234 GEOLOGY OF TONOPAH MINING DISTRICT, NEVADA. 



slowly decreasing with the increasing silica in the last. The phosphorus, though 

 present in still smaller amounts, behaves in much the same way, while the record 

 of the barium seems irregular. It appears, then, that even the resistant rutile 

 and apatite of the andesite were slowly attacked and in part dissolved by the 

 mineralizing waters. The amount of combined water in the different rocks does 

 not vary in any symmetrical way, and, indeed, remains nearly the same (about 

 3 per cent) except in No. 8. Carbonic acid was noted only in Nos. 1 and 2, but 

 microscopic analysis shows that siderite is usually present, often in very small 

 quantity, in most of the other rocks. 



RESUME OF EFFECTS OF MINERALIZING WATERS. 



The mineralizing waters, penetrating vigorously the rock on each side of 

 their main circulation channels, did not retain their metallic contents, which wei'e 



all deposited in favorable places in the main 

 channels or in special lateral channels which 

 became lesser veins. However, they at- 

 tacked the rocks vigorously by virtue of 

 the carbonic acid, probably also sulphuric 

 acid, and perhaps to a less extent by the 

 acids of chlorine and fluorine. The ferro- 

 magnesian minerals were decomposed, the 

 lime and magnesia were taken into solution, 

 and the iron was mainly dissolved, but in 

 part was altered to iron sulphide by the sul- 

 phur in the waters. The feldspar was al- 

 tered, probably by potassium carbonate, to 

 adularia, or to sericite and quartz, the lime 

 and soda being taken into solution. Tocom- 

 8 pensate for these dissolved materials, silica 



Scale:.OI(qyotientfigure)-iinch . , , , . , . 



F,<,74.-Diagr a m showing relative proportions of the WaS deposited f ro m the highly charged 



leas common elements in the various stages of altera- waters. So great W8S the llCCCSsitV of de- 

 tion ol the earlier andesite. 



positing the silica that it probably takes the 



place of part of the alumina, and also seems to have replaced even part of the 

 potash, though this is not certain. The waters, then, after passing through a rock 

 like No. 8, emerged poorer in silica and richer in all the other rock constituents. 

 On passing farther and traversing a rock like No. 7, the process was carried 

 further, though the excess of silica was not so great, and the capacity of the 

 solutions for the different rock materials became somewhat less. Hence the least 

 soluble, such as the alumina, was not so much dissolved, while lime, magnesia, 

 and soda were thoroughly extracted. On passing from rocks like 6, 5, and 4 the 



