The thesis area consists of 33 square miles in the south-central
Pueblo Mountains of Humboldt County, Nevada and Harney County,
Oregon. The Pueblo Mountains are tilted fault block mountains found
in the extreme northwestern part of the Basin and Range province and
were produced during Early Tertiary Basin and Range orogeny.
Northwest and northeast trending faults of Late Tertiary time have
since cut the entire stratigraphic sequence.
The oldest rocks exposed are metamorphosed Permian to
Triassic eugeosynclinal sedimentary rocks. The metamorphic
sequence is intruded by several granitic plutons of Late Jurassic to
Middle Cretaceous age. A thick sequence of Miocene basalt flows
unconformably overlies the pre- Tertiary rocks. A slight angular
unconformity separates the basalt sequence from overlying Miocene
tuffaceous sedimentary rocks, sillar flows, and welded tuffs.
Unconsolidated deposits of Quaternary alluvium include alluvial fan and
Mineralization within the area includes several gold prospects,
a mercury prospect, and a possible copper deposit. The copper
prospect consists of a large gossan (6, 000 feet by 3, 000 feet).
Mineralization and alteration from a Cretaceous porphyritic quartz
monzonite intrusion has produced potassic and quartz sericite hydrothermal
alteration in the host. Oxidation and weathering has removed
the sulfides from the surface leaving goethite, hematite, and limonite