148 NEW YORK STATE MUSEUM 



hint of their origin or relation to other minerals except that occa- 

 sionally they seem to be molded upon the mica. 



The rusty gneiss underlying the ore is strongly foliated and in 

 hand specimens shows abundant mica, quartz, some pyrite and 

 garnet. Thin sections show quartz, muscovite, bleached and altered 

 biotite, much garnet and chlorite, little or no graphite, and con- 

 siderable pyrite. The latter is sometimes molded upon other 

 minerals as in figure 4. 



In chlorite there is sometimes a very free growth of pyrite, as 

 shown in figure 5- . 



From these facts it is apparent that the pyrite has crystallized in 

 its present position after all the other minerals, including the 

 secondary chlorite but excepting sericite, were formed. This of 

 course makes the deposition of the pyrite subsequent to the meta- 

 morphism which converted the Grenville sediment into the existing 

 gneiss, since the chlorite in which the pyrite has grown is an altera- 

 tion product of the metamorphic minerals. This is an important 

 step toward determining the origin of the deposits if it can be proved 

 that the foregoing relations are not simply the result of circulation 

 and recrystallization of pyrite already present in the rock long before 

 this final precipitation. 



THE HENDRICKS MINE 



About two miles northeast of the Cole mine, on the Hendricks 

 farm, are some small openings of pyrite which have never got 

 beyond the stage of prospects, but are nevertheless of interest in 

 their bearing upon the problem of genesis. Here again, as at the 

 Cole mine, the pyrite deposits lie in the midst of Grenville rocks 

 with no large masses of igneous rocks near by. The pyrite is near 

 the bottom of a heavy body of fine, strongly laminated Grenville 

 gneiss, the ore being simply a pyritous and therefore " rusty " part 

 of the formation. This eneiss makes a hioh rid2:e north of the mine. 



I 





Fig. 6 Rusty gnsiss and ore shown by heavier shading 



while to the south there is a wide gap in outcrops except for some 

 fifty feet of typical limestone almost immediately beneath the ore. 

 The section is diagrammatically represented with little reference to 

 scale in figure 6. 



