20 



WILLIAM H. EMMONS 



Chlorides. — Chlorine is present in most mine waters. In 22 

 out of the 29 analyses it is reported as traces or as determined 

 quantities. The average of 29 analyses shows 873 parts per 

 million, but if the one abnormally rich sodium-chloride water of 

 Silver Islet, Lake Superior, is excluded, the remaining 28 analyses 

 show but in parts per million. This figure is probably a better 

 average. There are several sources of the chlorine in mine waters. 



TABLE I 



Average op 29 Analyses of Waters Taken from Gold, Silver, and Gold- 

 Silver Mines in Non-Calcareous Rocks 

 {Compiled by N. Sankowsky and C. Russell) 



The salt in sedimentary rocks may be dissolved by ground-water. 

 From the available analyses it appears that this source is of less 

 importance than would be supposed. The chlorine content of 

 composite samples of 78 shales and of 253 sandstones was only a 

 trace, while an analysis of a composite of 345 limestones showed 

 only 0.02 per cent. 1 In some rocks chlorine is present probably 

 as NaCl in the solid particles contained in fluid inclusions. The 

 work of R. T. Chamberlin, A. Gautier, and others has shown that 

 many granular igneous rocks, when heated to high temperatures, 

 1 F. W. Clarke, Bulletin No. 330, U.S. Geological Survey, 27(1908). 



