Bluff

Site Name

Primary: Bluff

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Commodity

Primary: Gold
Secondary: Tungsten

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Location

State: Alaska
District: Council

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Land Status

Not available

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Holdings

Not available

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Workings

Not available

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Ownership

Not available

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Production

Not available

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Deposit

Record Type: Site
Operation Category: Producer
Operation Type: Unknown
Years of Production:
Organization:
Significant:

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Physiography

Not available

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Mineral Deposit Model

Model Name: Low-sulfide Au-quartz vein

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Orebody

Not available

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Structure

Not available

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Alterations

Alteration Type: L
Alteration Text: The surface and near-surface gold-bearing rocks are oxidized, iron-staining is common, clay in quartz veins and veinlets is developed, and remnants of more massive arsenopyrite and pyrite are locally preserved. Quartz veining apparently accompanied gold mineralization. At the nearby Saddle prospect, alteration minerals in the host schist include plagioclase, chlorite, carbonate, white mica, biotite, titanite, and tourmaline.

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Rocks

Not available

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Analytical Data

Not available

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Materials

Ore: Scheelite
Ore: Pyrite
Ore: Gold
Ore: Chalcopyrite
Ore: Arsenopyrite
Gangue: Quartz
Gangue: Clay

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Comments

Comment (Exploration): Status = Active?

Comment (Geology): Geologic Description = muscovite and that in the schist is phengite. A sample of vein white mica gave a Ar/Ar plateau age of 109.3 +/- 0.3 Ma and metamorphic white mica in the host schist gave Ar/Ar plateau ages of 122.6 +/- 0.4 Ma and 122.4 +/- 0.2 Ma (Ford and Snee, 1996). The host schist is similar to that at the nearby Bluff (SO135), Swede Creek (SO133) and Koyana Creek (SO136) lode prospects. This schist is a band intercalated in Paleozoic marble (Herried, 1965; Mulligan, 1971; Till and others, 1986). . This deposit is also probably mid-Cretaceous, the age of some other lode gold deposits on southern Seward Peninsula. The southern Seward Peninsula lode gold deposits formed as a result of mid-Cretaceous metamorphism (Apodoca, 1994; Ford, 1993, Ford and Snee, 1996; Goldfarb and others, 1997) that accompanied regional extension (Miller and Hudson, 1991) and crustal melting (Hudson, 1994). This higher temperature metamorphism was superimposed on high pressure/low temperature metamorphic rocks of the region.

Comment (Geology): Geologic Description = The lode gold deposits at Bluff are preferentially developed in metasedimentary schist that is intercalated in Paleozoic marble (Collier and others, 1908; Cathcart, 1922; Herried, 1965; Mulligan, 1971; Till and others, 1986). The quartz mica (+/- graphite and chlorite) schist is locally iron-stained, sulfide impregnated (especially with arsenopyrite and pyrite), and cut by small, irregular quartz veins and veinlets. Exposures of the mineralization occur in the seacliffs 1,000 feet east of the mouth of Daniels Creek; also locally in old prospect pits and shafts, for a distance of 4,700 feet inland from the coast, and in a few dozer trenches. The seacliff exposures include a subhorizontal, massive arsenopyite-pyrite lens 4 feet wide and 20 feet long that pinches down to a foot or less at its ends. The east end of this lens becomes a foot-wide quartz vein. Elsewhere in this area, the schist is iron-stained and contains disseminated sulfides; a 100-foot-long chip sample across a sulfide-bearing part of this outcrop contained 0.045 ounces Au per ton and 0.08 ounces Ag per ton (Mulligan, 1971). A 4-foot chip sample across the massive sulfide lens contained 0.18 ounces Au per ton and 0.35 ounces per Ag ton (Herried, 1965). Other grab samples from the seacliff exposures contained 0.02 to 0.42 ounces Au per ton and 0.16 to 0.55 ounces Ag per ton (Herried, 1965). A sample of oxidized arsenopyrite-rich dump material beside an old shaft inland from the beach contained 2.76 ounces Au per ton and 1.49 ounces Ag per ton; eight other samples of dump materials contained 0.03 to 0.23 ounces Au per ton and 0.03 to 1.57 ounces Ag per ton (Herried, 1965). Herried (1965) reports that scheelite can be panned from some dump materials. Composite chip samples from four dozer trenches cut across the north-trending schist belt inland from the beach were locally mineralized and included some 10-foot intervals with up to 0.04 ounces Au per ton (Mulligan, 1971). Quartz-clay veinlets were common in the mineralized parts of the trench exposures. . The nearby Saddle prospect (SO175) is probably similar to the lode gold deposits at Bluff. The Saddle prospect is known from the work of Ford (1993) and Ford and Snee (1996). A large gold and arsenic anomaly in soils led to its discovery. Gold-bearing quartz veins are localized in extensional joints in quartz-muscovite schist that strike easterly and dip moderately to the south. The veins are discontinuous and commonly less than 3 inches thick. Gold grades are irregularly distributed; vein intersections up to 3.3 feet across have contained up to 1.8 ounces Au per ton. Minerals identified in the veins include arsenopyrite, biotite, carbonate, chlorite, fluorite, marcasite, plagioclase, pyrite, pyrrhotite, quartz, titanite, and white mica. Alteration minerals in the host schist include plagioclase, chlorite, carbonate, white mica, biotite, titanite, and tourmaline. The white mica in the veins is

Comment (Geology): Age = Mid-Cretaceous; at the nearby Saddle prospect (SO175) which is probably of the same age, a sample of vein white mica gave a Ar/Ar plateau date of 109.1 +/- 0.2 Ma and metamorphic white mica in the host schist gave Ar/Ar total-gas dates of 122.6 +/- 0.4 Ma and 122.4 +/- 0.2 Ma (Ford and Snee, 1996).

Comment (Deposit): Model Name = Discontinuous, irregular quartz veins and veinlets with dissemminated arsenopyrite and pyrite in metasedimentary schist; low sulfide-Au quartz vein (Cox and Singer, 1986; model 36a).

Comment (Production): Production Notes = Mulligan (1971) notes that the small volume of waste dumps scattered about the area suggests that very little ore was mined and processed. However, an old mill here indicates that some production probably took place.

Comment (Reference): Primary Reference = Ford, 1993

Comment (Workings): Workings / Exploration = Over 50 small prospect pits and shafts are scattered northward for 4,700 feet inland from the coast. This prospecting started in the early 1900's as the first lode claims were staked in 1900. Mulligan (1971) exposed bedrock in four dozer trenches totalling 3,300 feet in length. A short, adit, not caved, was driven in the seacliff exposures. Diamond drilling has probably occurred on this property since the 1970's but the operator and results are not known.

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References

Reference (Deposit): Hudson, T.L. 1994, Crustal melting events in Alaska, in Plafker, G., and Berg, H. C., eds., The Geology of Alaska: Boulder, Colorado, Geological Society of America, The Geology of North America, v. G-1, p. 657-670.

Reference (Deposit): 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.

Reference (Deposit): 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, 482 p.

Reference (Deposit): Miller, E.L., and Hudson, T.L., 1991, Mid-Cretaceous extensional fragmentation of a Jurassic-Early Cretaceous compressional orogen, Alaska: Tectonics, v. 10, p. 781-796.

Reference (Deposit): Cobb, E.H., 1978, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Solomon quadrangle, Alaska: U.S. Geological Survey Open-File Report 78-181, 185 p.

Reference (Deposit): Collier, A. J., Hess, F.L., Smith, P.S., and Brooks, A.H., 1908, The gold placers of parts of Seward Peninsula, Alaska, including the Nome, Council, Kougarok, Port Clarence, and Goodhope precincts: U.S. Geological Survey Bulletin 328, 343 p.

Reference (Deposit): Mulligan, J.J., 1971, Sampling gold lode deposits, Bluff, Seward Peninsula, Alaska, with a section on petrography by Walter L. Gnagy: U.S. Bureau of Mines Report of Investigations 7555, 40 p.

Reference (Deposit): Cathcart, S.H., 1922, Metalliferous lodes in southern Seward Peninsula: U.S. Geological Survey Bulletin 722, p. 163-261.

Reference (Deposit): Herreid, G.H., 1965, Geology of the Bluff area, Solomon quadrangle, Seward Peninsula, Alaska: Alaska Division of Geological and Geophysical Surveys, Geological Report 10, 21 p.

Reference (Deposit): 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.

Reference (Deposit): Till, A.B., Dumoulin, J.A., Gamble, B. ., Kaufman, D.S., and Carroll, P.I., 1986, Preliminary geologic map and fossil data, Soloman, Bendeleben, and southern Kotzebue quadrangles, Seward Peninsula, Alaska: U.S. Geological Survey Open-File Report 86-276, 10 p., 3 plates, scale 1:250,000.

Reference (Deposit): 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.

Reference (Deposit): Cobb, E.H., 1972, Metallic resources map of the Solomon quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-445, scale 1:250,000.

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