404 E. C. HARDER AND R. T. CHAMBERLIN 



geological agency, and the necessity for further investigation on this 

 most important subject. 



MANGANESE ORES 



With the exception of gold, manganese ore is the most important 

 of the metalliferous mineral products of Brazil at the present time. 

 Two mines in central Minas Geraes, the Morro da Mina mine 

 north of Lafayette, and the Wigg mine east of Miguel Burnier, 

 are in continuous operation, while several smaller mines produce 

 ore intermittently. Among these are the Rodeio mine near Kilo-- 

 meter 508, east of Miguel Burnier on the Ouro Preto branch of the 

 Central Railroad of Brazil, the Cocuruto mine southwest of La- 

 fayette, and the Queluz das Minas mine near the Morro da Mina 

 mine north of Lafayette. Many abandoned and inactive mines 

 occur in the general vicinity of the mines mentioned above. 



The manganese deposits of central Minas Geraes may be 

 separated into two distinct classes: (i) those occurring in the 

 basement complex and (2) those occurring in the overlying sedi- 

 ments. The deposits found in the region around Lafayette belong 

 to the first class, while those occurring along the Ouro Preto 

 branch railway east of Miguel Burnier are of the second class. 

 The centers of these two districts, having distinct types of deposits, 

 are not more than 25 kilometers apart, and some of the mines in the 

 one can be seen from the other. The deposits have been described 

 in detail by Derby^ and by Scott,^ so that only a general outHne 

 need be given here in order to show their relation to the general 

 stratigraphy. 



The manganese deposits which are found in the basement com- 

 plex consist of large irregular masses of manganese oxide inclosed 

 in, or bounded by, gneiss, granite, or crystalline schist. Individual 

 masses such as that at Morro da Mina may be more than a hundred 

 meters in their longer diameter. While irregular in shape, they 

 are usually somewhat elongated, suggesting lenses. They occur 



' O. A. Derby, "On the Manganese Ore Deposits of the Queluz (Lafayette) 

 District, Minas Geraes," Am. Jour. Sci., XII (1901), 18-32; "On the Original Type 

 of Manganese Ore Deposits of the Queluz District, Brazil," ibid., XXV (1908), 213-16. 



2 H. K. Scott, "The Manganese Ores of Brazil," Jour. Iron and Steel Just. (1900), 

 p. 179. 



