Geology of the Caribou Creek area, Big Delta quadrangle, east-central Alaska

Abstract

The Caribou Creek area, in the Big Delta C4 Quadrangle, East-Central Alaska, is known for significant placer gold, but no lode source. I present a new 200 km² area geologic map utilizing ground based mapping, airborne geophysical surveys, and follow-up laboratory investigations. Mapping and petrography delineate 10-20 km² blocks containing contrasting rock units and mineral assemblages. Amphibolite facies blocks contain abundant post-kinematic andalusite, with central blocks containing partially replaced kyanite, and blocks to the southeast and west containing post-kinematic sillimanite. Geothermobarometry shows that the amphibolite-facies blocks experienced pressures/temperatures of 11.5 kbars/650°C, followed by a collisional event associated with low-P/variable T post-kinematic recrystallization. The distribution of alumino-silicates suggests the central blocks were down dropped relative to adjacent blocks. Gold occurrences are found in west to northwest trending, steeply dipping quartz veins with stibnite ± arsenopyrite. Located in the central blocks, they are separated from a barren granodiorite pluton by a sinistral, northeast trending, high-angle fault. This study has shown the existence of major faults with significant vertical and horizontal movement, making gold source determination difficult. Future lode gold exploration in the area must take the high-angle faulting into consideration.