PROSPECTING FOR IRON ORE IN NEGAUNEB F0R:\IATI0N, 407 



the break across tlie quartzite in sec. 28, T. 47 N., R. 'IC, \Y., sug-g-ests that 

 there may be a north swmg of the formation at this phicc : and if so, this 

 would be a favorable point for exploration. Otlier fav()ral)l(; places niay 

 exist along the northern side of this syncline, but their exact positions can 

 not be pointed out. The second synclinal arm, running from the southeast 

 comer of sec. 20, T. 47 N., R. 2G W., in a northeasterly direction, has not 

 been explored at all. West of this arm is the great anticlinal dome of 

 Siamo slate. This dome is folded by minor rolls in an east-west direction, 

 thus furnishing on the west side of the iron formation a number of westward- 

 pitching synclinal troughs, in which are large deposits of ore. Doubtless 

 the same folded condition prevails on the eastern side, producing eastward- 

 pitching troughs, although here outcrops are not sufficient to accurately 

 delineate the bouudarj^ lines; but while the existence of a swamp in sees. 

 3, 4, 9, and 10 makes the area difficult to prospect, the sides of the arm are 

 worthy of exploration. In the south part of sec. 3, near the north-south 

 quarter line of the section, there is a ridge of greenstone. This is also the 

 end of the sjaicliue, which here plunges to the south. The junction of this 

 greenstone with the contact line between the Siamo slate and the Negaunee 

 iron formation is a favorable point. AVithin the iron formation in sees. 10 

 and 15 a great mass of greenstone forms a westward-facing amphitheater, 

 and here in the southwest cpiarter of sec. 10 would seem to be a favorable 

 place for exploration. 



It is not impossible that a close magnetic survey witli a dial compass 

 and dip needle across the approximate boundary lines of the Siamo slate and 

 the Negaunee formation, for these eastern arms, would enable the explorer 

 to more accurately delimit the iron- bearing formation and to determine 

 the probal)le positions of pitching troughs, if they exist, and thus point 

 out the more favorable points. This attempt ought certainly to be made 

 before money is spent in actual underground Avork. Exposures of these 

 eastern arms are so infrequent that it is not certainly known that the 

 iron-bearing formation maintains its pure nonfragmental character. If it 

 contains interstratified or intermingled clayey material, this wiuild lie 

 vuifavorable to the development of merchantable ore deposits. 



In the foregoing paragraphs it is not meant to imply tluit workable 

 iron-ore deposits will surely be found in these eastern arms, but merely that 

 the conditions are sufficiently favorable to warrant a search for them. 



