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Abstract
Gregg, Jay M., and Kevin L. Shelton,
DOI:10.1306/13331493M981487
2012 by The American Association of Petroleum Geologists.
Mississippi Valley-type Mineralization and Ore Deposits in the Cambrian–Ordovician Great American Carbonate Bank
Jay M. Gregg,1 Kevin L. Shelton2
1Boone Pickens School of Geology, Oklahoma State University, Stillwater, Oklahoma, U.S.A.
2Department of Geological Sciences, University of Missouri, Columbia, Missouri, U.S.A.
ACKNOWLEDGMENTS
This review is based on almost 29 yr of collaborative study of MVT and other types of base-metal deposits worldwide by the authors. We thank the National Science Foundation (NSF-EAR-9001986, NSF-EAR-9104590, NSF-INT-9729653, and NSF-EAR-0106388), the donors of the Petroleum Research Fund, administered by the American Chemical Society (PRF-16053-G2, PRF-19809-AC2, PRF-25926-AC8, and PRF 35893-AC8), the University of Missouri Research Board, and the U.S. Information Agency J. William Fulbright Foreign Scholarship Board for their financial support of these studies. We also thank all of the companies that provided us with financial and material support, including St. Joe Minerals Corporation, The Doe Run Company, Cominco American Inc., ASARCO, Texaco E
P Technology Division, BHP Petroleum, Phillips Petroleum Co., Conoco, Inc., and Amoco Production Company. We also thank the AAPG, the Geological Society of America, the Society of Economic Geologists, and Sigma Xi for grants, at various times, to our graduate students who were involved in these studies.
We thank our graduate students who participated in the studies of MVT deposits and the rocks that host them, including Rita Bauer, William Baugaard, Steve Becker, Isac Burstein, Natalie Gentry, Zenhao He, Aaron Johnson, Timothy Keller, Peter Laudon, Zsolt Nagy, Chris Persellin, Ry Stone, Bob Woody, and Wayne Wright.
We thank our colleagues, both from academia and industry, with whom we enjoyed many fruitful discussions and debates concerning MVT deposits, including but not restricted to Bruce Ahler, Greg Anderson, Frank Beales, Adrian Boyce, Milton Bradley, Andrew Childers, Rick Dingess, Bob Dunn, Tom Freeman, Frank Furman, Grant Garven, Marty Goldhaber, Bill Grundmann, Dick Hagni, Jim Husman, Steve Kesler, Dave Leach, Sal Mazzullo, George Moellering, Isabel Montanez, Eric Mountjoy, Norm Paarlberg, Jim Palmer, Danny Rye, Duncan Sibley, Bob Smith, Ian Somerville, Paul Spry, Peter Strogen, Dimitri Sverjensky, Mark Taylor, Bob Voss, Bud Walker, Jamie Wilkinson, and Chan Min Yoo. We especially thank Paul Gerdemann who was an inspiration, mentor (to J. M. G.), and endless source of information through our years of study.
This chapter benefited from comments on an earlier draft by Martin Appold and Patrick Medlock, and we thank editor Jim Derby for patiently working with us. We, however, take full responsibility for the final content of the chapter.
ABSTRACT
The Middle Cambrian through Lower Ordovician carbonate rocks of North America host some of the largest economic Mississippi Valley-type (MVT) base-metal sulfide deposits in the world. These rocks also host numerous subeconomic MVT deposits, minor and trace occurrences of mineralization, and hydrocarbon fields. Mississippi Valley-type deposits commonly contain bitumen, pyrobitumen, and/or liquid petroleum, suggesting that MVT mineralization is associated with the generation and migration of hydrocarbons and thus is a normal part of basin evolution.
In addition to sulfide and sulfate mineralization, common characteristics of MVT deposits are large-scale dissolution and brecciation of carbonate rocks, precipitation of large volumes of dolomite and calcite cements, epigenetic (hydrothermal) dolomitization, and recrystallization of preexisting dolomite. Mineralizing fluids have the effects both of increasing the original porosity by dissolution and brecciation and of occluding porosity because of precipitation of cements.
Mississippi Valley-type fluids are not localized but affect sedimentary rocks across large regions. It is likely that most, if not all, Cambrian–Ordovician carbonate rocks in North America have undergone at least some diagenetic alteration because of exposure to these fluids. This conclusion is supported by the observation that subeconomic MVT mineralization has been observed in Cambrian and Lower Ordovician carbonates throughout much of North America. These fluids commonly have affected carbonate petroleum reservoir rocks in regions distal from known ore deposits.
Mississippi Valley-type mineralization is believed to result from a complex mixing and/or cooling of saline fluids expelled from sedimentary basins. These fluids have temperatures ranging from 60 to 250
C. Most of the fluids originate from evaporated seawater or water that has dissolved halite and that has interacted with sedimentary rocks and, possibly, basement rocks. Several geochemical and hydrogeological mechanisms have been proposed for MVT deposits. However, the precise mechanisms driving fluid flow and deposition are not yet completely understood.
Major tectonic events associated with MVT mineralization of the great American carbonate bank strata include the Acadian orogeny (Late Devonian–Early Mississippian) for early mineralization in the Appalachian Mountain region, the Alleghanian-Ouachita orogeny (Pennsylvanian–Permian) for mineralization in the Appalachian and midcontinent regions, and the Laramide orogeny (Late Cretaceous–early Tertiary) for the Cordilleran region.
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