Highly radioactive topaz rhyolites of the Toano Range, northeastern Nevada

Journal Article · · American Mineralogist; (United States)

OSTI ID:6937747

Price, J G; Castor, S B ^[1]; Miller, D M ^[2]

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1. Univ. of Nevada, Reno (United States)
2. Geological Survey, Menlo Park, CA (United States)

Highly radioactive topaz rhyolites of Miocene age are described from a new locality in the Toano Range of northeastern Nevada. Quartz phenocrysts are blackened by radiation damage. High magmatic Th and U concentrations (87 and 46 ppm, respectively) allow the rhyolites to be readily distinguished on aeroradiometric maps. In addition to quartz, the rhyolites contain phenocrysts of sanidine, plagioclase, biotite, titanomagnetite, and rare fayalite. Vitrophyres have several unusual features: microphenocrysts of octahedral fluorite, rod- and worm-shaped microlite of iron oxide, and microlite of fayalite. Vapor-phase cavities in devitrified rocks contain topaz and quartz. The rhyolites occur as lava flows and pyroclastic deposits that originated from at least two vents. Emplacement of a nonwelded lithic tuff with topaz-rhyolite composition preceded the lava flows. Two groups of lavas are defined by petrographic differences and trace-element compositions. Rocks from the group with relatively large quartz phenocrysts and smaller, less abundant biotite phenocrysts tend to be more enriched in some incompatible trace elements, notably Th and REE, than the other group. Rocks that have undergone various amounts of postemplacement crystallization are locally enriched in elements that apparently were transported in the vapor phase, notably As, Sb, Au, and Hg. Because magma degassing, hydration of vitrophyres, vapor-phase crystallization, and devitrification can affect the rock composition, true magmatic abundances of these elements are uncertain.

• OSTI ID: 6937747
• Journal Information: American Mineralogist; (United States), Journal Name: American Mineralogist; (United States) Vol. 77:9-10; ISSN AMMIAY; ISSN 0003-004X
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ACTINIDES
ALUMINIUM COMPOUNDS
ALUMINIUM SILICATES
BIOTITE
CENOZOIC ERA
CHEMISTRY
DEVELOPED COUNTRIES
ELEMENTS
FEDERAL REGION IX
GEOCHEMISTRY
GEOLOGIC AGES
IGNEOUS ROCKS
MATERIALS
METALS
MICA
MINERALOGY
MINERALS
MIOCENE EPOCH
NATURAL RADIOACTIVITY
NEVADA
NORTH AMERICA
OXIDE MINERALS
OXYGEN COMPOUNDS
PETROGENESIS
PETROGRAPHY
QUARTZ
RADIOACTIVE MATERIALS
RADIOACTIVE MINERALS
RADIOACTIVITY
RARE EARTHS
RHYOLITES
ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
TERTIARY PERIOD
THORIUM
URANIUM
USA
VOLCANIC ROCKS