Petrographic and trace element analysis of uranium-rich tufa calcite, middle Miocene Barstow Formation, California, USA

Publication Type  Journal Article
Year of Publication  2004
Authors  Cole, J. M.; Rasbury, E. T.; Montanez, I. P.; Pedone, V. A.; Lanzirotti, A.; Hanson, G. N.
Journal Title  Sedimentology
Volume  51
Issue  3
Pages  433-453
Journal Date  Jun
ISBN Number  0037-0746
Accession Number  ISI:000221544500003
Key Words  carbonate; lacustrine; synchrotron xrf; trace elements; tufa; coral skeletal aragonite; zero-valent iron; southern california; mojave desert; pyramid lake; lacustrine stromatolites; uranyl incorporation; tio2 particles; organic-matter; walker lake

An integrated petrographic and spectroscopic (X-ray diffraction, phosphor imaging and synchrotron X-ray absorption spectroscopy) study of tufas from the Miocene Barstow Formation, California, relates sample morphology, mineralogy and geochemical composition. The tufas, composed mainly of calcite that formed at the interface between an ancient alkaline lake and ground or spring waters, have textures similar to those of microbially mediated terrestrial stromatolites and travertines. The tufas have elevated concentrations of a number of trace elements including Mn, Fe, Sr and U. Synchrotron X-ray fluorescence analyses show that U concentrations can exceed 500 p.p.m. X-ray absorption spectroscopy indicates that the U in these samples is incorporated as U(IV). It is suggested here that alkaline lake waters had a high U/Ca ratio and tufa calcite formed where groundwater or (possibly epithermal) springs brought in Ca and trace elements such as Sr. The rapid, and possibly microbially mediated, precipitation of calcite allowed for incorporation of high concentrations of trace metals as either structural substitutes or extremely fine-scale inclusions.


822MPTimes Cited:2Cited References Count:91

URL  <Go to ISI>://000221544500003
DOI  DOI 10.1111/j.1365-3091.2004.00631.x