USEFUL METALS 179 



Character of the Ore Bodies. Cassiterite occurs as a primary 

 Cation in the acid intrusives. It is found in fissure veins 

 traversing granites, pegmatites, gneisses, porphyries, mica schists, 

 chlorite schists, etc. Its home is often in veins of pegmatite 

 associated with lithium bearing minerals as tourmaline, lepidolite, 

 xinmvaldite and spodumene. This type of formation is pro- 

 nounced in Maine, the Carolinas, the Black Hills, and in South 

 Africa. 



The second type of formation might lead to the conclusion that 

 cassiterite is a product of secondary deposition. It is found in 

 veins, beds, and stocks in association with quartzose, crystalline 

 schists, and even traversing shales. (See Fig. 98.) Penrose has 

 reported tin in the Malay Peninsula as occurring in beds in lime- 

 stones and sometimes even in sandstones. 



The most important mode of occurrence is in quartz veins 

 traversing granites and pegmatites. The granite has become 

 greisenized, that is, orthoclase has altered to lepidolite and zinn- 

 waldite with topaz and tourmaline as associated minerals. The 

 presence of minerals bearing boron and fluorine, together with 

 the greisenization of the granite walls would lead to the con- 

 clusion that cassiterite may be formed by the injection of vapors 

 bearing tin and the well-known mineralizers fluorine and boron. 

 Fluorine is able at a high temperature to form a volatile compound 

 with tin, which at lower temperatures and in the presence of 

 steam would be decomposed into the oxide of tin and hydro- 

 fluoric acid according to the following equation, SnF4+2HzO = 

 SnO 2 +4HF. 



Geographical Distribution. There are five distinct belts of 

 tin-bearing minerals in the United States, but none of them 

 have assumed the proportions of a large producer. (1) The 

 Appalachian belt; (2) the Black Hills district; (3) the Cordilleran 

 section; (4) the Pacific Coast belt, and (5) the Alaskan district. 



(1) The Appalachian Belt. Numerous deposits of cassiterite 

 occur in this belt which stretches from Alabama to Maine. In 

 Maine tin ores occur in Hebron, Paris, Stoneham and Winslow. 

 In Massachusetts cassiterite occurs in Chesterfield and Goshen 

 associated with albite and tourmaline. In Virginia it is found in 

 Rockbridge County with wolframite. The most promising 

 field in this belt lies in the Carolinas. According to L. C. 

 Graton and H. Ries, it stretches from near Gaffney, Cherokee 

 County, South Carolina, across parts of Cleveland and Gaston 



