PRELIMINARY GEOLOGIC MAP OF THE DILLWYN 30X60-MINUTE QUADRANGLE, VIRGINIA, USA

The Dillwyn 30x60-minute quadrangle encompasses a geologically diverse region of nearly 5,000 km², stretching from the Piedmont of central Virginia northwestward across several regional tectonic boundaries to the Blue Ridge and eastern Valley and Ridge Provinces. Supported by the U.S. Geological Survey’s National Cooperative Geologic Mapping Program and the Virginia Department of Energy, this 1:100,000-scale geologic map integrates data from a range of sources, including modern 1:24,000-scale quadrangle maps (30% of the area), unpublished EDMAP-supported mapping (10%), and legacy 1:62,500-scale maps (30%). Approximately 25% of the region lacked adequate geologic coverage, prompting new fieldwork to fill these gaps. LIDAR coverage has proven useful in many areas, highlighting poorly mapped bedrock stratigraphic and structural features, and in mapping surficial deposits. High-resolution airborne geophysical data is currently available only in the easternmost 10% of the map area, but data acquisition is underway for a new airborne survey that will eventually cover much of this area.

This quadrangle is notable for its mineral resources, including historic districts such as the Gold-Pyrite Belt, the James River iron-manganese district, the Schuyler-Alberene soapstone quarries, and the Arvonia slate district, which boasts one of the longest-operating mines in the United States. Renewed interest in critical mineral exploration highlights the economic importance of the region. The area also includes a large part of the Central Virginia Seismic Zone, an area of historic and recent seismicity.

The map will be released as a GEMs Level 3 geodatabase, offering a critical tool for understanding regional tectonics, resource distribution, and seismic activity. By synthesizing diverse datasets and providing new data in previously unmapped areas, this work advances regional tectonic synthesis, and supports ongoing mineral exploration and hazard assessment in central Virginia.