CHAPTER IX. 

 ORE DEPOSITS. 



Geological History.— It is not tile iuteiitiou t<> enter into a detailed descrip- 

 tion of the various ore deposits of this region or of their mode of occur- 

 reuce. An excellent nionog-raph upon the mines and ores of Ruljy Hill 

 has been published by Mr. J. S. Curtis/ in which he gives in much detail 

 the results of his studies of the silver-lead deposits of the Richmond and 

 Eureka mines. 



This report, however, would be incomplete if the writer, after devoting 

 much time to an investigation of the structural features of the Eureka 

 Mountains, constant^" kee})ing in mind the relationship l^et^veen the ore 

 bodies and the sedimentary iiiid igneous rocks, should fail to state his con- 

 clusions as to the geological position of the ores, their age, and origin. 

 Moreover, as many geologists do not care for the details of mining develop- 

 ments, but feel a keen interest in all (questions relating to mineral deposi- 

 tion, it seems desirable to state here, for the use of the general reader, such 

 facts as bear directly upon the geological occurrence of the Eureka ore 

 bodies. 



It has been demonstrated beyond all question, from the facts presented 

 in the preceding chapters, that the Eureka Mountains are formed of 

 orographic blocks of Paleozoic strata made up of quartzites, limestones, 

 and shales. These blocks, strongly contrasted by their orogra])hic struc- 

 tm'e, are separated from each other by profound north and south faults. 

 Along the lines of these displacemeuts east of Prospect Ridge enormous 

 masses of igneous rocks have been poured out, which have tended still 

 more shai-ply to intensify the lines of demarcation between the in(li\ndual 

 blocks. The entire thickness of Paleozoic sediments can not be far from 



' Silver-lead deposits of Eureka, Nevada. Mou. U. S. Geol. .Survey, vii, Washington, 1884. 

 292 



