Question Mark

Prospect, Inactive

Commodities and mineralogy

Main commodities Cu
Ore minerals cuprite; iron oxides; native copper

Geographic location

Quadrangle map, 1:250,000-scale MM
Quadrangle map, 1:63,360-scale A-3
Latitude 63.2059
Longitude -151.1683
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Question Mark prospect (Cobb, 1980, p. 85 [OFR 80-363]) is at an elevation of about 4000 feet on the west side of an unnamed middle fork of upper Slippery Creek. It is in the SE 1/4 SW 1/4 sec. 3, T. 20 S., R. 19 W., Fairbanks Meridian. Its location is known mainly from a 1:6,000-scale map made by Earl Pilgrim in 1929 (Hawley and Associates, 1978, fig. 4.1-B). The location is accurate within a radius of 1000 feet. The prospect is number 29 of Cobb (1973 [MF-366]) and number 39 of MacKevett and Holloway (1977).

Geologic setting

Geologic description

The Question Mark lode is in a porphyritic mafic dike with fine-grained groundmass that cuts dark shale of Paleozoic age. The dike contains disseminated grains and tissue-thin seams of native copper. Copper oxide (cuprite) is locally present. The shale country rock is stained, probably by iron oxides (Moffit, 1933, p. 321). Pilgrim's map (fig. 4.1-B; Hawley and Associates, 1978) indicates that the dike trends west, possibly reflecting topographic deflection of a body that strikes northeast and dips southeast.
Geologic map unit (-151.170554854859, 63.2053789064294)
Mineral deposit model Native copper occurrence in a mafic igneous dike.
Age of mineralization Uncertain but possibly middle Tertiary, assuming that it is related to nearby antimony and polymetallic lodes on the north flank of the McGonagall pluton of Eocene or Oligocene age (Reed and Lanphere, 1973, 1974).
Alteration of deposit Oxidation of iron and copper minerals.

Production and reserves

Workings or exploration Some surficial material was removed to expose the lode, which was discovered by W. J. Shannon before 1929. The Question Mark prospect was restaked in 1930 by A. Taylor (Heiner and Porter, 1972, Mt. McKinley quadrangle, number 38).
Indication of production None

Additional comments

The prospect is in Denali National Park and Preserve.


MRDS Number A011247


Heiner, L.E., and Porter, Eve, 1972, Alaska Mineral Properties, volume 2: University of Alaska, Mineral Industry Research Laboratory Report 24, 669 p.
Reed, B.L., and Lanphere, M.A., 1973, Alaska-Aleutian Range batholith--Geochronology, chemistry, and relation to circum-Pacific plutonism: Geological Society of America Bulletin, v. 84, no. 8, p. 2583-2610.
Reed, B.L., and Lanphere, M.A., 1974, Offset plutons and history of movement along the McKinley segment of the Denali fault system, Alaska: Geological Society of America Bulletin, v. 85, p. 1883-1892.
Reporters C.C. Hawley
Last report date 12/12/2000