抄録
The area southeast of the Lake Towada lies in the eastern border of the Green Tuff region, which are characterized by submarine volcanic activities in the Miocene. Recently a number of boreholes were drilled through the Miocene sediments for the exploration of ore deposits. Core samples from these boreholes were used for vitrinite reflectivity study. Lateral and vertical changes in vitrinite reflectivity of the Miocene sediments are illustrated in the sections and plan showing isoreflectivity lines. Vitrinite reflectivity of the Miocene sediments increases rapidly from the east to the west. The isoreflectivity map at the top of the Yotsuzawa Formation shows changes in rank from subbituminous to anthracite at a short distance. Reflectivity gradient of the boreholes in the west of the area is steeper than in the east. Stratiform ore bodies of Kuroko and copper-lead-zinc veins occur in the west of the area. The mineralization were restricted to zones above 2% Rmax at the top of the Yotsuzawa Formation. Isoreflectivity pattern indicates the development of hydrothermal activities associated with the volcanism in the Miocene age.
