Mining, Minerals and More in the Western Ouachita Mountains

Geologic SettingThe Ouachita Mountains of west-central Arkansas are part of the largest surface exposure of amuch larger system of complexly folded and faulted band of Paleozoic strata that was upliftedduring the Ouachita Orogeny or mountain building event. This system is approximately 1300miles long and extends from east-central Mississippi westward and southward into west Texas(Fig. 1). The Ouachita Mountains in Arkansas consist of a series of east-west trending sharpridges, separated by narrow to broad valleys that extends from Little Rock to the westernborder of the state and has an average width of 80 miles (Fig. 2).Figure 1. Location of Ouachita Mountains region outlined in purple.The sedimentary rocks of the Ouachita Mountains range in age from Late Cambrian to MiddlePennsylvanian. They can be placed into two sequences based on rock type and rates ofdeposition (Fig 3). These two sequences were deposited in very different environments. Theolder sequence consists of rocks of Late Cambrian to Mississippian age and are composedmainly of thin-bedded black to dark gray shale and chert with minor limestone and sandstone.The younger sequence consists of rocks of middle Mississippian to middle Pennsylvanian ageand is composed of interbedded black to dark gray shale and sandstone.1