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E. C. HARDER AND R. T. CHAMBERLIN 



foreign material. They are of little or no importance as an ore 

 reserve. 



Rubble ore deposits occur on the hill slopes below outcrops of 

 hard ore. They are simply talus accumulations consisting of 

 high-grade iron ore, and frequently are large enough to be of some 

 importance for mining purposes. The fragments composing them 

 may vary in size from pebbles to fragments of several tons. In 



Fig. 15. — A cliff of canga on the side of the "Grotto" in Esmeril near Itabira de 

 Matto Dentro. The canga blanket here reaches a thickness of about 15 meters. 



many places, however, one finds rubble ore deposits with fragments 

 remarkably uniform in size. Rubble ores have practically the 

 same composition as the hard ore deposits with which they are 

 associated. 



Small deposits of enriched itabirite occur locally, but are of 

 little importance. They might be termed canga deposits formed 

 in situ, as they occur at the surface in itabirite areas where the 

 leaching of silica has been sufficient to leave the residual material 

 concentrated as iron ore. Frequently the iron oxide itself has been 

 dissolved and redeposited in the form of limonite in pores and along 



