|Quadrangle map, 1:250,000-scale||NB|
|Quadrangle map, 1:63,360-scale||A-2|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||This prospect is on the south side of the uppermost headwaters of Chathenda Creek. It is at an elevation of about 6,200 feet, 1.6 miles northeast of peak 7372. The site is in the SE1/4 of section 19, T. 4 N., R. 21 E. of the Copper River Meridian. This is locality 3 of Richter and Matson (1970 [OFR 70-275]), locality 44 of Richter and others (1975), and National Park Service locality WRST-72 (unpublished data). Cobb and Richter (1980) included this prospect under the name 'Johnson Cr.'. It is located to within a few hundred feet.|
Geologic descriptionAt this prospect, pyrite and chalcopyrite are disseminated in a small diorite stock and surrounding hornfels (Richter and others, 1975). The sulfide-bearing rocks are limonite stained and also locally contain abundant copper-staining along fractures (Richter and Matson, 1970 ([OFR 70-275]). Richter and others (1975) estimate that the area of hydrothermal alteration in diorite and hornfels is about 300 by 300 feet in size. The average grade of surface samples is about 0.15 percent copper and less than 0.01 percent molybdenum. A grab sample of copper-stained diorite and a grab sample representing 500 feet of pyrite-bearing argillite talus respectively contained 0.2 parts per million (ppm) and 0.04 ppm gold (Richter and Matson, 1970 [OFR 70-275]). The deposit has been estimated to contain 8 million tons with an average grade of 0.20 percent copper and very low amounts of molybdenum (Richter and others, 1975). The host diorite is inferred to be Cretaceous in age; it intrudes Jurassic or Cretaceous siliciclastic rocks (Richter and Jones, 1973).
|Geologic map unit||(-141.629437568137, 62.1092565391914)|
|Mineral deposit model||Porphyry Cu-Mo (Cox and Singer, 1986; model 21a)|
|Mineral deposit model number||21a|
|Age of mineralization||Cretaceous? The age of the host diorite is inferred to be Cretaceous (Richter and Jones, 1973).|
|Alteration of deposit||Quartz-pyrite (+/- sericite?) veining and replacement; oxidation has resulted in iron- and copper-staining.|
|Workings or exploration||Surface prospecting has occurred since 1967.|
|Indication of production||None|
|Reserve estimates||The deposit is estimated to contain about 8 million tons of material with a grade of 0.20 percent copper and very low amounts of molybdenum (Richter and others, 1975).|
Additional commentsThe prospect is in the Wrangell-St. Elias National Preserve.
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.
Richter, D.H., and Jones, D.L., 1973, Reconnaissance geologic map of the Nabesna A-2 quadrangle, Alaska: U.S. Geological Survey Miscellaneous Investigations Series Map I-749, 1 sheet, scale 1:63,360.
Richter, D.H., and Matson, N.A., Jr., 1970, Geochemical data from the Nabesna A-2 quadrangle, Alaska: U.S. Geological Survey Open-File Report 70-275, 12 p., 1 sheet, scale 1:63,360.
|Reporters||Travis L. Hudson (Applied Geology)|
|Last report date||11/24/2002|