Mississippi Valley-type Mineralization and Ore Deposits in the Cambrian–Ordovician Great American Carbonate Bank
Jay M. Gregg, Kevin L. Shelton, 2012. "Mississippi Valley-type Mineralization and Ore Deposits in the Cambrian–Ordovician Great American Carbonate Bank", Great American Carbonate Bank: The Geology and Economic Resources of the Cambrian—Ordovician Sauk Megasequence of Laurentia, James Derby, Richard Fritz, Susan Longacre, William Morgan, Charles Sternbach
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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 recrys-tallization 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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Great American Carbonate Bank: The Geology and Economic Resources of the Cambrian—Ordovician Sauk Megasequence of Laurentia
The Great American Carbonate Bank (GACB) comprises the carbonates (and related siliciclastics) of the Sauk megasequence, which were deposited on and around the Laurentian continent during Cambrian through earliest Middle Ordovician, forming one of the largest carbonate-dominated platforms of the Phanerozoic. The Sauk megasequence, which ranges upwards of several thousand meters thick along the Bank's margin, consists of distinctive Lithofacies and fauna that are widely recognized throughout Laurentia. A refined biostratigraphic zonation forms the chronostratigraphic framework for correlating disparate outcrops and subsurface data, providing the basis for interpreting depositional patterns and the evolution of the Bank. GACB hydrocarbon fields have produced 4 BBO and 21 TCFG, mostly from reservoirs near the Sauk-Tippecanoe unconformity. The GACB is also a source of economic minerals and construction material and, locally, serves as either an aquifer or repository for injection of waste material. This Memoir comprises works on biostratigraphy, ichnology, stratigraphy, depositional facies, diagenesis, and petroleum and mineral resources of the GACB. It is dedicated to James Lee Wilson who first conceived of this publication and who worked on many aspects of the GACB during his long and illustrious career.