LOCATING POSSIBLE UNKNOWN ECONOMIC MINERAL RESOURCES IN THE NORTHWEST ST. FRANCOIS TERRANE USING REGIONAL GRAVITY DATA, SOUTHEAST MISSOURI

Southwest Missouri has a rich history of profitable economic resource extraction which is currently undergoing transition after the rise in imported metals and ores over the previous 20 years. In the past Missouri’s most well-known mineral resources have been lead and iron ores which have become economically infeasible for extraction in recent years. As part of a USGS project on Setting and Origin of Iron Oxide-Copper-Cobalt-Gold- Rare Earth Element (Fe-Cu-Co-Au-REE) Deposits of Southeast Missouri over 700 new gravity stations were collected in regions with few previous recordings in and around the Pea Ridge iron deposit during the summers of 2013 and 2014. These stations were added to the 3000+ existing gravity stations in the Pea Ridge region and will give a much better understanding of the subsurface. The region is adjacent to the St. Francois Mountains, a 1.5 GA volcanic terrane which later was the center of the Ozark uplift. Since the currently known Fe-Cu-Co-Au-REE deposits exist near or within the crystalline Precambrian basement below the basal Lamotte Sandstone using geophysical methods is the best route to defining other possible Fe-Cu-Co-Au-REE deposits. The complete Bouguer gravity anomaly map indicates that the Pea Ridge deposit is associated with a localized low within a regional high gravity anomaly. There are also other similar anomalies within the larger regional high. In order to aid in delineating the anomalies a variety of filtered maps were created. Various wavelength filters applied to the data found the regional gravity maximum covers a much larger area than seen in the Bouguer maps. In order to quantitatively interpret the Precambrian geology and nature of the ore deposits three 2.5-D profiles were created. These models were created using geological mapping and bore holes penetrating the Precambrian lithologies. The final interpretation of the gravity data is aided by magnetic and well core data to give a more nuanced interpretation and help better define the structures within the terrane. The maps and models combined allow a new look into a poorly researched region of promise.