Why Are We Studying Offshore Sand Resources?

The Geology and Mineral Resources Program at the Virginia Department of Energy (Virginia Energy) has conducted investigations of mineral resources on the continental shelf offshore of Virginia since our initial partnership in 1985 with the U.S. Department of Interior, Minerals Management Service (MMS). The MMS was reorganized in 2010, and in 2011 the U.S. Bureau of Ocean Energy Management (BOEM) was created to manage federal offshore resources, including marine minerals such as sand and gravel. Recently completed work by Virginia Energy provides new information and data on deposits with compatible sand resources for use in coastal resilience projects. Additionally, potential economic heavy minerals that occur within marine sand deposits are at similar concentrations to historically mined heavy mineral sand placer deposits in the Virginia Coastal Plain. For additional information for projects pertaining to terrestrial placer deposits, please see our Earth Mapping Resources Initiative project page.

Coastal Resilience

Sand and gravel deposits are mined on land for natural aggregate and serve as vital material for construction activities in our communities. The supply and availability of onshore sand and gravel resources is constrained by several factors, most importantly the increasing costs of transporting material from the mine source to the end user, typically by truck or rail. Offshore sources of material located on the continental shelf in state and federal waters can be dredged and transported at relatively lower costs and can meet the increasing demands for larger quantities of sand. Offshore sand deposits also serve as emergency reserves for coastal restoration following natural disasters and help to provide mitigative measures against long-term shoreline erosion. This is especially critical in our coastal communities that face growing risks from tidal flooding, erosional damages caused by increased storm frequency and duration, and accelerated sea level rise.

Shoreline stabilization is a major concern in many areas of coastal Virginia, and various methods to accomplish this have included the construction of structural controls and barriers such as seawalls, groins, and breakwaters. In recent years, a more natural “living shoreline” approach has utilized vegetation plantings to enhance dune formation, and beach sand replenishment. Also known as “beach nourishment”, sand from a source area that meets certain textural and compositional requirements is dredged and transported to a beach that has been severely impacted by erosion. The source areas may include material dredged as part of channel maintenance, or from known sand deposits in state and federal waters. It is important to note that beach nourishment does not stop the erosive forces of the ocean, but rather provides a cost-effective means of reducing the risks associated with storms and flooding.

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 based on 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.). 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. Recently completed work provides new information about the thickness, lateral extent, and textural characteristics of potentially valuable deposits of clean, beach-quality sand that could be utilized to support coastal resilience projects (Figure 1; OFR 2019-02). Additional targeted sampling and geophysical data for offshore sand, gravel, and shell aggregate resources would provide data needed to help characterize sufficient areas that could be utilized for coastal resilience projects, benefiting local, state, and federal government stakeholders as well as private land holders.

Economic Heavy Minerals

Our studies have also identified economic heavy minerals that were deposited with offshore marine sediments in quantities ranging from trace amounts to over 10 weight percent. Heavy minerals have a specific gravity greater than about 2.9 g/cm³ (common quartz – not a heavy mineral – has a specific gravity of 2.65), and include ilmenite (FeTiO₃), leucoxene (altered ilmenite), rutile (TiO₂), zircon (ZrSiO₄), and monazite ((Ce,La,Y,Th)(PO₄)), among others. These minerals contain critical elemental commodities such as titanium (Ti), zirconium (Zr), and rare earth elements (REE) that have commercial value and are potentially recoverable as an integral part of beach nourishment operations.

Offshore sand deposits contain disseminated heavy minerals that 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 sillimanite minerals (Al₂2SiO₅), garnet ((Mg, Fe, Mn, Ca)Al₂Si₃O₁₂), and high-purity silica quartz (non-heavy mineral). Occurrences of these minerals reflect the geologic processes that have acted on Piedmont and Blue Ridge bedrock and sediments in Virginia’s Coastal Plain. Physical and chemical weathering, erosion, sediment transport, and deposition, combined with marine processes, have sorted and re-distributed sediments on the continental shelf. An example of this marine re-working and natural density separation is shown in the photo below. Depending upon the concentration, extent, and mineral composition of these resources, economically viable deposits could be co-extracted with marine sand for beach nourishment, or possibly as stand-alone heavy mineral mining operations.

Laboratory analysis of total heavy mineral (THM) concentrates from offshore samples has allowed for the quantification of the compositional variability of economic minerals, and the concentrations of the critical commodities they contain. The results also provide new information about grain size characteristics that, together with specific gravity and magnetic susceptibility, are important for the evaluation of recovery and separation methods.

To date, Virginia Energy has analyzed mineral concentrates from over 600 sediment samples for THM content. Mean THM content averaged approximately 3 percent by weight, with some concentrations upwards of 16 percent THM (Figure 2). Two percent of analyzed samples had THM concentrations greater than 10 percent by weight. The economic heavy mineral (EHM) portion (i.e., ilmenite, rutile, zircon, REE-bearing minerals) averaged about 42% of the THM. These concentrations compare favorably with known economic grades for onshore deposits that have been historically mined in the Coastal Plain of Virginia. Between 1997 and 2017, Iluka Resources, LLC recovered over 6 million tons of titanium- and zirconium-enriched heavy minerals from two separate deposits of Pliocene-age beach sand in Dinwiddie and Greensville Counties, Virginia (DMME, 2020). The estimated value of these concentrates was approximately $1.4 billion. These ancient beach sand deposits possibly represent an onshore analog to similar deposits located offshore.

Current Work

Our current BOEM-funded project is examining the capacity of recovering economic minerals containing Ti-Zr-REE from marine sand deposits during dredging and/or beach nourishment operations. Our primary goal in the study is to evaluate the benefits and drawbacks associated with offshore and onshore mineral separation methods. Methods consist of an extensive literature review of global heavy mineral placer operations, extraction and processing technologies, and permitting and regulatory considerations. Additionally, we are considering potential environmental impacts throughout the dredging, transport, and processing lifecycle. Virginia Energy convened a virtual forum in March 2022 to bring together a diverse group of stakeholders to facilitate information sharing, identify data needs, and discuss the current state of knowledge regarding the assessment and extraction of critical commodities from marine sand. A proceedings document with summaries and key takeaways from the forum is available here (OFR 2022-20).

To evaluate geochemistry and mineralogy for existing federal borrow/dredge areas, we are compiling historical mineral data (Figure 2) and examining and sampling vibracores from Sandbridge Shoal and the Atlantic Ocean Federal Navigation Channel offshore of Virginia Beach. We are using a Humphrey spiral (shown below) for gravity separation of these materials, and the concentrated fractions of high-density sands are being analyzed for modal mineralogy. Other tools include a handheld gamma spectrometer and portable x-ray fluorescence (XRF) analyzer for real-time field screening of major and trace element chemistry. Our final technical report will detail legal aspects, cost recovery potential, and stakeholder involvement required for heavy mineral sand separation during beach nourishment operations. Based on previous offshore sand mineralogy data, there is significant potential for the recovery of economic mineral resources offshore of Virginia that could offset the costs of dredging for beach sand nourishment projects. Please check out our Critical Minerals webpage for more information on economic heavy minerals.

Latest reports »

• Open File Report 2016-01 - Grain size distribution and heavy mineral content of marine sands in Federal waters offshore of Virginia.
• Open File Report 2019-02 – Assessment of offshore sand resources for beach remediation in Virginia.
• Open File Report 2019-03 – Economic heavy minerals on the continental shelf offshore of Virginia - new insights into the mineralogy, particle sizes, and critical element chemistry.
• Open File Report 2019-04 – Heavy mineral distributions in offshore sediments using Q-mode factor analysis.
• Open-File Report 2022-20 – Proceedings of the 2022 Mid-Atlantic Marine Heavy Mineral Sands Forum.

Acknowledgements
Funding for the sand and heavy mineral resource projects (open-file reports from 2016-2019) was provided by the U.S. Bureau of Ocean Energy Management (BOEM) under Cooperative Agreement M14AC00013 with additional funding from Virginia Energy. Funding for the capacity assessment study to assess recovery of economic minerals within marine sand deposits is provided by BOEM under Cooperative Agreement M21AC00010 with additional funding contributions from Virginia Energy. For more information about marine minerals on the Atlantic continental shelf, visit the BOEM web site.

Selected References:

Berquist, C.R., Jr., and C.H. Hobbs, III, 1986, Assessment of economic heavy minerals of the Virginia inner shelf: Virginia Division of Mineral Resources Open File Report 86-1. 13 p. and appendices.

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, 23 p. and appendices.

Berquist, C.R., Jr., [ed.], 1990, Heavy-mineral studies – Virginia inner continental shelf, Virginia Division of Mineral Resources Publication 103, 39 p. and appendices.

Berquist, C.R., Jr., [ed.], 2012, Heavy-mineral analysis of five samples: Addendum to sand resource evaluation on Virginia’s outer continental shelf coastal plain – Final technical report: Prepared for U.S. Bureau of Ocean Energy Management, Cooperative Agreement M10AC20021 for the performance period Sept 14, 2010, to Oct 31, 2011: 2 p. and Appendices.

Berquist, C.R., Jr., Lassetter, W.L., and Goodwyn, M.H., 2016, Grain size distribution and heavy mineral content of marine sands in Federal waters offshore of Virginia: Virginia Division of Geology and Mineral Resources Open File Report 2016-01, 22 p. and appendices.

Berquist, C.R., Jr., and Boon, J.D., 2019, Heavy mineral distributions in offshore sediments using Q-mode factor analysis: Virginia Division of Mineral Resources Open File Report 2019-04, 35 p.

Blanchette, J.S., and Lassetter, W.L., 2019, Assessment of offshore sand resources for beach remediation in Virginia: Virginia Division of Geology and Mineral Resources Open File Report 2019-02, 24 p. and Appendices.

DMME (Department of Mines, Minerals and Energy), 2012, Sand resource evaluation on Virginia’s outer continental shelf – Final Technical Report: Prepared for U.S. Bureau of Ocean Energy Management, Cooperative Agreement M10AC20021 for the performance period Sept 14, 2010 to Oct 31, 2011: 19 p.

DMME (Department of Mines, Minerals and Energy), 2020, Annual Production data reported to the Division of Mineral Mining.

Goodwyn, M.H., Enomoto, M.R., Lassetter, W.L., and Kuehl, S.A., 2016, GIS compilation of geophysical data on Virginia’s Outer Continental Shelf: Division of Geology and Mineral Resources Open File Report 2016-02. 10 p. and appendices.

Hawkins, D.W., and Lassetter, W.L., 2022, Proceedings of the 2022 Mid-Atlantic Marine Heavy Mineral Sands Forum: Virginia Geology and Mineral Resources Program Open File Report 2022-20, 21 p. and Appendices.

Lassetter, W.L., and Blanchette, J.S., 2019, Economic heavy minerals on the continental shelf offshore of Virginia - new insights into the mineralogy, particle sizes, and critical element chemistry: Virginia Division of Geology and Mineral Resources Open File Report 2019-03, 33 pp and Appendices.

Milligan, D.A., Kuehl, S.A., and Hardaway, C.S., 2016, Digital conversion of geologic core data, quality control, and preliminary assessment of sand resource area on Virginia’s Outer Continental Shelf: Virginia Institute of Marine Science, 14 p.

Other Resources:

Blanchette, J., and W.L. Lassetter, 2018, Marine mineral resources on Virginia’s outer continental shelf: quantifying sand deposits for coastal restoration and occurrences of economic heavy minerals [abs]: Geological Society of America Northeastern Sectional Annual Meeting, 17-20 March 2018, Burlington, VT.

Lassetter, W.L., Blanchette, J.S., and Holm-Denoma, C., 2019, Marine mineral resources on the continental shelf offshore of Virginia: new insights concerning economic heavy minerals: [abs]: Geological Society of America Southeastern Sectional Annual Meeting, 28-29 March 2019, Charleston, SC.