Location: This mine is in upper Waterfall Creek, a name and stream not currently shown on the Nome C-2 topographic map. The creek is a north tributary of Last Chance Creek; it flows south through sections 6 and 8, T. 9 S., R. 34 W., Kateel River Meridian. The location shown, at an elevation of about 1,500 feet, is the approximate intersection of a mineralized segment of the Penny River fault and Waterfall Creek. The area is complexly mineralized; vein deposits were developed in short adits southeast of the location down to about 1,100 feet elevation along Waterfall Creek. This location is approximately the same as locality 20 of Cobb (1972 [MF 463], 1978 [OFR 78-93]).
Geology: The Christophosen mine is on quartz-sulfide veins as much as 5 feet wide within a weakly mineralized shear zone hundreds of feet across. The shear zone strikes north-northeast and is a mineralized part of the Penny River fault. Discrete veins occur on subsidiary structures southeast of the main shear zone. Samples of the shear zone contained about 100 ppb gold and were strongly anomalous in arsenic. The associated quartz veins contain galena, stibnite, chalcopyrite and display surface stainings of azurite and malachite. The main activity on the claims occurred before 1916, when the mine was visited by Mertie (1918 [B 662-I, p. 425-449]). According to Mertie (1918 [B 662-I, p. 439]), the shear zone is about 100 feet across, strikes about N 20 E, and contains pyrite, pyrrhotite, stibnite, and gold. The mine produced about 2.5 tons of stibnite-rich material that assayed more than 58 percent antimony and contained some gold and silver. A mineralized quartz vein concordant to schistosity was cut off by the shear zone. Although the vein contained sulfides, including stibnite, Mertie proposed that the quartz was early, predating the sulfide mineralization. The prospect was also visited by Herreid (1970, p. 36), who called it the Last Chance prospect. Herreid reported scattered stibnite crystals about 0.25 inch across in one quartz vein and found about 0.1 ounce of gold per ton in a graphitic fault zone about 900 feet northeast of the prospect. The country rock near the mine was mapped as chlorite-rich metaturbite schist and marble by Bundtzen and others (1994).
Workings: The prospect was explored by surface pits and adits that were driven before 1916 on four mining claims (Mertie, 1918 [B 662-I, p. 425-449]). An upper adit was about 105 feet long; the lower adit, in part a crosscut, was driven N 25 W for about 270 feet. A total of about 2.5 tons of stibnite-bearing ore containing more than 58 percent antimony was mined and sold. The prospect was visited by Herreid (1970) and remapped and sampled by Kennecott Exploration Co. in about 1991.
Age: Mid-Cretaceous or younger; host structure crosscuts rocks metamorphosed in the mid-Cretaceous.
Alteration: Sulfidation along a wide shear zone.
Production: More than 2.5 tons of stibnite ore assaying more than 58 percent antimony were produced.

Commodities (Major) - Sb; (Minor) - Ag, Au, Cu, Pb
Development Status: Yes
Deposit Model: Low-sulfide Au-quartz veins; associated mineralized shear zone (Cox and Singer,

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Mineral List

9 valid minerals.