Geological and Geophysical Investigations and Mineral Resources Potential of the proposed Great Rift Wilderness Area, Idaho

Kuntz, Mel; Lefebvre, Richard; Champion, Duane; McBroome, Lisa; Mabey, Don; Stanley, W; Convington, H; Ridenour, James; Stotelmeyer, Ronald

The proposed wilderness area has only a few recently staked mining claims. Mineral potential of the area is confined to decorative stone, consisting of filamented pahoehoe, and cinders. Based on ground reconnaissance, it is estimated that these are about 116,000 tons of indicated stone resources and a half-million tons of inferred resources, most of which are in the southern part of the study area. In the northern part, there are at least 27 million cubic yards of cinders. Mineral, petroleum, and geothermal resources may exist beneath the lavas of the study area but extensive geophysical exploration and drilling would be required to prove their existence. Aeromagnetic, gravity, and magnetotelluric studies of the proposed wilderness area have yielded basic data on the nature of the crust beneath the young lava flows, and provided data for an assessment of potential resources. Magnetic anomalies in the area are complex and result from both strongly magnetized surface and near-surface lava flows and magnetic rocks underlying the flows. The magnetic data suggest that a deep intrusive body underlies the study area. Gravity anomalies are related to variations in the thickness of Cenozoic volcanic rocks and possibly to the inferred intrusive body. Magnetotelluric studies have provided data for interpreting the structure and possible rock types in the upper 10 km of the crust. The proposed Great Rift Wilderness area is a region of volcanic rocks less than about 15,000 years old in the eastern Snake River Plain, Idaho. The area is located adjacent to the Craters of the Moon National Monument along the Great Rift, a linear array of cinder cones, eruptive fissures, and open cracks that extend for a distance of about 85 km from the southern Pioneer ·' Mountains northwest of the map area, southeast through the Monument, to the southern margin of the Snake River Plain. The Great Rift is the site of volcanic vents that erupted lava flows of the Craters of the Moon, Kings Bowl, and Wapi lava fields. The Craters of the Moon lava field was formed between about 15,000 and 2,000 years ago during at least 7 periods of volcanic activity, each of which lasted about 1,000 years or less. The Kings Bowl and Wapi lava fields were both formed during a brief eruptive period about 2,250 years ago. 2

Geological and Geophysical Investigations and Mineral Resources Potential of the proposed Great Rift Wilderness Area, Idaho

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