Thursday, May 7, 2015

Clastic 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.

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 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.

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