Arsenic Creek

Prospect, Inactive

Commodities and mineralogy

Main commodities Hg
Other commodities As
Ore minerals cinnabar; orpiment; realgar
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale BH
Quadrangle map, 1:63,360-scale A-4
Latitude 60
Longitude -160.13
Nearby scientific data Find additional scientific data near this location
Location and accuracy Arsenic Creek is a small, south-headwater tributary of Rainy Creek (BH002). This lode prospect is on the south side of Arsenic Creek, at an elevation of about 1,700 feet and about 1,000 feet upstream of the confluence with Rainy Creek. This is locality 5 of Cobb (1972 [MF 455]) and of Hoare and Cobb (1977). It is in the Togiak National Wildlife Refuge and the Togiak Wilderness.

Geologic setting

Geologic description

Lode mercury mineralization was identified on Arsenic Creek sometime between 1910 and 1920 (Rutledge, 1948). In 1947, the U. S. Bureau of Mines completed 1,500 feet of dozer trenching and 1,440 feet of hand trenching in the area of known lode mineralization (Rutledge, 1948). Three separate small but high-grade lode deposits were identified over a distance of 200 feet on the south side of the creek. These deposits are along or within 50 feet of the creek. The larger deposit (Deposit 1 of Rutledge, 1948, p. 5) is a sheared and fractured zone that is primarily developed in sandstone. The enclosing shears strike N 30 to 35 E, approximately parallel to bedding, but dip 70 northwest, opposite to bedding. Mineralization in the sheared zone includes realgar, cinnabar, and quartz in vein stockworks and seams along fractures and bedding. Eight samples collected over the 25-foot wide zone ranged in grade from 0.6 to 35.4 pounds of mercury per ton; a weighted average for these samples is 3.4 pounds of Hg per ton. Rutledge (1948, p. 5) concluded that the mineralized zone had a rhombohedral, pipe-like form and could not be traced along strike. Another lode deposit, 100 feet upstream, is similar in form but smaller. Five samples from this deposit ranged in grade from 1.6 to 44.6 pounds of Hg per ton; the higher grades were from thin sulfide-rich zones, including silicified shale, only a few inches thick. The third lode deposit, 200 feet east of the first, includes small lenses of white and gray quartz with enclosed cinnabar along a vertical N 30 E-striking fault zone. A composite sample of three, 3- to 6-inch-thick high grade lenses contained 45.8 pounds of Hg per ton. Arsenic, up to 18 percent or more, is present in all samples. In the larger deposits, realgar is the most abundant sulfide mineral. Orpiment is locally present. A realgar- and orpiment-rich sample contained 0.05 ppm Au (Frost, 1990, table 1, sample 7TF003). Although specific lode deposits could not be traced along strike, dozer trenches revealed thin mercury-bearing zones over about 700 feet of length; 0.5- to 1.6-foot-wide samples from these trenches contained 0.2 to 3.4 pounds of Hg per ton and 0.05 to 0.1 percent As. The bedrock in Arsenic Creek is sandstone and shale of the mid-Cretaceous Kuskokwim Group locally intruded by mafic dikes or sills (Rutledge, 1948; Hoare and Cobb, 1977; Box and others, 1993).
Geologic map unit (-160.132244495627, 59.9992498959084)
Mineral deposit model Epithermal mercury.
Age of mineralization Post mid-Cretaceous, the age of the host sedimentary rocks. The mineralization may be Late Cretaceous or Early Tertiary, the age of widespread intermediate to felsic igneous activity in the region (Box and others, 1993).
Alteration of deposit Silicification.

Production and reserves

Workings or exploration In 1947, the U.S. Bureau of Mines completed 1,500 feet of dozer trenching and 1,440 feet of hand trenching, and collected 19 samples in the area of known lode mineralization (Rutledge, 1948).
Indication of production None
Production notes About 2,000 pounds of cinnabar concentrates were recovered during placer mining operations on Rainy Creek (BH002), mostly below the mouth of Arsenic Creek.

References

MRDS Number A013390
Reporters Travis L. Hudson
Last report date 3/24/2001