CHEMICAL METHODS 



957 



Figure 589 shows three general types of dispersion halos which may 

 be found under various conditions. These develop in a climate where the 

 soil- forming processes are not especially intense and where the ores are 

 not particularly deep below the surface. This is especially true of metals 

 of low solubility like molybdenum, tungsten, tin, and lead. Halos of this 

 type can be outlined by making a series of field tests on samples taken in 

 a grid pattern. The resulting map, on correlation with geologic data, may 

 be sufficient to warrant more expensive sampling in depth or drilling. This 

 method has been used successfully in Russiaf to locate economically 



Ore 



DISPERSION HALO OVER ORE 



IN FLAT RELIEF 



Ore- 



DISPERSION HALO MODIFIED 

 BY VEGETATION 



EXPLANATION 



|; ■•.;■/;'.■:[ Low amount of metal in soil 



Medium amount of metol in soil 



If.'y/^.y^'l Higti omount of metal in soil 



Maximum amount of metal in soil 



•Orfi 



DISPERSION HALO OVER 

 ORE ON SLOPE 



Fig. 589. — Typical dispersion halos formed under various conditions. 

 (A) ideal case; (B) disturbing effect of vegetation; (C) disturbing effect of 

 slope. (Courtesy of V. P. Sokoloff, "Geochemical Prospecting for Ore," ibid.) 



important ore bodies. According to the Russian literature, this method is 

 most successful in areas where residual soils are of only moderate thick- 

 ness ; and for certain metals occurring in minerals that are fairly resistant 

 to weathering. Prospecting for complex or for buried halos would be 

 difficult. 



Once the probability of geochemical anomalies has been established, 

 the problem then involves: (1) the selection of indicator elements for 

 which tests are to be made; (2) sampling procedures; (3) chemical tests; 

 and (4) interpretation of results. 



The indicator element does not necessarily have to be the same element 

 the prospector is seeking in the ore. Above some oxidized lead-zinc deposits, 

 for example, determinations of sulphate in the soil are fully as useful in 



t E. A. Sergeev, "Fisico-Himicheskii Metod Poiskov Rudnyh Saleshei," Materially Vsesoiuznogo 

 Nauchno-Issledovatelnogo Geologicheskogo Institute. Geofisica-Sbornik 9-10: 3-54. (Geochemical 

 Method in Prospecting for Ore Deposits.) 



