704 



ELECTRICAL METHODS 



[Chap. 10 



more important ores occur in the form of large lenses in the leptite forma- 

 tion. Others, likewise in the form of lenses, are found in black slates. 



The ore contains pyrite, 

 chalcopyrite, pyrrhotite, ar- 

 senopyrite, and gold. The 

 ore bodies are from 40 to 

 600 m long, from 5 to 30 m 

 wide, and are covered by 

 glacial moraine which has 

 an average thickness of 7 

 to 8 m. 



The more important ore 

 discoveries resulting from 

 the application of equipo- 

 tential-line methods were at 

 Kristineberg, Bjurfors, and 

 Bjurliden. (The Boliden 

 gold and arsenic deposit 

 was located largely by elec- 

 tromagnetic methods and is 

 discussed in that connec- 

 tion.) The equipotential 

 survey in the Kristineberg 

 field is illustrated in Fig. 

 10-44. Intervals between 

 the primary electrodes were 

 of the order of 150 to 200 m. 

 Ore boulders had been 

 found early in this field, and 

 numerous test pits and 

 trenches had been sunk. 

 The distribution of these 

 boulders first gave rise to 

 the assumption that the 

 strike of the deposits was 

 north-south but no ore was 

 found by these prospecting 

 activities. An equipoten- 

 tial-line survey was made 

 in 1918, and in the same year two important ore bodies were located. 

 By 1919 the entire field had been outlined. Out of eight prospecting 

 trenches dug to test the indications, five encountered ore. The ore 



'a 

 c 



H-1 



3 



cr 



