Anomalous isotope composition of xenon and krypton in minerals of the natural nuclear reactor

Shukolyukov, Yu. A.; Ashkinadze, G. Sh.; Verkhovskii, A. B.

doi:10.1007/bf01133202

Cited by 4 publications

(1 citation statement)

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“…The in tegrated neutron flux at certain points exceeded 1.5 x 1021 neutrons per cm2 (for more details, see "The Oklo Phenomenon" , Proceedings of a Roth, 1977;and by Hagemann and Roth, 1978; a book written in the Japanese language by Fujii, 1985; and several review ar ticles by Kuroda, 1975Kuroda, , 1982Kuroda, , 1983. In 1976, Shukolyukov and co-workers (Shukolyukov et al, 1976;Shukolyukov and Min, 1977;Shukolyukov and Minh, 1977) reported that they found an anomalous fission xenon component in the Oklo reactors. The isotopic composition of this anomalous fission xenon is such that the abundances of 131Xe and 132Xe relative to 136Xe are markedly enhanced when compared to the relative fission yields from the thermal neutron-induced fission of 235U.…”

Section: The Pre-fermi Natural Reactormentioning

confidence: 99%

Plutonium-244 in the early solar system and the Pre-Fermi natural reactor.

Kuroda

1992

Geochem. J.

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Section: The Pre-fermi Natural Reactormentioning

confidence: 99%

Plutonium-244 in the early solar system and the Pre-Fermi natural reactor.

Kuroda

1992

Geochem. J.

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Noble gases (Ar, Kr, Xe) and halogens (Cl, Br, I) in fluid inclusions from the Athabasca Basin (Canada): Implications for unconformity-related U deposits

Richard¹,

Kendrick²,

Cathelineau³

2014

Precambrian Research

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International audienceThe formation of unconformity-related uranium deposits in the Proterozoic Athabasca Basin (Canada) involved basin-scale circulation of U-bearing brines during high-grade diagenesis (150-200 degrees C) at similar to 1.6-1.5 Ga. The UO2 ores occur both sides of the unconformity and are associated with extensive brecciation and illite-sudoite-dravite alteration. Quartz and dolomite cementing veins and breccias are associated with alteration and mineralisation and contain a fairly uniform population of fluid inclusions characterised by variable Na:Ca and salinities of 25-35 wt.% salts and high U concentrations of up to 600 ppm U. In order to further constrain the origin of these U-rich brines, we analysed the naturally occurring isotopes of Ar, Kr and Xe, together with halogens (Cl, Br and I), K, Ca and U in irradiated quartz and dolomite samples containing representative fluid inclusions. This was achieved by the noble gas method for halogen measurement (extended Ar-40-Ar-39 methodology) using a combination of noble gas extraction techniques. The fluid inclusions opened by crushing quartz and dolomite samples in vacuum have similar molar Br/Cl ratios of 5.8 x 10(-3) to 10.4 x 10(-3), and molar I/Cl ratios of 1.8 x 10(-6) to 8.2 x 10(-6). These compositions lie over the top half of the modern-day seawater evaporation trajectory, consistent with the fluids deriving the bulk of their salinity by subaerial evaporation of seawater, beyond the point of halite saturation. The I/Cl ratios are much lower than is typical of fluids that have interacted with I-rich organic matter present in many sedimentary basins or fluid inclusions found in Mississippi Valley type (MVT) Pb-Zn ore deposits. This is significant because provided the U-rich fluid inclusions are representative of the ore-stage fluids, the low I/Cl ratios of the fluid inclusions do not favour fluid interaction with organic matter (or hydrocarbons), as a major process for localising U mineralisation. The majority of samples contain fluid inclusions with age-corrected Ar-40/Ar-36 of between the modern atmospheric value of similar to 300 and 450. These values are considered representative of the fluid's initial composition and are typical of upper crustal sedimentary formation waters. The fluid inclusions nonradiogenic Kr-84/Ar-36 and Xe-129/Ar-36 ratios are slightly enriched in Xe-129 relative to air and the fluid inclusions are estimated to contain 0.5-17.3 x 10(-10) mol g(-1) Ar-36 which is up to twenty times the Ar-36 concentration of air-saturated seawater. The data are interpreted to reflect acquisition of atmospheric noble gases from sedimentary rocks and suggest acquisition of radiogenic Ar-40 within K-rich basement rocks, that would have been an important source of excess Ar-40, was limited by temperatures of less than 200 degrees C. Taken together the halogen and noble gas composition of the U-bearing fluid inclusions are strongly controlled by subaerial evaporation and subsequent interaction with sedimentary rocks, showing that low tem...

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