174 



GEOLOGY OF TONOPAH MINING DISTRICT, NEVADA. 



This zone contains some silver sulphides and some good ore, although it is largely 

 of low grade. The one lying farthest north has been called the Macdonald vein. 



The Macdonald vein is a strong, rich vein having a strike a little north of 

 east, and a northerly dip varying from 45 to 65. It has been extensively 

 drifted on, on this level, and has produced a great deal of high-grade sulphide 



s ore, of the same character as the high-class 

 ores of the Montana vein. It has been fol- 

 lowed down to the 615-foot level. 



On both these levels and on the interven- 

 ing stopes this vein shows a complex fault- 

 ing, reminding one of the faulting that has 

 affected the Fraction vein. In a vertical 

 section such faults appear nearly parallel to 

 the vein, but curve and continually branch 

 and so become now steeper, now flatter in 



FIG. 63. Vertical sketched cross section of cross wall 

 limiting chief ore shoot of Montana vein below, as 

 displayed on the 512-foot level of the Montana Tono- 

 pah. a, Rich sulphide ore, sloped out; 6, silicifled 

 andesite, some quartz and ore, no rich ore; c, Earlier 

 andesite, wall rock. 



dip than the veins (tigs. 64, 65). If 

 straight this faulting would be like 

 that which has affected the vein of 

 the North Star, but the undulations 

 of the faults here in the Montana 

 Tonopah produce, in vertical section, 

 displacements of the vein to the north 

 on the under side of the faults. The 



FIG. &J. Vertical cross section (sketched), showing effect of 



line of faulting is not parallel in strike curving and branching faults on Mncdonald vein, in slopes 



above the 615-foot level on the Montana Tonopnh. 



or dip to the vein, though it sometimes 



so appears in vertical section; in fact, the flat portions of the fault pianos pitch east 

 on the vein at moderate angles; and striiv along the faults show that the real 

 direction of movement has been to the east along this pitch. In horizontal sec- 

 tion, however, these faults are seen to curve and branch in as complicated a 

 manner as in the vertical section, producing an unrivaled complexity (PI. XXII). 



zo feet 



