The equilibrium fractionation of O isotopes between synthetic siderite and water has been measured at temperatures ranging from 33?? to 197??C. The fractionation between siderite and water over this temperature range can be represented by the equation: 103 ln ?? = 3.13 ?? 106T-2 - 3.50. Comparison between the experimental and theoretical fractionations is favorable only at approximately 200??C; at lower temperatures, they generally differ by up to 2 permil. Siderite was prepared by the slow addition of ferrous chloride solutions to sodium bicarbonate solutions at the experimental temperatures. It was also used to determine the O isotope fractionation factors between phosphoric acid liberated CO2 and siderite. The fractionation factors for this pair at 25?? and 50??C are 1.01175 and 1.01075, respectively. Preliminary results of the measured C isotope fractionation between siderite and Co2 also indicate C isotopic equilibrium during precipitation of siderite. The measured distribution of 13C between siderite and CO2 coincides with the theoretical values only at about 120??C. Experimental and theoretical C fractionations differ up to 3 permil at higher and lower temperatures. ?? 1988.
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Experimental oxygen isotope fractionation between siderite-water and phosphoric acid liberated CO2-siderite