Lemon; Copper King Prospect, Chisana Mining District, Valdez-Cordova Census Area, Alaska, USAi

Regional Level Types
Lemon; Copper King Prospect	Prospect
Chisana Mining District	Mining District
Valdez-Cordova Census Area	Census Area
Alaska	State
USA	Country

The prospect is in the Wrangell-St. Elias National Preserve.
Location: 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 This is locality 23 of Richter and others (1975) and it is included in National Park Service locality WRST-31 (unpublished data).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.
Geology: 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 chyrsocolla, 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).
Workings: 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.
Age: 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: Calc-silicate, sulfide, and magnetite replacement of limestone. Oxidation has produced chrysocolla, malachite, azurite, and covellite.

Commodities (Major) - Ag, Au, Cu, Fe, Zn
Development Status: None
Deposit Model: Cu skarn (Cox and Singer, 1986; model 18b)

Other Databases

Link to USGS - Alaska:	NB044

Other Regions, Features and Areas containing this locality

References