Fluid inclusion and light stable isotope study of the Climax molybdenum deposits

The Climax mine contains three molybdenite ore bodies and widespread late quartz-pyrite-sericite barren mineralization, each related to separdte 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. •80 values of quartz range from +8.4 to 10.9 per mil; •80 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 350øC with 8•80 values of +3.0 to 5.5 per mil. •80 values of K-feldspars range from--4.5 to +7.5 per mil. This wide range indi-cates partial reequilibration of the feldspar with later, isotopically light, waters. Two muscovites have 8D values of--146 and--91 per mil; sericite ranges from--168 to--116 per mil. The calculated 8D values of water at 275øC 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 •O values of--0.9 to--2.2 and 8D values of--162 per mil. Calculated water at 250øC in equilibrium with kaolinitc 8•80 values of--4.7 to--6 and 8D 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