Unnamed (near Peak 3231, Darby Ridge)

Occurrence, Inactive

Commodities and mineralogy

Main commodities U
Other commodities Pb
Gangue minerals carbonate; chlorite; clay minerals; epidote; hematite; magnetite; pyrrhotite; quartz; sericite

Geographic location

Quadrangle map, 1:250,000-scale SO
Quadrangle map, 1:63,360-scale D-1
Latitude 64.8365
Longitude -162.4615
Nearby scientific data Find additional scientific data near this location
Location and accuracy
This occurrence is on a rugged east-west ridge that intersects the principal north-south divide crest of the Darby Mountains. Elevations in the area of the occurrence range more than 2,000 feet up to 3,243 feet at the top of an unnamed mountain about one mile northwest of the prospect. Drainage from the area is into the upper tributaries of Clear Creek. The main site is a high saddle on the east flank of peak 3231 in the S1/2 sec. 35, T. 5 S., R. 19 W. of the Kateel River Meridian, and additional sample sites are located at a cirque at 64.8653 N, 162.4624 W in section 26.
Accuracy of the location is about 1,500 feet.

Geologic setting

Geologic description

The Darby pluton is relatively homogeneous, mostly quartz monzonite and minor granite. Locally there are segregations of quartz-deficient, potassium-rich rocks including syenite and alkali granite. In the vicinity of Clear Creek, the rocks of the Darby pluton are mostly quartz monzonite containing biotite and lesser hornblende. The quartz monzonite is cut by tourmaline aplite, and rhyolite and tourmaline-bearing pegmatite dikes and a swarm of lamprophyre and apparently related variants of dark-colored sub-alkaline porphyritic dikes.
This occurrence consists of altered quartz monzonite intruded by a syenite dike. Radiometric measurements over argillic alteration in the quartz monzonite were two times background and a sample assayed 47 parts per million (ppm) uranium. A second sample of altered quartz monzonite from about 2,500 feet to the east reported 24 ppm uranium. Hawley and others (1978) reported up to 80 ppm uranium in soil samples from a gossan near the divide between Clear and Dry Canyon Creeks believed to be immediately north of this occurrence but the site was not re-located. Similar alteration occurs along the Darby Ridge two miles north (two samples of altered andesite assayed 40 and 50 ppm uranium) and three miles south of the Peak 3231 occurrence (soil sample assayed 77 ppm uranium) (Foley and Barker, 1986).
Geologic map unit (, )
Mineral deposit model Granite-hosted veins with uranium generally much greater than thorium; minimal REE and tin; uranium does not concentrate in resistant minerals as indicated by heavy mineral survey (Foley and Barker, 1986); mineralized shear zones with structural control, spatial association with lamprophyre dikes; no clear comparable examples available.
Age of mineralization Quartz monzonite of the Darby pluton is reported to be Late Cretaceous (Miller and Bunker, 1975; Eakins and others, 1977; Wilson and others, 2015).
Alteration of deposit Greisen float, locally intense argillic alteration, locations with hematitic staining with silicification formed in shear zones; discrete zones of sericite development, epidote, and chlorite alteration. Adjacent quartz monzonite exhibits propylitic alteration. Oxidation and clay minerals after argillic alteration (Foley and Barker, 1986).

Production and reserves

Workings or exploration This occurrence consists of altered quartz monzonite intruded by a syenite dike. Radiometric measurements over argillic alteration in the quartz monzonite were two times background and a sample assayed 47 parts per million (ppm) uranium. A second sample of altered quartz monzonite from about 2,500 feet to the east reported 24 ppm uranium. Hawley (1978) reported up to 80 ppm uranium in soil samples from a gossan near the divide between Clear and Canyon Creeks believed to be immediately north of this occurrence but the site was not re-located. Similar alteration occurs along the Darby Ridge two miles north (two samples of altered andesite assayed 40 and 50 ppm uranium) and three miles south of the Peak 3231 occurrence (soil sample assayed 77 ppm uranium) (Foley and Barker, 1986).
Indication of production None
Reserve estimates No reserves.

Additional comments

The Darby Mountain area was selected for study by the U.S. Bureau of Mines in 1979 as part of ongoing mineral land assessments in Alaska and land designations proposed by Congress, and because recent (1970s) private sector exploration had discovered sedimentary uranium in the Boulder Creek basin at the southern end of Death Valley about 10 miles to the northeast (Dickinson and others, 1987). No further work was performed; claims are active in southern Death Valley, in the Boulder Creek basin area.

References

Reporters J.C. Barker
Last report date 12/15/2016