Aurora

Prospect, Undetermined

Commodities and mineralogy

Main commodities Au; Ba; F; Zn
Other commodities Ag; Cu; Pb; Sb
Ore minerals arsenopyrite; barite; chalcopyrite; fluorite; galena; gold; pyrite; sphalerite; stibnite; tennantite
Gangue minerals ankerite; dolomite; quartz

Geographic location

Quadrangle map, 1:250,000-scale NM
Quadrangle map, 1:63,360-scale C-2
Latitude 64.7158
Longitude -165.5909
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Aurora prospect is at the head of Aurora Creek, an eastern tributary to the Cripple River, at an elevation of about 1,060 feet. The mineralization trends south-southeast in a zone that extends for about a mile to a similar prospect, the Christophosen (NM141). The Aurora prospect is about 0.6 mile north-northwest of the center of section 13, T. 9 S., R. 34 W. The location is accurate.

Geologic setting

Geologic description

The Aurora zinc-lead prospect was discovered in 1966 by a geochemical survey (Herreid, 1968). Resource Associates of Alaska then found a train of boulders trending north-northwest of disseminated to semi-massive sulfides, mainly sphalerite. Herreid (1970) defined a soil anomaly at least 7,000 feet long that extends to a similar prospect, the Christophosen (NM141). In 1976 and 1977, Cominco explored the deposit and drilled 22 holes. The drilling cut an interval more than 100 feet thick that contained 5 percent zinc but they considered the mineralization to be too thin and low grade to be of further interest. From 1990 to 1993, Kennecott Exploration Company explored the deposit with new soil surveys; they also dug a series of trenches and did some drilling. They proposed that the early mineralization was syngenetic and related to rhyolitic volcanism; the deposit was then remobilized during Cretaceous regional metamorphism when gold was introduced along northeast-striking faults.
The massive sulfides are mainly light orange to brown sphalerite; local barite zones contain disseminated pyrite. There is some arsenopyrite and chalcopyrite. Antimony and arsenic are persistent trace elements in drill samples and the higher-grade samples contain about 0.1 ounce of gold per ton.
Bundtzen and others (1984) identified three rock units that host the mineralization: 1) white, zircon-rich muscovite-quartz schist, 2) feldspar-rich porphyroblastic schist, and 3) tourmaline-bearing muscovite-quartz-feldspar schist. Ankerite and dolomite are common and locally abundant; purple fluorite occurs in knots in the schist. Locally barite is prominent in layers and lenses. Based on whole-rock analyses, they proposed that the white muscovite-quartz schist is a metarhyolite and that the deposit is a volcanogenic massive-sulfide deposit.
Slack and others (2011) reject a volcanogenic massive sulfide origin for the deposit and Till and others (2011) map the host rocks as part of the Devonian Nome Complex that consists of pelitic, calcareous, and graphitic schist. Their work suggests that the protolith of the metamorphic rocks are sedimentary and they see no evidence of volcanic rocks in the area. They base their conclusion on: 1) sulfur isotope analyses of the sulfides that indicate a marine origin for the sulfur, 2) isotopic analysis of the barite that indicate that the probable source of the sulfur is Devonian and Mississippi sea water, and 3) their whole-rock analyses of the host rocks of the mineralization that they interpret as originally being clastic sedimentary rocks. They propose a sedimentary-exhalative (SEDEX) origin for the deposit during rifting of the continental margin in Devonian-Missisippian(?) time. The rocks subsequently were subject to blueschist-grade metamorphism, then retrograded to greenschist-grade metamorphic rocks in the Jurassic and early Cretaceous.
Geologic map unit (-165.593520333928, 64.7150348392694)
Mineral deposit model Metamorphosed Kuroko-type volcanogenic massive sulfide (Cox and Singer, 1986; model 28a) or sedimentary exhalative (SEDEX) deposit (Cox and Singer, 1986, model 31a).
Mineral deposit model number 28a or 31a
Age of mineralization Massive sulfides were syngenetic in early Paleozoic (Devonian?) sedimentary and/or marine volcanic rocks with remobilization during mid-Cretaceous deformation and metamorphism. Mineralization along crosscutting structures is probably mid-Cretaceous or younger.
Alteration of deposit Remobilization of metallic minerals and carbonates during Cretaceous metamorphism.

Production and reserves

Workings or exploration Soil surveys were done by the Alaska Division of Geological and Geophysical Surveys in the late 1960s. Some work by Resource Associates of Alaska in the early 1970s. Cominco explored the deposit in 1976 and 1977 and drilled 22 holes. Kennecott Exploration explored the deposit with soil surveys and trenching from 1990 to 1993 and drilled some holes.
Indication of production None
Reserve estimates None.
Production notes None.

References

MRDS Number A012867

References

Slack, John, Till, A.B., Shanks, Wayne C., III, Ayuso, R.A., and Belkin, H.E., 2011, Stratabound Zn-Pb-Ag-Ba-F deposits and occurrences in the Nome Complex, Seward Peninsula: Characteristics, origin, and exploration application: Alaska Miners Association, 2011 Annual Convention, Abstracts, p. 24-25.
Reporters C.C. Hawley and Travis L. Hudson; D.J. Grybeck (Contractor, USGS)
Last report date 4/1/2012