| Main commodities | Au |
|---|---|
| Other commodities | Cu |
| Ore minerals | chalcopyrite; gold; pyrrhotite |
| Gangue minerals | quartz |
| Quadrangle map, 1:250,000-scale | JU |
|---|---|
| Quadrangle map, 1:63,360-scale | B-2 |
| Latitude | 58.3651 |
| Longitude | -134.4601 |
| Nearby scientific data | Find additional scientific data near this location |
| Location and accuracy | The Clark prospect is at an elevation of approximately 700 feet in Sawmill Creek, 1/4 mile upstream from its junction with Lemon Creek. It is in the NE1/4 section 35, T. 40 S., R. 66 E. of the Copper River Meridian. The location is accurate. |
Geologic descriptionThe Clark deposit was discovered in the 1880s and developed by open cuts and trenches. The deposit consists of quartz veins that cut phyllite and altered gabbroic dikes. The veins are up to 4 feet thick and contain pyrrhotite, some chalcopyrite, and gold (Spencer, 1906). This prospect is in the Juneau Gold Belt, which consists of more than 200 gold-quartz-vein deposits that have produced nearly 7 million ounces of gold. These gold-bearing mesothermal quartz vein systems form a zone 160 km long by 5 to 8 km wide along the western margin of the Coast Mountains. The vein systems are in or near shear zones adjacent to west-verging, mid-Cretaceous thrust faults. The veins are hosted by diverse, variably metamorphosed, sedimentary, volcanic, and intrusive rocks. From the Coast Mountains batholith westward, the host rocks include mixed metasedimentary and metavolcanic sequences of Carboniferous and older, Permian and Triassic, and Jurassic-Cretaceous age. The sequences are juxtaposed along mid-Cretaceous thrust faults (Miller and others, 1994). The sequences are intruded by mid-Cretaceous to middle Eocene plutons, mainly diorite, tonalite, granodiorite, quartz monzonite, and granite. Sheetlike tonalite plutons emplaced just east of the Juneau Gold Belt and undeformed granite and granodiorite bodies that are emplaced farther to the east are between 55 and 48 Ma (Gehrels and others, 1991). The structural grain of the belt is defined by northwest-striking, moderately to steeply northeast-dipping, penetrative foliation that developed between Cretaceous and Eocene time (Miller and others, 1994). The majority of the veins in the Juneau Gold Belt strike northwest. Isotopic dates indicate that the auriferous veins in the Juneau Gold Belt formed between 56 and 55 Ma (Miller and others, 1994; Goldfarb and others, 1997). | |
| Geologic map unit | (-134.461874185989, 58.3647752346906) |
|---|---|
| Mineral deposit model | Low-sulfide Au-quartz vein (Cox and Singer, 1986; model 36a) |
| Mineral deposit model number | 36a |
| Age of mineralization | Isotopic dates indicate that the auriferous veins in the Juneau Gold Belt formed between 56 and 55 Ma (Miller and others, 1994; Goldfarb and others, 1997). |
| Workings or exploration | The Clark deposit was discovered in the 1880s and developed by open cuts and trenches. |
|---|---|
| Indication of production | None |
| MRDS Number | A012007 |
|---|---|
ReferencesGehrels, G.E., McClelland, W.C., Samson, S.D., and Patchett, P.J., 1991, U-Pb geochronology of detrital zircons from a continental margin assemblage in the northern Coast Mountains, southeastern Alaska: Canadian Journal of Earth Sciences, v. 28, no. 8, p.1285-1300.
Goldfarb, R.J., Miller, L.D., Leach, D.L., and Snee, L.W, 1997, Gold deposits in metamorphic rocks in Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 151-190.
Miller, L.D., Goldfarb, R.J., Gehrels, G,E., and Snee, L.W., 1994, Genetic links among fluid cycling, vein formation, regional deformation, and plutonism in the Juneau gold belt, southeastern Alaska: Geology, v. 22, p. 203-206.
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| Reporters | J.C. Barnett and L.D. Miller (Juneau, Alaska ) |
| Last report date | 12/15/2001 |