NO. 2005. MOUNT LYELL COPPER DISTRICT— GILBERT & POGUE. 625 



Plate 51. 



Fig. 1. Quartz crystal partly replaced by enargite (light) and pyrite (dark). The 

 black areas are irregularities in the section. X 40. Mount Lyell Mine. 

 Cat. No. 77552. 



2. Intergrowth of bornite (dark) and chalcopyrite (light), indicative of simultane- 



ous development. North Mount Lyell Mine. X 40. Cat. No. 77601. 



3. Grain of bornite (fe) in gangue (g), surrounded by border of tetrahedrite and 



chalcopyrite (white). The tetrahedrite and chalcopyrite can not be differ- 

 entiated in the photograph, but their relations to bornite are similar; they 

 were probably developed simultaneously and are later than the bornite. 

 X200. North Mount Lyell Mine. Cat. No. 77597. 



80459°— Proc.N.M. vol.45— 13 40 



