538 hawkes. GE0CHEM1CAL PROSPECTING FOR ORES [Ch. 30 



p. 22), and examples have been described by Riley (1936), Newhouse 

 (1941, p. 144), and Lovering, Sokoloff, and Morris (1948). 



This chapter presents a review of methods of prospecting based on 

 systematic exploration for secondary dispersion patterns by chemical 

 analysis of soils, vegetation, and water. The dominant trend in the 

 zone of weathering is a scattering of the primary ore materials, as con- 

 trasted with the dominantly concentrating effect of ore-forming proc- 

 esses. Physical forces tend to break up the original minerals at the 

 same time as chemical agencies oxidize or otherwise modify the primary 

 minerals. Some of the weathering products are relatively insoluble in 

 water and tend to remain in the gossan or residual soil near their 

 source in the parent rock. Other material may be more soluble and 

 will be dispersed in ground and surface waters. This simple picture 

 is modified, however, by mechanical erosion and fluvial or glacial 

 transport of the insoluble residual materials, on the one hand, and by 

 immobilization of the water-soluble fraction by subsequent reprecipi- 

 tation, on the other. 



Effective prospecting based on studies of weathering products is 

 possible only where a diagnostic variation in the chemical composi- 

 tion of residual soils, glacial tills, alluvium, vegetation, or natural water 

 exists and can be readily detected and interpreted in terms of an un- 

 discovered deposit of valuable minerals. It requires an integration 

 of the principles and techniques of chemistry with specialized studies 

 of the local geology, processes of weathering and soil formation, 

 glaciology, sedimentation, botany, and hydrology. In spite of the 

 apparent complexity of the problem, considerable progress has been 

 made in the past 15 years both in understanding the basic principles 

 and in applying chemical techniques to practical exploration prob- 

 lems. 



The following review of the subject is an attempt to summarize in 

 integrated form the results of more or less independent work on geo- 

 chemical prospecting in Scandinavia, Russia, Canada, and the United 

 States during the past 15 years, together with pertinent related data 

 from the recent work of geologists, chemists, soil scientists, and bot- 

 anists. Except for a few very brief articles (Lundberg, 1940a, b, 

 1941; Sokoloff, 1948), earlier summaries have dealt specifically with 

 work in Scandinavia (Landergren, 1939; Hedstrom and Nordstrom, 

 1945; Rankama, 1941, 1947) and in Russia (Flerov, 1938; Ozerov, 

 1937; Sofronov and Sergeev, 1936; Sergeev, 1941; Sofronov, 1936; 

 Zaidina and Sergeev, 1938). The summary by Sergeev (1941) includes 

 a discussion of general principles as well as a review of direct practical 

 applications and is by far the most comprehensive treatement of the 



