Syenite Porphyry

Prospect, Inactive

Commodities and mineralogy

Main commodities Au; Hg; Sb
Other commodities Ag; As; Zn
Ore minerals cinnabar

Geographic location

Quadrangle map, 1:250,000-scale ID
Quadrangle map, 1:63,360-scale D-3
Latitude 62.90212
Longitude -157.07853
Nearby scientific data Find additional scientific data near this location
Location and accuracy This prospect is on peak 3957 at the head of Windy Creek in the western Beaver Mountains. It is at an elevation of about 3,950 feet in the SW1/4 SW1/4, section 33, T. 33 N. , R. 41 W., of the Seward Meridian. The location is accurate.

Geologic setting

Geologic description

The Syenite Porphyry prospect consists of fine-grained cinnabar and stibnite along fracture surfaces in an altered iron-stained roof pendant and intrusive rocks of the 70.3 Ma Beaver Mountain stock (Bundtzen and Laird, 1982). The roof pendant is a mudstone that has been altered to a hard, dark-gray hornfels. The underlying intrusion is a potassically altered, syenite-porphyry phase of the Beaver Mountains intrusion. The sulfide-bearing fractures contain amethyst, and smoky and chalcedonic quartz (Szumigala, 1993). Grab samples of mineralization collected by the U.S. Geological Survey contained more than 10 parts per million (ppm) mercury and 200 ppm zinc (McGimsey and others, 1988, Miller, Bundtzen, and Gray, 2005). Grab samples collected by Battle Mountain Mining Company contain up to 1,960 parts per billion (ppb) gold, 3.9 parts per million silver, 896 ppm arsenic, 1,896 ppm antimony, and more than 50 ppm mercury. Six of of the nine samples contained greater than 50 ppm mercury (Szumigala, 1993).
Geologic map unit (-157.080888548039, 62.9014610874749)
Mineral deposit model Hot springs Au-Ag (Cox and Singer, 1986; model 25a).
Mineral deposit model number 25a
Age of mineralization Undated; may be related to emplacement of the Beaver Mountains stock that has been dated at 70.3. Ma (Bundtzen and Laird, 1982).
Alteration of deposit Iron staining; potassic alteration.

Production and reserves

Workings or exploration The Alaska Division of Geological and Geophysical Surveys examined the Syenite Porphyry prospect in 1979 (Bundtzen and Laird, 1980 and 1982). Noranda Exploration looked at the occurrence in 1983 (John Dunbier, oral communication, 1983). Surface sampling was conducted by the U.S. Geological Survey in 1984 and 1985 (McGimsey and others, 1988). Battle Mountain Mining Company investigated the Syenite Porphyry prospect in 1990 (Szumigala, 1993).
Indication of production None



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.
Szumigala, D.J., 1993, Gold mineralization related to Cretaceous-Tertiary magmatism in the Kuskokwim Mountains of west-central and southwestern Alaska: Los Angeles, University of California Ph.D. dissertation, 300 p.
Szumigala, D.J., 1996, Gold mineralization related to Cretaceous-Tertiary magmatism in west-central Alaska-A geochemical model and prospecting guide for the Kuskokwim region: Geological Society of Nevada Symposium Proceedings, p. 1317-1340.
Reporters T.K. Bundtzen (Pacific Rim Geological Consulting, Inc.), M.L. Miller (U.S. Geological Survey); and C.C. Hawley (Hawley Resource Group)
Last report date 5/16/2003