Unnamed (Hulahula River) USBM Location A

Occurrence, Inactive

Commodities and mineralogy

Main commodities Cu
Other commodities Ag; Co; Pb; Zn
Ore minerals chalcopyrite; galena; malachite; sphalerite
Gangue minerals chlorite; clays; hematite; sericite

Geographic location

Quadrangle map, 1:250,000-scale ML
Quadrangle map, 1:63,360-scale A-2
Latitude 69.0967
Longitude -144.6228
Nearby scientific data Find additional scientific data near this location
Location and accuracy
Location A in an unpublished report (Barker, 1983) is on the east cut-bank of the Hulahula River and east of the airstrip. This location is part of a group of copper occurrences found over an area that extends five miles north to south and four miles east to west.
The Hulahula River flows north to the Arctic Ocean and its headwaters drain the north flank of the Continental Divide. The occurrence site is referred to as Location A in Barker, 1983, is in the W½ sec. 15, T. 4 S., R. 31 E, of the Umiat Meridian. Accuracy of the location is about 0.75 mile.

Geologic setting

Geologic description

Malachite and occasionally chalcopyrite blebs can be found in quartz-carbonate veins and as stratiform replacement in clastic sedimentary rocks of the pre-Mississippian Neruokpuk shale and phyllite that are interbedded with chert and mafic volcanic rocks. Location A is an area less than 1,000 feet across including bedrock exposures in the river bank. Clastic sedimentary rocks include sandstone, calcareous sandstone, dolostone, and argillite-phyllite rocks. Stratiform mineralization is concentrated in areas of rapid facies change over short distances. Two chip samples collected across outcropping, southwest-dipping black phyllite and shale at Location A in a river cut bank outcrop assayed 255 and 510 parts per million (ppm) copper. A small shale boulder on the river bar nearby was assayed and reported 2.6 percent copper with .07 percent cobalt, 0.17 percent nickel and 52 ppm silver. A narrow veinlet with trace galena and sphalerite in another nearby outcrop at Location A assayed 0.79 percent lead and 5.25 percent zinc. Another nearby cut bank site exhibits disseminated chalcopyrite occurring along thin southwest-dipping strata of calcareous shale up to 1.5 inches thick; a sample assayed 590 ppm copper with elevated cobalt (Barker, 1983).
Geologic map unit (, )
Mineral deposit model Besshi-type copper (Cox and Singer, 1986, model 24b); sedimentary-hosted copper in shale and phyllite (Cox and Singer, 1986, model 30b).
Mineral deposit model number 24b, 30b
Age of mineralization Mineral occurrences are hosted in pre-Mississippian clastic rocks of the Neruokpuk formation (Brosgé and Reiser, 1976).
Alteration of deposit Bleaching and iron staining are common features, locally with hematite staining and silicification, quartz stockwork, and minor veining (Barker, 1983).

Production and reserves

Workings or exploration Two chip samples collected across outcropping, southwest-dipping black phyllite and shale near Location A in a river cut bank assayed 255 and 510 parts per million (ppm) copper. A small shale boulder on the river bar nearby was assayed and reported 2.6 percent copper with 0.07 percent cobalt, 0.17 percent nickel and 52 ppm silver. A narrow veinlet with trace galena and sphalerite in another nearby outcrop at Location A assayed 0.79 percent lead and 5.25 percent zinc. Another nearby cut bank site exhibits disseminated chalcopyrite occurring along thin southwest-dipping strata of calcareous shale up to 1.5 inches thick; a sample assayed 590 ppm copper with elevated cobalt (Barker, 1983).
Indication of production None

Additional comments

The prospect area was selected for study by the U.S. Bureau of Mines in 1982 as part of on-going critical and strategic mineral investigations in Alaska. The area is now closed to mineral development; the site is located in the Arctic National Wildlife Range and classified as Wilderness.
Favorable regional potential for copper mineralization was advanced by Brosgé and Reiser in 1976, who suggested that the vicinity of the upper Hulahula River may contain significant copper mineralization due to widespread mafic volcanic rocks with high intrinsic copper content. Several copper showings are reported in the region. A group of stream sediment samples was consistently anomalous for copper along the upper segment of the Hulahula River (Brosgé and Reiser, 1976), who mapped widespread mafic sills in this region, which intrudes clastic rocks of the Neruokpuk formation (Reiser and others, 1971).

References

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