Unnamed (near Portage Creek)

Occurrence, Inactive

Commodities and mineralogy

Main commodities Au
Other commodities As
Ore minerals arsenopyrite; gold; pyrite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale TL
Quadrangle map, 1:63,360-scale A-6
Latitude 62.002
Longitude -152.928
Nearby scientific data Find additional scientific data near this location
Location and accuracy 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.

Geologic setting

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a porphyritic phase with potassium feldspar phenocrysts up to 10 millimeters in size (Cominco American Incorporated, unpublished report).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.
Geologic map unit (-152.930243645818, 62.0014085101206)
Age of mineralization 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).

Production and reserves

Workings or 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.
Indication of production None

Additional comments

Similar gold-sulfide veins are also present in the Estelle pluton, ARDF record TY019 to the south in the Tyonek quadrangle.

References