MANGANESE 



393 



erable depths; nearly all die out or change their 

 nature at depths of a few tens of meters to a few 

 hundred meters. Many veins reveal strongly increas- 

 ing percentages of hematite or barite with depth, 

 indicating a zonal pattern. A number of deposits in 

 brecciated volcanic rocks consist of myriad small 

 thin veinlets of nearly pure manganese oxide lining 

 fractures in the host rocks. 



Replacement deposits of manganese carbonate are 

 commonly in limestone or dolomite and tend to 

 form tabular or pipelike shoots and irregular pods 

 adjacent to faults or other conduits by which min- 

 eralizing solutions gained access to host rocks. Per- 

 meability of the host rock is a major control ; there- 

 fore brecciated zones are favored. Replacement on 

 a large scale is apparently confined to the more cal- 

 careous rocks, although tuffaceous rocks are replaced 

 locally. Hypogene manganese oxide deposits are 

 more generally confined to veins, generally filling 

 fissures but in some instances replacing fault gouge, 

 breccia, or other particularly permeable zones in 

 host rocks of various types. 



The vein deposits of manganese in the United 

 States, Mexico, and Morocco have yielded a small 

 tonnage of relatively high grade ore for many years. 

 Locally such ore is rather low grade in the vein but 

 can be hand sorted or mechanically concentrated to 

 bring it to merchantable grade. Few such deposits 

 yield as much as 100,000 tons; most contain a few 

 tens to thousands of tons of salable ore. The replace- 

 ment deposits may be much larger but generally are 

 lower in grade, as at Leadville, Pioche, and Philips- 

 burg. 



The hypogene ores are deposited from thermal 

 fluids originating at depth in the earth. Undoubtedly 

 some of these fluids are derived from crystallizing 

 magma; others are probably heated ground waters 

 that derived their metallic content while circulating 

 through and altering preexisting rocks of diverse 

 origin. As the fluids approach the surface, changes 

 in their environment and chemistry make the man- 

 ganese insoluble and it deposits on the conduit walls 

 or, if the chemistry is favorable, replaces the wall- 

 rocks. Experience has shown that there is little 

 likelihood of finding significant hypogene oxide de- 

 posits at depths of more than a hundred meters or 

 so; carbonate deposits may be found at greater 

 depths, usually associated with deposits of other 

 metals. 



RESOURCES 



IDENTIFIED AND HYPOTHETICAL RESOURCES 



There is no lack of identified manganese resources 



in the world today, but these resources are so dis- 

 tributed that only one industrialized country, the 

 U.S.S.R., is not almost completely dependent on 

 imports for its supply. Table 76 gives the general 



Table 76. — World manganese ore resources, in millions of 

 tons 



' Identified deposits from which minerals can be extracted profitably 

 with existing technology and under present economic conditions. 



^ Specific, identified mineral deposits whose contained minerals are not 

 profitably recoverable with existing technology and economic conditions. 



3 Undiscovered mineral deposits, whether of recoverable or subeconomic 

 grade, that are geologically predictable as existing in known districts. 



picture; firm data are available for few countries, 

 and the figures presented are personal estimates 

 based on evaluation of many sources, published and 

 unpublished. Queried figures are particularly weak 

 and could be wrong by an order of magnitude. Grade 

 of most resources and of ore ranges from 25 to 50 

 percent manganese. 



RESERVES 



Reserves are in bodies or districts being mined 

 today. This category includes proved, indicated, and 

 inferred reserves. 



CONDITIONAL RESOURCES 



Examples of conditional resources are the enor- 

 mous deposits of manganiferous material deep in 

 the Kalahari basin in South Africa that have been 

 cut by a few deep drill holes. Very large easily acces- 

 sible deposits are also available there, and accord- 

 ingly exploitation of the deep beds in the foreseeable 

 future is unlikely. Similarly, the sedimentary man- 

 ganese carbonate deposits, ranging from 20 to 36 



