X-RAY MICROSCOPY 





Fig. 6. Microradiograph corresponding to Fig. 

 5. X17 



Fig. 7. Tailings from a lead-zinc ore containing 

 galena, sphalerite and pyrite as the heavy min- 

 ■erals. Photomicrograph — ordinary light. X75 



a few ooliths. Well developed rhomb-shaped 

 •crystals of iron carbonate can be seen in the 

 cavity and in general the radiograph pro- 

 vides a much crisper picture of the struc- 

 ture than the photomicrograph. 



Another application in the field of indus- 

 trially important ores is in the examination 

 of tailings and hence the assessment of the 

 efficiency of mineral dressing operations. 

 The difficulties associated with different 

 opaque minerals and of fine particle size are 

 again the main ones in optical work but 

 Figs. 7 and 8 show the improvement obtain- 

 able by radiography. The material is a lead- 

 zinc ore containing the sulfides of lead 

 (galena), zinc (sphalerite) and iron (pyrite) 

 as the heavy constituents. The galena is 

 easily distinguished by its cubic cleavage but 

 the zinc and iron sulfides are not readily 

 differentiated. It would be possible, how- 

 ever, to get some change in contrast for these 

 two sulfides by changing the radiation from, 

 say copper or nickel to iron radiation. 



The specimens for this type of examina- 

 tion were made of a single layer of particles 

 mounted on a cover glass with Canada Bal- 

 sam. Provided the particle size was less 

 than about 100 micron diameter and of 



Fig. 8. Corresponding radiograph clearly shows 

 the cleavage of the galena but does not differenti- 

 ate between sphalerite and pyrite. X75 



576 



