640 



UNITED STATES MINERAL RESOURCES 



In other established mining areas, certain by- 

 products and coproducts have played an important 

 part in the establishment and life of tin mines. 

 Many placer mines produce important amounts of 

 columbite-tantalite (Nigeria) ; others produce sig- 

 nificant amounts of rare-earth minerals and thorium. 

 Often, the economic feasibility of an operation will 

 depend upon the byproducts. Unfortunately, such 

 mines are subject to closure by major discoveries of 

 deposits that contain the associated byproducts. 

 With the discovery of the large rare-earth deposits 

 at Mountain Pass, Calif., much of the market was 

 lost to byproduct monazite and other minerals con- 

 taining rare earths that formerly were recovered 

 commercially from tin placers. The capture of the 

 niobium market by pyrochlore from the Canadian 

 deposits seriously reduced the economic potential of 

 the placers of Nigeria, which historically had pro- 

 duced a salable columbite-tantalite concentrate. 



In some lode deposits, cassiterite is accompanied 

 by several valuable potential coproducts or byprod- 

 ucts, especially lead, zinc, silver, uranium, bismuth, 

 cadmium, tungsten, and fluorite, but most such by- 

 products are not yet marketable. One advantage of 

 complex ores, which helps offset expensive beneficia- 

 tion, is that prices of all commodities are unlikely 

 to be depressed simultaneously. 



Practically all the tin recovered in North America 

 is produced as a byproduct. The lead-zinc mine at 

 Sullivan, British Columbia, has produced over 

 10,000 tons of tin as a byproduct, and some tin is 

 recovered from the molybdenum mine at Climax, 

 Colo. Of perhaps greater significance is the silver 

 recovered from the complex Bolivian ores. In other 

 mines, as at the San Antonio mine, Mexico, the silver 

 produced has been as valuable as the tin. The large 

 Kochiu tin fields of China were originally opened 

 for their silver content. 



In short, a certain amount of the tin produced in 

 the world is dependent upon the value of the by- 

 products, but as the bulk of the tin is produced 

 from placers with limited production of salable by- 

 products, it is unlikely that byproducts will greatly 

 influence future tin production. 



ENVIRONMENTAL PROBLEMS 



By its nature, placer mining tends to reshape or 

 destroy valuable lands along river courses. Without 

 planned rehabilitation, placer tailings are useless for 

 agriculture, but in Malaysia, dredge pools have in 

 places been converted to fish hatcheries and fish 

 farms. Nevertheless, in places such as the Kinta 

 Valley, the richest tin placers lie beneath the most 

 productive farmlands. In such areas, land-use plan- 



ning far ahead of current operations is required for 

 extraction of the tin. In other areas, such as Bolivia, 

 lode mines are in lands virtually useless for agricul- 

 ture. That development of new lode mines need not 

 interfere with other land uses is illustrated by the 

 successful reopening of the South Crofty mine in 

 Cornwall, England, certainly one of the most scenic 

 areas on earth. 



As noted by Heindl (1970, p. 767), "Industrial tin 

 operations, because of the relatively high unit value 

 of the product and the size of the operations, are 

 not important contributors to industrial pollution. 

 Primary tin-smelting operations discharge SO2- 

 containing gas from a 250-foot stack." At present, 

 no tin smelters are in operation in the United States, 

 and no smelter-gas problem from tin ores exists. 



In Southeast Asia, where the greatest tin reserves 

 and resources are found, many of the tin placers are 

 beneath sea water, and no conflicting land-use prob- 

 lems exist. The same can be said for the Siberian 

 placers beneath the Arctic tundra. At present, there 

 is little likelihood that land-use conflicts or environ- 

 mental issues can seriously curtail world tin pro- 

 duction. 



GEOLOGIC ENVIRONMENT 



GEOCHEMISTRY ^ 



Tin is an element of atomic number 50 and atomic 

 weight 118.70, consisting of the isotopes, in percent, 

 Sn"% 0.95; Sn'», 0.65; Sn"% 0.34; Sn''\ 14.24; 

 Sn'^% 7.57; Sn"«, 24.01; Sn"^ 8.58; Sn'^", 32.97; 

 Sn^"', 4.71 ; and Sn'-S 5.98 — one of the more complex 

 isotopic compositions known. Tin has two common 

 valences, +2 and -f 4, with ionic radii respectively 

 of 0.93 A and 0.71 A. Table 132, modified from Bor- 

 chert and Dybek (1960), shows the ionic radii and 

 electronegativity of the more common ions with 

 which tin is associated. Tin also is amphoteric, form- 

 ing either acids or bases. Because of its similarity 



Table 132. — Ionic radii and electronegativity of ions similar 

 to Sn"* and Sn** 



