkalic environment during the late metallogenic period is characterized by formation of ankerite. The alkali environment during the postmineralization is characterized by formation of calcite.
2016, 41(1): 167-176.
doi: 10.3799/dqkx.2016.013
Abstract:
The dolomite reservoir plays an important role in the research of carbonate oil and gas reservoirs. The origin of dolomite is an integral component in analyzing the evolution of pore-cave-fracture system in high-quality dolomite reservoirs. The dolomites of Middle Permian Qixia Formation, SW Sichuan basin were studied in this paper by the method of petrology and geochemical analyses aiming at the discovery of the origin of dolomites. The dolomites are mainly controlled by fault zones, associated with zebra fabric. The dolomite fabrics exhibit non-planar saddle crystals and strongly undulose extinctions. In addition, the high degree of order is found in hydrothermal dolomites. The geochemical characteristics of saddle dolomites show noticeable negative δ18OPDB and an enrichment of strontium isotopes. In the end, the dolomites have been proved to be the product of structurally controlled hydrothermal dolomitization on the basis of comprehensive geologic research.
The dolomite reservoir plays an important role in the research of carbonate oil and gas reservoirs. The origin of dolomite is an integral component in analyzing the evolution of pore-cave-fracture system in high-quality dolomite reservoirs. The dolomites of Middle Permian Qixia Formation, SW Sichuan basin were studied in this paper by the method of petrology and geochemical analyses aiming at the discovery of the origin of dolomites. The dolomites are mainly controlled by fault zones, associated with zebra fabric. The dolomite fabrics exhibit non-planar saddle crystals and strongly undulose extinctions. In addition, the high degree of order is found in hydrothermal dolomites. The geochemical characteristics of saddle dolomites show noticeable negative δ18OPDB and an enrichment of strontium isotopes. In the end, the dolomites have been proved to be the product of structurally controlled hydrothermal dolomitization on the basis of comprehensive geologic research.
