Prospect, Active

Commodities and mineralogy

Main commodities Ag; As; Au; Bi; Sb
Other commodities Cu; Pb
Ore minerals arsenopyrite; pyrite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale BD
Quadrangle map, 1:63,360-scale B-1
Latitude 64.3151
Longitude -144.2017
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Bou prospect is about 0.7 mile east of the ridge of Black Mountain and about 0.7 mile east-southeast of peak 5020. The prospect is within a block of claims outlined by Barnes (2008). It is at about the southeast corner of section 8, T. 7 S., R. 18 E., of the Fairbanks Meridian. The location is accurate.

Geologic setting

Geologic description

The rocks in the area are part of the Yukon-Tanana Terrane of the northern Cordillera; they consist largely of late Paleozoic to Devonian medium- to high-grade metamorphic rocks that have been intruded by Cretaceous and Tertiary granitic stocks and batholiths (Baknes, 2008; Wilson and others, 1998). The metamorphic rocks are structurally complex with an older, middle to early Paleozoic and/or late Proterozoic unit that consists of gneiss, schist, quartzite, and amphibolite and a younger, Mississippian and/or Devonian unit that consists largely of augen gneiss that locally forms domal structures. The metamorphic rocks are intruded by 55 Ma to 107 Ma, granitic plutons. The structure of the area is complex and difficult to determine because of poor exposure but several major thrust fault have been identified as well as a series of northeast-trending, northwest-dipping high-angle faults.
The dominant mineralization in the area and the target of most of the exploration are deposits related to Cretaceous intrusions, several classic examples being the Fort Knox Mine (FB115) near Fairbanks and the nearby Pogo Mine (BD033). These deposits are characterized by an association with moderately reduced, I- and S- type granitic intrusions and a lithophile, gold-bismuth-tungsten-arsenic-tellurium-molybdenum(-tin-copper-lead-antimony) suite of elements. The deposits vary from low-sulfide, sheeted or stockwork deposits in the intrusions to replacement deposits, veins, and stockworks in the country rock. The mineralization at the nearby Pogo deposit is the model used in exploring this and other prospect in the area. The mineralization at Pogo consists of thick gently-dipping quartz veins that grade laterally into pegmatite dikes related to 107 Ma syenite and monzonite intrusions. The quartz veins contain about 3 percent sulfides, mainly arsenopyrite, pyrite, pyrrhotite, loellingite, chalcopyrite, bismuthinite, native bismuth and native gold. The veins are associated with biotite alteration overprinted by sericite-dolomite-chlorite-quartz alteration, that extends into the country rock for several meters.
Soon after the recognition of nearby Pogo as a major and economically attractive deposit in 1998, Rimfire Minerals Corporation in conjunction with several joint-venture partners began work in the area and identified this deposit. In 2008, they entered into a joint venture with Rubicon Minerals Corporation and commissioned a thorough technical report on their properties in the Goodpaster District (Baknes, 2008), which is the source of most of the information on this prospect.
The Bou prospect is almost entirely in Cretaceous, porphyritic biotite granite. The area is cut by numerous faults and lineaments of diverse orientation. The mineralization at Bou consists of quartz veins that are generally 15 to 30 centimeters thick but may reach 1 meter. The veins are commonly brecciated and are marked by pervasive sericitization and some sericitization. The veins contain disseminated pyrite and arsenopyrite. While the presence of sulfides is indicative of gold, their abundance does not seem to correlate to the gold values. Seven samples of the veins contained 1,050 to 3,960 parts per billion gold, 0.2 to 1.2 parts per million (ppm) silver, 1,245 ppm to more than 1 percent arsenic, less than 2 to 6 ppm bismuth, 16 to 3,299 ppm antimony, 4 to 50 ppm lead, and less than 1 to 5 ppm copper.
Geologic map unit (-144.204024378185, 64.3147357938753)
Mineral deposit model Quartz veins related to Cretaceous intrusives.
Age of mineralization Probably about 107 Ma based on similarities to the nearby Pogo Mine.
Alteration of deposit The granitic host rocks of the veins are marked by pervasive sericitization and some sericitization.

Production and reserves

Workings or exploration Surface sampling and geochemical surveys beginning in 1999 and continuing through 2007.
Indication of production None