982 Subsurface Geologic Methods 



their exploration use is restricted to sampling relatively flat-lying deposits 

 and providing access to underground-mine workings. 



Underground Drilling: The foregoing discussions apply to drill holes 

 from the surface, but diamond drilling and hammer drilling also are 

 extensively used underground where holes may be drilled up or down at 

 any angle. Coring underground with diamond drills is very little dif- 

 ferent from coring on the surface except that air or electric drills must 

 be used in place of those powered with gasoline. For holes drilled upward 

 all cuttings can be recovered readily, and under favorable conditions 

 hammer drills and diamond drills with noncoring bits can be advantage- 

 ously used. The purpose of drilling underground is the same as for 

 surface drilling. 



Mining Operations °^ — If geologic information indicates such a course, 

 and particularly if drilling shows favorable ore or even strong possibil- 

 ities of ore, exploratory mining operations may be instituted. Initial 

 mining operations may include sinking a vertical or inclined shaft, which 

 might follow or stay near the ore body. In country with relief, the orig- 

 inal underground workings may be nearly horizontal, either starting at 

 the outcrop and drifting with the ore or cross cutting to the ore body and 

 then drifting until the limits are reached. Exploratory work should be 

 closely watched by the geologist, who maps, records, and analyzes all 

 geologic data and sees that the sampling is adequate. Normally one level 

 is not sufficient, and, to develop further, additional levels will be drifted 

 out following the ore and limiting all possible extensions of the ore on 

 each level. To prospect a level thoroughly it might be necessary to drift 

 through barren rock or a barren vein in an attempt to find the continua- 

 tion of a known ore shoot or to find a new ore body. The different levels 

 will be connected by shafts or winzes, but wherever possible, because of 

 lower mining costs, connections and mining will be upward from a lower 

 level to a higher. Development, exploration, and mining methods differ for 

 dissimilar kinds of ore bodies. 



Sampling — Sampling means the taking of a small representative por- 

 tion of a mass in such a manner that it will accurately depict the entire 

 body.^^ ^^ ^^ Sampling techniques are not restricted in use to the mining 

 geologist. Every geologist has occasion to sample a geologic body, hoping 

 that in laboratory studies he will obtain a clearer picture of the larger 

 feature. Since all deposits differ in characteristics from place to place, 

 one sample will not accurately represent the entire body. To obtain more 

 representative results, a number of samples should be taken; but there 

 is an economic and practical limit to the amount of sampling possible, 

 and the actual number of samples will depend to a large extent on the 



^Jackson, C. F., and Hedges, J. H., Metal-Mining Practice: U. S. Bur. Mines Bull. 419, pp. 35-58, 

 1939. 



'•Torrester, J. D., op. cit., pp. 349-367, 1946. 

 "^ McKinstry, H. E., op. cit., pp. 35-69, 1948. 

 "* Jackson, C. F., and Hedges, J. H., idem, pp. 35-58, 1939. 



