Braided Creeks

Prospect, Inactive

Alternative names

Cathedral Creek
Manhattan

Commodities and mineralogy

Main commodities Ag; Au; Cu; Pb; Zn
Other commodities As
Ore minerals arsenopyrite; chalcopyrite; galena; gold; pyrargyrite; pyrite; pyrrhotite; sphalerite; tetrahedrite
Gangue minerals dolomite; quartz

Geographic location

Quadrangle map, 1:250,000-scale CG
Quadrangle map, 1:63,360-scale C-2
Latitude 56.527
Longitude -158.573
Nearby scientific data Find additional scientific data near this location
Location and accuracy This site represents a large color anomaly. The anomaly is approximately 3 miles north-south and 9 miles east-west, covering parts of T. 42 S., R. 59 and 60 W., of the Seward Meridian, encompassing the headwaters of Milk, Cathedral, and Braided Creeks (Cobb, 1972: MF-374, locality 1; U.S. Bureau of Mines, 1973, localilties 11, 12, 14, 15, and 18; MacKevett and Holloway, 1977, localities 1, 8-16, 18, and 19; Cox and others, 1981, locality 2; Nokleberg and others, 1987, locality AP 10). The map site is plotted at the location of the Manhattan prospect, near the headwaters of Braided Creek (map C-2). The location is accurate to within 1/2 mile.

Geologic setting

Geologic description

Rocks in this prospect area include a large diorite stock of Oligocene age and smaller andesite and dacite plug domes of Miocene and Oligocene ages. The diorite stock cuts dacite flows of Oligocene age and sedimentary rocks of the Meshik Formation (Detterman and others, 1981).
Mineralization within the main part of the stock has been described as a large, discontinuous sulfide system with low order copper and molybdenum anomalies (Fields, 1977). Cathedral and Milk Creeks drain an area distinguished by a cluster of silt samples containing anomalous values in copper and molybdenum. Fields, however, did not report any outcropping copper-molybdenum mineralization in this area, although chalcopyrite in quartz-chlorite veins was found in float. Nokleberg and others (1987) reported the occurrence of copper and molybdenite in zones of sericitic alteration within intrusives in the area.
Pervasive pyrite (2 to 7 percent) is present in the sedimentary rocks and to a minor degree in the volcanic rocks peripheral to the stock. In some areas the pyrite is accompanied by epidote, chlorite, and clay alteration. Other areas exhibit pervasive sericitization.
In the eastern part of the area of the color anomaly, base and precious metal veins crop out at the Manhattan prospect, near the headwaters of Braided Creek. Approximately 20 veins have been discovered, traceable for up to 700 feet on strike. These are up to several feet in thickness and contain arsenopyrite, chalcopyrite, galena, gold, pyrargyrite, pyrite, pyrrhotite, quartz, sphalerite, and tetrahedrite. The veins cut the Chignik Formation and dacite porphyry. They trend N 20 to 45 E It has been suggested that these veins represent a peripheral zone to the Cathedral Creek sulfide system (Wilson and Cox, 1983).
At the Manhattan prospect Pan American Exploration (now Amoco) carried out geophysical surveys and drilled 14 holes for a total of 2,539 meters in 1965-1967. Bear Creek Mining Company briefly explored the area in 1975. In 1979 Resource Associates of Alaska sampled a 2-3 foot thick vein traceable for 700 feet. Their assay results are as follows: copper to 2400 ppm, gold to 0.596 ounce per ton, lead to 1.06 percent, silver to 16.29 ounces per ton, zinc to 9.5 percent (Anderson and others, 1979). In 1984 Anaconda drilled approximately 6 holes on this vein system. They reported metal values of 0.25 to 0.5 ounce gold per ton, 1 to 10 ounces silver per ton, and 5 to 10 percent lead-zinc.
Young and others (1997) estimate a resource at the Manhattan prospect of 90,000 to 180,000 tonnes grading 0.6 ounce gold per ton, 10 ounces silver per ton, and 15 percent lead-zinc. Subsequent owners claim a resource of 575,000 tons grading 0.39 ounce gold equivalent per ton (Alaska Earth Science, 1997).
Geologic map unit (-158.575049038756, 56.5262195243586)
Mineral deposit model Polymetallic vein and possible upper level of a prophyry copper system (Cox and Singer, 1986; models 22c and 17?)
Mineral deposit model number 22c and 17?
Age of mineralization Tertiary or younger.
Alteration of deposit The sedimentary rocks peripheral to the stock exhibit pervasive sericitization in some areas and epidote, chlorite, clay alteration in others. Chloritization in the stock is common and localized areas of quartz-sericite alteration have been reported.

Production and reserves

Workings or exploration
Fourteen holes were drilled at the Manhatten prospect on Braided Creek by Pan American Exploration in 1965-67 for a total of 2539 meters. Bear Creek Mining Company examined and sampled the prospect for 3 days in 1975. Resource Associates of Alaska sampled a polymetallic vein here in 1979. Anaconda drilled approximately 6 holes on the Braided Creek showings in 1984.
Sampling of 1 vein by Resource Associates of Alaska assayed as follows: copper to 2400 ppm, gold to 0.596 ounce per ton, lead to 1.06 percent, silver to 16.29 ounces per ton, and zinc to 9.5 percent. Anaconda reported metal values of 0.25 to 0.5 ounce gold per ton, 1 to 10 ounces silver per ton, and 5 to 10 percent lead-zinc.
Indication of production None
Reserve estimates Young and others (1997) list a resource of 90,000 to 180,000 tonnes grading 10 ounces silver per ton, 0.6 ounces gold per ton, and 15 percent lead-zinc. Subsequent owners claim 575,000 tons grading 0.39 ounce gold equivalent per ton (Alaska Earth Science, 1997).

Additional comments

This site is located in Alaska Peninsula National Wildlife Refuge.

References

MRDS Number A012443

References

Alaska Earth Science, 1997, Mineral and oil and gas potential of the Bristol Bay region, southwestern Alaska: prepared for the Bristol Bay Native Corporation, 11 p. (Report held by Alaska Earth Sciences, Inc., Anchorage, Alaska.)
U.S. Bureau of Mines, 1973, Alaska 1:250,000-scale quadrangle map overlays showing mineral deposit locations, principal minerals, and number and type of claims: U.S. Bureau of Mines Open-File Report 20-73, 95 overlays (updated in 1986, 1987).
Reporters S.H. Pilcher (Anchorage)
Last report date 2/8/2000