Cortez Summit Property

Eureka County, Nevada

Carlin Gold’s Cortez Summit property, 60 miles southwest of Elko in the southern Cortez Mountains, is located between the historic Buckhorn district and the Horse Canyon portion of the Cortez district, Eureka County, Nevada. The property consists of 142 100%-owned unpatented lode claims (BH 1-18, 20, and 22-88, 91-114, 116-147) located in sections 23, 24, 25, 26, 35 and 36, T27N, R48E; and sections 30, 31, T27N, R49E; and section 6, T26N, R49E, MDBM. The east edge of the property lies 0.5 miles southwest of the Buckhorn Mine, and the west edge of the property lies 1.6 miles northeast of the Horse Canyon Mine. Barrick’s Cortez Hills operation (11 MM oz gold pre-production reserve/resource) lies 4 miles west of the property. The southwest corner of the property lies 1 mile northeast of Barrick’s new Red Hill –Goldrush discovery area in Horse Canyon.  As of December 31, 2011, Barrick reported a 7.0 million oz gold resource at Red Hill-Goldrush, open for expansion.  Barrick currently refers to the new discoveries as Goldrush.  Barrick has been drilling in the area with multiple rigs continuously throughout the year.

Figure 1 – Cortez Trend

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

  1. Carlin-style sediment-hosted Au,
  2. Buckhorn-style volcanic-hosted low sulfidation Au-Ag). Probable late Eocene Carlin-style mineralization at the Horse Canyon mine is controlled by a combination of NNW-, ENE- and NW-trending structures as well as favorable Devonian stratigraphy. Similar controls are reported at Red Hill-Goldrush and at Cortez Hills. The Buckhorn-style mineralization is associated with an extensive Miocene hot springs system (14.6 Ma) which is controlled by NNW-trending Northern Nevada rift structures.

Carlin Gold identified the area as prospective in 2007 based on the premise that published maps may have misinterpreted an important stratigraphic interval in the Cortez area within the lower plate of the Roberts Mountains Thrust (RMT). In the Cortez region, a significant interval of siliciclastic and calcareous clastic rocks conformably overlies carbonate rocks of the Devonian Wenban Formation. These rocks have been misidentified in some areas as upper plate Ordovician Vinini Formation, resulting in the Roberts Mountains Thrust (RMT) being erroneously placed at the stratigraphic break between carbonate and clastic rocks. Locally, the clastic rocks actually represent the Devonian-age Horse Canyon Formation. The Horse Canyon Formation is analogous to the Rodeo Creek Formation on the Carlin Trend – both are sequences of Devonian siliciclastic and calcareous clastic rocks that conformably overlie Devonian carbonate host rocks within the lower plate of the RMT. Both sequences are also host to Carlin-type mineralization.

The calcareous units of the Horse Canyon Formation  and the underlying  Wenban Formation comprise a favorable stratigraphic interval that hosts the Horse Canyon deposit, as well as portions of other deposits on the Cortez Trend. One challenge in investigating this stratigraphic concept at Cortez Summit is that, except for a narrow sliver of Paleozoic rocks 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.  Published mapping shows these rocks as Ordovician Vinini Formation, however it appears uncertain.  Where attitudes can be measured, the Paleozoic 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 toward the favorable rock sequence which hosts gold mineralization in the area.   On the west side of the property, the Paleozoic rocks are unconformably overlain by a Tertiary (Eocene? to Miocene) volcano-sedimentary sequence consisting of a lower gravel unit and an upper series of Miocene (15-16 Ma) basaltic andesite flows. The Tertiary sequence varies in thickness from zero on the west side of the property to >500 ft. on the east side. The Buckhorn deposits are primarily hosted by the basaltic andesite. Dikes, plugs and minor flows of Miocene (15 Ma) rhyolite locally intrude and overlie the gravel and basaltic andesite units.

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 intrusives may be correlative with early Oligocene quartz porphyry dikes which are common at the Horse Canyon, Cortez Hills and other Cortez district deposits.  In addition to the two phases described above, a rhyolite plug cuts the Miocene basalt in the southwest corner of the property in upper Willow Creek.

Two structural orientations dominate the Cortez Summit area: 1) N10-20W 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 ENE-trending structures exhibited by the drainage patterns eroding the basaltic andesite (ie. Willow Creek structure). The rhyolite plug of upper Willow Creek intrudes the inferred structural intersection between the ENE-trending Willow Creek structure and the NNW-trending Fourmile structure.   The Northern Nevada Rift structures associated with Buckhorn-style mineralization may also represent a shallow manifestation of the deep-seated feeder structures involved in older Carlin-style mineralization at depth. A third, potentially important, structural trend is indicated by the gravity data that Carlin Gold has collected. The horizontal gradient of the complete bouguer anomaly defines several strong NS features. The westernmost of these features appears to project to the south in the vicinity of the Red Hills fault zone, and important feature associated with the mineralization in Barrick’s Red Hill drilling area.

 

Cortez Summit and Cortez Deposits

Carlin Gold’s primary focus is for Carlin-style mineralization in a structural setting similar to that at the nearby deposits including the Cortez Hills mine and the Goldrush resource. In August 2012 a reverse circulation drill program was initiated to evaluate an untested conceptual structural and stratigraphic target:   the  lower Horse Canyon Formation and  select underlying units of the Wenban Formation at depth in proximity to the Fourmile structure and/or north projection Red Hills fault zone. Much of this target is blind, being covered by post-mineral gravel and basaltic andesite.  Where Paleozoic rocks are exposed, sampling along the Fourmile structural zone has yielded gold values of 0.447 and 0.263 gpt on the west edge of the property in altered siliciclastic rocks. Rock sampling along a drill road cut yielded 0.175 gpt gold over 50 feet in altered siltstones.  The most favorable area to test the target concept is in the southwest portion of the property in the vicinity of the Fourmile and/or Red Hills fault zone structures. 

In August and September 7 reverse circulation drill holes were completed to depths ranging between 1500 and 1800 feet, for a total of 11,720 feet.  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.   Carlin geologists have tentatively assigned this calcareous unit to the Devonian Horse Canyon Formation, which overlie the rocks believed to host the bulk of Barrick’s Goldrush resource. 

Anomalous gold with Carlin-type pathfinder elements is present in six of the seven holes drilled.  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 a prominent north-northwest oriented structure that trends for 4,500 feet (1,370 m) along the western side of the property.  This may be the Fourmile structure referred to above.

The Company is encouraged that the initial drill program, which focused only on a small portion of the property, has encountered favorable Carlin-type geology, alteration and geochemistry. Plans are being formulated to drill test other areas of the property and to extend some of the initial holes by diamond drilling to test deeper parts of the stratigraphic section in proximity to potentially favorable structures.  The Company is currently preparing to expand the permit area. 

The Cortez Summit property is well-situated in the Cortez trend between the Horse Canyon and Buckhorn mines.   Barrick’s Cortez Hills mine is located 4 miles west, and their new Red Hill-Goldrush discovery is located within a mile of the property.  Barrick is completing an announced a $64 million exploration program in the district for 2012.  The Cortez Summit project is located in the midst of an expanding number of gold deposits.  This strategic location, 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.