GEOLOGY OF CENTRAL MINAS GERAES, BRAZIL 391 



between 63 and 67 per cent, while the hydrated portions frequently 

 contain as high as o . 3 per cent phosphorus and rarely less than o . 05 

 per cent phosphorus. It is mainly a non-Bessemer ore. With in- 

 creasing quartz sand the content of metallic iron decreases until 

 the material becomes itabirite. Non-hydrated, laminated ore 

 resembles soft, powdery ore in composition. 



The phosphorus content of the surface ores is always higher than 

 that of the ore underground. Where surface ore contains 0.12 to 

 o. 18 per cent phosphorus, underground ore may contain only 0.04 

 to o . 08 per cent. This is due to the concentration of phosphorus 

 during the process of weathering. This same process also con- 

 centrates the iron in the uppermost foot or two, hardening it and 

 decreasing the pore space. 



The size of the different ore deposits varies from mere seams 

 inclosed in itabirite to beds several kilometers in length and several 

 hundred meters in thickness. The largest known deposits are of 

 laminated ore, but there are also hard ore deposits of large size. 

 The largest known laminated ore deposit in the district is that of 

 Alegria, where continuous outcrops occur over a distance of more 

 than 4 kilometers along the strike of the beds and for fully 1,700 

 meters across the beds. With an average dip of 35° the thickness 

 would be at least 1,200 meters.^ This great thickness, however, is 

 not entirely of pure ore, but will possibly be found to include 

 numerous minor beds of itabirite now concealed at the surface. 

 The largest body of hard ore in the district, which, however, has 

 a considerable admixture of soft ore and of hard ore fragments 

 intermixed with soft ore, is that of Periquito near Itabira de Matto 

 Dentro. It has a length of i kilometer and a maximum thickness 

 at right angles to the beds of 250 meters. Other large deposits 

 of hard ore are known in which the proportion of soft ore is very 

 small. Such are the peak of Caue (Fig. 12), the deposits on Serra 

 de Conceigao and Serra do Esmeril near Itabira de Matto Dentro, 

 Itabira Peak near Itabira do Campo, and Morro Agudo Peak near 

 Villa Rio Piracicaba. Deposits consisting largely of pure soft 

 powdery ore are as a rule much smaller than hard ore deposits but 

 more numerous. 



^ See Fig. 4 on p. 354, Part I of this article. 



