Black Mountain

Prospect, Inactive

Commodities and mineralogy

Main commodities Sn
Ore minerals cassiterite; galena; sphalerite
Gangue minerals diopside; epidote; fluorite; garnet; idocrase; plagioclase; quartz; tourmaline; wollastonite

Geographic location

Quadrangle map, 1:250,000-scale TE
Quadrangle map, 1:63,360-scale B-4
Latitude 65.483
Longitude -166.744
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Black Mountain area is a four square mile upland between Tozer Creek and the California River, in the northern Teller B-4 quadrangle and adjacent parts of the Teller C-4 quadrangle. Large parts of this area are thermally metamorphosed and tactite is widespread. However, the prospect area described here is at about 1700 feet elevation on the southwest ridgecrest between headwaters to Constance Creek and an unnamed east tributary to Tozer Creek. This is locality 13 of Cobb and Sainsbury (1972). Cobb (1975) summarized relevant references under the name 'Black Mtn.'.

Geologic setting

Geologic description

The upland including Black Mountain 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, 1983a) 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, p. B23) noted the presence of quartz-topaz greisen with cassiterite, pyrite, pyrrhotite, sphalerite, and galena in the northeast part of the exposed granite body but most of the mineralization and alteration in the area is associated with calc-silicate rocks. Calc-silicate rocks contain garnet, idocrase, tourmaline, wollastonite, and epidote. Cross-cutting veins and alteration along normal faults and fractures include quartz, tourmaline, fluorite, and sulfide minerals (pyrite, sphalerite, arsenopyrite, and probably others). Cassiterite and wolframite have not been conclusively identified in the calc-silicate rocks. Only reconnaissance geochemistry for a few rock samples is available (Sainsbury and Hamilton, 1967, p. B24; Hudson, 1984, p. 20). Tin is weakly anomalous in most tactite samples but one garnet-epidote-idocrase rock contained 1,800 ppm tin. Weak base metal, silver, and gold (60 and 100 ppb) and strong arsenic (400 ppm), fluorine (over 20,000 ppm), and boron (2,230 ppm) anomalies are present in some rocks.
Geologic map unit (-166.746712748118, 65.4822330419077)
Mineral deposit model Tin skarn (Cox and Singer, 1986; model 14b).
Mineral deposit model number 14b
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 Calc-silicate hornfels and tactite development is common; late quartz-fluorite +/- tourmaline veining and alteration is present along faults and fractures.

Production and reserves

Workings or exploration Some reconnaissance rock geochemistry and traverse geology, regional gravity and aeromagnetic surveys, and some onsite magnetic character and susceptibility determinations have been completed (Hudson, 1984; McDermott, 1983a; 1983b; Reed and others, 1989).
Indication of production None



Hudson, T.L., 1984, Tin systems of Seward Peninsula, Alaska: Anchorage, Anaconda Minerals Company internal report, 51 p. (Report held by Cook Inlet Region Inc., Anchorage, Alaska)
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.)
Reed, B.L., Menzie, W.D., McDermott, M., Root, H., Scott. W., and Drew, L. J., 1989, Undiscovered lode tin resources of the Seward Peninsula, Alaska: Economic Geology, v. 84, no. 7, p. 1936-1947.
Reporters Travis L. Hudson (Applied Geology)
Last report date 5/10/1998