USEFUL METALS 



106 



Character of the Ore Bodies. The sulphides of iron, pyrite 

 and pyrrhotite, occur in well-defined fissure veins, as primary 

 segre^at ions tVuin a sulphidie magma, as contact deposits bet 

 igneous and sedimentary rocks. As stated earlier, the sulphides of 

 iron play no part in the metallurgy of the metal in the United 

 States. Attempts have been made in the southern Appalachian 

 belt to manufacture high-grade pig iron from sulphides but these 

 efforts proved futile and the process was abandoned. 



Magnetite occurs (1) as lens-shaped masses differentiating from 

 a peridotite magma (see Fig. 103); (2) as lenticular masses in the 

 metamorphic rocks, this is by far the most important form of the 

 ore bodies of magnetite of commercial significance; (3) as contact 



IGNEOUS VCIN WITH SCHLIfKCN 



> XSXX 



- T XX 



FIG. 103. Vein of norite, 30 to 70 yd. in width with schlicrcn of 

 titaniferous iron ore. (After J. H. L. Vogt.) 



deposits between intrusives and sedimentaries, but often too 

 high in titanium to be of great commercial value; (4) as placer 

 sands arising from the decomposition of the higher rocks, often 

 auriferous, and (5) as beach sands on the shores of lakes and seas. 

 Hematite occurs as basin-shaped replacement deposits; as 

 bedded deposits and as contact deposits. Limonite is often 

 residuary. If fills the cracks, joint planes and fissures in the 

 earlier stages of the decomposition of ferriferous rocks. It oc- 

 curs also as replacement deposits. These are often concentrated 

 into beds of great thickness. In the weathering of pyritiferous 

 ore bodies and the leaching of chalcopyrite, limonite may be 

 formed in sufficient quantities to be of commercial significance 



