Geology, Mineralization, and Ore Controls at the Ken Snyder Gold-Silver Mine, Elko County, Nevada

ABSTRACT
The Ken Snyder mine exploits a volcanic-hosted, low-sulfidation,
selenium rich, gold-silver bearing quartz-adularia vein deposit
located in the Midas district (north-central Nevada) on the northwest
strike continuation of the Carlin Trend. Dr. Ken Snyder discovered
the deposit in 1994. At the end of 1998, underground mineable
reserves, using a 0.250 oz (7.775 g) gold / ton cut-off grade were,
2,726,800 tons grading 1.115 oz (34.676 g) gold / ton and 12.82 oz
(398.70 g) silver / ton totaling 3,738,500 oz (116,267,350 g) gold
equivalent.
Host rocks in the district are a mid-Miocene, bimodal assemblage
of felsic tuff, sediments and gabbro sills and dikes.
Hydrothermal alteration is widespread over an area measuring 1.5
miles (2.4 km) by 5 miles (8 km) elongated in a north-south direction.
Vein mineralogy consists of a gangue of banded quartz, calcite,
and adularia. Ore minerals occur as discrete bands deposited early in
vein growth consisting of silver selenides, electrum, and gold. Wall
rock alteration is predominantly propyllitic. Preliminary fluid inclusion
data from quartz and adularia indicate an average homogenization
temperature of 240¡C with fluid salinities of 0.6 equivalent wt%
NaCl. A recent 40Ar/39Ar age from adularia of 15.23±0.05 Ma was
obtained from the Colorado Grande vein.
Mineable reserves have been identified on seven veins. Known
reserves on the Colorado Grande vein occur over a strike distance of
6,500 feet (1,981 m) and a vertical range of 1,700 feet (518 m)
exhibiting remarkable continuity. The veins occupy faults orientated
at NS to N30¡W and N50¡-60¡W and dip steeply to the NE. These
faults exhibit pre-mineralization normal and right-lateral offset with
minor post-mineral offset.
Significant ore-grade material and well-developed veins do not
occur above 5,700 feet (1,737 m) true elevation, which is below current
erosional levels in the mine area. This ÒblindÓ vein top is
thought to represent the upper limits of boiling and/or cooling of
ascending mineralizing solutions and is a primary ore control.
Higher-grade and wider ore zones are also localized where veins
intersect lithic tuff and beneath sub-horizontal mafic sills and welllaminated
sedimentary units, both of which acted as ponding mechanisms.
Northeast-striking cross-faults may also act as ore loci.
Similarities in structural controls to mineralization exist
between the Midas district and deposits of the northern Carlin Trend.
Ore deposits in the Midas district could represent the northern extension
of the Carlin Trend, reflecting a regional dextral and normal slip
fault zone reactivated and mineralized during the Miocene.