Volcanic-Hosted Epithermal Mineralization, Dooley Summit area, Oregon
Type of Culminating Activity
Master of Science in Geology
Dr. Craig M. White
A.M.S. thesis project on the Miocene rhyolite volcanic rocks and epithermal gold-silver mineralization found at Dooley Summit in east-central Oregon was funded by Boise Cascade Corporation. The area is similar to low-sulfidation-type epithermal mineralization, such as that found in economic deposits at DeLamar and Florida Mountain. Eight lithologic units, a large concentration of faults (the Feeder Zone), and an area of strong alteration (the Intense Alteration Zone) were identified. The Feeder Zone is inferred to be the main fluid conduit of a fossil hydrothermal system, and the Intense Alteration Zone is inferred to be a slightly higher, cooler portion of the system, which was dominated by silicic alteration. Gold, silver, and other indicator elements are associated with these areas, and adularia is found in the Feeder Zone. Fluid inclusion and X-ray diffraction work indicate the principle mineralization was deposited at 281°C to 338°C, from a fluid with a 1.9 to 6.1 weight percent NaCl, and alteration is zoned around the Feeder and Intense Alteration Zones. Rhyolite dome rocks are the most favorable host for mineralization; however, low gold values (254 ppb and less), the association of mineralization with small structures, and high fluid inclusion temperatures suggest the potential for economic mineralization is extremely low.
Unsworth, Charles C., "Volcanic-Hosted Epithermal Mineralization, Dooley Summit area, Oregon" (1996). Boise State University Theses and Dissertations. 744.