Smith prospect; Treadwell Yukon Co.; Willoughby Island Mine, Hoonah-Angoon Census Area, Alaska, USAi

Regional Level Types
Smith prospect; Treadwell Yukon Co.; Willoughby Island Mine	Mine
Hoonah-Angoon Census Area	Census Area
Alaska	State
USA	Country

Dike-associated replacement mineralization in Paleozoic carbonate terrane. The site is in Glacier Bay Park and Preserve.
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.
Age: Tertiary.
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.

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Link to USGS - Alaska:	MF068

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References