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Geology
and Mineralization: Lower Paleozoic sedimentary strata have been
intruded by Jurassic age intrusives and overlain by Tertiary volcanics.
There is less than 5% outcrop on the property, and lithologies have
largely been defined by float mapping.
The oldest
rocks exposed on the property consist of black, thickly bedded, chert,
argillite, and rare quartzite and limestone of the Ordovician Valmy
Formation. Bedding attitudes are highly variable, indicating multiple
deformational events.
A similar, but lighter colored, unit of thin bedded, locally carbonaceous,
chert and argillite is the most commonly exposed lithology on the Yankee
Blade property. The unit is usually present in areas of lower elevation
such as creek valleys and the west margin of the range front. Irregular
bedding attitudes suggest a complex deformational history. These rocks are
interpreted to be part of the regionally extensive Devonian Slaven Chert,
and have been overthrust by the older Valmy strata. The thrust fault(s)
has not been recognized in outcrop on the Yankee Blade property, but the
distribution of lithologies suggests that the thrust approximately
parallels topography in the deeply incised east-west valleys. Both the
Valmy and Slaven strata are considered to be "upper plate" rocks in a
regional sense.
Although possibly missed due to the lack of outcrop, except for a single
thin (<5 m) bed of limestone in the Valmy, no carbonate rocks have been
encountered on the property. Lower plate carbonates are known to underlie
the Slaven Chert regionally.
Fine grained equigranular biotite-hornblende diorite and quartz monzonite
intrude the Paleozoic strata, and exposures are restricted to creek
valleys. These rocks are most likely related to the Jurassic Austin
plutonic complex. The high-grade gold values of the southern target all
occur within the dioritic intrusive. The intrusive contact zones are
variably hornfelsed, silicified, and limonitic.
Tertiary volcanic rocks ranging in composition from basaltic to rhyolitic
unconformably overlie, and are in fault contact with, all pre-Tertiary
rocks. Local subhorizontal flow banding in rhyolite suggests that the
rhyolite may, in part, be an intrusive dome.
Exposures
of Tertiary volcanic rocks are restricted to the north part of the
property, possibly suggesting (1) the area south of the current volcanics
was topographically higher during Tertiary volcanism, and/or (2) the area
has been tilted northward, thereby preserving the volcanics. In either
case, a deeper level of erosion is indicated at the south part of the
property.
Regionally, the
Cottonwood Canyon property is situated in a poorly defined transition zone
between silver-dominant mineralization of the Reese River district to the
south, and gold-dominant mineralization in the Iowa Canyon and Cove-McCoy
area to the north. Gold values from the property to date have a high
gold/silver ratio.
Targets:
Two distinct
targets occur at Cottonwood. The southern target, called the Cotton
is the most promising. Quartz-scorodite-arsenopyrite vein-type breccia
fragments have been identified at several areas in the southern part of
the property. Mineralization has been identified in the dumps of three
caved adits and to the east and west along the south side of Cottonwood
Creek. The distribution of mineralized fragments covers an area of about
100 x 700 meters, and closely corresponds with the location of a diorite
intrusive. The mineralized chips have assayed up to +1.0 oz/ton gold (34
g/t), and are anomalous in silver (<5.2 ppm), arsenic (>10,000 ppm),
bismuth (<137 ppm), antimony (<367 ppm), and tellurium (<155 ppm). No
drilling has been done in this area.
The YB Target
is located at the northwest corner of the property, and is characterized
by steeply dipping, north-south to northeast-southwest trending, quartz
veinlets and stockworks in argillite. The structural orientation of the
veinlets closely corresponds with an assumed range front fault immediately
to the west. Rock samples collected from historic hand pits have returned
up to 470 ppb gold, and are slightly anomalous in arsenic (101 ppm).
A total of seven
reverse circulation holes tested this area in 1986. Six of the seven holes
were vertical. The best intercept was 870 ppb gold across 1.4 meters. An
irregular bedded barite occurrence is present northeast of the YB Zone and
appears unrelated.
The primary
exploration model at Cottonwood is a Getchell type gold deposit, an
intrusive related arsenic-rich gold occurrence primarily hosted by
carbonates. The Getchell Mine contains over 5M ounces of gold. Both the
Cotton high-grade vein zone and the YB range front fault target should
intersect favorable carbonate host rocks at depth. |
