Tub Mountain

Prospect, Inactive

Commodities and mineralogy

Main commodities Fe
Other commodities Mn
Ore minerals goethite; hematite; limonite [so called]; pyrite
Gangue minerals calcite; dolomite; quartz

Geographic location

Quadrangle map, 1:250,000-scale NM
Quadrangle map, 1:63,360-scale D-2
Latitude 64.7827
Longitude -165.7491
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Tub Mountain prospect is on hill 956 in the SW1/4NW1/4 section 22, T. 8 S., R 35 W., Kateel River Meridian. It is 1.25 miles southwest of the confluence of Stewart and Sinuk Rivers and about 0.8 mile south of Sinuk River. The prospect is locality 6 of Hummel (1975) and locality 2 of Cobb (1972 [MF 463], 1978 [OFR 78-93]).

Geologic setting

Geologic description

The Tub Mountain prospect is a limonite-rich deposit about 300 by 600 feet that appears to be localized along high-angle faults in marble (Herreid, 1970). It is one of several similar deposits in the area (see NM014, NM014, NM017, NM019, and NM020). The limonite can be massive to granular, botryoidal, mammillary, or fibrous. The iron content ranges to as much as 59 percent in analyzed samples (Eakin, 1915). Hematite, pyrolusite, and calcite are present locally. Shallit (1942; Mulligan and Hess, 1965, table 3) estimated that 8,000 long tons of rock containing 10 to 20 percent iron is present at Tub Mountain.
This prospect and other iron deposits of the Sinuk River area are at or near the base of massive marble whose protolith age is probably lower Paleozoic (Sainsbury, Hummel, and Hudson, 1972; Bundtzen and others, 1994). The deposits are locally controlled by high-angle faults or folds, but they are in general crudely stratabound within the basal massive marble or underlying calc-schist (Mulligan and Hess, 1965; Herreid, 1970). This stratigraphic interval also hosts base metal sulfide-fluorite-barite deposits at the Galena (NM130) and Quarry prospects (NM135).
The origin and age of the iron deposits of the Sinuk River area are uncertain. The deposits may be, in part, gossan developed on oxidized sulfide deposits (Eakin, 1915 [B 622-I, p. 361-365];Mertie, 1918 [B662-I, p. 425-449]; Cathcart, 1922; Mulligan and Hess, 1965; Herreid, 1970). Several of the iron deposits, including American (NM014) and Monarch (NM017), are locally highly anomalous in zinc and lead. Arguing against a simple gossan origin is the paucity of diagnostic textures and structures in boxworks that would suggest derivation from specific sulfide minerals. Alternatively, these deposits could be hypogene iron oxide and carbonate deposits probably transitional to lead-zinc-barite deposits, such as Quarry (NM135), that are at about the same stratigraphic position.
The age of the iron deposits of the Sinuk River area is most likely post-mid-Cretaceous because faults that crosscut mid-Cretaceous metamorphic rocks are an important ore control. A Late Cretaceous age for the iron deposits was suggested by Brobst and others (1971) as this is the age of fluorine-rich tin granites of northwestern Seward Peninsula (Hudson and Arth, 1983). The youngest possible age appears to be Early Tertiary, when deep weathering, sandstone-type uranium mineralization, and possibly karst formation occurred to the east in the Solomon quadrangle (Hudson, 1999).
Geologic map unit (-165.75173913735, 64.781936449493)
Mineral deposit model Carbonate-hosted, iron oxide deposit.
Age of mineralization Late Cretaceous or Early Tertiary; post mid-Cretaceous metamorphism.
Alteration of deposit Dolomitization and oxidation.

Production and reserves

Workings or exploration Surface prospecting pits, dating to before WWI, are present.
Indication of production None
Reserve estimates Shallit (1942; table 3, Mulligan and Hess, 1965) estimated that the Tub Mountain prospect includes 8,000 long tons of rock containing 10 to 20 percent iron.


MRDS Number A012778


Hudson, T.L., and Arth, J. G., 1983, Tin granites of Seward Peninsula, Alaska: Geological Society of America Bulletin, v. 94, p. 768-790.
Reporters C.C. Hawley and Travis L. Hudson
Last report date 10/22/1999