972 Subsurface Geologic Methods 



ore deposits." They will have all the characteristics of a metamorphic 

 rock. 



Supergene Deposits ^^ ^^ 



All deposits formed by primary processes may be acted upon by 

 ground water producing characteristic downward changes through the 

 leached, oxidized, and supergene sulphide zones. 



Exploratory Procedures 



After accumulating all known data on the geology, grade, and size 

 of a deposit, a mining geologist considers various approaches to prove 

 the value of a given property. Generally, he thinks first in terms of ge- 

 ology; of the type and origin of the deposit and the possible ore controls 

 and guides. After such factors are weighed, further work may be in- 

 dicated to obtain more geologic data. Such additional work could involve 

 geologic mapping of the surface and accessible underground .workings, 

 sampling, laboratory study, and geophysical investigations. It also may be 

 advisable to carry out exploratory work to examine the deposit further 

 in order to obtain more geologic data and more information on grade 

 and size. The geologic data accumulated not only is important in evaluat- 

 ing the property but also aids the mining engineer in laying out mining 

 methods. 



Geologic Guides and Controls 



Structural Control — Of the various guides and controls used as aids 

 in locating ore perhaps the most important is structural. Regional control 

 is well explained by Fowler -^ in the Tri-State area where he has shown 

 that ore bodies are closely related to structural disturbances and that 

 where the beds are relatively undisturbed little or no ore is present. 

 Fowler also states:^* 



After initial discovery, drilling of 600 holes under informed geologic 

 guidance, in lieu of most of 30,000 actually drilled, could have prospected an 

 area of 37 square miles sufficiently to define the mining area and many 

 important features in and around it. 



Any fracture formed before mineralization is important as a control 

 in that the fault may be a pervious zone along which solutions can travel. 

 Fault surface deviations and irregularities can increase the permeability, 

 and detailed study of a^ein may show that ore bodies are localized at 

 changes of dip and strike, at intersections of veins, or at intersections of 

 veins and fractures. Even where no detailed control within a vein can be 

 established, it may be possible to locate channelways and show that ore 



^ Bateman, A. M., Economic Mineral Deposits, pp. 243-289, New York, John Wiley and Sons, Inc., 

 1942. 



22 Emmons, W. H., op. cit., pp. 105-140. 



23 Fowler, G. M., Tri-State Geology: Eng. and Min. Jour., vol. 144, no. 11, pp. 73-79, Nov. 1943. 

 2* Fowler, G. M., idem, p. 79. 



