|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 Banner prospect is on a hillside in the headwaters of Banner Creek and about 4.1 mile north of Richardson on the Richardson Highway. It is about 1.0 mile north of the mine symbol shown on the USGS 1:63-360-scale topographic map at the head of Banner Creek and about 0.3 mile west of the center of section 34, T. 6 S., R. 7 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 mineralized quartz-feldspar porphyry dike at the nearby Democrat Mine (BD014).
The Banner prospect was discovered in 1992 in the search for the source of visible gold in stream sediment and panned-concentrate samples (Vartanyan and others, 1992; 1998). Work in 1992 and 1998 consisted of considerable sampling in several long trenches, along road cuts, and in 30 hand-dug pits.
The northern portion of the prospect is mostly biotite-quartz-feldspar paragneiss intruded by a series of north-northwest-trending quartz-feldspar-porphyry dikes similar to the dike at the nearby Democrat Mine (BD014). The southern portion is in paragneiss and orthogneiss cut by two zones of steeply dipping granodiorite dikes that trend southeast. The quartz-feldspar porphyry varies from unaltered to intensely altered to greisen-like rock with pyrite veinlets and clots of pyrite. The alteration is strongest along the dike margins. Early quartz-sericite alteration is cut by brecciation, quartz veins, and quartz-sulfide veins.
The mineralization consists of sulfide-pyrite-quartz- veins, often with open-space textures (Freeman, 2011). The veins have up to 30 percent ore minerals; arsenopyrite and jamesonite are common; andorite, freibergite, sphalerite, and chalcopyrite less so. The 128 rock samples that were analyzed contained up to 1,729 parts per billion gold, up to 171.9 parts per million (ppm) silver, up to 2,454 ppm arsenic, up to 242 ppm copper, up to 3,948 ppm lead, up to 2,000 ppm arsenic, up to 51 ppm tin, and up to 91 ppm tungsten. Bismuth and tellurium were below the detection limit.Freeman (2011) interprets the prospect as a high-level, volatile-rich silver-tin-polymetallic hydrothermal system with strong affinities to intrusion-related gold deposits.
|Geologic map unit||(-146.348860215252, 64.3511917053546)|
|Mineral deposit model||Gold-silver-tin-polymetallic hydrothermal system with strong affinities to intrusion-related gold deposits.|
|Age of mineralization||Probably 90 Ma as is most of the gold mineralization in the Richardson district.|
|Alteration of deposit||The quartz-feldspar porphyry that hosts the veins varies from unaltered to intensely altered to greisen-like rock with pyrite veinlets and clots of pyrite. The alteration is strongest along the dike margins. Early quartz-sericite alteration is cut by brecciation, quartz veins, and quartz-sulfide veins.|
|Workings or exploration||The Banner prospect was discovered in 1992 in the search for the source of visible gold in stream sediment and panned-concentrate samples (Vartanyan and others, 1992; 1998). Work in 1992 and 1998 consisted of considerable sampling in several long trenches, along road cuts, and in 30 hand-dug pits.|
|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.
Foster, H.L., Albert, N.R.D., Griscom, Andrew, Hessin, T.D., Menzie, W.D., Turner, D.L, and Wilson, F.H., 1979, The Alaskan Mineral Resource Assessment Program; Background information to accompany folio of geologic and mineral resource maps of the Big Delta quadrangle, Alaska: U.S. Geological Survey Circular 783, 19 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.
Vartanyan, S.S., Volchcov, A.G., Zelikson, B.S., Bohme, D.M., 1998, Preliminary summary Report, 1998 Richardson District Exploration Program: Internal report for Tri-ValleyCorp., September 15, 1998, 35 p.
|Reporters||D.J. Grybeck (Contractor, USGS)|
|Last report date||4/1/2012|