9628150 Ruiz The duration of hydrothermal activity capable of forming a large ore deposit and the source of ore-forming elements are central questions in the study of metallogenesis. S particular isotopic method that can be useful in addressing these two questions is the Re-Os system because Os, as a siderophile element, is concentrated in sulfides. thus it is theoretically possible to directly date sulfides instead of associated silicates by the Re-Os isotopic system and it is also possible to use the isotopic ratio of Os to trace the relative importance of crustal and mantle sources in ore deposits. the P.I.s have already made great progress in using molybdenite to date ore deposits with Re-Os isotopes and here the P.I.s propose to: (1) Continue their investigations of the post-crystallization behavior of molybdenite. (2) Determine the usefulness of other sulfides to date base metal porphyry systems by the isochron method. (3) Constrain, using Re-Os isotopes, the source of metals in base metal porphyry deposits, which represent accumulations of chalcophile elements within the earth's crust. The results of this study will provide new insights into base metal porphyry metallogenesis and the crust mantle interactions in convergent margins.
