Rhyolitic volcanic rocks may be the ultimate source of Li in
brines beneath the playa in Clayton Valley, Nevada, one of the
worldÕs largest Li deposits. Resources exceed 700 million kg of Li.
ATertiary, high-silica rhyolite flow capping the western Montezuma
Range, east of Clayton Valley, and an underlying rhyolite ash-flow
tuff sequence both contain anomalously high amounts of Li. Lithium
is most concentrated in unweathered obsidian and in gray, relatively
unweathered ash-flow tuff, indicative of magmatic concentrations
considerably higher than normal igneous rocks (Li up to 228 ppm,
more than five times typical concentrations in granites and rhyolites
or the median value for rhyolitic obsidians). Perlite and oxidized,
devitrified rhyolite contain considerably less Li than unaltered
obsidian. Lithium in the ash-flow tuff is depleted from 119-192 ppm
in the least altered rock down to 23-34 ppm in nearby oxidized samples.
Leaching from these rocks, by weathering and other alteration,
could have yielded more than enough Li to account for the resource
in the Clayton Valley brines.