7i6 PETROLOGICAL ABSTRACTS AND REVIEWS 



indicative of a eutectic mixture. Various conclusions regarding the order of 

 crystallization in such magmas are drawn from petrographic data. The 

 crystallization temperature for the normal norites is calculated (estimated) 

 to lie between 1200° and 1300° at an atmosphere's pressure. From norite 

 magmas acid dikes are distinct differentiation products, hence very generally 

 associated with nickel-bearing norite. Petrographically the writer seeks to 

 establish in such basic rocks (of the picrite-norite series) the increase of the 

 nickel content with increase in hypersthene or bronzite; all the nickel deposits 

 associated with peridotite have an exceptionally high nickel content. 



The sulphides in the norite masses are supposed to be precipitated from the 

 melts with decreasing temperature and then to settle to the bottom; the 

 small amount of sulphides remaining later crystallized with the silicates and was 

 not wholly segregated. 



This work has demonstrated: (i) that the origin of nickel-pyrrhotite 

 deposits may be explained by the laws affecting a system liquid-Uquid; (2) 

 that the leucocratic acid pyritiferous dikes correspond to the end-product of 

 crystallization in a noritic magma bearing a slight amount of free quartz; (3) 

 that the numerous occurrences of a chalcopyrite-rich sulphide mixture in 

 locally distributed veins, especially such as are limited to the border phases 

 of the rock, depend upon the fact that the chal copy rite was concentrated in 

 the end magma through progressive solidification of the sulphide constituents. 



