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Setting and Origin of Iron Oxide-Copper-Cobalt-Gold-Rare Earth Element Deposits of Southeast Missouri : Geophysical Characterization

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Contact: Anne McCafferty, anne@usgs.gov

Southeast Missouri is covered by antiquated magnetic surveys, flown from 1946 to 1960 for iron exploration. The old surveys cover the important concealed deposits at Pea Ridge, Kratz Spring, Camels Hump, Bourbon, and Boss-Bixby. These surveys were flown prior to the modern geophysical and geographic positioning technology that exists today. Ground gravity data are coarsely spaced and provide little information at deposit scale. In order to properly delineate and characterize controls on potential IOCG mineralization, modern airborne magnetic and gravity data are required.

gravity map of project area
The first image, left, shows a Bouguer gravity anomaly map of the study area; the second shows an index map of gravity station locations.

 

The geophysical efforts of our project are threefold.

 

  1. First, a compilation of existing magnetic and gravity data are compiled and interpreted to determine overall basement architecture. The quality and resolution of the existing airborne magnetic and ground gravity data are only adequate to establish where large basement features occur and can be used to impart refinement on the existing basement map (Kisvarsanyi, 1981).
  2. Second, petrophysical measurements are made on an inventory of several hundred drill core, surface and underground mine samples collected by the USGS over the last decades. These samples are being statistically analyzed to determine relationships between petrophysical properties and alteration assemblages, ore mineralogy and chemistry. The petrophysical data will be also be used as input to a 3-D geophysical model of the Pea Ridge iron-ore rare earth element deposit.
  3. Third, because the existing magnetic and gravity data are insufficient to distinguish important features at deposit scale, the USGS has plans to fly a modern high resolution magnetic and gravity gradiometry survey later this that will cover the Pea Ridge, Kratz Spring, and the Bourbon iron deposits. The goal is to cover a number of the iron deposits so that a geologic framework can be established.
  4. The first image (below left) shows a magnetic anomaly map showing compilation of older magnetic surveys;
    the second image (below right) shows an index map of airborne magnetic survey coverage over study area.

    magnetic map of project area

     

     

     

     

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    Page Last Modified: 04-Dec-2013@14:26