180 



ECONOMIC GEOLOGY 



Counties, North Carolina, to Lincolnton, a distance of about 35 

 miles. The ore is irregularly distributed in pegmatite dikes 

 traversing the metamorphic sedimentaries. Both the acid and 

 the basic intrusives are present. The acid intrusives is the home 

 of the cassiterite (see Fig. 99). 



(2) The Black Hills District. This field represents the most 

 important occurrence of tin ores in the United States outside of 

 Alaska. The ore is of three types. In quartz veins, impregna- 

 tion deposits, and in placers. The last results in the normal 

 disintegration of the associated tin-bearing rocks and the con- 



FIG. 99. Sketch map showing the location of the Carolina tin belt. 

 After Graton. (By permission of the Macmillan Company, from Ries' 

 Economic Geology.) 



centration of the stream tin through the sorting power of water. 

 The placers carry the purest tin ores, for the other ores of lower 

 tin content associated with the lode deposits have become 

 oxidized at or near the surface. The ore occurs with wolframite 

 and scheelite. 



(3) The Cordilleran Section. A few reports of the presence of 

 cassiterite have been given for this district but the deposits are 

 not large. It occurs, however, near Dillon, Montana, and in 

 Crook County, Wyoming. 



(4) The Pacific Coast Beli; The Temescal tin mines are situ- 

 ated near the northern end of the San Jacinto estate in San 



