676 



ELECTRICAL METHODS 



[Chap. 10 



PIV 



boundaries, and (5) pipe corrosion. Since Schlumberger made his famous 

 measurements on the Sain Bel pyrite ore body in France in 1913, nu- 

 merous sulfide ore bodies and mine prospects have been surveyed by the 

 self-potential method in all parts of the world. 



A discussion of two examples will suffice. One is the survey of the 

 Hope Mine in British Columbia (see Fig. 10-25) (about eighty miles from 

 Vancouver). Nickeliferous pyrrhotites with a proved tonnage exceeding 



500,000 tons occur in the 

 vicinity of a pyroxenite dike 

 in granodiorites. In 1930 a 

 self-potential survey showed 

 a prominent indication near 

 the mine where ore was not 

 suspected. The potential 

 anomaUes exceeded 300 mill- 

 ivolts. A trench dug at the 

 indication (see figure) re- 

 vealed an ore body of p3rr- 

 rhotite about 40 feet wide. 

 One of two inclined drill 

 holes traversed a mineralized 

 zone about 70 feet wide, 

 leaving it at a depth of 176 

 feet. 



Self-potential phenomena 

 are not necessarily limited 

 to large and very massive ore 

 bodies. They have also been 

 observed on "stringer" types 

 of mineralizations. Fig. 10- 

 26 shows a self-potential 

 survey made in the Pallieres 

 region in the D^partement 

 du Gard in France. The 

 geologic section is characterized by an extended contact zone with Paleozoic 

 granites on the east and Triassic arkose and Rhetian shales on the west. 

 Resting unconformably on the shales are limestones and dolomites of 

 Hettangian age. The mineral solutions have been forced into the contact 

 zone from below and have followed the bedding planes and shattered 

 zones in the sandstone and shales as well as in the limestones, thus giv- 

 ing rise to the pattern shown in the figure. The self-potential survey clearly 

 reveals the areas of greatest mineral concentration (mostly p5aite). 



• Pottniial Pnfilt 

 ■ Equipointtlal Lint 



Pi/rrhotift 

 Ore Body 



100 700 soe 



Fig, 



ffft 



10-25. Self-potential profiles at Hope Mine, 

 British Columbia (after Geoffroy). 



