Iron Ore

Although iron ore is one of the most abundant metals in the earth's crust, only those rocks which contain 25 per cent or more of iron are considered worthy of exploitation as iron ores. The total reserves of iron ore in Britain are estimated at 3.8 billion tonnes.

Iron ores are widely found, though they differ in the manner of their formation, colour, appearance, iron content, chemical and physical properties and the quality of metal produced. British iron ores are of poor quality, their iron content ranging from 22 to 32 per cent. In Britain two chief types of iron ore are found: haematite and Jurassic. Haematite contains up to 70 per cent of metal and usually occurs in rocks of Cumberland, near Barrow-in-Furness. But this high-grade ore is nearly exhausted. The Jurassic iron ores contain only about half as much iron as haematite, or even less. They are frequently found in the rocks which extend from the Cleveland Hills, in Yorkshire southward through Lincolnshire and Northamptonshire, as well as in Lancashire and North Staffordshire.

In order to extract the metal from iron ore it is necessary to heat it with carbon. The original source of carbon used in this smelting process was charcoal, and many wellwooded areas where iron-making was at one time concentrated, were almost completely denuded of trees by charcoal-burners. Coke was first introduced in the early eighteenth century, and by 1750 it was being widely used in place of charcoal.

Most of ironfields in Great Britain are to be found in the areas of major coal-basins, and this created favouralbe conditions for the development of metallurgy, especially at early stages of its history. By about 1850 most of the best iron ores had been worked out, but the demand for iron ore was greater than ever — for making railway lines, locomotives, ships, machinery, bridges, and for constructional purposes generally. As a result, attention was turned to the lower quality ores in the Cleveland Hills. Teesside in North-East England rapidly grew into an important iron and steel centre, using not only local ore but also much imported from Spain, and later from Sweden. Developments in the Scunthorpe and Frodingham area of northern Lincolnshire followed soon afterwards, and in the 1930s the operations began in the Corby area of Northamptonshire on the local deposits of iron ore containing only about 32 per cent of iron. The Corby ores are quarried with large-scale excavating machinery and open-cast methods.

As the metallurgical industry expanded, the failing supplies of domestic ore could no longer keep pace with the demands for the production of pig-iron and steel. Home production was greatly supplemented, and later greatly surpassed, by imports. In 1913 domestic output of high-grade ore was 2.5 million tonnes against the imports of more than 7 million tonnes which came chiefly from Spain and North Africa. In 1920 home output had fallen still more greatly — to 1.5 million tonnes, and it continued to decline during the inter-war period and afterwards. At the beginning of the 1980s Britain produced only 900 thousand tonnes of iron ore — a very small proportion of its annual consumption of about 32 million tonnes (the remaining part being imported), in 1987 — only 300 thousand tonnes.

Meanwhile Sweden has emerged as the chief supplier of iron ore, followed in order by North Africa, Spain, Canada, West Africa and South America. Imported ores are generally far richer than those produced domestically and they can stand the cost of transport from a distance.

The production of other metallic minerals is overshadowed by the importance of coal and, more recently, petroleum. Great Britain has no large-scale sources of non-ferrous metals, but small scattered deposits of lead, tin, copper, zinc and even gold have been known and worked at various times during the last three thousand years. In the pre-Christian era Phoenicians visited Cornwall in search of tin, which is found in association with copper among igneous rocks. The Romans, who were pioneers of plumbing, worked lead mines in Derbyshire. As recently as a century ago, Britain was still a leading producer of non-ferrous ores, especially of tin in Cornwall and of lead in Derbyshire, Cumberland and elsewhere. But now hardly any deposits are being worked. Most of the mines are exhausted, while others lie neglected and flooded. In 1986 the production of metal from non-ferrous ores totalled 15,500 tonnes mainly lead mostly from northern England, and tin mostly from Cornwall. Small amounts of copper and silver are produced in association with tin and zinc. Britain's only tungsten mine, in Cumberland, was reopened in 1977 and its capacity increased in 1978, while permission to develop a considerable tungsten deposit near Plymouth is being studied.

Some other minerals are found but not extensively worked. Tin, which was once the chief mineral production in the British Isles, is now only worked spasmodically in two mines in Cornwall, while copper, also important at one time is no longer worked. Very small quantities of manganese are found in the tinmihing areas of Cornwall, and some bauxite occurs in beds among the volcanic rocks of Antrim near Ballymena and Larne in Northern Ireland.

The major bulk of non-ferrous metals indispensable for Britain's economy is imported.

Дата добавления: 2015-08-21