ORIGIN OF ORE DEPOSITS 33 



(,'nlil. Cold is sometimes found in copper-tourmaline v. in> 

 connected with intrusives. It is found principally in the quartz 

 and the tourmaline lies near the walls of the vein. This is 

 (specially true in Thelemarken. In Ontario auriferous-tourma- 

 line veins occur in which the walls of the country rock are 

 well tourmalinized. 



Titanite, rutile, anastase, and brookite are minerals often 

 formed by pneumatolytic action associated with fluorine and 

 boron-bearing minerals. Molybdenite is also found in quartz 

 veins, pegmatites and granites in such manner as to show pneu- 

 matolytic action. 



The Basic Intrusives. Ore bodies associated with the basic 

 intrusives, gabbros and diabases, are often markedly pneumat- 

 olytic, but not as common as in the granites, yet the process 

 is the same. The principal agent or mineralizer is chlorine 

 instead of fluorine or boron. Titanium would be extracted as 

 the chloride and deposited as the oxide according to the equation : 



TiCl 4 +2H 2 O = TiO 2 +4HCl. 

 Iron is similarly extracted: 



Fe 2 CU+3H 2 O = Fe 2 O 3 +6HCl. 

 The reactions of phosphorus and lead are similar: 



PbCl 2 +H 2 S = PbS+2HCl. 



Fluorine and boron are rare in the basic, but common in the 

 acid intrusives. 



Hydatogenesis. Hydatogenesis is the process by which ore 

 bodies connected with the intrusives of basic and acidic magmas 

 are formed outside the metamorphic aureole. In point of time 

 they are generally post-pneumatolytic. If it happens to be 

 contemporaneous then it must take place beyond the zone of 

 metamorphism. If they appear in the aureole or in the igneous 

 rock itself, they were not formed until solidification and meta- 

 morphism were complete. When the zone of metamorphism is 

 free from minerals indicating mineralizers, the lode may be 

 considered to belong to the hydatogenetic class. The ores are 

 sulphides and oxides of the metals, the former predominating. 

 To determine whether the ore body is of pneumatolytic or 

 hydatogenetic origin, the geologist must look first to the nature 



