250 ECONOMIC GEOLOGY 



are utilized directly in the manufacture of ferromanganese and 

 spiegeleisen. If the percentage of silver, lead, manganese and iron 

 are too low to pay for the profitable extraction of any one of these 

 metals the ores are sold directly as a flux and the lead and silver 

 content reclaimed as a by-product. 



The manganese zinc residuum is derived from the treatment of 

 the manganiferous and zinciferous ores of Franklin Furnace, 

 New Jersey. It consists largely of the oxides of manganese and 

 iron which remain after the zinc has been converted into its 

 oxide, ZnO. Zincite, willemite, franklinite and rhodochrosite 

 are the common minerals. Rhodochrosite is also found as a 

 gangue mineral at Rico, Colorado, and Butte, Montana. 



Geographical Distribution. Manganese minerals exist in 

 all deep-sea deposits, in many shallow-water deposits, and in 

 terrestrial deposits. There are four distinct belts of manganese 

 minerals in the United States: (1) The Appalachian belt; (2) the 

 Central district; (3) the Cordilleran section; and (4) the Pacific 

 Coast belt. 



(1) Appalachian belt: This belt stretches in a northeasterly 

 direction from Alabama on the south to Nova Scotia on the 

 north. The ores result from the decomposition of Cambro- 

 Ordovician limestones and shales and appear largely as nodular 

 masses in the residual clay. 



Two localities in Georgia are important. They are Carters- 

 ville and Cave Spring. In the former district the ores are found 

 in the residual clays derived from the decomposition of the 

 Beaver limestone and the Weisner quartzite, and in the latter field 

 the manganese deposits occur only in the clays that overlie the 

 Knox dolomite. R. A. F. Penrose attributed the source of the 

 manganese to the underlying Cambro-Silurian crystalline rocks. 

 T. L. Watson, however, considers that the crystalline terranes to 

 the east and the south furnished the ores, for no appreciable 

 amount of manganese is found in the parent rocks from which the 

 clays were derived. In any event the manganese was dissolved 

 from the older rocks as a carbonate or sulphate and deposited 

 from circulating solutions in the residual clays. 



According to H. Ries there are two localities also for manganese 

 minerals in Virginia, the James River valley in the Piedmont 

 region and the Appalachian area. In the former field the ores 

 occur in the residual clays and sands that have been derived from 

 their associated crystalline terranes. Nodular masses sometimes 



