|Quadrangle map, 1:250,000-scale||BD|
|Quadrangle map, 1:63,360-scale||B-5|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||The First Chance (lode) prospect is about 0.1 mile south of hill 1275; it is just north of the First Chance Creek placer mine (BD069). The First Chance lode prospect is about 10.2 miles north-northwest of Richardson on the Richardson Highway, about 2.6 miles northeast of the junction of Redmond Creek and Shamrock Creek, and about 0.7 mile southwest of the center of section 36, T. 5 S., R. 6 E., of the Fairbanks Meridian. The location is accurate.|
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).
Vartanyan and others (1991) indicate that the bedrock in the upper third of First Chance Creek is primarily pelitic schist. The schist in the lower two-thirds is deformed and contains numerous quartz veins and veinlets, and dacite (?) dikes 150 to 500 meters long.The First Chance lode deposit was discovered in 1991 during the search for the source of high gold and arsenic in panned concentrate samples from the south flank of hill 1275 on the north side of lower First Chance Creek (Vartanyan and others, 1991; Freeman, 2011). Subsequent soil sampling to the north and south of First Chance Creek identified a northwest-trending area anomalous in gold and arsenic; the area is about 1,500 meters long and about 400 meters wide on the hill slopes between Last Chance Creek and hill 1275 (Vartanyan and others, 2003). Twenty-four chip samples of quartz were collected in the anomalous area that contained up to 3 grams of gold per tonne.
|Geologic map unit||(-146.485367797754, 64.4304889670604)|
|Mineral deposit model||Intrusion-related gold.|
|Age of mineralization||Quaternary.|
|Workings or exploration||Limited geochemical and rock sampling in several episodes from 1991 to 2003.|
|Indication of production||None|
Dusel-Bacon, C., Wooden, J.L., and Layer, P.W., 2004, A Cretaceous Ion-Microprobe U-Pb zircon Age for the West Point Orthogneiss: Evidence for another Gneiss Dome in the Yukon-Tanana Upland in Galloway, J.P., ed., 2004, Studies by the U.S. Geological Survey in Alaska, 2001: U.S. Geological Survey Professional Paper 1678, p. 41 - 60.
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||D.J. Grybeck (Contractor, USGS)|
|Last report date||4/1/2012|