56 GEOPHYSICAL METHODS IN MINING [Chap. 5 



H. Gems and Precious Stones 



A direct location of gems by geophysical methods is out of the question. 

 In some instances a survey of the formation in which they occur may be of 

 assistance. Examples are the peridotite plugs in Arkansas and the blue- 

 ground pipes in South Africa. Where diamonds occur in sands and 

 gravels of stream and beach deposits, methods discussed under the heading 

 of engineering applications of geophysics may be useful for locating and 

 tracing lenses or channds. 



Specific applications of geophysical methods in mining are discussed in 

 Chapter 7 on pages 162, 286-292; in Chapter 8 on pages 409-422; in Chap- 

 ter 9 on pages 501-502 and Figs. 9-41, 9-49, 9-75; and in Chapter 10 on 

 pages 675-68.1, 703-706, 739-741, 755-757, 771-773, and 802-805. 



