HEAVY MINERAL ABUNDANCE IN OFFSHORE MUDDY FINE-GRAINED SANDS CONTAINING THE WORM TUBES SPIOCHAETOPTERUS COSTARUM

Over the past 3 years we have been analyzing large-volume grab samples from offshore of the Chesapeake Bay and Virginia Beach for potential beach nourishment quality and economic mineral content. The samples came from geotechnical studies supporting the proposed Virginia offshore wind farm and were located between 3 and 35 nautical miles from the shoreline. Supported by the U.S. Bureau of Ocean Energy Management (BOEM), we have made heavy mineral concentrates with a three-turn spiral for 95 samples with mineral identification and grain size completed for 60 samples. The average total heavy mineral (THM) abundance was 0.9%. In most of 7 samples where the total sand fraction consisted mainly of muddy fine- to very-fine sand (between 60 and 230 mesh) THM averaged 3.6% by weight with a maximum value of 9.8%. Most of these samples also contained abundant organic material including worms and worm tubes Spiochaetopterus costarum. The tubes are made of chitin and are about 1mm in diameter. The worm colonies have been observed elsewhere to range from 3 to almost 2700 individuals/m². Although the relationship between mineral abundance and organic-rich fine-grained sediment needs further research, we suggest that the worms tubes in dense colonies might provide bottom roughness to transported sediment and behave the same as a carpet or “miners moss” in a gold sluice, trapping the fine-grained heavy minerals.