Unnamed (at head of Rulby Creek)

Occurrence in Alaska, United States with commodity Iron

Geologic information

Identification information

Deposit ID 10307910
Record type Site
Current site name Unnamed (at head of Rulby Creek)

Geographic coordinates

Geographic coordinates: -165.7404, 64.77168 (WGS84)
Relative position This occurrence is about 0.8 mile south of the Tub Mountain prospect (NM018) near the head of Rulby Creek (NM016). The occurrence is at an elevation of 760 feet and is accurately located from Herreid (1970).
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Geographic areas

Country State
United States Alaska


Commodity Importance
Iron Primary

Materials information

Materials Type of material
Limonite Ore


  • (Local) Dolomitization and oxidation.

Nearby scientific data

(1) -165.7404, 64.77168

Comments on the geologic information

  • Geologic Description = This limonite occurrence is about 0.8 mile south of the Tub Mountain prospect (NM018). It is a few hundred feet across (Herreid, 1970) and one of several carbonate-hosted, iron-rich deposits in the area (NM014, NM014, NM017, NM018, and NM020). The limonite can be massive to granular, botryoidal, mamillary, or fibrous. The iron content ranges to as much as 59 percent in analyzed samples (Eakin, 1915 [B 622-I, p. 361-365]). Hematite, pyrolusite, and calcite are present locally. This occurrence 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 [B 662-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 that are transitional to lead-zinc-barite deposits such as the Quarry (NM135). 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 control on them. A Late Cretaceous age for the iron deposits was suggested by Brobst and others (1971) because 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).
  • Age = Late Cretaceous or Early Tertiary; post mid-Cretaceous metamorphism.

Economic information

Economic information about the deposit and operations

Development status Occurrence

Comments on exploration

  • Status = Probably inactive

Mining district

District name Nome

Comments on the workings information

  • Workings / Exploration = There may be small prospecting pits at this locality.

Reference information

Links to other databases

Agency Database name Acronym Record ID Notes
USGS Alaska Resource Data File ARDF NM019

Bibliographic references

  • Deposit

    Eakin, H.M., 1915, Placer mining in Seward Peninsula: U.S. Geological Survey Bulletin 622-I, p. 366-373.

  • Deposit

    Cathcart, S.H., 1922, Metalliferous lodes in southern Seward Peninsula: U.S. Geological Survey Bulletin 722, p. 163-261.

  • Deposit

    Shallit, A.B., 1942, Report on Sinuk River iron-ore deposits, Seward Peninsula, Alaska: Alaska Territorial Department of Mines Minerals Investigation, 46 p., 2 maps, scales 1:31,250, 1:4,800.

  • Deposit

    Mulligan, J.J., and Hess, H.D., 1965, Examination of the Sinuk iron deposits, Seward Peninsula, Alaska: U.S. Bureau of Mines Open-File Report 8-65, 34 p.

  • Deposit

    Herreid, G.H., 1970, Geology and geochemistry of the Sinuk area, Seward Peninsula, Alaska: Alaska Division of Mines and Minerals Geologic Report 36, 61 p., 3 sheets, scale 1:42,000.

  • Deposit

    Brobst, D.A., Pinckney, D.M., and Sainsbury, C.L., 1971, Geology and geochemistry of the Sinuk River barite deposits: U.S. Geological Survey Professional Paper 750-D, p. D1-D8.

  • Deposit

    Sainsbury, C.L., Hummel, C.L., and Hudson, Travis, 1972, Reconnaissance geologic map of the Nome quadrangle, Seward Peninsula, Alaska: U.S. Geological Survey Open-File Report 72-326, 28 p., 1 sheet, scale 1:250,000.

  • Deposit

    Cobb, E.H., 1972, Metallic mineral resources map of the Nome quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-463, 2 sheets, scale 1:250,000.

  • Deposit

    Cobb, E.H., 1978, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Nome quadrangle, Alaska: U.S. Geological Survey Open-File report 78-93, 213 p.

  • Deposit

    Hudson, T.L., and Arth, J. G., 1983, Tin-granites of Seward Peninsula, Alaska: Geological Society of America Bulletin, v. 94, p. 768-790.

  • Deposit

    Hudson, T.L., 1999, Alaska Resource Data File, Solomon quadrangle: U.S. Geological Survey Open-File Report 99-573, 360 p.

  • Deposit

    Bundtzen, T.K., Reger, R.D., Laird, G.M., Pinney, D.S., Clautice, K.H., Liss, S.A., and Cruse, G.R., 1994, Progress report on the geology and mineral resources of the Nome mining district: Alaska Division of Geological and Geophysical Surveys, Public Data-File 94-39, 21 p., 2 sheets, scale 1:63,360.

Comments on the references

  • Primary Reference = Herreid, 1970

General comments

Subject category Comment text
Deposit Model Name = Carbonate-hosted, iron oxide deposit.

Reporter information

Type Date Name Affiliation Comment
Reporter 22-OCT-99 Hawley, C.C. and Hudson, Travis L. Hawley Resource Group