192 University of California Publications. [Geology 



insufficient supply of oxygen, as occurs locally in this part of the 

 Central tunnel. 



The water surrounding' the sulphates and pyrite being de- 

 posited, is strongly acid, the most so where the pyrite is heaviest. 

 As the wall is worked into, the acidity becomes perceptibly less. 

 The ferrous sulphate appears to exercise the necessary protecting 

 influence over the pyrite to save it from attack by the free acid 

 or further attack by the small amount of free oxygen present. 



Analysis of Waters. — The analysis of the vadose water, from 

 Central tunnel, taken from a dropping stream out of the wall on 

 the lower level, is as follows:* 



Grams per liter. 



Si0 2 0.6160 



A1 2 3 18.2140 



FeA 7.1786 



Mn 3 4 1.2500 



CaO 1.7400 



MgO 10.8108 



CuO 0.1850 



SO, 70.1154 



CI 0.1276 



IF.0 trace 



Na = 0.7209 



Total solids 110.9583 



Free ILS0 4 125.0804 



The remarkable properties of this water are evident. Silica 

 is noticeable in amount, in spite of the strongly acid solution. 

 The salt is seen to be essentially a magnesian ferric aluminum 

 sulphate, with lime, copper and manganese. These mine solu- 

 tions vary, and the writer has taken from the roof of some of the 

 old stopes stalactites of quite pure copper sulphate. The water 

 analyzed was a fully oxidized solution ; the water depositing the 

 pyrite is only partially supplied with oxygen. 



Assay of Waters. — The assay of this vadose water gave the 



following results : L'oOcc. portions were used for each test. 



Silver 388.0912 mg. per ton of solution 



Gold 4.1528 mg. per ton of solution 



It is necessary again to note the fact that some of the east- 

 west veins which exist east of Bullion Ravine on the line dividing 



Analysis by N. B. Wilson. 



