Presentation Information
[O12-P72]Identification of Metal Contents in Rocks and Geological Considerrations at the Imooka Mine
*Miharu Tamura1, *Momoka Iwamoto1, *Kanon Sasaki1, *Miharu Motoyama1, *Hina Morisaki1 (1. Tsuyama high school Science and Math Department)
Keywords:
bismuth,Qualitative analysis,Hydrothermal deposit,Sericite formation
1 Background
Bismuth is used as a substitute for lead, and while demand has been increasing in recent years, Japan currently relies heavily on imports.
2 Objective
While researching bismuth, I came across a reference stating that bismuth deposits exist in the local town of Kagamino. Believing that large-scale extraction of bismuth in Kagamino could contribute to domestic production, I decided to investigate the characteristics of the rock that should be collected for bismuth recovery at the Imogahara Mine, located in Okutsu, Kagamino Town, Okayama Prefecture.
3 Methods
・Preparation
From the rock debris (tailings) scattered near the entrance of the Imooka Mine, we selected and collected samples with a high specific gravity that appeared likely to contain metal.
・Results
We observed a large number of rocks with a silvery or golden metallic sheen scattered around the mine entrance.
Most of the rocks we collected were granite, including pinkish and greenish varieties. We also observed dense stands of snake grass—an indicator plant for heavy metal contamination—growing along the mountain trail leading from the mine entrance.
・Experiment 1
We conducted a detailed identification of the ore and minerals using field guides, expert opinions, and a stereomicroscope. During this process, we collected samples of the minerals and assigned them sample numbers.
・Result 1
Photographs of Sample No. 2207 taken under a stereomicroscope revealed numerous crystals appearing to be specularite, as well as crystals identified as chalcopyrite,
malachite, and chalcopyrite. Furthermore, a mineral believed to be bismuth, exhibiting a blue metallic luster in some areas, was observed.
・Experiment 2
Following the flowchart, we identified the metals present.
・Result 2
When hydrochloric acid was added, the color of all solutions turned yellowish-brown, indicating that the ore contained iron. When hydrogen sulfide was passed through the samples, black precipitates formed in samples such as No. 2207—which contained chalcopyrite, limonite, and malachite—suggesting the possible presence of copper and bismuth. When ammonia was added, the solution turned a characteristic blue, indicating the presence of Cu. However, since the bismuth precipitate is colorless, it was not possible to determine its presence.
・Experiment 3
To determine whether bismuth was present—a conclusion that could not be reached in Experiment 2—we performed LIBS analysis, which is more precise than qualitative analysis, on mineral sample No. 2207, which was identified in Experiment 2 as potentially containing bismuth.
・Result 3
Bismuth and copper were detected in sample No. 2207, which contained malachite, confirming Result 2.
・Experiment 4
The rock’s texture was observed using a polarizing microscope.
・Result 4
It was observed that plagioclase had been sericite-ized and had undergone hydrothermal alteration.
4 Discussion
“Hydrothermal alteration” is believed to be related to the ‘color’ of rocks. When exposed to hydrothermal fluids, hornblende and biotite contained in the rock transform into a green mineral called “chlorite.” Therefore, it is presumed that the “green granite” in which bismuth was detected appears green because it underwent hydrothermal alteration and transformed into chlorite.
5. Conclusion
The minerals at the Imooka Mine consist primarily of iron and also contain metals such as copper and bismuth. However, the bismuth content is trace, and at this stage, it has been determined that bismuth has no economic value. Furthermore, it was shown that the bismuth-bearing minerals have a high specific gravity and occur within green granite rich in copper. It was also concluded that this is a hydrothermal deposit with granite as the host rock.
6. Acknowledgments
I would like to express my sincere gratitude to everyone who cooperated in this research, as well as to my professors.
7. References
Nihonnochisitu [tyuugokutihou] iinnkaihenn:nihonnnochisitu7 tyuugokutihou(1987)
KinoshitaKameki:gennsyokukousekizukann zoku gennsyokukousekizukian(1957)
Yamaguchidaigaku kougakubu gakujyutusiryoutenjisiryoukann:gennsobetukouseki (Bisumasukou)(2011)
Bismuth is used as a substitute for lead, and while demand has been increasing in recent years, Japan currently relies heavily on imports.
2 Objective
While researching bismuth, I came across a reference stating that bismuth deposits exist in the local town of Kagamino. Believing that large-scale extraction of bismuth in Kagamino could contribute to domestic production, I decided to investigate the characteristics of the rock that should be collected for bismuth recovery at the Imogahara Mine, located in Okutsu, Kagamino Town, Okayama Prefecture.
3 Methods
・Preparation
From the rock debris (tailings) scattered near the entrance of the Imooka Mine, we selected and collected samples with a high specific gravity that appeared likely to contain metal.
・Results
We observed a large number of rocks with a silvery or golden metallic sheen scattered around the mine entrance.
Most of the rocks we collected were granite, including pinkish and greenish varieties. We also observed dense stands of snake grass—an indicator plant for heavy metal contamination—growing along the mountain trail leading from the mine entrance.
・Experiment 1
We conducted a detailed identification of the ore and minerals using field guides, expert opinions, and a stereomicroscope. During this process, we collected samples of the minerals and assigned them sample numbers.
・Result 1
Photographs of Sample No. 2207 taken under a stereomicroscope revealed numerous crystals appearing to be specularite, as well as crystals identified as chalcopyrite,
malachite, and chalcopyrite. Furthermore, a mineral believed to be bismuth, exhibiting a blue metallic luster in some areas, was observed.
・Experiment 2
Following the flowchart, we identified the metals present.
・Result 2
When hydrochloric acid was added, the color of all solutions turned yellowish-brown, indicating that the ore contained iron. When hydrogen sulfide was passed through the samples, black precipitates formed in samples such as No. 2207—which contained chalcopyrite, limonite, and malachite—suggesting the possible presence of copper and bismuth. When ammonia was added, the solution turned a characteristic blue, indicating the presence of Cu. However, since the bismuth precipitate is colorless, it was not possible to determine its presence.
・Experiment 3
To determine whether bismuth was present—a conclusion that could not be reached in Experiment 2—we performed LIBS analysis, which is more precise than qualitative analysis, on mineral sample No. 2207, which was identified in Experiment 2 as potentially containing bismuth.
・Result 3
Bismuth and copper were detected in sample No. 2207, which contained malachite, confirming Result 2.
・Experiment 4
The rock’s texture was observed using a polarizing microscope.
・Result 4
It was observed that plagioclase had been sericite-ized and had undergone hydrothermal alteration.
4 Discussion
“Hydrothermal alteration” is believed to be related to the ‘color’ of rocks. When exposed to hydrothermal fluids, hornblende and biotite contained in the rock transform into a green mineral called “chlorite.” Therefore, it is presumed that the “green granite” in which bismuth was detected appears green because it underwent hydrothermal alteration and transformed into chlorite.
5. Conclusion
The minerals at the Imooka Mine consist primarily of iron and also contain metals such as copper and bismuth. However, the bismuth content is trace, and at this stage, it has been determined that bismuth has no economic value. Furthermore, it was shown that the bismuth-bearing minerals have a high specific gravity and occur within green granite rich in copper. It was also concluded that this is a hydrothermal deposit with granite as the host rock.
6. Acknowledgments
I would like to express my sincere gratitude to everyone who cooperated in this research, as well as to my professors.
7. References
Nihonnochisitu [tyuugokutihou] iinnkaihenn:nihonnnochisitu7 tyuugokutihou(1987)
KinoshitaKameki:gennsyokukousekizukann zoku gennsyokukousekizukian(1957)
Yamaguchidaigaku kougakubu gakujyutusiryoutenjisiryoukann:gennsobetukouseki (Bisumasukou)(2011)