R. H. Rastall — The Genesis of Tungsten Ores. 197 



mineralization here, as in Cornwall, is closely connected with the 

 pneumatolytic phase of the Hercvnian granite intrusions, and shows 

 very clearly the genetic association of tungsten with tin and the 

 highly volatile elements, fluorine, boron, and lithium. 



Although the mines of the Erzgebirge in Saxony and Bohemia 

 figure very largely in German mining literature and in textbooks, 

 their yield of tungsten ores does not appear to be large, so far as is 

 known. In 1912, the last year for which official statistics are 

 available, the output for the kingdom of Saxony is stated to be 

 TOl tons, while no other German state appears to have produced any. 

 In the same year the Austrian Empire is said to have produced only 

 66 tons. It is believed that most of the wolfram ores were obtained 

 by working over the old tin dumps. Nothing definite is known as 

 to the extent of the supplies still available, but the}' are probably 

 not very large. It is of course impossible to place great faith in the 

 reliability of German statistics in connexion with any product 

 connected with war preparations, but in this instance the figures 

 may be correct, since in the years before the War Germany imported 

 at least half of the world's total output of tungsten ores. Hence the 

 reserves at hand were probably considerable. 



Besides Great Britain the only other European producer of much 

 importance is Portugal, although Spain also supplies a certain amount. 

 In both these countries the ores are associated with cassiterite, 

 belonging therefore to the group now under consideration. According 

 to Granell * wolfram ores, usually accompanied by cassiterite, occur 

 in a zone consisting of granite intruded into crystalline schists and 

 Cambrian sediments, beginning in Galicia and extending through 

 TTorthern Portugal, Zaraora, Salamanca, and Caceres, and ending 

 where it is cut off abruptly by the great Guadalquivir fault. There 

 is also a similar mineral association in the mountain chains of Central 

 Spain, in the province of Toledo, at Mijas near Malaga, and in the 

 Almagrera Mountains; the latter was the locality of the original 

 manganese-free ferberite, first described by Breithaupt. Little 

 information is available as to the details of the wolframite ore- 

 deposits of Spain and Portugal, but they do not seem to present any 

 special features of interest, and a large part of the output is 

 apparently alluvial. In the Sierra deEstrellain Portugal wolframite 

 occurs in rich lodes up to 4 inches wide, associated with cassiterite 

 and arsenopyrite. 



In the Black Hills of Dakota wolframite occurs in two distinct 

 genetic types: 



1. With tinstone, as at Etta Knob and Nigger Hill. 



2, With siliceous gold-ores. 



The ore-deposit of Etta Knob is very remarkable, and in some ways 

 unique. It consists of a vertical pipe of pegmatite some 60 yards 

 in diameter, containing in addition to quartz, felspar, and mica also 

 cassiterite, wolframite, molybdenite, arsenopyrite, tantalite, columbite, 

 apatite, beryl, and spodumene, the latter in crystals over 30 feet 

 long. The characteristic elements here are evidently tin, tungsten, 



^ Granell, Boll. Soc. Esp. Hist. Nat., vol. ix, p. 81, 1909, and Zeits. fiir 

 Kryst., vol. I, p. 472, 1911. 



