Maps Showing Geology, Structure, and Geophysics of the Central Black Hills, South Dakota By Jack A. Redden1 and Ed DeWitt2 Including contributions by James Berry3, C. Gilbert Bowles2, W.A. Braddock4, C. Mark Cattermole2, J.C. Harkeson4, Robert Kucks2, Alvis L. Lisenbee1, James J. Norton2, Zell Peterman2, J.C. Ratté2, and R.E. Zartman5 1South Dakota School of Mines and Technology 2U.S. Geological Survey 3Homestake Mining Company, Lead, S. Dak. 4Deceased 5Max Planck Institute for Chemistry, Mainz, Germany Prepared in cooperation with the South Dakota School of Mines and Technology Foundation Pamphlet to accompany Scientific Investigations Map 2777 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior DIRK KEMPTHORNE, Secretary U.S. Geological Survey Mark D. Myers, Director U.S. Geological Survey, Reston, Virginia: 2008 About USGS Products For product and ordering information: World Wide Web: http://www.usgs.gov/pubprod Telephone: 1-888-ASK-USGS For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment: World Wide Web: http://www.usgs.gov Telephone: 1-888-ASK-USGS About this Product For more information concerning this publication, contact: Team Chief Scientist, USGS Central Mineral Resources Team Box 25046 Denver Federal Center MS 973 Denver, CO 80225-0046 (303) 236-1562 Or visit the Central Mineral Resources Team Web site at: http://minerals.cr.usgs.gov This publication is available online at: http://pubs.usgs.gov/sim/2777 Publishing support provided by: Denver Publishing Service Center, Denver, Colorado Manuscript approved for publication September 25, 2002 Map jacket by Amber Hess Suggested citation: Redden, J.A., and DeWitt, Ed, 2008, Maps showing geology, structure, and geophysics of the central Black Hills, South Dakota: U.S. Geological Survey Scientific Investigations Map 2777, 44-p. pamphlet, 2 sheets. 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ISBN 978-141132214-1 iii Contents Introduction ................................................................................................................................................... 1 Precambrian Rock Units ............................................................................................................................. 1 Archean Units ...................................................................................................................................... 3 Oldest Early Proterozoic Units (Pre-2,480 Ma) ............................................................................... 3 Older Early Proterozoic Units (2,480–1,900 Ma) ............................................................................. 3 Younger Early Proterozoic Units (Post-1,900 Ma) .......................................................................... 9 Phanerozoic Rock Units ............................................................................................................................ 10 Paleozoic Sedimentary Units .......................................................................................................... 10 Mesozoic Sedimentary Units .......................................................................................................... 11 Tertiary Sedimentary Units .............................................................................................................. 11 Tertiary Igneous Units ...................................................................................................................... 12 Quaternary Units ............................................................................................................................... 13 Proterozoic Plutonism and Metamorphism ........................................................................................... 13 Precambrian Structure ............................................................................................................................. 16 Folds and Foliation ............................................................................................................................ 16 D1 Event and Related Structures ............................................................................................ 17 D2 Event and Related Structures ............................................................................................ 18 D3 Event and Related Structures ............................................................................................ 22 D4 Event and Related Structures ............................................................................................ 22 D5 Event and Related Structures ............................................................................................ 26 Folds of Indeterminate Age ..................................................................................................... 26 Faults ................................................................................................................................................. 26 Phanerozoic Structure .............................................................................................................................. 30 Geophysics .................................................................................................................................................. 31 Magnetic Anomaly Map .................................................................................................................. 31 Gravity Map ........................................................................................................................................ 32 Regional Geologic Setting based on Geophysics and Exposed Rocks ................................... 33 Geochronology ........................................................................................................................................... 34 Mineral Deposits ........................................................................................................................................ 36 Ground Water ............................................................................................................................................. 37 Acknowledgments ..................................................................................................................................... 38 References Cited ........................................................................................................................................ 39 iv Figures 1. Index map of the central Black Hills ........................................................................................ 2 2. Generalized block diagrams showing stratigraphic and structural events ...................... 4 3. Photograph of “spotted” muscovite-biotite schist .............................................................. 15 4. Structural diagrams illustrating bedding, foliation, and plunge of minor folds .............. 20 5. Photograph and reconstructions showing doubly plunging minor folds ......................... 21 6. Photograph and drawing showing boudin development in metagraywacke. ................. 23 7. Diagrammatic cross section of late (D4) recumbent anticline and small thrust fault ... 24 8. Photograph and drawing showing boudinaged Bouma A units ....................................... 25 9. Map of 40Ar/39Ar dates on amphibolites and Rb-Sr whole-rock muscovite dates .......... 35 Tables 1. Late Archean and Early Proterozoic depositional and tectonic events ............................ 6 2. Characteristics of major faults ................................................................................................ 28 Introduction published geologic maps. Also, authors of the different source maps did not necessarily map the same units of Tertiary igne- Preparation of the 1:100,000-scale geologic map (map A) ous rocks and Quaternary surficial deposits both in Precam- began in the early 1980s with the original intent of limiting the brian and Phanerozoic areas. The authors have attempted to map to the Precambrian rocks, where there had been consider- achieve a general uniformity but recognize that errors will able recent mapping by U.S. Geological Survey personnel. exist. Precambrian rock units also may differ somewhat from Because there was also recent work on the Phanerozoic rocks, those in the original source maps. Such deviations—justified the map was extended to cover the area included in the U.S. or not—are the full responsibility of the authors. Geological Survey folio of the central Black Hills (Darton and Because the Black Hills has the easternmost exposures Paige, 1925). The map in that folio has served as a basis for of rocks generally referred to as Laramide or part of the Rock Mountain orogeny, and is the only exposed Precambrian part subsequent studies for more than 70 years. The reader can of the Trans-Hudeon orogeny in the northern United States, it compare the original folio map with the present map and see is widely visited and sampled by geologists. Hence, samples that there are relatively few differences in the portrayal of the of the Precambrian rocks are the subject of many scientific Phanerozoic rocks. If better base maps