Eureka Zone

Prospect, Active

Alternative names

Alpha Complex

Commodities and mineralogy

Main commodities Ag; Au; Co; Cu; Ni; Pd; Pt
Ore minerals ni-cu-pge sulfides
Gangue minerals olivine; serpentine

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale A-5
Latitude 63.2481
Longitude -146.1786
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Eureka Zone is a prospect within the Alpha Complex, an ultramafic-mafic complex composed of a sill-dike body 18 kilometers long and up to 600 meters wide, elongated northwest-southeast (Stone, 2005). The coordinates in this record are located approximately at the center of the prospect, about 2.5 miles from where Eureka Creek meets Broxson Gulch. It is located about 0.7 mile northeast of the center of section 27, T. 19 S., R. 8 E., of the Fairbanks Meridian. The accuracy is unknown; the location was estimated using a map of Eureka Zone on Pure Nickel Inc.'s website (Pure Nickel, 2014). The location is accurate to within 1/4 mile.

Geologic setting

Geologic description

 The Alpha complex lies within an area called the Eureka Zone (Findlay, 2013) or Eureka Complex (Stone, 2005). The Alpha Complex and Eureka Zone are part of Pure Nickel's MAN Project, designed for exploration of Nickel (Ni), Copper (Cu), and Platinum Group Element (PGE) mineralization in a series of mafic-utramafic intrusive complexes that are part of the Wrangellia Terrane (Pure Nickel, 2011; Findlay, 2013).
The region is known for the Nikolai Greenstone, a Late Triassic meta-basalt; associated are cogenetic ultramafic-mafic intrusions. These ultramafic-mafic intrusions characteristically weather to an orange-brown color, are generally serpentinized in tectonized zones, and may contain chromiferous magnetite, chromite, and/or disseminated sulfides (Ellis, 2002).
The intrusion complex is a very elongate sill-dike body composed dominantly of massive dunite with thin, marginal gabbro-norite layers. The complex dips moderately to the north, is slightly oblique to the stratigraphy, intruding sedimentary rocks of the Slana River Formation. A discordant magnetic high joins the Eureka Zone with the Fish Lake Complex to the south, interpreted as a potential feeder dike at depth (Ellis, 2002).
The Eureka Complex is truncated by faults related to the Broxson Gulch Thrust and felsic intrusions. Wall rock contacts are generally strongly serpentinized. Copper-magnetite skarns formed in calcareous rocks in contact with the Eureka Complex (Ellis, 2002).
Ni-Cu-PGE mineralization in this prospect is characterized by disseminated sulfides in ultramafic rock at contact with gabbro-norite layers (Stone, 2005). Electron microprobe results indicated most of the nickel is in sulfides with only 0.14 percent contained in olivine and 0.04 percent contained in serpentine, indicating that most of the nickel is recoverable (Findlay, 2013).
Geologic map unit (, )
Mineral deposit model Disseminated Ni-Cu-PGE in gabbro (Cox and Singer, 1986; model 5b).
Mineral deposit model number 5b
Age of mineralization Triassic, about 230 Ma (Findlay, 2013).
Alteration of deposit Serpentinization (Stone, 2005).

Production and reserves

Workings or exploration
From 1991 to 1997, this area was explored by American Copper and Nickel Company (ACNC) working with Fort Knox Gold Resources, Inc. Their work included drilling, surface UTEM, and borehole and EM on three holes. From 1997 to 2003, the area was explored by Nevada Star Resource Corp (US), whose work included a geological mapping program in addition to an AEM survey over the northern and southern portion of the MAN Project area. From 2004 to 2005, the area was briefly explored by Anglo American Exploration (USA). Their work included geological mapping, prospecting, and a soil geochemical sampling survey (Pure Nickel Inc., 2014).
In 2005, Nevada Star Resources Corp., resumed work and completed a 35-kilometer TEM survey over four loop areas, 177-kilometer ground magnetometry, and 1057 soil samples over the general MAN Project area, including eight diamond drill holes in Alpha, which is in the central part of the property. Alpha is a prospect area within the MAN Project area (Pure Nickel Inc., 2014).
In 2007, Pure Nickel gained control of the leases, and it is now 100 percent owned by them, after a joint venture partnership with ITOCHU Corporation of Japan from 2008 to 2013. During this partnership, approximately 23.5 million US dollars were spent on exploration at the general MAN Project area (Pure Nickel Inc., 2014).
In 2011, Pure Nickel completed exploration work focused on the Alpha complex. One of the key objectives of the 2011 program was to evaluate the potential for 'reef' style Platinum Group Elements (PGE) mineralization in the Alpha complex. The possible presence of this type of mineralization was inferred from the occurrence of highly anomalous PGE values associated with a distinctive gabbro/pyroxenite sequence interpreted as discrete layers in the complex. Three holes targeting the potential 'reef' successfully intersected the correct lithological sequence, but assay results did not confirm the presence of economic concentrations of PGE (Findlay, 2013).
In 2012, Pure Nickel completed detailed mapping, and soil and IP surveys at the Alpha complex. Follow-up drilling tested the soil and IP anomalies (Findlay, 2013).
In 2013, Pure Nickel completed an exploration program that included an eight hole, 2,991-meter drill program primarily targeting the Eureka Zone in the central part of the Alpha mafic-ultramafic complex. The drill program successfully intersected the Eureka Zone, first recognized in 2012, in six of the seven holes that were targeted (Pure Nickel Inc., 2014).
The drill results confirm the presence of what is now interpreted as a continuous zone of magmatic sulfide mineralization containing elevated concentrations of nickel, copper, cobalt, gold, silver, platinum and palladium. Estimated true widths of intersection for 2013 drill holes cutting the Eureka Zone in the central Alpha segment range from 120 meters to 250 meters. Composite intersection grades across the mineralized zone in the drill holes range from 123 parts per billion (ppb) to 212 ppb gold + platinum + palladium, 0.05 to 0.16 percent copper, and 0.17 to 0.24 percent nickel. The mineralization also includes minor silver and cobalt. Higher grade mineralization over narrower widths is present in most of the holes (Pure Nickel Inc., 2014).
Indication of production None

Additional comments

In 2007, Pure Nickel gained control of the leases, and it is now 100 percent owned by them, after a joint venture partnership with ITOCHU Corporation of Japan from 2008 to 2013. During this partnership, approximately US$23.5 million was spent on exploration at the general MAN Project area (Pure Nickel Inc., 2014).

References

References

Findlay, J., 2013, An Overview of Pure Nickel Inc.'s MAN and Salt Chuck Exploration Projects in Alaska, Pure Nickel Inc.: Alaska Miners Association, 2013 Annual Convention, Abstracts, p. 31.
Pure Nickel Inc., 2011, Pure Nickel MAN Alaska Exploration Update: http://www.purenickel.com/s/NewsReleases.asp?ReportID=497855 (News release on December 21, 2011, as of July 9, 2014).
Reporters V.C. Zinno (Alaska Earth Sciences, Inc.)
Last report date 3/15/2016