Geologic description
The country rocks in the area of Diamond Point include Jurassic quartz monzonite, andesite of the Jurassic Talkeetna Formation, and undivided Tertiary(?) volcanic rocks (Detterman and Reed, 1980). The contact between the quartz monzonite and the andesite is steep and strikes north-northeast. It is roughly parallel to a fault that separates the Talkeetna Formation from basalt of the Triassic Cottonwood Bay Formation. Martin and Katz (1912) described an 8- to 12-foot-wide shear zone on the Iliamna Bay side of the prospect and about a 100-foot-wide shear zone on the Cottonwood Bay side. The 100-foot-wide zone contains narrow veins and stringers of pyrite. Martin and Katz (1910, 1912) reported that rocks assayed privately contained about 0.1 ounce of gold per ton. Detterman and Reed (1964) characterized the occurrence at Diamond Point as an association of gold, silver, and copper along with other metals. Their sample 118, collected on or near Diamond Point, contained 100 parts per million (ppm) copper and 15 ppm tin. Samples that they collected to the north on Iliamna Bay (nos. 122 &123) contained 150 ppm copper and as much as 20 ppm tin. |
