Geologic description
The headwaters of Squirrel Creek are on the southeast flank of Red Mountain. About the upper 1/3 of the drainage is in dunite of the Jurassic Red Mountain ultramafic pluton. Bedrock in the lower 2/3 of the creek is sheared argillite, graywacke, and mafic to intermediate, fine-grained igneous rocks that are difficult to identify because of their extensively decomposed character where exposed in mining cuts (Mertie, 1940). These country rocks to the Red Mountain pluton are included in a regional sedimentary and volcanic assemblage that ranges in age from Paleozoic to Mesozoic (Hoare and Coonrad, 1978).
Gravels in Squirrel Creek are commonly 13 feet thick but are locally up to 20 feet thick. In the lower part of the creek the gravels are subrounded to subangular but in the upper creek the cobbles and boulders are more angular; all the alluvial material is locally derived. The gravels are covered by 2 to 3 feet of vegetation-rich materials. The gravels have been mined from the confluence of Squirrel and Platinum Creeks upstream to an elevation of 350 feet, a distance of about 3/4 mile. In the 150- to 500-foot-wide pay streak, platinum is concentrated on bedrock, in the overlying 2 to 3 feet of gravel, and in fractures in bedrock. PGM grades were locally up to 0.1 ounce per cubic yard, but averaged about 0.03 ounce per cubic yard. The recovered platinum-bearing grains are generally coarser than on other nearby creeks and nuggets up to 1.5 ounces have been found (Mertie, 1940). The mean precious metal content of 22 samples (recomputed free of impurities) is 77.21% Pt, 15.68% Ir, 3.92% Os, 0.72% Ru, 1.58% Rh, 0.34% Pd, and 0.55% Au (Mertie, 1976). Three samples of Squirrel Creek tailings contained 0.0006 to 0.0033 ounce of PGM per cubic yard. Platinum-bearing grains from these samples contained 0.5 to 1.9 percent Rh, 0.3 to 0.9 percent Ru, 47 to 88.4 percent Pt, 0.7 to 37.4 percent Ir, 0.5 to 9.2 percent Os, and 4.1 to 9.0 percent Fe (Fechner, 1988). Platinum-bearing phases that were identified in these grains included iron-platinum alloy containing 8 to 30 percent Fe; iron-platinum alloy with minor osmiridium inclusions; osmiridium; and osmiridium with subordinate iron-platinum alloy. There are an estimated 50,000 cubic yards of tailings on Squirrel Creek with an average grade of 0.002 ounce of PGM per cubic yard. In the area of the Goodnews Bay Mining Company camp, there are an estimated 37,000 cubic yards of unmined alluvium grading 0.0135 ounce of PGM per cubic yard (Fechner, 1988, p. 81). |
