EVALUATION OF OFFSHORE HEAVY MINERAL RESOURCES OF SOUTHERN DELAWARE

Heavy mineral samples from Pliocene and Pleistocene sand deposits offshore Delaware and onshore outcrops and beaches were analyzed to: 1) determine to what extent the deposits are economically viable; 2) to determine the extent to which heavy minerals can be used to ascertain provenance. Eight 15-20 ft vibracores from offshore Delaware were divided into 5ft sections to more accurately represent heavy mineral abundances at depth. In addition seven onshore Pleistocene outcrops and modern beaches were also sampled. All samples were wet sieved to isolate the sand fraction (grains < 2.00 mm but > 63 μm); then the sand was spiraled using a 3-turn Humphrey Spiral to produce a heavy mineral sand concentrate that could be analyzed for mineralogy. Actlabs determined the weight percent of each mineral by point counting a representative portion of each concentrate.

Total heavy mineral concentration in the cores ranges from 0.77% to 0.07% and is not correlated with core depth or location. Given current prices these concentrations are not economically valuable to mine, but a more focused expedition might uncover more abundant deposits. The proportions of sand, gravel, and mud were recorded to determine beach nourishment potential. The southernmost samples, which represent the Quaternary sheet sands, had the least gravel and mud and so have the highest potential for providing beach nourishment quality sand.

The sparse heavy minerals in the offshore Delaware deposits are dominated by ilmenite (28.88% to 77.06%), pyroxene/amphibole (0.04% to 41.46%), and epidote (0.02% to 11.87%). The beach samples contain minimal pyroxene/amphibole (0.47% to 3.59%) and epidote (0.98% to 3.42%) but have a higher average concentration of ilmenite (62.81% compared to 40.82%). The cores remained fairly consistent in composition with depth, but composition changes drastically with latitude. This trend is apparent even within the same formation. Based on initial findings, leucoxene (altered ilmenite enriched in titanium) increases in abundance towards the south (increased distance from the Delaware Bay mouth), while epidote decreases further south. These preliminary results suggest that transportation and alteration processes played a larger role than initially hypothesized in the heavy mineral composition offshore of southern Delaware.