984 Subsurface Geologic Methods 



the level maps. In mines of simple geology, the stopes may be mapped 

 geologically only at critical points. For use in conjunction with level and 

 stope maps, the geology of all shafts, raises, and winzes is recorded, and 

 then by using all sources of information more reliable sections can be 

 made. 



To supplement level and stope maps, cross sections are prepared 

 showing geologic relations in a vertical plane as contrasted to the hori- 

 zontal plane of the level map. For a simple vein one or two cross sec- 

 tions may show all necessary information, but in more complex districts, 

 sections developed at 50-foot intervals may be needed. Most sections 

 differ from level maps in that information is not plotted directly but 

 must be projected to a plane. Should it be through a shaft, raise, winze, 

 drill hole, or mapped stope, more direct information can be obtained, 

 and the cross section will be more accurate. Sections must be constantly 

 revised to fit all new data. A cross section, even though from projected 

 data, is an extremely important aid for visualization of three-dimensional 

 relations and thus aids in the search for ore. 



To give a third picture, all geology and mine workings are projected 

 to a longitudinal section, which generally is a vertical plane approxi- 

 mately parallel to the strike of the vein. As veins are rarely regular in 

 dip and strike, some distortion is produced in projecting geology and 

 mine workings to a vertical plane. On longitudinal sections the relation 

 of ore bodies or ore shoots to the vein and wall rock are very well shown 

 and structural and stratigraphic controls may become apparent that were 

 unnoticed in other sections or in plan. Because the wall rock on opposite 

 sides of an ore structure may differ, the reference wall of the longitudinal 

 section must be specified (fig. 524). 



A combination of plan maps and cross and longitudinal sections 

 shows the geology in three major planes, but in more complicated mines 

 three-dimensional representations are often helpful. To show general re- 

 lations isometric or block diagrams can be used (fig. 525). For de- 

 tailed representation models are more informative. Numerous kinds of 

 models have been made,®^ but the one most used by geologists is the trans- 

 parent type with the geology and mine workings shown on either horizon- 

 tal or vertical sheets of glass or plastic. Backed by a strong light source, 

 it is possible to look through the transparent sheets and see the exact re- 

 lations as they are known in the mine. 



Numerous other ways of representing ore structures have been at- 

 tempted. One of the most useful is a method by which contours of a 

 vein are made which refer to a datum plane that can be horizontal, vertical, 

 or inclined. ^^ For showing subtle changes in dip or strike and the rela- 

 tion between ore distribution and the structure of the vein, an inclined 



" McKinstry, H. E., op. cit., pp. 180-182, 1948. 



^ Conolly, H. J. C, A Contour Method of Revealing Some Ore Structures : Econ. Geology, vol. 31, 

 pp. 259-271, 1936. 



