Rex

Site Name

Primary: Rex

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Commodity

Primary: Gold
Primary: Copper
Secondary: Zinc
Secondary: Lead
Secondary: Molybdenum

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Location

State: Alaska
District: Alaska Peninsula

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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: Porphyry Cu-Au

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Orebody

Not available

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Structure

Not available

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Alterations

Alteration Type: L
Alteration Text: This prospect exhibits zoned potassic, phyllic, and propylitic alteration.

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Rocks

Name: Diorite
Role: Associated
Age Type: Associated Rock
Age Young: Pliocene

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Analytical Data

Not available

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Materials

Ore: Chalcopyrite
Ore: Galena
Ore: Gold
Ore: Molybdenite
Ore: Pyrite
Ore: Sphalerite
Gangue: Barite
Gangue: Quartz

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Comments

Comment (Deposit): Model Name = Porphyry copper-gold (Cox and Singer, 1986; model 20c)

Comment (Deposit): Other Comments = This prospect is located on land selected by the Koniag Native Corporation.

Comment (Geology): Age = Oligocene or younger.

Comment (Exploration): Status = Inactive

Comment (Reference): Primary Reference = Hedderly-Smith, 1977

Comment (Workings): Workings / Exploration = This prospect was originally identified in 1975 by Resource Associates of Alaska in the basis of the color anomaly and a stream-sediment survey (Hedderly-Smith, 1977).? Bear Creek Mining Company did extensive mapping and sampling at the Rex prospect in 1977 (Church and others, 1989: B-1858). A small area in the intrusive was found to contain 1350 to 3900 ppm copper and 26 to 56 ppm molybdenum (Hedderly-Smith, 1977). In a separate(?) 500-foot wide zone, copper values of 0.2 to 0.25 percent were reported. Elsewhere in the intrusive, sporadic copper values of 500 to 1000 ppm were indicated. Gold values up to 0.37 ppm were found to be coincident with the higher copper values. The average copper, gold, and molybdenum values are not available.? In the 1980's the U.S. Geological Survey did a silt and rock geochemical survey which included the area around this prospect (Church and others, 1989: B-1858).

Comment (Geology): Geologic Description = At the Rex prospect, sedimentary rocks of the Cretaceous Chignik and Eocene Tolstoi Formations are cut by an Oligocene porphyritic quartz diorite stock (Church and others, 1989: B-1858). The site is marked by a color anomaly and by copper, molybdenum, lead, zinc, silver, gold and tungsten stream-sediment anomalies. Panned concentrates taken in the vicinity of the prospect contain free gold.? Chalcopyrite and molybdenite are present mostly in a zone of potassic alteration which occurs over an area of 1 mile square within the stock (Church and others, 1989: B-1858). The chalcopyrite occurs as disseminations and in stockwork fractures, whereas the molybdenite is locally present only in the stockwork fractures. Sampling by Bear Creek Mining Company indicated a small area containing 1350 to 3900 ppm copper and 26 to 56 ppm molybdenum (Hedderly-Smith, 1977). In a separate? area he describes a 500-foot wide zone containing 0.2 to 0.25 percent copper. Elsewhere values of 500 to 1000 ppm copper were found sporadically. Gold values, up to 0.37 ppm, were coincident with the higher copper values. Float samples of intrusive with secondary potassium feldspar and tourmaline contained 0.2 to 0.25 percent copper. Scattered galena and sphalerite are present in the altered rocks peripheral to the copper mineralization. Occasional anomalies of 40 to 60 ppm lead and 100 to 300 ppm zinc have been detected (Hedderly-Smith, 1977). Pyrite is present in the mineralized zone and in the surrounding altered sedimentary rocks in amounts up to 10 percent.? Beyond the potassic mineralized zone, defined by the presence of seondary biotite, some phyllic alteration has developed. The dominant alteration at this prospect is propylitic and is present in the sedimentary rocks surrounding the stock.

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References

Reference (Deposit): Church, S.E., Frisken J.G., Wilson, F.H., 1989, Interpretation of exploration geochemical data from Ugashik, Bristol Bay, and western Karluk quadrangles, Alaska: U.S Geological Survey Bulletin 1858, 45 p.

Reference (Deposit): Nokleberg, W.J., Bundtzen, T.K., Berg, H.C., Brew, D.A., Grybeck, D.J., Robinson, M.S., Smith, T.E., and Yeend, W., 1987, Significant metalliferous lode deposits and placer districts of Alaska: U.S. Geological Survey Bulletin 1786, 104 p.

Reference (Deposit): Wilson, F.H., and Shew, N., 1992, Map and tables showing geochronology and whole rock geochemistry of selected samples from Ugashik, Bristol Bay, and part of Karluk quadrangle, Alaska: U.S. Geological Survey Map MF-1539-E, 34 p., 1 map sheet, scale 1:250,000.

Reference (Deposit): MacKevett, E.M., Jr., and Holloway, C.D., 1977, Map showing metalliferous mineral deposits in the western part of southern Alaska: U.S. Geological Survey Open-File Report 77-169-F, 38 p., 1 sheet, scale 1:1,000,000.

Reference (Deposit): Hedderly-Smith, D.A., 1977, 1977 Annual report, Alaska search, Koniag Inc. region: Bear Creek Mining Company, Spokane Office, 23 p. (Report held by Kennecott Alaska, Anchorage).

Reference (Deposit): Church, S.E., Detterman, R.L., and Wilson, F.H., 1989, Mineral and energy resource assessment maps of the Ugashik, Bristol Bay, and western Karluk quadrangles, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF 1539-I, 2 map sheets, scale 1:250,000.

Reference (Deposit): Eakins, G.R., Bundtzen, T.K., Robinson, M.S., Clough, J.G., Green, C.B., Clautice, K.H., and Albanese M.A., 1983, Alaska's mineral industry, 1982: Alaska Division of Geological and Geophysical Surveys Special Report 31, 63 p.

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