|Quadrangle map, 1:250,000-scale||KC|
|Quadrangle map, 1:63,360-scale||B-4|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||
The Gold Banner claim is in section 18, T. 75 S., R. 94 E., of the Copper River Meridian. It straddles Gokachin Creek about 0.4 mile upstream from its mouth at Thorne Arm The map site is roughly at the midpoint of the claim. The site corresponds to loc. 95 in Elliott and others (1978), and to loc. 304 (2-6) in Maas and others (1995). The location is accurate within 0.1 mile.Also see Additional comments.
The country rocks in this part of Revillagigedo Island are marine, interbedded, andesitic and basaltic metavolcanic rocks and subordinate pelitic metasedimentary rocks that are intruded by stocks, sills, and dikes of Cretaceous feldspar-porphyritic granodiorite (Berg and others, 1988). The strata and some of the granodiorite were regionally metamorphosed to greenschist grade in Late Cretaceous time. These regionally metamorphosed rocks subsequently were locally remetamorphosed to hornblende hornfels near the contacts of Cretaceous granodiorite plutons that were emplaced after the regional metamorphism. The premetamorphic age of the strata is uncertain. Berg and others (1988) assign them a Mesozoic or (late) Paleozoic age. Berg (1982) and Crawford and others (2000) assign them to the Gravina belt, of Late Jurassic or Cretaceous age, or to the Taku terrane, of late Paleozoic to Late Triassic age. The metamorphic and intrusive rocks locally are overlain by basalt and andesite lava flows of Quaternary or Tertiary age.
Wright and Wright (1908, p. 147) describe the Gold Banner deposit as a 1-6 foot thick, auriferous quartz fissure vein in several types of schist. The schist is intruded by a porphyry dike that forms the hanging wall of the vein at the surface. The vein, traced on the surface for several hundred feet, strikes N65E and dips 70-80SE, at an acute angle to the foliation of the schist, which generally strikes NW and dips steeply SW. In addition to sparse particles of free gold, the vein contains pyrite, galena, and sphalerite. The deposit was explored in the early 1900s by a shaft and a 60-foot tunnel.
Maas and others (1995, p. 215-218) describe the deposit as an auriferous quartz fissure vein in hydrothermally altered mafic metavolcanic rock that also carries gold values adjacent to the vein (see Alteration). In addition to free gold, the vein contains pyrite and minor amounts of galena and sphalerite. Forty-seven samples that Maas and others (1995) collected averaged 1.0 ppm Au, and the mean value of 46 of the samples was 2048 ppb Au. Workings include 4 adits, one 160 feet long, one 128 feet long, and two caved; a shaft at least 18 feet deep; a 72-foot-deep glory hole; and several trenches. Maas and others (1995, p. 218) report a minimum production, probably all in the early 1900s, of 0.3 kg Au and 0.2 kg Ag.Maas and others (1995, p. 215) note that the quartz in the veins in the Sea Level mine area is not recrystallized; the veins thus are probably younger than most or all of the Late Cretaceous regional metamorphism.
|Geologic map unit||(-131.183693850232, 55.3676601129233)|
|Mineral deposit model||Low-sulfide Au-quartz veins (Cox and Singer, 1986; model 36a)|
|Mineral deposit model number||36a|
|Age of mineralization||Maas and others (1995, p. 215) note that the quartz in the veins in the Sea Level mine area is not recrystallized; the veins thus are probably younger than most or all of the Late Cretaceous regional metamorphism.|
|Alteration of deposit||The Gold Banner vein, like most of the other principal veins in the Sea Level mine area, is bordered by a hydrothermally altered zone up to three feet thick, characterized by generally fine-grain, light-gray to bluish-gray, massive, carbonate- and sericite-bearing rock that commonly contains cubic pyrite crystals up to an inch across (Maas and others, 1995, p. 215). Maas and others (1995) interpret this zone as hydrothermally altered mafic metavolcanic rock. Early miners called this altered rock 'blue porphyry,' which they interpreted as crosscutting altered dikes that predate the quartz veins, but are closely associated with some of the orebodies (Brooks, 1902, p. 65; Wright and Wright, 1908, p. 143). Gold content of these pyritic altered zones is high adjacent to the quartz veins and diminishes away from them. Weathered altered rocks have a reddish-brown, oxidized rind up to three inches thick.|
|Workings or exploration||The deposit was explored in the early 1900s by a shaft and a 60-foot tunnel. At the time of Maas and others' (1995) investigation, workings included 4 adits, one 160 feet long, one 128 feet long, and two caved; a shaft at least 18 feet deep; a 72-foot-deep glory hole; and several trenches. Forty-seven samples that Maas and others (1995) collected averaged 1.0 ppm Au, and the mean value of 46 of the samples was 2048 ppb Au.|
|Indication of production||Yes; small|
|Production notes||Maas and others (1995, p. 218) report a minimum production, probably all in the early 1900s, of 0.3 kg Au and 0.2 kg Ag.|
Additional commentsEarly reports refer to this property as the Golden Banner or Golden Tree claim (Wright and Wright, 1908, p. 147).
Berg, H.C., 1982, The Alaska Mineral Resource Assessment Program; guide to information about the geology and mineral resources of the Ketchikan and Prince Rupert quadrangles, southeastern Alaska: U.S. Geological Survey Circular 855, 24 p.
Berg, H.C., Elliott, R.L., and Koch, R.D., 1988, Geologic map of the Ketchikan and Prince Rupert quadrangles, southeastern Alaska: U.S. Geological Survey Mineral Investigations Series Map I-1807, 27 p., scale 1:250,000.
Brooks, A.H., 1902, Preliminary report on the Ketchikan mining district, Alaska, with an introductory sketch of the geology of southeastern Alaska: U.S. Geological Survey Professional Paper 1, 120 p.
Crawford, M.L., Crawford, W.A., and Gehrels, G.E., 2000, Terrane assembly and structural relationships in the eastern Prince Rupert quadrangle, British Columbia, in H.H. Stowell and W.C.McClelland, eds., Tectonics of the Coast Mountains, southeastern Alaska and British Columbia: Geological Society of America Special Paper 343, p. 1-21.
Elliott, R.L., Berg, H.C., and Karl, S.M.,1978, Map and table describing metalliferous and selected non-metalliferous mineral deposits in the Ketchikan and Prince Rupert quadrangles, Alaska: U.S. Geological Survey Open-File Report 78-73B, 17 p., 1 sheet, scale 1:250,000.
Maas, K.M., Bittenbender, P E., and Still, J.C., 1995, Mineral investigations in the Ketchikan mining district, southeastern Alaska: U.S. Bureau of Mines Open-File Report 11-95, 606 p.
|Reporters||H.C. Berg, USGS|
|Last report date||7/4/1999|