Abstract
The conditions of formation of dawsonite-bearing carbonate veins in the northern flank of the Izumi Mountains (southern Osaka prefecture) are investigated on the basis of oxygen acd carbon isotopic compositions of carbonates. The calculated isotopic ratios of calcite largely support the precipitation from CO2-bearing fluid having isotopic characteristics similar to the end-member Arima-type hot brine (Kazahaya et al., 2009).