Unnamed (west-central tier of claims, Mt. Eielson district)

Prospects, Inactive

Commodities and mineralogy

Main commodities Pb; Zn
Other commodities Ag; Au; Cu
Ore minerals azurite; chalcopyrite; galena; malachite; pyrite; sphalerite
Gangue minerals calcite; epidote; quartz

Geographic location

Quadrangle map, 1:250,000-scale MM
Quadrangle map, 1:63,360-scale B-1
Latitude 63.3989
Longitude -150.3364
Nearby scientific data Find additional scientific data near this location
Location and accuracy This record describes prospects on the following claims, herein called the west-central tier of claims of the Mt. Eielson or Copper Mountain district: Snowdrift (Wolf); Virginia (Eva); Denver (Lillian); Marjorie (Kentucky or Martin); Matheson (Mary); and Weasel north of the Snowdrift. The tier is bisected by Grant Creek, a tributary to the Thorofare River on the northwest flank of Mt. Eielson. The claims form a block about 1500 feet east-west by 3300 feet north-south. The block is east of, and adjoins, the west tier of claims described in record MM164. The west-central tier of claims are between 3300 and 4000 feet elevation. For this record, the site is approximately at the center of the side line between the Virginia and Mary claims, near the center of section 36, T. 17 S., R. 15 W., Fairbanks Meridian. Based on Reed's 1:24,000-scale map (1933, pl. 24), the location is accurate within about 500 feet.

Geologic setting

Geologic description

The country rocks in the area of the west-central tier of claims are Paleozoic, thin-bedded limestone and lesser amounts of clastic sedimentary rocks and schist, intruded by Eocene or Oligocene porphyritic granodiorite. Locally, the bedded rocks and the granodiorite are cut by Tertiary basaltic dikes. Exposures are poor on the northernmost Snowdrift claim, but are moderately good on the other claims of the group. The surficial deposits on the Snowdrift claim are part of an extensive alluvial fan (Reed, 1933, plate 24).
The mineral deposits are mainly replacement skarns, rich in sphalerite and galena, developed in limy sedimentary rocks. They are similar to the other deposits in the Mt. Eielson district (MM166).
The strata mostly are nearly horizontal and are cut by dikes and sills of porphyritic granodiorite. Most of the replacement deposits are nearly parallel to original bedding, which is well preserved. Reed reported a crosscutting ore body adjacent to a dike, along with relatively abundant vein quartz (1933, p. 278-279). Xenoliths of sedimentary rocks up to about 10 feet across in the granodiorite are largely replaced by sulfide ore. One such body at least 12 feet thick assayed 0.90 ounce of silver per ton, 0.14 percent copper, 3.56 percent lead, and 3.99 percent zinc. Sparse exposures along Grant Creek on the Snowdrift claim consist of epidotized limy sedimentary rocks containing small amounts of pyrite, chalcopyrite, and sphalerite (Reed, 1933, p. 278).
Gates and Wahrhaftig (1944) mapped extensive sulfide bodies on the Virginia claim, then called the Eva. Sampling by the U. S. Bureau of Mines (Muir, Thomas, and Sanford, 1947, nos. E-17 to E-22) showed some moderately high silver values in addition to lead and zinc. Sample E-18 (3.1 feet) assayed 9.8 ounces of silver and 0.015 ounce of gold per ton, 5 percent lead, 4.99 percent zinc, and 0.90 percent copper. One sample contained 1.15 percent copper and about 11 percent combined lead and zinc. A picked but representative sample from the Big Cliff claim west of Grant Creek assayed 6.8 percent lead, 8.7 percent zinc, and 2 ounces of silver per ton.
Relict bedding on the Denver claim dips 55 N, which is much steeper than the nearly horizontal bedding on the Virginia claim (Reed, 1933, p. 279). According to Reed, a north-dipping mineralized bed about 10 feet thick on the Denver claim may correlate with a more gently-dipping mineralized bed on the Virginia claim. Reed also reports that chalcopyrite is relatively abundant on these claims and that it is locally oxidized to azurite and malachite.
Reed (1933, p. 280) reports relatively high gold and copper values in samples from the Marjorie claim, and cites assays by Harry Townsend of 0.03 ounce of gold per ton in two samples. (Townsend worked for the U. S. Geological Survey in the 1920s and for Anaconda Copper Company in the 1930s.) One of the samples contained 2.3 percent copper in addition to 10.5 percent combined lead and zinc. The southernmost Matheson claim is on steeply north-dipping epidotized rock containing disseminated sphalerite.
Geologic map unit (-150.338653716252, 63.3984065007599)
Mineral deposit model Polymetallic replacement deposits; Zn-Pb-(Cu) skarn deposits (Cox and Singer, 1986, models 19a, 18c).
Mineral deposit model number 19a, 18c
Age of mineralization The mineral deposits are inferred to be mid-Tertiary, slightly younger than the Eocene or Oligocene granodiorite (Reed and Lanphere, 1974; Decker and Gilbert, 1978; Cole, 1998).
Alteration of deposit Introduction of epidote and quartz into calcareous sedimentary rocks; extensive sulfide replacement of inclusions engulfed in the granodiorite. Local oxidation of copper minerals.

Production and reserves

Workings or exploration The claims were originally staked by O. M. Grant and Hugh Matheson before 1931 and prospected fairly systematically into the 1930s. Government agencies examined the claims during World War II, but since then there has been little activity. By World War II, the claims were owned by O. M. Grant, John Anderson, and Mrs. Frank McGarvey (Muir, Thomas, and Sanford, 1947). The Virginia claim was developed by pits and two short adits.
Indication of production None

Additional comments

The claims are in Denali National Park and Preserve.

References