Hinkley Gulch

Mines, Inactive

Commodities and mineralogy

Main commodities Au
Other commodities Ag; As; Bi; Cu; Pb; Sb; Sn; U; W; Zn
Ore minerals gold

Geographic location

Quadrangle map, 1:250,000-scale BD
Quadrangle map, 1:63,360-scale B-5
Latitude 64.3061
Longitude -146.313
Nearby scientific data Find additional scientific data near this location
Location and accuracy Hinkley Gulch is a small northwest flowing tributary to lower Banner Creek. The gulch is not labeled on the USGS topographic maps but 'Hinkley Gulch' has long been used locally and in various mining-related publications. The mine is about 1.6 miles north-northeast of Richardson on the Richardson Highway, in the southwest corner of section 14, T. 7 S., R. 7 E., of the Fairbanks Meridian.

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 mineralized quartz-feldspar porphyry dike at the nearby Democrat Mine (BD014).
Placer gold was discovered nearby on Tenderfoot Creek (BD039) in 1905 and Hinkley Gulch was probably mined soon after. Ellsworth and Parker (1911) noted mining in Hinkley Gulch in open cuts and by drifting. There was at least one episode of mining after WWII. Don May (oral communication, 1998 ) said that Terry Anderson recovered 3,000 ounces of gold from Hinkley Gulch, but details are lacking. In recent years, there has been considerable production from a residual gold placer at May's Pit (BD007) about a half mile to the southeast on the saddle at the head of Hinkley Gulch and there has been speculation that the gold in the placers at May's Pit and Hinkley Gulch share a common origin (Freeman, 2011). Glover (1950) reported that the gold from Hinkley Gulch was 677 to 680 fine and Bundtzen and Reger (1977) said it averaged 670 fine.
Since the late 1980s there has been intermittent but extensive exploration in the Richardson district for lode gold deposits and some of that work has overlapped or involved sampling and mapping along Hinkley Gulch. Swainbank and others (1984) mapped highly altered rocks exposed along Hiinkley Gulch. Intervals up to 60 feet wide consist of sheared and oxidized epidote-amphibolite and garnet-amphibole skarn. A breccia exposed along the gulch that consists of clasts of quartz-feldspar porphyry, schist, quartzite and gneiss could be traced northeast for about 1,500 feet. A chip sample of porphyry contained 0.30 parts per million (ppm) gold, and low levels of copper, lead, zinc, antimony, and uranium. In 2005, an extensive soil sampling program defined several areas over or near Hinkley Gulch that were anomalous in gold, silver, arsenic, bismuth, tin, tungsten, copper, lead, and zinc (Noyes and others, 2006). In view of the altered rocks and the geochemical anomalies, Freeman (2011) suggests that the Hinkley Gulch may be over or near a distal intrusion-related gold deposit similar to the one at the Democrat Mine (BD014).
Geologic map unit (-146.315355733379, 64.3056926160209)
Mineral deposit model Placer Au (Cox and Singer, 1986; model 39a).
Mineral deposit model number 39a
Age of mineralization Quaternary placer and a 90 Ma intrusion-related gold deposit.
Alteration of deposit Rock in the vicinity of the placer on Hinkley Gulch are locally highly altered, sheared, oxidized, and brecciated.

Production and reserves

Workings or exploration Placer gold was discovered nearby on Tenderfoot Creek (BD039) in 1905 and Hinkley Gulch was probably mined soon after. Ellsworth and Parker (1911) noted mining in Hinkley Gulch in open cuts and by drifting. There was at least one episode of mining after WWII. Since the late 1980s there has been intermittent but extensive exploration in the Richardson district for lode gold deposits and some of that work has overlapped or involved sampling and mapping along Hinkley Gulch. In 2005, an extensive soil sampling program defined several anomalous areas over or near Hinkley Gulch.
Indication of production Yes; small
Reserve estimates Unknown.
Production notes There is little document production from Hinkley Gulch but 3,000 ounces of gold reportedly was produced some time after was WWII.

References

MRDS Number D002677

References

Freeman, C.J., 2011, Geology and mineralization of the Richardson gold property, Richardson Mining District, Alaska: Geologic report for Select Resources Corp. Inc., http://tri-valleycorp.com/docs/NI_43-101_Report.pdf (as of February 24, 2012).
Graham, G., 2002. Geology and gold mineralization of the Richardson District, east-central Alaska. Unpublished M.S. Thesis, University of Alaska, Fairbanks, 138 p.
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.
Weber, F.R., Foster, H.L., Keith, T.E.C., and Dusel-Bacon, Cynthia, 1978, Preliminary geologic map of the Big Delta quadrangle, Alaska: U.S. Geological Survey Open-File Ellsworth, C.E., and Parker, G.L., 1911, Placer mining in the Yukon-Tanana region: U.S. Geological Survey Bulletin 480-F, p. 173-217.
Reporters Cameron S. Rombach (ADGGS); D.J. Grybeck (Contractor, USGS)
Last report date 4/1/2012