|Quadrangle map, 1:250,000-scale||KC|
|Quadrangle map, 1:63,360-scale||C-6|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||The Rainy Day prospect is at an elevation of about 200 feet, approximately 0.2 mile inland from the southwest shore of Helm Bay, and about 1.4 miles from the mouth of the bay. The site is in section 19, T. 72 S., R. 88 E., of the Copper River Meridian. It corresponds to loc. 251 in Maas and others (1995, fig. 46), and to loc. 31 in Elliott and others (1978). The location is accurate within 0.1 mile.|
The country rocks at this site are flyschlike metasedimentary rocks that gradationally intertongue with andesitic and basaltic metatuff (Berg and others, 1988, p. 17-19). The strata were regionally metamorphosed to greenschist-grade phyllite and semischist in Late Cretaceous time (Brew, 1996, p. 27). Their premetamorphic age is uncertain. Berg and others (1988, p. 17) state that they closely resemble Upper Jurassic to mid-Cretaceous marine flysch and volcanic rocks nearby on Gravina Island. At the prospect, the bedded rocks are intruded by a 600-1000-foot-thick dike of granite porphyry (Wright and Wright, 1908, p. 156) or granodiorite (Maas and others, 1995, fig. 46). The dike probably is Late Cretaceous or younger, assuming that it postdates the regional metamorphism.
The deposit consists of a 3- to 3.5-foot-thick quartz fissure vein in granite porphyry (Brooks, 1902, p. 58; Wright and Wright, 1908, p. 156). The vein strikes northwest and has been traced in outcrop for 300-500 feet; it contains small amounts of pyrite, sphalerite, and galena, and minute particles of native gold. The prospect was developed in the early 1900s by an opencut and a 105-foot tunnel. Maas and others (1995, table 25) report the following average metal contents in their samples from the Rainy Day prospect: 6.28 ppm Au, 13.2 ppm Ag, 48 ppm Cu, 732 ppm Pb, and 14 ppm Zn.Fluid inclusion studies of quartz vein material from several of the Helm Bay lodes suggest that the veins formed at temperatures and pressures consistent with conditions during the Late Cretaceous greenschist-grade regional metamorphism (Maas and others, 1995, p. 184).
|Geologic map unit||(-131.969683084952, 55.614637193556)|
|Mineral deposit model||Low-sulfide gold-quartz veins (Cox and Singer, 1956; model 36a)|
|Mineral deposit model number||36a|
|Age of mineralization||Late Cretaceous.|
|Workings or exploration||The prospect was developed in the early 1900s by an opencut and a 105-foot tunnel. Maas and others (1995, table 25) report the following average metal contents in their samples from the Rainy Day prospect: 6.28 ppm Au, 13.2 ppm Ag, 48 ppm Cu, 732 ppm Pb, and 14 ppm Zn.|
|Indication of production||None|
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.
Brew, D.A., 1996, Geologic map of the Craig, Dixon Entrance, and parts of the Ketchikan and Prince Rupert quadrangles, southeastern Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-2319, 53 p., 1 sheet, 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.
Elliott, R.L., Berg, H.C., and Karl, S.M., 1978, map and table describing metalliferous and selected non-metalliferous mineral deposits, Ketchikan and Prince Rupert quadrangles, Alaska: U.S. Geological Survey Open-File Report 78-73-B, 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||6/30/1999|