Abstract

Khawar  Sultan^1,2

DOI : http://dx.doi.org/10.13005/ojc/310107

This paper reports experimental results on the low-temperature (<100 ºC) δ¹⁸O and δ ²H fractionation of goethite (hematite)-water in a closed system.  Both goethite (α-FeOOH) and hematite (α-Fe₂O₃) exhibited closer fractionation factor values but the α_Hematite-_Water value is slightly higher (~0.9932) than the α_Goethite-_Water (~0.9924) for the ¹⁸O isotope. The average fractionation factor (1000 ln²α; at 70 ºC) value for ²H in the goethite-water is determined to be -115.78 which is more negative than the 1000ln¹⁸α 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 δ²H (average~2.02‰) than the δ¹⁸O (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 α-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.

Goethite; Hematite; Hydrogen and Oxygen isotope; Fractionation factor; Temperature

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