|Quadrangle map, 1:250,000-scale||KC|
|Quadrangle map, 1:63,360-scale||B-6|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||This site includes several prospects or occurrences in about a square-mile area in and near the city of Ketchikan. They are at elevations below 500 feet, mainly between Hoadley Creek and Carlanna Creek, and near sea level along the highway northwest of town for about a half mile (sections 14, 15, and 23, T. 75 S., R. 90 E., of the Copper River Meridian). The location is accurate within about 0.5 mile. The site represents loc. 60 in Elliott and others (1978), and locs. 267-269 and 271-274 in Maas and others (1995). Old workings on several of the prospects are concealed by construction and other city development, or are on private lots had have been filled in or covered by the owners (Maas and others, 1995, p. 194).|
This part of Revillagigedo Island is underlain mainly by marine, pelitic sedimentary rocks and subordinate andesitic or basaltic volcanic rocks that are intruded by Cretaceous stocks, sills, and dikes of feldspar-porphyritic granodiorite, and by a stock and probably related plugs of Tertiary gabbro (Berg and others, 1988). The strata were regionally metamorphosed to greenschist-grade phyllite and semischist in Late Cretaceous time. They subsequently were contact metamorphosed to hornblende hornfels: locally, near some of the Cretaceous granodiorite contacts, and, more widely, peripheral to the Tertiary gabbro. The premetamorphic age range of the strata is uncertain. Berg and others (1988) note that they closely resemble Upper Jurassic to mid-Cretaceous flysch and volcanic rocks nearby on Gravina Island. The country rocks are cut by a high-angle fault along Tongass Narrows that displays about 4 miles of right-lateral offset.
The Ready Mix occurrence is in an industrial rock quarry and consists of quartz lenses in the contact zone between metasedimentary and dioritic intrusive rocks (Maas and others, 1995, loc. 267). Samples collected in the early 1990s by the U.S. Bureau of Mines contained up to 1176 ppb Au (Maas and others, 1995).
At the Carlanna Creek rock quarry, a deposit discovered in the early 1990s during a U.S. Bureau of Mines investigation consists of wisps, fracture coatings, and disseminations of molybdenite in silicified porphyritic quartz diorite, and of fracture coatings of molybdenite in adjacent metasedimentary country rocks (Maas and others, 1995, loc. 268: p. 194-200). The molybdenite occurs in varying amounts for about 300 horizontal feet in the quarry walls and adjacent rocks. The richest mineralization is in the quartz diorite, and in contact zones between the quartz diorite and the metasedimentary rocks. The mineralogy and geological character of the deposit suggest a Quartz Hill (KC105) type porphyry molybdenum deposit. A 40-foot sample across a quartz diorite-metasedimentary rock contact contained 1532 ppm Mo; other samples contained 6 to 3295 ppm Mo. Near this quarry, panned concentrates from Carlanna Creek contained 3.06 ppm Au (Maas and others, 1995, loc. 269).
There are four occurrences along and near Hoadley Creek: (1) the Hoadley Creek occurrence consists of pyrite and pyrrhotite disseminated in quartz diorite (Maas and others, 1995, loc. 274). Samples of this rock contained up to 21.6 ppm Au; (2) the upper Hoadley Creek occurrence, explored by a 70-foot adit, consists of a sulfide vein that assayed up to 1044 ppb Au and 4695 ppm Cu (Maas and others, 1995, loc. 271); (3) the lower Hoadley Creek occurrence, explored by a 9-foot adit, consists of a quartz vein that assayed up to 1101 ppm Cu (loc. 272); (4) and the so-called 'Trapdoor' Hoadley Creek occurrence, developed by a 66-foot adit, consists of a quartz vein that assayed up to 7237 ppb Au (loc. 273). All of the workings date to the early 1900s.According to U.S. Bureau of Mines (1977) claim records, the Little Sue prospect, which appears to be in metasedimentary rocks near the intrusive contact of Tertiary gabbro, was staked for gold. No other information about it has been made public.
|Geologic map unit||(-131.681685772995, 55.3596528250255)|
|Mineral deposit model||Low-sulfide Au-quartz veins or polymetallic veins (Cox and Singer, 1986; models 36a or 22c); Porphyry Mo, low-F (Cox and Singer, 1986; model 21b)|
|Mineral deposit model number||36a or 22c and 21b|
|Age of mineralization||Cretaceous or younger.|
|Alteration of deposit||Metasedimentary rocks are contact metamorphosed to hornblende hornfels near intrusive contacts of Tertiary gabbro. Cretaceous or younger quartz diorite at Carlanna Creek quarry is silicified.|
|Workings or exploration||
Several of the prospects were explored in the early 1900s by opencuts, adits, and shafts. Most of these workings have been covered by housing or other developments in the city of Ketchikan. The Carlanna Creek occurrence is in an active rock quarry.Several of the prospects and occurrences were mapped and sampled in the early 1990s by the U.S. Bureau of Mines (Maas and others, 1995). The results of their sampling are summarized in the Geologic description.
|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.
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.
U.S. Bureau of Mines, 1977, Claim map, Ketchikan quadrangle: U.S. Bureau of Mines Map 120, scale 1:250,000.
|Reporters||H.C. Berg, USGS|
|Last report date||7/2/1999|