ORES PRODUCED BY IGNEOUS PROCESSES. 1045 



In consequence of their low grade and the difficulty of smelting them, 

 titanium ores are at present of little or no economic importance. In the 

 future, when high-grade nontitaniferous ores are exhausted, or nearly 

 exhausted, it is possible that such ores will be an important future resource 

 for iron. 



In connection with iron ores produced by magmatic segregation the 

 question naturally arises as to why they are titaniferous. The answer is 

 substantially that they are titaniferous because they are magmatic segrega- 

 tions. The magnetite in diabase, gabbro, and other basic rocks is almost 

 universally titaniferous. This being true, it naturally follows that where 

 this magnetite is segregated in sufficient quantity to be an ore such ore is 

 titaniferous. 



So far as I know, all of the iron ores which have been shown to be 

 magmatic segregations are titaniferous. The majority of the great iron-ore 

 deposits which are at present worked are known to have been produced by 

 the action of aqueous solutions. (See pp. 1193-1197.) In view of this fact 

 and the history of titaniferous magnetites, it seems to me highly probable 

 that none of the nontitaniferous ores of iron are magmatic segregations. 



Certain corundum deposits are the result of direct igneous processes. 

 For instance, the corundum syenite of eastern Ontario, Canada, is to all 

 appearances, as shown by its textures and structures, a coarse igneous 

 rock. 11 Apparently the magma was so very" aluminous that at the time of 

 crystallization not all of the alumina was able to combine with the various 

 acids, and hence a part of it separated as an oxide, or corundum, precisely 

 as iron oxide, which does not unite with the acids. 



As to the production of titanic magnetite and corundum ores by 

 magmatic processes there is no difference of opinion. But it appears to 

 me that a point which should be emphasized in this connection is that 

 aluminum and iron are the two most abundant metals of nature, and 

 therefore they are the ones which are most likely during crystallization of 

 magmas to segregate as oxides to such an extent as to produce ores. 



The extent to which magmatic segregation must take place in order to 

 produce an igneous ore of iron or aluminum is comparatively small. To 

 illustrate, the average amount of metallic iron in original igneous rocks is 

 4.64 per cent, 6 and in the basic rocks in which magmatic iron ores occur it 



« Miller, W. G., Economic geology of eastern Ontario; corundum and other minerals: Rept. 

 Bureau of Mines, vol. 7, pt. 3, 1898, pp. 210-213. 



b Clarke, F. W., Analyses of rocks, laboratory of the IT. S. Geol. Survey, 1880-1899: Bull. U. S. 

 Geol. Survey No. 168, 1900, p. 15. 



