Fortress (ARDF #WI131) Au

Fortress

Occurrence, Inactive

Commodities and mineralogy

Main commodities	Au
Other commodities	As
Ore minerals	gold; pyrite
Gangue minerals	ankerite; calcite; hematite; quartz

Geographic location

Quadrangle map, 1:250,000-scale	WI
Quadrangle map, 1:63,360-scale	B-1
Latitude	67.4994
Longitude	-150.1451
Nearby scientific data	Find additional scientific data near this location
Location and accuracy	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.

Geologic setting

Geologic description 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.
Geologic map unit	(-150.147851002264, 67.4989758235321)
Mineral deposit model	Low-sulfide Au-quartz vein (Cox and Singer, 1986; model 36a)
Mineral deposit model number	36a
Alteration of deposit	The wallrock adjoining the veins apparently is not altered.

Production and reserves

Workings or exploration	Surface sampling and geologic mapping.
Indication of production	None

References

References Eden, K., 2000, Geology and gold mineralization of the Nolan area in the Brooks Range, Alaska: U.S. Bureau of Land Management Open-File Report 78, 87 p. Kurtak, J.M., Klieforth, R.F., Clark, J.M., and Williams, E.M., 1999, Mineral investigations in the Koyukuk mining district, northern Alaska--Progress Report: U.S. Bureau of Land Management Open-File Report 74, 158 p.
Reporters	J.M. Britton (Anchorage)
Last report date	8/9/2002