MASS DEPENDENT STABLE SR ISOTOPIC FRACTIONATION AND COORDINATION ENVIRONMENT IN CONTINENTAL BARITE FROM ZODLETONE SPRING, OKLAHOMA

Microbially mediated barite (BaSO₄) precipitation in a continental setting occurs at Zodletone Spring, Slick Hills, southwestern Oklahoma and shows mass dependent stable Sr isotopic fractionation (d^88/86Sr), exhibiting lower values in the mineral barite relative to the solution from which it precipitated as expected. Zodletone Spring flows into a stream, which merges into the southern bank of Saddle Mountain Creek. Barite is saturated in both the spring and creek. The saturation index of barite for the spring is 1.5 at 20.5⁰C and 1.9 in the creek at 33.6⁰C under conditions when sampled during the summer. Strontium (Sr) can easily substitute for barium (Ba) in barite during precipitation from solution allowing for the presence of multiple phases in the mineral phase (e.g., BaSO₄, Sr_x-Ba_1-xSO₄, SrSO₄). Results show the stable isotope fractionation during precipitation (Δ^88/86Sr barite-water) ranges from -0.31‰ to -0.34‰ in the spring and the creek respectively (±0.05 2σ). The distribution coefficient of Sr in barite (Kd_Sr) precipitated from the spring is 0.119 whereas 0.004 in the creek. Individual microcrystals of barite from the spring wall show variations in the magnitude of the Sr peak in the EDAX spectrum. Micro-XRF, micro-XRD, and micro-XAFS spectroscopy were performed to understand the presumed variations in Sr within the individual crystals (seen in the EDAX spectrum). The specific Sr-bearing phases present and their spatial distribution within the natural spring sample will be presented. The data shows that Sr distribution in the continental barite is not uniform. Some barite crystals in the sample show Sr hotspots. Micro-XRF, micro-XRD, and micro-XAFS spectroscopy of barite precipitated in the laboratory without the influence of microbes will be compared to results from the natural spring sample.