-448 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



lized granodiorite shows impoverishment in the more mobile hornblende and 

 accessories, which are segregated into intercalated recrystallized bands. Thus 

 hornblende-free, crushed rock indistinguishable in composition from the rock 

 of the Eastern phase occurs sporadically in many local areas within the normal 

 crushed granodiorite of the Western phase. 



In summary, then, the Eemmel granodiorite, gneissic biotite granite, biotite 

 gneiss, biotite-quartz diorite, and hornblende gneiss appear to belong to a single 

 batholithic intrusion. The mean of the two chemical analyses corresponds to 

 the analysis of a fairly typical granodiorite. In view of the greater volume of 

 the Western phase it appears that the average original rock of the whole bath- 

 olith was a granodiorite quite close in its composition to a quartz-hornblende- 

 biotite diorite. 



This mass has been dynamically and hydrothermally metamorphosed with 

 intense shearing in zones trending 1ST. 20° to 25° W. Over most of the 

 batholith so far investigated these zones of physical and chemical alteration 

 are not so well developed as to obscure the essential nature of the primary 

 magma (Western phase)-. The shearing and transformation are much more pro- 

 found in a wide belt elongated in the general structural direction 1ST. 25° W. 

 Here the rocks are well banded biotite gneisses, the material of which is residual 

 after the deep seated, wholesale leaching of the more basic mineral matter from 

 the crushed granodiorite (Eastern phase). 



Kruger Alkaline Body. 



GeneiHl Description. — All the way from the Great plains to the Pacific 

 waters nepheline rocks are extremely rare on the Eorty-ninth Parallel. The 

 Boundary section is now so far completed that it can be stated that in the entire 

 section the Kruger body is the only plutonic mass bearing essential nepheline; 

 it is likewise the most alkaline plutonic mass. 



One of its principal characteristics is great lithological variability. It 

 varies signally in grain, in structure, and* above all in composition. (Plate 39). 

 All the varietal rock types carry essential feldspars of high alkalinity — micro- 

 perthite, microcline, soda-orthoclase, and orthoclase. Nephelite, biotite, olive-' 

 green hornblende, a pyroxene of the segerite-augite series, and melanite complete 

 the general list of essentials. Titanite, titaniferous magnetite or ilmenite, 

 rutile, apatite, and acid andesine, Ab. An, (the last entirely absent in most of 

 the rock phases), form the staple accessories, though any one or more of the 

 coloured silicates may be only accessory in certain phases. Muscovite, 

 hydronephelite, kaolin, calcite, epidote, and chlorite are secondary, but on 

 account of the notable freshness of the rocks are believed to be due to crush- 

 met amorphism more than to weathering. 



According to the relative proportions of the essential minerals, at least ten 

 different varieties of alkaline rock have been found in the body. These are:— 



Angite-nepbelite malignite, Hornblende-nephelite syenite, 



-Augite-biotite-neplielite malignite, Biotite-melanite-nepkelite syenite, 



Augite-biotite-inelanite malignite, Augite-biotite-nepbelite syenite, 



Homblende-augite malignite, Porpbyritic angite syenite, 



.Augite-nepbelite syenite, Porpbyritic alkaline biotite syenite. 



