Chap. 8] MAGNETIC METHOD 409 



A. Magnetic Surveys in Mining 



1. Surveys of iron ore: magnetite, hematite, and brown iron deposits. 

 Probably the most famous example of magnetic iron ore exploration is the 

 survey of the Kursk magnetic anomaly. This anomaly, near Krjukowa 

 and Bielgorod, was discovered by I. N. Smirnow in 1874; it was further 

 explored by Piltchikow, Sergijevsky, and Rodd, and was briefly discussed 

 by Moureaux in 1896.^°^ A systematic magnetic survey was started in 

 1889 by E. Leyst, who from 1896 to 1909 surveyed some 4500 stations. 

 He left Russia in 1918 and died abroad. The survey data and original 

 maps could not be recovered after his death and a commission was organ- 

 ized in 1919 under the direction of P. Lasareff. Between 1919 and 1926 

 about 20,000 stations were occupied. In an area of some 500 square kilo- 

 meters not only were magnetic data collected, but also gravitational 

 anomahes were surveyed by pendulum and torsion balance. In 1923 the 

 first diamond-drill hole at Stschigry reached the ore body at 163 meters. 

 Altogether thirteen holes were put down in this area by 1926, and further 

 drilling revealed additional bodies in the Saltikowsky, Oribuiansky, and 

 Tim districts. 



According to a recent notice in the Soviet press, the iron ore reserves 

 proved to date in the Kursk region amount to 290,000 million tons while 

 the quantities- of potential deposits are estimated at over 600,000 million 

 tons. 



The anomalies have been described by many authors, notably by 

 Lasareff, from 1921 to 1926.^^° They are located east and southeast of 

 Kursk in two parallel strips. One, through Stschigry, is almost 160 km 

 long and 2 to 20 km wide. The other, near Bielgorod, is almost 50 km 

 long and 40 km wide. The strike of the anomalies is NNW-SSE. In 

 the zones mentioned, the vertical intensity anomalies are of the order of 0.5 

 gauss (that is, the same magnitude as the earth's field), and at some loca- 

 tions they reach 2 gauss. The horizontal intensity anomalies have ex- 

 tremes of 4-0.8 and —0.6 gauss; extremes in declination differ by 180°. 

 For the vicinity of Stschigry and Stary Oscoe, the magnetic, gravity, and 

 torsion-balance anomalies have been described by Lasareff .^^^ In Fig. 8-59, 

 the torsion-balance and magnetic anomalies in the vicinity of Stschigry 

 are reproduced, together with the geologic section as determined by drill- 

 ing. The sediments in this section are Tertiary, Triassic, and Devonian. 

 At a depth ranging from 152-186 m the basement rocks (gneiss, quartzite) 



i«9C.R., 122, 1478, (1896). 



"" For a list of Lasareff's publications see Ambronn, op. cit., Bibl., p. 327, items 

 910-915. 



1" Gerl. Beitr., 16(1/2), 71-89, 91-102 (1926). 



