CHAPTER VI. 



THE ORE DEPOSITS. 



ciassiHcation of the ore deposits. — The ore deposits of Eureka District, though 

 they contain gold, can be classed under the head of silver-lead deposits in 

 limestone The type of deposits to which those of Eureka belong is one 

 often met with in the older limestones of the Great Basin, and although 

 these particular deposits have been of more value, and are more widely 

 known than any of the others, and exhibit some very interesting structural 

 features, yet they cannot be said to form an isolated class. An extended 

 comparison of these deposits either with similar ones in the Great Basin or 

 with others of the same general character elsewhere, does not come within 

 the scope of this report, but it may be well to present some points, both of 

 resemblance and difference between them and the best known examples of 

 similar types in other mining regions. Although the gold and silver in the 

 Eureka ores are the metals which render their mining possible, yet the 

 quantity of them present in these ores, measured by weight, is so small, in 

 comparison with the lead, that a classification based upon these metals alone 

 would be misleading. As in many of their features they resemble other 

 lead deposits in limestone, it seems best to regard them simply as lead 

 deposits, in which the gold and silver are merely accessory, though very 

 important ingredients. All lead ores carry some silver, and with it some 

 gold, though in many of them it is only possible to obtain traces of these 

 metals. 



Lead deposits in limestone of the Great Basin. TlirOUghollt tll6 Great BaSm there are 



a large number of lead deposits, all of which exhibit many features of sim- 

 ilarity. They occur in limestones and dolomitic limestones of Palaeozoic 

 age, and are mostly of very irregular form. Their ores consist principally 



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