11:00 〜 13:00
[HRE13-P06] Geochemical characteristics of the black and yellow ores in the Ezuri Kuroko deposit, Akita, Japan
キーワード：Ezuri, Kuroko, Hokuroku, Sulfur isotopes
The Ezuri Kuroko deposit is located in the central part of the Hokuroku district, Akita Prefecture, Japan. The stratiform black and yellow ores are typical occurrence of the deposits, which are hosted by Miocene basaltic tuff and dacitic lava in the Miocene age.
In this study, the samples of black and yellow ores from the Ezuri mine were examined under the microscope. The minerals in the ores are principally fine-grained. The black ores are composed of sphalerite, galena, pyrite, chalcopyrite, tetrahedrite and minor covellite. The yellow ores consist mainly of pyrite, chalcopyrite, bornite, minor sphalerite and galena. The gangue minerals in the ores are mainly quartz, gypsum and barite.
We carried out bulk chemical analysis on the black and yellow ores using atomic absorption spectroscopy for copper, zinc and lead and inductively coupled plasma mass spectrometry for gold and silver. The average contents of the black ores are 19.1 wt% Zn, 5.49 wt% Cu and 3.51 wt% Pb, while the yellow ores contain 14.9 wt% Cu, 1.51 wt% Zn and 0.20 wt% Pb. Gold concentration in the black ores ranges from 0.05 to 22.8 ppm with a mean value of 2.88 ppm, while silver concentration ranges from and 23.4 to 4135 ppm with a mean value of 606 ppm. The yellow ores contain gold ranging from 0.81 to 1.68 ppm with an average value of 1.25 ppm and silver ranging from 77.0 to 659 ppm with an average value of 368 ppm. Positive correlation between Cu and Ag, Zn and Ag, and Au and Ag were observed.
Pyrite, chalcopyrite, galena and sphalerite from both the black and yellow ores were chosen for sulfur isotope analysis. The analysis yielded δ34S = -2.5 to +5.1‰, suggesting the source of sulfur was most likely from a magma.
In this study, the samples of black and yellow ores from the Ezuri mine were examined under the microscope. The minerals in the ores are principally fine-grained. The black ores are composed of sphalerite, galena, pyrite, chalcopyrite, tetrahedrite and minor covellite. The yellow ores consist mainly of pyrite, chalcopyrite, bornite, minor sphalerite and galena. The gangue minerals in the ores are mainly quartz, gypsum and barite.
We carried out bulk chemical analysis on the black and yellow ores using atomic absorption spectroscopy for copper, zinc and lead and inductively coupled plasma mass spectrometry for gold and silver. The average contents of the black ores are 19.1 wt% Zn, 5.49 wt% Cu and 3.51 wt% Pb, while the yellow ores contain 14.9 wt% Cu, 1.51 wt% Zn and 0.20 wt% Pb. Gold concentration in the black ores ranges from 0.05 to 22.8 ppm with a mean value of 2.88 ppm, while silver concentration ranges from and 23.4 to 4135 ppm with a mean value of 606 ppm. The yellow ores contain gold ranging from 0.81 to 1.68 ppm with an average value of 1.25 ppm and silver ranging from 77.0 to 659 ppm with an average value of 368 ppm. Positive correlation between Cu and Ag, Zn and Ag, and Au and Ag were observed.
Pyrite, chalcopyrite, galena and sphalerite from both the black and yellow ores were chosen for sulfur isotope analysis. The analysis yielded δ34S = -2.5 to +5.1‰, suggesting the source of sulfur was most likely from a magma.