Unnamed (on hill 2321)

Occurrence, Probably inactive

Commodities and mineralogy

Main commodities Be; Th; U
Ore minerals beryl; unknown thorium- and uranium-bearing minerals
Gangue minerals feldspar; garnet; quartz; tourmaline

Geographic location

Quadrangle map, 1:250,000-scale NM
Quadrangle map, 1:63,360-scale D-1
Latitude 64.9021
Longitude -165.499
Nearby scientific data Find additional scientific data near this location
Location and accuracy The occurrence is a composite of several pegmatites mapped by Hummel (1975, localities 85 and 86) on hill 2321, about 2 miles south-southwest of Mosquito Pass. These occurrences are almost at the west boundary of the Nome D-1 quadrangle. They are at an elevation of about 2,300 feet and about 1 mile west-southwest of the tactite occurrence at NM044. Mining claims were staked from this locality across the unnamed creek to the west (Alaska Division of Geological and Geophysical Surveys, 1982).

Geologic setting

Geologic description

These pegmatites are south of the Thompson Creek orthogneiss, and their age is uncertain. Granite pegmatites are abundant in the Kigluaik Mountains, and others may be present near these occurrences. The pegmatites are noticeably radioactive; radioactivity measured on the ground with a scintillometer is as much as 500 counts per second or 3 to 5 times common background (Hawley and Associates, 1978, Section IV). Tourmaline and garnet are common accessory minerals, and the more radioactive pegmatites commonly contain smoky quartz. Beryl occurs in some of the pegmatite, including a body described by Moffit (1913, p. 25) about 1 mile west of the mouth of North Star Creek (NM046).
Some granite pegmatites are within the Thompson Creek orthogneiss or appear to be spatially associated with it, particularly on its south or hanging wall side (Hummel, 1962 [MF 248]; Till, 1980). The Thompson Creek orthogneiss has been dated as latest Proterozoic (555 Ma, Amato and Wright, 1998), and some pegmatites may also be this age. However, metasedimentary rocks of the Kigluaik Mountains underwent granulite facies metamorphism and partial melting in the mid-Cretaceous, and some pegmatites are crosscutting to local structure and are mid-Cretaceous in age (Throckmorton and Hummel, 1979; Till, 1983; Miller and Hudson, 1991; Hudson, 1994; Till and Dumoulin, 1994; Amato and others, 1994; Amato and Wright, 1997, 1998).
The host rocks to these pegmatites are amphibolite facies metasedimentary rocks that are derived from Precambrian or early Paleozoic protoliths (Sainsbury, 1972; Bunker and others, 1979; Till and Dumoulin, 1994). They are thought to have undergone regional high-pressure metamorphism along with many other rocks of Seward Peninsula in the Late Jurassic or Early Cretaceous (Sainsbury, Coleman, and Kachadoorian, 1970; Forbes and others, 1984; Thurston, 1985; Patrick, 1988; Patrick and Evans, 1989; Armstrong and others, 1986; Hannula and McWilliams, 1995). Higher temperature metamorphism overprinted these rocks in conjunction with regional extension, crustal melting, and magmatism in the mid-Cretaceous (Throckmorton and Hummel, 1979; Till, 1983; Evans and Patrick, 1987; Leiberman, 1988; Patrick and Leiberman, 1988; Miller and Hudson, 1991; Miller and others, 1992; Dumitru and others, 1995; Hannula and others, 1995; Hudson and Arth, 1983; Hudson, 1994; Amato and others, 1994; Amato and Wright, 1997, 1998). Uplift of the higher temperature metamorphic rocks took place in the mid- to Late Cretaceous and in the Eocene (Calvert, 1992; Dumitru and others, 1995).
Geologic map unit (-165.501632454383, 64.9013402383007)
Mineral deposit model Simple granite pegmatite with rudimentary zoning.
Age of mineralization Late Proterozoic or mid-Cretaceous; either the age of the Late Proterozoic Thompson Creek orthogneiss or mid-Cretaceous amphibolite facies metamorphism.

Production and reserves

Workings or exploration Reconnaissance uranium exploration including airborne radiometrics, stream sediment surveys, and ground traverses have been completed in the Kigluaik Mountains.
Indication of production None

References

MRDS Number 10307929

References

Alaska Division of Geological and Geophysical Surveys, 1982, Mining claim location maps -- Nome quadrangle: Alaska Division of Geological and Geophysical Surveys, 8 p., 3 sheets, scales 1:63,360 and 1:250,000.
Armstrong, R.L., Harakal, J.E., Forbes, R.B., Evans, B.W., and Thurston, S.P., 1986, Rb-Sr and K-Ar study of metamorphic rocks of the Seward Peninsula and southern Brooks Range, Alaska, in Evans, B.W., and Brown, E.H., eds., Blueschists and eclogites: Geological Society of America Memoir 164, p. 184-203.
Calvert, A.T., 1992, Structural evolution and thermochronology of the Kigluaik Mountains, Seward Peninsula, Alaska: Stanford, Calif., Stanford University, M.Sc. thesis, 50 p.
Evans, B.W. and Patrick, B.E., 1987, Phengite 3-T in high pressure metamorphosed granitic orthogneisses, Seward Peninsula, Alaska: Canadian Mineralogist, v. 25, part 1, p. 141-158.
Hannula, K.A., and McWilliams, M.O., 1995, Reconsideration of the age of blueschist facies metamorphism on the Seward Peninusla, Alaska, based on phengite 40Ar/39Ar results: Journal of Metamorphic Geology, v. 13, p. 125-139.
Hannula, K.A., Miller, E.L., Dumitru, T.A., Lee, Jeffrey, and Rubin, C.M., 1995, Structural and metamorphic relations in the southwest Seward Peninsula, Alaska; Crustal extension and the unroofing of blueschists: Geological Society of America Bulletin, v. 107, p. 536-553.
Hawley, C.C., and Associates, 1978, Uranium evaluation of the Seward-Selawik area, Alaska: Department of Energy, Grand Junction, Colo., Open-File Report GJBX-105(78), 91 p.
Hudson, T.L., 1994, Crustal melting events in Alaska, in Plafker, G., and Berg, H. C., eds., The Geology of Alaska: Geological Society of America, DNAG, The Geology of North America, Vol. G-1, p. 657-670.
Hudson, T.L., and Arth, J. G., 1983, Tin granites of Seward Peninsula, Alaska: Geological Society of America Bulletin, v. 94, p. 768-790.
Leiberman, J.E., 1988, Metamorphic and structural studies of the Kigluaik Mountains, western Alaska: Seattle, University of Washington, Ph.D. dissertation, 191 p.
Miller, E.L., Calvert, A.T., and Little, T.A., 1992, Strain-collapsed metamorphic isograds in a sillimanite gneiss dome, Seward Peninsula, Alaska: Geology, v. 20, p. 487-490.
Patrick, B.E., 1988, Synmetamorphic structural evolution of the Seward Peninsula blueschist terrane, Alaska: Journal of Structural Geology, v. 10, p. 555-565.
Patrick, B.E., and Evans B.W., 1989, Metamorphic evolution of the Seward Peninsula blueschist terrane: Journal of Petrology, v. 30, p. 531-555.
Patrick, B.E., and Leiberman, J.E., 1988, Thermal overprint on blueschists of the Seward Peninsula, the Lepontine in Alaska: Geology, v. 16, p. 1100-1103.
Thurston, S.P., 1985, Structure, petrology, and metamorphic history of the Nome Group blueschist terrane, Salmon Lake area, Seward Peninsula, Alaska: Geological Society of America Bulletin, v. 96, p. 600-617.
Till, A.B., 1980, Crystalline rocks of the Kigluaik Mountains, Seward Peninsula, Alaska: Seattle, University of Washington, M.Sc. thesis, 97 p.
Till, A.B., 1983, Granulite, peridotite, and blueschist--Precambrian to Mesozoic history of Seward Peninsula: Alaska Geological Society Journal, Proceedings of the 1982 Symposium on Western Alaska Resources and Geology, p. 59-65.
Reporters C.C. Hawley and Travis L. Hudson
Last report date 10/22/1999