GEOLOGY OF GRAVES MOUNTAIN 



207 



* Classed as of II. 



Geology of Graves Mountain. The rock composing Graves Mountain 

 which, as indicated on the map, fig. 1, lies between the group of gold mines 

 along Little River and the Seminole mine but nearer the latter, is a fine- 

 grained quartzite. It varies from moderatelj^ thinly foliated to essentially 

 massive in structure. Its position is along the northwest margin of a 

 metamorphic sedimentary series of crystalline rocks. The dip of the quart- 

 zite is toward the northwest at a variable angle and the strike is north- 

 northeast. No igneous rocks have been observed at Graves Mountain but 

 acid and basic intrusions occur at other localities within the general area 

 as described above. The basal portion of the mountain and for some dis- 

 tance up the slope on the northwest side the rock is the foliated variety 

 quartzite-schist, while the crest and for an undetermined distance down the 

 slopes the rock is massive quartzite, with only a tendency to schistosity 

 indicated. This latter phase (massive) of the quartzite has been designated 

 by Shepard* the rather rare variety kno^\^l as itacolumite. On top of the 

 mountain the quartzite is cut by quartz veins, some of the larger ones of 

 which measure several feet in thickness. These do not appear to have been 

 crushed or brecciated and are apparently barren. Smaller quartz veins 

 only a few inches wide contain rutile and iron oxide. The rock from some 

 of the small openings shows fracturing and brecciation. 



The quartzite schist is light in color when fresh but is very generally 

 discolored at the surface some shade of red by iron oxide from weathering. 

 It is composed of quartz and less sericite as the essential minerals, with 

 cyanite and occasional small grains of rutile and black oxide of iron as the 

 principal accessory minerals. A partial chemical analysis of this rock gave 

 SiOo 79.18 per cent; AI2O3, 14.14 per cent; and FejOs, 3.17 per cent. 



Under the microscope thin sections of the rock show a fine-grained 

 mosaic of angular quartz, colorless mica (sericite), stout columnar crystals 

 of colorless cyanite with frayed out and ragged ends, usually partly altered 

 to muscovite and red oxide of iron, and frequently containing inclusions of 

 rutile and quartz. In some cases the iron oxide obscures much of the cyan- 



*Shepard, Chas. U., Amer. Journ. Sci., 1859, vol. 27. 



