ADIRONDACK MAGNETIC IRON ORES 



95 



the lines of outcrop are shifted laterally. In the heading of the 

 south shaft of the Nelson Bush mine a fault of this kind was 

 observed. Its throw could not be determined but it is probably 

 small. Other examples which have been noted by Emmons occur 

 in the old workings on the southern section, where the outcropping 

 ore is offset by slight displacements that have taken place obliquely 

 to the dip. The maximum offset found on the surface is about 15 

 feet. In this case a thin dike has been intruded along the fault 

 plane [fig. 15]. 



The wall rock is mainly the augite variety of acid gneiss already 

 described. Along the contact with the ore it has been considerably 

 altered, with the development of chlorite and biotite as resultant 

 products from the augite, while it also contains much clear quartz 

 of secondary infiltration. A black hornblende gneiss is encoun- 



Fig. 15 Faulting of the ore bodies as seen on the surface near 

 the Indian pit. A diabase dike has been intruded along the 

 fault plane at the right. 



tered on the walls of the Nelson Bush mine, and may represent an 

 included band of the sedimentary gneisses to which it corresponds 

 in composition. 



Nelson Bush mine. This mine is the most northerly of the 

 Arnold hill workings. It consists of two shafts about 600 feet 

 apart driven on the course of two lenses which have nearly the 

 same horizontal axis. Underground the shafts run off as inclines, 

 the northern starting at an angle of 6o° and flattening gradually 

 to 30 and the southern at an angle varying from 42 to 35 . They 

 are intended to follow as nearly as possible the pitch of the lenses 

 which is about 40 north. The north shaft is down some 900 feet 

 on the incline. The lens of ore as seen in the workings is 25 feet 

 thick in its maximum development and averages perhaps 18 feet. 

 In the south shaft the lens ranges from 10 to 15 feet across the 

 walls. The two shafts are not connected underground. 



The ore is coarsely granular as a rule and contains too much 



