A schematic model showing the sources of hot waters being discharged at the surface in the Kuju-Iwoyama of the Kuju volcano has been developed. Based on the isotopic characteristics of these fluids it is inferred that deep magmatic fluid mixes with thermal waters derived from rainwater in a shallow geothermal reservoir, and with local groundwaters in a deeper reservoir. These thermal waters feed hot springs that discharge waters with Cl/SO(4) ratios that differ from that of the fumaroles on Kuju-Iwoyama, due to the addition Of SO(4)(2)- ions produced by the decomposition of native sulfur and mixing with magmatic fluid of high Cl content. (C) 2009 Elsevier Ltd. All rights reserved.