Ruby Creek Prospect, Port Clarence Mining District, Nome Census Area, Alaska, USAi

Regional Level Types
Ruby Creek Prospect	Prospect
Port Clarence Mining District	Mining District
Nome Census Area	Census Area
Alaska	State
USA	Country

Location: Ruby Creek is a small east headwater tributary to Glacier Canyon Creek that flows northward across the Kigluaik Mountain front 0.4 miles northeast of Glacier Canyon Creek. This creek is not identified by name on USGS topographic maps; its name comes from a location map made by Coats (1944). This location is 11.8 miles due east of White River and 2.4 miles northeast of the Christophosen mine (TE 103) at elevations of 550 to 650 feet. It is 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 'Ruby Cr.'.
Geology: 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 locality to the west and Graphite Creek locality to the east). 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. To the west of Ruby Creek, a 50-foot trench along strike exposes lenses up to 1 foot wide that are estimated to contain 70% graphite by volume. This zone of high-grade lenses has been traced along strike for 500 feet and is exposed over a vertical extent of 175 feet. The width of the graphite-rich zone was not recorded. A sample from this exposure contained 60% graphite of which 65% was coarser than 30 mesh to the inch (Coats, 1944). Other graphite-rich zones are present along Ruby Creek including a faulted section 4 feet wide with 1 to 6 inch wide graphite stringers and a 12 foot wide section with several 4 to 12 inch thick graphite-rich lenses. Individual lenses are not more than 20 feet long and seem to be about 12 times their width in length. The lenses overlap one another and come and go through the graphite-rich section (Coats, 1944). A sample of schist (plagioclase-biotite-quartz schist) with disseminated graphite from this locality was thought to have 5 to 10% graphite in thin section but laboratory analysis indicated a graphite content of 3% (Wolgemuth, 1982).
Workings: A 50 -foot long surface trench and a 20 foot-long drift were noted by Coats (1944) and other small surface workings (pits) are probably present. Exploration activity in the general area took place as recently as 1994 (Swainbank and others, 1995).
Age: The metamorphism that has developed coarse graphite in these rocks is Late Jurassic to Early Cretaceous in age.
Alteration: Some shearing and deformation of graphite-rich lenses has accompanied faulting and oxidation of disseminated pyrrhotite has led to orange-staining of graphite-bearing rocks but other types of alteration are not identified.
Production: Some 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).
Reserves: The few miles of strike between the area of the Christophosen Creek deposit and the Graphite Creek deposit to the east has been estimated to contain 65,000 tons averaging about 60% graphite (Coats, 1944). This zone has also been estimated to contain, overall, more than 10 million tons of 10% or more graphite (Weiss, 1973).

Commodities (Major) - Graphite
Development Status: Yes, small
Deposit Model: Flake graphite in disseminations and tabular lenses within amphibolite facies me

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Link to USGS - Alaska:	TE104

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References