| Main commodities | Au |
|---|---|
| Other commodities | Cu |
| Ore minerals | chalcopyrite; gold; marcasite; pyrite; pyrrhotite |
| Quadrangle map, 1:250,000-scale | NB |
|---|---|
| Quadrangle map, 1:63,360-scale | B-5 |
| Latitude | 62.3824 |
| Longitude | -143.006 |
| Nearby scientific data | Find additional scientific data near this location |
| Location and accuracy | This prospect is low on the east flank of White Mountain. It is at an elevation of about 3,600 feet, 4,500 feet north-northeast of Nabesna. The site is in the SE1/4 of section 16, T. 7 N., R. 13 E. of the Copper River Meridian. This is locality M2 of Lowe and others (1982), locality 12 of Richter and others (1975), and National Park Service locality WRST-13 (unpublished data). Cobb and Richter (1980) included this prospect under the name 'Nabesna (Mining Corp.)'. It is located to within a few hundred feet. |
Geologic descriptionA surface exposure of massive pyrrhotite with some pyrite and late marcasite was discovered at this prospect in 1940 (Wayland, 1943). The massive pyrrhotite was exposed over a length of 52 feet, a vertical distance of 34 feet, and a width of 19 feet. The pyrrhotite is coarse grained; some crystal are 2 inches in diameter. The pyrrhotite also forms crystals in vugs and Wayland (1943) observed minor chalcopyrite and late marcasite under the microscope. Wayland (1943) reported that 14 samples of the massive sulfide assayed as much as 2.43 ounces of gold per ton and averaged 0.92 ounce of gold per ton (assuming a gold price of $35.00 per ounce). The massive sulfide body replaces Triassic limestone peripheral to a mid-Cretaceous granodiorite and quartz diorite stock (Lowe and others, 1982). Skarn assemblages are exposed about 3,000 feet to the southwest at the Nabesna mine (NB022) where calcic skarn containing abundant garnet and pyroxene and magnesian skarn containing magnetite and serpentine are well developed (Weglarz, 1991; Newberry and others, 1997). Chalcopyrite and other sulfide minerals are common in the calcic skarn and Newberry and others (1997) consider the principal deposits in the area to be gold-rich copper skarns. A concordant biotite/hornblende K/Ar date for the intrusive rocks is 114 +/- 3.4 Ma (Richter, Lanphere, and Matson, 1975). | |
| Geologic map unit | (-143.008133547592, 62.3820227830988) |
|---|---|
| Mineral deposit model | Cu skarn (Cox and Singer, 1986; model 18b) |
| Mineral deposit model number | 18b |
| Age of mineralization | Mid-Cretaceous. A concordant biotite/hornblende K/Ar date for the intrusive rocks is 114 +/- 3.4 Ma (Richter, Lanphere, and Matson, 1975). |
| Alteration of deposit | Oxidation. Marcasite replacement of pyrrhotite. |
| Workings or exploration | This deposit is exposed at the surface and has probably been explored by diamond drilling and and other techniques since its discovery in 1940 . It was an active prospect as recently as the 1980s (Lowe and others, 1982). |
|---|---|
| Indication of production | Undetermined |
Additional commentsThe mine is in the Wrangell-St. Elias National Preserve. | |
| MRDS Number | A011386 |
|---|---|
ReferencesNewberry, 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.
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.
Weglarz, T.B., 1991, Skarn genesis at the Nabesna mine, southcentral Alaska: Fairbanks, University of Alaska, M.S. thesis, 173 p.
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| Reporters | Travis L. Hudson (Applied Geology) |
| Last report date | 11/24/2002 |