2:15 PM - 2:30 PM
[SCG54-03] Chronological study on Togi mine, Shika town, Hakui gun, Ishikawa Prefecture
★Invited Papers
Keywords:Togi mine, chronology, gold-silver deposit, formation of the Sea of Japan
Estimating ages of deposits and alteration zones are important to consider a formation of deposits, and thus, various chronological methods are applied to economic geology. In this study, we measured an age of the Togi gold-silver deposit using thermoluminescence and K-Ar methods to reveal the formation process and the period of the Togi mine.
The Togi mine is classified as vein-type gold-silver deposits. Host igneous rocks of the deposits are pyroxene andesite lava and pyroclastic rocks belonging to the Neogene Anamizu formation. The mining areas of the Togi mine are divided into 7 areas. We targeted at the Togo No.3 tunnel, Urukami area.
A part of gold-silver deposits accompanied by igneous rocks in Japan are formed after 2 Ma. At first, the formation age of the Togi deposit were measured by thermoluminescence method to consider the possibility of the formation age that is newer than 1 Ma. White clayey sample was collected from the Togo No.3 tunnel. An acquired age are 7.8±3.4 Ma, however, it might be undervalued age because it estimated from the extrapolation. Therefore, K-Ar method were applied to reveal more accurate age. Two samples were measured; one is bluish gray clayey sample, the other is fresh pyroxene andesite. The bluish gray clayey sample were collected from the outcrop, apart about 380 m from the Togo No.3 tunnel, where might be related to the thermal fluid that formed the Togi deposit. The fresh pyroxene andesite is also measured to validate the relationship between the Togi deposit and the host rock. The ages of the Togi deposit and the host rock were estimated to 17.68±0.41 Ma and 17.52±0.43 Ma, respectively, and their ages are very close. Thus, it is considered that the gold-silver deposits of the Togi mine were formed by the hydrothermal activity which are related to the pyroxene andesite surrounding the Togi deposit.
Furthermore, the age of the Togi deposit and the host rock are coincided with the period of expansion of the Sea of Japan. The faults related to the expansion of the Sea of Japan in this region have NE-SW streak. The Togigawa Nangan Fault also has same streak, and the dip angle has been estimated to about 60º. Thus, the Togigawa Nangan Fault might be formed during the period of expansion of the Sea of Japan. Finally, the formation of Togi vein-type gold-silver deposits are considered that the thermal fluid contains Au and Ag elements filled the fractures formed by the activity of the Togigawa Nangan Fault.
As this study has shown, gold-silver ore formation in Japan is intimately related to tectonics occurred in specific period. If the relationship between tectonics in each country and ore formation are clarified, it should be a valuable information to effective mining.
The Togi mine is classified as vein-type gold-silver deposits. Host igneous rocks of the deposits are pyroxene andesite lava and pyroclastic rocks belonging to the Neogene Anamizu formation. The mining areas of the Togi mine are divided into 7 areas. We targeted at the Togo No.3 tunnel, Urukami area.
A part of gold-silver deposits accompanied by igneous rocks in Japan are formed after 2 Ma. At first, the formation age of the Togi deposit were measured by thermoluminescence method to consider the possibility of the formation age that is newer than 1 Ma. White clayey sample was collected from the Togo No.3 tunnel. An acquired age are 7.8±3.4 Ma, however, it might be undervalued age because it estimated from the extrapolation. Therefore, K-Ar method were applied to reveal more accurate age. Two samples were measured; one is bluish gray clayey sample, the other is fresh pyroxene andesite. The bluish gray clayey sample were collected from the outcrop, apart about 380 m from the Togo No.3 tunnel, where might be related to the thermal fluid that formed the Togi deposit. The fresh pyroxene andesite is also measured to validate the relationship between the Togi deposit and the host rock. The ages of the Togi deposit and the host rock were estimated to 17.68±0.41 Ma and 17.52±0.43 Ma, respectively, and their ages are very close. Thus, it is considered that the gold-silver deposits of the Togi mine were formed by the hydrothermal activity which are related to the pyroxene andesite surrounding the Togi deposit.
Furthermore, the age of the Togi deposit and the host rock are coincided with the period of expansion of the Sea of Japan. The faults related to the expansion of the Sea of Japan in this region have NE-SW streak. The Togigawa Nangan Fault also has same streak, and the dip angle has been estimated to about 60º. Thus, the Togigawa Nangan Fault might be formed during the period of expansion of the Sea of Japan. Finally, the formation of Togi vein-type gold-silver deposits are considered that the thermal fluid contains Au and Ag elements filled the fractures formed by the activity of the Togigawa Nangan Fault.
As this study has shown, gold-silver ore formation in Japan is intimately related to tectonics occurred in specific period. If the relationship between tectonics in each country and ore formation are clarified, it should be a valuable information to effective mining.