Bonanza, Beef

Prospect, Probably inactive

Commodities and mineralogy

Main commodities Mo; Pb; W; Zn
Other commodities Ag; Cu
Ore minerals chalcopyrite; molybdenite; pyrrhotite; scheelite; sphalerite
Gangue minerals calc-silicate minerals; garnet; pyroxene; quartz

Geographic location

Quadrangle map, 1:250,000-scale BT
Quadrangle map, 1:63,360-scale C-1
Latitude 66.6301
Longitude -150.0261
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Bonanza prospect is near the center of a small hill informally called Windy Knob, which is about 14.8 miles at an azimuth of 302 degrees from the high peak of Dall Mountain. it is about 0.3 mile south-southwest of the center of section 19, T. 21 N., R. 12 W., of the Fairbanks Meridian. Other similar, lower grade deposits are scattered over an area about 1.5 miles wide and 5.5 miles long, which extends east into the adjacent Beaver 1:250,000-scale quadrangle. The coordinates are the center of the Bonanza claim block, which is the locus of the principal mineral showings in the area. The location is accurate.

Geologic setting

Geologic description

The Bonanza prospect was found by BP Exploration in 1976 by following up a stream-sediment anomaly (Kurtak and others, 2002). From 1978 to 1982, the prospect was mapped and sampled by WGM Inc., Union Carbide, and Patino Inc. Six trenches were cut.
The Bonanza prospect is the most significant of several deposits along a 5-mile long, east-striking belt of intermittent skarn mineralization along the north side of the Cretaceous Kanuti Pluton which intrudes Proterozoic and lower Paleozoic sedimentary rocks (Clautice, 1983, 1984, 1987; Kurtak and others, 2002; Patton and others, 2009). At the Bonanza prospect, small masses of limestone are altered to calc-silcate rocks that vary from fine-grained, siliceous pyroxene-garnet skarn to dark green, pyroxene skarn. The skarn contains up to 10 percent pyrrhotite, coarse-grained scheelite, sphalerite, and minor chalcopyrite, molybdenite, and galena. The scheelite commonly occurs as disseminated grains in relatively sulfide-free pyroxene-garnet skarn. Scheelite also occurs on fracture surfaces in calc-silicate schist and less commonly in quartz veins. Molybdenite typically occurs as rosettes and small flakes in quartz veins in biotite-quartz monzonite and less commonly in aplite, pegmatite, and calc-silicate rock. The skarn zones are discontinuous, irregularly shaped, and are up to 16 feet wide and 50 feet long. Kurtak and others (2002) collected several samples that contained up to 1.44 percent tungsten, 1,438 parts per million (ppm) zinc, and 936 ppm lead. Clautice (1983) collected a sample that contained 0.89 percent tungsten, 300 grams of silver per tonne, and 0.65 percent copper.
Kurtak and others (2002) briefly examined similar, lower grade skarn mineralization at the Beef claims, about 1.6 mile east of the Bonanza prospect. Trace molybdenite was identified along fractures in the skarn; a sample contained 521 ppm tungsten and 80 ppm molybdenum.
Geologic map unit (-150.028757800879, 66.629655914564)
Mineral deposit model W skarn deposit (Cox and Singer, 1986; model 14a).
Mineral deposit model number 14a
Age of mineralization Cretaceous skarn deposit at the periphery of a felsic pluton.
Alteration of deposit Calc-silicate skarn.

Production and reserves

Workings or exploration The Bonanza prospect was found by BP Exploration in 1976 by following up a stream sediment anomaly (Kurtak and others, 2002). From 1978 to 1982, the prospect was mapped and sampled by WGM Inc., Union Carbide, and Patino Inc. Six trenches were cut.
Indication of production None

Additional comments

The skarn mineralization extends east into the Beaver, 1:250,000-scale, quadrangle.
MAS No. 0020390051

References

MRDS Number 10307304
Reporters J.M. Britton (Anchorage, Alaska); D.J. Grybeck (Contractor, U.S. Geological Survey)
Last report date 4/18/2010