MIZPAH VEIN. 119 



EFFECTS OF TRANSVERSE PREMIXERAL FRACTURES. 



There were also minor fractures, among which some striking in a general north- 

 south direction, and dipping east, can be recognized. 



Cross walls. These are shown by jogs in the vein following these planes, or, very 

 frequently, by a change from a highly silicified or mineralized condition to a less 

 altered one, while the vein zone is continuous and undisturbed. These jogs or offsets 

 may occur on both sides of the vein, and thus may simulate faults, from which they 

 are distinguished by the lack of evidence of movement; or they may be restricted to 

 one side of the vein (fig. 19), in which case they can not be mistaken. Sometimes the 

 vein may jog in opposite directions on the two sides of such a critical cross plane or 

 premineral fracture, and so become markedly larger or smaller (fig. 19, B). 



Branching veins. Small veins which diverge from the main vein also testify to 

 these crosscutting premineral fractures. 



Besides the north-south premineral fractures, there were other fractures 

 having a variety of strikes intermediate between that of the main vein zone and 

 the cross fractures. Among other things this is evidenced by the portions of 

 the veins which split up from the main vein and reunite with it. This splitting 

 and reuniting takes place in both a horizontal and a vertical direction, and the 

 general result can best be explained by illustrations (fig. 20). The veins thus belong 

 to the class of linked veins, and this same relation is exhibited on a larger scale 

 between some of the larger veins, and will be described. 



The intersections of the minor veins with the vein zone seem, as a rule, to 

 pitch to the east also, like the main crosscutting premineral fractures. 



Origin of ore shoots. The main crosscutting fractures, striking north and 

 south and dipping east, as above explained, in many places separate the highly 

 silicified and mineralized vein zone, often by a sharp division, from a portion 

 which has not been so much altered. These richer portions ma}- be considered 

 ore shoots; and while their internal size and richness are very irregular, a 

 careful plotting of the results of the assay chart" shows that the richer portions 

 of the vein may be separated into broad east-dipping shoots, of which there are 

 three within the developed vein. The internal distribution of the ore in these 

 shoots would make an interesting study if enough data were on hand. 



Fig. 21 shows the shoot-like distribution of the richest portions. The space 

 between and beyond the shoots is, however, good ore. The company does not 

 desire to have the figures published, but it may be said that the amount of gold 

 and silver in those parts of the vein left blank on the diagram is fully equal to 

 that contained in the greater part of the ore produced by the Comstock during 



a Kindly furnished to the writer by the Tonopah Mining Company. 



