Park. — Magmatic Segregation. 15 



Vyzaj and Kaiva Elvers, on the western flanks of the Urals, 

 consists of olivine-gabbro containing disseminated grains of 

 platinum, but not apparently in payable quantities. An 

 olivine rock was discovered in 1893 at Goroblago-datsk, on 

 the western side of the Urals, containing chromite and pla- 

 tinum, the latter at the rate of lldwt. 9gr. to the ton of rock. 

 Since the discovery of platinum in the nickel-copper sul- 

 phide ore at Sudbury, in Canada, careful analysis has dis- 

 closed the presence of the metal in minute quantity in many 

 sulphide ores throughout the world. But in this and all 

 cases where platinum occurs in sulphide-beds or in veins, its 

 occurrence is probably not the result of direct magmatic segre- 

 gation. 



Eruptive Processes. 



The importance of the role played by igneous rocks in the 

 formation of ore-deposits has been specially urged in late 

 years by Professor Vogt,* of Christiania ; Professor Kemp,t 

 of New York; Professor Suess,} of Vienna; and more recently 

 by Waldemar Lindgren§ and W. H. Weed.^i of the United 

 States Geological Staff. 



Vogt directs renewed attention to the close relationship 

 existing between ore-deposits and eruptive processes. Ore- 

 deposits which are generally connected with eruptive magmas 

 are grouped by him into two principal classes, as under : — 



(1.) Ore-deposits formed by magmatic segregation. 



(2.) Ore-deposits formed by eruptive after-actions. 



Ore-deposits belonging to the first group are infrequent,, 

 and therefore economically subordinate in importance to those 

 of the second group. They include, according to Vogt, — 



(a.) The occurrences of titanic-iron ores in basic and semi- 

 basic eruptives ; 



(b.) Chromite in peridotite ; 



(c.) Sulphide deposits, including the nickeliferous pyrrho- 

 tite of Sudbury, in Canada ; 



(d.) Platinum metals in highly basic eruptive rocks ; 



(e.) Copper and metallic nickel-iron in serpentinised peri- 

 dotite. 



* Prof . J. H. L. Vogt, "Problems in the Origin of Ore-deposits," 

 " The Genesis of Ore-deposits," 1901, p. 636. 



| J. F. Kemp, " The Role of the Igneous Rocks in the Formation cf 

 Veins," loc. cit., p. 681 ; also Trans. Amer. Inst. M.E., vol. xxxix, 1902, 

 p. 681. 



I Prof. Edward Suess, Lecture, " Royal Geographical Journal," vol. xx, 

 1902, p. 520. 



§ Waldemar Lindgren, " Character and Genesis of certain Contact 

 Deposits," " Genesis of Ore-deposits," 1901, p. 716. 



II W. H. Weed, " Ore-deposits near Igneous Contacts," Trans. Amer. 

 Inst. M.E., vol. xxxiii, 1903. 



