Mineral resource potential map of the Great Rift Instant Study Area, Blaine, Butte, Minidoka, and Power counties, Idaho

Ridenour, James, Stotelmeyer, Ronald B., Kuntz, Mel A.-, Mabey, Don R. · 1983 · Report

A high potential exists for development of decorative building stone resources from slabby, glassy-surfaced pahoehoe lava flows

This 1983 document, Mineral resource potential map of the Great Rift Instant Study Area, Blaine, Butte, Minidoka, and Power counties, Idaho, is preserved in the Mountain Man Mining Library for research and reference. Original source: pubs.usgs.gov.

DEPARTMENT OF THE INTERIOR UNITED STATES GEOLOGICAL SURVEY MISCELLANEOUS FIELD STUD~S MAP MF-1462-B PAMPHLET MINERAL RESOURCE POTENTIAL OF THE GREAT RIFT INSTANT STUDY AREA BLAINE, BUTI"E, MINIDOKA, AND POWER COUNTIES, IDAHO By James Ridenour and Ronald B. Stotelmeyer, U. S. Bureau of Mines and Mel A. Kuntz, Don R. Mabey, Duane E. Champion, Richard H. Lefebvre, and W. D. Stanley, U.S. Geological Survey STUDIES RELATED TO WILDERNESS Bureau of Land Management Wilderness Study Areas The Federal L~d Policy and Management Act (Public Law 94-579, October 21, 1976) requires the U.S. Geological Survey and the U.S. Bureau of Mines to conduct mineral surveys on certain areas to determine their mineral resource ~ot~ntial. Results must be made av~ilable to the public and be s~emitted to the President .and the Congress. report presents the results of a mmeral · survey of the Great Instant Study Area, Blame, Butte, Minidoka, and ~ower Counties, Idaho. MINERAL RESOURCE POTENTIAL SUMMARY STATEMENT A high potential exists for development of decorative building stone resources from slabby, glassy-surfaced pahoehoe lava flows, particularly in the Wapi lava field where the largest volume and variety of stone occurs. ·. The unique appearance of the Blue Dragon flow material from the Craters of the Moon lava field may enhance its potential as a decorative stone resource. Locating speculative resources (uraniferous sediment, auriferous gravel, and geothermal reservoirs) and hypothetical resources (oil and gas) that · may underlie the geologically young lava flows of the study area would require extensive geophysical exploration a;nd drilling. INTRODUCTION The Great Rift Instant Study Area is located in the Snake River Plain of south central Idaho. The study area consists of two parts, a northern part comprising 287,800 acres (1,165 km ) partly surrounding the Craters of the Moon National Monument, a southern part comprising 86,600 acres (350 km ) (fig. 1). Both parts encompass young, fresh basaltic lava flows that have been erupted from fissure-controlled vents along the Great Rift. The study area ranges in elevation from about 4,400 ft (1,340 m) to about 5,750 ft (1,750 m) and is relatively flat, except in local areas near cinder cones and steep lava flow fronts. The young lava flows and their vent. areas have hummocky, blocky, and cindery surfaces that are almost completely free of soil and vegetation. There are no roads in the study area and it is currently free of any commercial or agricultural development. GEOLOGY The Great Rift is a volcanic rift zone, a set of volcanic vents, eruptive fissures, and noneruptive fissures (Prinz, 1970). The Great Rift extends about 55 mi (85 km) from the southern Pioneer Mountains southeastward through Craters of the Moon National Monument and the northern part of the study area to Pillar Butte, located about 20 mi (30 km) northwest of American Falls, in the southern part of the study area. Three Holocene and latest Pleistocene lava fields are alined along the Great Rift. The Craters of the Mo~n lava field covers an area of about 600 mi 2 (1600 km ) and consists of more than 40 lava flows that were erupted from more than 25 cinder cones and eight eruptive fissures. Most of these vents are located within the Craters of the Moon National Monument but some extend into the northern part of the study area. The northern part of the study area includes a large part of the Craters of the Moon lava field that is not included in the Craters of the Moon National Monument. The Kings Bowl lava fie!d is mad~ up of lava flows of limited extent (1.3 mi , 3.2 km ) that were erupted from fissure vents in the southern part of the Great Rift. The Kings Bowl lava field is not included in the Great Rift Instant Study Area. The Wapi lava field is a bro!d shield v~lcano that covers an area of about 120 mi (310 km ); its vent complex constitutes Pillar Butte. The southern part of the study area covers nearly all of the Wapi lava field. All three lava fields consist of mostly fresh, largely unweathered pahoehoe and a'a lava flows;-The Craters of the Moon Lava field formed during eight eruptive periods, each less than 1,000 years long and separated from one another by intervals that were several hundred to as much as several thousand years long. The first eruptive period began about 15,000

200 KILOMETERS iOO MILES

/ EXPLANATION BASIN AND RANGE MOUNTAINS FAULT ---APPROXIMATE BOUNDARY OF STUDY AREA Figure 1.--Index map showing the location of the Great Rift instant Study Area.

years ago and the last eruptive period occurred about 2,100 year5 ago-. The .Kings Bowl and Wa;ei lava fields both were formed during short, prob~bly simtt1taneous_ eruptions along separate segments of the southern part of the Great Rift about 2, 200 years ago. The lava flows of the three lava fields are dark colored and dense in hand· specimen; they have fresh, nearly unweathered crusts; and they are largely free pf _soil and vegetation. Cones formed at point sources on fissures consist of cinders, blocks, bombs, lapilli, and ash, some of which is locally agglutinated. Eruptive fissures are bordered by spatter ramparts~ GEOPHYSICS Magnetic anomalies in the study area are complex and reflect 3 primary factors: .. (1) local surface relief, (2) direction of magnetization, and (3) thickness and depth of sequences of flows with normal or reverse magnetization. The magnetic field also reflects magnetic masses underlying and within .the basalt flows, including intrusive basalt, volcanic rocks older than the basalt flows, large silicic intrusives, and perhaps a magnetic basement complex. A magnetic high centered beneath the Craters of the Moon National Monument and the northern part of the study area is interpreted to reflect a deep-seated intrusive body that is related to a northwest-trending structure ~hat lies parallel to the Great Rift and extends northwest beyond tl_le limits of the Snake River Plain. Magnetic data suggest that the northern part of the study area may reflect anomalously high temperatures in the crust. A broad g-::-avity low is roughly coincident with the magnetic high in the Craters of the Moon area; both anomalies could be produced by a silicic intrusive body. A magnetotelluric investigation of .the study area reveals a four-part upper crustal region that consists of four layers of varying resistivity. From the surface to a depth of about 12 mi (20 km), the 'four layers are believed to represent basaltic lava flows, rhyolitic lava flows, b'basement rocks of high resistivity, ! and basement rocks of low . (Kuntz and others, 19S3). ASSESSMENT OF' MINERAL RESOURCE No mining districts exist in either the northern or southern parts of the Great Rift Instant Study Area. No mining claims have been filed i:h the northern part of the study area, but a group of eight claims, presumably· for building stone, was located at Pillar Butte in 1980. Identified resources in the study area are confined mainly to decorative building stone and volcanic cinders (figs. 2 and 3). Decorative building stone consists chiefly of slabs of pahoehoe lava, 1-4 in. (2.5-10 em ) thick, that occur at the margins of flows and flow units, near vent rims, and in squeeze-ups. Resources of building - ston~ in the northern part of the study area are about 5,500 tons .(5,400 t), and 10,000 tons (9,100 t) are inferred. Inferred .surface resources of useable buil,ding stoll,e in the southern part of the study area may approach a half million tons, Volcanic cinders for use as road metal, fill, and so on;-;are found in cinder cones along the Great Rift, mainly in the northern part of the study area. Speculative resources of geothermal water, auriferous gravel, uraniferous silt, and hypothetical reservoirs of oil and gas . that may lie within and beneath the basaltic lava flows of the study area may be inferred on the basis of occurrences largely outside the study area. Locating such resources would require extensive geophysical exploration and drilling. REFERENCES CITED Kuntz, M. A., Mabey~ D. R., Champion, D. E., Stanley, W. D., Lefebvre, R. H., Spiker, E. C., McBroome, L. A., and Covington, H. R., 1983, Geologic and geophysical maps of the Great Rift Instant Study Area, Blaine, Butte, Minidoka, and Power Counties, Idaho: U.S. Geological Survey, MF1462-A. Prinz, M., 1970, Idaho rift system, Snake River Plain, Idaho: Geological Society of America Bulletin, v. 81, no. 3, p. 941-947.

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Figure 3.--Mineral resource potential map showing sites investigated for decorative building stone in the souther~ part of the Great Rift Instant Study Area.