SPATIAL AND TEMPORAL LINKS BETWEEN MINERALIZATION AND THE FORMATION, AMALGAMATION, AND DISRUPTION OF ACCRETED TERRANES IN THE BLUE MOUNTAINS OF OREGON

Pre-Tertiary terranes in the Blue Mountains can be delineated by their distinctively different mineral deposits. Syngenetic deposits hosted by the northernmost, island-arc dominated Wallowa Terrane include strata-bound, copper-gold exhalative deposits, weakly mineralized, coeval, subvolcanic intrusions, and reefal limestones. Syngenetic deposits within the central Baker Terrane include chert-hosted, stratabound managanese pods, ultramafic-hosted chromite pods, and olististromal limestones. The southernmost Olds Ferry Terrane contains stratabound gypsum and limestone deposits and silver-copper strata-bound volcanogenic deposits. Other terranes, such as the Grindstone, Izee, and the higher-grade metamorphic rocks of the Mountain Home Metamorphic Complex are notably lacking in syngenetic mineral deposits.

Mineralized, post-amalgamation, Late Jurassic – Early Cretaceous intrusions that cut across terrane boundaries are typically zoned, with central copper-molybdenum or silver-tungsten mineralized intrusive cores grading outward into fringing gold-silver veins. Mineralized, post-accretion, Paleogene sub-volcanic intrusions that cut the Olds Ferry – Baker terrane boundary form strongly zoned porphyry systems wherein gold mineralization is confined to Baker Terrane rocks. Neogene epithermal hot springs systems occur within both the Olds Ferry and Baker terranes.