Fortress Occurrence, Koyukuk Mining District, Yukon-Koyukuk Census Area, Alaska, USAi

Regional Level Types
Fortress Occurrence	Occurrence
Koyukuk Mining District	Mining District
Yukon-Koyukuk Census Area	Census Area
Alaska	State
USA	Country

Location: This occurrence is at elevation of about 3,000 feet on the north end of the ridge at the head of Buckeye Gulch; it is about 0.4 mile east-northeast of the center of section 24, T. 31 N., R. 12 W., of the Fairbanks Meridian. The occurrence is the site of a gold-bearing sample that contained gold (Eden, 2000). Similar occurrences are included that occur south along the ridge for about 0.2 mile. The location is accurate.
Geology: This occurrence consists of veins that contain coarse, white quartz crystals which fill cavities, and euhedral calcite crystals (Eden, 2000). Ankerite, with pyrite, and hematite after pyrite, occurs along the margins of the veins. The veins strike northwest-southeast, dip almost vertically, and are up to one inch thick. Several samples of the veins contain 5 to 58 ppb gold and 15 to 138 ppm arsenic (Kurtak and others, 1999). The samples were taken in quartz veins about 1 inch thick that contain minor pyrite, +/- hematite, +/- siderite. One continuous chip sample from an outcrop, described as a hematite- and pyrite-bearing quartz vein in phyllite, contains 8,301 ppb gold and 1,134 ppm arsenic (Eden, 2000, sample 10650). Eden (2000) notes that the occurrences at this site are extensions of a gold-quartz vein system in the Nolan Creek area (WI101). In general, the mineralization in the Nolan Creek consists of quartz veins with lesser calcite, ankerite and dolomite, arsenopyrite sometimes, and varying amounts of a variety of accessory sulfide and oxide minerals including pyrite, marcasite, chalcopyrite, pyrrhotite, hematite, sphalerite, galena, and rutile.
Workings: Surface sampling and geologic mapping.
Alteration: The wallrock adjoining the veins apparently is not altered.

Commodities (Major) - Au; (Minor) - As
Development Status: None
Deposit Model: Low-sulfide Au-quartz vein (Cox and Singer, 1986; model 36a)

Other Databases

Link to USGS - Alaska:	WI131

Other Regions, Features and Areas containing this locality

References