270 ECONOMIC GEOLOGY 



Origin of the Ores. Wolframite is both a primary and a 

 secondary mineral. In the Cornish tin mines, wolframite is a 

 companion of cassiterite, the most important ore of tin. The 

 two minerals may appear as primary segregations. While 

 tungsten is an annoying impurity, a by-product is obtained 

 which is used in the manufacture of the sodium tungstate of 

 commerce. According to J. D. Irving, wolframite occurs with 

 cassiterite in the Etta tin district of the Black Hills, South 

 Dakota. Primary wolframite has been observed in quartz 

 veins cutting granite; and secondary wolframite in associated 

 limestones, apparently formed by metasomatic replacement. 

 At Oscola, Nevada, the tungstate of manganese is abundant in 

 veins of quartz cutting a porphyritic granite. Scheelite, the 

 tungstate of calcium, is also present in the same veins. Hiib- 

 nerite occurs with scheelite and wolframite in similar veins in the 

 Dragoon Mountains, Arizona. At Trumbull, Conn., the ores 

 are wolframite, scheelite and tungstite. At Longhill, Conn., 

 scheelite occurs along the contact of limestones with hornblende 

 gneiss and diorite. Scheelite occurs in the Province of Quebec 

 in quartz veins cutting slates and sandstones. Its association 

 is with the acid intrusives, as granites and pegmatites, rather than 

 the ultra-basic rocks, as peridotite. 



Character of the Ore Bodies. Tungsten minerals occur as 

 masses (lens-shaped) in the early segregation of an acid magma; 

 in veins cutting acid intrusives; in limestones, by metasomatic 

 replacement; and as contact deposits between limestones and 

 their intrusives. 



Geographical Distribution. There are three belts of tungsten 

 minerals in the United States: the New England, the Cordilleran, 

 and the Western belt. 



Geological Horizon. The ores seem to be confined to the acid 

 intrusives of the older geological formations. 



Method of Extraction. The metal is most easily extracted 

 from scheelite, the tungstate of calcium. 



Uses. The largest and the most important use of tungsten 

 is in the manufacture of tool steel. It imparts both hardness 

 and toughness to the steel. It is this use which renders the 

 mining of tungsten minerals profitable. According to F. L. Hess: 



" The introduction of tungsten into steel gives it the property of holding 

 a temper at a much higher temperature than high-carbon steels. When 

 lathe tools are made from tungsten steel, the lathes may be speeded up 

 until-the chips leaving the tool are so hot that they turn blue." 



