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Unnamed (near Portage Creek)

Occurrence in Alaska, United States with commodities Gold, Arsenic
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Geologic information

Identification information

Deposit ID 10308448
Record type Site
Current site name Unnamed (near Portage Creek)

Geographic coordinates

Geographic coordinates: -152.93079, 62.00149 (WGS84)
Relative position Reed and others (1978, locality 35) locate this occurrence on the south side of the north fork of Portage Creek in the northwest quarter of Section 15, T. 22 N., R. 20 W., of the Seward Meridian at about 3900 feet.
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Geographic areas

Country State
United States Alaska

Commodities

Commodity Importance
Gold Primary
Arsenic Secondary

Materials information

Materials Type of material
Arsenopyrite Ore
Gold Ore
Pyrite Ore
Quartz Gangue

Nearby scientific data

(1) -152.93079, 62.00149
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Comments on the geologic information

  • Geologic Description = Reed and others (1978) describe altered granodiorite float with thin (<5 millimeters wide) veinlets of arsenopyrite and pyrite with up to 1.5 ppm gold. . The occurrence lies within the Late Cretaceous /early Tertiary (65 m.y. to 66 m.y.) granodiorite of Mount Estelle (Te) that intrudes Mesozoic marine sedimentary rocks (KJs) (Reed and Nelson, 1980). At this locality the pluton has a leucocratic equigranular phase and a porphyritic phase with potassium feldspar phenocrysts up to 10 millimeters in size (Cominco American Incorporated, unpublished report). The granodiorite of Mt. Estelle probably reflects the same plutonic event as the composite plutons (Tcp) to the north described by Reed and Nelson (1980). About 2 miles N72E of this location gold-sulfide-bearing veinlets are described at an unnamed site (TL052). . Similar gold-sulfide veins are also present in the Estelle pluton, ARDF record TY019 to the south in the Tyonek quadrangle.
  • Age = Late Cretaceous/early Tertiary; mineralization is interpreted to be related to the granodiorite of Mt. Estelle for which hornblende ages are about 65 to 66 m.y. (Reed and Nelson, 1980).

Economic information

Economic information about the deposit and operations

Development status Occurrence

Comments on exploration

  • Status = Inactive

Mining district

District name Yentna

Comments on the workings information

  • Workings / Exploration = Rock chip sampling and silt sampling by the U.S. Geological Survey (Reed and others, 1978) and mapping, rock chip sampling and silt sampling Cominco American Incorporated in the late 1980s have been done in the area. Reed and others (1978) describe altered granodiorite float with thin (less than 5 millimeters wide) veinlets of arsenopyrite and pyrite with up to 1.5 ppm gold. Other private companies have conducted reconnaissance programs in the area at various times between the 1960s to present.

Reference information

Links to other databases

Agency Database name Acronym Record ID Notes
USGS Alaska Resource Data File ARDF TL063

Bibliographic references

  • Deposit

    Reed, B.L., Nelson, S.W., Curtin, G.C., and Singer, D.A., 1978, Mineral resources map of the Talkeetna Quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-870-D, 1 sheet, scale 1:250,000.

  • Deposit

    Cobb, E.H., and Reed, B.L., 1980, Summaries of data and lists of reference to metallic and selected nonmetallic mineral deposits in the Talkeetna quadrangle, Alaska: U.S. Geological Survey Open-File Report 80-884, 106 p.

  • Deposit

    Reed, B.L., and Nelson, S.W., 1980, Geologic map of the Talkeetna quadrangle: U.S. Geological Survey Miscellaneous Investigations Map I-1174, scale 1:250,000.

Comments on the references

  • Primary Reference = Reed and others, 1978

General comments

Subject category Comment text
Deposit Other Comments = Similar gold-sulfide veins are also present in the Estelle pluton, ARDF record TY019 to the south in the Tyonek quadrangle.

Reporter information

Type Date Name Affiliation Comment
Reporter 10-AUG-98 Madelyn A. Millholland Millholland & Associates