For skarn type deposits , there are two lands of skarns , skarn formed by filtrating-diffusing metasomatism and vein skarn formed by filling . The vein skarn , discussed this paper and considered to be magmatic genesi...For skarn type deposits , there are two lands of skarns , skarn formed by filtrating-diffusing metasomatism and vein skarn formed by filling . The vein skarn , discussed this paper and considered to be magmatic genesis , is characterized by: (1) occurring as vein with distinct boundaries with country rocks , yet just the same even in marble easy to be replaced ; (2) composed of a mineral assemblage similar to that of granite ,containing pegmatite as wen as coarse skarn mineral pockets ,and sometimes transited with dike rocks ; (3) dear crystalline feature of deposition ; (4) sideronitic texture ; (5) stowing vesicular, bean-like and flow structures ; (6) very common liquid immiscibility; (7) vertical zoning of gravitational differentiation caused by volatile concentration upwards; (8) associated and transited with non-copper ore bodies of magmatic genesis and tungsten-bearing quartz veins of silicate magmatic genesis rich in volatile ; (9) melt inclusions . Two origins of skam magma . originated by assimilation of silicate magma at its emplacemeot or below it and generated owe to assimilation of deep magma ,corrosion of carbonate strata and liquation , are presented .展开更多
Granitic pegmatites are commonly thought to form by fractional crystallization or by liquid immiscibility of granitic magma; however, these proposals are based mainly on analyses of fluid and melt inclusions. Here, we...Granitic pegmatites are commonly thought to form by fractional crystallization or by liquid immiscibility of granitic magma; however, these proposals are based mainly on analyses of fluid and melt inclusions. Here, we use the Jiajika pegmatite deposit, the largest spodumene deposit in Asia, as a case study to investigate ore forming processes using isotope dating. Dating of a single granite sample from the Jiajika deposit using multiple methods gave a zircon U-Pb SHRIMP age of 208.4 ~ 3.9 Ma, an 4~Ar/39Ar age for muscovite of 182.9 ~ 1.7 Ma, and an 4~Ar/39Ar age for biotite of 169.9 ＋ 1.6 Ma. Based on these dating results and the 4~Ar/39Ar age of muscovite from the Jiajika pegmatite, a temperature-time cooling track for the Jiajika granite was constructed using closure temperatures of the different isotope systems. This track indicates that the granite cooled over ^-40 m. y., with segregation of the pegmatite fluid from the granitic magma at a temperature of ~700~C. This result suggests that the Jiajika pegmatite formed not by fractional crystallization, but by segregation of an immiscible liquid from the granitic magma. When compared with fractional crystallization, the relatively early timing of segregation of an immiscible liquid from a granitic magma can prevent the precipitation of ore-forming elements during crystallization, and suggests that liquid immiscibility could be an important ore-forming process for rare metal pegmatities. We also conclude that isotope dating is a method that can potentially be used to determine the dominant ore-forming processes that occurred during the formation of granite-related ore deposits, and suggest that this method can be employed to determine the formation history of the W-Sn ore deposits found elsewhere within the Nanling Metallogenic Belt.展开更多
文摘For skarn type deposits , there are two lands of skarns , skarn formed by filtrating-diffusing metasomatism and vein skarn formed by filling . The vein skarn , discussed this paper and considered to be magmatic genesis , is characterized by: (1) occurring as vein with distinct boundaries with country rocks , yet just the same even in marble easy to be replaced ; (2) composed of a mineral assemblage similar to that of granite ,containing pegmatite as wen as coarse skarn mineral pockets ,and sometimes transited with dike rocks ; (3) dear crystalline feature of deposition ; (4) sideronitic texture ; (5) stowing vesicular, bean-like and flow structures ; (6) very common liquid immiscibility; (7) vertical zoning of gravitational differentiation caused by volatile concentration upwards; (8) associated and transited with non-copper ore bodies of magmatic genesis and tungsten-bearing quartz veins of silicate magmatic genesis rich in volatile ; (9) melt inclusions . Two origins of skam magma . originated by assimilation of silicate magma at its emplacemeot or below it and generated owe to assimilation of deep magma ,corrosion of carbonate strata and liquation , are presented .
基金supported by grants from the National Natural Science Foundation of China (40702014)the China Postdoctoral Science Foundation (2008044018,200902580)+1 种基金the Chinese SinoProbe Project (SinoProbe-03-01)the National Nonprofit Institute Research Grant of IMR,GAGS(K1001)
文摘Granitic pegmatites are commonly thought to form by fractional crystallization or by liquid immiscibility of granitic magma; however, these proposals are based mainly on analyses of fluid and melt inclusions. Here, we use the Jiajika pegmatite deposit, the largest spodumene deposit in Asia, as a case study to investigate ore forming processes using isotope dating. Dating of a single granite sample from the Jiajika deposit using multiple methods gave a zircon U-Pb SHRIMP age of 208.4 ~ 3.9 Ma, an 4~Ar/39Ar age for muscovite of 182.9 ~ 1.7 Ma, and an 4~Ar/39Ar age for biotite of 169.9 ＋ 1.6 Ma. Based on these dating results and the 4~Ar/39Ar age of muscovite from the Jiajika pegmatite, a temperature-time cooling track for the Jiajika granite was constructed using closure temperatures of the different isotope systems. This track indicates that the granite cooled over ^-40 m. y., with segregation of the pegmatite fluid from the granitic magma at a temperature of ~700~C. This result suggests that the Jiajika pegmatite formed not by fractional crystallization, but by segregation of an immiscible liquid from the granitic magma. When compared with fractional crystallization, the relatively early timing of segregation of an immiscible liquid from a granitic magma can prevent the precipitation of ore-forming elements during crystallization, and suggests that liquid immiscibility could be an important ore-forming process for rare metal pegmatities. We also conclude that isotope dating is a method that can potentially be used to determine the dominant ore-forming processes that occurred during the formation of granite-related ore deposits, and suggest that this method can be employed to determine the formation history of the W-Sn ore deposits found elsewhere within the Nanling Metallogenic Belt.
