Unnamed (north of VABM Point)

Prospect, Inactive

Commodities and mineralogy

Main commodities Au; Bi; Cu; W
Other commodities Ag; As; Sn; U
Ore minerals goethite after sulfide
Gangue minerals diopside; garnet

Geographic location

Quadrangle map, 1:250,000-scale SM
Quadrangle map, 1:63,360-scale A-1
Latitude 61.01267
Longitude -156.03235
Nearby scientific data Find additional scientific data near this location
Location and accuracy This prospect is near the top an an unnamed, northeast trending ridge at the head of an eastern tributary of the Hoholitna River. The prospect is at an elevation of about 1,400 feet, about 0.6 mile north-northwest of triangulation station 'Point' and about 0.2 mile southwest of the center of section 28, T. 11 N., R. 38 W., of the Seward Meridian. The location is accurate.

Geologic setting

Geologic description

This prospect is a garnet-diopside-quartz skarn that is developed in coarsely crystalline limestone adjacent to a medium grained, equigranular, hornblende, biotite granite of unknown age (M.L. Miller, unpublished field data, 1999). The limestone was included in the Holitna Group of Cady and others (1955), and the Farewell terrane of Decker and others (1994). LePain and others (2000) have mapped the limestone that hosts the skarn prospect as an algal-rich, lime mudstone of Silurian age.
A granitic pluton exposed 3 kilometers northeast of this skarn occurrence has a 40Ar/39Ar age of 67 Ma (R. Wilson, oral communication, 2003). The skarn is developed for about 300 feet but practically all of the skarn minerals are developed at the contact between granite and limestone; the granite has been altered to chlorite at its contact zone. The skarn has abundant, pink-colored garnet and green masses of diopside. This occurrence is geologically and geochemically similar to the Nixon Fork (MD 061) and Nixon Fork-Crystal (MD062) Mines in the Medfra quadrangle (Bundtzen, 1999; Bundtzen and Miller, 1997).
Late stage? quartz veins with abundant goethite that formed from the sulfides cut the skarn zone. No sulfides were identified. Three grab samples of goethite-rich quartz vein from the skarn zone contained up to 800 parts per billion (ppb) gold, 400 ppb silver, 381 parts per million (ppm) bismuth, 880 ppm copper, 3,530 ppm tungsten, 809 ppm arsenic, 79 ppm tin, and 195 ppm uranium (M.L. Miller, unpublished analytical data, 1999).
Geologic map unit (-156.034639177702, 61.011979914983)
Mineral deposit model Copper-gold skarn (Cox and Singer, 1986; model 18b).
Mineral deposit model number 18b
Age of mineralization Unknown. A granitic pluton exposed about 2 miles northeast of this skarn has a 40Ar/39Ar age of 67 Ma (R. Wilson, oral communication, 2003).
Alteration of deposit Diopside-epidote skarn formed at the contact of limestone and granite.

Production and reserves

Workings or exploration There are old prospect pits, now caved-in and grown over, in the skarn zone. The U.S. Geological Survey examined the occurrence in 1999.
Indication of production None

References

References

Bundtzen, T.K., and Miller, M.L., 1997, Precious metals associated with Late Cretaceous-early Tertiary igneous rocks of southwestern Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 242-286.
Decker, J., Bergman, S.C., Blodgett, R.B., Box, S.E., Bundtzen, T.K., Clough, J.G., Coonrad, W.L., Gilbert, W.G., Miller, M.L., Murphy, J.M., Robinson, M.S., and Wallace, W.K., 1994, Geology of southwestern Alaska, in Plafker, G. and Berg, H.C., eds., The Geology of Alaska: Geological Society of America DNAG, The Geology of North America, v. G-1, p. 285-310.
Reporters T.K. Bundtzen (Pacific Rim Geological Consulting, Inc.) and M.L. Miller (U.S. Geological Survey)
Last report date 5/9/2003