Abstract

New Re–Os molybdenite and U–Pb zircon dates from deposits of the Tombstone Gold Belt provide direct timing constraints for sulphide mineralization and crystallization of spatially associated plutons. At Clear Creek Re–Os molybdenite dates (93.6 ± 0.3 to 92.4 ± 0.4 Ma) are in excellent agreement with the host intrusion U–Pb zircon age (92.3 ± 0.3 Ma). Consequently we propose the nominally younger existing 40Ar/39Ar hydrothermal mica ages (91.7 ± 0.4 and 90.0 ± 0.3 Ma) for Clear Creek are a result of slow cooling. At Dublin Gulch, the Re–Os molybdenite date (93.2 ± 0.3 Ma) for a late stage vein is nominally younger than the host intrusion U–Pb zircon age (94.0 ± 0.3 Ma), in agreement with the deposits paragenesis. The U–Pb zircon date (92.1 ± 0.2 Ma) for the Mactung pluton, which lies adjacent to the W-skarn, has a younger age than the Re–Os molybdenite dates (97.5 ± 0.5 Ma). Fluid inclusion geochemical data for ore-fluid indicate a magmatic origin for the W-skarn. However, the U–Pb and Re–Os age data suggest that the exposed Mactung stock is not the source of ore-fluid for the W-skarn and that the progenitor pluton for ore-fluid is unknown. The robust age constraints obtained for mineralization and magmatism in this study are in accord with the hypothesis that these deposits are intrusion-related ore systems. The results are also in agreement with previous studies demonstrating that the Re–Os molybdenite chronometer can provide accurate and precise dates for the timing of metallic mineralization with rigorous sampling protocol.

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