56 



THE AURIFEROUS GRAVELS OF THE SIERRA NEVADA. 



Butte and Plumas, partly because the rocks begin to be more and more cov- 

 ered with volcanic materials, and partly because of other conditions, to be 



hereafter explained. 



It is true, in a general way, that the region of auriferous gravels is also 

 that of quartz veins. For in the Sierra Nevada, as almost everywhere 

 else in the world, there seems to be an intimate and not easily explained 

 connection between the metal gold and the mineral quartz. It cannot be 

 said that quartz is the exclusive " gangue" or accompanying vein-stone of 

 gold ; but this metal is found, with comparatively small exceptions, in the 

 veins of quartz which intersect metamorphic rocks, and also, to some extent, 

 in the slates which lie adjacent to such veins. A large portion of the gold 

 actually obtained, however, throughout the world comes from the debris of 

 such veins and rocks, formed by the operation of those eroding and disinte- 

 grating agencies which are and have been at work ever since rocks began to 

 be formed. There are regions of the earth where gold has been procured in 

 large quantities from " washings," — that is, from the working of detrital 

 materials, especially of gravels and sands, and where no mining in the solid 

 rock has ever been attempted, or indeed any veins of quartz discovered ; but 

 it is, perhaps, not unreasonable to say, that, in any region where this metal 

 is found in the superficial detritus in even a moderate amount, there or 

 somewhere in the vicinity metamorphic rocks would be discovered, after some 

 search, and that these would be found to be intersected with veins or masses 

 of quartz. Further investigations would prove, in the great majority of 

 cases, that the gold in the detritus came from those quartz veins, or from the 

 rocks immediately adjacent to them. Every great gold-producing district in 

 the world furnishes a portion of the metal from washings, and another part 

 from mining in the solid rock. There have been facts observed in California, 

 however, which would seem to indicate a different origin for a portion of the 

 gold there obtained, as will be mentioned farther on. 



It is a remarkable fact that the veins which are productive of gold, the 

 world over, are in a very great majority of cases, much simpler in their mode 

 of occurrence than those which are productive of the ores of the other metals. 

 Auriferous quartz veins are made up of quartz alone, with little or no admix- 

 ture of other earthy minerals, such as calcite, brown-spar, heavy-spar, and fluor- 

 spar, which, in ordinary veins, are of frequent occurrence, often making up a 

 large part of the gangue. The writer has never seen, among the many quartz 

 veins examined in the Sierra Nevada, a trace even of fluor-spar, or anything 



