Chemical U and S Isotopic Compositions and Genesis of Oilfield Brine in Nanyishan,Qaidam Basin,Northwestern China
The oilfield brine in Nanyishan,contains multiple resource elements,but has not been ex-ploited.Using(234U/238U)firstly,and with the chemical compositions and S isotopic compositions,this pa-per studied the postdepositional change of the chemical compositions and the transformation of the oilfield brine in Nanyishan.The contents of SO42-and U,0.08～2.24 g/L and 1.41～5.38 μg/Lrespectively,are es-pecially lower in the oilfield brine,compared with the intercrystalline brine unsaturated with halite in Dalangtan and the salt lake brine saturated with halite in Gas Hure.The values of δ34S,53.59‰～58.46‰,are high,and(234U/238U)Values change from 1.07 to 1.14 exhibiting the excess of 234U,in the oilfield brine.Reduction of SO42-,induced by anaerobic bacteria and organic matters,resulted in the transformation,de-creases of SO42-contents,and increases of δ34S,and sulphureted hydrogen produced during SO42-reduction advanced the U reduction,leading decreases of U contents and increases of(234U/238U).The surface waters and water rock reactions had little effects on the chemical compositions,δ34S and(234U/238U)in the oilfield brine.In this situation,U is unable to enriched in the oilfield brine.The chloride-type oilfield brine in Nany-ishan had transformed from the sulfide-type brine in ancient salt lake after buried.
Oilfield brinesulfur isotopeUranium isotopeTransformationNanyishan area
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