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A shallow environment of formation has been inferred for Kuroko ores in northern Japan at least in part because of their association with vesicular basalt flows. Consideration of the PTX conditions which affect vesiculation demonstrates that reliable depth inferences can be made only if the volatile content of the melt can be independently determined. Vesicle volume and calculated water solubilities are used to estimate the initial water content of the Kuroko basalts. The calculated H 2 O values indicate that most of the vesiculated Kuroko basalts could have been generated at seawater depths up to 4,000 mat total H 2 O contents near 2 wt percent. Analytical data on volatiles in island-arc related lavas, and on the distribution of vesicles in some abyssal basalts, suggest that such volatile concentrations are realistic in environments similar to that of the Kuroko deposits. The vesicular basalts associated with the ores are thus not reliable indicators of the depth of ore formation and do not restrict the Kuroko deposits to depths of less than 1,000 m.

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