Big Bar

Prospect, Probably inactive

Commodities and mineralogy

Main commodities Ag; Cu; Pb; Zn
Ore minerals chalcopyrite; malachite
Gangue minerals feldspar; limonite; muscovite; pyrite; quartz

Geographic location

Quadrangle map, 1:250,000-scale BN
Quadrangle map, 1:63,360-scale B-1
Latitude 65.43
Longitude -162.17
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Big Bar prospect is 5 miles southeast of Kiwalik Mountain on a ridge crest north of Big Bar Creek. It is 4,000 feet downslope to the southwest from elevation 1,230 feet on this ridge. This locality is at an elevation of 850 feet.

Geologic setting

Geologic description

Big Bar is a volcanogenic massive sulfide deposit in an interlayered metavolcanic and metasedimentary sequence that strikes northwest and dips moderately south. It was discovered and initially explored by Anaconda Minerals Company from 1982 to 1984 (North Pacific Mining Corporation, 1991). The interbedded sequence includes metapelitic schist, white to tan siliceous muscovite schist, and muscovite-quartz-feldspar schist. The felsic schist contains apple green muscovite and up to 50 percent feldspar porphyroblasts. The mineralized schists are highly oxidized and limonitic blebs and and streaks are common along the foliation. Only a few remnants of pyrite and chalcopyrite are observed at the surface. Exposure is primarily frost-riven rubble although one non-mineralized felsic schist outcrop is present upslope of the defined mineralization. The prospect is primarily defined by the geochemical results from a 3,900 by 3,000 foot soil sample grid. Sample spacing along strike was 330 feet (100 meters) and 165 feet (50 meters) along dip. This sampling defined a copper anomaly greater than 200 ppm that was over 3,900 feet long and 165 to 330 feet wide. Copper values within this anomaly were locally greater than 1,000 ppm. A zinc anomaly greater than 200 ppm in soils overlaps the copper anomaly to the west but is roughly parallel and displaced downslope from it to the east. The lead soil anomaly greater than 100 ppm) is irregular and more discontinuous than the copper anomaly. Both the east and west limits of the anomaly are on slopes where downslope migration of surficial materials is to be expected but copper values greater than 200 ppm do extend to both the northwest and southeast limits of the sample grid. A soil sample with gossan fragments contained 920 ppm Cu, 605 ppm Pb, 3,900 ppm Zn, and 1.6 ounces/ton Ag. Silver values in soil samples were only locally greater than 1 ppm however. Initial soil samples in the area (Hudson and Wyman, 1983) contained some low level gold values up to 25 ppb. Some reconnaissance geophysical surveys (IP, MAXMIN, EM, gravity, and magnetics) were completed on the prospect. One distinct IP anomaly, coincident with a magnetic high, was identified upslope of the copper anomaly. The metamorphic assemblage that hosts this prospect is peripheral to the Devonian Kiwalik Mountain gneiss (Till and others, 1986). The assemblage appears to contain metatuff and metarhyolite components that resemble lithologies in the Ambler district of the southern Brooks Range. The metavolcanic-bearing assemblage of the Kiwalik Mountain area has only locally been separately mapped along Independence Creek (Till and others, 1986). This assemblage flanks Kiwalik Mountain to the east, south, west and northwest. The HOM prospect (BN119) is another volcanogenic massive sulfide deposit associated with this assemblage.
Geologic map unit (-162.172650356487, 65.4293090662082)
Mineral deposit model Kuroko massive sulfide (Cox and Singer, 1986; model 28a)
Mineral deposit model number 28a
Age of mineralization Devonian?; this is a stratiform deposit and the host felsic schist is interpreted to be similar in age to the Devonian gneiss at Kiwalik Mountain (Till and others, 1986).
Alteration of deposit This prospect is highly oxidized. Quartz-sericite-pyrite alteration may be present in unoxidized parts of the prospect.

Production and reserves

Workings or exploration Some blasting has been done in an unsuccessful attempt to expose bedrock mineralization. The prospect is primarily defined by the geochemical results from a 3,900 by 3,000 foot soil sample grid. Sample spacing along strike was 330 feet (100 meters) and 165 feet (50 meters) along dip. Some reconnaissance geophysical surveys (IP, MAXMIN, EM, gravity, and magnetics) were completed on the prospect. One distinct IP anomaly, coincident with a magnetic high, was identified upslope of the soil copper anomaly.
Indication of production None

References

MRDS Number 10307277

References

Hudson, T.L., and Wyman, W. F., 1983, Interim report on areas of Seward Peninsula warranting further prospecting and evaluation: Anchorage, Anaconda Minerals Company internal report, 84 p., 7 plates. (Report held by Cook Inlet Region Inc., Anchorage, Alaska.)
North Pacific Mining Corporation, 1991, Big Bar Prospectus: Anchorage, unpublished internal report, 8 p. (Report held by Cook Inlet Region Inc.)
Reporters Travis L. Hudson (Applied Geology)
Last report date 3/15/1999