Graphite Creek

Prospect, Active

Commodities and mineralogy

Main commodities Graphite
Ore minerals graphite; pyrrhotite
Gangue minerals amphibole; biotite; garnet; muscovite; plagioclase; quartz; sillimanite; sphene; zircon

Geographic location

Quadrangle map, 1:250,000-scale TE
Quadrangle map, 1:63,360-scale A-2
Latitude 65.04
Longitude -165.535
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Graphite Creek Prospect is located near the center of section 22, T. 5 S., R. 34 W., of the Kateel River Meridian. Graphite Creek flows northward across the Kigluaik Mountain front 0.9 mile northeast of Glacier Canyon Creek and 0.5 mile northeast of Ruby Creek. This creek is not identified by name on USGS topographic maps; its name comes from a location map made by Coats (1944). Its mouth is on the east shore of Windy Cove on Imuruk Basin, 0.75 mile northeast of the mouth of Glacier Canyon Creek. The graphite deposits are at about 750 feet elevation at the abrupt break in slope on the north side of the mountain front, just upslope of the surface trace of the active Kigluaik normal fault. The graphite-bearing rocks are in the footwall of this fault. This location was not shown by Cobb and Sainsbury (1972), but Cobb (1975) summarized relevant references under the name 'Graphite Cr.' Location is accurate within 500 feet.

Geologic setting

Geologic description

Flake graphite occurs as disseminations and high-grade tabular lenses within amphibolite facies metasedimentary rocks (Coats, 1944). The metamorphic rocks are primarily biotite-quartz schist with some sillimanite and garnet (Sainsbury, 1972). Small granitic plugs, dikes, and sills locally intrude the metamorphic rocks. The graphite-bearing schists are sharply bound to the north by the recently active Kigluaik fault, the principal fault along which late Cenozoic uplift of the Kigluaik Mountains has taken place (Hudson and Plafker, 1978). The graphite-bearing schists strike approximately parallel to the mountain front and dip north between 25 and 65 degrees. They form a zone along the mountain front that is 200 to 400 feet thick and possibly 20,000 feet long (Hudson, 1981; also see Christophosen Creek (TE103) to the west). To the south, the graphite-bearing schists are in conformable contact with other amphibolite facies metasedimentary rocks. The latter appear to be feldspathic and contain much less graphite. The graphite-bearing schists make up two general sequences; (1) a heterogeneous sequence of garnet-sillimanite-biotite-quartz schist with disseminated graphite and graphite-rich lenses, and (2) a more evenly layered biotite-quartz schist with disseminated graphite. The latter contains disseminated pyrrhotite and commonly weathers orange.
West of Graphite Creek a 30 foot-long pit exposes a garnet-bearing schist with disseminated graphite and graphite-rich lenses. A 13-foot section here contained 3 feet of garnet -bearing schist with graphite and a 3.5 foot thick high-grade graphite lense with quartz stringers. A sample of the garnet-bearing schist contained 12 percent graphite of which 80 percent was coarser than 30 mesh per inch and a sample of the graphite-rich material contained 59 percent graphite of which 83 percent was coarser than 30 mesh per inch (Coats, 1944). A 25-foot thick zone containing disseminated graphite and a 3-foot wide high-grade lens is exposed on the east side of Graphite Creek. Twenty feet of this section is estimated to contain 10 percent disseminated graphite. This zone has been traced eastward on the surface for a distance of 480 feet and where it is well exposed, a 3- to 4-foot wide high-grade lens is present (Coats, 1944).
In 2016, Graphite One Resources conducted a comprehensive product-development program for graphite from their Graphite Creek deposit. Significant results include: test work exceeded graphite-purity threshold requirements; produced premium‐grade spherical graphite (SPG) from purified graphite; achieved almost 75 percent conversion of STAX graphite (Spheroidal, Thin, Aggregate, and eXpanded naturally‐occurring morphologies present in graphite sourced from the Graphite Creek deposit) to SPG in the size range suitable for electric-vehicle applications compared to typical industry yields of 30 to 40 percent; successful, near-theoretical-limit discharge-capacity tests on coated and uncoated spherical graphite; nearing completion of preliminary test work on mineral-processing circuit for producing high-grade graphite concentrate; and, demonstrated potential to produce products that will effectively compete in the high-end battery market (for both electric vehicles and power storage) as well as other markets for purified graphite and graphite byproducts (Athey and Werdon, 2017).
Geologic map unit (-165.537643268112, 65.0392401257631)
Mineral deposit model Disseminated flake graphite (Orris and Bliss, 1992; model 37f).
Mineral deposit model number 37f
Age of mineralization The metamorphism that has developed coarse graphite in these rocks is Late Cretaceous, based on K/Ar and Ar/Ar dating which is immediately preceding or coincident with the intrusion of the Kigluaik Pluton (Eccles and Nicholls, 2014).
Alteration of deposit The graphite occurs as massive to semi-massive segregations and disseminations in amphibolite grade biotite-quartz schist with zones of sillimanite-garnet-biotite-quartz schist with high-grade graphite within 1 km of a fault zone (Eccles and Nicholls, 2014).

Production and reserves

Workings or exploration
Surface pits, including one 30 feet long from which 50 tons of high-grade material were recovered, are present. Exploration activity in the general area took place in 1994 (Swainbank and others, 1995).
In January 2012, Graphite One Resources (Graphite One) entered an option agreement to earn 100 percent interest in claims encompassing known graphite showings over a three year period. The total Graphite Creek Property land package comprises 129 claims totaling 16,801 acres (6,799 hectares) (Duplessis and others, 2013).
During 2011 and 2012, Graphite One conducted exploration work at the Graphite Creek Property. The majority of the exploration work was completed during the summer 2012 including: a time-domain helicopter-borne electromagnetic survey; geological mapping; surface grab, channel and bulk pit sampling; and an 18 drillhole program to test the graphitic units at depth (Duplessis and others, 2013). In 2013, a 10 drillhole program expanded the area of mineralization both easterly and westerly, more than doubling the length of the graphite zone, which was about 2.2 kilometers in 2012, and became 4.8 kilometers in 2013 (Eccles and Nicholls, 2014).
In 2014 infill drilling along a 730 meter strike length at Graphite Creek was completed by Graphite One. Twenty-two holes were drilled for a total of 2313 meters. Two of these drill holes were for metallurgical work. The other 20 drill holes, along with drill holes from previous years, provided enough drill coverage and confidence to estimate an indicated and inferred resource at Graphite Creek. Highlights from the 2014 drilling include 23.43 meters of 8.66 percent graphitic carbon (Cg), 38.87 meters of 10.50 percent Cg, 42.81 meters of 6.27 percent Cg, 38.80 meters of 7.80 percent Cg, and 24.56 meters of 6.76 Cg (Eccles and others, 2015).
Indication of production Yes; small
Reserve estimates
The few miles along strike between the area of the Christophosen Creek (TE103) deposit and the Graphite Creek deposit to the east has been estimated to contain 65,000 tons averaging about 60 percent graphite (Coats, 1944). This zone has also been estimated to contain, overall, more than 10 million tons of 10 percent or more graphite (Weiss, 1973).
The first mineral resource estimate for Graphite Creek, which includes Christophosen Creek (TE103) and Ruby Creek (TE104), calculated according to modern standards was by Duplessis and others in 2013. Eccles and Nicholls (2014) updated this estimate with an inferred resource of 186.86 million tonnes of 5.5 percent graphitic carbon with a recommended cut-off grade of 3 percent graphitic carbon and in-situ graphite of 10,346,000 tonnes.
With more infill drilling completed, in 2015 an indicated resource at Graphite Creek was finally able to be estimated by Eccles and others (2015). The indicated resource at a 3 percent cut-off grade is 17.95 million tonnes at 6.3 percent graphitic carbon and 1,133,000 tonnes in-situ graphite. The inferred resource was updated at a 3 percent cut-off grade to 154.36 million tonnes at 5.7 percent graphitic carbon and 8,764,000 tonnes of in-situ graphite (Eccles and others, 2015).
Graphite One Resources plans to release Graphite Creek’s inaugural Preliminary Economic Assessment, including a refined resource estimate, in February 2017. As of April 2015, Graphite Creek’s indicated resources include 17.95 million tonnes grading 6.3 percent carbon-as-graphite (Cg) for an in situ 1.13 million tonnes of graphite, and inferred resources of 154.36 million tonnes grading 5.7 percent Cg for an in situ 8.76 million tonnes of graphite (Graphite One Resources, 2015). Resources are based on 48 drill holes, using a cut-off grade of 3 percent. The deposit remains open along strike in both the east and west directions, as well as down dip.
Production notes Most of the graphite shipments reported for the Alaska Graphite Company may have come from this locality. These shipments include 35 tons (1907) and 100 tons (1916 or 1917) of hand-sorted, high-grade material (Mertie, 1918; Harrington, 1919; Coats, 1944). Coats (1944) reports that about 50 tons were recovered in 1916 from the 30-foot long pit on the west side of Graphite Creek.

References

MRDS Number A015734
Reporters Travis L. Hudson (Applied Geology); V.C. Zinno (Alaska Earth Sciences, Inc.); N.V. King (Alaska Earth Sciences, Inc.); M.B. Werdon (DGGS)
Last report date 8/26/2017