Unnamed (near Black Crag)

Prospect, Undetermined

Commodities and mineralogy

Main commodities Ag; Au; Cu; Mo; Zn
Other commodities Ce; La; Nd; Sm; Th; U
Ore minerals chalcopyrite; molybdenite; pyrite

Geographic location

Quadrangle map, 1:250,000-scale BC
Quadrangle map, 1:63,360-scale C-6
Latitude 56.5367
Longitude -131.6992
Nearby scientific data Find additional scientific data near this location
Location and accuracy This unnamed site is about a mile southeast of Black Crag near the Alaska-British Columbia boundary in section 36, T. 61 S., R. 88 E., of the Copper River Meridian. The location is accurate.

Geologic setting

Geologic description

Still and others (2002) found possible evidence of claim staking here and were told of drilling for molybdenum in the 50s but there is no information about exploration here prior to their work. They briefly examined the area and collected several mineralized samples as part of a regional mineral assessment for the Bureau of Land Management. The site might be part of the prospect several miles to the southwest (BC004) that was explored in the 1970s.
The country rocks in the general area of Black Crag are a Miocene (?) alkali-feldspar granite stock and associated quartz-porphyritic rhyolite dikes (Koch, 1996). The prospect is near the margin of the stock, which intrudes Eocene granodiorite and quartz monzonite plutons and Mesozoic or Paleozoic pelitic schist and paragneiss.
On the east side of the valley, Still and others (2002) collected several samples of float that consisted of: 1) quartz porphyry with molybdenite along fractures; 2) fine-grained silicified felsite cut by a 0.1-foot-thick seam of molybdenite; and 3) silicified granite with pyrite and chalcopyrite. Samples of the molybdenite-bearing rocks contained 735 and 1,348 parts per million (ppm) molybdenum and the copper-bearing sample contained 1,508 ppm copper. A sample of silicified breccia cemented by pyrrhotite contained 93 parts per billion gold, 43.5 ppm silver, and 558 ppm zinc. At the head of the valley under a hanging glacier, volcanic rock with molybdenite along fractures is abundant. Samples contained 23 to 2,529 ppm molybdenum, 119 to 713 ppm zinc, and up to 1,740 ppm cerium, 954 ppm lanthanum, 440 ppm neodymium, 60 ppm samarium, 72.6 ppb thorium, and 16 ppm uranium.
Geologic map unit (-131.700894154812, 56.5363724254346)
Mineral deposit model Porphyry Cu-Mo (Cox and Singer, 1986; model 21a).
Mineral deposit model number 21a
Age of mineralization Tertiary or younger based on the age of the host rocks.
Alteration of deposit Mineralized rocks are silicified.

Production and reserves

Workings or exploration Still and others (2002) found possible evidence of claim staking here and were told of drilling for molybdenum in the 1950s but there is no information about exploration here prior to their work. They briefly examined the area and collected several mineralized samples as part of a regional mineral assessment for the Bureau of Land Management. The site might be part of the prospect several miles to the southwest (BC004) that was explored in the 1970s.
Indication of production None

References

Reporters D.J. Grybeck (Port Ludlow, WA)
Last report date 3/4/2008