Titanium mineral resources in heavy-mineral sands in the Atlantic coastal plain of the southeastern United States
<p>This study examined titanium distribution in the Atlantic Coastal Plain of the southeastern United States; the titanium is found in heavy-mineral sands…
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Titanium Mineral Resources in Heavy-Mineral Sands in the Atlantic Coastal Plain of the Southeastern United States U.S. Department of the Interior U.S. Geological Survey Scientific Investigations Report 2018–5045
Cover. Upper left: Layered deposits of heavy-mineral sands exposed by an open-pit mine within the Trail Ridge complex, near the town of Starke in northeastern Florida. Lower right: A concentrate of heavy minerals created from the first-stage processing of a heavy-mineral sands deposit. The mineral concentrate is primarily ilmenite, an important source of titanium oxide and zircon, used in refractory products such as ceramics and tiles. Lower left: Modern deposits of heavy minerals (dark sediments) on a beach of Little Talbot Island near Jacksonville, Florida. Photographs by B.S. Van Gosen, August, 2017.
Titanium Mineral Resources in Heavy-Mineral Sands in the Atlantic Coastal Plain of the Southeastern United States By Bradley S. Van Gosen and Karl J. Ellefsen Scientific Investigations Report 2018–5045 U.S. Department of the Interior U.S. Geological Survey
U.S. Department of the Interior RYAN K. ZINKE, Secretary U.S. Geological Survey William H. Werkheiser, Deputy Director exercising the authority of the Director U.S. Geological Survey, Reston, Virginia: 2018 For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment—visit ://www.usgs.gov or call 1–888–ASK–USGS. For an overview of USGS information products, including maps, imagery, and publications, visit ://store.usgs.gov. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner. Suggested citation: Van Gosen, B.S, and Ellefsen, K.J., 2018, Titanium mineral resources in heavy-mineral sands in the Atlantic Coastal Plain of the southeastern United States: U.S. Geological Survey Scientific Investigations Report 2018–5045, 32 p., ://doi.org/10.3133/sir20185045. ScienceBase data release files that support this report are available at ://doi.org/10.5066/F7J38R16. ISSN 2328-0328 (online)
Contents Abstract 1 Keywords 1 Introduction 1 Heavy-Mineral Sands 3 Industrial Uses and Significance of Titanium and Zircon 8 Production of Titanium Mineral Concentrates and Industrial Applications 8 Industrial Applications of Zircon Derived from Heavy-Mineral Sands 8 Zircon Distribution in the Atlantic Coastal Plain 8 Outlook for Heavy-Mineral Sands Production 10 The Bedrock Provenance of Titanium Minerals 10 Lithologic Sources of Ilmenite and Rutile 10 Bedrock Sources of Ilmenite and Rutile in the Southeastern United States 11 The Atlantic Coastal Plain of the Southeastern United States 11 The Fall Zone 13 Heavy-Mineral Sands Mining Districts in the Atlantic Coastal Plain 13 The Jacksonville District 13 Deposits of Heavy-Mineral Sands along the Fall Zone in Virginia and North Carolina 15 HMS Deposits of the Lakehurst District, New Jersey 16 Previous Mineral Resource Assessments in the Atlantic Coastal Plain 16 Study Techniques 17 Geochemical Dataset 17 Geochemical Analyses 17 Data Processing 17 Study Results 18 Anomalous Area A 18 Anomalous Area B 18 Anomalous Area C 23 Anomalous Area D 23 Anomalous Area E 26 Summary and Conclusions 26 References Cited 28 Figures Map showing the extent of Upper Cretaceous and Cenozoic sediments of sand, gravel, silt, clays, and peat (yellow area) that form the Atlantic Coastal Plain of the southeastern United States 2 Schematic cross sections showing the features commonly used to describe shoreline depositional environments associated with heavy-mineral sands 5 Example of recently deposited heavy-mineral sands on a modern beach on Little Talbot Island, northeast Florida. A, Photograph of a layered deposit of heavy minerals on the shoreface; B, Photograph of a close-up view of heavy mineral layers in the area 6
Table
1. Common minerals in heavy-mineral sand deposits, listed in order of average specific gravity 4
4. A, Photograph of heavy minerals deposits that were brought from offshore sediments up to the beach by a strong storm surge along a shoreline of the Atlantic Ocean at Vero Beach, Florida. B, Heavy minerals (black sands) deposited in the foreshore of a modern beach on Little Talbot Island, northeastern Florida 7
5. Recent mining at the Trail Ridge deposits (Maxville mines) of the Chemours Company, located in northeastern Florida. A, open-pit (dry) mining. B, dredge mining 9
6. Relationships of rutile, ilmenite, and titanite (sphene) to the composition of metamorphic rocks and grade of metamorphism 10
7. Map showing the metamorphic and igneous rocks within the Piedmont Region and the Appalachian Mountains that are permissive bedrock sources for the ilmenite and rutile found in sediments of the Atlantic Coastal Plain 12
8. Map showing the location of notable deposits of heavy-mineral sands in the Jacksonville district of northeastern Florida and southeastern Georgia 14
9. Photograph of the Concord mine of Iluka Resources during dry-mining operation in November 2012 15
10. Map showing the mean titanium concentrations in the Atlantic Coastal Plain 19
11. Map showing standard deviation of titanium concentrations in the Atlantic Coastal Plain 20
12. Map showing the anomalous titanium concentrations in area A coastal plains sediments that border the Fall Zone in Georgia, from the Columbus area to the Augusta area 21
13. Map showing the anomalous titanium concentrations in area B, near the border between South Carolina and North Carolina 22
14. Map showing the anomalous titanium concentrations in area C, the upper and middle coastal plain of North Carolina 24
15. Map showing the anomalous titanium concentrations in area D, the coastal plain of Virginia 25
16. Map showing the anomalous titanium concentrations in area E, the outer coastal plain of South Carolina 27
Conversion Factors U.S. customary units to International System of Units Multiply By To obtain Length foot (ft) meter (m) mile (mi) kilometer (km) Area acre square kilometer (km2) International System of Units to U.S. customary units Multiply By To obtain Length meter (m) foot (ft) Mass gram (g) ounce, avoirdupois (oz) kilogram (kg) pound avoirdupois (lb) metric ton (t) ton, short (2,000 lb) metric ton (t) ton, long (2,240 lb) Abbreviations GIS Geographic Information System HMS heavy-mineral sands ICP-AES inductively coupled plasma-atomic emission spectrometry IP induced polarization NGS National Geochemical Survey (://mrdata.usgs.gov/geochem/) REE rare earth element U.S. United States USGS U.S. Geological Survey
Titanium Mineral Resources in Heavy-Mineral Sands in the Atlantic Coastal Plain of the Southeastern United States By Bradley S. Van Gosen and Karl J. Ellefsen Abstract This study examined titanium distribution in the Atlantic Coastal Plain of the southeastern United States; the titanium is found in heavy-mineral sands that include the minerals ilmenite (Fe2+TiO3), rutile (TiO2), or leucoxene (an alteration product of ilmenite). Deposits of heavy-mineral sands in ancient and modern coastal plains are a significant feedstock source for the titanium-dioxide pigments industry. Currently, two heavy-mineral sands mining and processing operations are active in the southeast United States producing concentrates of ilmenite-leucoxene, rutile, and zircon. The results of this study indicate the potential for similar deposits in many areas of the Atlantic Coastal Plain. This study used the titanium analyses of 3,457 stream sediment samples that were analyzed as part of the U.S. Geological Survey’s National Geochemical Survey program. This dataset was analyzed by an integrated spatial model ing technique known as Bayesian hierarchical modeling to map the regional-scale, spatial distribution of titanium concentrations. In particular, clusters of anomalous con centrations of titanium occur (1) along the Fall Zone, from Virginia to Alabama, where metamorphic and igneous rocks of the Piedmont region contact younger sediments of the Coastal Plain; (2) a paleovalley near the South Carolina and North Carolina border; (3) the upper and middle Atlantic Coastal Plain of North Carolina; (4) the majority of the Atlantic Coastal Plain of Virginia; and (5) barrier islands and stretches of the modern shoreline from South Carolina to northeast Florida. The areas mapped by this study could help mining companies delimit areas for exploration. Keywords Titanium resources, Atlantic Coastal Plain, heavy-mineral sands, stream sediments. Introduction This study examined the distribution of titanium (Ti) in deposits of ancient and recent sediments within the Atlantic Coastal Plain of the southeastern United States (U.S.), a broad flat plain along part of the eastern seaboard of the U.S bor dered on the east by the Atlantic Ocean. Large areas of the Atlantic Coastal Plain contain clastic sediments enriched in heavy minerals, “heavy-mineral sands,” representing sources of titanium, in the form of the minerals ilmenite (Fe2+TiO3), rutile (TiO2), and leucoxene (an alteration product of ilmenite). We used the titanium concentrations of 3,457 preexisting stream sediment samples that were analyzed as part of the U.S. Geological Survey’s (USGS) National Geochemical Survey (NGS) program (USGS, 2004). The samples selected for this study were those collected from stream channels associated with the coastal plain. Titanium concentrations in the stream sediments were used as a proxy for mapping the distribution of potential titanium resources within the coastal plain. The stream-sediment sample sites were well distributed across the study area. This dataset was analyzed by an integrated spatial modeling technique known as Bayesian hierarchical modeling to map the regional-scale, spatial distribution of titanium con centrations, which are related to ilmenite, leucoxene, and rutile abundances in heavy-mineral sands across the vast surface of the Atlantic Coastal Plain. Our study area for this report includes the region of the Atlantic Coastal Plain that extends from eastern Alabama and northern Florida to Virginia (fig. 1). This study builds upon an earlier geospatial study of the Atlantic Coastal Plain by Ellefsen and others (2015). That study was designed to map areas in the Atlantic Coastal Plain that appear most favorable for exploration and development of titanium minerals, zircon (ZrSiO4), and rare earth element (REE) resources (hosted in the minerals monazite and xeno time). Ellefsen and others (2015) integrated concentrations of titanium, zirconium (Zr), and REEs in the stream sediments (as proxies for titanium minerals, zircon, monazite and xeno time, respectively) with geological, geophysical, hydrological, and geographical data, as well a large set of airborne measure ments of equivalent thorium concentrations (as a proxy for
2 Titanium Mineral Resources in Heavy-Mineral Sands in the Atlantic Coastal Plain of the Southeastern United States Figure 1. Map showing the extent of Upper Cretaceous and Cenozoic sediments of sand, gravel, silt, clays, and peat (yellow area) that form the Atlantic Coastal Plain of the southeastern United States (modified from Gohn, 1988). Red dots indicate recent heavy-mineral-sands operations: (1) the Concord and (2) Brink mines of Iluka Resources in southeastern Virginia; (3) the Mission mine of Southern Ionics Inc. in southeastern Georgia; and the (4) Trail Ridge operations (Trail Ridge, Maxville, and Highlands deposits) of the Chemours Company in northeastern Florida. The “Fall Zone” (or “Fall Line”) is a regional term used to describe the contact zone between the lithified basement rocks of the Piedmont region on the west and much younger sediments of the Atlantic Coastal Plain on the east. WASHINGTON, D.C. RICHMOND Norfolk RALEIGH TALLAHASSEE NEW JERSEY DELAWARE MARYLAND VIRGINIA WEST VIRGINIA PENNSYLVANIA KENTUCKY TENNESSEE NORTH CAROLINA Wilson Laurinburg COLUMBIA Myrtle Beach Augusta Savannah Charleston Macon ATLANTA Jacksonville SOUTH CAROLINA GEORGIA FLORIDA ALABAMA Wilmington Fall Zone Fall Zone Piedmont region Atlantic Ocean Southern study area boundary Northern study area boundary Western study area boundary Gulf of Mexico Figure 8 Amelia Island Cumberland Island Cape Hatteras Little Talbot Island Appalachian
Mountai ns 200 KILOMETERS 80 120 160 200 MILES Base from ESRI ArcGIS, 2017 Geographic projection, decimal degrees Datum World Geodetic System 1984 (WGS 84) Map area 85° 80° 75° 40° 35° 30° Atlantic Coastal Plain Recent heavy-mineral-sands
operations with identifier EXPLANATION
Heavy-Mineral Sands 3 monazite and xenotime) (Hill and others, 2009). The study by Ellefsen and others (2015) established the foundation for this current investigation. Bayesian hierarchical modeling as used in the current study is a robust way to map both the titanium concentrations and their variability. This study has identified several areas where clusters of titanium-rich sediments occur within the Atlantic Coastal Plain. These clusters, described in this report, indicate areas that could be investigated for exploration of undeveloped titanium resources. An accompanying data release (Ellefsen, 2017) provides the raw data used in the analyses. This USGS data release can be accessed through ScienceBase at ://www. sciencebase.gov/catalog/item/59245249e4b0b7ff9fb2723b or ://doi.org/10.5066/F7J38R16. Heavy-Mineral Sands Ancient and modern coastal deposits of heavy-mineral sands (HMS) are sources of several “heavy” industrial minerals with mining and processing operations on many coastal regions worldwide (Van Gosen and others, 2014). For example, HMS deposits are a significant source of titanium feedstock for the titanium dioxide (TiO2) pigments industry. The titanium feedstock is extracted from the minerals ilmenite (Fe2+TiO3), rutile (TiO2), and leucoxene (an alteration product of ilmenite). HMS deposits are also the principal source of zircon (ZrSiO4), which is used mostly in refractory products. Sometimes monazite [(Ce,La,Nd,Th)PO4] is recovered as a byproduct mineral and is sought for the rare earth elements and thorium that it contains (Ault and others, 2016; Sengupta and Van Gosen, 2016; Van Gosen and Tulsidas, 2016). HMS are sediments containing dense (heavy) minerals that accumulate with sand, silt, and clay in coastal environ ments locally forming economic concentrations of heavy minerals. Economic (mined) HMS deposits include Holocene (Recent) sediments on modern coasts (such as examples in India and Brazil) (Van Gosen and others, 2014), as well as coastal deposits formed by transgressions and regressions of the seas during intervals in the Quaternary, Tertiary (Paleogene and Neogene), and Cretaceous (such as in Australia and the southeastern U.S.) (Gohn, 1988; Van Gosen and others, 2014; Hou and Keeling, 2017). Economic deposits typically contain heavy-mineral concentrations of at least 2 percent. Individual “heavy minerals” are commonly defined as minerals with a specific gravity greater than about 2.85 (table 1). These minerals are generally resistant to chemical weathering and physical degradation and thus survive well in fluvial and coastal environments. Heavy minerals in coastal HMS deposits may include, in order of general abundance: ilmenite, leucoxene, rutile, magnetite, zircon, staurolite, kyanite, sillimanite, tourmaline, garnet, epidote, hornblende, spinel, iron oxides (hematite, goethite, and limonite), sulfides (such as pyrite), anatase, monazite, cassiterite, and xenotime. Of these, ilmenite, leucoxene, rutile, and zircon are the primary economic minerals; garnet, staurolite, monazite, cassiterite, and xenotime are occasionally recovered as byproducts. The heavy minerals as a suite usually make up no more than 15 weight percent of a deposit, and most often much less; quartz grains and clay minerals generally form the bulk of the sediment. Typically, approximately 80 percent of a heavy-mineral suite is ilmenite, rutile, iron-oxide minerals, and zircon, with lesser amounts of leucoxene, monazite, garnets, sillimanite, and stau rolite. The geology of HMS deposits and examples of signifi cant districts are summarized in Van Gosen and others (2014). To form HMS deposits, heavy minerals are disaggregated from inland source rocks by weathering and erosion, and the detritus is transported by streams and rivers to coastal areas. Here, the sediments are deposited, reworked by the actions of waves, tides, longshore drift, and wind. These physical processes sort the light and heavy minerals based primarily on their density, thereby concentrating the heaviest minerals as layered sediments in a variety of coastal depositional environ ments. The principal zone of mineral separation is the upper part of the beach face, also known as the foreshore or swash zone (fig. 2). The heaviest grains, which have the highest settling velocities, are deposited at the bottom of the swash zone. Coarse low-density detritus is carried by backwash to the wave zone, whereas heavy minerals tend to settle out and accumulate on the upper beach face (Komar and Wang, 1984). HMS can accumulate in deltas, the beach face, sand dunes landward of the shore, the offshore (seaward of the beach), in barrier islands, and in tidal lagoons, as well as the channels and floodplains of rivers, streams, and estuarine channels; see Hou and Keeling (2017) for a discussion on various HMS dep ositional environments. Economic deposits of heavy-mineral sands represent innumerable thin layers of heavy-mineral accumulations separated by very small unconformities (fig. 3). Processes that one can observe now provide modern ana logues to the processes that are assumed to have formed the ancient deposits (figs. 3 and 4). That is, the natural processes that act upon coastal areas today, such as effects of waves, storm surges, tides, longshore drift, and a sediment supply from inland sources are assumed to be similar processes to those that formed HMS over thousands to millions of years ago along ancient shores across the world. Dozens of coastal deposits of HMS are serving as inter nationally important sources of some industrial minerals with active mining and processing operations on every continent except Antarctica (Van Gosen and others, 2014). Since about 2010, about 96 percent of the zircon, 90 percent of the rutile, 30 percent of the ilmenite, and 80 percent of the monazite pro duced by the global minerals industry was mined from coastal placer deposits of HMS (Australian Atlas of Mineral Resources, Mines, and Processing Centres, 2013). Ilmenite and rutile are the principal economic minerals derived from HMS, and zircon is typically recovered as a profitable coproduct. Australia and China are the major global producers of HMS (Australian Atlas of Mineral Resources, Mines, and Processing Centres, 2013). Recent exploration for HMS deposits has occurred in Australia, India, Kenya, Madagascar, South Africa, Sri Lanka, the U.S., and other countries (Van Gosen and others, 2014).
4 Titanium Mineral Resources in Heavy-Mineral Sands in the Atlantic Coastal Plain of the Southeastern United States Table 1. Common minerals in heavy-mineral sand deposits, listed in order of average specific gravity. “Heavy minerals” are generally defined as minerals that have a specific gravity greater than 2.85; leucoxene is an informal name for altered ilmenite. In nature, the specific gravity of a mineral varies from the mineral’s pure form due to impurities and alterations. The principal minerals of this study are shown in bold. For comparison, the common gangue minerals section lists other minerals most commonly mixed with the heavies in this deposit type, in particular, quartz. Hardness defined using Mohs hardness scale.—Continued Heavy minerals Ideal composition Specific gravity Hardness Color Stability in weathering Provenance Cassiterite SnO2 6–7 reddish, brown, yellow high Igneous rocks, pegmatites, hydrothermal veins Hematite Fe2O3 5–6 steel-gray, black low-moderate Igneous, sedimentary and metamorphic rocks Magnetite Fe3O4 5.5–6.5 black, dark gray moderate Igneous and metamorphic rocks, hydrothermal veins Pyrite FeS2 6–6.5 yellow low Igneous, sedimentary and metamorphic rocks, hydrothermal veins Monazite (Ce,La,Y,Th)PO4 4.9–5.5 5–5.5 brownish red high Igneous and metamorphic rocks Pyrolusite MnO2 2–6.5 black, dark gray low Sedimentary, hydrothermal, and secondary Ilmenite FeTiO3 5–6 black moderate-high Igneous and metamorphic rocks Zircon (Zr,Hf,U)SiO4 7.5–8 many high Igneous and metamorphic rocks Barite BaSO4 3–3.5 shades of white, yellow low Pegmatites, hydrothermal veins Xenotime YPO4 4.4–5.1 4–5 brown, yellow high Igneous and metamorphic rocks Goethite ɑFeO·OH 5–5.5 brown, yellow low Sedimentary and hydrothermal, weathering product Rutile TiO2 4.2–4.3 6–6.5 brownish red high Igneous and metamorphic rocks Corundum Al2O3 colorless, blue, red low-moderate Igneous and metamorphic rocks Uranothorite (Th,U)SiO4 4.5–5 reddish moderate Pegmatites, hydrothermal veins Leucoxene FeTiO3 to mostly TiO2 3.5–4.5 4–4.5 white to yellow-brown high Igneous and metamorphic rocks Anatase TiO2 3.8–4 5.5–6 many colors high Metamorphic rocks Staurolite Fe2Al9O6(SiO4)4(O,OH)2 3.7–3.8 7–7.5 brown high Metamorphic rocks Limonite FeO(OH)·nH2O 2.7–4.3 4–5.5 light brown low Oxidized zones of iron-bearing deposits Spinel MgAl2O4 3.6–4.1 7.5–8 black, blue, red low-moderate Igneous and metamorphic rocks Sphene/Titanite CaTiO(SiO4) 3.4–3.6 5–5.5 yellowish-green, brown moderate Igneous and metamorphic rocks Epidote Ca2(Al2Fe)(Si2O7)(SiO4)O(OH) 3.4–3.5 yellowish-green, green low Mostly metamorphic rocks, less in igneous rocks Clinozoisite Ca2Al3(Si2O7)(SiO4)O(OH) 3.3–3.4 green, gray, pink high Igneous and metamorphic rocks Garnets (Mg,Fe,Mn,Ca)Al2Si3O12 (general fomula) 3.1–4.3 7–7.5 colorless, all colors moderate Mostly metamorphic but igneous also Kyanite Al2SiO5 3.5–3.7 5.5–7 blue, white, gray, green, black high Metamorphic rocks, rarely in igneous rocks Sillimanite Al2SiO5 6.5–7.5 colorless, white, various colors high Metamorphic rocks, sometimes granite Andalusite Al2SiO5 3.1–3.2 6.5–7.5 pink to red brown high Metamorphic rocks Tourmaline (Ca,K,Na,)(Al,Fe,Li,Mg,Mn)3 (Al,Cr, Fe,V)6 (BO3)3(Si,Al,B)6O18(OH,F)4 3.0–3.3 black, various colors high Granitic pegmatites, some metamorphic rocks Apatite Ca5(PO4)3(F,Cl,OH) 3.1–3.2 white, yellow, brown high Igneous and metamorphic rocks, and pegmatite Hornblende Ca2(Mg, Fe, Al)5 (Al,Si)8O22(OH)2 2.9–3.4 5–6 black, dark green moderate Igneous and metamorphic rocks
Heavy-Mineral Sands 5 Table 1. Common minerals in heavy-mineral sand deposits, listed in order of average specific gravity. “Heavy minerals” are generally defined as minerals that have a specific gravity greater than 2.85; leucoxene is an informal name for altered ilmenite. In nature, the specific gravity of a mineral varies from the mineral’s pure form due to impurities and alterations. The principal minerals of this study are shown in bold. For comparison, the common gangue minerals section lists other minerals most commonly mixed with the heavies in this deposit type, in particular, quartz. Hardness defined using Mohs hardness scale.—Continued Common gangue minerals Ideal composition Specific gravity Hardness Color Stability in weathering Provenance Amphibole W0-1X2Y5Z8O22 (OH,F)2 (general formula) 2.85–3.6 5–6 dark green, dark brown, black low Igneous and metamorphic rocks Biotite K(Mg,Fe)3(AlSi3O10)(OH)2 2.8–3.2 2.5–3 blackish brown low Igneous and metamorphic rocks Muscovite KAl2(AlSi3O10)(OH)2 2.8–2.9 2–2.9 white, gray low Igneous and metamorphic rocks Quartz SiO2 colorless high Igneous and metamorphic rocks Kaolinite Al2Si2O5(OH)4 1.5–2 white low Igneous and metamorphic rocks Feldspars (K,Na,Ca)Al Si3O8 2.54–2.76 6–6.5 pink, white, gray, brown low-moderate Igneous and metamorphic rocks Figure 2. Schematic cross sections showing the features commonly used to describe shoreline depositional environments associated with heavy-mineral sands. Upper cross section: mainland beach depositional environment; the foreshore (the beach) is sometimes referred to as the “swash zone.” Lower cross section: barrier-tidal lagoon shoreline depositional environment (modified from Roy and others, 1994). Bedrock Sand dunes Sea or Ocean Shoreface Shoreface Sea or Ocean Sea Level rise Bedrock Foredune (Transgressive) Barrier Lagoon sediments Lagoon Sediments Foreshore High tide level Backshore
6 Titanium Mineral Resources in Heavy-Mineral Sands in the Atlantic Coastal Plain of the Southeastern United States Figure 3. Example of recently deposited heavy-mineral sands on a modern beach on Little Talbot Island, northeast Florida. A, Photograph of a layered deposit of heavy minerals on the shoreface; B, Photograph of a close-up view of heavy mineral layers in the area indicated by the arrow in 3A. The notebook is 7 inches tall for scale. Photographs by B.S. Van Gosen, 2017. A B The thin dark lines within the sand are examples of heavy-mineral layers.
Heavy-Mineral Sands 7 Figure 4. A, Photograph of heavy minerals deposits (black sands, indicated by arrows) that were brought from offshore sediments up to the beach by a strong storm surge along a shoreline of the Atlantic Ocean at Vero Beach, Florida (location: lat 27.6708°N., long –80.3570°W.). Hurricane Frances, a Category 4 hurricane (The Saffir–Simpson hurricane wind scale, SSHSW), hit this area on September 5, 2004, and deposited these concentrations of heavy minerals. Storms can bring heavy minerals from the shallow shoreface to the foreshore (most commonly referred to as “the beach,” fig. 2), where the actions of waves, tidal currents, and wind can mechanically sort the heavy minerals into layered deposits. Modern processes observed today on a wide variety of coastal environments provide direct analogues to the processes that formed the ancient heavy-mineral sands deposits. This view was photographed on September 8, 2004, by the U.S. Geological Survey St. Petersburg Coastal and Marine Science Center (accessed February 7, 2018, at ://coastal. er.usgs.gov/hurricanes/jeanne/site.php?storm_id=10&site_id=23&location_number=13). B, Heavy minerals (black sands) deposited in the foreshore of a modern beach on Little Talbot Island, northeastern Florida (see figs. 2 and 6). Yellow notebook is 7 inches in length for scale. Photograph by B.S. Van Gosen, September 2017. A B
8 Titanium Mineral Resources in Heavy-Mineral Sands in the Atlantic Coastal Plain of the Southeastern United States Industrial Uses and Significance of Titanium and Zircon Production of Titanium Mineral Concentrates and Industrial Applications Deposits of heavy-mineral sands are usually mined by surface operations involving dredging or dry surface mining techniques (fig. 5). Onsite gravity separation operations carry out the initial heavy-mineral separation utilizing the density contrasts between the light and heavy minerals by settling out the “heavies” from slurries of sediment-water mixtures. Fur ther processing and separation of the heavy-mineral suite are accomplished at specialized separation plants, usually offsite, using magnetic, electric, and electrostatic techniques. Ilmen ite and rutile are the two principal mineral concentrates for titanium, with ilmenite accounting for about 92 percent of the world’s consumption of titanium minerals (Bedinger, 2016a). Ilmenite is typically the most abundant titanium mineral in HMS deposits. It has a stoichiometric TiO2 content of 53 per cent, but intercalation and weathering causes the TiO2 content to vary significantly. After deposition in sediments, weathering enhances the TiO2 content of some titanium-oxide minerals. In particular, iron is leached from ilmenite by weathering, which thereby naturally upgrades the TiO2 content of the ilmenite (Force, 1991). Ideal rutile contains about 95 percent TiO2, but rutile is usually less abundant than ilmenite in HMS deposits. Ilmenite is often further processed to produce a titanium concentrate, either as synthetic rutile or titaniferous slag. Natu ral ilmenite usually contains about 55 to 65 percent TiO2 with the remaining content being iron oxide. Heating of ilmenite in a rotary kiln with air converts the iron to iron (III) oxide, while leaving a residue with at least 90 percent TiO2, known as synthetic rutile (Australian Atlas of Mineral Resources, Mines, and Processing Centres, 2007). Although numerous technolo gies are used to produce synthetic rutile, nearly all are based on either selective leaching or thermal reduction of iron and other impurities in ilmenite (Bedinger, 2013). Most titanium derived from the processing of ilmenite, rutile, and leucoxene is not consumed in its metal form but as titanium dioxide (TiO2). In powder form, TiO2 is a white pigment used in paints, paper, and plastics because it provides even whiteness, brightness, very high refractive index, and opacity (Woodruff and Bedinger, 2013). In 2015, on a gross weight basis, 95 percent of the U.S. domestic consumption of titanium mineral concentrates was used to produce TiO2 pig ment (Bedinger, 2016a). The remaining 5 percent, mainly from rutile, was used in welding-rod coatings and for manufacturing carbides, chemicals, and metal. For example, some rutile and leucoxene are blended to produce HiTi (High-grade titanium with a TiO2 content of 70 percent to 95 percent), which is used as a feedstock to produce titanium dioxide to make titanium metals for the aerospace industry and to manufacture weld ing rods (Woodruff and Bedinger, 2013; Bedinger, 2016a). Titanium metal, derived from processing rutile, ilmenite, and (or) leucoxene is also used in spacecraft, guided missiles, jew elry, artificial joints, and heart pacemakers to name a few. The estimated value of titanium mineral concentrates consumed in the U.S. in 2015 was $670 million (Bedinger, 2016a). Thus, titanium mineral concentrates obtained from HMS deposits are a significant contributor to the industrial minerals industry, and hence the U.S. economy. Industrial Applications of Zircon Derived from Heavy-Mineral Sands As noted earlier, more than 90 percent of the zircon (ZrSiO4) produced globally is obtained as a coproduct along with the separation of the titanium minerals from HMS deposits. Micronized zircon (zircon “flour”) offers high light reflectivity and thermal stability, and thus is used mostly in refractory products as an opacifier for glazes on ceramics such as tiles, and as foundry sands (Bedinger, 2016c; Zircon Industry Association, 2017). In 2015, the dominant end-use market for zircon was the ceramics industry, which accounted for about 50 percent of the total zircon market (Bedinger, 2016b, 2016c). Zircon flour is used in abrasives, chemicals, pharmaceuticals and medicine, nuclear fuel cladding, chemical piping in corrosive environments, heat exchangers, and also in various specialty metal alloys, food, welding rod coatings, cosmetics, lightweight warm and protective clothing, ballpoint pens, and wear-resistant knives (Bedinger, 2016c; Zircon Industry Association, 2017). Zircon Distribution in the Atlantic Coastal Plain Zircon is ubiquitous in the sediments of the Atlantic Coastal Plain. The study by Ellefsen and others (2015) found no obvious relationship between zirconium and titanium concentrations in stream sediments. Their study suggested that the geologic processes governing the distribution of zirconium in the Atlantic Coastal Plain (as a proxy for zircon) differ from those governing the distribution of titanium minerals. Our current study did not pursue an explanation for the complex distribution of zirconium (as a proxy for zircon) in the study area, nor did we notice an obvious spatial pattern. It is assumed that titanium minerals will be the principal miner als of economic interest in the coastal plain, and that zircon exists in sufficient quantities to be a coproduct commodity if titanium minerals are mined.
Industrial Uses and Significance of Titanium and Zircon 9 Figure 5. Recent mining at the Trail Ridge deposits (Maxville mines) of the Chemours Company, located in northeastern Florida (fig. 1). Photographs courtesy of Chemours Company. A, open-pit (dry) mining; B, dredge mining. Photographs taken in 2016. Used with permission. A B
10 Titanium Mineral Resources in Heavy-Mineral Sands in the Atlantic Coastal Plain of the Southeastern United States Outlook for Heavy-Mineral Sands Production We believe heavy-mineral sands will continue to serve as a major source of titanium oxide pigment, zircon sand for foundries, and zircon powder for ceramics because: Economic deposits are typically located at shallow depth or near the surface, buried by thin sedimentary/ regolith covers. The deposits currently mined are voluminous, typically comprising >10 million metric tons (t) of ore (the total size of the individual sand-silt body) and containing or 3 percent heavy-mineral content. The deposits are easy to excavate with most being mined today varying in coherence from unconsolidated to poorly consolidated, such that they are generally easily excavated and worked with heavy equipment. Well established, highly mechanized mineral-separation techniques are used at onsite plants that can process a continuous feed of high volumes of ore materials and efficiently perform the initial separation processes. The deposits can potentially supply several salable minerals as coproducts to the titanium minerals and zircon, such as staurolite, garnets, or monazite. The Bedrock Provenance of Titanium Minerals Lithologic Sources of Ilmenite and Rutile While many types of igneous rocks can contain acces sory ilmenite, studies indicate that metamorphic rocks of upper amphibolite facies to granulite facies are the principal source of ilmenite and rutile grains in placers (Force, 1991). Titanium-bearing silicate phases of titanite (sphene), biotite, and hornblende are the most stable titanium minerals in lower grade metamorphic rocks, while titanium minerals in oxide forms are those that are stable in higher grade metamorphic facies (fig. 6). Titanium in the rock becomes bound to tita nium oxide phases, ilmenite and rutile, as metamorphism progresses to higher temperature and pressure facies, specifi cally to sillimanite and higher metamorphic grades (Ramberg, 1948, 1952). Subsequent studies by Force (1976, 1991) and Figure 6. Relationships of rutile, ilmenite, and titanite (sphene) to the composition of metamorphic rocks and grade of metamorphism. Modified from Force (1991, his figure 2, p. 12). μ, chemical potential. Greenschist facies Chlorite zone Amphibolite facies Granulite facies Eclogite facies Biotite and garnet zones Kyanite and sillimanite zones Aluminous rocks (sillimanitekyanitestaurolite) “Normal” rocks (chlorite-biotitemuscovitegarnet) Calcic rocks (amphiboleclinopyroxenecalcite) Rutile + magnetite Rutile + titanite Ilmenite + titanite Titanite Titanite Titanite Titanite Titanite Titanite Ilmenite Titanite + ilmenite Titanite + ilmenite Titanite Titanite Titanite + ilmenite Titanite Ilmenite Ilmenite Ilmenite Rutile Rutile Rutile Rutile Ilmenite + rutile Ilmenite + rutile Rutile Rutile Rutile Rutile Rutile Increasing temperature and pressure Increasing µAl2O3/µCaO FeO/MgO high FeO/MgO low
The Atlantic Coastal Plain of the Southeastern United States 11 Goldsmith and Force (1978) confirmed this relationship. They describe the transformation of titanite (CaTiSiO5) to ilmenite (Fe2+TiO3) or rutile (TiO2), which involves the transfer of calcium from titanite to plagioclases and amphiboles during progressive metamorphism. As a result, in granulite-facies metamorphic rocks, ilmenite and rutile are by far the most common titanium minerals, while titanium-rich silicates (titanite, biotite, and hornblende) disappear (Force, 1976, 1991). As noted earlier, rutile can remain stable in metamor phic rocks of eclogite facies, while ilmenite disappears (fig. 6). In addition to a range of high-grade metamorphic rocks, ilmenite can occur in a broad variety of igneous rocks. Igneous rocks with the highest ilmenite content include anorthositeferrodiorite massifs and alkaline plutonic complexes (Force, 1991; Woodruff and others, 2013). In alkalic complexes, significant enrichments of ilmenite can occur in pyroxenites (Force, 1991; Woodruff and others, 2013). Lesser concentra tions of ilmenite, yet significant in total volume, can occur in some granitoids, basaltic rocks, and layered mafic intrusions. Woodruff and others (2013) describe economic and subeco nomic examples of magmatic ilmenite deposits in detail. According to Force (1980, p. 485), “…high-grade regional metamorphic terranes are the most important bedrock source of rutile…” and these rock types are the primary source of “… rutile [that is] sufficiently coarse to contribute sand-size grains to sediments.” For example, a study of metamorphic units in the Great Smoky Mountains of North Carolina Blue Ridge by Goldsmith and Force (1978) found that: (1) pelitic metamorphic rocks contain rutile grains only in zones of upper amphibolite facies (kyanite and sillimanite zones) and higher-grade meta morphism; and (2) a variety of metamorphic rocks of granulite and eclogite facies also contain rutile (fig. 6). While metamorphic rocks are substantial bedrock sources of rutile, studies by Force (1980, 1991) concluded that igneous rocks are not a significant source of rutile. Exceptions are: (1) some hydrothermally altered igneous rocks in which rutile forms as an alteration phase; (2) alkalic igneous rocks, including alkalic anorthosites; and (3) kim berlites. Force (1980, p. 486) stated that “…in fresh granitic rocks, rutile is extremely sparse.” In summary, the ilmenite grains in most HMS deposits were predominantly sourced by metamorphic rocks of sillimanite and granulite facies, with lesser contributions from a variety of igneous rocks. The bedrock sources of rutile are primarily meta morphic rocks of granulite and eclogite facies. Rutile is limited in occurrence in most igneous rocks, with the notable exception of alkalic igneous intrusions. These relationships are detailed by Force (1991) and summarized graphically in figure 6. Bedrock Sources of Ilmenite and Rutile in the Southeastern United States The western boundary of the Atlantic Coastal Plain abuts the Piedmont region of the southeastern U.S. (fig. 1). The Piedmont region is mountainous and hilly terrain that is between the Atlantic Coastal Plain and the Appalachian Mountains and extends approximately from southern New Jersey to central Alabama. Bedrock in this region, with contributions from the Appalachian Mountains farther west, have served for millennia as sources of detrital ilmenite, rutile, zircon, and other heavy minerals to the coastal plain. Extensive areas of the Piedmont region and the Appalachians contain rock types that are permissive as sources of ilmenite and rutile, including moderate- to high-grade metamorphic rocks (Espenshade and Potter, 1960), as well as several varieties of igneous intrusions (fig. 7). Metamorphic rocks in the Piedmont region and Appalachians Mountains that could contribute ilmenite and rutile grains to the Atlantic Coastal Plain include amphibolite and a variety of schists, gneisses, and metamorphosed igne ous rocks (as described on the State geologic maps compiled in Horton and others, 2017); specifically amphibole-schist, biotite-gneiss, meta-igneous (unspecific), biotite-schist, gneiss (unspecific), metatonalite, granulite, hornblende-gneiss, mica-schist, muscovite-gneiss, muscovite-schist, orthogneiss, pelitic schist, paragneiss, quartz-feldspar-schist, and schist (non-specific). To a lesser extent, igneous rocks of the Piedmont region and the Appalachians that are potential sources of ilmenite and rutile include alaskite, hornblendite, quartz diorite, alkali feldspar-syenite, leucocratic-granitic quartz monzonite, anorthosite, monzogranite, syenite, charnockite, monzonite, tonalite, diorite, norite, trondhjemite, granite (unspecific), pegmatite, ultramafic rocks, granodiorite, and pyroxenite. The Atlantic Coastal Plain of the Southeastern United States The Atlantic Coastal Plain of the U.S. (fig. 1) is composed predominantly of thinly layered sequences of weakly consoli dated clastic and carbonate sediments that are the products of numerous sea level transgressions and regressions during the Cretaceous (Owens and Gohn, 1985; Coffey and Sunde, 2014), the Tertiary (Paleogene and Neogene) (Segall and others, 1997), and the Quaternary (Pirkle and others, 1970; Toscano and York, 1992; Kulpecz, 2008; Parham and others, 2013; Pirkle and oth ers, 2013), as well as coastal and shoreline processes still active today (Roberts and others, 2013). The Atlantic Coastal Plain is a complex, diverse mosaic of sand, gravel, silt, clay, soils, and carbonate sediments in peneplains, stream and river channels, wetlands, tidal lagoons, offshore barrier islands, and many other coastal plain features (Whittecar and others, 2016). Deposits of HMS can occur in any of these depositional environments in a coastal plain. Clusters of titanium-rich HMS, regardless of depositional setting, were identified and mapped on a regional scale where they occur within the Atlantic Coastal Plain. Based on the mining history of HMS deposits in this region and the results of our study, we believe there may be substantial titanium mineral resources that remain in clastic sediments within the Atlantic Coastal Plain.
12 Titanium Mineral Resources in Heavy-Mineral Sands in the Atlantic Coastal Plain of the Southeastern United States Figure 7. Map showing the metamorphic and igneous rocks within the Piedmont Region and the Appalachian Mountains that are permissive bedrock sources for the ilmenite and rutile found in sediments of the Atlantic Coastal Plain. Geologic map units obtained from Horton and others (2017). WASHINGTON, D.C. RICHMOND Norfolk Jacksonville Melbourne TALLAHASSEE MONTGOMERY Columbus ATLANTA COLUMBIA Macon Savannah Brunswick Augusta Charleston Myrtle Beach RALEIGH Wilmington CHARLESTON FRANKFORT NASHVILLE WEST VIRGINIA KENTUCKY TENNESSEE Charlotte FLORIDA ALABAMA GEORGIA OHIO INDIANA NORTH CAROLINA VIRGINIA SOUTH CAROLINA MARYLAND DELAWARE Atlantic Coastal Plain Atlantic Ocean Gulf of Mexico Appalachian
Mountains Map area 85° 75° 80° 35° 30° 200 KILOMETERS 200 MILES EXPLANATION Igneous rocks Metamorphic rocks Base from ESRI ArcGIS, 2017 Geographic projection, decimal degrees Datum World Geodetic System 1984 (WGS 84)
The Atlantic Coastal Plain of the Southeastern United States 13 The Fall Zone “The Fall Zone” (or “Fall Line”) is a regional term used to describe the contact zone between the lithified basement rocks of the Piedmont region on the west and much younger sediments of the Atlantic Coastal Plain on the east (fig. 1). The age of the Atlantic Coastal Plain sediments along the Fall Zone range from Cretaceous to Tertiary in age; these Atlantic Coastal Plain sediments are derived predominantly from the erosion of bedrock of the Piedmont region and subsequent fluvial transport of the eroded sediment to the ancient coasts. Some of the sedi ments originated from bedrock sources farther to the west in the Appalachian Mountains (Darby and Tsang, 1987; Naeser and others, 2016). The package of sediments that overlie the base ment rocks in the Atlantic Coastal Plain range in thickness from thin wedges along the Fall Zone to as much as 3,000 meters (m) near Cape Hatteras, North Carolina (Trapp and Meisler, 1992). Heavy-Mineral Sands Mining Districts in the Atlantic Coastal Plain Many deposits of HMS have been identified in the Atlantic Coastal Plain, including more than a dozen deposits that have been mined. Three Atlantic Coastal Plain districts have seen the bulk of the HMS production and these districts are (1) the Jack sonville district in northeastern Florida and southeastern Georgia, (2) a sequence of deposits along the Fall Zone in southeastern Virginia, and (3) the Lakehurst district in southern New Jersey. The Jacksonville District The Jacksonville district encompasses a large region of Atlantic Coastal Plain environments around Jacksonville, Florida (fig. 8). Several known HMS deposits occur in this region; they range in age from Pleistocene to modern sedi ments (Force, 1991; Pirkle, Pirkle, and Reynolds, 1991). The evolution, geology, character, and mining history of the HMS deposits of the Jacksonville district are well described by Neiheisel (1962), Staatz and others (1980), Pirkle and others (1991), and Elsner (1997). The first commercial production of ilmenite concentrate from this district occurred in 1916, from a modern beach near Mineral City (now named Ponte Vedra) (Staatz and others, 1980; Elsner, 1997). HMS production in the district was active at many sites during the 1940s to 1960s. Larger production occurred during the 1970s, derived mainly from the Folkston, Boulogne, Trail Ridge, Highland, and Green Cove Springs deposits (Pirkle, Pirkle, and Reynolds, 1991). HMS production continued until 2005 at Green Cove Springs (Iluka Resources Ltd., 2017). Currently (as of 2017), HMS production continues along the Trail Ridge complex (includ ing the Highland and Maxville deposits), which is considered to be the largest HMS deposit of the southeastern U.S. HMS production is also currently active at the Mission mine in southeastern Georgia (fig. 8). For the last few decades, HMS in the U.S. have been principally produced by the Chemours Company opera tions (a spin-off from DuPont) located along “Trail Ridge” in northeastern Florida (figs. 1, 5, and 8). Their operations dredge mine and dry mine HMS deposits of the Trail Ridge complex to recover ilmenite, leucoxene, zircon, and staurolite; rutile is minor in amount. DuPont geologists discovered these depos its in 1947 and mining began in 1949 (Carpenter and others, 1953). DuPont began their open-pit mining and heavy-mineral processing facilities on the southern end of Trail Ridge, 7 kilo meters (km) east of the town of Starke, Fla. (fig. 8). Subsequent mining along Trail Ridge has accelerated in recent years by the Chemours Company, progressing along the ridge at several sites, terminating against the south side of U.S. Interstate High way 10; about 4 km east of Macclenny, Fla. Mining operations along Trail Ridge are open-pit mines using dredge and drymining techniques. The Trail Ridge complex is composed of medium-grained eolian sands interbedded with fine sands, silt, and layers of peat. Although the deposits vary in grade along strike and lat erally, the Trail Ridge deposits have an average heavy-mineral content of about 4 percent (Force and Rich, 1989). The Trail Ridge complex is 1 to 2 km wide and about 11 m thick on average. The entire geomorphologic feature of Trail Ridge extends from south to north for more than 200 km, extending from near Starke, Florida, to near Jesup in southeastern Geor gia (Neiheisel, 1962; Force and Rich, 1989; Pirkle, Pirkle, and Reynolds, 1991) (fig. 8). According to the analyses of Elsner (1997), the northern parts of Trail Ridge began as barrier islands and the southern part of the ridge formed as inland dunes. Elsner (1997) concluded that the Trail Ridge complex correlated with a global sea-level high 1.9±1 million years ago (Ma). Studies and descriptions of the Trail Ridge deposits include Creitz and McVay (1948), Spencer (1948), Pirkle and Yoho (1970), Pirkle and others (1971, 1977), Pirkle (1975), Force and Garnar (1985), Force and Rich (1989), Force (1991), and Elsner (1997). Descriptions of other HMS deposits of the Jacksonville district (fig. 8) include those for the Yulee (Pirkle and others, 1984); Altama (Pirkle and others, 1989); Cabin Bluff (Pirkle and others, 1991; Neiheisel, 1962); Cumberland Island (Smith and others, 1967); and Folkston and Amelia Island (Pirkle and others, 1993). Mining of HMS deposits also occurred near the modern eastern coastline of Florida to the south of the Jack sonville district (250 to 325 km to the south) near Melbourne (mined from 1939 to 1955), Winter Beach (1954 to 1965), and Vero Beach (1943 to 1963) (Pirkle, Pirkle, and Reynolds, 1991; Elsner, 1997; Staatz and others, 1980). In May 2015, Southern Ionics Inc. completed construc tion of its mineral sands processing plant near Offerman in Charlton County, Georgia, and began to process heavy-mineral concentrates from its Mission mine, which is also in Charlton County. In February 2016, Southern Ionics announced a curtailment of operations owing to a decreased demand for titanium concentrates (Bedinger, 2016b). The mine resumed operations at the Mission mine in 2017, conducting dry
14 Titanium Mineral Resources in Heavy-Mineral Sands in the Atlantic Coastal Plain of the Southeastern United States Figure 8. Map showing the location of notable deposits of heavy-mineral sands in the Jacksonville district of northeastern Florida and southeastern Georgia. The location symbols (red diamonds) do not reflect the size and shape of each deposit. Altama Mission Cumberland Island Little Talbot Island Ponte Vedra Jacksonville Amelia Island Folkston Yulee Cabin Bluff Boulogne Jacksonville Green Cove Springs Green Cove Springs Trail Ridge Highland Maxville Brunswick Folkston Macclenny Starke Jesup Offerman Atlantic Ocean St Johns River A tamaha River FLORIDA GEORGIA Map area 81° 82° 31° 30° EXPLANATION Heavy-mineral sand deposit and identifier Approximate location of Trail Ridge Trail Ridge 30 KILOMETERS 30 MILES Base from The National Map digital data,1:2,000,000, 2018 Universal Transverse Mercator projection Zone 17N
The Atlantic Coastal Plain of the Southeastern United States 15 mining to produce high-purity individual concentrates of ilmenite, leucoxene, rutile, and zircon for sale (staurolite is also recovered for possible future sale). This HMS deposit is thought to be a barrier island complex (Pirkle and others, 1993), about 1.2 to 1.5 km wide, which is located to the east of (and not part of) the Trail Ridge complex. Deposits of Heavy-Mineral Sands along the Fall Zone in Virginia and North Carolina Berquist (1987) was the first to recognize and report heavy-mineral-rich sand deposits in southern Virginia. His report prompted exploration for this deposit type in southeastern Virginia, leading to the discovery of the Old Hickory deposit (Newton and Romeo, 2006), which was subsequently mined by Iluka Resources until 1998 (Iluka Resources Ltd., 2013). The HMS deposits of this belt formed in the upper Atlantic Coastal Plain, just east of the Fall Zone in the contact zone between the basement rocks of the Piedmont region on the west and much younger sediments of the Atlantic Coastal Plain on the east (Berquist and others, 2015). Heavy-mineral sands in the western parts of the coastal plain of Virginia and northern North Carolina are interpreted to be Pliocene sedimentary deposits that formed during worldwide transgression-regression events between 3.5 and 3.0 Ma (Carpenter and Carpenter, 1991). At the end of 2015, Iluka Resources ended production of heavy-mineral concentrate at its two remaining operations in southeastern Virginia, the Concord mine in Sussex County and the Brink mine in Greensville County (figs. 1 and 9), and started remediating the mine sites in 2017 (Bedinger, 2016b; Iluka Resources Ltd., 2017). These HMS deposits are of Pliocene and possibly Miocene age, lying just east of the Fall Zone. Iluka Resources produced final products of chloride ilmenite, zircon, Figure 9. Photograph of the Concord mine of Iluka Resources during dry-mining operation in November 2012; mining ended here in late 2015. Located near the Fall Zone in south-central Virginia (see fig. 1), the mine excavated weakly consolidated Pliocene-age sand-silt deposits containing about 4 percent heavy minerals. The sediments were processed at nearby separation plants, extracting ilmenite, leucoxene, rutile, and zircon for sale. Photograph by B.S. Van Gosen, 2012.
16 Titanium Mineral Resources in Heavy-Mineral Sands in the Atlantic Coastal Plain of the Southeastern United States and staurolite from the Virginia operations. They reported that the HMS deposits contained an average HMS content of 4.4 percent, in which ilmenite composed about 64 percent of the heavy minerals and zircon composed about 16 percent. Along this same Pliocene-Miocene strandline within Virginia, Iluka Resources selected another proposed mine site called the Hickory deposit that did not reach production, located between the city of Richmond and the Concord mine to the south. Carpenter and Carpenter (1991) described this 160-kmlong northeast-trending zone of HMS deposits along the Fall Zone as the “North Carolina-Virginia heavy mineral belt.” The northern end of this belt includes the previously mentioned Old Hickory deposit, located 60 km south of Richmond, Virginia, and the belt’s southern end includes deposits located west of Wilson, N.C. (fig. 1) (Carpenter and Carpenter, 1991). On the basis of heavy-mineral estimates for 19 deposits within this belt, Carpenter and Carpenter (1991) calculated a total (semiquantitative) regional resource of 22.7 million metric tons of heavy minerals in 377.8 million metric tons of sand, with an average heavy-mineral content of 6 percent. Average mineral distribution within the heavy-mineral suite was estimated to be 60 percent ilmenite, 2.5 percent rutile, 12.5 percent zircon, 8.5 percent staurolite, 0.7 percent tourmaline, 3.0 percent kyanite, 1.3 percent sillimanite, and 11.5 percent other heavy minerals (mostly limonite) (Carpenter and Carpenter, 1991). HMS Deposits of the Lakehurst District, New Jersey From 1962 to 1982, the Lakehurst district near the city of Lakehurst, southern New Jersey (outside of this study area), was a principal supplier of altered ilmenite, which was produced by two companies that mined from open pits in the Neogene Cohansey Sand. Its highest-grade intervals are about 5-m thick and contain 5–25 percent heavy minerals (Puffer and Cousminer, 1982; Force, 1991). Carter (1978) determined that the Cohansey Sand is most enriched in heavy miner als near the top of the swash zone along the Tertiary beach. Puffer and Cousminer (1982) suggested that the sands were deposited during a period of erosion between the Miocene and Pliocene resulting in a unit dominated by altered ilmenite (85 percent), as well as containing zircon (7 percent), sillimanite (3 percent), staurolite (1 percent), and tourmaline (1 percent) (Puffer and Cousminer, 1982). Previous Mineral Resource Assessments in the Atlantic Coastal Plain Several earlier studies have evaluated the potential for HMS deposits in the Atlantic Coastal Plain. Most of these studies analyzed data from geophysical surveys or geochemical surveys, or both. Initial screening for prospective areas of HMS principally utilized regional-scale data collected as (1) total count and spectral gamma-ray aeroradiometric data; and (2) reconnaissance stream sediment geochemical data. Measurements of radioactivity, whether collected by airborne or by on-the-ground methods, are often used in HMS exploration to detect the presence of monazite, the rare earth elements (REE)-thorium-phosphate mineral [(REE,Th) PO4]. Monazite is usually the heaviest of the heavy-mineral suite in coastal sands and thus an indicator of the presence of HMS deposits. Although monazite typically occurs in modest amounts in the coastal sediments (usually no more than 4.4 to 5.5 weight percent (Grosz and others, 1992; Bern and others, 2016), its concentrations are usually adequate to be detected and mapped by airborne radiometric surveys when they are within a few centimeters of the surface (Grosz and Schruben, 1994; Shah and others, 2017). Monazite accumulations in the Atlantic Coastal Plain represent potential sources of the light rare earth elements (Bern and others, 2016; Shah and others, 2017) and thorium (Ault and others, 2016). Geochemical surveys, such as analyses of stream sedi ments, have been used to identify areas of shallow HMS deposits, as described by Grosz (1993) and Grosz and Schruben (1994). The potentially commercial heavy miner als, which include ilmenite (FeTiO3), rutile (TiO2), zircon [(Zr,Hf,U)SiO2], monazite [(La,Ce,Th)PO4], and xenotime (YPO4) can be identified in stream sediments by concen trations of titanium, zirconium, hafnium (Hf), and REEs (Lanthanum [La], Cerium [Ce], Neodymium [Nd], Samarium [Sm], Dysprosium [Dy], Ytterbium [Yb], and Yttrium [Y]). Examples of reconnaissance HMS studies in the Atlantic Coastal Plain include the following: To explore for HMS deposits in the vicinity of Charles ton, S.C., Force and others (1982) created contoured maps of aeroradioactivity data using data that were recently (the early 1980s) collected by airborne surveys financed by the Coastal Plains Regional Commission and contracted by the USGS. Their study tested this method for mapping this type of data for exploration. The study identified 14 HMS accumulations in the Charleston area in “sands of old beach complexes,” which were confirmed by field checking sites where totalcount anomalies were found in the airborne-collected radio activity data. A study of the HMS deposits of the coastal plain in Virginia by Grosz (1983) applied total-count aeroradiometric maps as a technique to explore for HMS. His study found that when surveyed on the ground, HMS accumulations produce radiometric spectra of intermediate to low intensity with thorium producing the strongest radiation component and with lesser contributions from uranium and potassium. Wynn and Grosz (1985) carried out a study of the induced polarization (IP) response of fossil beach HMS deposits in northeastern Florida (Green Cove Springs and Trail Ridge). They found that IP response over these deposits “is unusually strong,” suggesting that the IP method could be used as a field evaluation tool. Their field and laboratory studies on sediment and stockpile samples indicated that altered ilmenite has a strong IP response while that of rutile is weak. In the northern peninsular and panhandle of Florida, Grosz and others (1989) used total count and spectral
Study Techniques 17 gamma-ray aeroradiometric maps followed by field investi gations of radiation anomalies to locate and evaluate HMS deposits. Radiation anomalies, whether associated with fluvial or marine HMS, showed that radiometric spectra are domi nantly due to thorium radiation. Along the inner coastal plain in North Carolina, adjacent to the Fall Zone, Grosz and others (1992) sampled sediments in areas that were identified as high gamma-ray anomalies by aero radiometric surveys. Auger samples from these sites revealed relatively high concentrations of ilmenite, rutile, zircon, mona zite, and minor gold in Cretaceous sediments, with much lower concentrations of heavy minerals in post-Cretaceous sediments. Two recent studies by Bern and others (2016) and Shah and others (2017) focused on assessing the potential REE resources in the Atlantic Coastal Plain by integrating aerora diometric data, mineralogical data, geology, and stream sedi ment geochemistry. The REE resources occur in the form of the minerals monazite and xenotime. Radiometric equivalent thorium (eTh) was shown to be useful as a proxy for locat ing monazite and xenotime. These two studies demonstrated how incorporating large digital datasets in tandem, such as geophysical, geochemical, and geologic information could be used to locate prospective HMS deposits. Using Geographic Information System (GIS), statistical, and geospatial tools can greatly assist exploration by allowing the display, query, and integrated analysis of multiple, geologically associated factors. The potential for heavy minerals resources deposited offshore of the Atlantic Coast of the U.S. was examined by Grosz (1987). He reported that “studies based on surficial grab samples suggest an average of [approximately 2 weight-per cent heavy minerals] in Atlantic continental shelf sediments” (Grosz, 1987, p. 339). Sediments offshore of the East Coast of the U.S. remain (as of 2017) an undeveloped potential source of heavy minerals. Similarly, many inlets, bays, and estuaries along the Atlantic Coast of the U.S. have been demonstrated to host sediments rich in heavy minerals. Examples include inlets and deltaic areas near Charleston, South Carolina (Shah and Harris, 2012), the Savannah River, South Carolina (Neiheisel, 1976), and the Chesapeake Bay of Maryland (Shah and others, 2012). Study Techniques Geochemical Dataset The titanium concentrations were obtained from the USGS National Geochemical Survey database (U.S. Geological Survey, 2004). Titanium concentrations were mea sured in stream sediment samples collected within the Atlantic Coastal Plain of the southeastern U.S.; this area includes parts of Virginia, North Carolina, South Carolina, Georgia, Florida, and Alabama. The number of samples, and hence the number of concentrations, is 3,457. Ellefsen (2017) compiled the data set that was used in this study. Geochemical Analyses Inductively coupled plasma-atomic emission spec trometry (ICP-AES) was used to measure concentrations in milligrams/kilogram (mg/kg, which is equivalent to parts per million [ppm]) for 40 different elements, including titanium, in the 3,457 stream sediment samples in our dataset. Prior to ICP-AES analyses, each sample was dissolved in a mixture of hydrochloric, nitric, perchloric, and hydrofluoric acids. Additional information about the ICP-AES method is found in Briggs (2002) and U.S. Geological Survey (2004). None of the titanium concentrations in our dataset had values below the reporting limits for the ICP-AES technique, which is 50 mg/kg. Thus, our dataset (Ellefsen, 2017) contains no censored data. The titanium concentrations range from a low value of 100 mg/kg to a high value of 20,920 mg/kg. The concentrations are relative to the bulk stream sediment sample, not just the heavy-mineral fraction of it. Data Processing The titanium concentrations are a type of compositional data, which have special properties making it difficult to directly analyze them (Pawlowsky-Glahn and others, 2015). Consequently, the titanium concentrations are transformed to a real-valued, linear vector space (that is, Cartesian coordi nates) using the isometric log-ratio transform. Preliminary analysis of the transformed concentrations shows that both the mean and the variance change across the study area. In statistical terminology, the transformed concentrations are non-stationary. A statistical model of these transformed concentrations must account for the spatial properties of the data, its nonstationarity, and the moderately large number of measurements. We are unaware of any existing model that accounts for these three characteristics, so we built a new model, which uses basis functions to account for these three characteristics. The model is formulated as a Bayesian hierarchical model. The parameters in the model are estimated using Hamiltonian Monte Carlo sampling. The sampling is checked using various numerical and graphical measurements to ensure that the sampling is done properly. In addition, the parameters are used to generate maps of the mean and the variance across the survey. These maps are then checked to ensure that they are geologically plausible. Although the mean and variance are estimated from the transformed concentrations, they are back-transformed to the equivalent statistics for concentrations, namely compositional center and compositional total variance (Pawlowsky-Glahn and others, 2015, p. 108–112). In the remainder of this report, the compositional center will be called the “mean titanium concentration” or just “mean,” and may be interpreted as an average. The square root of the compositional total variance will be called the “standard deviation of the titanium concen tration,” and may be interpreted as the spread of the concentra tions around the mean.
18 Titanium Mineral Resources in Heavy-Mineral Sands in the Atlantic Coastal Plain of the Southeastern United States Study Results Along the Fall Zone from Virginia to Alabama, anomalous concentrations of titanium exist in sediments (fig. 10), which is a reflection of enrichments in detrital ilmenite, leucoxene, and rutile. This relationship concurs with the results of recent studies by Bern and others (2016) and Shah and others (2017), which found that the highest concentrations of monazite and xenotime (potential sources of REEs) occur primarily along the Fall Zone. Our study outlined several other areas in the Atlantic Coastal Plain where the mean titanium concentrations are anomalously high. For discussion purposes, these areas are designated as anomalous areas A to E (labeled on figs. 10 and 11). We suggest that these areas A to E with the highest (most anomalous) titanium concentrations are regions where exploration for ilmenite-, leucoxene-, and rutile-bearing HMS deposits could be focused. These areas are described sepa rately in the sections that follow. The standard deviation in the titanium concentrations is mapped in figure 11. Standard deviation is highest in the southern areas of the study area, including southern Georgia, southeastern Alabama, and northern Florida, as well as the northern part of the study area in northern Virginia (fig. 11). Areas with high standard deviations have relatively high uncertainty in the titanium concentrations, which increases risk when exploring for ilmenite-, leucoxene- and rutilebearing HMS deposits. There are limitations to the maps shown in figures 10 and 11. The samples are derived from stream sediments, which are composites of soils and sediments that were eroded from the land surface within the respective watershed. Consequently, the properties of the stream sediments do not necessarily reflect the properties of the sediments that are below the land surface. This limitation is one reason that the HMS depos its in northeastern Florida and southeastern Georgia (fig. 8) do not appear as anomalies in the map of the mean titanium concentration (fig. 10). Specifically, the map does not show anomalous titanium concentrations at the areas of economic HMS deposits in the Trail Ridge complex (Trail Ridge, High land, and Maxville mines), nor areas near other Pleistocene ridge systems represented by the Green Cove Springs deposit and the Mission mine deposit. However, the mean titanium concentrations are high along the coastline near Jacksonville, Fla. (fig. 10). These anomalies are associated with Quaternary sediments, such as the HMS deposits of Cumberland Island, Amelia Island, and Little Talbot Island (fig. 8). In this case, the stream sediments probably include high concentrations of ilmenite, leucoxene and rutile, which are even visible on the beaches (figs. 3 and 4). The second limitation is spatial resolution. That is, the maps (figs. 10 and 11) are spatially smooth representations of the actual titanium concentrations. Consequently, features with small spatial scale (that is, less than about 10 km) may not be discernible in the maps. This limitation is another reason that Trail Ridge, which is 1 to 2 km wide, does not appear as an anomaly on the map of mean titanium concentration (fig. 10). Anomalous Area A Coastal plains sediments that border the Fall Zone in Georgia, from the Columbus area to the Augusta area (fig. 12), contain anomalous concentrations of titanium in Cretaceous and Tertiary sediments of the coastal plain. The standard devi ation in the titanium concentrations is generally low across this region of the Atlantic Coastal Plain (fig. 11), indicating low variation around the mean concentrations. The Piedmont region along the Fall Zone in Georgia is dominated by gneiss and granite (fig. 12), which are likely sources of detrital grains of ilmenite and rutile in this area of the coastal plain. Areas with a high probability of HMS in the Augusta area of Georgia and South Carolina were also recognized by Grosz (1993) and Grosz and Schruben (1994). Anomalous Area B Anomalous area B, near the border between South Carolina and North Carolina (fig. 13), contains a zone of anomalous concentrations of titanium in Cretaceous and Tertiary sediments, as well as along a paleovalley that carried titanium minerals from the Piedmont to a Pleistocene-age paleo-shoreline in South Carolina. The standard deviation in the titanium concentrations is generally low across this region of the Atlantic Coastal Plain (fig. 11), indicating low variation around the mean concentrations. It must be noted that the geologic mapping of the Cretaceous and Tertiary sedimentary deposits of the Atlantic Coastal Plain in this region is not consistent (thereby not defin itive), as shown in figure 13. Interpretations of the Atlantic Coastal Plain map units, in particular differences in the interpreted age of the lithologies, differ considerably between the State geologic maps of South Carolina and North Carolina (see Horton and others, 2017). For example, lithologic units that cross the state border in South Carolina are Pliocene in age, but are mapped as Cretaceous in age in adjacent North Carolina. Resolving these age differences is beyond the scope of this study. We can say that anomalous titanium concentra tions were found in coastal sediments in this region that have been mapped variously as Cretaceous and as Tertiary in age. This anomalous region extends as much as 100 km to the east of the Fall Zone in North Carolina. The Piedmont region bedrock units adjacent to anomalous area B contain a relative paucity of high-grade metamorphic rocks. Two granitic plu tons lie along the Fall Zone (fig. 13), which could have sup plied some of the ilmenite and (or) rutile to the upper coastal plain. More likely, most of the detrital titanium minerals were transported to the Fall Zone from metamorphic complexes in the distant Appalachian Mountains (fig. 7) during the Creta ceous. The studies of Grosz and others (1992), Grosz (1993), and Grosz and Schruben (1994) also recognized areas with a high probability of HMS deposits along the Fall Zone in the region of the South Carolina-North Carolina boundary. A drainage basin now occupied by the Pee Dee River and its tributaries (fig. 13) carried and deposited titanium-bearing
Study Results 19 Figure 10. Map showing the mean titanium concentrations in the Atlantic Coastal Plain. Labels A to E designate areas of anomalous concentrations of titanium. A, upper coastal plain along the Fall Zone in Georgia (fig. 12); B, area near the border between South Carolina and North Carolina (fig. 13); C, upper and middle coastal plain of North Carolina (fig. 14); D, The majority of the coastal plain in Virginia (fig. 15); E, the outer coastal plain of South Carolina (fig. 16). WASHINGTON, D.C. RICHMOND Norfolk Jacksonville Melbourne TALLAHASSEE MONTGOMERY Columbus ATLANTA COLUMBIA Macon Savannah Brunswick Augusta Charleston Myrtle Beach RALEIGH Wilmington WEST VIRGINIA KENTUCKY TENNESSEE Charlotte FLORIDA ALABAMA GEORGIA OHIO NORTH CAROLINA VIRGINIA SOUTH CAROLINA MARYLAND DELAWARE Atlantic Ocean Gulf of Mexico A B E D 85° 75° 80° 35° 30° 200 KILOMETERS 200 MILES Base from ESRI ArcGIS, 2017 Geographic projection, decimal degrees Datum World Geodetic System 1984 (WGS 84) EXPLANATION Mean Titanium Concentration Letters A–E indicate areas of
anomalously high titanium
concentrations Highest Lowest E Map area
20 Titanium Mineral Resources in Heavy-Mineral Sands in the Atlantic Coastal Plain of the Southeastern United States Figure 11. Map showing standard deviation of titanium concentrations in the Atlantic Coastal Plain. Labels A to E designate areas of anomalous concentrations of titanium. A, Upper coastal plain along the Fall Zone in Georgia (fig. 12); B, area near the border between South Carolina and North Carolina (fig. 13); C, upper and middle coastal plain of North Carolina (fig. 14); D, the majority of the coastal plain in Virginia (fig. 15); E, the outer coastal plain of South Carolina (fig. 16). WASHINGTON, D.C. RICHMOND TALLAHASSEE MONTGOMERY Columbus ATLANTA COLUMBIA Macon Augusta RALEIGH WEST VIRGINIA KENTUCKY TENNESSEE Charlotte FLORIDA ALABAMA GEORGIA OHIO NORTH CAROLINA VIRGINIA SOUTH CAROLINA MARYLAND DELAWARE Atlantic Ocean Gulf of Mexico A B E D Norfolk Jacksonville Melbourne Savannah Brunswick Charleston Myrtle Beach Wilmington 85° 75° 80° 35° 30° 200 KILOMETERS 200 MILES Base from ESRI ArcGIS, 2017 Geographic projection, decimal degrees Datum World Geodetic System 1984 (WGS 84) E EXPLANATION Standard deviation Highest Lowest Letters A–E indicate areas of
anomalously high titanium
concentrations Map area
Study Results 21 Figure 12. Map showing the anomalous titanium concentrations in area A coastal plains sediments that border the Fall Zone in Georgia, from the Columbus area to the Augusta area and contain anomalous concentrations of titanium in Cretaceous and Tertiary sediments of the coastal plain. The standard deviation in the titanium concentrations is generally low across this region of the Atlantic Coastal Plain (see fig. 11), indicating low variation around the mean concentrations. Refer to figure 10 for spatial reference within the larger Atlantic Coastal Plain region. Geologic map units from Horton and others (2017). S O U T H
AROL IN A ATLANTA Macon Augusta Columbus ALABAMA GEORGIA GEORGI A Fall Zone 85° 84° 83° 82° 34° 33° 32° 75 KILOMETERS 75 MILES Base from ESRI ArcGIS, 2017 Geographic projection, decimal degrees Datum World Geodetic System 1984 (WGS 84) Map area EXPLANATION Gneiss Granite Anomalous titanium content Approximate outline of
anomalous area Coastal plain sediments
22 Titanium Mineral Resources in Heavy-Mineral Sands in the Atlantic Coastal Plain of the Southeastern United States Figure 13 (continued on following page). Map showing the anomalous titanium concentrations in area B, near the border between South Carolina and North Carolina, which contains a zone of anomalous concentrations of titanium in Cretaceous and Tertiary sediments, as well as along a paleovalley that carried titanium minerals from the Piedmont to a Pleistocene-age paleo-shoreline Darlington Bennettsville Lauringburg Rockingham Marion Camden COLUMBIA Myrtle Beach Pee Dee River Fall Zone Fall Zone Cape Fear Arch Atlantic Ocean SOUTH CAROLINA NORTH CAROLINA 81° 80° 79° 35° 34° 40 KILOMETERS 40 MILES Base from ESRI ArcGIS, 2017 Geographic projection, decimal degrees Datum World Geodetic System 1984 (WGS 84) Map area EXPLANATION Tertiary Cretaceous or Tertiary-Cretaceous Gneiss Granite Approximate outline of
anomalous area Quaternary Piedmont region Anomalous titanium content
in sediment Coastal Plain sediments
Study Results 23 sediments to the lower coastal plain of South Carolina. Numerous Pleistocene-age river terraces exist along this drain age basin, indicating that this river basin was active during the Pleistocene. The terrace sediments contain anomalous titanium concentrations. This large drainage system could have transported grains of ilmenite and rutile for considerable distances to the coastal plain of South Carolina during periods of Pleistocene glaciation, and perhaps more expediently, dur ing periods of glacial melting. The majority of the anomalous titanium concentrations in the lower coastal plain of South Carolina, as shown in figure 13, occur primarily in Pleistoceneage sediments. Anomalous Area C In sediments mapped as Cretaceous and as Tertiary, anomalous titanium concentrations occur in the upper and middle coastal plain of North Carolina (fig. 14). The stan dard deviation in the titanium concentrations is generally low across this region of the Atlantic Coastal Plain (fig. 11), indi cating low variation around the mean concentrations. Large expanses of gneiss and granite bound the Fall Zone of north-central North Carolina (fig. 14), the likely sources of the ilmenite, leucoxene (altered ilmenite), and rutile grains in this part of the coastal plain. Headward erosion of these Piedmont crystalline rocks near the coasts during the Creta ceous and Tertiary was likely a significant source of the heavy minerals. In addition, during the Pleistocene and thereafter, large river drainage systems further transported and distributed detrital ilmenite and rutile across large areas of the coastal plain of North Carolina. An exception to the widespread titanium enrichment in sediments in this region is the lack of anomalous titanium in the area that overlies a coastal uplift referred to as the Cape Fear arch (southeastern part of North Carolina, in fig. 14). The Cape Fear arch is a northwest-southeast-trending structural ridge formed in crystalline basement rocks that lie beneath the Atlantic Coastal Plain near the North Carolina-South Carolina border (Gohn, 1988; Klitgord and others, 1988). The crest of the arch (ridge) lies about 500 m beneath the Atlantic Coastal Plain surface of the region and extends into the offshore continental shelf (Gohn, 1988; Klitgord and others, 1988). Basins bound each side of the arch. Uplift of the arch has been interpreted to have occurred during the Pliocene and Pleisto cene (Soller, 1988). Erosion of the sediments atop the arch, as well as diversion of drainage systems to areas northeast of the arch (Soller, 1988), probably were the main influences for the lack of heavy-mineral deposition (or preservation) across the arch since the late Pliocene. As noted earlier, Carpenter and Carpenter (1991) iden tified 19 HMS deposits in the upper Atlantic Coastal Plain along the Fall Zone in southern Virginia and northern North Carolina, a strip of deposits they named the “North CarolinaVirginia heavy mineral belt.” This belt of Pliocene strandline deposits extends north to south from the area of Richmond, Va. (Newton and Romeo, 2006; Berquist and others, 2015) to the vicinity of Wilson, N.C. (figs. 1 and 14). In addition to this “heavy mineral belt,” the results of our study suggest that HMS deposits are not only concentrated along the Fall Zone, but also that similar HMS deposits could be found for several tens of kilometers east of the Fall Zone (fig. 14). Anomalous Area D Our study determined that a majority of the coastal plain of Virginia could have the potential to host titanium-rich depos its of HMS (figs. 10 and 15). Some of the highest titanium concentrations found in our study area of the Atlantic Coastal Plain occur along the western coast of the Chesapeake Bay in Virginia (fig. 15). Although this area also contains some of the highest variability in concentrations (high standard deviation) (fig. 11), the large number of clusters of titanium anomalies indicate that this area may have high potential for HMS. In particular, the areas between the James and the Potomac Rivers (fig. 15) exhibited some of the highest tita nium concentrations in the entire study area. These anoma lies occur in Pliocene-Miocene and Pleistocene sedimentary deposits (Berquist and others, 2015; Horton and others, 2017). The highest titanium values occur in the outer coastal plain, the region most distant (eastward) of the Fall Zone (fig. 15). This relationship likely indicates a progressive remobiliza tion, re-concentration, and re-deposition of the heavy minerals along eastward-developing coastlines that existed from the Pliocene to the Pleistocene (Oaks and Coch, 1963, 1973; Bick and Coch, 1969; Johnson, 1969, 1972, 1976; Oaks and others, 1974). Heavy-mineral-rich river terrace deposits of Pleis tocene age occur along the major drainages of the Virginia coastal plain, which are well exemplified by the terraces along the James River, York River, and Rappahannock River (Bick and Coch, 1969; Johnson, 1969; Force and Geraci, 1975; Berquist and others, 2015). Headward erosion of bedrock along the Fall Zone was a principal source of ilmenite and rutile during the Pliocene and Miocene, as suggested by Shah and others (2017). Subsequently during the Pleistocene, major drainage systems, represented now by the large modern rivers, transported additional detritus carrying heavy minerals to the Atlantic Coastal Plain from the metamorphic and igneous terranes of the Piedmont Region (Minard and others, 1976). Figure 13 (continued from previous page). in South Carolina. The standard deviation in the titanium concentrations is generally low across this region of the Atlantic Coastal Plain (see fig. 11), indicating low variation around the mean concentrations. Refer to figure 10 for spatial reference within the larger Atlantic Coastal Plain region. Geologic map units from Horton and others (2017). Mismatches in geologic units across the borders of North Carolina and South Carolina reflect interpretive differences between the State geologic maps.
24 Titanium Mineral Resources in Heavy-Mineral Sands in the Atlantic Coastal Plain of the Southeastern United States Figure 14. Map showing the anomalous titanium concentrations in area C, the upper and middle coastal plain of North Carolina. Anomalous titanium concentrations occur in sediments mapped as Cretaceous and as Tertiary. The standard deviation in the titanium concentrations is generally low across this region of the Atlantic Coastal Plain (see fig. 11), indicating low variation around the mean concentrations. Refer to figure 10 for spatial reference within the larger Atlantic Coastal Plain region. Geologic map units from Horton and others (2017). Mismatches in geologic units across the borders of North Carolina, South Carolina, and Virginia reflect interpretive differences between the State geologic maps. Durham Roanoke Rapids Rocky Mount Wilson Greenville Fayetteville Wilmington Jacksonville RALEIGH Cape Fear Arch Atlantic Ocean NORTH CAROLINA VIRGINIA SOUTH CAROLINA NORTH CAROLINA Fall Zone Fall Zone 78° 77° 76° 79° 36° 35° 34° 75 KILOMETERS 75 MILES Base from ESRI ArcGIS, 2017 Geographic projection, decimal degrees Datum World Geodetic System 1984 (WGS 84) EXPLANATION Tertiary Cretaceous or Tertiary- Cretaceous Gneiss Granite Approximate outline of
anomalous area Axis and plunge of arch Quaternary Piedmont region Anomalous titanium content
in sediment Coastal Plain sediments Map area
Study Results 25 Figure 15 (continued on following page). Map showing the anomalous titanium concentrations in area D, the coastal plain of Virginia. Some of the highest titanium concentrations found in our study area of the Atlantic Coastal Plain occur along the western coast of the Chesapeake Bay in Virginia. Although this RICHMOND VIRGINIA MARYLAND Fredericksburg Williamsburg Petersburg Norfolk James River Rappahannock River Potomac River Chesapeake Bay Fall Zone Fall Zone Fall Zone Old Hickory deposit Concord deposit Brink deposit Yo r k
R ive r 78° 77° 38° 37° 40 KILOMETERS 40 MILES Base from ESRI ArcGIS, 2017 Geographic projection, decimal degrees Datum World Geodetic System 1984 (WGS 84) EXPLANATION Tertiary Gneiss Granite Quaternary Piedmont region Anomalous titanium content in sediment Heavy-mineral sand (HMS) deposit and identifier Coastal Plain sediments Map area Brink deposit
26 Titanium Mineral Resources in Heavy-Mineral Sands in the Atlantic Coastal Plain of the Southeastern United States Heavy minerals are still being deposited today along the modern coastlines of this region, where they are worked by the actions of waves, longshore currents, and wind (fig. 4). Grosz (1983) carried out an exploration assessment of the HMS deposits along the coastal plain of Virginia. His study employed total-count aeroradiometric maps followed by field checking of 80 identified anomalies by ground radio metric surveys and sediment samples. The heavy-mineral assemblages of the 80 sediment samples were processed and individual minerals separated to measure the percentage of each heavy mineral (those with a specific gravity >2.85). The majority of the sediment samples contained less than 1 percent total heavy minerals. Grosz (1983, p. 16) concluded from his study that “no currently economic heavy-mineral deposits are at or near the surface in the coastal plain of Virginia.” Force and Geraci (1975) documented the heavy-mineral content in sands deposited alongside the modern Atlantic Ocean coast and barrier islands of Virginia, as well as in sands of presumed Pleistocene age near the mouths of the James, York, and Rappahannock Rivers. Based on 54 sediment sam ples distributed across these areas, they found that (1) ilmenite composed 48 to 79 percent of the heavy-mineral concen trate; (2) the TiO2 content of the ilmenite ranged from 46 to 55 percent; and (3) the highest heavy-mineral content was only 1.6 percent. Although the heavy-mineral content of the sands is relatively low for most economic deposits, the TiO2 content is in the acceptable range for pigment manufacture. Several types of metamorphic and igneous rocks that may contain ilmenite and (or) rutile occur in the Piedmont Region of central Virginia, dominated by varieties of gneiss and granite (fig. 15). These rock types are volumetrically the most likely sources of the bulk of ilmenite, leucoxene, and rutile grains in the coastal sediments of Virginia (Minard and others, 1976). Anomalous Area E Anomalous concentrations of titanium occur in Quater nary sediments along the entire outer coastal plain of South Carolina (fig. 16). Some of the highest titanium concentrations found in this study of the Atlantic Coastal Plain were found to occur in barrier islands of southeastern South Carolina, in particular on Hilton Head Island and St. Phillips Island (fig. 16). The majority of the high-titanium sediments along the South Carolina coast are in Pleistocene-age deposits. The bar rier islands are transgressive features (fig. 2), which presum ably formed during sea level rise in tandem with an increase in sediment load to the coastal plain. These conditions most likely occurred during periods of melting and retreat of Pleistocene glaciation in the northern U.S. Numerous rivers in South Carolina originate in the Piedmont region and cross the Atlantic Coastal Plain (fig. 16); the alluvial deposits (placers) in many of these rivers can also contain HMS deposits (Williams, 1967; Neiheisel, 1976; Force and others, 1982). The rivers brought heavy minerals to the coast for further concentration by waves, wind, and tides (Pirkle, Pirkle, and Reynolds, 1991; Elsner, 1997). Longshore transport along the coast, which is dominantly from north to south along the South Carolina coast (van Gaalen, 2004), has also redistributed the heavy minerals along coastal strandlines through time. Hilton Head Island in southeastern South Carolina (fig. 16) has been shown to host several HMS deposits, including some with high heavy-mineral content. In 1954, the U.S. Bureau of Mines reportedly drilled 265 shallow holes (5 to 54 feet [ft] in depth) and 64 auger holes 4.5 to 15 ft in depth) into Hilton Head Island to evaluate its HMS potential (McCauley, 1960). According to McCauley (1960, p. 4), their “…analysis revealed an average heavy mineral content of 2.19 percent to an average depth of 11.1 feet.” A HMS deposit that covers about 4,630 acres was calculated to contain an average heavy-mineral content of about 2.3 percent (Wil liams, 1967). The titanium mineralogy of the heavy-mineral fraction was dominated by ilmenite (about seven times the rutile content). At about the same time period, the National Lead Company drilled 545 holes into Hilton Head Island to a depth of about 40 ft each (McCauley, 1960). They found similar results, “The average percentage of heavy minerals contained in the top 10 feet of the 545 drill holes was 2.24” (McCauley, 1960, p. 5). Other barrier islands along the South Carolina coast that are located to the northeast of Hilton Head Island also report edly contain high-grade HMS deposits that are potentially economic. Listed in decreasing order of potential (according to Neiheisel, 1958), these islands (that are too small to show on figure 16) include Bull Island, Capers Island, Isle of Palms, Edisto Island, Fripp Island, and Dewees Island. Summary and Conclusions This study carried out a geospatial analysis of the tita nium concentrations measured from 3,457 stream sediment samples distributed across the Atlantic Coastal Plain of the southeastern U.S. The raw data used to carry out the geospatial analyses are provided in the data release that accompanies this report (Ellefsen, 2017). The geospatial analysis involved developing a new Bayesian hierarchical model from which both the mean and the variance of the concentrations are estimated over a region. The mean may be interpreted as an average, and the square root of the variance may be interpreted as the spread of the concentrations around the mean. Maps of these two quantities help delimit regions that might be favor able to mining of titanium-bearing minerals. Figure 15 (continued from previous page). area also contains some of the highest variability in concentrations (high standard deviation) (see fig. 11), the large number of clusters of titanium anomalies indicate that this area may have high potential for heavy-mineral sands. Refer to figure 10 for spatial reference within the larger Atlantic Coastal Plain region.
Summary and Conclusions 27 The study results indicate that considerable resources of titanium, in the form of detrital grains of ilmenite, leucoxene, and rutile, could exist in large areas of the Atlantic Coastal Plain. These HMS deposits represent possible domestic sources of titanium that have yet to be developed. Identifying poten tial domestic resources of titanium is useful because titanium has significant industrial applications, and because the great majority of titanium mineral concentrates consumed in the U.S. are imported (91 percent in 2016; Ober, 2017). Only two HMS mining operations are currently (as of 2017) active in the U.S., due to closure of the HMS mines in southern Virginia. To assist in the search and discovery of additional HMS deposits in the U.S., our study outlines areas where exploration for such deposits could focus within the Atlan tic Coastal Plain. In addition to zones of HMS deposits that parallel the Fall Zone, the results of this study suggest that substantial heavy-mineral resources in a variety of settings could exist some distance from the Fall Zone. Specific areas Figure 16. Map showing the anomalous titanium concentrations in area E, the outer coastal plain of South Carolina. Some of the highest titanium concentrations found in this study of the Atlantic Coastal Plain were found to occur in barrier islands of southeastern South Carolina, in particular on Hilton Head Island and St. Phillips Island. Refer to figure 10 for spatial reference within the larger Atlantic Coastal Plain region. Myrtle Beach Atlantic Ocean Charleston Savannah Hilton Head Island St. Phillips Island G E ORGI A S O UT H
CAR O LIN A 81° 80° 79° 33° 32° 40 KILOMETERS 40 MILES Base from ESRI ArcGIS, 2017 Geographic projection, decimal degrees Datum World Geodetic System 1984 (WGS 84) EXPLANATION Tertiary Quaternary (Pleistocene and
Holocene) Anomalous titanium content
in sediment Coastal Plain sediments Map area
28 Titanium Mineral Resources in Heavy-Mineral Sands in the Atlantic Coastal Plain of the Southeastern United States with anomalous titanium concentrations, shown regionally in figure 10 and in more detail in figures 12 to 16, might be considered as focus areas for future exploration for HMS deposits. Many prospective areas for HMS deposits in the Atlantic Coastal Plain occur near the modern shores or on barrier islands, for example, the coasts of South Carolina, southeastern Georgia, and northeastern Florida. Much of the modern coastal areas are covered by infrastructure or designated protected wet lands. Thus, land-use and permitting considerations may limit mineral development along the modern coast. Shah and others (2017), utilizing regional aeroradiomet ric data, evaluated the mapping of potential rare earth elements resources in the Atlantic Coastal Plain in the form of monazite and xenotime. Their studies indicate that concentrations of monazite and xenotime are highest near the Fall Zone, and their concentrations remain relatively high for approximately 40 km eastward of the Fall Zone. The phenomenon of higher monazite concentrations in the upper Atlantic Coastal Plain is understandable, because monazite is typically the heaviest (most dense) of the minerals in the sediments, and thereby less amenable to long distance transport. Our study focused on the potential for titanium resources (ilmenite, leucoxene, rutile), which our study suggests is more widespread in the Atlantic Coastal Plain than monazite. The application of stream sediment sampling to identify HMS in coastal plains has some advantages over aeroradio metric surveys. As examples of the limits of aeroradiometric surveys, Grosz (1983) noted several factors can subdue or enhance the radioactivity measured by an airborne survey: (1) high moisture content of the sediment can subdue radio activity; (2) a small concentration of radioactive minerals (monazite, zircon) can prevent detection of HMS deposits; (3) fertilizers applied in agricultural lands can be radioactive because of their potash and phosphate; (4) radioactivity can be contributed by some clay-sized minerals (as also described by Force and Bose, 1977); (5) thick vegetation cover can subdue radioactivity; and (6) some cultural features contribute radio activity, such as buildings made of granite or road gravels of crushed gneiss or granite. While this study was able to map the distribution of titanium-rich sediments, it also revealed limitations of using stream sediment samples to locate HMS deposits. One limita tion is that the stream sediment samples are representative of the soils and sediments near the land surface. Consequently, economically profitable deposits that are well beneath the land surface will not be detected using this method. Another limita tion is spatial resolution; maps of titanium concentrations show regional-scale features, not deposit-scale features. This study demonstrates an application of Bayesian hier archical modeling for mapping titanium concentrations on a regional scale. Mapping titanium concentration in the Atlantic Coastal Plain area of the U.S. (fig. 10) indicates where the average concentration is high; such areas might be suitable for exploration. The map of the standard deviation in titanium concentrations in the Atlantic Coastal Plain area of the U.S. (fig. 11) indicates how the concentrations vary about the aver age; areas with high average concentration and low variability may be less risky than areas with high average concentration and high variability. Mapping these data could help mining companies delimit areas for exploration. References Cited Ault, Timothy, Van Gosen, B.S., Krahn, Steven, and Croff, Allen, 2016, Natural thorium resources and recovery— Options and impacts: Nuclear Technology, v. 194, no. 2, p. 136–151. Australian Atlas of Mineral Resources, Mines, and Process ing Centres, 2007, Mineral sands—Mineral fact sheets: Canberra, Geoscience Australia, accessed October 10, 2017, at ://web.archive.org/web/20070830005748/://www. australianminesatlas.gov.au/info/factsheets/titanium.jsp. Australian Atlas of Mineral Resources, Mines, and Process ing Centres, 2013, Mineral sands: Canberra, Geoscience Australia, accessed October 11, 2017, at ://www. australianminesatlas.gov.au/aimr/commodity/mineral_ sands.#mineral_sands. Bedinger, G.M., 2013, Titanium, in 2013 Minerals yearbook, 2013: U.S. Geological Survey. Available at ://minerals. usgs.gov/minerals/pubs/commodity/titanium/. Bedinger, G.M., 2016a, Titanium mineral concentrates, in Mineral commodity summaries, 2016: U.S. Geological Survey, p. 178–179. Available at ://minerals.usgs.gov/ minerals/pubs/commodity/titanium/mcs-2016-timin.pdf. Bedinger, G.M., 2016b, Zirconium: Mining Engineering, v. 68, no. 7, p. 83–84. Bedinger, G.M., 2016c, Zirconium and hafnium—Statistics and information: U.S. Geological Survey website, :// minerals.usgs.gov/minerals/pubs/commodity/zirconium/. Bern, C.R., Shah, A.K., Benzel, W.M., and Lowers, H.A., 2016, The distribution and composition of REE-bearing minerals in placers of the Atlantic and Gulf coastal plains, USA: Journal of Geochemical Exploration, v. 162, p. 50–61. Berquist, C.R., 1987, Minerals in high-level gravel deposits along the Fall Zone of Virginia: Virginia Minerals, v. 33, no. 4, p. 37–40. Berquist, C.R., Shah, A.K., and Karst, A., 2015, Placer deposits of the Atlantic Coastal Plain—Stratigraphy, sedimentology, mineral resources, mining and reclamation, Cove Point, Maryland, Williamsburg and Stony Creek, Virginia, SEG Post-GSA Conference Field Trip, Nov. 5–6, 2015: Guidebook Series of the Society of Economic Geolo gists, Inc., Guidebook 50, ISBN: 978-1-629494-87-6.
References Cited 29 Bick, K.F., and Coch, N.K., 1969, Geology of the Williamsburg, Hog Island, and Bacons Castle quadrangles, Virginia: Virginia Division of Mineral Resources Report of Investigations 18, 28 p. Briggs, P.H., 2002, The determination of forty elements in geological and botanical samples by inductively coupled plasma-atomic emission spectrometry, chap. G of Taggart, J.E., ed., Analytical methods for chemical analysis of geologic and other materials: U.S. Geological Survey Open-File Report 02–223, p. 1–18. Available at :// pubs.er.usgs.gov/publication/ofr02223. Carpenter, R.H., and Carpenter, S.F., 1991, Heavy mineral deposits in the Upper Coastal Plain of North Carolina and Virginia: Economic Geology, v. 86, no. 8, p. 1657–1671. Carpenter, J.H., Detweiler, J.C., Gillson, J.L., Weichel, E.C., Jr., and Wood, J.P., 1953, Mining and concentration of ilmenite and associated minerals at Trail Ridge, Fla.: Mining Engineering, v. 5, no. 8, p. 789–795. Carter, C.H., 1978, A regressive barrier and barrier-protected deposit—Depositional environments and geographic setting of the late Tertiary Cohansey Sand: Journal of Sedimentary Petrology, v. 48, no. 3, p. 933–949. Coffey, B.P., and Sunde, R.F., 2014, Lithology-based sequence-stratigraphic framework of a mixed carbonatesiliciclastic succession, Lower Cretaceous, Atlantic Coastal Plain: American Association of Petroleum Geologists, v. 98, no. 8, p. 1599–1630. Creitz, E.E., and McVay, T.N., 1948, A study of opaque miner als in Trail Ridge, Florida, dune sands: American Institute of Mining and Metallurgical Engineers Technical Publica tion 2426, 7 p. Darby, D.A., and Tsang, Y.W., 1987, Variation in ilmenite element composition within and among drainage basins— Implications for provenance: Journal of Sedimentary Petrology, v. 57, no. 5, p. 831–838. Ellefsen, K.J., 2017, Titanium concentrations in stream sedi ments from the Atlantic Coastal Plain of the southeastern U.S. (1975–1999): U.S. Geological Survey data release accessed February 7, 2018 at ://doi.org/10.5066/F7J38R16. Ellefsen, K.J., Van Gosen, B.S., Fey, D.L., Budahn, J.R., Smith, S.M., and Shah, A.K., 2015, First steps of integrated spatial modeling of titanium, zirconium, and rare earth element resources within the Coastal Plain sediments of the southeastern United States: U.S. Geological Survey OpenFile Report 2015–1111, 40 p., accessed on February 7, 2018, at ://dx.doi.org/10.3133/ofr20151111. Elsner, Harald, 1997, Economic geology of the heavy mineral placer deposits in northeastern Florida: Florida Geological Survey Open-File Report no. 71, 138 p. Espenshade, G.H., and Potter, D.B., 1960, Kyanite, silliman ite, and andalusite deposits of the southeastern states: U.S. Geological Survey Professional Paper 336, 121 p. [Also available at ://pubs.er.usgs.gov/publication/pp336.] Force, E.R., 1976, Metamorphic source rocks of titanium placer deposits—A geochemical cycle: U.S. Geological Survey Professional Paper 959–B, 16 p. [Also available at ://pubs.usgs.gov/pp/0959a-f/report.pdf.] Force, E.R., 1980, The provenance of rutile: Journal of Sedimentary Petrology, v. 50, no. 2, p. 485–488. Force, E.R., 1991, Geology of titanium-mineral deposits: Geological Society of America Special Paper 259, 112 p. Force, E.R., and Bose, S.K., 1977, Gamma aeroradioactivity map of parts of Norfolk and Eastville quadrangles, outer Coastal Plain, North Carolina and Virginia: U.S. Geological Survey Miscellaneous Field Studies Map MF–863, scale 1:250,000. [Also available at ://pubs.er.usgs.gov/ publication/mf863.] Force, E.R., and Garnar, T.E., Jr., 1985, High angle aeolian crossbedding at Trail Ridge, Florida: Industrial Minerals, August 1985, v. 215, p. 55, 57, and 59. Force, E.R., and Geraci, P.J., 1975, Map showing heavy min erals in Pleistocene(?) shoreline sand bodies of southeastern Virginia: U.S. Geological Survey Miscellaneous Field Studies Map MF–718, scale 1:250,000. [Also available at ://pubs.er.usgs.gov/publication/mf863.] Force, E.R., and Rich, F.J., 1989, Geologic evolution of Trail Ridge eolian heavy-mineral sand and underlying peat, northern Florida: U.S. Geological Survey Pro fessional Paper 1499, 16 p. [Also available at :// pubs.er.usgs.gov/publication/pp1499.] Force, E.R., Grosz, A.E., Loferski, P.J., and Maybin, A.H., 1982, Aeroradioactivity maps in heavy-mineral exploration— Charleston, South Carolina, area: U.S. Geological Survey Professional Paper 1218, 19 p., 2 pl., scale 1:500,000. [Also available at ://pubs.er.usgs.gov/publication/pp1218.] Gohn, G.S., 1988, Late Mesozoic and early Cenozoic geology of the Atlantic Coastal Plain—North Carolina to Florida, in Sheridan, R.E., and Grow, J.A., eds., The geology of North America, the Atlantic continental margin, U.S., v. 1–2: Geological Society of America, p. 107–130. Goldsmith, Richard, and Force, E.R., 1978, Distribution of rutile in metamorphic rocks and implications for placer deposits: Mineralium Deposita, v. 13, p. 329–343. Grosz, A.E., 1983, Application of total-count aeroradiometric maps to the exploration for heavy-mineral deposits in the Coastal Plain of Virginia: U.S. Geological Survey Profes sional Paper 1263, 20 p., 5 pl., scale 1:250,000. [Available at ://pubs.er.usgs.gov/publication/pp1263.]
30 Titanium Mineral Resources in Heavy-Mineral Sands in the Atlantic Coastal Plain of the Southeastern United States Grosz, A.E., 1987, Nature and distribution of potential heavymineral resources offshore of the Atlantic coast of the United States: Marine Mining, v. 6, p. 339–357. Grosz, A.E., 1993, Use of geochemical surveys in Ti-Hf-REE-Th-U placer exploration—A Mid-AtlanticStates example, part 4, chap. R of Scott, R.W., Jr., Detra, P.S., and Berger, B.R., eds., Advances related to United States and international mineral resources—Developing frameworks and exploration technologies: U.S. Geological Survey Bulletin 2039, p. 181–188, [Also available at :// pubs.er.usgs.gov/publication/b2039.] Grosz, A.E., Cathcart, J.B., Macke, D.L., Knapp, M.S., Schmidt, W., and Scott, T.M., 1989, Geologic interpreta tion of the gamma-ray aeroradiometric maps of central and northern Florida: U.S. Geological Survey Professional Paper 1461, 48 p., 5 pl. [Also available at ://pubs. er.usgs.gov/publication/pp1461.] Grosz, A.E., San Juan, F.C., Jr., and Reid, J.C., 1992, Heavymineral concentrations associated with some gamma-ray aeroradiometric anomalies over Cretaceous sediments in North Carolina—Implications for locating placer mineral deposits near the Fall Zone: U.S. Geological Survey OpenFile Report 92–396, 27 p. [Also available at ://pubs. er.usgs.gov/publication/ofr92396.] Grosz, A.E., and Schruben, P.G., 1994, NURE geochemical and geophysical surveys—Defining prospective terranes for United States placer exploration: U.S. Geological Survey Bulletin 2097, 9 p., 2 pl. [Also available at :// pubs.er.usgs.gov/publication/b2097.] Hill, P.L., Kucks, R.P., and Ravat, D., 2009, Aeromagnetic and aeroradiometric data for the conterminous United States and Alaska from the National Uranium Resources Evaluation (NURE) Program of the U.S. Department of Energy: U.S. Geological Survey Open-File Report 2009–1129. [Also available at ://pubs.usgs.gov/of/2009/1129/.] Horton, J.D., San Juan, C.A., and Stoeser, D.B., 2017, The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States: U.S. Geological Survey Data Series 1052, 46 p., ://doi.org/10.3133/ds1052. Hou, B., and Keeling, J., 2017, Geological and exploration models of beach placer deposits—Integrated from casestudies of southern Australia: Ore Geology Reviews, v. 80, p. 437–459. Iluka Resources Ltd., 2013, Fact sheet, Virginia: Iluka Resources Ltd. website, accessed September 27, 2017, at ://www.iluka.com/docs/3.3-operations/virginia-factsheet-2013.pdf?=2. Iluka Resources Ltd., 2017, Iluka, Company overview— Operations & projects: Iluka Resources Ltd. website, accessed September 26, 2017, at ://www.iluka.com/ company-overview/operations. Johnson, G.H., 1969, Guidebook to the geology of the York-James Peninsula and south bank of the James River: Williamsburg, Va., College of William and Mary, Depart ment of Geology, Guidebook 1, 33 p. Johnson, G.H., 1972, Geology of the Yorktown, Poquoson West, and Poquoson East quadrangles, Virginia: Virginia Division of Mineral Resources Report of Investigations 30, 57 p. Johnson, G.H., 1976, Geology of the Mulberry Island, New port News North, and Hampton quadrangles, Virginia: Virginia Division of Mineral Resources Report of Investiga tions 41, 72 p. Klitgord, K.D., Hutchinson, D.R., and Schouten, H., 1988, U.S. continental margin—Structural and tectonic frame work, in Sheridan, R.E., and Grow, J.A., eds., The geology of North America, the Atlantic continental margin, U.S., v. 1–2: Geological Society of America, p. 19–55. Komar, P.D., and Wang, Chi, 1984, Processes of selective grain transport and the formation of placers on beaches: Journal of Geology, v. 92, no. 6, p. 637–655. Kulpecz, A.A., 2008, Sequence stratigraphy of the Mid-Atlantic Coastal Plain—An evaluation of eustasy, sediment supply variations, and passive-aggressive tectonism: New Bruns wick, N.J., Rutgers University, Ph.D. dissertation, 271 p. McCauley, C.K., 1960, Exploration for heavy minerals on Hilton Head Island, South Carolina: South Carolina State Development Board, Division of Geology Bulletin 26, 13 p. Minard, J.P., Force, E.R., and Hayes, G.W., 1976, Alluvial ilmenite placer deposits, central Virginia: U.S. Geologi cal Survey Professional Paper 959–H, 15 p., 1 pl., scale 1:62,500. [Also available at ://pubs.er.usgs.gov/ publication/pp959H.] Naeser, C.W., Naeser, N.D., Newell, W.L., Southworth, S., Edwards, L.E., and Weems, R.E., 2016, Erosional and depo sitional history of the Atlantic passive margin as recorded in detrital zircon fission-track ages and lithic detritus in Atlan tic Coastal Plain sediments: American Journal of Science, v. 316, no. 2, p. 110–168. Neiheisel, James, 1958, Heavy mineral beach placers of the South Carolina coast: South Carolina State Development Board, Division of Geology, Monthly Bulletin, v. 2, no. 1, p. 1–7. Neiheisel, James, 1962, Heavy-mineral investigations of Recent and Pleistocene sands of the lower coastal plain of Georgia: Geological Society of America Bulletin, v. 73, no. 3, p. 365–374. Neiheisel, James, 1976, Heavy minerals in aeroradioactive high areas of the Savannah River flood plain and deltaic plain: South Carolina Division of Geology Geologic Notes, v. 20, p. 45–51.
References Cited 31 Newton, M.C., III, and Romeo, A.J., 2006, Geology of the Old Hickory heavy mineral sand deposit, Dinwiddie and Sussex Counties, Virginia, in Reid, J.C., ed., Proceedings of the 42nd Forum on the Geology of Industrial Minerals: North Carolina Geological Survey Information Circular 34, p. 464–481. Oaks, R.Q., Jr., and Coch, N.K., 1963, Pleistocene sea levels, southeastern Virginia: Science, v. 140, no. 3570, p. 979–983. Oaks, R.Q., Jr., and Coch, N.K., 1973, Post-Miocene stratigraphy and morphology, southeastern Virginia: Virginia Division of Mineral Resources Bulletin 82, 135 p. Oaks, R.Q., Jr., Coch, N.K., Sanders, J.E., and Flint, R.F., 1974, Post-Miocene shorelines and sea levels, southeastern Virginia, in Oaks, R.Q., Jr., and DuBar, J.R., eds., PostMiocene stratigraphy, central and southern Atlantic Coastal Plain: Logan, Utah State University Press, p. 53–87. Ober, J.A., 2017, Annual review 2016—Mining review: Mining Engineering, v. 69, no. 5, p. 50–59. Owens, J.P., and Gohn, G., 1985, Depositional history of the Cretaceous Series in the U.S. Atlantic Coastal Plain— Stratigraphy, paleoenvironments and tectonic controls of sedimentation, in Poag, C.W., ed., Geologic evolution of the United States Atlantic Margin: New York, Van Nostrand Reinhold Company, p. 25–86. Parham, P.R., Riggs, S.R., Culver, S.J., Mallinson, D.J., Rink, W.J., and Burdette, Kevin, 2013, Quaternary coastal lithofacies, sequence development and stratigraphy in a passive margin setting, North Carolina and Virginia, USA: Sedimentology, v. 60, no. 2, p. 503–547. Pawlowsky-Glahn, Vera, Egozcue, J.J., and Tolosana-Delgado, Raimon, 2015, Modeling and analysis of compositional data: John Wiley and Sons, Ltd., 247 p. Pirkle, F.L., 1975, Evaluation of possible source regions of Trail Ridge sands: Southeastern Geology, v. 17, no. 2, p. 93–114. Pirkle, F.L., Pirkle, E.C., Pirkle, W.A., Dicks, S.E., Jones, D.S., and Mallard, E.A., 1989, Altama heavy mineral deposits in southeastern Georgia: Economic Geology, v. 84, no. 2, p. 425–433. Pirkle, E.C., Pirkle, F.L., Pirkle, W.A., and Stayert, P.R., 1984, The Yulee heavy mineral sand deposits of northeastern Florida: Economic Geology, v. 79, no. 4, p. 725–737. Pirkle, F.L., Pirkle, E.C., and Reynolds, J.G., 1991, Heavy mineral deposits of the southeastern Atlantic Coastal Plain, in Pickering, S.J., Jr., ed., Proceedings of the Symposium on the Economic Geology of the Southeastern Industrial Minerals: Georgia Geologic Survey Bulletin no. 120, p. 15–41. Pirkle, F.L., Pirkle, E.C., Reynolds, J.G., Pirkle, W.A., Henry, J.A., and Rice, W.J., 1993, The Folkston West and Amelia heavy mineral deposits of Trail Ridge, southeastern Geor gia: Economic Geology, v. 88, no. 4, p. 961–971. Pirkle, F.L., Pirkle, E.C., Reynolds, J.G., Pirkle, W.A., Jones, D.S., and Spangler, D.P., 1991, Cabin Bluff heavy mineral deposits of southeastern Georgia: Economic Geology, v. 86, no. 2, p. 436–443. Pirkle, F.L., Pirkle, W.A., and Rich, F.J., 2013, Heavy-mineral mining in the Atlantic Coastal Plain and what deposit loca tions tell us about ancient shorelines: Journal of Coastal Research, Special Issue 69, p. 154–175. Pirkle, E.C., Pirkle, W.A., and Yoho, W.H., 1977, The High land heavy-mineral sand deposit on Trail Ridge in northern peninsular Florida: Florida Bureau of Geology Report of Investigation no. 84, 50 p. Pirkle, E.C., and Yoho, W.H., 1970, The heavy mineral ore body of Trail Ridge, Florida: Economic Geology, v. 65, no. 1, p. 17–30. Pirkle, E.C., Yoho, W.H., and Hendry, C.W., Jr., 1970, Ancient sea level stands in Florida: State of Florida Department of Natural Resources, Bureau of Geology Geological Bulletin no. 52, 61 p. Pirkle, E.C., Yoho, W.H., and Hendry, C.W., Jr., 1971, North Florida setting for 15th field conference, Southeastern Geological Society, in Geological review of some north Florida mineral resources: Tallahassee, Fl., Southeastern Geological Society, p. 1–15. Puffer, J.H., and Cousminer, H.L., 1982, Factors controlling the accumulation of titanium-iron oxide-rich sands in the Cohansey Formation, Lakehurst area, New Jersey: Economic Geology, v. 77, no. 2, p. 379–391. Ramberg, Hans, 1948, Titanic iron ore formed by dissociation of silicates in granulite facies [Greenland]: Economic Geology, v. 43, no. 7, p. 553–569. Ramberg, Hans, 1952, The origin of metamorphic and metaso matic rocks: Chicago, University of Chicago Press, 317 p. Roberts, T.M., Wang, Ping, and Puleo, J.A., 2013, Stormdriven cyclic beach morphodynamics of a mixed sand and gravel beach along the Mid-Atlantic Coast, USA: Marine Geology, v. 346, p. 403–421. Roy, P.S., Cowell P.J., Ferland, M.A., and Thom, B.G., 1994, Wave-dominated coasts, in Carter, R.W.G., and Woodroffe, C.D., eds., Coastal evolution—Late Quaternary shoreline morphodynamics: Cambridge University Press, p. 121–186. Segall, M.P., Colquhoun, D.J., and Siron, D.L., eds., 1997, Evolution of the Atlantic Coastal Plain—Sedimentology, stratigraphy and hydrogeology: Sedimentary Geology, v. 108, no. 1–4, p. 1–229. Sengupta, Debashish, and Van Gosen, B.S., 2016, Placer-type rare earth element deposits, chap. 4, of Verplanck, P.L., and Hitzman, M.W., eds., Rare earth and critical elements in ore deposits: Reviews in Economic Geology, v. 18, p. 81–100.
32 Titanium Mineral Resources in Heavy-Mineral Sands in the Atlantic Coastal Plain of the Southeastern United States Shah, A.K., and Harris, M.S., 2012, Shipboard surveys track magnetic sources in marine sediments—Geophysical studies of the Stono and North Edisto Inlets near Charleston, South Carolina: U.S. Geological Survey Open-File Report 2012–1112, accessed on February 7, 2018 at ://pubs. usgs.gov/of/2012/1112/. Shah, A.K., Vogt, P.R., Rosenbaum, J.G., Newell, Wayne, Cronin, T.M., Willard, D.A., Hagen, R.A., Brozena, John, and Hofstra, Albert, 2012, Shipboard magnetic field “noise” reveals shallow heavy mineral sediment concentrations in Chesapeake Bay: Marine Geology, v. 303–306, p. 26–41. Shah, A.K., Bern, C.R., Van Gosen, B.S., Daniels, D.L., Benzel, W.M., Budahn, J.R., Ellefsen, K.J., Karst, A., and Davis, R., 2017, Rare earth mineral potential in the south eastern U.S. Coastal Plain from integrated geophysical, geochemical, and geological approaches: Geological Society of America Bulletin, 18 p., accessed on February 7, 2018 at ://bulletin.geoscienceworld.org/content/ early/2017/05/11/B31481.1. Smith, J.W., Pickering, S.M., Jr., and Landrum, J.R., 1967, Heavy-mineral-bearing sand of the coastal region of Georgia: Georgia Division of Conservation, Department of Mines, Mining and Geology, South Georgia Minerals Program Project Report no. 8, 68 p. Soller, D.R., 1988, Geology and tectonic history of the lower Cape Fear River valley, southeastern North Carolina: U.S. Geological Survey Professional Paper 1466–A, 60 p. [Also available at ://pubs.er.usgs.gov/publication/pp1466A.] Spencer, R.V., 1948, Titanium minerals in Trail Ridge, Florida: U.S. Bureau of Mines Report of Investigation 4208, 21 p. Staatz, M.H., Hall, R.B., Macke, D.L., Armbrustmacher, T.J., and Brownfield, I.K., 1980, Thorium resources of selected regions in the United States: U.S. Geological Survey Circular 824, 32 p. [Also available at ://pubs.er.usgs. gov/publication/cir824.] Toscano, M.A., and York, L.L., 1992, Quaternary stratigraphy and sea-level history of the U.S. Middle Atlantic Coastal Plain: Quaternary Science Reviews, v. 11, no. 3, p. 301–328. Trapp, Henry, Jr., and Meisler, Harold, 1992, The regional aquifer system underlying the northern Atlantic coastal plain in parts of North Carolina, Virginia, Maryland, Delaware, New Jersey, and New York—Summary: U.S. Geological Survey Professional Paper 1404–A, 33 p., 11 pl., scale 1:2,000,000. [Also available at ://pubs.er.usgs. gov/publication/pp1404A.] U.S. Geological Survey, 2004, The National Geochemical Sur vey—Database and documentation, version 5.0 (2008): U.S. Geological Survey Open-File Report 2004–1001, available at ://mrdata.usgs.gov/geochem/doc/home.htm. van Gaalen, J.F., 2004, Longshore sediment transport from northern Maine to Tampa Bay, Florida—A comparison of longshore field studies to relative potential sediment trans port rates derived from Wave Information Study Hindcast Data: Tampa, Fla., University of South Florida, M.S. thesis, 104 p. Van Gosen, B.S., Fey, D.L., Shah, A.K., Verplanck, P.L., and Hoefen, T.M., 2014, Deposit model for heavy-mineral sands in coastal environments: U.S. Geological Survey Scientific Investigations Report 2010–5070–L, 51 p., accessed on February 7, 2018, at ://pubs.usgs.gov/sir/2010/5070/l/. Van Gosen, B.S., and Tulsidas, Harikrishnan, 2016, Thorium as a nuclear fuel, chap. 10, of Uranium for nuclear power— Resources, mining and transformation to fuel: Elsevier Ltd., p. 253–296. Whittecar, G.R., Newell, W.L., and Scott, E.L., 2016, Land scape evolution in Virginia, in Bailey, C.M., Sherwood, W.C., Eaton, L.S., and Powars, D.S., eds., The geology of Virginia: Martinsville, Va., Virginia Museum of Natural History Special Publication, v. 18, p. 259–290. Williams, Lloyd, 1967, Heavy minerals in South Carolina: Columbia, S.C., South Carolina State Development Board, Division of Geology, Bulletin 35, 35 p. Woodruff, Laurel, and Bedinger, George, 2013, Titanium— Light, strong, and white: U.S. Geological Survey Fact Sheet 2013–3059, 2 p., accessed on February 7, 2018 at, :// pubs.usgs.gov/fs/2013/3059/. Woodruff, L.G., Nicholson, S.W., and Fey, D.L., 2013, A deposit model for magmatic iron-titanium-oxide deposits related to Proterozoic massif anorthosite plutonic suites: U.S. Geological Survey Scientific Investigations Report 2013–5091, 58 p., accessed on February 7, 2018 at :// pubs.er.usgs.gov/publication/sir20135091. Wynn, J.C., and Grosz, A.E., 1985, Induced polarization and magnetic response of titanium-bearing placer deposits in the southeastern United States: U.S. Geological Survey Open-File Report 85–756, 41 p. [Also available at :// pubs.er.usgs.gov/publication/ofr85756.] Zircon Industry Association, 2017, Applications: Zircon Indus try Association website, accessed September 25, 2017, at ://www.zircon-association.org/applications..
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Van Gosen and Ellefsen—Titanium Mineral R esources in Heavy-Mineral Sands in the Atlantic Coastal Plain of the Southeastern U.S.—SIR 2018–5045 ISSN 2328-0328 (online) ://doi.org/10.3133/sir20185045