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Unnamed Occurrence (ARDF - EA088; east of Bonanza Bar), Southeast Fairbanks Census Area, Alaska, USAi
| Regional Level Types | |
|---|---|
| Unnamed Occurrence (ARDF - EA088; east of Bonanza Bar) | - not defined - |
| Southeast Fairbanks Census Area | Census Area |
| Alaska | State |
| USA | Country |
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Latitude & Longitude (WGS84):
64° 15' 32'' North , 141° 10' 4'' West
Latitude & Longitude (decimal):
Köppen climate type:
Location: This occurrence is exposed at river level along the north side of the Fortymile River 0.4 mile downstream from Bonanza Bar and about 1.0 miles upstream from the mouth of Nugget Creek. The occurrence is in section 34, T. 7 S., R. 33 E., of the Fairbanks Meridian. The location is accurate.
Geology: The rocks in the vicinity of this occurrence are Paleozoic amphibolite-facies quartzite of the Fortymile River assemblage that has been intruded by granitic and ultramafic rocks of Jurassic age (Foster, 1976; Dusel-Bacon and others, 2002). Sulfides occur as layers within biotite + quartz +/- staurolite +/- garnet schist and biotite quartzite. The sulfides are present in two modes: (A) a finely laminated, rusty-weathering, approximately 1-meter-thick oxidized layer, including a 1- to 2-centimeter-thick layer of massive pyrite or limonite after pyrite; and (B) a massive, foliation-parallel, quartz layer (quartz sweat?), in which layers of galena are apparently concordant with metamorphic layering. Petrographic analysis shows that the quartz-rich layer contains minor white mica and rare patches of sericitized and (or) kaolinitized feldspar; quartz grains are strained and have sutured contacts; tiny, thin, scattered white mica crystals occur between some quartz grains. A sample from mode A contains 260 ppm copper, 130 ppm lead, 2.8 ppm silver, and 20 ppb gold. A sample from mode B contains 6,350 ppm lead, 137 ppm copper, 13 ppm silver, and 295 ppb gold. Slightly elevated bismuth (as much as 10 ppm) and tungsten (as much as 680 ppm) in one quartz-rich rock suggests mineralization may be pluton related (Cynthia Dusel-Bacon, USGS, written commun., 2002).
Alteration: Sericitized/kaolinitized feldspar?
Commodities (Major) - Ag, Au, Cu, Pb; (Minor) - Bi, W
Development Status: None
Deposit Model: Slightly elevated bismuth (as much as 10 ppm) and tungsten (as much as 680 ppm)
Select Mineral List Type
Standard Detailed Gallery Strunz Chemical ElementsCommodity List
This is a list of exploitable or exploited mineral commodities recorded at this locality.Mineral List
2 valid minerals.
Gallery:
List of minerals arranged by Strunz 10th Edition classification
| Group 2 - Sulphides and Sulfosalts | |||
|---|---|---|---|
| ⓘ | Galena | 2.CD.10 | PbS |
| ⓘ | Pyrite | 2.EB.05a | FeS2 |
List of minerals for each chemical element
| S | Sulfur | |
|---|---|---|
| S | ⓘ Galena | PbS |
| S | ⓘ Pyrite | FeS2 |
| Fe | Iron | |
| Fe | ⓘ Pyrite | FeS2 |
| Pb | Lead | |
| Pb | ⓘ Galena | PbS |
Other Databases
| Link to USGS - Alaska: | EA088 |
|---|
Other Regions, Features and Areas containing this locality
North AmericaContinent
North America PlateTectonic Plate
- Yukon-TananaVolcanic Arc
- Yukon-Tanana upper DomainDomain
USA
- Alaska
- Fortymile Mining DistrictMining District
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