88 Group Occurrence, Circle Mining District, Yukon-Koyukuk Census Area, Alaska, USAi

Regional Level Types
88 Group Occurrence	Occurrence
Circle Mining District	Mining District
Yukon-Koyukuk Census Area	Census Area
Alaska	State
USA	Country

Location: The 88 Group claims can be reached via an 8 mile long dirt road that starts in Circle Hot Springs. The claims are on the Portage Creek side of the divide along Portage Creek road.
Geology: The 88 Group occurrence appears to be a dark mafic intrusive phase contact with a coarse porphyritic granite. Both lode and placer gold is found at these claims (Vetter, 1995). Wiltse and others (1995) mapped the bedrock in the area and described the Cretaceous granite as a chloritized porphyritic (hornblende) biotite monzogranite to syenogranite. They also mapped a mafic dike in the area of the 88 Group claims which is described as black to dark gray, aphanitic to slightly porphyritic with major plagioclase, augite, hornblende and magnetite. Gold mineralization occurs within heavily Fe-oxide stained, quartz-filled greisen zones (up to six feet across), within fractures, and in stockwork veining. A significant aspect of the prospect is the large amount of grus development, 10 to 20 feet, that pans considerable gold. Other heavy minerals concentrated in the pans include abundant sphalerite, and small amounts of arsenopyrite, chalcopyrite, cassiterite (?), and monazite (?). Continuous gold anomalies occur in the vicinity of the 88 Group discovery outcrop along approximately 2000 feet of ditch exposure along the Portage Creek road. The mineralization occurs within heavily Fe-oxide stained, quartz-filled greisen zones of variable width (3 inch average). Phyllic and argillic alteration is present along vein margins and is also controllled by fractures. Strong zinc anomalies (up to 0.5 percent) and moderate arsenic values are present. Tin was not detected in the rock samples, however, two pan concentrates contain anomalous values. The dominant trend in mineralization is N 50 W with near vertical dips (Bakke,1991).
Workings: Exploration was restricted to surface sampling.
Alteration: Mineralization occurs within heavily Fe-stained, quartz-filled greisen zones of variable width (3 inch average). Phyllic and argillic alteration is present along vein margins and is also controllled by fractures (Bakke, 1991).

Commodities (Major) - Au
Development Status: None
Deposit Model: Gold-bearing greisen zones in granite.

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Link to USGS - Alaska:	CI001

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References