Chapter 30 



GEOCHEMICAL PROSPECTING FOR ORES * 



H. E. Hawkes 



Geologist, U. S. Geological Survey 

 Washington, D. C. 



Geochemical methods of prospecting are based on the premise that a 

 chemical pattern exists in relatively accessible natural material that 

 can be used as a guide in locating relatively inaccessible deposits of 

 valuable minerals. Such chemical patterns are most commonly the 

 result of the dispersion of elements and compounds from the site of 

 primary deposition of the ore, and they assume shapes controlled by 

 the characteristics of the agents of dispersion and the structure and 

 composition of the material through which the dispersion takes place. 



In petroleum exploration, most methods classified as "geochemical" 

 depend on analysis of soils, soil moisture, or soil air for hydrocarbons 

 or radioactive elements derived by diffusion from the underlying oil 

 pool. This subject has been discussed at length in the literature of 

 petroleum exploration (Rosaire, 1939; Sokolov, 1947; see also entries 

 under Geochemical Prospecting in the Geophysical Abstract series of 

 the U. S. Geological Survey and U. S. Bureau of Mines). 



In work on ore deposits, two distinct varieties of dispersion patterns 

 have been reported: primary or "genetic" patterns, formed by hydro- 

 thermal or magmatic processes related more or less directly to the ore- 

 forming process itself; and secondary patterns resulting from the de- 

 composition and scattering of ore material by present-day weathering 

 processes. 



Genetic dispersion patterns include the distribution of minerals and 

 elements in the wall rock, alteration zones, and barren vein systems 

 deposited by the mineralizing fluids responsible for the introduction of 

 the ore. The problem is so closely related to the primary ore-forming 

 process that it can be most effectively studied as an integral part of 

 the general geologic setting of the deposits. The general aspects of 

 genetic dispersion patterns have been discussed by Sergeev (1941, 



* Published by permission of the Director, U. S. Geological Survey. 



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