Unnamed (near 'Fluorite Creek')

Occurrence, Inactive

Commodities and mineralogy

Main commodities F
Other commodities Ag; Mo
Ore minerals fluorite; pyrite; pyrrhotite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale NM
Quadrangle map, 1:63,360-scale D-2
Latitude 64.9131
Longitude -165.9751
Nearby scientific data Find additional scientific data near this location
Location and accuracy Fluorite Creek was a local name assigned by Sainsbury, Kachadoorian, and Smith (1970) to an upper tributary to Tisuk River in the NW1/4 section 4, T. 7 S., R. 36 W., Kateel River Meridian. The occurrence is at an elevation of about 1,800 feet and located within about 1,000 feet of the coordinates.

Geologic setting

Geologic description

Fluorite was found in two breccia pipes at this locality (Sainsbury, Kachadoorian, and Smith, 1970). The easternmost pipe is 40 to 60 percent fluorite and 20 feet wide; it consists of a central core of crystalline fluorite surrounded by a margin of banded silica and fluorite with pyrite. Locally this breccia is silicified, pyritized, and cemented by fluorite. The central fluorite-rich core is cut by iron-stained veinlets 0.25 to 0.5 inch thick. The second pipe, located 350 feet west of the first, is smaller and more pyritized and contains a higher percentage of silicified breccia. A large fault, spatially associated with the pipes, is marked by a 30- to 40-foot-wide jasperoid containing a few percent fluorite. A sample of the pyrite-bearing jasperoid breccia contained 3 ppm silver and 70 ppm molybdenum; no gold was detected. The wall rock along normal faults in the general area are mineralized with pyrrhotite, pyrite, and traces of other sulfides.
Mid-Cretaceous granite stocks and felsic dikes are common in the western Kigluaik Mountains where they intrude amphibolite facies metasedimentary schist and gneiss (Sainsbury, Smith, and Kachadoorian, 1972). The metasedimentary rocks are derived from a late Proterozoic or early Paleozoic protolith (Till and Dumoulin, 1994; Hannula and others, 1995), perhaps correlative with parts of the Nome Group. Like the Nome Group, these rocks probably underwent regional blueschist facies metamorphism in the Late Jurassic or Early Cretaceous (Sainsbury, Coleman, and Kachadoorian, 1970; Forbes and others, 1984; Thurston, 1985; Armstrong and others, 1986; Hannula and McWilliams, 1995). The blueschist facies rocks were recrystallized to greenschist facies or higher metamorphic grades in conjunction with regional extension, crustal melting, and magmatism in the mid-Cretaceous (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 (-165.97774168717, 64.9123317933554)
Mineral deposit model Fluorite breccia pipe in amphibolite facies metasedimentary rocks.
Age of mineralization Cretaceous; breccias crosscut mid-Cretaceous amphibolite facies metamorphic rocks and may be related to Cretaceous granitic rocks in the area.
Alteration of deposit Fluorite and silica replacement.

Production and reserves

Workings or exploration Only natural surface exposures are present.
Indication of production None

References

MRDS Number A012968

References

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.
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.
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.
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.
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., and Dumoulin, J.A, 1994, Geology of Seward Peninsula and St. Lawrence Island, in Plafker, G., and Berg, H.C., eds., The Geology of Alaska: Geological Society of America, DNAG, The Geology of North America, v. G-1, p. 141-152.
Reporters C.C. Hawley and Travis L. Hudson
Last report date 10/22/1999