182 THE CRYSTAL FALLS IKOX-BEAEING DISTRICT. 



One of the best results gives as high as 61.5 per cent metalhc Mn. 

 The ores thus range from a mangauiferous iron ore to a manganese ore. 

 The further statement is made that the bed lies very close to the surface, 

 and is from 6 inches to 3 feet in thickness. From 4 to 6 feet of bog iron 

 is found underlying the bed of manganese. 



RELATIONS TO ADJACENT ROCKS. 



The ore is associated with white or reddish chert, which in places is 

 jaspery. The cherty iron formation passes into ore by a decrease of the 

 silica. An intermediate phase is chert with "bands and shots" of ore. In 

 places the chert is more or less brecciated, and the ore often has a similar 

 character. Commonly the ore is completely surrounded by the chert beds, 

 or chert and ore, forming the so-called mixed and lean ore. In such cases 

 they form both the foot and hang'ing walls of the ore 

 body. But the ore-bearing chert formation is always 

 associated with black carbonaceous slates, which consti- 

 tute the base on which the ore-bearing formation rests. 

 In the Youngstown mine 3 feet of so-called "graphite" 



Fig. 14.— Sketch to illus- n i f i i i ^ 



trate the occurrence of ore was passed tlirough oeiore the usual carbonaceous slates 

 were reached.^ The hanging wall is also cai'bonaceous 

 slate. At places thin quartzitic beds which approach a true quartzite are 

 associated with the slate. 



The ores occiu- in the cherts in pockets and lenticular masses, which 

 always agree in greater dimensions with the strike of the beds with which 

 they are associated. The lenticular character is well shown in the Dunn, 

 Columbia, and Great Western mines. In the Dunn mine the bodies over- 

 lap. In the Great Western mine in 1887 seven different ore bodies in an 

 east-west line, separated by areas of barren rock, mostly slate, were being 

 mined. In following these isolated ore bodies to the east, at various jjlaces 

 thev are found to turn around a horse of rock. Their occurrence is illus- 

 trated by the horizontal section, iig. 14. Evidently the ore bodies accumu- 

 lated in westward-pitching synclinal troughs, in which the hanging wall 

 appears to the miners as a horse of rock. 



The ore bodies in general pitch to the west at varying angles corre- 



'This informatiou was fuvnisheiT by Mr. C. T. Roberts, of Crystal Falls. It was not possible to 

 obtaiu a specimeu of the graphite for examiuation. 



