THE ADIRONDACK GRAPHITE DEPOSITS 133 



in which graphite occurs, amorphous and flake graphite must be 

 treated differently. Difficulties arise if the character of the ore 

 changes as mining operations proceed, and this is regarded as one 

 of the principal sources of trouble. The selection of a method of 

 milling seems to have been made often without any regard to what 

 the general run of the mine was likely to be. Test holes should be 

 made to determine the character of the ore before mill equipment 

 is bought. In fact, the construction of a mill should proceed only 

 when all the conditions of the deposit, the character of the ore as 

 well as the extent of the ore body, are fully known. 



" It is quite certain that there is no single process that is a 

 universal panacea for all the difficult problems of ore treatment. 

 For certain ores one process is best adapted; for other ores another 

 process. For still other ores the best results may be achieved by 

 a combination of two or three, or even more of the special 

 processes. ' n 



The presence of micaceous minerals, biotite, phlogopite, chlorite 

 etc. offers the greatest problem. Although they are higher in 

 specific gravity than graphite, the flaky nature of the former pre- 

 vents separation by gravity methods as they are floated off in com- 

 pany with the graphite. The particles of mica " are of approximate 

 similar size, and being frequently of the black variety (biotite), they 

 may be readily overlooked in the hand specimen or in the graphite 

 concentrate. The easiest method of detecting the mica and of 

 estimating its relative proportion to the graphite, is to examine the 

 material under the microscope when the former can be readily 

 distinguished by its translucency." 2 



It is quite possible that a more complete separation of the mica 

 can be effected through the electrostatic method. This can be briefly 

 described as follows : It is based upon the fact that graphite is 

 capable of receiving and retaining an electric charge, while mica- 

 ceous minerals, as well as most of the other gangue materials, 

 refuse to do so. The machine consists of horizontal parallel rods 

 of brass set one above another like the rungs of a ladder, which 

 are charged with a high potential. Down past these flows the 

 dry, pulverized rock ; the gangue materials, not affected, fall verti- 

 cally and drop into a receiver, while the graphite is repelled 

 laterally away from the bars and drops into troughs arranged in 

 front. The process is repeated until a complete separation is 



1 Ingalls, W. R., Eng. and Min. Tour., 1905, p. 643. 



2 Newland, D. H., N. Y. State Mus. Bui. 179, p. 34. 



