GillespieClintonDale1970.pdf

• Main Author: Gillespie, Clinton Dale
• Language: unknown
• Subjects: north slope; Alaska
• Online Access: https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/8p58pg777

The central Bond Creek area is on the north slope of the Wrangell Mountains approximately 15 miles east of Nabesna, Alaska. The entire area is underlain by plutonic rocks of the Monte Cristo batholith of probable Jurassic age. Early members of this complex are hornblende diorite, quartz diorite, and granodiorite of plutonic origin. Later members are hypabyssal porphyries ranging in composition from andesite to rhyolite. These form numerous dikes and plugs, Intrusion breccias and intrusive explosion-breccias are associated with these rocks. Most large faults trend northwest and are defined by dikes. These faults are possibly related to regional faulting and folding. Fractures are abundant in all rock units and are randomly oriented. Foliation is common only in the youngest of the intrusive rocks such as the andesite, dacite, and rhyolite porphyries. Hydrothermal alteration consists of both the propylitic and potassic types. Propylitic alteration is characterized by the formation of "white mica," epidote, chlorite, and calcite. Potassic alteration. is restricted to breccias and areas of intense fracturing. It is characterized by biotite and orthocl.ase.in the intrusive explosion-breccia, and quartz, "white mica," and orthoclase in theintrusion breccias and areas of intense fracturing. Sulfide mineralization is most abundant in zones of potassic alteration. Pyrite is the most common sulfide, but chalcopyrite is locally abundant. Molybdenite is restricted to an area of stockwork veining.