|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 3,600 feet on Monte Cristo Creek. It is about 3.6 miles upstream of the mouth of the creek and near the west boundary of the Nabesna A-4 quadrangle. The site is in the NE1/4 of section 16, T. 5 N., R. 13 E. of the Copper River Meridian. This is locality 1 of Richter (1973), locality 16 of Richter and others (1975), and National Park Service locality WRST-20 (unpublished data). Cobb and Richter (1980) included this prospect under the name 'Monte Cristo Cr.'. It is located to within a few hundred feet.|
Geologic descriptionDisseminated molybdenite and quartz-pyrite-molybdenite veins occur in hydrothermally altered volcanic breccia of the Lower Cretaceous, Chisana Formation at its contact with a granodiorite pluton (Richter and others, 1975). A composite chip sample across 200 feet of the contact contained 5 parts per million molybdenum and 100 parts per million copper (Richter and Matson, 1970 [OFR 70-276]). The volcanic rocks of the Chisana Formation are extensively replaced by gypsum-quartz-pyrite assemblages in this part of Monte Cristo Creek (Richter and Matson, 1970 [OFR 70-276]; Richter, 1973, 1976). Richter and others (1975) and Richter, Lanphere, and Matson (1975) consider the granodiorite to be part of the mid-Cretaceous Nabesna pluton that has been dated by K/Ar methods as from 105 +/- 4.0 to 114 +/- 3.4 Ma.
|Geologic map unit||(-142.999725798392, 62.2183102367269)|
|Mineral deposit model||Porphyry Mo, Low-F (Cox and Singer, 1986; model 21b)|
|Mineral deposit model number||21b|
|Age of mineralization||Mid-Cretaceous. The deposit is at the contact of a granodiorite considered to be part of the mid-Cretaceous Nabesna pluton for which K/Ar dates range from 105 +/- 4.0 to 114 +/- 3.4 Ma (Richter and others, 1975; Richter, Lanphere, and Matson, 1975).|
|Alteration of deposit||Oxidation is indicated by abundant iron-oxide staining. This part of Monte Cristo Creek is marked by extensive gypsum-quartz-pyrite replacement of the volcanic rocks of the Chisana Formation (Richter, 1973; 1976).|
|Workings or exploration||The deposit has been prospected one or more times since 1967.|
|Indication of production||None|
|Reserve estimates||The porphyry molybdenum deposits in the Nabesna quadrangle are each estimated to contain 50 million tons grading 0.01 percent 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., 1976, Geologic map of the Nabesna quadrangle, Alaska: U.S. Geological Survey Miscellaneous Investigations Series Map I-932, 1 sheet, scale 1:250,000.
Richter, D.H., and Matson, N.A., Jr., 1970, Geochemical data from the Nabesna A-4 quadrangle, Alaska: U.S. Geological Survey Open-File Report 70-276, 14 p., 1 sheet, scale 1:63,360.
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.
|Reporters||Travis L. Hudson (Applied Geology)|
|Last report date||11/24/2002|