1917] Clark: Geology and Ore Deposits of the Leona Rhyolite 373 



Underground Development. — The mine of the Leoua Chemical 

 Company is opened by two tunnels entering the hill at two levels, 

 75 feet apart. The approximate position of the tunnels and of the 

 ore body is shown in figures 2 and 3. The ore observed in the workings 

 is in a potato-shaped mass in the mineralized zone, and is of two kinds. 

 The soft ore is nearly everywhere surrounded by gouge ranging from 

 a few inches to two or three feet in thickness. The hard ore, which 

 forms but a small part of the deposit, is highly silicified, contains more 

 chalcopyrite, and is not bounded by fault gouge. 



Most of the ore has been taken from the lower level, although quite 

 important bodies extend above the upper tunnel. A winze was put 

 down 40 feet from the north crosscut on the lower level, and it is said 



Fig. 3. Diagrammatic vertical section of ore body along line A-A'. 



that ore was encountered all the way down. A raise was driven from 

 the southeast part of the lower tunnel and ore was struck 20 feet above 

 the level, so that it is evident that the ore body dips into the hill, as 

 is shown in the vertical section. 



Occurrence. — The ore is confined to the rhyolite and is not in 

 contact with any other rocks so far as is known, but the deposit 

 described by Mace 12 rests on a shale, probably Knoxville, and not a 

 part of the Franciscan, as he suggests. The pyrite is massive and has 

 fragments of country rock included in it. The ore occurs in a fracture 

 zone in the rhyolite, which is jointed and faulted so that considerable 

 quantities of gouge and small displacements may be seen nearly every- 

 where in the mine ; but there is abundant evidence of more intense 

 fracturing and differential movement that has probably caused the 

 localization of the ore bodies. 



At nearly every place in the mine where the margin of the ore is 



is op. ext., p. 1320. 



