Exploitable deposit

Uranium, too, is widely distributed and, since it probably crystallized late in the formation of igneous rocks, tends to be scattered in the faults of older rocks. Some concentration by leaching and subsequent re-precipitation has produced a large number of oxide minerals of which the most important are pitchblende or uraninite, U3O8, and camotite, K2(U02)2(V04)2.3H20. However, even these are usually dispersed so that typical ores contain only about 0.1% U, and many of the more readily exploited deposits are nearing exhaustion. The principal sources are Canada, Africa and countries of the former USSR. 

The present indications do not project a progressive scarcity of many minerals on a world wide scale. There are, however, some signs of regional and countrywise depletion. This is particularly true for the industrialised countries. There are examples of such countries which have shifted from being a net exporter to a net importer of many minerals. This situation is not necessarily due to the exhaustion of all exploitable deposits of the pertinent minerals. Rather, it is a consequence of the facts that some of the remaining deposits have not proved... 

The main interest in wollastonite in polymer applications is due to its acic-ular nature which gives it reinforcing properties. Principal uses in thermoplastics are in polyamides and polypropylene. Only a few exploitable deposits exist and this may have inhibited the growth of polymer applications which tend to require the highest aspect ratio material. 

Strontium occurs chiefly as sulfate (celestite, SrSO,i) and carbonate (strontianite. SrCO ) although widely distributed in small concentration. The commercially exploited deposits are mainly in England. The sulfate or carbonate is transformed into chloride, and the electrolysis of die fused chloride yields strontium metal,... 

These studies have demonstrated the utility of SIMS in understanding the concentration and distribution of precious metals in a number of different ore-deposit types and have often resulted into new insights into the formation of the deposits. This improved understanding can be applied both to search for new deposits and to improve the efficiency of extraction techniques in currently exploited deposits. Given these strengths, it is likely that the use of SIMS in the study of precious metal deposits will continue to grow. 

The platinum-group metals consist of ruthenium, rhodium, palladium, osmium, iridium, and platinum. Each of the metals occurs naturally in its native form, and in economically exploitable deposits the elements occur overwhelmingly as individual platinum-group mineral (PGM) species. Mutual substitution of the various PGE is common, but substitutions in other minerals, such as base-metal sulfides, typically occur to only a limited extent. A comprehensive review of PGM and PGE geochemistry is given by Cabri (2002). 

Synthetic rutile. In recent years the prices for natural rutile have increased due to the increasing scarcity of economically exploitable deposits. Processes for removing iron from ilmenite ore have been developed, to provide a cheap raw material for the chloride process in which the particle form is retained, as this is particularly favorable for fluidized bed chlorination. 

Only a small part, about one third, of the natural zeolite types reported in Table 1 have been found in sedimentary occurrences, as those described above [33,41], In some instances such occurrences are rare, as in the case of faujasite, whose only known sedimentary formation is in the Arilayn region, Jordan [42] in other instances they are very frequent [31. Clinoptilolite-rich luffs, for instance, arc widely spread in numerous locations all over the world and reserves are being continuously discovered. At present exploited deposits (or in view of possible exploitation) arc present in Europe (Bulgaria, Greece, Hungary, Italy, Romania, Slovakia, Slovenia, Turkey, Yugoslavia) [41], in Russia and several states of the... 

Zirconium is ubiquitous in the biosphere and constitutes 0.021% of the Earth s crust. It is classified as the 20th most common element, between barium and chromium, and is consequently more abundant than nickel, tin, copper, and lead. Suitably exploitable deposits exist in Australia, South Africa, the Soviet Union, and other countries. 

Despite the term traditionally applied to this group of elements, rare earths, their crustal abundance is not particularly low. Cerium ranks around 25 in the listing of all the naturally occurring elements, its abundance being similar to that of Ni or Cu [1]. Even the least abimdant lanthanoid elements, Tb, Tm, and Lu, are more abundant than Ag [2]. Because of their geo-chemical characteristics, however, the rare earth-containing minerals consist of mixtures of the elements with relatively low concentration of them [3]. Accordingly, the number of their exploitable deposits, mainly consisting of phosphates and fluoro-carbonates, is rather small [1,3]. 

Exploitable deposits of the above minerals are found on all six continents as shown in Table II, which lists world reserves in units of tons of Reoxide. 

Large exploited deposits exist in Spain, Mexico, Turkey, China, and Iran. There are much less important deposits in Algeria, Cyprus, Argentina, and Morocco. Mining in the United Kingdom, the traditional producer, ended in 1992. 

According to Heaton (1928) Devonshire clay was a then-current alternate term for china clay (kaolin, q.v.). Most kaolin production in the UK comes from Cornwall, where there are extensive deposits in the western half of the St Anstell granite. However, commercially exploitable deposits also occur in nearby granites such as diose on Dartmoor in Devon as well as other granite masses of south-west England. 

These ancient evaporites are typically made up of several distinct layers thin, powdery chuca (10-30 cm of silt, sand, and small rocks) on the surface, moderately to firmly cemented costra (0.5-2 m of either hard or brittle material), and then the caliche, 1-3 m of firmly cemented nitrate underlaid by coba, an uncemented regolith (fig. 3.3). Veins and layers of very pure nitrate are common in some areas, rare in others. Nitrogen content of these deposits varied widely nitrate accounted for as little as 6.5% of the extracted mass in the poorest caliche, and as much as 70% in some salitreras of Tarapaca. Typical share of NaNOs in the exploited deposits was initially 40-50%, but by the beginning of the twentieth century it fell to below... 

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