Abstract

In the Central Missouri barite district, barite samples were taken from four barite deposits and carbonate samples from the Lower Ordovician Jefferson City and Gasconade Dolomites in two road cuts and from the Mississippian Burlington Limestone in a quarry. The samples were tested paleomagnetically using detailed alternating field and thermal demagnetization and saturation isothermal remanent magnetization methods. An A magnetization direction of declination = 153.5 degrees , inclination = 17.6 degrees (N = 35, k = 17, alpha 95 = 4.8 degrees ) is carried by pseudosingle domain magnetite in the barite-rich zones of three open-pit mines as an ore-synchronous component, in the Jefferson City Dolomite as a secondary component, and in collapse breccia blocks of probable post-Middle Devonian age in the dolomite to give a negative "conglomerate" test. The A paleopole at 121.0 degrees E, 36.6 degrees N (dp = 2.6 degrees , dm = 4.9 degrees ) falls within the Kiaman reversed magnetic polarity interval on the Late Pennsylvanian to early Early Permian part of the apparent polar wander path for North America. A B magnetization direction of declination = 36.8 degrees , inclination = 77.8 degrees (N = 21, k = 13, alpha 95 = 92 degrees ) is found in the other units. It is a hybrid magnetization dominated by hematite produced by weathering and by viscous remanence in magnetite, both of Quaternary origin. The Kiaman magnetization in the barite ores and host rocks of the Central Missouri district agrees with known Kiaman magnetizations in the lead-zinc ores and host rocks of the adjacent Southeastern Missouri and Northern Arkansas districts. This agreement provides strong support for the Ouachita tectonic uplift model of genesis for the origin of the Mississippi Valley-type ore deposits in the midcontinental region of the United States.

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