Sedimentary Ore Deposits

Sedimentary Ore Deposits

Clastic Sedimentary Ore Deposits

Clastic Sedimentary Ore Deposits

Silica"Sand & Gravel"

Sedimentary deposits are formed through the erosion, transportation, and redeposition of minerals that can survive the rigors of transportation. The most common is silica, which forms a number of materials, including silica sand, sand and gravel, and flint. The precursor is igneous quartz (e.g., in granite), and then the sedimentary deposit may undergo metamorphism and recementing to produce quartzite. Sand and gravel for construction use is extremely common, and production is more dependent on local markets than availability. Certain areas are, however, noted for producing industrial sand that is sufficiently pure to be used in the manufacture of glass, ceramics, sodium silicate, and the like.
Examples include the midwestern United States; Badgeley Island, Ontario, Canada; Cheshire in northwest England; certain areas of Belgium and the Netherlands; Cape Flattery Island, Queensland, Australia; and Sarawak, Malaysia. In many cases, the use of local sand is based on price rather than quality. The United States is the largest producer of industrial sand, accounting for more than one quarter of world production. Production of flint is much more restricted, based largely on the chalk deposits of southern England and northern France.

Clays

Several clays composed mainly of kaolinite are of sedimentary origin. Premier deposits of ball clay, the carbon content of which indicates that it was deposited in swampy conditions, occur in the Kentucky–Tennessee area of the United States, Devon in southwest England, and the Czech Republic. Flint clay, as produced commercially in the United States, China, Australia, and Argentina, is generally derived from the weathering of soil and deposition in shallow basins. Fire clay or refractory kaolin is a kaolinite material common in many parts of the world, particularly in association with coal deposits. A 400-km belt of kaolinite-rich rocks extends from Aiken, South Carolina, to Eufaula, Alabama, and includes areas supplying high- and medium-quality kaolin and refractory kaolin. Another belt of kaolin, bauxite, and bauxitic and kaolinitic clays extends from western Tennessee into northeastern Mississippi. Other areas include southwest England and over the English Channel into France (kaolin and ball clay); various parts of the Czech Republic (kaolin and ball clay); Spain; the Amazon Basin in Brazil (bauxite, kaolin); Japan (kaolin, refractory clay, roseki, and toseki); and Queensland, Australia (bauxite, kaolin).

Volcanic ash deposited as part of a sedimentary sequence eventually forms sodium or calcium bentonite. Important bentonite deposits occur in the United States in the Wyoming–Montana region (sodium-based bentonite) and in the Mississippi–Texas region (calcium-based). Almost 40% of the world’s bentonite production is from these and some smaller deposits in the United States. More modest tonnages are produced in Mexico and Canada. In Europe, bentonite is mined on Milos Island in Greece, Turkey, Sardinia in Italy, Bavaria in Germany, southwestern England, Ukraine, and Spain. In Asia, production is centered in Japan, India, and China. Attapulgite and sepiolite (fuller’s earth) are more restricted, being produced in Georgia and Florida in the United States (75% of world production), Germany, the United Kingdom, Senegal, and Spain.

Titanium

Titanium is found in many minerals. Ilmenite (FeTiO3) and rutile (TiO2) are the most important sources of titanium. Ilmenite provides about 90% of the titanium used every year. It is estimated that the resources of ilmenite in the world contain 1 billion tons of titanium dioxide. The estimated resources of rutile in the world contain about 230 million tons of titanium dioxide. Rutile and ilmenite are extracted from sands that may contain only a few percent by weight of these minerals. After the valuable minerals are separated, the remaining sands are returned to the deposit and the land recultivated. In the United States, titanium-rich sands are mined in Florida and Virginia. Even though the United States mines and processes titanium and titanium dioxide, it still imports significant amounts of both. Metallic titanium is imported from Russia (36%), Japan (36%), Kazakhstan (25%), and other nations (3%). TiO2 pigment for paint is imported from Canada (33%), Germany (12%), France (8%), Spain (6%), and other nations (36%).

Most titanium is used in its oxide form. TiO2 is a white pigment used in paint, varnishes and lacquers (49%), plastics (25%), paper (16%), and other products such as fabrics, printing inks, roofing granules, and special coated fabrics.

Zirconium Minerals (Rare Earths)

Placer and palaeo-placer mineral deposits are important sources of heavy minerals such as ilmenite, rutile, and zircon. The rare earth sources monazite and xenotime are invariably associated with the mineral sands deposits. Many titanium/zirconium/rare earth mineral deposits are Tertiary and Quaternary in age because this was a period of geological uplift that provided the correct conditions for accumulation, plus the fact that older examples have been destroyed. Most placer deposits are in marine sand deposits along or near present coastlines, where they are concentrated by a combination of tidal action, longshore currents, waves, winds, and natural traps such as a cape. Most commercial placer deposits are recent beaches and dunes along coastlines, with some older deposits being stranded by land elevation or ocean withdrawal. Important areas include the east and west coasts of Australia, parts of Florida and Georgia in the southeastern United States, around Richards Bay in South Africa, Sierra Leone in Africa, the coastal areas of Tamil Nadu and Kerala states in southern India extending into eastern Sri Lanka, and the coastal areas of Brazil. Consequently, supplies are dominated by Australia with 45% of the ilmenite supply, 100% of the leucoxene, and more than 50% of the rutile, followed by South Africa, the United States, Ukraine, and India. Hard-rock ilmenite deposits are exploited in Quebec, Canada, and Norway. Except for the United States, most of the production is exported for use in the production of titanium dioxide pigment.

Rare earths have been mined worldwide from a variety of ores. The principal ores and ore minerals are bastnäsite and monazite. China is the largest producer of bastnäsite.

Diamonds

Major diamondiferous beach placers extend along the southwest coast of Africa and are exploited in South Africa and Namibia.

Chemical (Evapourite) Sedimentary Ore Deposits

Chemical (Evapourite) Sedimentary Ore Deposits

Certain minerals are found dissolved in seawater and various other brines; evaporate deposits form when the concentration reaches saturation and precipitation occurs. This process requires favorable conditions such as a barred basin or broad shelf environment, plus a hot, dry climate that encourages evaporation. Once formed, the fragile deposit needs to be preserved in subsequent geological events such as burial. Halite, gypsum, and anhydrite, often interbedded with limestone and dolomite, are the most common minerals present in marine evaporates, which often extend over hundreds of square kilometers and attain a thickness greater than several thousand meters. In rarer cases, other evaporate minerals are present, such as potassium minerals, borates, and strontium minerals. 

Salt

Common salt lives up to its name by being ubiquitous in most brines and many evaporate deposits. It is exploited commercially from seawater where the modern climate allows evaporation (e.g., in Western Australia, Mexico, Bahamas, Netherlands Antilles, Chile, India, Brazil, Italy, and Spain). Large, buried rock salt and salt dome deposits are important in the northeastern, southern, and midwestern areas of North America; central and northern Europe; parts of the former U.S.S.R.; and the Middle East. Saline lakes are worked in the western United States, for example, the Great Salt Lake in Utah (which yields or has yielded sodium sulfate, potassium minerals, magnesium chloride, bromine, and lithium as well as salt) and Searles Lake in California (sodium sulfate and borates). Despite the widespread production of salt, three quarters of the world’s production is accounted for by the United States, China, Germany, India, Canada, Mexico, Australia, France, Brazil, Chile, and the United Kingdom.

Potassium Minerals

In some cases, potassium minerals are found associated with salt. During the Permian period in Europe, for example, the Zechstein Basin extended from northern Britain through the Netherlands, Denmark, and Germany to Poland. This was a shallow stable sea that allowed thick evaporate sequences to accumulate, resulting in the large potash and salt deposits that are exploited today. To the east, three basins contain vast reserves of potash—Stebnik/Kalush in Ukraine near the border with Poland, Soligorsk near Minsk in Belarus, and Solikamsk/Berezniki west of the Urals. In western Canada during the Silurian to mid-Devonian period, the land subsided to form a large basin stretching southward into the United States. This allowed vast thicknesses of evaporates to be formed, including the potash resources of Saskatchewan, Canada. A large potash/salt-rich basin identified in Thailand has potential for commercial production. Despite its strategic importance as a fertilizer, large-scale potash production is fairly restricted with just 10 countries—Canada, Russia, Germany, Belarus, Israel, the United States, Jordan, the United Kingdom, Spain, and Brazil—accounting for 97% of world production.

Celestite

Strontium is recovered from two strontium minerals, strontianite (strontium carbonate) and celestite (strontium sulfate). Virtually all the world’s celestite is mined in just six countries— Mexico, Spain, Turkey, Argentina, Iran, and Pakistan. In northern Mexico, the output from several mines accounts for half of the world’s production; Spain contributes an additional 40%.

Most strontium (76% of the strontium consumed each year) is used to make compounds that are applied to the glass picture tubes on color television sets. This compound blocks the X-rays created by the picture tube.Some strontium (10%) is used to make special magnets called ferrite ceramic magnets. Strontium is the element that gives road flares and fireworks a bright red color. Pyrotechnics and flares account for 5% of the annual strontium consumption.

Barite

As mentioned previously, barite can be associated with evaporate minerals such as celestite and gypsum. In addition, barite is also found as a hydrothermal vein filling associated with stratiform massive sulfide deposits and as a residual deposit. China has emerged as the world leader in barite production, accounting for more than 50% of the world total. In contrast, barite production in the United States has declined to 6% of world production because of the availability of imports from China and, to a lesser extent, Mexico and Morocco. Other suppliers are India, Iran, and Turkey.

Borates

About 60% of the world’s borate production is controlled by the United States and Turkey, with Argentina, Chile, and Russia supplying most of the balance. Part of the production is based on brines and encrustations in Searles Lake, California, and from small concentrations along a stretch of the Andes Mountains encompassing Argentina, Bolivia, Chile, and Peru. The major source of borate minerals is a buried mass of sodium borate at Boron in the Mojave Desert of California. Other buried and surface borate deposits occur in Death Valley, including the Billie colemanite deposit, which was mined until the mid-1980s. In Turkey, borates are concentrated in six areas—the most important being the Emet and Kirka areas (both sodium borate) and the Bigadiç area (calcium borates).

Nitrates
Natural nitrate production is now confined to an area of northern Chile that has an annual rainfall of less than 1 cm. In addition, iodine is co-produced from the caliche ore and accounts for more than 50% of world production. Elsewhere, commercial iodine production is based on brines largely found in Japan (35% of world production), the United States (Oklahoma), China, Azerbaijan, Russia, and Turkmenistan. Bromine is also extracted from well brines in Arkansas and Michigan in the United States, the Dead Sea in Israel, potash brines in Germany and France, and seawater in the United Kingdom, France, Spain, and Japan. The United States and Israel combine to account for 75% of world production. 

Biogenic Sedimentary Ore Deposits

Biogenic Sedimentary Ore Deposits

Limestone 

Limestone is an extremely common rock formed as shell beds on a shallow sea floor. Purity depends on the environment of deposition and the subsequent mineralogical and tectonic history that may include metamorphism to marble. Limestone is exploited for uses ranging from construction aggregates and railroad ballast to cement and lime manufacturing, and glassmaking to GCC used as functional fillers in paper, plastics, and paint. The relatively modest price even for the high-calcium and high-brightness grades of GCC (less than $200/t) means that consumption is generally close to the point of production (i.e., a local or regional market). In the United States, for example, crushed limestone is produced in all states except for Louisiana (which does produce shell), includes more than 2,500 quarries, and accounts for two thirds of the nation’s crushed stone output. High-quality, filler-grade GCC produced in Vermont, Massachusetts, and Ontario in Canada serves many parts of the United States, including the Northeast, Maryland, the mid- Atlantic states, Georgia, Alabama, Illinois, Texas, California, and Washington. In Western Europe, chalk is important in the United Kingdom, France, and Belgium, whereas crushed marble is often used in Italy and Greece.

Dolomite 

Has many of the uses outlined for limestone, plus several others, including in refractories, in seawater magnesia and magnesium metal production, and as a dimension stone. Although less common than limestone, dolomite production, particularly for aggregates, is extremely widespread. In the United States, nonaggregate production is concentrated in California, Ohio, Michigan, Alabama, Texas, Connecticut, and Pennsylvania. Europe has an active dolomite industry where it is used extensively as a raw material for refractories and seawater magnesia production. The main producers are Spain, the United Kingdom, Belgium, France, Germany, Norway, Sweden, and Finland.

Diatomite

Diatomite deposits are formed through the accumulation of the frustules of diatoms, small animals that thrived after the Cretaceous period. Diatoms require marine or freshwater rich in nutrients like phosphates, nitrates, and silica, and relatively free of sediment. In many cases, the diatomite is associated with volcanic activity, which may be the source of silica. Important diatomite production sites include the western United States—especially California, Nevada, Washington, and Oregon. Almost three quarters of the world’s production comes from the United States, China, Japan, and Denmark (although the last produces mainly moler, an impure diatomite product). Other producers are Spain, Germany, Italy, Iceland, and Korea.

Phosphate Rock

The bulk of commercial phosphorus-based compounds are derived from marine sedimentary phosphate rock deposits, with much of the rest derived from igneous deposits. Sedimentary phosphate deposits are concentrated in two main belts, the trade-wind belt that is aligned north–south from the equator to 50° latitude, and the equatorial belt, oriented west to east in low latitudes. In the tradewind belt, deposits are located in the southeastern and northwestern United States (Florida, North Carolina, and Idaho); Baja California, Mexico; Sechura Desert, Peru; and the Caribbean Sea. In the equatorial belt, deposits are found in North Africa (Morocco, Tunisia, Algeria, Togo); the Middle East (Jordan, Israel, Syria, Senegal, Iran); the former U.S.S.R.; Venezuela; and Colombia.

More than 80% of the world’s phosphate rock production comes from the United States, Morocco, China, Russia, Tunisia, and Jordan. Morocco is particularly important because it the leading exporter. A series of middle-range producers include Brazil, Israel, Togo, and South Africa. The production in Russia, Brazil, and South Africa is largely derived from igneous deposits that may also yield rare earths, vermiculite, or copper.

Sulfur

The discretionary extraction of sulfur has declined as more and more production is based on nondiscretionary by-product sulfur extracted to comply with environmental regulations at nonferrous smelters and roasters, natural gas and crude petroleum processing plants, coking plants, and the like. Native sulfur associated with the cap rock of salt domes and in sedimentary deposits is still mined by the Frasch hot-water method (mainly in Poland but no longer in the United States), and the mining of pyrite as a source of sulfur is restricted to China.