America; West of Shetlands oilfields. Selby’s research has developed a unique geochemical toolbox using rhenium, osmium, platinum and palladium that constrain more accurate geological models leading to better reserve predictions. The toolbox provides previously unavailable geological time constraints and source identification of resources e. The underpinning research carried out by Selby TOTAL Reader in Petroleum Geoscience, appointed and his research group at Durham University from appointment to present addresses longstanding academic industry-related issues concerning the development of subsurface Earth resources. Specifically, exactly when, how and where do resources, such as oil and copper, form in rocks? Analytical and technological advances, developed in part by research at Durham, have permitted the use of previously challenging geochemical methods to help answer old, but critically important geological questions. Selby, his research group and international collaborations 6 PhD students, 2 post-doctoral researchers, United States and Canada Geological Survey research staff; Prof.
Rhenium—osmium dating , method of determining the age of the important ore mineral molybdenite; the method is based upon the radioactive decay of rhenium to osmium The rhenium—osmium ratio in most minerals is too low to be of general use as a dating technique, but molybdenite molybdenum disulfide, MoS 2 has a very high ratio of rhenium to osmium; and workers have found that the osmium in molybdenite is practically pure radiogenic osmium Ores as old as 3,,, years and as young as 38,, years have been dated this way.
Rhenium—osmium dating. Info Print Cite.
Introduction: The Re-Os isotopic system is the most recent of a series of long-lived radiogenic isotope systems used for the study of early solar system materi-.
The Re-Os model ages for the molybdenites range between and Ma and apparently correspond to the early stages of metamorphism connected with pre-Variscan rift-related tectono-metamorphic events, which affected and recrystallized sedimentary CLM material rich in Mo-Th-Nb-REE. There is no geological evidence for the participation of fluids mobilized from host rocks in the formation of the CLM.
Because the Re-Os chronometer in molybdenite is demonstrably stable through later Variscan facies metamorphism, the molybdenite chronometer has not been affected by subsequent thermal overprints associated with the Variscan orogeny. Atencio D. Mineralogist 48, — Bingen B. Earth Planet. Earth Sci. Czech Geol. Craig J. In: Eliopoulos D. Fiala F.
Copyright remains with the author s or their institution s. Permission for reuse free in most cases can be obtained from RightsLink. The Shimadong porphyry Mo deposit is located in eastern Yanbian, in the eastern part of the north margin of the North China craton, northeastern China. Here, we present the whole-rock major and trace elements, zircon U—Pb and Hf isotope data, and molybdenite Re—Os data for the Shimadong deposit. The porphyry was emplaced at The porphyritic monzogranite had high SiO 2
Re-Os Dating of Black Shales: Timing and Duration of Sedimentary Processes*. Judith L. Hannah. 1., Holly J. Stein. 1., Gang Yang. 1.
In order to resolve the controls on the distribution of these elements, chemical and isotope mapping of MoS 2 grains from representative porphyry copper-molybdenum deposits were performed using electron microprobe and nano-scale secondary ion mass spectrometry. Our results show a heterogeneous distribution of , Re and Os isotopes in MoS 2 , and that both Re and Os isotopes are not decoupled as previously thought.
We conclude that Re and Os are structurally bound or present as nanoparticles in or next to molybdenite grains, recording a complex formation history and hindering the use of microbeam techniques for Re-Os molybdenite dating. Our study opens new avenues to explore the effects of isotope nuggeting in geochronometers. Ore deposits are the main source of metals for society, and their efficient and sustainable exploration requires a precise understanding of the factors that control their distribution within the upper crust.
Rhenium is radioactive and decays to radiogenic Os by beta emission. The Re-Os system follows the law of radioactivity where the total number of Os atoms in the sample at the present time is equal to the number of atoms of Os incorporated in the sample at the time of mineral formation and the Os atoms produced by decay of the Re parent radionuclide. Due to their chalcophile affinity and behavior during partial melting of the mantle, Re and Os will be concentrated in sulphide phases usually at low ppb and ppt levels, respectively.
Geochronology and Isotopes
Isotopic composition of osmium and of the parents of its radiogenic isotopes rhenium and platinum. Lindner and co-workers measured a half-life of Very precise Re-Os isotopic measure-ment of iron meteorites yield a half-life of The application of the Re— Os isotopic method has been fraught with analytical difficultes, which hampered development after the pioneering efforts of Herr and co-workers.
Abundances of Re and Os are best determined by isotope dilution, which requires addition to the weighed sample of isotopically enriched spikes e.
Structural characteristics and Re–Os dating of quartz-pyrite veins in the Lewisian Rhenium–osmium (Re–Os) geochronology on pyrites collected from these.
Over the years, Chemostrat has expanded the services on offer to now include more advanced isotopic techniques that so far have been used only in academia. The information presented below briefly outlines how Chemostrat is utilising two of these techniques, i. Re and Os become concentrated in the organic, hydrogenous fraction of organic rich shales, thus the time when the shale was deposited can be dated. Furthermore, as Re and Os have been inherited from the source rocks, Os isotopes can be employed to correlate an oil with its source.
Despite this application mainly being associated with the economic extraction of minerals, it can be employed by the oil and gas industry to date the formation of disseminated sulphide minerals within basement rocks and so the basement itself. Moreover, when these minerals are found in fractures it can be used to provide a minimum date for when the fracture network was open. Re-Os Radiogenic Isotope Dating Methods and Applications Over the years, Chemostrat has expanded the services on offer to now include more advanced isotopic techniques that so far have been used only in academia.
Research (Crustal Re-Os Geochronology)
While whole-rock peridotite Re-Os isotopic signatures are the core of such investigations, the Re-Os dating of individual peridotite minerals—base metal sulfides BMS and platinum group minerals PGM —that are the main hosts for Re and Os in the mantle peridotites came into play two decades ago. This is, however, not a rule of thumb as clear evidence of crust-mantle age decoupling also exist.
As such, they are the mantle equivalents of crustal zircons. Abrajano, T.
These unique characteristics explain why Re-Os molybdenite dating using the whole mineral approach is currently the most widely used single.
A suite of pyroxenites from the Beni Bousera peridotite massif, northern Morocco, have been analysed for Re—Os and Lu—Hf isotopic compositions. In general, the Nd—Hf isotope compositions of the pyroxenites lie close to the mantle array. As with the Sm—Nd and Rb—Sr systems, parent—daughter and isotopic ratios for the Lu—Hf system have been recently decoupled by a partial melting event associated with transfer of the massif from mantle to crust. The near-solidus extraction of a siliceous melt from the pyroxenites is also a possible explanation for the orthopyroxene-rich margins to numerous pyroxenite layers, via reaction with peridotite.
Pyroxenite Os isotope compositions are much more radiogenic than their host peridotites. In contrast to cratonic eclogites, most pyroxenites analysed here and those reported in the literature lie close to the mantle Nd—Hf isotope array. The Nd—Sr—Pb—Hf isotopic compositions and stable isotope characteristics of these pyroxenites reflect signatures from recycled oceanic crust and sediment. Hence, mixing of such material, if present within the convecting mantle, with peridotite, could account for some of the heterogeneity seen in oceanic basalts.
Small amounts of pyroxenite incorporated into peridotite can also produce the radiogenic Os isotope signatures evident in the source of oceanic basalts.
Return Pre Home. The Re-Os isotope system, based on its unusual qualities, has been widely used on the dating and tracing in the geoscience and geochemistry. As a reflection of the international development of the Re-Os isotope geochemistry, Chinese geoscientists have also done a large quantity of work in this research field.
Keywords: Re–Os isotopic dating; Cu-Ni deposit; Geodynamic process; Hongqiling; NE China. Introduction. The complicated orogenic processes of the Central.
Degao Zhai, Anthony E. Economic Geology ; 5 : — Native gold is intergrown with molybdenite and pyrite in auriferous quartz veins hosted by a monzogranite-monzonite stock and locally by Proterozoic gneiss, thereby offering an excellent opportunity to directly date the mineralizing event. Uranium-Pb age determinations for zircon yielded ages for the monzogranite and monzonite of Numerous mafic to felsic dikes, which are crosscut by ore veins pre-ore , parallel to these veins possibly synore , or crosscut by them post-ore , were carefully examined and dated.
The age of mineralization was determined directly using the Re-Os method applied to molybdenite. A total of 19 molybdenite samples separated from auriferous quartz veins yielded widely differing Re-Os model ages of to Ma, and replicate analyses of individual samples also yielded widely differing ages. Significantly, the wide range is attributable entirely to the results obtained for some coarse-grained molybdenite samples and is interpreted to be due to Re and Os isotope decoupling, the considerable spatial Re heterogeneity, the analytical procedure e.
Thus, the molybdenite Re-Os ages are identical, within uncertainty, to those of the dikes that are parallel to the ore veins, indicating that these dikes were emplaced contemporaneously with the ore and that they and the Haigou gold mineralization are of late Paleozoic age ca. Our new geochronological data provide evidence for late Paleozoic gold mineralization in Haigou, which makes it the oldest known lode gold deposit in the easternmost Central Asian orogenic belt, a finding that has important implications for precious metal mineral exploration in the eastern part of the Solonker-Xar Moron-Changchun-Yanji suture zone between the Central Asian orogenic belt and the North China craton.
This study also indicates that accurate and reproducible molybdenite Re-Os ages representing the true timing of ore deposition need an integrated combination of careful petrography, proper sampling procedures, sufficiently large analyzed aliquots, multiple analyses of individual samples, and multiple dating methods. Shibboleth Sign In. OpenAthens Sign In.
Canadian Journal of Earth Sciences
Development of Re-Os geochronology for crustal matrices has been ongoing since in the laboratory. This work has resulted in major advancements in the direct isotopic dating of crustal sulfide minerals, petroleum source-rocks, and natural hydrocarbons, using Re-Os isotopes. For sulfide minerals, Re-Os geochronology has direct application to the timing and duration of hydrothermal ore deposit formation.
Some key papers include:.
Rhenium—osmium dating is a form of radiometric dating based on the beta decay of the isotope Re to Os. This normally occurs with a half-life of Rhenium—osmium dating is carried out by the isochron dating method. Isochrons are created by analysing several samples believed to have formed at the same time from a common source. The Re-Os isochron plots the ratio of radiogenic Os to non-radiogenic Os against the ratio of the parent isotope Re to the non-radiogenic isotope Os.
The stable and relatively abundant osmium isotope Os is used to normalize the radiogenic isotope in the isochron. A good example of an application of the Re-Os isochron method is a study on the dating of a gold deposit in the Witwatersrand mining camp, South Africa. Rhenium and osmium were strongly refractory and siderophile during the initial accretion of the Earth which caused both elements to preferentially enter the Earth’s core.
Re tends to enter the melt phase incompatible while Os remains in the solid residue compatible. In this regard, the Re—Os system to study the geochemical evolution of mantle rocks and in defining the chronology of mantle differentiation is extremely helpful.