944 



EXPLORATION GEOPHYSICS 



depth, and name of prospect, and delivered to the analytical laboratory. 

 Samples are usually taken at depths ranging from eight to twelve feet and 

 if possible at even greater depths, the actual depth chosen depending largely 

 upon the area under investigation. Whenever possible, the samples are 

 collected at the various locations from a constant depth below the surface. 

 In this way, all samples are taken from a zone of fairly uniform aeration. 

 In carrying out broad reconnaissance surveys in search of large features, 

 use is made of all available roads. Samples are first taken about one-fourth 

 to one-half mile apart, sufficiently to one side of the road to avoid possible 



Fig. 579.— Stations are located by moans 

 of an alidade and plane table. 



Fig. 580. — Sample being removed from 

 auger and placed in pint glass jar. (Courtesy 

 of Horvitz Research Laboratories, Houston, 

 Texas.) 



contamination. In this manner, large areas can be prospected within a 

 relatively short period of time. If the analytical data indicate a hydrocarbon 

 anomaly of interest, additional samples are taken to produce a more dense 

 and uniform sampling pattern in the interesting areas. 



In the case of areas where anomalies can be expected to cover approxi- 

 mately 500 acres, a sample density of 1 to 80 acres is usually sufficient for 

 reconnaissance. In the case of accumulations of small areal extent, such 

 as on the flanks of piercement type domes, where the accumulations may 

 be only several hundred feet wide, samples are often taken as close as 200 

 feet apart. 



Analytical Technique. — In using the earlier analytical technique, f 

 the jar containing the soil sample is attached directly to the analytical 



t Leo Horvitz, "On Geochemical Prospecting," Geophysics, Vol. 4, No. 8, pp. 210-325, July 

 1939. 



