Landscape Evolution at an Active Plate Margin - Biological Science ...

vironmental opposition has delayed plans. During a
visit in 2008 no evidence of recent activity was noted.
Mine Development Associates (2008) reports that the
gold deposit is underlain by rock units related to caldera
formation and subsequent resurgence. Lithologies
include volcaniclastic siltstones and sandstones
deposited in a lacustrine setting within the caldera,
debris flows with local intercalated silica sinter, and
rhyolite flows and dikes. All lithologies have been
altered and/or mineralized to various degrees.
The north–south trending Hilton Creek fault defines
the eastern limit of the resurgent dome within the
central part of the Long Valley caldera and extends
beyond the caldera to the south. Vista believes that
this fault system controls the distribution of gold
mineralization at the Blue Chert deposit.
The epithermal (hot springs) gold and silver mineralization
falls within the low sulfidation (quartz–
adularia) deposit type. Several favorable exploration
targets, termed the North, Central, South, Southeast,
and Hilton Creek zones, are mineralized with low
grades of gold and silver along north–south trending
zones up to 8,000 ft in length with widths ranging
from 500 ft to 1500 ft. The tabular bodies are generally
flat-lying or have shallow easterly dips. Mineralized
zones are typically from 50 to 200 ft thick and
exposed at (or very near) the surface. These zones
correlate with areas of intense argillic alteration and/
or silicification. The predominant clay mineral is kaolinite,
while the silicification varies from chalcedony
to amethystine quartz or opal. Multiple periods of
brecciation and silicification are evidenced by crosscutting
veinlets and silicified breccia zones.
Mineralization consists of poorly crystalline pyrite,
often with framboidal texture, and lesser euhedral
pyrite. Investigations have shown submicroscopic
gold occurs within the framboidal pyrite. Where gold
grains have been observed, the grains are small (1 to
6 microns) and have low amounts of contained silver.
A significant portion of the gold resource is present in
material which has been at least partly oxidized. The
pyrite is altered to iron oxides (goethite), releasing the
gold. See Jessey (this volume), for discussion of ore
genesis and a model for ore deposition.
This fossil hot spring hill is in the lower reaches of a
Jeffrey pine (Pinus jeffreyi) forest covering much of
the Long Valley resurgent dome. Individual pines can
be seen in sagebrush scrub of Long Valley south and
D. R. Jessey and R. E. Reynolds
east to Benton Crossing Road. Jeffrey pine extends
from Baja California to the Siskiyou Mountains in
northern California, where it is found on ultramaficderived
soils. Typically the Jeffrey pine is found on
well drained soils at elevations from 6000 ft. to 8000
feet. At higher elevations (Mammoth Lakes), Jeffrey
pine is replaced by California red fir (Abies magnifica)
and then Sierra lodgepole pine (Pinus contorta ssp.
murrayana). Highest elevation trees are the whitebark
pine (Pinus albicaulis), which form krummholtz in
windswept areas. Logging transported timber by rail
to Bodie, where it became mine timbers, stamp mills,
and siding for bars and brothels.
Great Basin sagebrush to the east gives way to seasonally
wet alkaline meadows in Long Valley. These
wet “saltgrass meadows” are fed by streams slowly
meandering to the Owens River. Saltgrass (Distichlis
spicata) is dominant, while other important halophytic
plants include clustered field sedge (Carex praegracilis),
arrow grass (Triglochin maritima), and clustered
goldenweed (Pyrrocoma racemosa). The closest
published flora to Long Valley is northeast at Glass
Mountain (el. 11,123 ft) towering 4,400 feet above the
Owens River in the floor of Long Valley (Honer, 2001;
Michael Honer of Rancho Santa Ana Botanic Garden)
This study samples saltgrass meadows, sagebrush
series, subalpine forests and meadows, and arid alpine
peaks and ridges.
RETRACE via Antelope Springs Road (3S05) to
Highway 395.
87.0 .(1.4) TURN RIGHT at Huntley Mine and 5-way
intersection.
87.9 (0.9) Pass a left turn; continue on graded road.
90.4 (2.5) TURN RIGHT on Owens River Road.
90.9 (0.5) Cross Hot Creek.
91.0 (0.1) TURN RIGHT on Hot Creek Hatchery
Road toward Whitmore Tubs Road.
91.6 (0.6) BEAR LEFT on 2507 toward Whitmore
Hot Springs. Avoid Hot Creek Road to the right.
92.9 (1.3) STOP 2-10. Regroup at View Stop. From
the rise, view 12:00 to 1:00 of moraines at Convict
Creek; 11:00 moraines in McGee Creek; 10:00 moraines
in Rock Creek.
93.1 (0.2) Continue past a left turn.
94.4 (1.3) Stop sign at junction of paved Benton
Crossing Road (2584). Whitmore Hot Springs are
42 2009 Desert Symposium