USING GEOMORPHOLOGY, LIDAR AND GEOLOGIC MAPPING TO DEVELOP CONSISTENT PROTOCOLS FOR DEFINING FOCUS AREAS INCLUDED IN THE PLACER MINERAL SYSTEM ON THE ATLANTIC COASTAL PLAIN AND ADJACENT ENVIRONS OF THE SOUTHEASTERN USA (EAST REGION)

To transcend state boundaries and simplify the USGS catalog of Mineral Systems, Focus Areas, and Focus Area Identifiers for the EAST region of the U.S., we provide here a genetically-based, source-to-sink, depositional systems approach to classifying heavy mineral placer deposits associated with the southeast Atlantic Coastal Plain Province (ACP). Heavy minerals include ilmenite (FeTiO3), rutile (TiO2), zircon (ZrSiO4), and monazite (CePO4), which contain economically valuable critical commodities such as titanium, zirconium, and rare earth elements. Focus Area compartments are defined here using geomorphology (LiDAR) and detailed geologic mapping that includes correlation of alloformations between states and identification of common settings for regolith- and facies-controlled heavy mineral deposits.

The ACP includes a set of regionally extensive, relict Pliocene and Pleistocene paleoshorelines and marine terraces that step down in elevation and age to sea level; these are dissected by incised valleys that include sets of fluvial, estuarine and marine terrace deposits that are connected downstream to a marine terrace and associated paleoshoreline or the Holocene shoreline. Upstream, incised valleys of the Coastal Plain may transition into Piedmont alluvial systems. Each source to sink depositional systems tract includes source rocks and regolith, Piedmont source streams, a set of terraces in the connecting incised valleys, and a paleoshoreline/marine terrace complex. Placers may also occur as older in-place or reworked sedimentary facies (e.g. Cretaceous) that lack discernable geomorphic signatures. In the Fall Zone, regolith placers (weathered in-situ bedrock) may overlap with paleoshoreline generated placers.

The solution proposed here is to subdivide the Placer Mineral System for heavy minerals using geomorphology and detailed geologic mapping to identify the following compartments in the source to sink system: 1) paleoshorelines, 2) incised valley, 3) upstream alluvial (Piedmont), 4) regolith, 5) formation controlled (e.g. Cretaceous), and 6) the Holocene depositional system. Optimally, LiDAR should be used to map environmental geologic map units that will define depositional systems and their upstream and downstream landform elements.