956 EXPLORATION GEOPHYSICS 



The greatest potential value of geochemical methods lies in their pos- 

 sible application to the search for stratigraphic traps. However, their use 

 for this purpose will have to await wider acceptance by the oil industry, 

 which will not come until sufficient statistical evidence is available to show 

 that the chemical methods can assist materially in the search for oil. As 

 more is learned concerning the mechanisms through which geochemical 

 anomalies are produced and as improvements continue to be made in the 

 quality of the collected data and their interpretation, the place of geo- 

 chemistry among the established methods of prospecting may eventually be 

 assured. 



Geochemical Prospecting for Ore 



The application of geochemical techniques to the location of hidden 

 ore deposits is a relatively recent development. f The method is founded 

 on the assumption that many ore deposits, either at the time of their forma- 

 tion or at some later time, emitted traces of the components of the ore or 

 solutions that had permeated the environment of the ore. Traces of the 

 metals may thus be found in the overlying or surrounding soils, or in the 

 ground or surface waters at a considerable distance from the ore. The metal 

 content of the plants in the area of metal dispersion may also be influenced. 



Surface Waters. — When investigating a new area, the average 

 concentration of heavy metals in the surface waters of the area as a whole 

 is first determined. The search is then continued to determine whether 

 any unusually high concentrations are to be found locally. For reconnais- 

 sance testing, diphenyl thiocarbazone, an organic dye which forms colored 

 compounds with sixteen metallic elements, is of considerable value. A 

 concentration of less than one part per million of zinc, copper, lead, silver, 

 gold, mercury, and other metals can be detected with this reagent. Separa- 

 tion of these metals, in the field test, is impracticable and unnecessary, as 

 the chief purpose of the water testing is to provide a background for more 

 detailed studies as to the kind and extent of mineralization in the area. 

 By observing the relative intensities of colors developed by the reaction of 

 the dye with the dissolved metals, and by following the colors upstream, 

 the source of the metals in question can generally be located. 



Soils. — Geochemical anomalies, that is, abnormally high concen- 

 trations of some particular element in the soil or the soil materials, are 

 quite commonly associated with mineralized bedrock. The anomalies may 

 fan out both horizontally and vertically from the mineralized source area. 

 A series of such anomalies, related to underlying mineralized material, is 

 called a dispersion halo. Having determined the origin, kind, shape, and 

 extent of a dispersion halo, it is then often possible to deduce its spatial 

 relation to an ore body. 



t This discussion is based largely on an address entitled "Geochemical Prospecting for Ore," 

 delivered by V. P. Sokoloff at the annual meeting of the Colorado Mining Association, Denver, 

 Colorado, February 7, 1948. 



