RD8

Occurrences, Undetermined

Commodities and mineralogy

Main commodities Au; Ba; Co; Zn
Other commodities As; Cu; Hg; Ni; Pb; Sb
Ore minerals pyrite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale PE
Quadrangle map, 1:63,360-scale D-5
Latitude 56.8384
Longitude -133.5709
Nearby scientific data Find additional scientific data near this location
Location and accuracy This record covers a scattering of several occurrences in an area about 5 miles by 2 1/2 mile in size with the long dimension oriented north. The center of the area is east of the head of Big John Creek near hill 1908 which is southwest of Towers Lake and about 0.3 mile southwest of the center of section 14, T. 58 S., R. 74 E.

Geologic setting

Geologic description

This site was originally of interest because of widespread geochemical anomalies in a large suite of elements, zinc in particular. The samples commonly contain anomalous copper, molybdenum, and nickel, and various samples were anomalous in silver, lead, cadmium, manganese, mercury, arsenic, and antimony (Bittenbender and others, 2001). Still and others (2002) indicate that the suite suggests the presence of volcanogenic massive sulfide deposits. In following up these anomalies, they found several occurrences of mineralization in scattered borrow bits and road cuts. None seemed to explain the magnitude of the widespread geochemical anomalies but they do lend support to the concept of massive sulfide mineralization in the area.
The rocks in the area are part of the Cannery Formation of Permian and Mississippian age (Karl and others, 1999); they are a heterogeneous unit of chert, cherty argillite, silicified limestone, siltstone, and graywacke, with minor conglomerate, tuff, and volcanic rocks. In the three most notable areas of outcrop where the mineralization was found, it consists of: 1) pyrite in seams and layers in a 20-foot-thick unit of silicified schist, chert, and graphitic schist, 2) seams and patches of fine-grained to crystalline pyrite in quartz veins and silicified schist and slate, and 3) layers of pyrite up to 2 inches thick in a layer of silicified schist at least 10 feet thick in a unit of argillite. Numerous samples were collected and analyzed. None had high values in any of the common ore elements but many had values above background. The highest values were 136 parts per billion gold, 1,762 parts per million (ppm) zinc, 0.9 ppm silver, 166 ppm copper, 920 ppm lead, 727 ppm arsenic, 486 ppm nickel, and 9,176 ppm barium.
Geologic map unit (-133.572631651245, 56.8380575942318)
Mineral deposit model Volcanogenic massive sulfide deposit.
Age of mineralization Probably contemporaneous with the Permian and Mississippian host rocks.
Alteration of deposit The schists is commonly silicified.

Production and reserves

Workings or exploration The only work was sampling by the Bureau of Land Management during a regional mineral assessment.
Indication of production None

References

References

Bittenbender, P.E., Bean, K.W., and Still, J.C., 2001, Stikine airborne geophysical survey followup, central Southeast Alaska, 2000: Bureau of Land Management, Alaska Technical Report 37, 116 p.
Still, J.C., Bittenbender, P.E., Bean, K.W., and Gensler, E.G., 2002, Mineral assessment of the Stikine area, central Southeast Alaska: U.S. Bureau of Land Management Technical Report 51, 560 p.
Reporters Donald Grybeck (Port Ludlow, WA)
Last report date 4/8/2007