Garnet is a primary mineral in skarn deposits and plays a significant role in recording copious mineralization and metallogenic information.This study systematically investigates the geochemistry and geochronology of ...Garnet is a primary mineral in skarn deposits and plays a significant role in recording copious mineralization and metallogenic information.This study systematically investigates the geochemistry and geochronology of garnet and zircon in the Dafang Au-Pb-Zn-Ag deposit,which represents prominent gold mineralization in southern Hunan,China.Garnet samples with distinct zoning patterns and compositional variations were identified using various analytical techniques,including Backscattered Electron(BSE)imaging,Cathodoluminescence(CL)response,textural characterization,and analysis of rare-earth elements(REE),major contents,and trace element compositions.The garnet was dated U-Pb dating,which yielded a lower intercept age of 161.06±1.93 Ma.This age is older than the underlying granodiorite porphyry,which has a concordia age of 155.13±0.95 Ma determined by zircon U-Pb dating.These results suggest that the gold mineralization may be related to the concealed granite.Two groups of garnet changed from depleted Al garnet to enriched Al garnet,and the rare earth element(REE)patterns of these groups were converted from light REE(LREE)-enriched and heavy REE(HREE)-depleted with positive europium(Eu)anomalies to medium REE(MREE)-enriched from core to rim zoning.The different REE patterns of garnet in various zones may be attributed to changes in the fluid environment and late superposition alteration.The development of distal skarn in the southern Hunan could be a significant indicator for identifying gold mineralization.展开更多
The Baoshan Cu–Pb–Zn deposit, located in the central part of the Qin–Hang belt in South China, is closely related to the granodiorite-porphyry. However, the characteristics and the source of the ore-forming fluid a...The Baoshan Cu–Pb–Zn deposit, located in the central part of the Qin–Hang belt in South China, is closely related to the granodiorite-porphyry. However, the characteristics and the source of the ore-forming fluid are still ubiquitous. According to the crosscutting relationships between veinlets and their mineral assemblages, three stages of hydrothermal mineralization in this deposit were previously distinguished. In this contribution, two different colored fluorites from the major sulfide mineralization stage are recognized:(1) green fluorites coexisting with Pb–Zn ores;and(2) violet fluorites coexisting with pyrite ores. Y/Ho ratios verify the green fluorites and violet fluorites were co-genetic. The fluorites display elevated(La/Yb)Nratios, which decrease from 1201 to 5710 for green fluorites to 689–1568 for violet fluorites, indicating that they precipitated at the early hydrothermal sulfide stage,and Pb–Zn ores crystallized earlier than pyrite ores. The similar Tb/La ratios of the fluorites also indicate that they precipitated at an early stage within a short time. From the green fluorites to violet fluorites, the total rare earth element(ΣREE)concentrationsdecreasefrom1052–1680 ppm to 148–350 ppm, indicating that the green fluorites precipitated from a more acidic fluid. The Eu/Eu*ratios increase from 0.17 to 0.30 for green fluorites to0.29–0.48 for violet fluorites, and the Ce/Ce* ratios decrease from 1.08–1.13 to 0.93–1.11, suggesting a gradual increase in oxygen fugacity(fO_(2)) and pH value of the mineralization fluid. Though the fluorites display similar REE patterns to the granodiorite-porphyry and limestone,the ΣREE concentrations of the fluorites are significantly higher than those of limestone and the granodiorite-porphyry, suggesting that an important undetected non-magmatic source is involved to provide sufficient REE for fluorites. The most plausible mechanism is fluid mixing between magma fluid and an undetected non-magmatic fluid.展开更多
Southern Hunan Province is famous for its intensive rare, radioactive and other metal elements’ mineralizations. There is a relation between the basaltic rocks and mineralizations in space, time and ore forming eleme...Southern Hunan Province is famous for its intensive rare, radioactive and other metal elements’ mineralizations. There is a relation between the basaltic rocks and mineralizations in space, time and ore forming elements. The Jurassic Cretaceous （204\81 Ma） basaltic rocks consists mainly of alkali\|basalt and tholeiitic basalt formed in plate environment. Trace elements and Sr, Nd, Pb isotopic compositions show that the regional mantle source was metasomatized shortly before the partial melting. The alkali basalt and tholeiitic basalt might be 3%\5% and 10%\15% of the partial melting of the enriched mantle source respectively. Obviously the enrichment of the regional mantle played an important role in formation of the large and super\|large deposits in southern Hunan Province.展开更多
Deep xenolith are important samples for us to know composition and nature of the deep crust. There are many new volcanos which can all kinds of xenoliths such as a lower crustal graulite, and upper mantle derived peri...Deep xenolith are important samples for us to know composition and nature of the deep crust. There are many new volcanos which can all kinds of xenoliths such as a lower crustal graulite, and upper mantle derived peridolite and lherzolite. In eastern China, there occured many deep xenoliths in Mesozoic Cenzoic alkaline basalt. Besides these, some small volcanos eruptions were founded in southern Hunan province, which age is about 132-151 Ma. Because there are many kinds of xenoliths in basalt, many geologists paid attention to them. We studied host basalt and its xenoliths in detail, and obtained some new results as follows: Huziyan basalt belongs to the typical alkaline basalt. While the magma erupted out, it took many xenoliths from deep crust and upper mantle. These xenoliths include: mafic granulite, gabbro and feldspar gneiss as well as mantle drived xenoliths such as pyroxenite, peridotite and spinel lherzolite. The age of granulite and gabbro xenoliths is not definite, for example, gabbro age is 1 141±67 Ma, and the age also may be regarded as 224±24 Ma. The author gained new results by using zircon U Pb dating, and the interceptions of the cordia and discordia are 787±30 Ma and 298±27 Ma. The two ages display two geological events respectively, the former is the age of gabbroic magma formation definetly, the later may indicates the metamorphic age of lower crust. Feature parameters of lithophile element of host basalt and xenoliths are different, i.e., host basalt K *=2K N/(Nb N+La N)=2.08>1, which shows the origin area of magma had suffered the metasomatism, its Nb *=2K N/(Nb N+La N)=0.30<1, which shows the magma hybridized with crustal rocks after it erupted; while the lower crust xenoliths (gabbro and granulite) are different, K * and Nb * of gabbro are 0.94 and 0.54. They just displayed basic magma suffered hybridization after it intruded to crust. K * and Nb * of granulite xenolith are 6.4 and 0.25, which also suggested the strong interaction between upper mantle and lower crust. Its mineral inner isochron age is 544±14 Ma, and its ε Nd =-6.6, these results imply that granulite xenolith has been contaminated by crust. The two stage mode age of Nd reequilibrium is 1 766 Ma, so rock forming age is inferred to be the Proterozoic era. From above discussion, it can be concluded that there are several period of magma intrusive events in lower crust, may be regraded as the middle Proterozoic (1 766 Ma), late Proterozoic (787±30 Ma), metamorphism of granulite and metamorphic event of gabbro may suggest there would be magmatic process between mantle and crust in Caledonian (544 Ma±) and early Indosinian (298 Ma±) period. So the author suggests the intrusion of basic magma and its uderplating to lower crust resulted in the overgrowth of continent crust in southern China. It is a kind of vertical accretion which is quite different from lateral overgrowth apparently.展开更多
基金financially supported by the National Key Research and Development Plan(Grant No.2023YFC2906801)。
文摘Garnet is a primary mineral in skarn deposits and plays a significant role in recording copious mineralization and metallogenic information.This study systematically investigates the geochemistry and geochronology of garnet and zircon in the Dafang Au-Pb-Zn-Ag deposit,which represents prominent gold mineralization in southern Hunan,China.Garnet samples with distinct zoning patterns and compositional variations were identified using various analytical techniques,including Backscattered Electron(BSE)imaging,Cathodoluminescence(CL)response,textural characterization,and analysis of rare-earth elements(REE),major contents,and trace element compositions.The garnet was dated U-Pb dating,which yielded a lower intercept age of 161.06±1.93 Ma.This age is older than the underlying granodiorite porphyry,which has a concordia age of 155.13±0.95 Ma determined by zircon U-Pb dating.These results suggest that the gold mineralization may be related to the concealed granite.Two groups of garnet changed from depleted Al garnet to enriched Al garnet,and the rare earth element(REE)patterns of these groups were converted from light REE(LREE)-enriched and heavy REE(HREE)-depleted with positive europium(Eu)anomalies to medium REE(MREE)-enriched from core to rim zoning.The different REE patterns of garnet in various zones may be attributed to changes in the fluid environment and late superposition alteration.The development of distal skarn in the southern Hunan could be a significant indicator for identifying gold mineralization.
基金financially supported by the National Natural Science Foundation of China(No.42102079)the Natural Science Foundation of Sichuan Province(No.22NSFSC2765)+1 种基金State Key Laboratory of Ore Deposit Geochemistry Key Laboratory Open Project Fund(No.201804)the Southwest University of Science and Technology Doctoral Fund(No.16zx7132)。
文摘The Baoshan Cu–Pb–Zn deposit, located in the central part of the Qin–Hang belt in South China, is closely related to the granodiorite-porphyry. However, the characteristics and the source of the ore-forming fluid are still ubiquitous. According to the crosscutting relationships between veinlets and their mineral assemblages, three stages of hydrothermal mineralization in this deposit were previously distinguished. In this contribution, two different colored fluorites from the major sulfide mineralization stage are recognized:(1) green fluorites coexisting with Pb–Zn ores;and(2) violet fluorites coexisting with pyrite ores. Y/Ho ratios verify the green fluorites and violet fluorites were co-genetic. The fluorites display elevated(La/Yb)Nratios, which decrease from 1201 to 5710 for green fluorites to 689–1568 for violet fluorites, indicating that they precipitated at the early hydrothermal sulfide stage,and Pb–Zn ores crystallized earlier than pyrite ores. The similar Tb/La ratios of the fluorites also indicate that they precipitated at an early stage within a short time. From the green fluorites to violet fluorites, the total rare earth element(ΣREE)concentrationsdecreasefrom1052–1680 ppm to 148–350 ppm, indicating that the green fluorites precipitated from a more acidic fluid. The Eu/Eu*ratios increase from 0.17 to 0.30 for green fluorites to0.29–0.48 for violet fluorites, and the Ce/Ce* ratios decrease from 1.08–1.13 to 0.93–1.11, suggesting a gradual increase in oxygen fugacity(fO_(2)) and pH value of the mineralization fluid. Though the fluorites display similar REE patterns to the granodiorite-porphyry and limestone,the ΣREE concentrations of the fluorites are significantly higher than those of limestone and the granodiorite-porphyry, suggesting that an important undetected non-magmatic source is involved to provide sufficient REE for fluorites. The most plausible mechanism is fluid mixing between magma fluid and an undetected non-magmatic fluid.
文摘Southern Hunan Province is famous for its intensive rare, radioactive and other metal elements’ mineralizations. There is a relation between the basaltic rocks and mineralizations in space, time and ore forming elements. The Jurassic Cretaceous （204\81 Ma） basaltic rocks consists mainly of alkali\|basalt and tholeiitic basalt formed in plate environment. Trace elements and Sr, Nd, Pb isotopic compositions show that the regional mantle source was metasomatized shortly before the partial melting. The alkali basalt and tholeiitic basalt might be 3%\5% and 10%\15% of the partial melting of the enriched mantle source respectively. Obviously the enrichment of the regional mantle played an important role in formation of the large and super\|large deposits in southern Hunan Province.
文摘Deep xenolith are important samples for us to know composition and nature of the deep crust. There are many new volcanos which can all kinds of xenoliths such as a lower crustal graulite, and upper mantle derived peridolite and lherzolite. In eastern China, there occured many deep xenoliths in Mesozoic Cenzoic alkaline basalt. Besides these, some small volcanos eruptions were founded in southern Hunan province, which age is about 132-151 Ma. Because there are many kinds of xenoliths in basalt, many geologists paid attention to them. We studied host basalt and its xenoliths in detail, and obtained some new results as follows: Huziyan basalt belongs to the typical alkaline basalt. While the magma erupted out, it took many xenoliths from deep crust and upper mantle. These xenoliths include: mafic granulite, gabbro and feldspar gneiss as well as mantle drived xenoliths such as pyroxenite, peridotite and spinel lherzolite. The age of granulite and gabbro xenoliths is not definite, for example, gabbro age is 1 141±67 Ma, and the age also may be regarded as 224±24 Ma. The author gained new results by using zircon U Pb dating, and the interceptions of the cordia and discordia are 787±30 Ma and 298±27 Ma. The two ages display two geological events respectively, the former is the age of gabbroic magma formation definetly, the later may indicates the metamorphic age of lower crust. Feature parameters of lithophile element of host basalt and xenoliths are different, i.e., host basalt K *=2K N/(Nb N+La N)=2.08>1, which shows the origin area of magma had suffered the metasomatism, its Nb *=2K N/(Nb N+La N)=0.30<1, which shows the magma hybridized with crustal rocks after it erupted; while the lower crust xenoliths (gabbro and granulite) are different, K * and Nb * of gabbro are 0.94 and 0.54. They just displayed basic magma suffered hybridization after it intruded to crust. K * and Nb * of granulite xenolith are 6.4 and 0.25, which also suggested the strong interaction between upper mantle and lower crust. Its mineral inner isochron age is 544±14 Ma, and its ε Nd =-6.6, these results imply that granulite xenolith has been contaminated by crust. The two stage mode age of Nd reequilibrium is 1 766 Ma, so rock forming age is inferred to be the Proterozoic era. From above discussion, it can be concluded that there are several period of magma intrusive events in lower crust, may be regraded as the middle Proterozoic (1 766 Ma), late Proterozoic (787±30 Ma), metamorphism of granulite and metamorphic event of gabbro may suggest there would be magmatic process between mantle and crust in Caledonian (544 Ma±) and early Indosinian (298 Ma±) period. So the author suggests the intrusion of basic magma and its uderplating to lower crust resulted in the overgrowth of continent crust in southern China. It is a kind of vertical accretion which is quite different from lateral overgrowth apparently.
