DIFFUSIONAL O-18 LOSS FROM INCLUSION WATER IN A NATURAL HYDROTHERMAL QUARTZ FROM THE KANEUCHI TUNGSTEN DEPOSIT, JAPAN

In hydrothermal quartz from the Kaneuchi tungsten deposit of Honsyu is land, Japan, the smaller primary fluid inclusions have the lower delta O-18 values. This correlation is well accounted for by a quantitative model based on (isotropic or anisotropic) O-18 diffusion through quar tz. The model yields a room temperature O-18 diffusivity that is close to the extrapolated diffusivity of water molecules measured by Cordie r et al. (1988) but much higher than the extrapolated diffusivity of s tructural oxygen measured by Farver and Yund (1991). The observed corr elation between the size of primary fluid inclusions in quartz and the ir delta(18)O((water)) is thus, well explained by relatively fast diff usion of oxygen as water molecules.