3:30 PM - 5:00 PM
[SCG48-P06] Contact metmorphism and gold mineralization in the Mano deposit, Miyagi, Japan
Keywords:Kitakami mountains, contact metamorphism, gold mineralization, reaction rim
There are many vein-type gold deposits which are related to the intrusion of Cretaceous granitoid in Kitakami Mountains, Northeast Japan. These are classified into mesothermal gold deposit, and they are suggested to be related to the surrounding granitic magma.
In this study, we conducted geologic survey, petrography, and chemical analysis of sulfide mineral to clarify the genesis of the Mano deposit, in Miyagi Prefecture, Japan.
Based on geological survey, hornfels, diorite which intrude hornfels, and quartz veins which are hosted by hornfels were observed in the Mano deposit. Three quartz veins are observed and up to 4 cm wide, which strike NE and dip S. Quartz textures in the quartz vein show sutured quartz grain boundary and undulous extinction. A reaction rim is observed in the hornfels, with a green band and a red band 2 mm wide outside the green one surrounding the blue-gray and white parts, with differences in the composed minerals and their grain sizes.
According to microscopic observation, hornfels is composed of quartz, plagioclase, clinopyroxene, chlorite, pyrrhotite, pyrite, and arsenopyrite. The outer of reaction rim of hornfels is composed of quartz, plagioclase, clinopyroxene, and only trace amounts of pyrrhotite are observed as sulfide mineral. Diorite is composed of plagioclase, amphibole and clinopyroxene. The ore minerals in quartz are native gold, native bismuth, bismuth-tellurium mineral, and pyrite. They occur as microfracture infill. The occurrences of gold can be classified into 4 types: (1) occur independent; (2) occur around bismuth-tellurium mineral; (3) occur associated with bismuth-tellurium mineral; (4) occur an alternate part of bismuth-tellurium mineral.
EPMA analysis reveals that the gold concentrations of the pyrrhotite and arsenopyrite in inner of the reaction rim of hornfels are up to 840 ppm and up to 1010 ppm, respectively.
The quartz textures such as sutured quartz grain boundary and undulous extinction and the occurrences of ore minerals show that quartz veins are affected by metamorphism.
These results suggest that the gold mineralization in the Mano deposit is closely related to contact metamorphism and may involve the leaching of gold associated with the loss of sulfide minerals due to the reaction between hornfels and hydrothermal fluids, as observed at outcrop of hornfels.
In this study, we conducted geologic survey, petrography, and chemical analysis of sulfide mineral to clarify the genesis of the Mano deposit, in Miyagi Prefecture, Japan.
Based on geological survey, hornfels, diorite which intrude hornfels, and quartz veins which are hosted by hornfels were observed in the Mano deposit. Three quartz veins are observed and up to 4 cm wide, which strike NE and dip S. Quartz textures in the quartz vein show sutured quartz grain boundary and undulous extinction. A reaction rim is observed in the hornfels, with a green band and a red band 2 mm wide outside the green one surrounding the blue-gray and white parts, with differences in the composed minerals and their grain sizes.
According to microscopic observation, hornfels is composed of quartz, plagioclase, clinopyroxene, chlorite, pyrrhotite, pyrite, and arsenopyrite. The outer of reaction rim of hornfels is composed of quartz, plagioclase, clinopyroxene, and only trace amounts of pyrrhotite are observed as sulfide mineral. Diorite is composed of plagioclase, amphibole and clinopyroxene. The ore minerals in quartz are native gold, native bismuth, bismuth-tellurium mineral, and pyrite. They occur as microfracture infill. The occurrences of gold can be classified into 4 types: (1) occur independent; (2) occur around bismuth-tellurium mineral; (3) occur associated with bismuth-tellurium mineral; (4) occur an alternate part of bismuth-tellurium mineral.
EPMA analysis reveals that the gold concentrations of the pyrrhotite and arsenopyrite in inner of the reaction rim of hornfels are up to 840 ppm and up to 1010 ppm, respectively.
The quartz textures such as sutured quartz grain boundary and undulous extinction and the occurrences of ore minerals show that quartz veins are affected by metamorphism.
These results suggest that the gold mineralization in the Mano deposit is closely related to contact metamorphism and may involve the leaching of gold associated with the loss of sulfide minerals due to the reaction between hornfels and hydrothermal fluids, as observed at outcrop of hornfels.