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[SCG48-P04] Characteristics of the hydrothermal fluids that formed the Waga-sennin iron skarn deposit, Iwate Prefecture, Japan.
Keywords:hematite ore deposit, garnet, hornblende geothermobarometer
Waga-sennin iron skarn deposit in Iwate Prefecture is dominated by hematite ore, and is the only deposit in Japan other than the Akatani iron ore deposit in Niigata Prefecture that is rich in such hematite.
The objective of this study is to identify the physicochemical conditions of the hydrothermal fluids that formed Waga-sennin iron skarn deposit.
Research methods include geological survey and rock description, chemical composition analysis of garnet, a prominent skarn mineral, and chemical composition analysis of granodiorite whole rocks and hornblende.
The limestones found at this deposit are often observed graphite due to contact metamorphism. The granodiorite observed as intrusive rocks shows peraluminous composition. The granodiorite contains hornblende up to 3 cm in diameter with Al2O3 content ranging from 5.64 to 8.40 (wt%).
The abundance of skarn minerals is garnet > clinopyroxene. The garnet is classified into two types: isotropic (without zoning) and anisotropic (with zoning). Most of the hematite crystals are plate-euhedral shape, and rarely magnetite-forming crystals are observed. Regardless of its form, garnet is enriched in andradite as a endmember. The isotropic ones have a composition of Andradite95>, and those with zoning alternate between Adr-rich bands (Adr90-99, Grs0.1-10) and grossular-rich bands ( Adr65-99, Grs0.1-34). (Adr : Ca3Fe2Si3O12) (Grs : Ca3Al2Si2O12)
The abundance of hematite, the predominance of iron in garnet, and the fact that garnet > clinopyroxene strongly suggest that Waga-sennin deposit was formed in an oxidizing environment. Grossulars tend to form in a reducing environment, and the fact that Adr and Grs grow alternately and have a zoning texure suggests the existence of oxidizing and reducing environments. From the results of quantitative analysis of hornblende, values of 660~700°C and 1.60~3.05 (kbar) were obtained using a hornblende geothermobarometer. The pressure indicates that the formation depth is approximately 4.81-10.58 km, suggesting that the granodiorite was intruded in a relatively shallow environment within the iron skarn deposit.
The temperature of the granodiorite that formed Waga-sennin deposit was 660-700°C and was penetrated at a depth of 4.81-10.58 km, indicating that the hydrothermal environment was a hydrothermal environment that underwent repeated oxidation-reduction cycles.
The objective of this study is to identify the physicochemical conditions of the hydrothermal fluids that formed Waga-sennin iron skarn deposit.
Research methods include geological survey and rock description, chemical composition analysis of garnet, a prominent skarn mineral, and chemical composition analysis of granodiorite whole rocks and hornblende.
The limestones found at this deposit are often observed graphite due to contact metamorphism. The granodiorite observed as intrusive rocks shows peraluminous composition. The granodiorite contains hornblende up to 3 cm in diameter with Al2O3 content ranging from 5.64 to 8.40 (wt%).
The abundance of skarn minerals is garnet > clinopyroxene. The garnet is classified into two types: isotropic (without zoning) and anisotropic (with zoning). Most of the hematite crystals are plate-euhedral shape, and rarely magnetite-forming crystals are observed. Regardless of its form, garnet is enriched in andradite as a endmember. The isotropic ones have a composition of Andradite95>, and those with zoning alternate between Adr-rich bands (Adr90-99, Grs0.1-10) and grossular-rich bands ( Adr65-99, Grs0.1-34). (Adr : Ca3Fe2Si3O12) (Grs : Ca3Al2Si2O12)
The abundance of hematite, the predominance of iron in garnet, and the fact that garnet > clinopyroxene strongly suggest that Waga-sennin deposit was formed in an oxidizing environment. Grossulars tend to form in a reducing environment, and the fact that Adr and Grs grow alternately and have a zoning texure suggests the existence of oxidizing and reducing environments. From the results of quantitative analysis of hornblende, values of 660~700°C and 1.60~3.05 (kbar) were obtained using a hornblende geothermobarometer. The pressure indicates that the formation depth is approximately 4.81-10.58 km, suggesting that the granodiorite was intruded in a relatively shallow environment within the iron skarn deposit.
The temperature of the granodiorite that formed Waga-sennin deposit was 660-700°C and was penetrated at a depth of 4.81-10.58 km, indicating that the hydrothermal environment was a hydrothermal environment that underwent repeated oxidation-reduction cycles.