1044 A TREATISE ON METAMORPHISM. 



Since upon, the whole Vogt has most closely studied ores produced by 

 magmatic segregation, and has been the most vigorous advocate for the 

 existence of such, I quote from him a parag-raph giving a list of deposits 

 which he believes to be of igneous origin : 



Ore deposits formed by simple magmatic differentiation are confessedly infre- 

 quent, and therefore relatively subordinate in importance to other classes. Under 

 this head niay be named: (1) The occurrences of titanic iron ores in basic and inter- 

 mediate eruptives, perhaps also of iron ores in acid eruptives; (2) those of chromite 

 in peridotites and their secondary serpentines (and also according to J. H. Pratt, 

 those of corundum in the peridotites of North Carolina); (3) a number of deposits of 

 sulphide ores, particularly the nickeliferous pyrrhotites occurring in gabbro (at Sud- 

 bury, Canada, Lancaster Gap, Pennsylvania, many places in Norway and Sweden, 

 and Varallo, in Piedmont); (4) according to some authorities, the auriferous pyrites 

 of Rossland, British Columbia; (5) according to B. Lotti, the high-grade copper 

 ores occurring in serpentinized peridotites in Tuscany and Liguria, Northern Italy 

 (for instance at Monte Catini), and analogous occurrences in other regions; (6) the 

 occurrences of metallic nickel-iron (without economic value) in eruptive rocks; (7) 

 those of the platinum metals in highly basic eruptive rocks, etc. 



It may be pretty safely assumed that the foregoing list will be enlarged by 

 future investigations, though it can never become very extensive/' 



Of these classes the first mentioned, the titanic iron ores, is probably 

 the largest. This class of ore deposits has been elaborately considered by 

 Vogt, and a full list of illustrative localities is given by him. 6 Of such ore 

 deposits the only ones with which I am familiar are the titaniferous mag- 

 netites at the base of the Duluth gabbro in the Lake Superior region. 

 While I have not studied these deposits closely I have no reason to dissent 

 from Vogt's belief that they are differentiation products of the gabbro 

 magma. Recently Lindgren has described a very large titanic iron ore 

 deposit at Iron Mountain, Wyoming, which I understand him to believe to 

 be derived by magmatic segregation from an igneous rock/ The total 

 mass of titaniferous iron ores is large, but much of this material is of low 

 grade. It is for the most part high in titanium, averaging about 12 to 20 

 per cent of titanium oxide, but occasionally having as little as 3 per cent. d 



«Vogt, J. H. L., Problems in the geology of ore deposits: Genesis of ore deposits, 2d ed., pub- 

 lished by Am. Inst. Min. Eng. 1902, pp. 642-643. 



6 Vogt, J. H. L., Weitere TJntersuchungen iiber die Ausscheidungen von Titaneisenerzen in ba- 

 sischen Eruptivgesteinen : Zeit. fur prak. Geol., Jahrgang 1900, pp. 233-242, 370-382; Jahrgang 1901 r 

 pp. 9-19, 180-186, 289-296, 327-340. 



'Lindgren, Waldernar, A deposit of titanic iron ore in Wyoming [a paper presented to. the 

 Geological Society of Washington]: Science, new ser., vol. 16, 1902, pp. 984-985. 



^Kemp, J. F., Titaniferous iron ores of the Adirondacks: Nineteenth Ann. Rept. U. S. Geol. 

 Survey, pt. 3, 1899, pp. 387-388. 



