A HISTORY AND FUTURE INSIGHTS OF RHENIUM-OSMIUM GEOCHRONOLOGY OF SEDIMENTARY ROCKS, PETROLEUM SYSTEMS, AND ORE DEPOSITS

Geochronology is fundamental to understand the age, rates and durations of Earth processes. This concerned Arthur Holmes for much of his career with the task of defining a geological time scale. A topic still important to Earth Scientists today and specifically concerns the dating of sedimentary rocks. Herein I explore the Re-Os geochronology of sedimentary rocks, petroleum and sulphide minerals.

The past decade has seen the pioneering research of Re-Os organic-rich sedimentary rock geochronology blossom into a tool that can now to be used to determine depositional ages of organic-rich rock units that have experienced up to low grade greenschist metamorphism. This direct sedimentary rock dating has been critical in the absence of volcanic horizons. As a result, this ability has been applied to timescale calibration, basin correlation, Formation duration and the timing of key Earth events, e.g., Neoproterozoic glaciations.

Earth Scientists are also concerned with the absolute timing of petroleum generation and source fingerprinting. The organophilic behavior of Re and Os has permitted the use of the Re-Os geochronometer to date petroleum generation in several oil fields. This direct petroleum generation dating method yields ages indistinguishable from basin models and another absolute dating methods (e.g., UK North Atlantic). In addition to Re-Os dating of petroleum, the ¹⁸⁷Os/¹⁸⁸Os of petroleum is inherited from the source rock and thus can be used, together with Pt/Pd, to fingerprint petroleum to its source, and has shown the Canadian Oil Sands are sourced from the Jurassic Gordondale Fm and not the Exshaw Fm.

Geochronology is key for developing genetic models for ore deposits. Direct dating of sulphide mineralization using the Re-Os geochronometer has been proven viable using molybdenite, pyrite, chalcopyrite and bornite. This has permitted the ability to define multiple mineralization events, evaluate the origin of metals and improve genetic models (e.g., Fort Knox, Murantau, Ruby Creek).

The future for Re-Os geochronology in petroleum and sulphide systems holds considerable promise. The improved precision of isotopic measurements, calibrated tracer (spike) solutions and decay constant will allow increased precision of ages from low ppt Re-Os bearing petroleum and sulphide minerals.