USING THE U.S. GEOLOGICAL SURVEY GEOTEK MULTI-SENSOR CORE LOGGER SYSTEM TO ANALYZE AND PRESERVE CORE FROM THE OLD HICKORY HEAVY MINERAL DEPOSIT, SOUTHEASTERN VIRGINIA

Researchers from the U.S. Geological Survey (USGS), the North Carolina Geological Survey, and the Virginia Energy Geology and Mineral Resources Program collected core from an unmined part of the Old Hickory heavy mineral (HM) sand deposit in Dinwiddie County, VA. Current mapping assigns paleoplacer sands and gravels to two units in the upper part of the Pliocene to Pleistocene Chesapeake Group that are considered near-shore marine deposits along paleoshorelines. Because host sediments are non-fossiliferous, there is little consensus as to their age, stratigraphic position, or nomenclature.

Our team aims to define and date the stratigraphy using cosmogenic nuclides, characterize sedimentary facies and mineralogy of the HM deposit, and determine its provenance using detrital zircon geochronology. For this study, a 44-ft-long core of Coastal Plain sediment and saprolite was graphically logged in the field and analyzed with the USGS GeoTek Multi-Sensor Core Logger System prior to sampling. For each 4-ft-long core section, high resolution (200 pixel/cm) imaging, magnetic susceptibility (MS) and portable XRF elemental data were collected at 1.5- to 1-cm intervals. This dataset provides unprecedented detail on the stratigraphy and geochemistry of the Old Hickory HM deposit and the host sands and gravels of the uppermost Coastal Plain.

XRF elemental abundances highlight significant correlations with MS measurements, core lithology, and mineralogy of the HM-enriched zones. For instance, higher Si total values relative to lower Al, K, and Fe values correlate with sand and gravel-rich beds in the core. Higher Al, K, and Fe values correspond to zones with higher clay contents. High MS readings correspond to melanocratic HM-enriched zones. High Ti and Zr values represent high concentrations of ilmenite, rutile, leucoxene and zircon. Some melanocratic zones are richer in Zr and P and suggest variable zircon and monazite content throughout the units. Elevated concentrations of Y correspond to some HM-enriched zones but are also present in higher concentrations in non-HM zones. Given that the core was heavily sampled for multiple analyses, the GeoTek system is an excellent tool for data preservation.

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