ZINC ORES OF THE EDWARDS DISTRICT 37 



been formed by the same process as the Christiania ores, but by 

 gases exceptionally poor in hydrogen sulphide. 



Mr Newland, in the paper previously cited, refers to the similarity 

 between the Edwards ores and those of Long Lake, Ontario, which 

 have, however, been considered l as deposited before the meta- 

 morphism of the wall rock and subjected to this process with the 

 latter. If this interpretation is correct, it implies a decided genetic 

 difference between the ores of the two localities but, in spite of this, 

 there is marked resemblance in mode of occurrence, age and geology 

 of the country rocks. 



As a matter of fact, zinc ores of the age and character of the 

 Edwards deposits are distinctly rare, as Mr Newland has pointed 

 out. 



From the genetic standpoint, the arsenic-gold ores of Reichenstein 

 in Silesia have much in common with the Edwards ores, though 

 there are great differences in detail, both mineralogical and 

 geological. 



In a recent discussion of these ores, Beyschlag and Krusch 2 have 

 arrived at conclusions the substance of which follows : 



1 The ore deposits are due to granite intrusions into limestones. 



2 An older period of contact metamorphism, during which 

 diopside and tremolite were formed, was followed by a younger 

 period of serpentinization effected by magmatic thermal waters. 



3 Contrary to the earlier views of Wienecke, who advocated two 

 periods of ore formation, one during the high-temperature meta- 

 morphism and the other during the thermal water period, there was 

 but one period of arsenic deposition, that of the thermal water 

 periodj and the ores replaced not only calcite but also diopside of 

 the earlier period. 



4 All observations indicate the contemporaneity of the arsenic 

 ores and the main mass of the serpentine, while smaller quantities 

 of a younger serpentine occur filling cracks in the older minerals. 



Thus, the hot waters that produced the serpentine also deposited 

 the arsenic ores, as well as the gold which they carry. 



The parallelism between these views and those here expressed 

 as to the origin of the serpentine is obvious, and while the deposition 



1 Uglow, W. L., Ore Genesis and Contact Metamorphism at the Long Lake 

 Mine, Ontario ; Economic Geology, XI, 1916, p. 231-45. 



2 Beyschlag, F. & Krusch, P., Das Arsenerzvorkommen von Reichenstein, 

 Die Erzlagerstatten von Frankenstein und Reichenstein in Schlesien ; 

 Abhandlungen der Koniglich Preussischen Geol. Landesanstalt, Neue Folge, 

 Heft 73, 1913, PP- 55-92. 



