Smith prospect; Treadwell Yukon Co.; Willoughby Island Mine, Juneau District, Skagway-Hoonah-Angoon Borough, Alaska, USA
This page is currently not sponsored. Click here to sponsor this page.
Location: The deposit is on the west side of Willoughby Island at an elevation near 450 feet and about 1.5 miles south of the north tip of the island. Accuracy is uncertain. The prospect was not located by MacKevett and others (1971) in 1966. The map site is about the same as location number 96 (Kimball and others, 1978). It is probably correct within 0.1 to 0.2 mile. The site is also about the same as location number 48 of Cobb (1972). Rossman (1963, p. K51) was also uncertain of the location of the deposit, but the prospect was found by Reed (1938).
Geology: Mineral deposits on Willoughby Island occur in a reefoid marble of Devonian or Silurian age that is part of a large carbonate package that underlies much of central Glacier Bay (Brew and others, 1978). At the mine, sulfide-rich replacement veins, as much as 1 foot thick, occur in marble at and near the intersection of lamprophyre dikes (Reed, 1938, p. 70-71). The lamprophyre dikes are relatively young, probably Tertiary in age. One vein was traced for about 100 feet. Sulfide minerals also occur as joint-fillings in the marble host rock. Buddington (1924) reported very high grade ore from the property, which was optioned by Treadwell Yukon Co. in 1925. Assays of as much as 1.74 ounces of gold and 42 ounces of silver were reported, in addition to 25 percent each of lead and antimony, suggesting the presence of jamesonite or a similar sulfantimonide at the property. Buddington reported jamesonite at another occurrence on western Willoughby Island. Chalcopyrite and tetrahedrite have also been reported from the prospect site.
Workings: The deposit was located in 1907 and leased to Treadwell Yukon Co. in 1925 (Shephard, 1926). Probably about that time, a forty-four foot long adit was driven, but it failed to hit the dike intersection that appeared to localize the ore on the surface. Buddington (1924) reported that a high-grade sample contained 1.74 ounces of gold and 42 ounces of silver per ton, and 25 percent each of lead and antimony, suggesting the possibility of jamesonite, which Buddington reported at another site on western Willoughby Island. Shephard (1926) sampled a 1-foot-thick massive sulfide vein at the property; the sample contained 0.12 ounce per ton gold, 11.9 ounces of silver per ton, 13.4 percent antimony, and 29.75 percent lead. The U.S. Geological Survey failed to find the prospect in 1966 (MacKevett and others, 1971), but the party mostly searched south of this location and the country is steep and overgrown with vegetation.
Alteration: Extensive pyritic and ankeritic alteration of lamprophyre.
Production: Probable small production of high-grade ore.
Commodities (Major) - Ag, Au; (Minor) - Cu, Pb, Sb
Development Status: Yes; small
Deposit Model: Replacement sulfide veins.
5 entries listed. 5 valid minerals.
The above list contains all mineral locality references listed on mindat.org. This does not claim to be a complete list. If you know of more minerals from this site, please register so you can add to our database. This locality information is for reference purposes only. You should never attempt to visit any sites listed in mindat.org without first ensuring that you have the permission of the land and/or mineral rights holders for access and that you are aware of all safety precautions necessary.
Brew, D.A., Johnson, B.R., Grybeck, D., Griscom, A., Barnes, D.F., Kimball, A.L., Still, J.C., and Rataj, J.L., 1978, Mineral resources of the Glacier Bay National Monument Wilderness Study Area, Alaska: U.S. Geological Survey Open-File Report 78-494, 670 p., 7 sheets. Buddington, 1924 (written communication cited by MacKevett and others, 1971). Cobb, E.H., 1972, Metallic mineral resources map of the Mount Fairweather quadrangle, AK: U.S. Geological Survey Miscellaneous Field Study Map MF-436, 1 sheet, scale 1:250,000. Kimball, A.L., Still, J.C., and Rataj, J.L., 1978, Mineral resources, in Brew, D. A., and others, Mineral resources of the Glacier Bay National Monument wilderness study area, Alaska: U.S. Geological Survey Open-File Report 78-494, p. C1-C375. MacKevett, E.M., Jr., Brew, D.A., Hawley, C.C., Huff, L.C., and Smith, J.G., 1971, Mineral resources of Glacier Bay National Monument, Alaska: U.S. Geological Survey Professional Paper 632, 90 p., 12 plates, scale 1:250,000. Reed, J.C., 1938, Some mineral deposits of Glacier Bay and vicinity, Alaska: Economic Geology, v. 33, p. 52-80. Rossman, Darwin, 1963, Geology of the eastern part of the Mount Fairweather quadrangle, Glacier Bay, Alaska: U.S. Geological Survey Bulletin 1121-K, p. K1-K57. Shephard, J.G., 1926, Smith Prospect, Willoughby Island, Juneau precinct: Alaska Territorial Department of Mines Prospect Evaluation 111-4, 3 p.