On ¹⁴C Age of Coalified Wood found in the Kaolin Deposit of the Itaya Mine, Yamagata Prefecture, Japan

Abstract

The Itaya mine, the largest domestic kaolin mine for paper clay, is located on the eastern slope of the Quaternary Azuma volcano where formations of lavas, pyroclastic rocks and mud flows are extensively distributed. The underlying Tertiary formations are exposed at several places as windows.
Two kaolin bodies are under operation at present. Kaolinite is a common mineral of both bodies, while sericite is found only in the layer deposit No.1, and dickite is locally found at the center of the deposit No.2. It has been made clear that they were both formed by hydrothermal alteration. Nevertheless, the controversy about the age of original rocks and alteration has not been settled.
In 1968, the writer found a piece of coalified wood in a kaolinized andesite lava of the deposit No.2. The absolute age of the coalified wood was determined by ¹⁴C method in the laboratory of Prof. Kigoshi, Gakushuin University, to be
30, 600±2, 200 yrs. B.P.
This result reveals the highest possibility of the Upper Pleistocene age of original rocks of the deposit No. 2, and denies the Tertiary mineralization. The actual age of the hydrothermal alteration that formed the kaolin deposit must be some time between the age determined and the present. Geologic evidences and the dating result indicate that the deposit No.2 was formed by volcanic activities of the Azuma volcano.