Cortez Summit Property

Eureka County, Nevada

Carlin Gold’s Cortez Summit property is located in the Cortez gold trend. The property consists of 142 100%-owned unpatented lode claims and is located in the midst of an expanding number of gold deposits.  Carlin Gold’s primary target is Carlin-style mineralization in a structural and stratigraphic setting similar to that at the nearby deposits, including the new Goldrush discovery and Cortez Hills mine.   The Goldrush resource is hosted primarily in a favorable interval in the Devonian Wenban Formation, a carbonate unit that is also an ore host in other deposits in the Cortez trend.   Carbonates of the overlying Horse Canyon Formation are minor hosts at Goldrush and in some of the other deposits in the district.  The geographical and structural relationships of the mineralized trends are illustrated in Figures 1 and 2.  Deepening of a prior reverse circulation hole with core in 2013 established that the sedimentary rock units at Cortez Summit adjacent to the important Fourmile structure are stratigraphically equivalent to the mineralized host units at the nearby Goldrush discovery.  The presence of favorable mineralized host rock stratigraphy in the vicinity of a strong structure combine with the property’s strategic location to make Cortez Summit an excellent exploration target.

The southwest corner of the property lies within one mile northeast of Barrick Gold Corporation’s new Goldrush discovery.  As of December 31, 2013, Barrick reported a 15.6 million oz gold resource at Goldrush, grading 0.135 oz per ton Au, open for expansion.   Barrick’s 2013 annual report states that a prefeasibility study is underway and is expected to be complete by mid-2015.  Barrick’s Cortez Hills operation (11 MM oz gold pre-production reserve/resource) is located 4 miles west of the property. The east edge of the property lies 0.5 miles southwest of the Buckhorn Mine, and the west edge of the property is 1.6 miles northeast of the Horse Canyon Mine.

Figure 1 - Cortez Trend

 

Figure 2 – Central Cortez Trend Structural Setting
 

Carlin Gold identified the area as prospective in 2007, prior to Barrick’s initial September 2011 announcement of the Goldrush discovery.   The company was encouraged by initial rock sample geochemistry results from silicified and iron-stained siltstones from the NNW trending Fourmile structural zone on the west edge of the property.  Grab samples collected from this area contained up to 0.447  gpt gold and 307 ppm arsenic (Figure 3). 

Two types of mineralizing systems exist on or adjacent to the Cortez Summit property: 

  1. Carlin-style sediment-hosted Au.   The adjacent Carlin-style deposits (Goldrush, Cortez Hills, Horse Canyon) contain typical structural and stratigraphic controls that characterize Carlin-type deposits in north-central Nevada.  These deposits are probably late Eocene (±40 Ma) in age.  Most Carlin-style mineralization occurs in the favorable carbonate section that constitutes the ‘Lower Plate’ of the Roberts Mountain thrust fault system.  This is the primary target at Cortez Summit.
  2. Buckhorn-style volcanic-hosted low sulfidation Au-Ag.  This style of mineralization is associated with an extensive Miocene epithermal system (14.6 Ma) which is controlled by NNW-trending Northern Nevada rift structures.

Except for a narrow sliver of Paleozoic ‘Upper Plate’ siliciclastic rocks of the Ordovician Vinini Formation poorly exposed on the west edge of the property, the Cortez Summit property is covered by Miocene-age basalts and gravels which postdate the Carlin-style mineralization event.  Where attitudes can be measured, the Paleozoic sedimentary rock sequence strikes northeasterly and dips moderately northwest on the western edge of the property. As you approach the property from the west, therefore, you are traveling down the Upper Plate section, toward the favorable Lower Plate Devonian-age carbonate rock sequence which hosts gold mineralization in the area.   On the west side of the property, the Vinini Formation is unconformably overlain by a Tertiary volcano-sedimentary sequence consisting of a lower gravel unit and an upper series of Miocene (15-16 Ma) basaltic andesite flows. The Miocene sequence varies in thickness from zero on the west side of the property to >500 ft. (150 m) on the east side. The Buckhorn deposits are primarily hosted by basaltic andesite in this sequence. Dikes, plugs and minor flows of Miocene (15 Ma) rhyolite locally intrude and overlie the gravel and basaltic andesite units, including the rhyolite plug exposed in the southwest corner of the property (Figure 3, geology map). 

Two intrusive phases are recognized just west of the property including: 1) Jurassic-age quartz monzonite of the Mill Canyon pluton; and 2) probable Tertiary-age quartz porphyry dikes and small intrusive bodies. These quartz porphyry intrusions may be correlative with early Oligocene quartz porphyry dikes which are common at the Horse Canyon, Cortez Hills and other Cortez district deposits.  

Two structural orientations dominate the Cortez Summit area: 1) NNW horst and graben structures that define the Northern Nevada Rift structural trend and control mineralization along the Aspen and Buckhorn mineralized trends, and 2) less well-defined NE-trending structures exhibited by the drainage patterns eroding the basaltic andesite (ie. Willow Creek structure). The Northern Nevada Rift structures associated with Buckhorn-style mineralization potentially represent shallow manifestations of the deep-seated feeder structures involved in older Carlin-style mineralization at depth. A good example of this is the prominent NNW trending Fourmile structural zone that trends for 4,500 feet (1370 m) along the west side of the property and appears to be associated with Carlin-style alteration and geochemistry.  The Miocene rhyolite plug of upper Willow Creek in the southwest corner of the property intrudes the inferred structural intersection between the NE-trending Willow Creek structure and the NNW-trending Fourmile structural zone.   Carlin geologists believe this is an interesting target for future drill testing.

Cortez Summit and Cortez Deposits

In August 2012 a reverse circulation drill program was initiated to establish the presence and depth of the favorable Lower Plate carbonate section on the west side of the property, in proximity to the Fourmile structural zone in the southwest portion of the property. Most of this target area is covered by post-mineral gravel and basaltic andesite.  Where Paleozoic rocks are exposed on the west edge of the property, sampling along the Fourmile structural zone has yielded gold values of 0.447 and 0.263 gpt in altered siliciclastic rocks. Rock sampling along a drill road cut yielded 0.175 gpt gold over 50 feet (15 m) in altered siltstones (Figure 3).  

7 reverse circulation drill holes were completed in 2012 to depths ranging between 1500 and 1800 feet (457-549 m), for a total of 11,720 feet (3,573 m).  All holes encountered Paleozoic sedimentary rocks.  One hole was collared in the Paleozoic rocks and the remainder were drilled into Paleozoic rocks beneath younger Miocene basalts and gravels.  Lithologies include grey-black siltstone, with lesser sandstone and chert.   CS12-7 penetrated and bottomed in a 300 foot interval containing variably laminated calcareous siltstones.

Anomalous gold with Carlin-type pathfinder elements is present in six of the seven holes drilled in 2012.  The following table shows significant gold values (≥ 0.100 gpt Au) encountered in the drill program.

 
HOLE INTERVAL (FT) GOLD VALUE (gpt) COMMENT
CS12-1 1170-1175 0.120 brown sandstone with calcite veinlets
CS12-2 1600-1605 0.101 black siltstone with pyrite and calcite veinlets
  1700-1705 0.114 Rhyolite intrusive, weakly silicified
CS12-3 275-280 0.120 limonitic sandstone and siltstone
  590-605 0.267 quartz-sericite-pyrite altered siltstone
  1110-1120 0.139 silicified siltstone/sandstone
CS12-4 990-995 0.113 Intermediate to mafic intrusive
CS12-5 515-525 0.105 Gravel/fault scarp breccia various clast types
  990-1005 0.169 Strongly Silicified siltstone/sandstone
CS12-7 840-860 0.149 gray silicified siltstone
 

Anomalous arsenic zones (>100 ppm) range up to 115 feet (35 m) in drilled thickness and contain values up to 1,530 ppm arsenic, 70 ppm antimony, 3 ppm thallium and 1.8 ppm mercury.  Two holes with the longest anomalous arsenic intervals were drilled 1,900 feet (580 m) apart on the west side of the property, and are located in close proximity to the Fourmile structural zone.  These intervals occur in the Upper Plate strata above the Lower Plate Horse Canyon and Wenban formations encountered in the drilling described below.

In September 2013 the Company re-entered vertical reverse circulation hole CS12-2 and deepened it from 1,760 ft. (537 m) to 4,032 ft. (1,229 m).  Short intervals of anomalous gold values to 0.667 grams/tonne  and Carlin-type pathfinder elements were encountered in hole CS12-2C, as well as longer intervals  of  anomalous arsenic values (>100 ppm) ranging up to 85 ft. (25 m) of drilled thickness.  The bottom 900 feet (274 m) consisted of variably calcareous mudstone/sandstone, and silty/sandy, laminated, variably carbonaceous limestone, interpreted to be  Lower Plate strata of the Horse Canyon and Wenban formations.  This material locally displays Carlin-type alteration features such as decalcification, clay alteration and calcite veining.  Carlin geologists are encouraged that favorable Lower Plate carbonate rocks are present near the projection of the gold-bearing Fourmile structural corridor, at depths consistent with some of the holes in the north portion of Barrick’s neighboring Goldrush discovery.  

In an effort to further enhance the understanding of the encouraging geology encountered in hole CS12-2C, the Company engaged the services of Dr. Harry Cook, President/CEO of Carbonate Geology LLC.  Dr. Cook is very familiar with the Cortez District and Barrick has acknowledged his important role in developing an understanding of the gold-hosting Paleozoic stratigraphy in the area, including the neighboring Goldrush discovery.  Dr. Cook examined the lower 984.5 feet (300 m) of hole CS12-2C, which resulted in his interpreting the bottom 650 feet (198 m) of the hole to contain Devonian strata.  The base of the Roberts Mountain Thrust Fault is interpreted at a hole depth of 3,382 feet (1,031 m).  Dr. Cook states that “Core CS12-2C strata are comprised of very favorable gold-host rocks within both the Wenban Formation and Horse Canyon Formation.  These strata are coeval with the nearby Wenban Fm. And Horse Canyon Fm. carbonate gold-host strata that comprise the gold hosts in Barrick’s Goldrush discovery.”  The Lower Plate strata are comprised of carbonate debris flows, turbidites, slides, slumps and lime and quartz siltstones and mudstones.  The geological setting represents an optimal depositional environment for Carlin-type gold deposits.  Dr. Cook’s interpretations are based on fossil and sedimentologic evidence in addition to his extensive field, pit and core experience at many locations and mine sites throughout Nevada.  Further drilling is warranted, according to Dr. Cook.

Only a small portion of the property has been evaluated, and the Fourmile structural corridor in particular requires more attention.  Plans are being formulated to follow up the 2013 deep core hole, and to drill test other areas of the property. The Company expanded the permit area in 2013.  

This strategic location of the project, along with the similarity in geologic setting to the neighboring Carlin-style deposits, makes Cortez Summit a high quality target for Carlin-style gold mineralization.

Figure 3 –Cortez Summit Geology Map