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Lithium Isotope Geochemistry of the Yellowstone Hydrothermal System

By
Neil C. Sturchio
Neil C. Sturchio
Department of Earth and Environmental Sciences, University of Illinois at Chicago, Chicago, Illinois 60607
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Lui-Heung Chan
Lui-Heung Chan
Department of Geology and Geophysics, Louisiana State University, Baton Rouge, Louisiana 70803
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Published:
January 01, 2005

Abstract

An exploration of the Li isotope variations of thermal waters and various rock types from drill cores and outcrops in the Yellowstone National Park, Wyoming-Montana, hydrothermal system was undertaken to investigate simple models for the Li cycle and to consider their implications for the geochemical dynamics of the system. Thermal waters have Li concentrations ranging from 0.27 to 6.5 mg/kg, and δ7Li values from 1.0 to 6.5 per mil. Rocks have Li concentrations ranging from 2.0 to 32.7 mg/kg (in sedimentary rock), and 15.2 to 282 mg/kg (in rhyolite); Li concentrations in rhyolite increase with the extent of hydrothermal alteration because Li from thermal water is incorporated in hydrothermal minerals. The range in δ7Li values for the sedimentary rock is 1.6 to 22.4, and δ7Li is generally higher in limestone than in shale. The range of δ7Li values for the rhyolite is −3.6 to +7.5 per mil; δ7Li values generally increase with an increasing extent of hydrothermal alteration. Relationships of Li and Cl concentrations in thermal waters indicate a loss of Li by incorporation into hydrothermal minerals in altered rhyolite. Simple isotopic fractionation models for Li isotope exchange between thermal water and altered rhyolite, with mass transfer constraints from Li/Cl ratios of thermal waters, can account for the observed variations in δ7Li. Massbalance considerations indicate that the long-term discharge of Li from the Yellowstone hydrothermal system may be sustained in large part by deep input of high-salinity magmatic brine.

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Special Publications of the Society of Economic Geologists

Volcanic, Geothermal, and Ore-Forming Fluids: Rulers and Witnesses of Processes within the Earth

Stuart F. Simmons
Stuart F. Simmons
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Ian Graham
Ian Graham
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Society of Economic Geologists
Volume
10
ISBN electronic:
9781629490342
Publication date:
January 01, 2005

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