NC Mineral Resources - An Overview

North Carolina, U.S.A.: An Industrial Mineral Storehouse

The following material was taken from Carpenter, P.A., III, Reid, Jeffrey C., and Gardner, Charles H., 1995, North Carolina, U.S.A.: An industrial mineral storehouse, in Brian J. Walker, editor, Claudette M. Simard, compiler, Proceedings of the 28th Symposium on Industrial Minerals, May 3-8, 1992, Martinsburg, West Virginia, USA, West Virginia Geologic and Economic Circular C-46, p. 65-70. Copies of the complete paper including maps and figures, and references are available from the authors upon request. Use of this material should be accompanied by appropriate citation.
North Carolina's varied and complex geology is reflected in the diversity of its mineral industry. Although no metallic minerals are mined presently, North Carolina has a long-established industrial minerals industry. North Carolina leads the nation in the production of feldspar, lithium minerals, scrap mica, olivine, and pyrophillite, and also leads in the production of clay used for brick manufacture. The state ranks second in phosphate rock production. Additional production is from crushed stone, sand and gravel, dimension stone, kaolin, peat and gem stones. Recently discovered heavy mineral deposits will be produced in the near future. Typically North Carolina's annual mineral production is over $500 million dollars.
North Carolina's varied and complex geology is reflected in the diversity of its mineral industry. Although metallic no metallic minerals are presently mined, the long established production of a variety of industrial minerals allows the state to maintain a position in the top 21 mineral producers by value in the nation. Typically, North Carolina's annual mineral production exceeds $500 million dollars.
Lithium minerals, phosphate rock, and crushed stone account for the bulk of the annual mineral production. North Carolina leads the nation in the production of feldspar, lithium minerals, scrap mica, olivine and pyrophyllite. The state leads the nation in the production of clay used for brick manufacture and ranks seconds in phosphate rock production. North Carolina does not produce significant quantities of metallic minerals but has potential resources.
Industrial minerals are mined thoughout North Carolina in the Mountain, Piedmont and Coastal Plain provinces. Sand and gravel are mined in about half the counties and a variety of igneous and metamorphic rocks are quarried in many Mountain and Piedmont counties for the production of crushed stone and dimension stone. The Coastal Plain has a few limestone quarries which produce crushed stone and agricultural limestone.
Clay - Common clays suitable for the manufacture of brick and tile products are found throughout the Coastal Plain, Piedmont, and Mountain Provinces. These clays provide the raw materials for the manufacture of bricks. North Carolina is annually the nation's leader in brick production. Mines in the the central Piedmont obtain clays from weathered slate belt rocks. In Lee and Moore counties, clays are mined from Triassic sediments. In addition to face brick, other major uses for clay are for lightweight aggregate, cement, common brick, sewer pipe, and to a lesser extent, structural, drain tile, and glazed tile. Kaolin is recovered as a byproduct of feldspar and mica benficiation in Avery and Cleveland counties.
Crushed stone - For many years, crushed stone has been the leading mineral commodity by value in the state. Annually, it accounts for almost one-half of the total mineral production value. Leading counties in the production of crushed stone are Wake, Mecklenburg, Guilford, Forsyth, and Buncombe. The top five companies produce over 80 percent of the tonnage. These companies are Martin Marietta Aggregates Company, Nello L. Teer Company (Beazer, USA), Vulcan Materials Company, and Wake Stone Corporation.
Granite and related crystalline rocks in the Piedmont and Blue Ridge geologic belts provide the principle sources of crushed stone in North Carolina. Other quarries are located in the dense fine-grained rocks of the Carolina Slate belt. Crystalline limestone and marble are quarried, in limited amounts, in the Piedmont and Mountain regions. Shell limestone from the Castle Hayne and River Bend formations and the Rocky Point Member of the Peedee Formation are the primary sources of crushed stone in the Coastal Plain.
Dimension stone - Most dimension stone in North Carolina is produced from granite, agrillite, quartzite, marble, and sandstone. The North Carolina Granite Company operates one of the largest granite dimension stone quarries in the world at Mt. Airy in Surry County. The Mount Airy granite ia a light-colored biotie granitoid (monzogranite). The rock is used as street curbing, ashlar for masonry walls, rubble, rip-rap, monuments, and sawed blocks for buildings. Dimension granite is also quarried in Rowan County from light-colored gray to pink granite of the Salisbury pluton. This granite is used for foundations, street-curbing, paving, and monuments. Dark bluish-gray argillite (Mudstone Member of the Cid Formation) is quarried by Jacobs Creek Stone Company from slate belt rocks in Montgomery and Davidson counties. This stone's smooth, natural cleavage allows it to be used extensively in flooring, stair treds, borders, and window sills. Marble is quarried near Murphy as market conditions dictate. A variety of rocks, such as metasandstone, quartzite, phyllite, and other metamorphic rocks are quarried in the Blue Ridge and Piedmont for dimension stone uses.
Sand and gravel - Sand and gravel for construction purposes are mined in about half the counties in North Carolina. The Sandhills region in Anson, Moore, Lee, Harnett, and Richmond counties is the principle producing area. Much of the sand is obtained from the Pinehurst Formation. Gravel is mined from the overlying terrace gravels. Material from this area is shipped to many parts of the state and to South Carolina. In western North Carolina, Buncombe County is the largest producer of sand and gravel. Most sand is used for concrete aggregate, asphaltic concrete, and fill.
Industrial sand is mined primarily in Anson and Richmond counties in the Sandhills region. Additional tonnages are also obtained during feldspar and lithium beneficiation in the Spruce Pine and Kings Mountain areas. Most of the sand is used in the container and flat-glass industries and also for ferrosilicon, filtration, sandblasting, and traction industries.
Feldspar - Feldspar was first mined in North Carolina in 1911 in the Spruce Pine district, the main feldspar-producing district in North America. Original mining was from pegmatite bodies but current mining is from alaskite,a very coarse-grained, light-colored, feldspar-quartz-muscovite rock. Composition of the rocks averages about 40 percent plagioclase (soda-spar), 25 percent quartz, 20 percent microcline (potash-spar), and 15 percent muscovite. The alaskite is processed using a three-stage acid circut floation. By-product mica and silica are also recovered. Most of the production is from mines in Mitchell County, but companies in the Kings Mountain-Cherryville area recover a feldspar-silica concentrate during mica and lithium beneficiation.
Feldspar production has decreased each year since reaching a record high $15.5 million in 1986. The U.S. feldspar producers receive strong competition from Canadian producers of nepheline syenite. Nepheline syenite is used for many of the same purposes as feldspar.
The main uses of feldspar are in whiteware, tile, and glass fiber insulation. Feldspar is used both in the body of the ware and the glaze of ceramics.
Mica - Mica mining began on a large scale in western North Carolina about 1868. The area has become the most important producer of mica in the U.S. Sheet mica was the principal product for many years, but other materials have eliminated many of the uses for sheet mica. Consequently, North Carolina has not produced significant amounts of sheet mica since about 1962. Scrap mica is still produced in large quantities. Primary sources are alaskite and pegmatites.
North Carolina annually leads the nation in the production of scrap mica, producing about 60 percent of the total. Primary production is from Mitchell County in the Spruce Pine district, and in Cleveland County in the Kings Mountain district. Mica is produced as a coproduct of feldspar, silica, and kaolin mining and as a byproduct of lithium mining.
Both wet- and dry-ground products are produced. Dry-ground mica is used primarily in the manufacture of gypsum plasterboard joint cement, wall board, and well-drilling muds. Wet-ground mica is used in cosmetics, paint, and plastic manufacture.
Lithium - Although first recognized as early as 1906, the economic significance of the spodumen-bearing pegmatites of the Kings Mountain district was not realized until 1942. Today, this relatively small area in Cleveland and Gaston counties contains more than 80 percent of the known lithium ore reserves in the U.S. Estimated proved and probable reserves of 70 million short tons of 20 percent spodumene or 1.5 percent Li2O.
The lithium-bearing pegmatites crop out along a 1-mile-wide zone on the west flank of the Kings Mountain Shear zone. This shear zone separates high-grade metamorphic rocks of the Inner Piedmont on the west from lower grade metamorphic rocks of the Kings Mountain belt on the east. The pegmatites contain approximately 20 percent spodumene, 32 percent quartz, 27 percent albite, 14 percent microcline, and 6 percent muscovite. The pegmatite zone was originally referred to as the tin-spodumene belt because cassiterite occurs in some pegmatites in this same zone.
Spodumene is mined to produce lithium carbonate, lithium metal, and chemical compounds. Lithium is also used to manufacture of ceramics, glass, greases, TV glass, and batteries. In recent years, increased foreign production of lithium carbonate has resulted in temporary closings at several of the mines.
Olivine - Olivine occurs as isolated dunite bodies, or alpine-type peridotites, in the Blue Ridge. Two main districts, the Webster-Balsam district in Jackson County and the Spruce Pine district in Yancey and Mitchell counties, have produced most of the olivine. The deposits contian 50 to 90 percent olivine. Vermiculite and anthophyllite asbestos also occur in the same rocks as the olivine and have been mined in the past. North Carolina leads the nation in olivine production, although production is presently limited to the Daybrook Mine near Burnsville in Yancey County.
Olivine is a magnesium silicate used principally as a refactory. It is becoming increasingly important as a molding sand in the foundry industry. Olivine is being studied for heat-storage blocks for heat-storage furnaces.
Olivine production has declined in recent years because of a decline in steel production and because of increased competition from olivine imports.
Phosphate - In the late 1950's a phosphate deposit was found beneath a large portion of Beaufort County in the Miocene Pungo River Formation. Subsequent exploration deliniated a minable ore body that contained about 2 billion tons of phosphate ore. North Carolina is now the second-leading phosphate producer behind Florida. About 95 percent of the total United States phosphate production comes from North Carolina and Florida.
Phosphate is produced by Potash Corporation of Saskatchewan who purchased the assets of Texasgulf, Incorporated in 1985. Phosphate production is from the large open-pit Lee Creek mine located near Aurora in Beaufort County. The major portion of the output from this mine is used in nearby chemical facilities to produce phosphoric acid, triple superphosphate, and diammmonium phosphate. In 1985, Texasgulf, Incorporated, purchased North Carolina Phosphate Corporation (NCPC). NCPC was developing a mine and plant near the Texasgulf operation.
Deposits of phosphorite also occur off North Carolina's coast in the northeast Onslow Bay district and the Frying Pan Shoals district. The lower part of the Pliocene Yorktown Formation contains phosphorite in the Aurora phosphate district and represents a potential resource. Further exploration may lead to production from these deposits.
Pyrophyllite and talc - Pyrophyllite is a high alumina mineral that, in North Carolina, occurs exclusively within hydrothermally altered felsic volcanic rocks of the Carolina Slate belt. The mineral was first mined commercially in North Carolina in 1855 and has been mined almost continuously since that time. Pyrophyllite is mined near Robbins and Glendon in Moore County and at Hillsborough in Orange County. Major uses for the pyrophyllite are in the refactory, ceramic, paint, and insecticide industries and as a joint compound filler. The Orange County deposit contains andalusite in addition to pyrophyllite. Other pyrophyllite deposts in the slate belt have been mined and prospected and may provide additional reserves.
Talc deposits are associated with the white, siliceous, dolomitic Murphy Marble in Cherokee and Swain counties. These deposits were mined as early as 1859 but are currently inactive.
Heavy minerals - Deposits of heavy minerals, including ilmenite, rutile, and zircon have been discovered in the upper Coastal Plain of North Carolina. Total reserves are estimated at 25 million shorttons of heavy minerals. In North Carolina, the deposits are located in Wilson, Nash, and Halifax counties. Southeast Tisand is evaluating a deposit for possible development near Roanoke Rapids, and RGC (USA) Minerals, Inc. is evaluating deposits in the Aurelian Springs and Bailey areas.
Gemstones - North Carolina has long been famous for the variety of precious and semi-precious stones found in the Piedmont and Mountain regions of the state. Several dozen commercially operated collecting localities are open to the public. Amateur collectors seach for emeralds, rubies, sapphires, hiddenite, garnet, and other semi-precious stones. North Carolina ranks first in the east in the mining and marketing of gemstones and mineral speciments.
The main gem-collecting counties are Alexander (emeralds and hiddenite), Macon (rubies, sapphires, and garnets), and Mitchell (emeralds and aquamarine).
Other non-metallic minerals - Additional minerals may eventually be discovered in economic quantities in North Carolina. Monazite, a mineral that contains rare-earth elements, was once mined in the western Piedmont, and occurrences are also known in the eastern Piedmont. Monazite, ilmenite, and rutile may occur with other heavy minerals offshore.
Diamonds - The source of 13 diamonds found in North Carolina during the mid- to late-1800's has never been determined. Recent NCGS research on lamproites in the Charlotte area may provide clues to the source of these diamonds and for diamond prospecting in other areas of the Piedmont.
Mineral fuels provide the primary sources of energy currently consumed in the world. They include coal, petroleum, natural gas, and uranium. North Carolina is deficient in the mineral fuels and must import these resources from outside sources in order to meet its energy requirements.
Coal - Only one area in North Carolina is known to contain coal beds of potential commercial importance. This area is the Deep River coal field which lies along the Deep River in Chatham, Moore, and Lee counties. The coal field is in the Deep River Triassic Basin and occupies a zone of about 35 miles long and 5 to 10 miles wide. Its center lies about 10 miles northwest of Sanford, North Carolina.
The medium volatile bituminous coal occurs in beds in the Cumnock Formation. It is associated with shales, siltstones, and sandstone. Coal beds in the Cumnock range from a few inches to 48 inches thick. The Cumnock and the Carolina coal mines produced coal from this seam intermittently from 1854 to 1953.
There were three important periods of coal production in the Deep River coal field. The first was from 1861 to 1873 during, and as a result of, the Civil War. The second period was from 1889 to 1905, when the Cumnock Mine was the only producer. The third was from 1918 to 1930, when both the Cumnock and Carolina Mines were open. During 1949 approximately 14,000 tons of coal were produced from the Carolina mine. However, because the coal seam is deeply buried and badly broken by numerous dissecting faults, production in the Deep River area ceased in 1953.
It is estimated that 110,337,000 tons of steam and coking coal exists. However, because of faulting in the area, less than half of this coal might be mined. In order to recover a large quantity of coal from this area, much subsurface structural geologic mapping and drilling must be done to determine the locations of faulted coal seams.
Peat - Fuel-grade peat deposits cover about 677,000 acres in Coastal North Carolina. Total reserves are about 500 million tons of moisture-free peat. These deposts formed in the past 10,000 years in swamps or pocosins, Carolina bays, and river flood plains. Most of the peat occurs at the surface with no overburden. The peat ranges from 1 to 15 feet thick and averages 4.5 feet thick. The largest deposits are in the Albemarle-Pamlico peninsula and the Dismal swamp. Many environmental concerns must be faced before these environmentally sensitive areas can be mined. Production, to date, has been for use in agricultural products such as soil conditioners and potting soil. Other uses of peat include as a heat source, a feed stock for synthetic compounds, a waste treatment material, and as a filter material.
Petroleum and natural gas - Approximately 125 exploratory oil and gas wells have been drilled in North Carolina since the first one was drilled in 1925. Most have been in the outer Coastal Plain. Traces of oil and gas have been detected in a few of these wells but no producing wells have been developed.
Several areas in North Carolina are considered to have potential to produce oil and gas. The main area is the outer Coastal Plain. It contains a relatively thick pile of sedimentary rocks including some excellent trap or reservoir rocks, but source rocks may not be present.
Seismic surveys in the Blue Ridge suggest that sedimentary rocks are deep beneath the crystalline rocks. These sediments may be similar to oil- and gas-bearing sediments in the Valley and Ridge Province. Detailed studies have not been conducted to verify the seismic surveys.
The Triassic basins have received attention from oil and gas exploration companies during recent years. Excellent source rocks are present, but the sandstones are not permeable. Fine-grained material fills pore spaces between the sand grains, preventing the migration of hydrocarbons. The Cumnock and Gulf coal beds have been studies for possible in-situ methane gas generation.
Mobil Oil Corporation proposed to drill for natural gas of the Atlantic shelf off the North Carolina coast.
Uranium minerals - A number of the uranium-bearing minerals occur as minor constituents in the pegmatites of North Carolina. These pegmatites are principally in the Spruce Pine district and adjacent areas. Radioactive minerals have found in schists and underlying granitic rocks in northern Burke, Mitchell, Avery, and adjacent counties. However, it is not likely that any of these occurrences is large enough to be of commercial value. Trace amounts of uniformly distributed uranium are associated with the phosphate deposits of Beaufort County.
In 1982 Marine Uranium Corporation announced the discovery of a 30-million-ton uranium ore body in Pittsylvania County, Virginia. The ore body was in augen gneiss adjacent to the Chatham Fault, along the west side of the Danville Triassic basin. Because of a drop in uranium ore prices and local opposition to the project, these deposits were not developed. Similar rocks farther south in Rockingham County, North Carolina, were also explored.
Metallic minerals are associated principally with the igneous and metamorphic rocks of the Piedmont and Blue Ridge geologic belts. Ores of chromium, copper, gold and silver, iron, lead and zinc, manganese, molybdenum, nickel, tin, titanium, and tungsten all occur in either the Piedmont or Mountain Provinces.
Although of little importance in the state's mining industry today, gold, copper, iron, and tungsten were produced in the past. During the 1950's, the Hamme Mine in Vance County was the largest tungsten mine in the U.S. The mine was reopened as the Tungsten Queen Mine for a short time about 1970 but closed in the fall of 1971 because of declining tungsten prices. Considerable reserves of tungsten remain at the site.
North Carolina was the nation's leading gold producer prior to the 1849 discoveries in California. Because of its geologic similarity to important metal mining districts in Canada, the Carolina Slate Belt has been an area of extensive exploration. It is considered a good site for the discovery of base metal deposits (copper, lead and zinc) and gold associated with ancient hot-spring systems. The use of heap-leaching methods to recover gold from low-grade ore has revive interest in the slate belt. The recent development of four mines in South Carolina has encouraged continued exploration in similar geologic settings in North Carolina.