Title:

Stratigraphic Relationships in Mesozoic Basement Rocks at the Desert Peak East EGS Area, Nevada

Authors:

Susan Juch Lutz, Ann Robertson-Tait, Christy L. Morris

Key Words:

stratigraphic relationship, mesozoic basement rocks

Geo Location:

Desert Peak, Nevada

Conference:

Stanford Geothermal Workshop

Year:

2004

Session:

GEOLOGY

Language:

English

File Size:

380KB

View File:

Abstract:

Several plutonic units within Mesozoic basement
rocks of the east Desert Peak area are potential EGS
reservoirs. Sill-like Jurassic diorites and Cretaceous
granodiorite intrusives occur at temperatures
exceeding 400?F (204?C) within the basement.
Geologic studies are being conducted to determine
the lateral and vertical distribution of the basement
lithologies, the nature of contacts (depositional, fault,
or intrusive) with surrounding schistose
metasedimentary rocks, and the character and
mineralogy of natural fractures and veins in the rocks
to identify suitable targets for stimulation in
subsequent phases of this enhanced geothermal
system (EGS) project.
Dioritic intrusives in the Jurassic section are
tentatively correlated to the Humboldt mafic
complex; a sequence of gabbroic to intermediate
composition intrusives and comagmatic basaltic
volcanics that are closely associated with shallow
marine metasediments (quartz arenite of the Boyer
Ranch Formation; gypsum and carbonate of the
Lovelock Formation), and which host the high-temperature
Dixie Valley geothermal system 75 km
to the east. In the Desert Peak geothermal area, a
thick (100 m) quartz monzodiorite sill within the
Jurassic section can be correlated across the EGS
project site (drillholes DP 23-1 and 35-13 TCH) and
to outcrops near the Desert Queen mine (about 6 km
NE of the EGS area). However, complicated
structural and stratigraphic relationships with
surrounding Jurassic intrusive and metasedimentary
units and the presence of both Cretaceous and
Miocene dikes in the monzodiorite suggest variable
physical and mechanical properties and possible
unpredictable behavior as a result of well stimulation
procedures. A better lithologic target for future
wellbore stimulation may be the Cretaceous-aged
granodiorite that intrudes the Jurassic section. The
homogeneous Cretaceous granodiorite is a more
with only a few discrete fracture/fault zones.


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