McDuffee

Mine, Active?

Alternative names

McDuffie

Commodities and mineralogy

Main commodities Au
Other commodities Ag; Sb
Ore minerals gold; pyrite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale NM
Quadrangle map, 1:63,360-scale D-1
Latitude 64.7577
Longitude -165.3824
Nearby scientific data Find additional scientific data near this location
Location and accuracy The McDuffee mine is on the east side of Steep Creek between elevations of about 600 and 900 feet; it is 1 mile south of Mount Distin. Vein float can be found above mine workings to an elevation of about 1,000 feet. The mine is about 4,000 feet north-northeast of the intersection of the road along Goldbottom Canyon and a jeep trail that gives access to the mine. The McDuffee is several hundred feet south of the Tanner prospect (NM091). The prospect described here as McDuffee was shown as MacDuffee (East) and MacDuffee (West), localities 10 and 11, by Hummel (1962 [MF 248]). It was included with locality 23 of Cobb (1972 [MF 463], 1978 [OFR 78-93]).

Geologic setting

Geologic description

The McDuffee mine was developed by shafts, adits, and open cuts on gold-bearing quartz veins along faults that cut the host rock schistosity at a high angle. The veins are best developed in a metabasite sill in mica schist that underlies massive marble (Hummel, 1962 [MF 248]; Bundtzen and others, 1994); it is uncertain whether the veins extend into the overlying marble. The McDuffee is a composite vein; the southernmost and strongest part of the vein system strikes northeast and is nearly vertical. It occupies a fault which cuts off the metabasite and faults it against mica schist to the south. The vertical displacement on the fault is probably more than 100 feet, the south side displaced down, if a metabasite sill in Steep Creek below the mine is the same as the one in the mine. In general the vein is narrow. In underground workings, it appears to be 1 to 3 feet across and is largely stoped out. At a point near the lower adit, a second vein splits from the main vein structure. This vein strikes about east-west and is near vertical. The vein (fault) displaces the upper contact of metabasite about 10 to 20 feet. Both the main and east-west vein segments appear to be stronger where they have one or both walls in metabasite. Old surface workings developed in the cliff face on the east side of Steep Creek probably mined residual placers on the lodes.
Little is known concerning the productivity of the vein. It is largely stoped out in the upper adit workings, so it is inferred to have been fairly rich. Gamble and others (1985) collected one sample that assayed 120 ppm or nearly four ounces of gold per ton; they also collected another sample that contained four ppm gold. Oxygen isotope data on the vein samples collected by Gamble and others (1985) are consistent with a metamorphic origin of the vein-forming fluids.
In about 1990, BHP geologists defined a nearly east-west belt of anomalous gold and antimony in soils that includes the area of the McDuffee mine and the nearby Tanner prospect (NM091). In general, the anomalous soils coincide most closely with the main contact of mica schist and overlying marble exposed in Steep Creek; locally, anomalous values could reflect high-grade vein zones. One of the compilers (C.C. Hawley) worked in this region in 1995 for Kennecott Exploration Company and mapped the area at 1 inch to 1,000 feet, with some mapping near the prospects at 1 inch to 50 feet.
The metamorphic rocks at the McDuffie mine are part of the Nome Group, derived from Proterozoic to early Paleozoic protoliths (Till and Dumoulin, 1994). The Nome Group 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 (Hudson and Arth, 1983; Miller and Hudson, 1991; Miller and others, 1992; Dumitru and others, 1995; Hannula and others, 1995; Hudson, 1994; Amato and others, 1994; Amato and Wright, 1997, 1998). Lode gold mineralization on Seward Peninsula is mostly related to the higher temperature metamorphism in the mid-Cretaceous (Apodoca, 1994; Ford, 1993 [thesis]; Ford and Snee, 1996; Goldfarb and others, 1997).
Geologic map unit (-165.385020992781, 64.7569388413202)
Mineral deposit model Low sulfide, Au-quartz vein (Cox and Singer, 1986; model 36a).
Mineral deposit model number 36a
Age of mineralization Probably mid-Cretaceous; controlled by structures that postdate regional metamorphism; probably similar in age to some other lode gold deposits of Seward Peninsula.

Production and reserves

Workings or exploration
The McDuffee vein is developed principally by two adits at elevations of about 730 and 780 feet. These adits develop the northeast-striking part of the vein. The vein splits near the lower adit; a north branch trends about due west downslope and is developed by a shallow shaft and, where it transects metabasite, by surface workings. The southerly branch trends downhill about west-southwest and is developed by surface workings where its north wall is formed by the metabasite. There are probably several hundred feet of underground workings.
The vein was apparently unknown when the area was visited by Cathcart in 1920 (Cathcart, 1922), although he shows the Nelson lead-zinc prospect in upper Steep Creek and studied the Hed & [and] Strand, Breen, and Sliscovich antimony workings at that time. The workings were certainly in place when the area was mapped by Hummel (1962 [MF 248]). The area was investigated by BHP in about 1990 and by Kennecott Exploration Company in 1995.
Indication of production Yes; small
Production notes A small amount of gold is assumed to have been mined and milled.

Additional comments

The area is in the regional selections of the Bering Straits Native Corporation.

References

MRDS Number 10307942

References

Apodoca, L.E., 1994, Genesis of lode gold deposits of the Rock Creek area, Nome mining district, Seward Peninsula, Alaska: Boulder, Colorado, University of Colorado, Ph.D. dissertation, 208 p.
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.
Ford, R.C., 1993, Geology, geochemistry, and age of gold lodes at Bluff and Mt. Distin, Seward Peninsula, Alaska: Golden, Colorado School of Mines, Ph.D. dissertation, 302 p.
Ford, R.C., and Snee, L.W., 1996, 40Ar/39Ar thermochronology of white mica from the Nome district, Alaska--The first ages of lode sources to placer gold deposits in the Seward Peninsula: Economic Geology, v. 91, p. 213-220.
Goldfarb, R.J., Miller, L.D., Leach, D.L., and Snee, L.W, 1997, Gold deposits in metamorphic rocks in Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 151-190.
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