Hot Springs Dome; Barrett; Donnelly Prospect, Hot Springs Mining District, Yukon-Koyukuk Census Area, Alaska, USAi

Regional Level Types
Hot Springs Dome; Barrett; Donnelly Prospect	Prospect
Hot Springs Mining District	Mining District
Yukon-Koyukuk Census Area	Census Area
Alaska	State
USA	Country

Location: The site of the Hot Springs Dome prospect is at an elevation of about 2100 feet, about 0.3 mile southwest of the summit of Manley Hot Springs Dome. The prospect is in section 2, T. 2 N., R. 16 W., of the Fairbanks Meridian. The site corresponds to location 6 of Cobb (1972).
Geology: The country rocks in the area of Hot Springs Dome consist of Tertiary biotite granite, Cretaceous, predominantly marine, clastic sedimentary rocks, and a zone of contact-metamorphosed sedimentary rocks (hornfels) peripheral to the granite (Chapman and others, 1982; Reifenstuhl and others, 1998). The hornfels zone is approximately 1/4 mile wide. Dikes ranging from 3 inches to 4 feet thick cut the granite (Waters, 1934). Most of the dikes contain tourmaline, in amounts ranging from less than 1 percent to 15 percent; monazite was also identified in one specimen. The lode deposits of Hot Springs Dome are in granite and in metamorphosed sedimentary rocks along its contact. The deposits are marked by gossans that trend northeast, approximately parallel to the contact between the granite and the country rocks. The gossans contain abundant iron-oxide veins, along with some iron-carbonate and quartz veinlets, and apparently have developed along shear or breccia zones. Exposures of the mineralization, however, are poor. Eakin (1913) reported gold-bearing hematite deposits near Hot Springs Dome and Roughtop Mountain, in breccia zones ranging from a few inches to several feet wide. Mertie (1934) described six east-trending shear zones in metamorphosed sedimentary rocks on the northwest side of the granite body on Hot Springs Dome. At the Barrett prospect, a shear zone contains veins of galena and pockets of limonite, siderite, and possibly manganese minerals. Other reported minerals include chalcopyrite, pyrrhotite, pyrite, malachite, azurite, chalcocite, and native sulfur; erythrite occurs in quartz stringers and in crevices of schistose rock. Wedow and others (1952) reported that the galena is argentiferous. Moxham (1954) reported that the Barrett prospect shear zone is 20- to 35-feet wide, and can be traced horizontally for 2,000 feet. He also reported cerussite as the main ore in the oxidized zone. Very few sulfides have been identified in drilling, most likely due to their oxidation. The U.S. Bureau of Mines diamond-drilled eight holes in 1954, with a total length of 3,198 feet and a maximum length of 515 feet. Even at a depth below the surface of 446 feet, the rocks are intensely oxidized. The drilling intersected gossan comprising limonite, goethite, pyrolusite, hematite, magnetite, rutile, and minor anglesite and erythrite (Maloney, 1971). Fresh galena, however, was intersected in one drill hole at a depth of 400 feet, and a stringer of pyrrhotite, chalcopyrite, and pyrite was intersected at a depth of 18 feet in another hole. Wayland (1961) reported that one oxidized quartz-siderite-galena vein was traceable on the surface for 1,500 feet and another for 500 feet. Those veins also contained calcite, pyrite, pyrrhotite, and erythrite. Exploratory pits and adits driven by the U.S. Bureau of Mines on Hot Springs Dome in 1953-54 yielded little more than iron and manganese oxides (Maloney, 1971). Earlier reports of small amounts of lead, zinc, copper, and cobalt sulfides were confirmed by drilling and surface sampling, whose results included the following maximum metal values: 3.7 percent lead, 0.32 percent zinc, 1.20 percent copper, 0.02 percent cobalt, 3.90 percent manfanese, 0.17 ounce of gold per ton, and 0.53 ounce of silver per ton. Most samples, however, contained only trace amounts of metals. The Donnelly prospect is just south of the Barrett prospect. Little work has been done there, and its description has not been made public (Heiner and others, 1968).
Workings: Workings (3 shallow shafts, 1 short adit, several trenches and pits) caved by 1931. Diamond drilling (8 holes, 3,198 feet total) completed by U.S. Bureau of Mines in 1954.
Age: Tertiary. The granite has a [whole-rock?] K-Ar age date of 62 +/- 3 Ma (Chapman and others, 1982), and a biotite 40Ar/39Ar age date of 59 +/- 0.8 Ma (Reifenstuhl and others, 1998).
Alteration: All metallic minerals are oxidized except for a few pockets containing small amounts of galena, pyrrhotite, chalcopyrite, and pyrite.

Commodities (Major) - Au; (Minor) - Ag, Co, Cu, Mn, Pb, Zn
Development Status: None
Deposit Model: Polymetallic veins (Cox and Singer, 1986; model 22c).

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Link to USGS - Alaska:	TN103

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