34 NEW YORK STATE MUSEUM 



In this connection, the work of Goldschmidt^ on the zinc deposits 

 of the Christiania region, Norway, is of much interest. As the 

 deposits in question occur in Paleozoic rocks which have not under- 

 gone the pronounced regional metamorphism which characterizes 

 the Adirondack rocks, it is possible to work out the history of the 

 minerals in much greater detail than in the Edwards district and, 

 in spite of marked differences between the two regions, Gold- 

 schmidt's conclusions with reference to the one have a direct bear- 

 ing upon the other. 



The Christiania ores, according to Goldschmidt, are of contact 

 origin, and are formed in limestone as a result of the intrusion of 

 various igneous rocks but, particularly, granite. The ores occur 

 either directly at, or adjacent to, the contact between the igneous 

 rocks and the limestones or in bodies some distance away from the 

 contact, which are localized by the presence of fissures or channels 

 in the rocks at the time of the intrusion. Evidently, it is to the 

 latter type that the Edwards ores are analogous. 



In the Christiania deposits, there is a much greater variety of 

 minerals, both ores and silicates, than at Edwards, and there is 

 further, an abundance of pneumatolytic minerals, or minerals 

 formed by gaseous magmatic emanations, which are conspicuously 

 lacking at Edwards. Evidently, in the Christiana district, the con- 

 tact metamorphism was more localized and more intense than at 

 Edwards and involved the action of abundant " mineralizers " such 

 as fluorine, chlorine etc. 



According to Goldschmidt's interpretation, the blende and other 

 metalliferous minerals were deposited at a temperature near that 

 of the high-temperature silicates, although the sulphides are stated 

 (page 218) to be somewhat younger than the silicates, as is the case 

 with the Edwards deposits. 



While, at Edwards, no direct clue has been found as to the prob- 

 able reactions involved in the transfer of the zinc from the granite 

 to the limestone, Goldschmidt (page 251) maintains that, in the 

 Christiania district, the metal was originally present in the granite 

 magma as sulphide and was converted into chloride by magmatic 

 hydrochloric acid, according to the equation 



2HCI + ZnS = ZnCl^ + H,S. 



The zinc chloride, having a boiling point of only 700 C, was 

 volatilized and, together with the other magmatic gases, traversed 

 fissures in the surrounding rocks, permeating their walls. When 

 these gases came in contact with limestone, any free acid would be 



^Goldschmidt, V. M., Die Kontaktmetamorphose im Kristianiagebiet, 191 1, 

 p. 40-55, 63-65, 86-90, 211-20. 



