39^ 



E. C. HARDER AND R. T. CHAMBERLIN 



Concentration ores. — Concentration ores occur in the neighbor- 

 hood of other ore deposits or of iron-formation beds by the disinte- 

 gration of which they are formed. They are in the form of surface 

 deposits and do not go to a great depth. Of such deposits the canga 

 ores are the most widespread, occurring as surface blankets of great 

 horizontal extent over a large portion of the areas of iron formation, 

 as well as over areas of other rocks bordering the iron-formation 



Fig. 14. — The Fazenda de Alegria. The prominent mountain is the Serra do 

 Caraga. The lower range of hills in the middle distance are the hills of laminated 

 iron ore. The ranch house is built upon canga-covered Piracicaba schist. 



belts. They are composed of material resulting from the disinte- 

 gration, not only of the iron ore portions of the iron formation, 

 but from the itabirite phase as well. 



Canga consists of different sized fragments of iron ore mixed 

 in places with fragments of itabirite, the whole cemented together 

 by iron oxide. The incorporated fragments vary ip size from sand 

 grains to bowlders weighing perhaps several tons. Some of them 

 consist of pure massive ore, others of laminated ore or itabirite. 

 The fragments have been mechanically concentrated and have 



