Lithological observations and mineralogical analyses on pyroxene and hornblende megacrysts and pyroxene and hornblende cumulates in xenoliths in the Mesozoic plutons of the Tongling region, Anhui Province, provide evi...Lithological observations and mineralogical analyses on pyroxene and hornblende megacrysts and pyroxene and hornblende cumulates in xenoliths in the Mesozoic plutons of the Tongling region, Anhui Province, provide evidence for the magmatic underplating of mantle-derived alkali-olivine basalt at circa 140 Ma. The pyroxene and hornblende megacrysts and cumulates were formed through the AFC process at depths ranging from 27 to 35 km.展开更多
Some pyrrhotite-chalcopyrite-bearing amphibole megacrysts (including pyroxene megacrysts) were discovered in Mesozoic augite diorite-porphyrite at Caoshan in Tongling area, Anhui Province. The amphibole megacrysts,bel...Some pyrrhotite-chalcopyrite-bearing amphibole megacrysts (including pyroxene megacrysts) were discovered in Mesozoic augite diorite-porphyrite at Caoshan in Tongling area, Anhui Province. The amphibole megacrysts,belonging mainly to pargasite and magnesiohastingsite, are characteristic of the amphibole composition derived from mantle and crystallized in lower crust. In general, the aggregates of pyrrhotite-chalcopyrite take the shapes of cylinder and sphere. Three occurrences have been recognized in the amphibole megacrysts: parallel linear, bunchy and scattered. The unique cylinder-like shape of the aggregates and remarkable Ni-poor sulfides in Caoshan are distinctively different from the spherical Ni-rich sulfides in pyroxene megacrysts and any other kinds of megacrysts. In terms of composition, the amphibole megacrysts and their sulfides in Caoshan are similar to those in the pyroxenite xenoliths in Qilin, Guangdong Province. In terms of origin, the pyrrhotite-chalcopyrites as exsolution products resulted from the subsolidus re-equilibration of sulfide solid solution within amphibole megacrysts. Such pyrrhotite-chalcopyrite-bearing amphibole megacrysts were first discovered inside and outside China. This discovery is important for the study of regional magma evolution and its associated mineralizations and ore sources as well.展开更多
The Pengshan Sn-Pb-Zn polymetallic orefield is located in the Jiujiang-Ruichang region, which is a segment of the middle-lower Yangtze River metallogenic belt. The Pengshan late Yanshanian buried pluton with granitic ...The Pengshan Sn-Pb-Zn polymetallic orefield is located in the Jiujiang-Ruichang region, which is a segment of the middle-lower Yangtze River metallogenic belt. The Pengshan late Yanshanian buried pluton with granitic composition is a calc-alkaline pluton, intrusion of which is responsible for the formation of the Sn-Pb-Zn polymetallic deposit through providing thermodynamic condition and ore-forming material. The long-active basement rifts initially formed in the Jinning period and the domal structure with induced secondary order faults formed by emplacement of the pluton, such as ring-detachment fault, top-detachment fault and joint fissure, act as the passage-way for magma and ore-forming fluid and impounding structure for ore deposit. The magma to form the pluton with DI>90 is intensively differentiated. The variation of the ore-forming fluid in composition with falling in temperature caused by action of magmatic hydrothermal convection system combined with groundwater convection system attributes to mineralization of various types in the orefield. The mineralization process can be divided into six stages, i.e., greisenization, skarnization of early stage, fluorite-stanniferous silication stage, skarnization of advanced stage, quartz and cassiterite-sulfuration stage and carbonation stage. The mineral assemblages formed in different mineralization stages are different owing to temperature changing and may be overlapped in space. Malayaite is recognized from the mineral assemblage formed in the fluorite-stanniferous silication stage. The ores in the Pengshan Sn-Pb-Zn polymetallic deposit are spatially zoned with variation from As-Sn mineral assemblage of high temperature in the inner zone through Sn-Pb and Pb-Zn-Ag mineral assemblage of middle temperature in the middle zone to fluorite mineral assemblage of low temperature in the outer zone. The exchanging of Sn, Mg and Fe between biotite and hydrothermal fluid resulted from variation of physicochemical condition during evolution processes of the hydrothermal fluid and its role in mineralization are also discussed in this paper.展开更多
A number of Fe-Ti oxide and Fe-Cu sulfide exsolution phases are found in amphibole cumulate xenoliths from Mesozoic granodioritic plutons at Jiguanshi and Jin- kouling in Tongling, Anhui Province. Most of amphiboles i...A number of Fe-Ti oxide and Fe-Cu sulfide exsolution phases are found in amphibole cumulate xenoliths from Mesozoic granodioritic plutons at Jiguanshi and Jin- kouling in Tongling, Anhui Province. Most of amphiboles in the xenoliths have been identified as pargasite, and deter-mined as a crystallization phase in the lower crust. The oxide exsolutions commonly acicular, are distributed parallel to [100] of amphibole with a typical Schiller texture. They con-tain 0.29%—51.07% of TiO2, and correspond to magnetite, titaniferous magnetite, titanomagnetite or ilmenite. All ex-solved sulfide grains, being rounded to extended rounded in shape, are regularly arranged in sub-paralleled or closely beaded groups, except for a few of grains that are scattered or isolated. The exsolved sulfide phases comprise mostly pyrrhotite, secondarily cubanite and chalcopyrite, and rarely pyrite. A few grains of magnetite can coexist with pyrrhotite in most samples. The sulfide phases are poor in nickel (usu-ally Ni < 0.5%, Ni/Fe < 0.003), while relative enrichments in copper (up to 2.93%) typify the pyrrhotite. Additionally, both oxides and sulfides may be exsolved in the same area of amphibole. Occurrence of Fe-Ti oxide and Fe-Cu sulfide exsolution phases in the xenoliths leads to inference that ore-forming materials such as S, Fe, Cu, etc. have been pri-marily dissolved in Mesozoic magma within the lower crust beneath the Tongling area.展开更多
基金the NationalNatural Science Foundation of China(Grants 40272034, 40133020)the Ministry of Science and Technology of China(Grant 1999043206) the Korea Science and Engineering Foundation(Grant KOSEF-20005-131-03-02).
文摘Lithological observations and mineralogical analyses on pyroxene and hornblende megacrysts and pyroxene and hornblende cumulates in xenoliths in the Mesozoic plutons of the Tongling region, Anhui Province, provide evidence for the magmatic underplating of mantle-derived alkali-olivine basalt at circa 140 Ma. The pyroxene and hornblende megacrysts and cumulates were formed through the AFC process at depths ranging from 27 to 35 km.
文摘Some pyrrhotite-chalcopyrite-bearing amphibole megacrysts (including pyroxene megacrysts) were discovered in Mesozoic augite diorite-porphyrite at Caoshan in Tongling area, Anhui Province. The amphibole megacrysts,belonging mainly to pargasite and magnesiohastingsite, are characteristic of the amphibole composition derived from mantle and crystallized in lower crust. In general, the aggregates of pyrrhotite-chalcopyrite take the shapes of cylinder and sphere. Three occurrences have been recognized in the amphibole megacrysts: parallel linear, bunchy and scattered. The unique cylinder-like shape of the aggregates and remarkable Ni-poor sulfides in Caoshan are distinctively different from the spherical Ni-rich sulfides in pyroxene megacrysts and any other kinds of megacrysts. In terms of composition, the amphibole megacrysts and their sulfides in Caoshan are similar to those in the pyroxenite xenoliths in Qilin, Guangdong Province. In terms of origin, the pyrrhotite-chalcopyrites as exsolution products resulted from the subsolidus re-equilibration of sulfide solid solution within amphibole megacrysts. Such pyrrhotite-chalcopyrite-bearing amphibole megacrysts were first discovered inside and outside China. This discovery is important for the study of regional magma evolution and its associated mineralizations and ore sources as well.
文摘The Pengshan Sn-Pb-Zn polymetallic orefield is located in the Jiujiang-Ruichang region, which is a segment of the middle-lower Yangtze River metallogenic belt. The Pengshan late Yanshanian buried pluton with granitic composition is a calc-alkaline pluton, intrusion of which is responsible for the formation of the Sn-Pb-Zn polymetallic deposit through providing thermodynamic condition and ore-forming material. The long-active basement rifts initially formed in the Jinning period and the domal structure with induced secondary order faults formed by emplacement of the pluton, such as ring-detachment fault, top-detachment fault and joint fissure, act as the passage-way for magma and ore-forming fluid and impounding structure for ore deposit. The magma to form the pluton with DI>90 is intensively differentiated. The variation of the ore-forming fluid in composition with falling in temperature caused by action of magmatic hydrothermal convection system combined with groundwater convection system attributes to mineralization of various types in the orefield. The mineralization process can be divided into six stages, i.e., greisenization, skarnization of early stage, fluorite-stanniferous silication stage, skarnization of advanced stage, quartz and cassiterite-sulfuration stage and carbonation stage. The mineral assemblages formed in different mineralization stages are different owing to temperature changing and may be overlapped in space. Malayaite is recognized from the mineral assemblage formed in the fluorite-stanniferous silication stage. The ores in the Pengshan Sn-Pb-Zn polymetallic deposit are spatially zoned with variation from As-Sn mineral assemblage of high temperature in the inner zone through Sn-Pb and Pb-Zn-Ag mineral assemblage of middle temperature in the middle zone to fluorite mineral assemblage of low temperature in the outer zone. The exchanging of Sn, Mg and Fe between biotite and hydrothermal fluid resulted from variation of physicochemical condition during evolution processes of the hydrothermal fluid and its role in mineralization are also discussed in this paper.
基金supported by the National Natural Science Foundation of China (Grant Nos.40272034 and 40133020)Chinese Ministry of Science and Technology(Grant No.G1999043206)Korea Science and Engineering Foundation (Grant No.KOSEF-20005-131-03-02).
文摘A number of Fe-Ti oxide and Fe-Cu sulfide exsolution phases are found in amphibole cumulate xenoliths from Mesozoic granodioritic plutons at Jiguanshi and Jin- kouling in Tongling, Anhui Province. Most of amphiboles in the xenoliths have been identified as pargasite, and deter-mined as a crystallization phase in the lower crust. The oxide exsolutions commonly acicular, are distributed parallel to [100] of amphibole with a typical Schiller texture. They con-tain 0.29%—51.07% of TiO2, and correspond to magnetite, titaniferous magnetite, titanomagnetite or ilmenite. All ex-solved sulfide grains, being rounded to extended rounded in shape, are regularly arranged in sub-paralleled or closely beaded groups, except for a few of grains that are scattered or isolated. The exsolved sulfide phases comprise mostly pyrrhotite, secondarily cubanite and chalcopyrite, and rarely pyrite. A few grains of magnetite can coexist with pyrrhotite in most samples. The sulfide phases are poor in nickel (usu-ally Ni < 0.5%, Ni/Fe < 0.003), while relative enrichments in copper (up to 2.93%) typify the pyrrhotite. Additionally, both oxides and sulfides may be exsolved in the same area of amphibole. Occurrence of Fe-Ti oxide and Fe-Cu sulfide exsolution phases in the xenoliths leads to inference that ore-forming materials such as S, Fe, Cu, etc. have been pri-marily dissolved in Mesozoic magma within the lower crust beneath the Tongling area.
