GENERAL AXD ECONOMIC GEOLOGY 



269 



The ores occur at two horizons, namely, in the Archean complex and in 

 the early Paleozoic series of rocks. The mines worked are in the vicinity 

 of Lafayette, in the Archean, and at Miguel Burnier, on the Central 

 Railway, in the Paleozoic. Later discoveries have been made on the 

 properties of the Saint John del Key Mining Company at Capitao do 



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Figure 15. — Brazilian method of Diamond ivashing with the icooden Batea 



Matto and Cachoeirinha near Morro Velho. Valuable papers on the 

 manganese deposits of Minas are by Derby, Greven, Lisboa, Lustosa, 

 Michaeli, Scott, Singewald, and Thomas. 



The iron deposits of Minas have long been known, but only within a 

 few years have they attracted the attention to which they are justly en- 

 titled. They are probably the most important iron ores known, though 

 they are as yet but little used. A paper by Dr. Francisco de^Paula Oli- 



FiGURE 16. — Section at the Miguel Burnier Manganese Mines 

 This section is at kilometer 501 of the Central Railway. After Scott. 



veira, published in the Annaes da Escola de Minas, number 3, pages 135- 

 194, tells of the efforts to make iron in the state. The iron ores are in 

 sedimentary rocks, either in and forming parts of the early Paleozoic 

 rocks or they are later deposits derived therefrom. The most important 

 papers on the geology of the ores are those of Chamberlin, Berby, Dupre, 



XIX — Bull. Geol. Soc. Am., Vol. 30, 1918 



