Ptarmigan Creek

Prospects, Inactive

Commodities and mineralogy

Main commodities Mo
Other commodities Au
Ore minerals molybdenite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale D-6
Latitude 63.8029
Longitude -146.5229
Nearby scientific data Find additional scientific data near this location
Location and accuracy The prospects are in a canyon on lower Ptarmigan Creek just above where the creek enters the wide flood plain of Delta Creek. The prospect area is at the east end of the mountain mass called Molybdenum Ridge. The location for this record is on the south side of Ptarmigan Creek about 1,000 feet north-northeast of the center of section 11, T. 13 S.. R. 6 E., Fairbanks Meridian. It is near the center of an area of mineralization reported to extend about one mile along the canyon. The site corresponds to locality 1 of Cobb (1979 [OFR 79-238] and to locality N3 in table 2 of Nokleberg and others (1991). It is accurate as a general location of a mineralized area, but may not exactly correspond to the location of the Ptarmigan Creek prospects reported by Smith (1942 [B 926-C]) and Joesting (1942). (MH312 in the A-2 quadrangle is also named Ptarmigan Creek.)

Geologic setting

Geologic description

The Ptarmigan Creek prospects are mainly in Cretaceous granodiorite near the contact of the intrusion with schist and slate (Nokleberg and Aleinikoff, 1985; Nokleberg and others, 1991). Smith (1942 [B 926-C]) reported that the mineralization is in a zone about one mile long along Ptarmigan Creek; Martin (1920) noted that it is concentrated in an 800- to 900-foot-wide zone. Molybdenite occurs sparsely in quartz veins scattered through the granodiorite; in places, the veins are numerous enough to form a stockwork in the granodiorite. Individual veins are a few inches to more than 2 feet thick (Smith, 1942 [B 926-C, p. 195]). Gold-quartz veins also occur in the granodiorite (Joesting, 1942).
Most of the veins are of low grade, but selected samples contained as much as 2.71 percent molybdenite (Smith, 1942 [B 926-C]; it is not certain whether the values are of molybdenum or of the sulfide). The veins were discovered in about 1914 and were prospected during World War I, from 1937 to 1940, and probably during World War II.
Geologic map unit (-146.52520353567, 63.8024886983157)
Mineral deposit model Porphyry Mo (Cox and Singer, 1986; model 21b).
Mineral deposit model number 21b
Age of mineralization Probably Cretaceous, related to emplacement of granodiorite.
Alteration of deposit Silicification; formation of quartz veins and stockworks in granodiorite.

Production and reserves

Workings or exploration The molybdenite deposit was discovered in 1914 by Frank Gillespie, who explored it between 1914 and 1918. He drove drifts as much as 30 feet long (Smith, 1942 [B 926-C]). The prospect was active again from 1937 to 1940; Joesting (1942) reported one adit 106 feet long and three shorter ones. The prospect was briefly visited in the 1980s by the U.S. Geological Survey; a grab sample collected at that time contained 50 parts per million (ppm) molybdenum and 0.1 ppm gold (Nokleberg and others, 1991).
Indication of production Undetermined
Production notes Some ore was stockpiled in World War I but was not shipped.

Additional comments

No commercial mining has occurred, and the occurrences are fairly well prospected.