Tippy Occurrence, Aniak District, Dillingham Borough, Alaska, USA

Location: This occurrence is at an elevation of about 3,000 feet on a ridge 1,000 feet south of USGS benchmark Tippy, near the south boundary of the Taylor Mountains C-8 quadrangle. The map site is in the NW1/4 of section 27, T 5 N, R 54 W, of the Seward Meridan. It is locality 13 of Clark and others (1970) and locality 6 of Cobb (1972 [MF 384]; 1976 [OF 76-606]).
Geology: At this locality, shale and graywacke, inferred to be part of the mid-Cretaceous Kuskokwim Group, is intruded and baked by a 15-foot wide, Cretaceous or Tertiary felsic dike (Clark and others, 1970). The limonite-stained dike contains some small cavities lined with apple green crystals of bindheimite (?), and small clots of acicular tourmaline. Quartz veins in the hornfels are up to 0.25 inch wide and contain 1 to 2 percent arsenopyrite and minor chalcopyrite; fracture surfaces are stained by malachite. Rock samples from this locality (Clark and others, 1970, samples AMM 777 and 799) contained up to 2,000 ppm B, 15,000 ppm Cu, 200 ppm Ag, 15 ppm Mo, 10,000 ppm Sb, 1.5 ppm Au, and greater than 10 ppm Hg. Rock samples collected up to 3,000 feet north-northwest along the ridge from this locality also contained anomalous levels of some metals, especially Ag, Cu, B, and Hg (Clark and others, 1970, sample localities 11 and 12).
Workings: At least surface examination and sampling has taken place.
Age: Late Cretaceous or Tertiary. Mineralization postdates deposition and deformation of mid-Cretaceous clastic sedimentary rocks and emplacement of Upper Cretaceous or Tertiary intrusive rocks.
Alteration: Silicification (quartz veining in hornfels) and oxidation.

Commodities (Major) - Au, Cu; (Minor) - Ag, Hg
Development Status: None
Deposit Model: Polymetallic veins (Cox and Singer, 1986; model 22c)

References:
Clark, A. L., Condon, W. H., Hoare, J. M., and Sorg, D. H., 1970, Analyses of rock and stream sediment samples from the Taylor Mountains C-8 quadrangle, Alaska: U. S. Geological Survey Open-File Report 437, 94 p. Clark, A. L., Condon, W. H., Hoare, J. M., and Sorg, D. H., 1970, Analyses of rock and stream sediment samples from the Taylor Mountains C-8 quadrangle, Alaska: U. S. Geological Survey Open-File Report 438, 89 p. Clark, A. L., Condon, W. H., Hoare, J. M., and Sorg, D. H., 1970, Analyses of rock and stream sediment samples from the Taylor Mountains C-8 quadrangle, Alaska: U. S. Geological Survey Open-File Report 439, 110 p. Cobb, E.H., 1972, Metallic mineral resources map of the Taylor Mountains quadrangle: U.S. Geological Survey Miscellaneous Field Studies Map MF-384, 1 sheet, scale 1:250,000. Cobb, E.H., 1976, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Dillingham, Sleetmute, and Taylor Mountains quadrangles, Alaska: U.S. Geological Survey Open-File Report 76-606, 92 p.