Chap. 8] 



MAGNETIC METHOD 



413 



Magnetic anomalies on magnetite deposits formed by contact or dynamo- 

 metamorphism are usually more regular in appearance than on deposits 

 produced by magmatic differentiation/^^ 



In this country the iron ore districts of the Lake Superior region were 

 surveyed extensively at an early date. Field and interpretative technique 

 were described by Smyth^^^ and Hotchkiss.^^^ In recent years dip needle 

 surveys have been made in Wisconsin by Aldrich^^* and in Michigan by 

 Stearn and Swanson. Further studies of magnetic anomalies on iron 

 ore deposits are described by Stratton and Joyce.'" Traverses across 

 scattered magnetite veins near the Errington mine in Ontario are described 



i^ 



0r9 Country 6an^ Maquftic 



fioek Vfihr 



Fig. 8-61. Underground magnetic vector survey in Kallmerberg mine, Sweden (after 



Keilhack). 



by Eve and Keys'^^ with the remark that the anomalies had no relation 

 to the ore sought in this area. A similar experience was recorded by Edge 

 and Laby'^^ who found, at Kadina, South Australia, an anomaly of about 



i« U. S. Bur. Mines Tech. Paper No. 439 (1929). 



1=^2 U.S.G.S. Monograph No. 36, Part II, 336-373 (1899). 



123 Wis. Geol. and Nat. Hist. Survey Bull. No. 44 (1915). 



1" A.I.M.E. Geophysical Prospecting, 393 (1929). 



1" N. H. Stearn, A.I.M.E. Geophysical Prospecting, 361-362 (1929). 



128A.I.M.E. Geophysical Prospecting, 290-312 (1934). 



"^ U. S. Bur. Mines Tech. Paper No. 528 (1932). 



128 Canad. Geol. Survey Mem. 165, 143 (1931). 



129 Edge and Laby, The Principles and Practice of Geophysical Prospecting, p. 

 (1931). 



192 



