West Vulcan Creek No. 2

Occurrence, Inactive

Commodities and mineralogy

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

Geographic location

Quadrangle map, 1:250,000-scale SO
Quadrangle map, 1:63,360-scale D-1
Latitude 64.9297
Longitude -162.3009
Nearby scientific data Find additional scientific data near this location
Location and accuracy
The West Vulcan Creek No. 2 consists of a group of mineral showings located on the ridge forming the south side of a east flowing tributary to Vulcan Creek. Elevation of the prospect area ranges from 1,800 to 2,200 feet.
Vulcan Creek is one of several creeks that drain the east flank of the Darby Mountains and is a tributary to the Tubutulik River, which is located east of the report area. The occurrence site is in the NW1/4 sec. 34, T. 6 S., R. 18 W. of the Kateel River Meridian and is the approximate midpoint of the 2,000 foot-long northeast trend of alteration and mineral showings.
Accuracy of the location is about 1,000 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 Vulcan Creek and adjacent Rock Creek area the Darby pluton is quartz monzonite containing biotite and lesser hornblende. The pluton is also cut by lamprophyre, rhyolite, aplite, and tourmaline-bearing pegmatite dikes. These later dikes contain euhedral biotite, amphibole, corroded quartz xenocrysts and, more rarely, clinopyroxenite or olivine in a groundmass of altered plagioclase and minor potassium feldspar (Foley and Barker, 1986).
Generally, the Vulcan and Creek Rock Creek area has higher radiometric levels than the surrounding region. At West Vulcan Creek No. 2 radiometric measurements vary from 1.5 to 6 times background over frost boils along the 300 foot-long exposed strike of the northeast-trending quartz system in a small avalanche gully. The zone goes under surficial cover on both ends but where exposed it appears to be about 40 feet wide. The prospect is marginal to silica-poor sheared chloritic, argillic-altered quartz monzonite.
Test pits exposed irregular replacement-style masses of red hematitic quartz pods 6-10 feet wide mixed in a kaolinized and sheared biotite quartz monzonite and quartz stockwork marginal to the shear zone. The altered shear zone and secondary quartz occur where exposed by erosion along the steeply descending, northeast trending gully. Test pits encountered intense radiation. Fragments of quartz-sericite-chlorite greisen with boxwork after sulfides were also found in additional nearby test pits along strike. Assays of fourteen samples ranged up to 435 parts per million (ppm) uranium. An unidentified radioactive yellow oxide was also noted within the silicified zone. Higher uranium values are associated with lead values up to 3,000 ppm lead, and slightly elevated copper values; these are from the silicified masses, whereas altered marginal quartz monzonite assayed lower uranium values, between 10 to 24 ppm. Very little thorium was reported in any of the quartz-rich samples, though slightly elevated thorium values (up to 76 ppm) are found in the altered quartz monzonite.
No ore minerals were identified but there was a radioactive yellow oxide noted in the silicified shear zone. Gangue minerals include chlorite, clay minerals, hematite, replacement quartz, and sericite. Epidote, plagioclase that is generally altered to carbonate and white mica with opaque minerals including clay minerals, magnetite, and pyrrhotite.
Geologic map unit (, )
Mineral deposit model Granite-hosted veins with uranium values generally much greater than thorium; minimal REE, tin; uranium values that do not concentrate in resistant minerals as indicated by heavy mineral survey (Foley and Barker, 1986); mineralized shear zones by 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, locally argillic, pervasive hematitic staining and corroded quartz occurring in wide zones of sericite and chlorite alteration. Alteration is best exposed in avalanche gullies and/or some structurally controlled swales along exposed ridges (Foley and Barker, 1986).

Production and reserves

Workings or exploration Test pits exposed irregular replacement-style masses of red hematitic quartz pods 6-10 feet wide mixed in a kaolinized and sheared biotite quartz monzonite and quartz stockwork marginal to the shear zone. The altered shear zone and secondary quartz occur where exposed by erosion along the steeply descending, northeast trending gully. Test pits encountered intense radiation. Fragments of quartz-sericite-chlorite greisen with boxwork after sulfides were also found in additional nearby test pits along strike. Assays of fourteen samples ranged up to 435 parts per million (ppm) uranium. An unidentified radioactive yellow oxide was also noted within the silicified zone. Higher uranium values are associated with lead values up to 3,000 ppm lead, and slightly elevated copper values; these are from the silicified masses, whereas altered marginal quartz monzonite assayed lower uranium values, between 10 to 24 ppm. Very little thorium was reported in any of the quartz-rich samples, though slightly elevated thorium values (up to 76 ppm thorium) are found in the altered quartz monzonite. Distinctly higher radiometric measurements generally are recorded over hydrothermally altered veins and structurally controlled high-angle shear zones and breccia masses. Radiometric readings will locally exceed the calibration of handheld scintillometers. These radiometric anomalies generally feature hematite, black iridescent manganese staining, quartz stockwork, ferruginous quartz, jasper, drusy and vuggy quartz.
Indication of production None
Reserve estimates No reserves.

Additional comments

The West Vulcan-Rock Creek 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 in southern Death Valley about 6 miles to the north (Dickinson and others, 1987). No further work was performed.

References

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