Breccia Occurrence (south of Snowcap Mountain), McGrath Mining District, Bethel Census Area, Alaska, USAi

Regional Level Types
Breccia Occurrence (south of Snowcap Mountain)	Occurrence
McGrath Mining District	Mining District
Bethel Census Area	Census Area
Alaska	State
USA	Country

Location: This occurrence is at an elevation of about 4,500 feet on the east side of a small glacier, 2.9 miles southeast of Snowcap Mountain. It is in the SE1/4 section 4, T 15 N, R 24 W, of the Seward Meridian. The location is accurate to within 0.2 mile.
Geology: A tourmaline-cemented breccia as much as 80 feet across is present in monzogranite at this locality (Gamble and others, 1989). The breccia, includes vein quartz, light-colored angular rock fragments, and monzogranite clasts to about 3 feet across suspended in a black tourmaline matrix that also contains lesser amounts of sericite, quartz, calcite, and chlorite. Discontinuous quartz-tourmaline-sulfide veins to a foot wide cut the breccia along vertical, north-south-trending fractures. Sulfides in the veins include arsenopyrite, chalcopyrite, pyrrhotite, pyrite, and lesser amounts of galena and sphalerite; gangue minerals include quartz, tourmaline, chlorite, and epidote. A composite grab sample of 5 veins in the breccia contains as much as 4.1 ppm gold, 7 ppm silver,and greater than 2,000 ppm arsenic. Selected sulfide-rich samples contain as much as 21 ppm gold, 150 ppm silver, 10,000 ppm copper, and greater than 2,000 ppm arsenic and 1,000 ppm bismuth (Gamble and others, 1989).
Workings: Reconnaissance sampling has been done in this area (Gamble and others, 1989).
Age: Cretaceous or Tertiary? The breccia and veins crosscut granitic rocks that may be Late Cretaceous or Tertiary parts of the Alaska-Aleutian Range batholith.
Alteration: Tourmaline replacement and veining.

Commodities (Major) - Ag, Au, Cu; (Minor) - Bi
Development Status: None
Deposit Model: Tourmaline-cemented breccia in granitic rocks

Other Databases

Link to USGS - Alaska:	LH026

Other Regions, Features and Areas containing this locality

References