Wide Zone

Prospect, Active

Commodities and mineralogy

Main commodities Au
Other commodities Ag; As; Pb; Sb; Zn
Ore minerals arsenopyrite; galena; gold; pyrite; stibnite; lead-antimony sulfosalts
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale BD
Quadrangle map, 1:63,360-scale B-5
Latitude 64.3214
Longitude -146.3325
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Wide Zone prospect is about 2.6 miles north of Richardson on the Richardson Highway. It includes most of the section 10, T. 7 S., R. 7 E., of the Fairbanks Meridian, northeast of the mouth of Buckeye Creek and the coordinates are near the center of the section.

Geologic setting

Geologic description

The Richardson District is characterized by gentle slopes and broad, alluvium-filled valleys (Prindle and Katz, 1913). The area is unglaciated and largely overlain by windblown silt, sand, and loess, locally up to 50 meters thick (Foster and others, 1979). The rocks consist of three structure-bounded units (Weber and others, 1978; Swainbank and others, 1984; Noyes and others, 2006; Freeman, 2011). There is a core that consists mainly of biotite-hornblende-feldspar-quartz gneiss and lesser amphibolite, quartzite, marble and calc-silicate hornfels. The core is bounded on the north and south by amphibolite-grade pelitic schist. The contacts between the units are probably low-angle faults; north-trending vertical faults occur widely. Weber and others (1978) assign the pre-metamorphic age of the rocks to the Precambrian or Paleozoic. They were metamorphosed in the Middle to Late Devonian and recrystallized in the Early Cretaceous (Dusel-Bacon and others, 2004; Freeman, 2011). The metamorphic rocks are intruded by 90 Ma, felsic to intermediate dikes and plugs, notable the quartz-feldspar porphyry dike at the nearby Democrat Mine (BD014).
The rocks at the Wide Zone prospect are mainly quartz- muscovite schist cut by faulted or pinched-out bodies of quartz-feldspar porphyry similar to the 90 Ma porphyry that is associated with the mineralization at the Democrat Mine (BD014) about a mile to the northwest. Reconnaissance geochemical sampling in 1991 and 2005 identified numerous areas anomalous in gold, arsenic, bismuth, lead, antimony, and tungsten (Vartanyan and others, 1991; Noyes, 2006). The geochemical data and the presence of the characteristic quartz-feldspar porphyry associated with mineralization in the area suggests that the prospect hosts a distal intrusion-related gold deposit (Freeman, 2011). The prospect may be in a down-dropped block of mineralized ground that fills the gap from the mineralization at the Democrat Mine (BD014) to the mineralization at Hinkley Gulch (BD019) and May's Pit (BD007).
Geologic map unit (-146.334857110893, 64.3209921148587)
Mineral deposit model Intrusion-related gold deposit.
Age of mineralization Probably 90 Ma as is other mineralization of the same type in the immediate area.

Production and reserves

Indication of production None

References

MRDS Number 10307235

References

McCoy, D.T.; Newberry, R.J.; Layer, P., DiMarchi, J.; Bakke, A.; Masterman, J.S. and Minehane, D.L., 1997, Plutonic-related gold deposits of interior Alaska: in Economic Geology Monograph 9, p. 191-241.
Rogers, J. A., McCoy, D. T., Graham, G., and Nerup, M., 1999, Placer Dome-Tri-Valley Option Agreement, 1999 Annual Report, Richardson Project: Confidential Private Report, 46 p.
Vartanyan, S.S., Konstantinov, V.Y., Oreshin, V.Y., Rodionov, V.A., Pyatnitshy, V.A., Brovkin, V.A., Zagoskin, B.S. and Zelikson, B.S., 1991, Estimation of gold potential of the Richardson Mining District, Alaska: Internal TsNIGRI report to Tri-Valley, December, 1991, 40 p.
Reporters Cameron S. Rombach (ADGGS); D.J. Grybeck (Contractor, USGS)
Last report date 4/1/2012