Roger's Knob

Prospect, Inactive

Commodities and mineralogy

Main commodities Hg
Other commodities As; Au; Sb; W
Ore minerals cinnabar
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale SM
Quadrangle map, 1:63,360-scale C-4
Latitude 61.54174
Longitude -157.49432
Nearby scientific data Find additional scientific data near this location
Location and accuracy This prospect is on a knob that is informally called Rogers Knob; it is about 0.5 mile south of hill 1083, just west of upper Vreeland Creek. The prospect is at an elevation of about 850 feet, about 0.2 mile west of the southeast corner of section 19, T. 17 N., R. 46 W., of the Seward Meridian. This hill is approximately 200 feet wide, 400 feet wide, and 50 feet high. The location is accurate.

Geologic setting

Geologic description

The rocks at this prospect are poorly known because of poor exposure. The prospect consists of weak, quartz-cinnabar mineralization that cuts sandstone of the Upper Cretaceous, Kuskokwim Group near a small altered mafic dike (Cady and others, 1955; Muntzert and others, 1975; M.L. Miller and T.K. Bundtzen, unpublished field data, 1997 and 1998). Only rubble crop and talus is exposed at the site. The quartz veins are up to 10 centimeters wide and are associated with silicification of the host rocks. The vein density is difficult to determine due to poor exposure, but there appears to be a vein every foot or two. about two veins per meter. The rocks are intensely fractured. This fracture system might be related to a northeast-striking fault that follows nearby Vreeland Creek (Cady and others, 1955). A northwest fracture set intersects this northeast striking fault at Rogers Knob, and the structural intersection could have played a role in localizing the mercury mineralization (Muntzert and others, 1975).
Cinnabar occurs in quartz veins and finely disseminated in the host rocks, sandstone of the Kuskokwim Group. The maximum amount of cinnabar observed in quartz veins was about 3 percent (Muntzert and others, 1975). Pyrite was also observed in some veins as well as an unidentified, secondary brown mineral. The Rogers Knob prospect does not appear to be similar to the other mercury deposits in the Kuskokwim mercury province (Sainsbury and MacKevett ,1965). The mineralization at the Rogers Knob deposit It is more disseminated and there is a notable lack of a concentration of cinnabar.
Thirty channel samples cut by Resource Associates of Alaska, Inc. over about 650 of strike length averaged 400 parts per million (ppm) mercury. Two selected high grade samples contained 1.50 percent and 0.75 percent mercury (Muntzert and others, 1975). Four grab samples of disseminated cinnabar mineralization collected by Calista Corporation and the U.S. Geological Survey contained up to 2,940 ppm mercury, 100 parts per billion (ppb) gold, 27.0 ppm antimony, 158 ppm arsenic, and 30 ppm tungsten (M.L. Miller and J.Y. Foley, unpublished analytical data, 1997).
Geologic map unit (-157.496680047353, 61.5410422264726)
Mineral deposit model Silica-carbonate mercury? (Cox and Singer, 1986; model 27c).
Mineral deposit model number 27c?
Alteration of deposit Silica-carbonate alteration of mafic dikes.

Production and reserves

Workings or exploration Rogers Knob was investigated by Resource Associates of Alaska, Inc. in 1974. The U.S. Geological Survey and Calista Corporation sampled the site in 1997.
Indication of production None

References

References

Gray, J.E., Gent, C.A., Snee, L.W., and Wilson, F.H., 1997, Epithermal mercury-antimony and gold-bearing vein lodes of southwest Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 287-305.
Muntzert, J., Haverslew, R.E., Hirst, P.E., Knaebel, J., and Heiner, L.E., 1975, Land and mineral resource evaluation for Calista Corporation-final report of exploration activities during 1974: Fairbanks, Alaska, Resource Associates of Alaska, Inc. unpublished report, p. 20-22.
Wells, J.T., and Ghiorso, M.S., 1988, Rock alteration, mercury transport, and metal deposition at Sulphur Bank, California: Economic Geology, vol. 83, p. 606-618.
White, D. E., and Robinson, C. E., 1962, Sulphur Bank, California, a major hot spring quicksilver deposit, in Engel, A.E.J., James, H.L., and Leonard, B.F., eds., Petrologic studies: A volume in honor of A.F. Buddington: Boulder, Colorado, Geological Society of America p. 397-428.
Reporters T.K. Bundtzen (Pacific Rim Geological Consulting, Inc.) and M.L. Miller (U.S. Geological Survey)
Last report date 5/9/2003