Rock Creek (lode)

Site Name

Primary: Rock Creek (lode)
Secondary: Nugent

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Commodity

Primary: Gold
Secondary: Lead
Secondary: Antimony
Secondary: Silver
Secondary: Zinc
Secondary: Tungsten

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Location

State: Alaska
District: Nome

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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: Prospect
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 Text: Early alteration consists of locally extensive albitization and sulfidization (introduction of arsenopyrite; late alteration consists of minor sericitization and albitization along with introduction of sheeted veins; and local development of ankerite.

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Rocks

Not available

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Analytical Data

Not available

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Materials

Ore: Arsenopyrite
Ore: Sphalerite
Ore: Scheelite
Ore: Pyrite
Ore: Limonite
Ore: Hematite
Ore: Gold
Ore: Galena
Ore: Boulangerite
Gangue: Albite
Gangue: Ankerite
Gangue: Calcite
Gangue: Quartz

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Comments

Comment (Exploration): Status = Active

Comment (Geology): Geologic Description = the schist. Well-developed, fold-controlled quartz-albite zones were exposed in Kennecott trench RCT-94-8. The trench and adjacent hill slopes display arsenic-rich lodes of northwest strike. This area has locally been called Arsenic Hill. The Reinisch hydraulic pit (NM213) is in this area. A distinct vein called the Albion (NM211) was exposed by mine workings in upper Rock Creek; it probably is partly coincident with sheeted veins typical of the main Rock Creek deposit. The deposit at the Walsh Cut (NM214) resembles that at the Reinisch. Most of the country rocks exposed at the prospect belong to the chlorite-rich metaturbidite schist and marble unit of Bundtzen and others (1994) or to the lower part of the 'mixed unit' of Till and others (1986). Graphitic mica schist and graphitic quartz schist are common; the graphitic quartz schist is locally a good marker unit. Schistosity generally strikes northeast and dips are low to moderate southeast. Quartz veins of the sheeted set are close to orthogonal to the schistosity. The schist appears to be a phyllonite. Although schistosity appears to be close to concordant with lithology, it is penetrative. Some coarse-grained units have incipient augen structure and are believed to have been sheared during a period of metamorphism that could be contemporaneous with early mineralization. Locally, schist is strongly mineralized with arsenopyrite and albite concordant to schistosity. Bedrock in the area probably is of early Paleozoic protolith age (Hummel, 1962 [MF 247]; Sainsbury, Hummel, and Hudson, 1972 [OFR 72-326]; Till and Dumoulin, 1994; Bundtzen and others, 1994). Detailed mapping for Kennecott Exploration Company identified a strong northeast-striking fault that appears to cut off the Sophie Gulch fault. The fault, called the Arsenic Hill fault, is exposed in Placer Dome trench RRT-87-1 and in Kennecott Exploration Company trench RCT-94-8. The fault appears to localize complexly sheared graphitic quartz veins and may have both pre- and post-mineral history. It is subparallel and en echelon to the Albion (NM211) and proposed Calle (NM212) vein-fault structures. Apodaca (1994) studied fluid inclusions and other detailed aspects of the vein geology at Rock Creek. Her work indicates that Rock Creek formed from low-salinity fluids relatively rich in carbon dioxide, methane, and nitrogen, along with some hydrogen sulfide. Fluid inclusions indicate an estimated temperature of formation in the range of 225 to 275 degrees Centigrade. The Rock Creek deposit is probably similar in age (109 Ma) to the gold-quartz deposits at Bluff (Ford and Snee, 1996).

Comment (Geology): Geologic Description = Gold-bearing, northeast-striking quartz veins in schist were known on Rock Creek by 1903 (Collier and others, 1908). Sheeted veins were later described, massive veins were locally worked, and some residual placer gold and scheelite were produced from weathered sheeted vein complexes (Moffit, 1913, p. 75-76; Mertie, 1918 [B 662-I, p. 436]; Cathcart, 1922). Lodes in the Rock Creek area were principal examples of disseminated lode gold deposits identified in a regional mineral assessment during the 1970's (Hudson and others, 1977; Hudson and DeYoung, 1978). This deposit is the most extensively explored gold lode in the Nome mining district. Significant exploration, including extensive trenching and drilling, has taken place episodically through the 1980's and 1990's since its relocation by geologist R. V. Bailey of Denver in the early 1980's. Active exploration, primarily infill drilling to better define gold grades, continues at the time of this writing (May, 2000). The most typical and highest grade part of the Rock Creek lode consists of a sheeted vein complex. The veins strike northeast and generally dip at a high angle to the northwest. They generally range from 1 inch to 6 inches thick, although some veins are more than 1 foot thick. Vein spacing is locally about one per foot. Cathcart (1922, p. 246) described a sheeted zone near the mouth of Sophie Gulch (NM208), where 23 quartz veins from 1 inch to 8 inches thick are in a zone 28 feet wide. In general, sheeted veins are well exposed in mechanical and hydraulic cuts in a 1,000-foot-long interval north of Sophie Gulch (NM208). Although good mineralization was found in some drill holes south of the Sophie Gulch fault, such as in Placer Dome RR-8-088, this fault appears to cut off or displace the best mineralization. The quartz and quartz-calcite veins of the sheeted set are composed mainly of white quartz with some internal crustification, but they are not banded. Albite tends to occur on the selvages and in adjacent wall rocks. Cathcart (1922) and others have reported muscovite in the veins. Sulfides tend to be relatively abundant close to the selvage, but are disseminated throughout the quartz. They consist mainly of pyrite, galena, stibnite, and sphalerite. Arsenopyrite is present but is more abundant in schist than in the veins. Lead sulfosalts such as boulangerite occur locally. Limonite tends to form on weathered veins, hematite on weathered arsenopyrite zones. The deposit is relatively long compared to its apparent thickness. Sheeted veins and most of the gold appear to lie above a marble-rich stratum at a depth of 250 to 300 feet. Individual quartz stringers pinch and swell and may end abruptly at a slip plane parallel to schistosity. The main Rock Creek deposit intergrades with other types of deposits. Opposite the mouth of Sophie Gulch, sheeted veins 2 to 3 feet apart are in quartz-mica schist, but there are extensive arsenic- and albite-rich zones in

Comment (Geology): Age = Mid-Creatceous. The country rocks are part of the Nome Group derived from Proterozoic to lower Paleozoic protoliths (Till and Dumoulin, 1984). The Nome Group underwent regional blueschist facies metamorphism in the Late Jurassic or Early Cretaceous (Sainsbury and others, 1970 [P 750-C]; Forbes and others, 1984; Thurston, 1985; Armstrong and others, 1986; Hannula and McWilliams, 1995). The blueschist facies rocks were recrystallized to greenschist 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).

Comment (Reference): Primary Reference = This report

Comment (Deposit): Model Name = Low-sulfide Au-quartz veins (Cox and Singer, 1986; model 36a).

Comment (Workings): Workings / Exploration = Gold-bearing, northeast-striking quartz veins in schist were known on Rock Creek by 1903 (Collier and others, 1908). Sheeted veins were later described, massive veins were locally worked, and some residual placer gold and scheelite were produced from weathered sheeted vein complexes (Moffit, 1913, p. 75-76; Mertie, 1918 [B 662-I, p. 436]; Cathcart, 1922). Lode prospects in the Rock Creek area were principal examples of disseminated lode gold deposits identified in a regional mineral assessment during the 1970's (Hudson and others, 1977; Hudson and DeYoung, 1978). This deposit is the most extensively explored gold lode in the Nome mining district. Significant exploration including extensive trenching and drilling has taken place episodically through the 1980's and 1990's since its relocation by geologist R. V. Bailey of Denver in the early 1980's. Active exploration, primarily infill drilling to better define gold grades, continues at the time of this writing (May, 2000). Bailey reopened trenches in the hydraulic cuts north of Sophie Gulch and exposed and sampled the sheeted veins. His work brought Placer Dome into the project in 1987 to 1989. Placer Dome drilled dozens of holes on regular, northwest-aligned fences approximately 200 feet apart for nearly 2,000 feet northeast from the mouth of Sophie Gulch. Both core and RC holes were drilled, and essentially all were steeply inclined to the southwest, perpendicular to the strike of the sheeted veins. Some of this drilling was difficult. The water table is close to the surface and some holes had artesian flow. The program was sufficient to outline a geologic resource, but it was considered subeconomic by Placer Dome. An extensive soil geochemical survey was completed in the area by BHP in 1989, and the property was optioned by Newmont Miing Company in 1992. Some new drill holes, including holes to confirm Placer Dome tests, were drilled by Newmont. The property was further explored in 1994 and 1995 by Kennecott Exploration Company, who drilled a few holes along the northwest fences. The holes were inclined to the northwest so that they would be nearly at right angles to bedrock schistosity in lower Rock Creek. Both Placer Dome and Newmont carried out preliminary metallurgical work; it appears that about 70 percent of the gold is present as free gold; the balance is in auriferous sulfides, principally pyrite and arsenopyrite. Exploration is continuing on the prospect in 2000 by Novagold Resources. In 1999, they announced that better recovery and analytic techniques suggested higher average grades for the deposit, perhaps about 3 grams of gold per metric tonne.

Comment (Reserve-Resource): Reserves = The drill-indicated resource, including inferred material, is about 740,000 ounces of gold at a grade of 2.88 grams per metric tonne above a cut off of 1 gram gold per metric tonne (Novagold Resources, written communication, April 17, 2000).

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References

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): Bundtzen, T.K., Reger, R.D., Laird, G.M., Pinney, D.S., Clautice, K.H., Liss, S.A., and Cruse, G.R., 1994, Progress report on the geology and mineral resources of the Nome mining district: Alaska Division of Geological and Geophysical Surveys, Public Data-File 94-39, 21 p., 2 sheets, scale 1:63,360.

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): 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.

Reference (Deposit): 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.

Reference (Deposit): Amato, J.M., Wright, J.E., Gans, P.B., and Miller, E.L., 1994, Magmatically induced metamorphism and deformation in the Kigluaik gneiss dome, Seward Peninsula, Alaska: Tectonics, v. 13, p. 515-527.

Reference (Deposit): Dumitru, T.A., Miller, E.L., O'Sullivan, P.B., Amato, J.M., Hannula, K.A., Calvert, A.T., and Gans, P.B., 1995, Cretaceous to Recent extension in the Bering Strait region, Alaska: Tectonics, v. 14, p. 549-563.

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): 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, The Geology of North America, DNAG, v. G-1, p. 141-152.

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): 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): 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): 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.

Reference (Deposit): Sainsbury, C.L., Hummel, C.L., and Hudson, Travis, 1972, Reconnaissance geologic map of the Nome quadrangle, Seward Peninsula, Alaska: U.S. Geological Survey Open-File Report 72-326, 28 p., 1 sheet, scale 1:250,000.

Reference (Deposit): Hudson, T.L., Miller, M. L., and Pickthorn, W. J., 1977, Map showing metalliferous and selected nonmetalliferous mineral deposits, Seward Peninsula, Alaska: U.S. Geological Survey Open-File Report 77-796-B, 46 p., one sheet, scale 1:1,000,000.

Reference (Deposit): Cobb, E.H., 1978, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Nome quadrangle, Alaska: U.S. Geological Survey Open-File report 78-93, 213 p.

Reference (Deposit): 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.

Reference (Deposit): 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.

Reference (Deposit): Hudson, T.L., and DeYoung, J. H., Jr., 1978, Map and tables describing areas of mineral resource potential, Seward Peninsula, Alaska: U.S. Geological Suvey Open-File Report 78-1-C, 62 p., one sheet, scale 1:1,000,000.

Reference (Deposit): Hudson, T.L., and Arth, J. G., 1983, Tin-granites of Seward Peninsula, Alaska: Geological Society of America Bulletin, v. 94, p. 768-790.

Reference (Deposit): Forbes, R.B., Evans, B.W., and Thurston, S.P., 1984, Regional progressive high-pressure metamorphism, Seward Peninsula, Alaska: Journal of Metamorphic Geology, v. 2, p. 43-54.

Reference (Deposit): Cobb, E.H., 1972, Metallic mineral resources map of the Nome quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-463, 2 sheets, scale 1:250,000.

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

Reference (Deposit): Hummel, C.L., 1962, Preliminary geologic map of the Nome C-1 quadrangle, Seward Peninsula, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-247, 1 sheet, scale 1:63,360.

Reference (Deposit): Moffit, F.H., 1913, Geology of the Nome and Grand Central quadrangles, Alaska: U.S. Geological Survey Bulletin 533, 140 p.

Reference (Deposit): Amato, J.M., and Wright, J.E., 1997, Potassic mafic magmatism in the Kigluaik gneiss dome, northern Alaska -- A geochemical study of arc magmatism in an extensional tectonic setting: Journal of Geophysical Research, v. B102, no. 4, p. 8065-8084.

Reference (Deposit): Amato, J.M., and Wright, J.E., 1998, Geochronologic investigations of magmatism and metamorphism within the Kigluaik Mountains gneiss dome, Seward Peninsula, Alaska, in Clough, J.G., and Larson, Frank, eds., Short Notes on Alaskan Geology 1997: Alaska Division of Geological and Geophysical Surveys Professional Report 118a, p. 1-21.

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.

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