17 Geological Surveys and Resource Mapping/Evaluation Studies

This session highlights studies from state geologic surveys and the U.S. Geological Survey regarding natural resource evaluations. We welcome submissions with relevance to critical minerals, rare earth elements, various energy sectors, and the construction industry.

Tuesday, 10 March 2026
8:30 AM - 10:00 AM
RCC, 103

Preliminary observations from USGS mapping in the eastern Piedmont of central Georgia

Paper number: 17-3
Program: Technical Sessions
Time: 8:52 AM – 9:07 AM

Authors

Abstract

The USGS has begun detailed geologic mapping on the USF&W Piedmont National Wildlife Refuge (PNWR) in the eastern Piedmont of central Georgia, for natural resource management and critical mineral studies.  Our study area comprises the southernmost end of the Charlotte terrane, north of the Pine Mountain window.  We recognize several upper amphibolite facies metaigneous and metasedimentary units. Multiple generations of granitoids are present in the northern and southern parts of the field area, whereas migmatitic biotite gneiss and amphibolite are the primary lithodemes in the central portion of the PNWR. Biotite gneiss and interlayered amphibolite are the oldest rocks and occur as outcrop- to map-scale xenoliths within granitoids.  Younger amphibolitized mafic dikes crosscut igneous contacts and older metamorphic fabrics and are variably transposed into the penetrative regional foliation.  These rocks may be feeder dikes to olivine gabbros of the Silurian-Devonian Concord-Salisbury Plutonic Suite that are present in the northern part of the field area. Strain is highly partitioned. Sigmoidal megalithons, 10s to 100s of m thick, of relatively low strain but still dextrally sheared rocks are bound by panels of northeast-southwest-striking, steeply dipping migmatitic mylonites. Greenschist facies overprint is sparsely localized and consists of white mica growth along foliation planes in some rocks, and static replacement of metagabbro by chlorite-talc-tremolite. 

All units host pegmatites and mineralogy varies by host rock. Pegmatites in metagabbro have feldspathic margins and quartz-muscovite cores; these have been mined for feldspar. Pegmatites in amphibolite commonly contain nonmagnetic metallic minerals. Granitoids tend to be deeply saprolitized, with variably thick overlying pedogenic regolith. Contacts between regolith, saprolite and fresh rock may be sharp or gradational over several to 10s of meters; where discernible, saprolite fronts are commonly vertical.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1

doi: 10.1130/abs/2026SE-411582

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