GEOLOGY OF CENTRAL MINAS GERAES, BRAZIL 355 



Several minor offshoots to the east occur from the northward 

 extension of the range, and at a point west of Serro the range 

 divides, one branch running northeastward, forming the Serra do 

 Chifre, on the divide between Rio Doce and Rio Jequitinhonha, and 

 the other continuing northward past Diamantina toward the state 

 of Bahia. 



The northeast-southwest belt of sediments previously men- 

 tioned as cutting off the north-south overturned syncline near 

 Bello Horizonte consists mainly of Itabira iron formation and 

 Piracicaba schist dipping southeast. Locally a thin layer of 

 argillaceous and quartzitic schist, representing the Caraga quart- 

 zite, occurs at the base. The belt is of considerable extent, be- 

 ginning at a point northeast of Caethe, east of the main Serra do 

 Espinhafo, and running first southwestward past Bello Horizonte 

 and the end of the north-south overturned syncline already men- 

 tioned, and then westward and northwestward toward Pitanguy. 

 It forms a prominent range known as the Serra da Piedade which 

 consists for the most part of iron formation. Toward the west, 

 however, the quartzite becomes more prominent, forming some con- 

 spicuous mountains. 



The Caraga quartzite, while present almost throughout the 

 district, varies greatly in thickness. In the isolated sedimentary 

 areas in the eastern part of the district, as near Villa Rio Piracicaba, 

 there are places where it is less than 30 meters thick ; in the region 

 south and east of Bello Horizonte it appears to be in places entirely 

 absent, while along the main Serra do Espinhago it reaches thick- 

 nesses greater than 1,500 or 1,800 meters. The latter is the more 

 typical development of this great formation. 



The ordinary phase of the Caraga quartzite consists of quartz 

 grains intermixed with more or less white mica. Where highly 

 metamorphosed, and this is especially true where the formation is 

 thin, the mica is sometimes coarsely crystalline so that individual 

 flakes frequently reach half an inch in diameter. When quartz 

 occurs in these phases it is also coarsely crystalline. Such coarsely 

 crystalline phases, however, are rare. Where the formation con- 

 sists largely of quartzite, it is prominent topographically, but 

 where the schist layers are abundant and well developed, it gives 

 way rapidly to erosion. 



