USES OF TIN
Tin, ordinarily considered one of the minor metals, is nevertheless a metal of prime importance in the world’s present state of development. In 1913 the value of the world’s output of tin was $131,000,000, which was greater than the value of the world’s output of either lead or zinc. Without tin it is very doubtful if the present methods of food packing and distribution could have been accomplished. The principal use of tin is in the manufacture of tin plate, from which are fabricated the so-called “tins” or “tin cans” that everyone knows. The second largest consumption of tin is for the alloys, solder and babbitt made with lead, and brass and bronzes made with copper. Minor amounts of tin are used for making fine metal tubing, tin foil, and collapsible tubes for packing such materials as dental and toilet creams, artists colors, etc. Tin is consumed by the makers of silk, principally to give weight and “rustle” to their product.
In 1917 the consumption of tin in the United States was approximately 93,000 tons,[141] of which 19,000 tons was recovered from scrap materials. Of the total consumption 31,000 short tons was used for making tin plate, 20,400 short tons for solder, 13,800 short tons for bearing metals, (babbitt, bronzes, etc.,), and 27,700 short tons for the many minor uses, items of which are 1,000 tons for the silk industry, 5,000 tons for foil, 4,000 tons for collapsible tubes, 3,000 tons for white metal.
[141] In this report the figures for tons refer to metric tons (2,204 pounds avoirdupois) unless otherwise stated, and are given in round numbers because errors in statistics and in conversion do not warrant closer figuring.
It is difficult to distinguish between the essential and the non-essential uses of tin in the industries. Surely tin plate is essential, yet some saving of tin containers was made during the war shortage by curtailing the use of tin and substituting paper and other substances for packages carrying non-perishable products. Solders, bearing metals, and bronzes are unquestionably essential, but variation in alloy specifications made possible, during the war period, a considerable saving of tin without detriment to the results. In fact some of the standards set under the emergency were superior to those used before. Aluminum foil is to some extent replacing tin foil, but no suitable substitutes have been found for tin in the manufacture of collapsible tubes, which are necessities.
GEOLOGICAL DISTRIBUTION
Over 70 per cent. of the tin produced in the world is won from placer deposits, although in the last few years the exploitation of tin-bearing lodes has become of considerable importance. Tin ores are intimately connected with siliceous igneous rocks. Practically all of the known lode deposits are either in or lie near siliceous igneous rocks such as granite, granite-porphyry, quartz-porphyry or monzonitic types. In Mexico and the United States unimportant tin deposits have been found in rhyolite. In only one or two places in the world are tin lodes known where siliceous igneous rocks do not show on the surface, and in these places geologic evidence points to the presence of granitic rocks at no great depth. In the world’s chief centers of tin production—the Malay Peninsula, Bolivia, Australia, Nigeria, Cornwall, and South Africa—the granitic rocks are everywhere in evidence, and the tin lodes are so closely related to these granites that there is no question of their origin.
Fluorine-bearing minerals such as fluorite and topaz, tourmaline, and the tungsten mineral, wolframite, are found in practically all tin deposits. Molybdenite and bismuth minerals are present in many tin deposits, though their distribution is not so general as that of the former minerals. Copper, lead, zinc, and iron sulphides, the latter often arsenical, are common in tin lodes, and quartz and feldspar are the chief gangue minerals.
It is generally accepted that the tin lodes were formed near the close of intrusive activity by the final differentiates of the acid magmas. These final solutions are notable for their pneumatolitic action and their ability to cause the profound change of granite to greisen and the formation of stanniferous pegmatite and quartz veins. Greisen, an alteration product of granite, consists of quartz, mica and varying amounts of topaz and tourmaline. It is commonly developed along fractures, and in favorable places large masses of rock may be greisenized.
Tin deposits are most often found as lodes, both fissure and pegmatitic, or stockworks, but some segregations are known. A peculiar pipe-like form of deposit is found at places in the Transvaal and Tasmania.