Aurora Prospect, Nome Mining District, Nome Census Area, Alaska, USAi

Regional Level Types
Aurora Prospect	Prospect
Nome Mining District	Mining District
Nome Census Area	Census Area
Alaska	State
USA	Country

Location: The Aurora prospect is in the headwaters of Aurora Creek, an eastern tributary to upper Cripple River. The mineralization trends north-northwest in a zone that extends for more than 2 miles to a related deposit about 1 mile south of the Aurora prospect called the Christophosen (NM141). The location of the Aurora prospect is at the intersection of the mineralized trend with Aurora Creek; it is at an elevation of 700 feet. This location is the approximate discovery point; it is accurate within about 500 feet. This is locality 69 of Cobb (1972 [MF 463], 1978 [OFR 78-93]).
Geology: The Aurora zinc (lead) deposit was discovered in 1966 as the result of followup of a geochemical survey using the cold extraction-dithizone method (Herreid, 1968). Prospecting fairly quickly found boulders of disseminated to semi-massive sulfides, especially sphalerite, scattered along a north-northwest trend bisected by Aurora Creek. The occurrence was located and initial work was done by Resource Associates of Alaska. Herreid (1970) also conducted more work in the area; he defined a soil anomaly along the deposit at least 7,000 feet long. In 1976 and 1977, Cominco mapped, explored, and drilled a series of 22 holes in the deposit. In general, mineralized intervals were too thin to be significant, but drillhole 76-17 found an interval more than 100 feet thick that contained about 5 percent zinc and some gold. In 1990, Kennecott Exploration Company began to explore the deposit, partly to evaluate a volcanic exhalative hypothesis for the origin of the deposit. Kennecott conducted new soil surveys, excavated a series of trenches by tracked backhoe, and completed some new drilling. The extent of mineralization was similar to that found by Cominco, and the prospect, leased from Bering Straits Regional Corporation, was allowed to lapse. The work suggests that the origin of Aurora is very complex; early mineralization was probably syngenetic and related to rhyolitic volcanism. Remoblization of mineralization probably took place during Cretaceous metamorphism of the deposit. Gold was possibly introduced along northeast-striking faults during waning stages of Cretaceous tectonism. Where the deposit crosses Aurora Creek, disseminated and semi-massive sulfide deposits grade into a nearly white quartz-sericite schist which contains knots of purple fluorite. This unit is part of the felsic, muscovite-bearing, metavolcanic schist mapped by Bundtzen and others (1994). The unit has at least three distinct facies; (1) zircon-rich muscovite quartz schist, (2) feldspar-rich porphyroblastic schist, and (3) tourmaline-bearing muscovite-quartz-feldspar schist. Ankerite and dolomite are commonly present and locally abundant. Whole-rock analyses obtained by Kennecott Exploration Company on samples of the nearly white quartz-muscovite schist indicated from 69 to 82 percent silica, 9.5 to 15.3 percent alumina, very low calcium, magnesium, and sodium, and 2.2 to 4.8 percent potassium (C.C. Hawley, Cindy Buxton, and D.L. Olson, written communication, 1992). Iron (reported as ferric iron) ranged from 1.9 to 6.6 percent, suggesting some ferrophengitic mica is present. Fluorine exceeded 1 percent in all four rock samples; all had high background zinc (hundreds of parts per million) and one sample contained 700 ppm lead. Except for their low content of sodium, the analyses are fairly typical of felsic igneous rocks. The white quartz sericite schist, believed to be a metarhyolite, stratigraphically overlies graphitic quartz schist. The geology of a section through Cominco drillhole 76-17 is consistent with thickening of the mineralized section by folding. This drill hole also contains about 0.1 ounce of gold per ton. This part of the deposit is also cut by a strong northeast-trending fault. The fault displaces the zinc-rich layer and possibly was the conduit for late gold mineralization. Other parts of the Aurora prospect are carbonate hosted. Locally, there are zones that are mostly barite accompanied by fine-grained pyrite. Antimony and arsenic are the characteristic trace elements in the deposit. There is some arsenopyrite, but the antimony and arsenic may also be in a sulfosalt, such as tennantite. Pyrite exceeds arsenopyrite, and chalcopyrite is locally present. In almost all samples, sphalerite is the dominant sulfide; it is commonly light orange to brown, suggesting a low iron content.
Workings: Soil surveys conducted by Alaska Division of Geological and Geophysical Surveys (Herreid, 1970); shallow diamond drilling by Cominco in 1976-77; soil surveys, trenching, and drilling by Kennecott Exploration in 1991-93.
Age: Syngenetic in early Paleozoic (Devonian?) sedimentary and marine volcanic rocks with remobilization during mid-Cretaceous deformation and metamorphism. Mineralization along crosscutting structures is mid-Cretaceous or younger.
Alteration: Remobilization of metallic minerals and carbonates during Cretaceous metamorphism.

Commodities (Major) - Zn; (Minor) - Ag, As, Au, Cu, F, Pb, Sb
Development Status: None
Deposit Model: Metamorphosed volcanogenic massive sulfide (Cox and Singer, 1986; model 28a [Ku

Other Databases

Link to USGS - Alaska:	NM140

Other Regions, Features and Areas containing this locality

References