|Quadrangle map, 1:250,000-scale||NB|
|Quadrangle map, 1:63,360-scale||A-4|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||This prospect is at an elevation of about 4,800 feet on the west flank of the high ridge east of Orange Hill. It is 1.1 miles southeast of the summit of Orange Hill and 1.2 miles southwest of peak 7521. The site is near the southeast corner of section 21, T. 5 N., R. 14 E. of the Copper River Meridian. This is locality 23 of Richter and others (1975) and it is included in National Park Service locality WRST-31 (unpublished data). Cobb and Richter (1980 [OFR 80-927]) included this prospect under the name 'Orange Hill'. It is probably located to within a thousand feet.|
This skarn deposit was probably discovered and staked as part of the Orange Hill mineralized system as early as 1902 (Mendenhall and Schrader, 1903). By 1940, 18 mining claims had been patented, including contiguous claims that extend southeast from the Orange Hill porphyry-copper deposit across contact metamorphic deposits on the Lemon claims (Moffit, 1943, 1954). It has been explored by short adits and diamond drilling.
The deposit on the Lemon claims contains disseminated pyrrhotite, pyrite, and chalcopyrite in magnetite-rich skarn and veins of pyrite, chalcopyrite, and sphalerite cutting magnetite bodies and skarn (Richter and others, 1975). Oxidation has produced local concentrations of chrysocolla, malachite, azurite, and covellite. A 188-foot core sample from the Lemon Extension #2 claim contained 0.3 to 3.8 percent copper and averaged 0.95 percent copper (Pilgrim, 1931). Channel samples from this claim had weighted averages of 0.71 percent copper, 0.024 ounce of gold per ton and 0.66 ounce silver per ton (Van Alstine and Black, 1944). An 8-foot long channel sample across a massive sulfide body 30 feet long and 3 to 8 feet wide assayed 0.32 percent copper, 0.08 ounce of gold per ton, 6.12 percent zinc, and 38.84 percent iron (Van Alstine and Black, 1944).The deposit displays mineral zoning typical of porphyry copper-related copper skarns (Newberry and others, 1997). Red garnet with magnetite and chalcopyrite grades outward through zones with brown garnet, green garnet with bornite, to wollastonite with or without sphalerite. Diopside tends to occur with the brown and green garnet. The skarn is developed in Permian limestone adjacent to the Orange Hill porphyry copper deposit (NB043), which is hosted by quartz diorite and granodiorite of the mid-Cretaceous Nabesna pluton. K/Ar ages for the Nabesna pluton range from 105 +/- 4.0 to 114 +/- 3.4 Ma (Richter and others, 1975; Richter, Lanphere, and Matson, 1975). Many varieties of hornblende-plagioclase porphyry form irregular intrusive bodies in the Nabesna pluton and other regional bedrock units in the area; these are considered to be Tertiary in age (Richter, 1973).
|Geologic map unit||(-142.82222705766, 62.1916100127633)|
|Mineral deposit model||Cu skarn (Cox and Singer, 1986; model 18b)|
|Mineral deposit model number||18b|
|Age of mineralization||Early Cretaceous. The skarn is developed in Permian limestone adjacent to the Orange Hill porphyry copper deposit (NB043), which is hosted by quartz diorite and granodiorite of the mid-Cretaceous Nabesna pluton. K/Ar ages for the Nabesna pluton range from 105 +/- 4.0 to 114 +/- 3.4 Ma (Richter and others, 1975; Richter, Lanphere, and Matson, 1975).|
|Alteration of deposit||Calc-silicate, sulfide, and magnetite replacement of limestone. Oxidation has produced chrysocolla, malachite, azurite, and covellite.|
|Workings or exploration||This skarn deposit was probably discovered and staked as part of the Orange Hill mineralized system as early as 1902 (Mendenhall and Schrader, 1903). By 1940, 18 mining claims had been patented, including contiguous claims that extend southeast from the Orange Hill porphyry copper deposit across contact metamorphic deposits on the Lemon claims (Moffit, 1943, 1954). It has been explored by short adits and diamond drilling.|
|Indication of production||None|
Additional commentsThe prospect is in the Wrangell-St. Elias National Preserve.
|MRDS Number||A010707; A011396|
Cobb, E.H., and Richter, D.H., 1980, Summaries of data on and list of references to metallic and selected nonmetallic mineral deposits in the Nabesna quadrangle, Alaska: U.S. Geological Survey Open-File Report 80-927, 117 p.
Mendenhall, W.C., and Schrader, F.C., 1903, The mineral resources of the Mount Wrangell District, Alaska: U.S. Geological Survey Professional Paper 15, 71 p., 1 sheet.
Moffit, F.H., and Wayland, R.G., 1943, Geology of the Nutzotin Mountains, Alaska, with a section on The igneous rocks: U.S. Geological Survey Bulletin 933-B, p. 103-199.
Moffit, F.H., 1954, Geology of the eastern part of the Alaska Range and adjacent area: U.S. Geological Survey Bulletin 989-D, p. 65-218.
Newberry, R.J., Allegro, G.L., Cutler, S.E., Hagen-Levelle, D.D., Adams, D.D., Nicholson, L.C., Weglarz, T.B., Bakke, A.A., Clautice, K.H., Coulter, G.A., Ford, M.J., Myers, G.L., and Szumigala, D.J., 1997, Skarn deposits of Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 355-395.
Pilgrim, E.R., 1931, Alaska Nabesna Orange Hill copper claims, in Stewart, B.D., Report on cooperation between the Territory of Alaska and the United States in making mining investigations and inspection of mines for the biennium ending March 31, 1931: Alaska Terrirorial Department of Mines, p. 69-74.
Richter, D.H., Lanphere, M.A., and Matson, N.A., Jr., 1975, Granite plutonism and metamorphism, eeastern Alaska Range, Alaska: Geological Society of American Bulletin, v. 86, p. 819-820.
Richter, D.H., Singer, D.A., and Cox, D.P., 1975, Mineral resources map of the Nabesna quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-655-K, 1 sheet, scale 1:250,000.
|Reporters||Travis L. Hudson (Applied Geology)|
|Last report date||11/24/2002|