The mineralogy of the Snake Creek-Williams Canyon pluton, southern Snake Range, Nevada

The Snake Creek-Williams Canyon pluton of the southern Snake Range crops
out over an area of about 30 km 2, about 60 km southeast of Ely, Nev. This
Jurassic intrusion displays large and systematic chemical and mineralogical
zonation over a horizontal distance of 5 km. Major-element variations compare
closely with Dalyls average andesite-dacite-rhyolite over an SiO 2 range of 63
to 76 percent.
For various reasons it was originally thought that assimilation played a
dominant role in development of the Snake Creek-Williams Canyon pluton.
However, based on modeling of more recently obtained trace element and
isotopic data, we have concluded that the zonation is the result of in-situ
fractional crystallization, with little assimilation at the level of
crystallization.
This report summarizes data available for each of the mineral species
present in the zoned intrusion. Special attention has been paid to trends
that might relate to the variation in the chemical petrology of the pluton.