Willow Branch of Tozer Creek

Prospect, Inactive

Commodities and mineralogy

Main commodities Zn
Other commodities Sn
Ore minerals cassiterite; sphalerite
Gangue minerals arsenopyrite; fluorite; garnet; pyrite; quartz

Geographic location

Quadrangle map, 1:250,000-scale TE
Quadrangle map, 1:63,360-scale C-4
Latitude 65.507
Longitude -166.742
Nearby scientific data Find additional scientific data near this location
Location and accuracy 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.'.

Geologic setting

Geologic description

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 precursor granite phase rather than an mineralizing 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.
Geologic map unit (-166.744715564193, 65.5062344461341)
Mineral deposit model Fault-controlled replacement and veining. Possibly tin skarn (14b) or tin vein (15b) model after Cox and Singer (1986).
Age of mineralization 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 of deposit Garnet and sulfide-rich tactite replaces calc-silicate rock (hornfels); possibly some later quartz-fluorite veining.

Production and reserves

Workings or exploration Surface reconnaissance mapping and an analysis of one random chip sample is all the information available for this prospect.
Indication of production None


MRDS Number 10308439


Hudson, T.L., and Arth, J. G., 1983, Tin granites of Seward Peninsula, Alaska: Geological Society of America Bulletin, v. 94, p. 768-790.
McDermott, M.M., 1983, Investigation of the magnetic contact aureoles of the Khotol and Black Mountain granites, Alaska: Anchorage, Alaska, Anaconda Minerals Company internal report (Report held by Cook Inlet Region, Inc., Anchorage, Alaska).
McDermott, M.M., 1983, Seward Peninsula reconnaissance 1982 geophysical report: Anchorage, Anaconda Minerals Company internal report, 29 p. (Report held by Cook Inlet Region, Inc., Anchorage, Alaska.)
Reporters Travis L. Hudson (Applied Geology)
Last report date 5/10/1998