Geologic description
This mineralization was discovered by Still and others (2002). The rocks in this borrow pit consist mainly of fine- to medium-grained gray to dark green diorite. Intrusive rocks were previously unknown at this site although intermediate intrusive rocks of Cretaceous age have been mapped to the north and south of the pit (Brew and others, 1984). Pyrrhotite makes up 1-2 percent of the diorite and fine-grained chalcopyrite is common in the pit. The sulfides occurs as thin coatings along fractures. Rare molybdenite was also identified. The intrusive in the pit is cut by several faults and the sulfides are commonly localized along them. One of the faults contains bands of sulfides, mainly pyrrhotite with chalcopyrite, sphalerite, galena, arsenopyrite, and pyrite. Hornfels, probably metamorphosed from Cretaceous phyllite, is exposed north of the pit (Brew and others, 1984). Still and others (2002) collected 12 samples from 8 to 20 feet long in the pit. They averaged 163 parts per million (ppm) copper. A select sample of sulfide-rich material contained 3,271 parts per billion (ppb) gold, 12.9 ppm silver, 3.025 ppm copper, 4,708 ppm lead, 1.4 percent zinc, and 9,762 ppm arsenic. Other samples contained up to 855 ppm molybdenum and 1,365 ppm nickel. |
