Willow Branch of Tozer Creek Prospect, Port Clarence Mining District, Nome Census Area, Alaska, USAi

Regional Level Types
Willow Branch of Tozer Creek Prospect	Prospect
Port Clarence Mining District	Mining District
Nome Census Area	Census Area
Alaska	State
USA	Country

Location: This prospect is on the south side of the Willow Branch of Tozer Creek in the south-central Teller C-4 quadrangle. Willow Branch is a south tributary to Tozer Creek, a major east tributary to the Don River. Mineralization is along a fault that is about 500 feet south and parallel to Willow Branch at elevations between 440 and 600 feet. This is locality 12 of Cobb and Sainsbury (1972). Cobb (1975) summarized relevant references under the name 'Black Mtn.'.
Geology: The Willow Branch of Tozer Creek is in the northwest part of the upland that includes Black Mountain. This upland is an area of hornfels, calc-silicate hornfels, and tactite intruded by a locally exposed biotite granite. The metasedimentary rocks, fine-grained metapelitic and metacarbonate rocks, are of unknown but probable Paleozoic age. The Late Cretaceous (79.1 +/- 2.9 my, Hudson and Arth, 1983, p. 769) biotite granite, medium-grained and equigranular, is exposed in a small area on the southern flanks of the upland and is interpreted to be part of an early precurser granite phase rather than an mineralyzing granite phase (Hudson and Arth, 1983, p. 784; Hudson and Reed, 1997, figure 3). The wide distribution of thermally metamorphosed rocks and the results of gravity and aeromagnetic surveys (McDermott, 1983) indicate that most of the Black Mountain area is underlain by granite at depth. The area is transected by many normal faults and related fractures. Sainsbury and Hamilton (1967) mapped a northwest-trending fault along the south side of Willow Branch that is noticeably mineralized over a distance of about 2,500 feet. This fault juxtaposes metapelitic rocks to the north against calc-silicate rocks to the south. Along the fault, calc-silicate rocks are variably replaced by garnet and sulfide-rich assemblages over widths of a few to 12 feet. The sulfide minerals include sphalerite, pyrite, arsenopyrite, and a sooty, black unidentified material. Fluorite and fine-grained silica are noted as gangue minerals in this assemblage (Sainsbury and Hamilton, 1969, p. B23). One sample of the sulfide-rich material has been analyzed (Sainsbury and Hamilton, 1967, p. B24). This sample contained 3% zinc, 700 ppm tin, 300 ppm copper, and 300 ppm lead.
Workings: Surface reconnaissance mapping and an analysis of one random chip sample is all the information available for this prospect.
Age: Late Cretaceous; the Black Mountain biotite granite, interpreted to be linked to alteration and mineralization in this area, has been determined to be 79.1 +/- 2.9 my old by the K/Ar method (Hudson and Arth, 1983, p. 769).
Alteration: Garnet and sulfide-rich tactite replaces calc-silicate rock (hornfels); possibly some later quartz-fluorite veining.

Commodities (Major) - Zn; (Minor) - Sn
Development Status: None
Deposit Model: Fault-controlled replacement and veining. Possibly tin skarn (14b) or tin vein

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Link to USGS - Alaska:	TE089

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References