Gold 3 1 1 



of rocks, or Basement Complex. Distinction is made between 

 the Tertiary and Recent rocks called the superjacent series 

 and the pre-Tertiary rocks, called the bed-rock series. The 

 latter contain the quartz veins, the former the placer deposits 

 resulting from the disintegration of the veins. In the intrusions 

 of molten rock from below, and the uplifting, folding and com- 

 pressing of the sedimentary and injected igneous rocks, veins 

 were formed, and into these veins mineralized solutions were 

 driven under great pressure and in superheated condition. 

 During the slow process of cooling minerals crystallized out of 

 the solutions, and gold came to be a part of the filling of the 

 veins. 



"The compressive stresses to which the range was subjected 

 after the intrusions of molten granitic rock (granodiorite) pro- 

 duced joint systems in different directions traversing all of the 

 rocks of the bed-rock series. Sometimes the joint planes are 

 thin; at other places the spacing was much larger, and a series 

 of parallel fissures was produced. The faults on the veins are 

 in general small, but in one notable case (the Merrifield and 

 Ural veins) great movement has taken place resulting in a 

 throw of over 1,000 feet, measured along the dip of the veins. 

 The origin of the fissure system is shown to be compressive 

 stresses. "* 



Gold-Bearing Qiiartz Veins Occur 

 at All Depths 



Quartz with native gold and metallic sulphides of other 

 minerals is one of the products of the vein-forming agencies. 

 The great veins are formed by deposition in the open spaces 

 along the fissures and constitute the richest and generally the 

 only kind of ore. The gold is generally in a finely divided state, 

 though in many mines coarse gold also occurs. Free gold 

 occurs at all depths, and is generally associated with suphides of 

 other metals. The average width of large veins may be from 



* F. E. Matches, U. S. G. S. Prof. Paper 160. 



