Sand Resources and Economic Heavy Minerals on
Virginia’s Continental Shelf
Virginia’s continental shelf contains potentially valuable resources of natural aggregates consisting mainly of unconsolidated sand and gravel. Natural aggregates are widely used in the transportation and building construction industries. Clean, quartz-rich beach-quality sand is required for beach restoration projects and coastal ecosystem protection. The recovery and utilization of marine aggregates can be cost-effective when sufficient volumes of high-quality material are available in deposits located relatively close to shore. Since about 1995, beach-quality sand has been dredged from two shoal deposits located in Federal waters managed by the U.S. Bureau of Ocean Energy Management (BOEM). The Federal Outer Continental Shelf Lands Act (OCSLA) authorizes BOEM to lease and regulate marine minerals seaward of the State–Federal boundary line located three nautical miles (nm) from shore.
In some areas of the continental shelf, offshore sediments are also known to contain disseminated heavy minerals that have value as industrial commodities. Heavy minerals include ilmenite (FeTiO3), rutile (TiO2), and zircon (ZrSiO4), among others that are characterized by specific gravity greater than about 2.9 (common quartz – not a heavy mineral – has a specific gravity of 2.65). Occurrences of these minerals reflect the geologic processes that have acted on bedrock and sediments in Virginia’s Coastal Plain – erosion, sediment transport, and deposition – combined with marine processes that have sorted and re-distributed the sediments on the continental shelf.
Geologists from the Virginia Division of Geology and Mineral Resources (DGMR) are working cooperatively with the U.S. Bureau of Ocean Energy Management (BOEM) to better define the location, extent, mineralogy, and grain size characteristics of marine mineral resources.
Coastal region of Virginia showing generalized on-shore surficial geology, continental shelf, and locations of Federal marine sand lease areas.
Investigations and Reports
In 2010-11, DGMR partnered with BOEM on State Cooperative Agreement M10AC20021 to build a database of geological and geophysical data pertaining to Virginia’s Outer Continental Shelf (OCS). The database includes information from vibracore samples, seafloor grab samples, side-scan sonar images, sub-bottom profile images, and available bathymetry. The data sources included DGMR archives, Virginia state agencies, federal agencies, and academic work groups. The project included a reconnaissance field survey and data collection in the Sandbridge Shoal area conducted August 3-5, 2011. A total of 93 grab samples were collected along with side scan sonar images at specific sample sites. Grain size analyses were completed for 90 samples and heavy mineral separation and mineralogical analyses were performed on 3 samples. The results of this work are documented in the Final Technical Report.
In May 2016, DGMR and BOEM completed a two-year initial round of studies as part of State Cooperative Agreement M14AC00013. Funding for the project was provided though the Hurricane Sandy rebuilding initiatives implemented under the Federal Disaster Relief Appropriations Act of 2013. The project study area encompasses the OCS region extending from the Virginia-Federal boundary at 3 nautical miles (nm) offshore to 8 nm offshore. The primary goal of the Cooperative Agreement is to improve the capability of Federal and State agencies and localities to plan for cost-effective coastal protection and restoration projects utilizing marine mineral resources on Virginia’s OCS in a manner that is protective of the environment.
Three reports are available for download:
- Grain size distribution and heavy minerals content of marine sands in Federal waters offshore of Virginia: Open-File Report 2016-0
- GIS compilation of geophysical data on Virginia’s outer continental shelf: Open-File Report 2016-02
- Digital conversion of geologic core data, modeling, and visualization of sand resources on Virginia’s continental shelf: Open-File Report 2016-03
The management of coastal environments has become increasingly important in the wake of sea-level rise. Coastal communities have turned to stabilization efforts to try and combat the erosive power of the ocean. Coastal stabilization is separated into two broad categories, hard stabilization and soft stabilization. Hard stabilization refers to the construction of hard structures such as seawalls, groins, and breakwaters. Soft stabilization refers to solutions not involving hard structures like dune creation, addition of vegetation, and beach sand nourishment. Many coastal communities in Virginia, including Virginia Beach, Wallops Island, and Chincoteague, have turned to beach nourishment as a viable option to maintain their beaches. Beach nourishment is a process that widens the existing beach by pumping sand, from elsewhere, onto the eroding shoreline. This process does not stop erosion; it just provides new sand for the erosive forces to “chew on”.
Virginia’s oceanfront is prone to coastal erosion from the impacts of seasonal hurricanes, tropical and winter storms, and nor’easters often with devastating effects to the natural coastal environments and the communities that depend on them. Shoreline protection and improved resiliency are vital to the economic growth and vitality of popular tourist destinations such as Chincoteague Island and Virginia Beach. Since 1951, the City of Virginia Beach has annually replenished beach sands along the city’s waterfront that are lost to the natural processes of longshore drift. To date, over 20 million cubic yards of dredged sand have been placed in the area known as Resort Beach (VA Beach, 2002). Initially sand was dredged from nearby Rudee Inlet and hauled by truck to the beachfront. In the mid-1990’s, the City of Virginia Beach and U.S. Army Corps of Engineers partnered in a long-term contract to manage dredging operations from nearby channels and offshore shoals. Sandbridge Shoal, a Federal sand lease area managed by the BOEM Marine Minerals Program has provided an estimated 9.3 million cubic yards of sand for beach nourishment programs at Virginia Beach and Sandbridge Beach. The dredged sand is pumped directly on the beach where it is spread and contoured to restore and stabilize the beach width and height.
Beach nourishment operations at Sandbridge Beach
(photo courtesy of Virginia Institute of Marine Science Shoreline Studies Program).
Recreational beaches are not the only vulnerable sites on Virginia’s coastline. NASA’s Wallops Flight Facility at Wallops Island and Naval Air Station Oceana Dam Neck Annex near Virginia Beach are also located along the Atlantic shore. In March 2013, NASA estimated the loss of about 20 percent of the beach and dune system fronting the Wallops Flight Facility as a direct consequence of Hurricane Sandy (NASA, 2013). Beach nourishment projects at Wallops Island completed in 2012 and 2014 utilized over 4 million cubic yards of marine sand dredged from shoals located offshore of the Delmarva Peninsula (BOEM, 2016).
Offshore Sand Resources
Marine sand deposits occur in a variety of settings including submerged shoals, lenticular sand sheets, and buried alluvial channels. Sand bodies that are considered suitable for dredging are identified on the basis of economic factors including the thickness and lateral extent of recoverable material, grain size and shape characteristics, suitable mineralogy, distance from shore, and the thickness of overburden. Equally important are environmental considerations to ensure the protection of sensitive benthic communities, marine faunal and floral habitats, minimizing post-dredging impacts on ecosystem services, and avoidance of archaeological and other restricted sites (military use, underwater cables, pipelines, etc.).
Economic Heavy Minerals
Offshore sand deposits often contain disseminated heavy minerals such as ilmenite (FeTiO3), leucoxene (altered ilmenite), rutile (TiO2), and zircon (ZrSiO4). These minerals are sources of titanium- and zirconium-oxides used in the manufacture of pigment for paints, plastics, ceramic glazes, and other industrial uses. Other minerals of potential economic interest include monazite ((Ce,La,Y,Th)PO4), sillimanite minerals (Al2SiO5), garnet ((Mg, Fe, Mn, Ca)Al2Si3O12), and high-purity silica quartz. Depending upon the concentration, extent, and mineral composition of these resources, economically viable deposits may be co-extracted with marine sand for beach nourishment, or possibly as stand-alone heavy mineral mining operations.
Past investigations have reported concentrations of one or more economic minerals in marine sand deposits that are comparable to those of onshore sand deposits presently mined in Dinwiddie and Greenville Counties (Berquist and others, 1990; DMME, 2016). In general, concentrations of about 5 percent or greater are considered of economic interest. The onshore deposits occur in Pliocene-age beach sand dunes that may have formed by wave action in much the same way as offshore sand shoals are formed.
Heavy minerals (dark areas in center of photo) concentrated by wave action on Sandbridge Beach.
Grain size distribution and heavy minerals content of marine sands in Federal waters offshore of Virginia: Open-File Report 2016-01
GIS compilation of geophysical data on Virginia’s outer continental shelf: Open-File Report 2016-02
Digital conversion of geologic core data, modeling, and visualization of sand resources on Virginia’s continental shelf: Open-File Report 2016-03
A final report describing the results of studies completed in cooperation with BOEMRE is in preparation and will be available in the near future. For more information about this project and on-going related studies, contact DGMR at 434-951-6340, or e-mail us at DgmrInfo@dmme.virginia.gov.
This work was supported by a grant from the U.S. Bureau of Ocean Energy Management, Regulation and Enforcement as part of the Marine Mineral Resource Evaluation Cooperative Program. For more information about this program, visit the BOEMRE web site.
Berquist, C.R. Jr. 1990, Heavy Mineral Studies- Virginia Inner Continental Shelf: Virginia Division of Mineral Resources Publication 103, 124 p.
Berquist, C. R., Jr., and C. H. Hobbs, III, 1988, Study of economic heavy minerals of the Virginia inner continental shelf: Virginia Division of Mineral Resources Open-File Report 88-4.
Dame, J.K. II, 1990, Origin of a solitary sand shoal offshore of Sandbridge Beach, Virginia: Unpublished Master's Thesis, College of William and Mary, School of Marine Science, Virginia Institute of Marine Science, Gloucester Point, Virginia, 94p.
Hobbs, C.H. III, 1990, Acoustic geology of a portion of Virginia's innermost continental shelf in: Berquist, C.R., Jr., ed., Heavy Mineral Studies - Virginia Inner Continental Shelf: Virginia Division of Mineral Resources Publication 103, p. 1-11.