Trio East Occurrence, Tok Mining District, Southeast Fairbanks Census Area, Alaska, USAi

Regional Level Types
Trio East Occurrence	Occurrence
Tok Mining District	Mining District
Southeast Fairbanks Census Area	Census Area
Alaska	State
USA	Country

Location: The Trio East occurrence is about 5 miles southeast of the confluence of the Robertson River and Rumble Creek at an elevation of about 6,200 feet. The location is the area that was drilled by Phelps Dodge in 1990, about 0.1 mile south-southwest of the center of section 14, T. 17 N., R. 7 E., Copper River Meridian. Additional exposures of the mineralized layer or unit occur about one-half mile to the north at an elevation of about 5,900 feet. The location is accurate.
Geology: The Trio East occurrence follows an intermittently exposed siliceous (metavolcanic or exhalative) pyritic schist unit with semimassive sulfide mineralization; it is in a sequence of carbonaceous metasedimentary rocks. Local blocks of semimassive to massive sulfide as much as 5 feet thick are found in talus near this altered unit (C. Schaefer, oral communication, 2003). Most samples were only moderately enriched in metals and contain as much as 0.1 percent copper, 0.2 percent lead, 0.5 percent zinc, no silver, and 0.2 part per million gold (S.S. Dashevsky, unpublished data, 2003). An analysis of massive sulfide samples reported by Resource Associates of Alaska showed 0.85 percent copper, 9.2 percent lead, 4.5 percent zinc, and 130.6 grams of silver per ton (Lange and others, 1993).
Workings: The Trio East area was covered by a number of geological and geophysical surveys in the late 1970's and in 1990. Phelps Dodge drilled one hole near this occurrence in 1990; it intersected extensive quartz-pyrite-sericite alteration but no significant values in base or precious metals (R. Cheff, unpublished Phelps Dodge Exploration, Inc. report, 1990).
Age: The lower Lagoon unit, which is part of the metamorphic sequence that includes the rocks at this deposit, has been dated as Devonian on the basis of one SHRIMP U-Pb zircon age of 372 +/- 6 Ma at the LZ East prospect (MH328) (Dashevsky and others, 2003).
Alteration: Strong to intense sericite-quartz-CO3 +/- kaolin +/- andalusite alteration (Lange and others, 1993).

Commodities (Major) - Ag, Pb, Zn; (Minor) - Cu
Development Status: None
Deposit Model: Kuroko massive sulfide (Cox and Singer, 1986; model

Other Databases

Link to USGS - Alaska:	MH337

Other Regions, Features and Areas containing this locality

References