Isotope geochemistry of mercury in source rocks, mineral deposits and spring deposits of the California Coast Ranges, USA

Autor: Stephen E. Kesler, James J. Rytuba, Christopher N. Smith, Joel D. Blum
Rok vydání: 2008
Předmět:
Zdroj: Earth and Planetary Science Letters. 269:399-407
ISSN: 0012-821X
Popis: We present here the first study of the isotopic composition of mercury in rocks, ore deposits, and active spring deposits from the California Coast Ranges, a part of Earth's crust with unusually extensive evidence of mercury mobility and enrichment. The Franciscan Complex and Great Valley Sequence, which form the bedrock in the California Coast Ranges, are intruded and overlain by Tertiary volcanic rocks including the Clear Lake Volcanic Sequence. These rocks contain two types of mercury deposits, hot-spring deposits that form at shallow depths ( The Franciscan Complex and Great Valley Sequence contain clastic sedimentary rocks with higher concentrations of mercury than volcanic rocks of the Clear Lake Volcanic Field. Mean mercury isotopic compositions (δ202Hg) for all three rock units are similar, although the range of values in Franciscan Complex rocks is greater than in either Great Valley or Clear Lake rocks. Hot spring and silica-carbonate mercury deposits have similar average mercury isotopic compositions that are indistinguishable from averages for the three rock units, although δ202Hg values for the mercury deposits have a greater variance than the country rocks. Precipitates from spring and geothermal waters in the area have similarly large variance and a mean δ202Hg value that is significantly lower than the ore deposits and rocks. These observations indicate that there is little or no isotopic fractionation (
Databáze: OpenAIRE
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