i5° 



.4. F. BUDDINGTON 



Where it occurs as patches or specks it bears no apparent relation 

 to the surface. Furthermore, the pinitic material has undergone 

 dynamic metamorphism and is sheared and cleaved, while chemi- 

 cally its origin involves the introduction of alumina and potash 

 through replacement. 



GENERAL OBSERVATIONS 



It is quite probable that the foregoing processes operated under 

 conditions of some dynamic movement, as their characteristic 

 development is along shear zones, and their products assume a 

 lenticular structure which is as characteristic of the minuter struc- 

 tures of the rocks as of the veins themselves. Moreover, the 

 rocks themselves have been sheared and possess a more or less 

 prevalent cleavage, conditioned by the growth of their constituent 

 minerals in more or less parallel arrangement. 



It is probable that the factors determining which of these three 

 rocks — pyrophyllite, pinite, and quartz-pyrophyllite — shall form are 

 to be found in the temperature, pressure, and chemical content of 

 the solutions themselves, in the relative effectiveness of hydrolysis, 

 and in the mass-action effects of the compounds in solution. 



The concentration of the potash in the pinite, and the silica in 

 the quartz-pyrophyllite rocks may be accounted for on the theory 

 of a redistribution of the elements, but the tremendous contribu- 

 tions of alumina represented by the pyrophyllite, and to a minor 

 extent by the pinite, must be accounted for otherwise. The close 

 connection between the pyrophyllite deposits and the granite- 

 Avondale Volcanics contact south of Manuels and between the 

 pinitized rhyolites and the Woodfords monzonite stock is hence of 

 significance. It may be that there is no genetic connection between 

 these minerals and the intrusives, and that their formation was 

 entirely dependent on the locus of fault zones in those localities. 

 But there are numerous other profound fault and shear zones in 

 this area with no exceptional alterations. 



Hence it seems probable that when faulting took place between 

 the volcanics and the intrusive granite or monzonite, the still hot 

 magmatic waters were released and found their way upward along 

 these fault zones, either contributing the alumina directly, or per- 



