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. 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. Peridotite xenoliths which are thought to sample the upper mantle sometimes contain supra-chondritic Os-isotopic ratios. This combination of radiogenic Os that was created by decay of Re and nonradiogenic melts helps to support the theory of at least two Os-isotopic reservoirs in the mantle. The second reservoir is chondritic in composition.
Problems with the U-Pb Radioisotope Dating Methods—1. Common Pb
To this end we have developed unrivalled in-house expertise in the Rhemium — Osmium Re-Os isotopic dating technique as well the more established Uranium — Lead U-Pb geochronology methods. Re – Os Isotopes The Re-Os isotope system provides a means of absolute dating in carbon-rich sediments and therefore fits perfectly into our stratigraphic portfolio. However, it also provides oil generation timing and timing of sulphide mineral formation.
Geochronology of mudrocks Re and Os become concentrated in the organic, hydrogenous fraction of organic rich shales and by analysis of between six and eight samples from approximately the same stratigraphic interval, an absolute age for the deposition of the shale is generated. Establishing dates for the generation of oils When oil is formed from a source rock, a proportion of the Re and Os from the source rock is transferred to the oil.
By directly dating on the primary copper mineral chalcopyrite, The Re–Os isochron age of ± Ma is interpreted to represent the age of the Cu mineralization of the South Meiling deposit. Field and optical microscopy observations indicate that sphalerite formed synchronously with chalcopyrite .
Suitable lithologies for Re-Os geochronology include black shales and organic-rich carbonates. Applications of Re-Os geochronology The Re-Os geochronometer can be used to date sedimentary successions lacking suitable horizons for traditional geochronology techniques such as Ar-Ar or U-Pb zircon geochronology. For example, the boundaries of many Phanerozoic systems, epochs, and stages are marked by the deposition of black shale units, several of which are coincident with mass extinction events.
As such, the Re-Os geochronometer can be used to directly date some stratigraphic boundaries. Proterozoic sedimentary successions often record enormous portions of geological time, yet many of them lack volcanic horizons and are bereft of fossils suitable for relative age dating. As a result, accurate and precise ages are difficult to determine for these successions, which hampers attempts to correlate successions across different regions.
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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 .
References Generic Radiometric Dating The simplest form of isotopic age computation involves substituting three measurements into an equation of four variables, and solving for the fourth. The equation is the one which describes radioactive decay: The variables in the equation are: Pnow – The quantity of the parent isotope that remains now. This is measured directly. Porig – The quantity of the parent isotope that was originally present.
This is computed from the current quantity of parent isotope plus the accumulated quantity of daughter isotope. Standard values are used, based on direct measurements. Solving the equation for “age,” and incorporating the computation of the original quantity of parent isotope, we get: Potential problems for generic dating Some assumptions have been made in the discussion of generic dating, for the sake of keeping the computation simple.
Such assumptions will not always be accurate in the real world. The amount of daughter isotope at the time of formation of the sample is zero or known independently and can be compensated for. No parent isotope or daughter isotope has entered or left the sample since its time of formation.
Metamorphism and multiple folding of the basin fill occurred during the Svecofennian orogeny 1. The Rompas Au—U mineralization is hosted within deformed and metamorphosed calcsilicate veins in mafic volcanics. Textural evidence suggests that deposition and periods of uraninite re-mobilization were followed by localized hydrocarbon-bearing fluid flow which produced pyrobitumen crusts around grains of uraninite.
Gold precipitated during the latest hydrothermal event at around 1. In situ U—Pb dating of uraninite by laser ablation inductively coupled mass spectroscopy LA-ICP-MS , and Re—Os dating of molybdenite, indicate that primary hydrothermal uranium mineralization forms two age clusters; about 2.
Rhenium-Osmium dating is a form of radiometric dating based on the beta decay of the isotope Re to normally occurs with a half-life of × 10 9 y, but studies using fully ionised Re atoms have found that this can decrease to only 33 y. Both rhenium and osmium are strongly siderophilic (iron loving), while Re is also chalcophilic (sulfur loving) making it useful in.
Due to the lack of precise mineralization ages, the metallogenesis of this area has long been a matter of debate. The deposit consists of two parts: The principal ore minerals are pyrite, chalcopyrite, sphalerite, minor tetrahedrite, galena and pyrrhotite. Gangue minerals include quartz, sericite and barite, and minor chlorite, plagioclase and carbonate minerals. The Hongshi Cu deposit represents a hydrothermal vein system hosted in the mafic volcanic rocks of Daliugou Formation.
The orebodies are associated with quartz veins and controlled by subsidiary faults of the Kalatag fault. The ore-forming process can be divided into the early, middle and late stages and is characterized by quartz—pyrite, quartz—chalcopyrite—pyrite and quartz—carbonate—gypsum veins, respectively. Re—Os analyses of chalcopyrite from the Hongshi Cu deposit yield an isochron age of Since chalcopyrite is the primary copper mineral, we interpret these isochron ages as the timing of Cu mineralization, based on field geology and petrographic evidence.
These results suggest that the Re—Os ages presented here provide, for the first time, a direct constraint on an early Paleozoic Cu mineralization event of the eastern Tianshan Orogen. Moreover, we propose that the VMS mineral system and hydrothermal vein system of the Kalatag district were related to the south-dipping subduction of the Kalamaili oceanic plate during the Late Ordovician—Silurian.
Age of the Earth
They are observed in upper-mantle peridotites and oceanic basalts, in mantle xenoliths, and are also the most common mineral inclusion in diamonds. Thus, sulfides control the behaviour of the chalcophile elements during magmatic processes. Periodic table showing chalcophile elements highlighted in yellow.
The Re-Os Geochronometer The Rhenium-Osmium (Re-Os) geochronometer is a novel tool for dating ancient sedimentary successions. Analytical and instrument developments over the past 25 years have improved the reliability and accuracy of the method such .
Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic. Radiometric dating is a method used to determine the age of rocks and other materials based on the rate of radioactive decay. Learn about three common types of radioactive decay: Radiometric Dating Determining your age is easy. You simply subtract your birth date from the current date. But determining the age of a rock After all, a rock can’t tell you when it was born.
Chalcophile Elements and Sulfides in the Upper Mantle
Typically, asphaltene ASPH , the heaviest and most Re—Os rich oil fraction, from multiple oils within an oil field or a larger petroleum system are analyzed to obtain sufficient spread in Re—Os isotopic ratios, a mathematical necessity for precise Re—Os isochrons. Here we offer a new approach for Re—Os geochronology of oil based on isotopic analyses of different fractions within a single sample of crude oil.
We studied three oils from the Gela oil field, southern Sicily, Italy, recovered from Triassic—Jurassic stratigraphic intervals Streppenosa, Noto, and Sciacca Formations within the Gela-1 well. ASPH insoluble in n-alkane and maltene MALT, soluble in n-alkane fractions of oil were separated using n-pentane, n-hexane, n-heptane and n-decane solvents. We present an optimized Re—Os procedure with sample digestion in a high-pressure asher, followed by isotopic measurements using negative thermal ionization mass spectrometry.
Very high metal contents of Gela oils allowed acquisition of precise Re—Os data.
Molybdenite Re–Os dating is widely used to constrain the age of hydrothermal ore deposits (e.g. McCandless and Ruiz McCandless, T.E., and Ruiz, J., , Rhenium–osmium evidence for regional mineralization in Southwestern North America: Science, v. , p.
The Cretaceous age of this granite and its Mo-W mineralization is shown using two independent methods: U-Pb on zircon and Re-Os on molybdenite. The studied zircons have a typical homogeneous character with oscillatory zoning and scarce restite cores. Two molybdenite- bearing samples of very different character affirm a genetic relation between W-Mo mineralization and the Rochovce granite. The second molybdenite occurs as mm disseminations in finegrained granite, and provides an age of Both Re-Os ages are identical within their 2-sigma analytical uncertainty and suggest rapid exhumation as a consequence of post-collisional, orogen-parallel extension and unroofing.
The Rochovce granite represents the northernmost occurrence of Cretaceous calc-alkaline magmatism with Mo-W mineralization associated with the Alpine-Balkan-Carpathian-Dinaride metallogenic belt. Resource Geology 48, Rb-Sr geochronology of the leucocratic granitoid rocks from the Spissko-Gemerske Rudohorie. Regional setting and geochronology of the Late Cretaceous banatitic magmatic and metallogenetic belt.
Geophysical research of the Tatroveporic crystalline basement – the Kralova hol’a and Kohut areas. Hidden granite intrusion near Rochovce with Mo- W stockwork mineralization First object of its kind in the West Carpathians.