Absolute timing of sulfide and gold mineralization: A comparison of Re-Os molybdenite and Ar-Ar mica methods from the Tintina Gold Belt, Alaska

doi:10.1130/0091-7613(2002)030<0791:ATOSAG>2.0.CO;2

Absolute timing of sulfide and gold mineralization: A comparison of Re-Os molybdenite and Ar-Ar mica methods from the Tintina Gold Belt, Alaska

¹Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada
²Yukon Geology Program, Box 203 (F-3), Whitehorse, Yukon Y1A 2C6, Canada
³Department of Geology and Geophysics, University of Alaska Fairbanks, P.O. Box 755780, Fairbanks, Alaska 99775-5780, USA
⁴Teck Cominco Limited, Suite 600-200 Burrard Street, Vancouver, British Columbia V6C 3L9, Canada
⁵Fairbanks Gold Mining Inc., P.O. Box 73726, Fairbanks, Alaska 99707, USA
⁶U.S. Geological Survey, Box 25046, MS 964, Denver Federal Center, Denver, Colorado 80225-0046, USA

Abstract

New Re-Os molybdenite dates from two lode gold deposits of the Tintina Gold Belt, Alaska, provide direct timing constraints for sulfide and gold mineralization. At Fort Knox, the Re-Os molybdenite date is identical to the U-Pb zircon age for the host intrusion, supporting an intrusive-related origin for the deposit. However, ⁴⁰Ar/³⁹Ar dates from hydrothermal and igneous mica are considerably younger. At the Pogo deposit, Re-Os molybdenite dates are also much older than ⁴⁰Ar/³⁹Ar dates from hydrothermal mica, but dissimilar to the age of local granites. These age relationships indicate that the Re-Os molybdenite method records the timing of sulfide and gold mineralization, whereas much younger ⁴⁰Ar/³⁹Ar dates are affected by post-ore thermal events, slow cooling, and/or systemic analytical effects. The results of this study complement a growing body of evidence to indicate that the Re-Os chronometer in molybdenite can be an accurate and robust tool for establishing timing relations in ore systems.