The Climax mine contains three molybdenite ore bodies and widespread late quartz-pyrite-sericite barren mineralization, each related to separate intrusive phases of the Climax stock. Alteration zones spatially related to each molybdenite ore body include a silica zone below, a potassium-silicate zone that approximately coincides with ore, and overlying quartz-sericite-pyrite-topaz, argillic, and propylite zones.delta 18 O values of quartz range from +8.4 to 10.9 per mil; delta 18 O values of muscovite and sericite range from --0.8 to +7.5 per mil. Eight of ten sericite values are between +5.8 and +7.5. All of the quartz and most of the sericite is in isotopic equilibrium with a calculated water at 350 degrees C with delta 18 O values of +3.0 to 5.5 per mil.delta 18 O values of K-feldspars range from --4.5 to +7.5 per mil. This wide range indicates partial reequilibration of the feldspar with later, isotopically light, waters.Two muscovites have delta D values of --146 and --91 per mil; sericite ranges from --168 to --116 per mil. The calculated delta D values of water at 275 degrees C in equilibrium with sericite are --144 to --92. This range is the same as that of fluid inclusions in ore samples.Kaolinite in the argillic zone has delta 18 O values of --0.9 to --2.2 and delta D values of --162 per mil. Calculated water at 250 degrees C in equilibrium with kaolinite delta 18 O values of --4.7 to -6 and delta D of about -130 per mil.The isotopic and fluid inclusion data best fit a model whereby the Climax ore bodies were formed from a hydrothermal fluid that originated by mixing light and heavy waters. The light water is isotopically similar to present-day meteoric water; the heavy water has the isotopic composition postulated for magmatic water, although it could be meteoric water that was heavier than present-day meteoric water.