990 Subsurface Geologic Methods 



in order that future geologists at the property will not be hindered by 

 inefficiency in ore finding. 



In this paper it has been the intention to emphasize that geologic 

 representation is of two types carried out in connection with two phases of 

 work leading to ore finding: (1) field and underground representation 

 techniques leading to efficient and detailed collecting of geologic data, and 

 (2) office representation as related to the efficient and complete utilization 

 of such data to predict the localization of ore. The importance of the 

 first phase is fairly obvious. Perhaps there is more of a tendency to 

 underrate the importance of the latter phase of representation. Many geolo- 

 gists seem to think that a map is a map, and that the map layout, scheme 

 of colors or symbols, scale, and types of materials used in the preparation 

 are of minor importance so long as the data have been collected and are 

 available. As an illustrative example of the relative importance of office 

 map representation the following is cited: During a two-year period at a 

 certain mining property, the writer's ore-finding efficiency, utilizing ordin- 

 ary methods of office map representation, was 12 tons of new ore added to 

 reserve for each foot of sill development driven. During the next year, 

 uitlizing improved representation on supplementary maps, the ore-finding 

 efficiency was 54 tons of new ore per foot of development. 



Objectives of Geologic Representation 

 The Purpose of Geologic Mapping 



The main purpose of geologic mapping is to find mineral deposits, 

 arrive at solutions to engineering problems, and increase the general 

 knowledge of geologic processes. 



Inasmuch as the controls of ore deposition are usually subtle, tech- 

 niques of underground, field, and office representation of geologic data 

 must be capable of expressing graphically subtle qualitative and quantita- 

 tive variations of texture, composition, and structure in their relative spa- 

 tial relationships. 



All megascopically visible features should be mapped and described. 

 These features include : 



1. Physiography (topography and drainage). 



2. Man-made features such as excavations, timber, cribbing, lagging, 

 fill or gob, roads, buildings, installations, and survey points. All 

 should be indicated and described on the note sheet. 



3. Structural features including primary flow structure, bedding 



planes, fissures and faults, veins, and joints. 



4. Compositional components such as the type of rock, color and 

 facie variations, mineral components, degree or rate of gradation 

 of one rock type to another, superimposed metamorphic or hydro- 

 thermal effects, vein fillings, and composition of soil or over- 

 burden. 



5. Textural components such as grain size, variation in grain size, 



