Stable Oxygen and Hydrogen Isotope Fractionation Factors for the Goethite (hematite)-water System

This paper reports experimental results on the low-temperature (<100 oC) 18O and  2H fractionation of goethite (hematite)-water in a closed system. Both goethite (-FeOOH) and hematite (-Fe2O3) exhibited closer fractionation factor values but the Hematite-Water value is slightly higher (~0.9932) than the Goethite-Water (~0.9924) for the 18O isotope. The average fractionation factor (1000ln2; at 70 oC) value for 2H in the goethite-water is determined to be -115.78 which is more negative than the 1000ln18á values for 18O. The isotopic change from initial waters to the final waters in which these minerals were synthesized, was observed to be larger for the 2H (average~2.02‰) than the 18O (average~0.55‰). Variations in the fractionation factors of goethite and hematite reported in various studies is probably related to the procedures such as drying, washing, type of reactants, pH, and extraction and measurement of 18O and 2H isotopes and, therefore, invite further research for the understanding of -T relation. Formation temperatures of goethite (~70 oC) and hematite (~90 oC) seem to have less impact in altering mineral-water fractionation as compared to the formation water.