Unnamed (near Crescent Creek)

Occurrence, Inactive

Commodities and mineralogy

Main commodities W
Other commodities Li; Sn
Ore minerals cassiterite; scheelite
Gangue minerals amphibole; chlorite; epidote; garnet; muscovite; quartz; sericite; tourmaline

Geographic location

Quadrangle map, 1:250,000-scale EA
Quadrangle map, 1:63,360-scale D-6
Latitude 64.9654
Longitude -143.6824
Nearby scientific data Find additional scientific data near this location
Location and accuracy An unnamed tungsten occurrence is located on the north bank of Crescent Creek at the confluence of an unnamed northerly tributary stream. The site lies about 2 miles west of Beverly Creek, which is another tributary to Crescent Creek. All local drainages are to the Charley River, located east of the site. The occurrence is in the SE1/4 sec. 28, T. 2 N., R. 20 E., of the Fairbanks Meridian, and the location given is the approximate midpoint of an area of hornfels boulders. Accuracy of the location is about 1,000 feet.

Geologic setting

Geologic description

Local igneous rocks, mostly biotite-quartz monzonite and its more felsic segregations, are part of a much larger Mesozoic to Tertiary age intrusive complex in east-central Alaska (Foster and others, 1973; Foster, 1976; Brabb and Churkin, 1969). North of Crescent Creek the granitic rocks intrude biotite gneiss, amphibolite and subordinate quartz-biotite gneiss, schist, and marble (Foley and Barker, 1981). Near this site leucocratic aplite dikes are also common. Contact margins between these rocks are locally retrograded to plagioclase- and pyroxene-hornfels and banded calc-silicate.
Near the confluence of an unnamed creek with Crescent Creek green siliceous carbonate rock with scheelite occurring as layered and dissemination of aggregate grains is reported, as well as minor disseminated scheelite in some granitic boulders (Foley and Barker, 1981). Locally minor scheelite also occurs as isolated interstitial grains in aplite and within quartz veinlets cutting these dike rocks. Minor constituent minerals in the aplite groundmass include garnet, tourmaline, muscovite and epidote. Dravite-filled fractures in granitic rock and disseminated scheelite are noted in the vicinity. Lithium in the granitic rocks was also found substantially anomalous. Local areas of sericite greisen occur in the quartz monzonite along joints and faults. Placer scheelite occurs in the stream bed about two miles upstream (Foley and Barker, 1981).
Geologic map unit (, )
Mineral deposit model Tungsten greisen (Cox and Singer, 1986; model 15c); Skarn tungsten (Cox and Singer, 1986; model 14a).
Mineral deposit model number 15c, 14a
Age of mineralization Granitic rocks that host primary scheelite occurrences are believed to be Cretaceous with some subordinate granitic rocks of early Tertiary age (Brabb and Churkin, 1969; Foster, 1976). Mineralization appears concordant with the younger (Tertiary) intrusive phase.
Alteration of deposit Silicification and greisen formation with scheelite and minor cassiterite (Foley and Barker, 1981).

Production and reserves

Workings or exploration This unnamed tungsten occurrence was selected for study by the U.S. Bureau of Mines in 1977 because reconnaissance sampling had defined a broad southeasterly trend of mostly poorly known or unreported tungsten occurrences beginning near Pinnell Mountain in the Circle mining district and extending eastward across the headwaters of the Charley and Seventy Mile Rivers (Barker, 1978; Foley and Barker, 1981). Stream sediment and heavy mineral surveys of the upper Charley River basin were part of the Bureau’s land assessment surveys for the proposed Alaska Lands legislation. The occurrences of tungsten mineralization first reported in 1978, were later studied and reported in greater detail in 1981 (Foley and Barker, 1981) and included ultraviolet scanning of the occurrence near Crescent Creek. Twelve samples of granitic rocks from this site, located about 2 miles west of Beverly Creek, were analyzed for lithium and tungsten, yielding lithium values ranging from less than 20 to more than 1,000 parts per million (ppm). Tungsten values were generally less than 20 ppm, though one quartz monzonite sample yielded 1357 ppm tungsten and a hornfels sample 96 ppm tungsten.
Indication of production None

Additional comments

The assessment of the Crescent Creek tungsten occurrence was done in 1977-1978; the occurrence is now within the Yukon-Charley Rivers National Preserve and mineral development is prohibited.

References

Reporters J.C. Barker
Last report date 4/6/2017