22 WILLIAM H. EMMONS 



Alumina. — In some waters aluminum sulphate is abundant 

 (the average of aluminum, 333 parts per million). It forms where 

 sulphate waters attack kaolin, setting free Si0 2 and taking alumina 

 into solution. 



Nitrates. — Nitrates are not abundant in mine waters. In one 

 analysis only 1 is N0 3 reported (1.60 parts per million), and this 

 in a deep-seated water of questionable genesis. 



Phosphates. — Traces only of P0 4 are reported from two mine 

 waters; others contained none, if determinations were made. 



Silica. — Silica (35 parts per million) appears high for acid 

 waters. The analyses include a manganiferous sulphate water 

 from the Comstock, abnormally high in silica. 2 



Iron. — Iron is the most abundant metal in the waters of gold 

 mines. Ferric iron (603 parts per million) is, according to these 

 analyses, more than twice as abundant as ferrous iron (277 parts 

 per million). Ferrous iron is much more abundant below than 

 above the water-table. 



Manganese. — If manganiferous minerals are present in the 

 primary ore, they oxidize in the upper portion of the deposit to 

 manganese dioxide or other high oxides of manganese; and these, 

 in turn, oxidize ferrous sulphate, in the presence of sulphuric acid, 

 to ferric sulphate. 



Copper. — One analysis shows 147 parts of copper per million. 

 Two other analyses show traces. Small amounts must be present 

 in many other waters, since gold ores often carry copper. Pos- 

 sibly, small traces of the heavy metals were not looked for in many 

 of the waters analyzed. 



III. CHEMICAL EXPERIMENTS IN THE SOLUTION AND DEPOSITION 



OP GOLD 



The migration of gold in the deposits takes place at low tem- 

 peratures. At the surface the temperatures range between o° 

 and 50 C. and pressures do not exceed one atmosphere. With 

 the normal gradient of increase, the temperatures, even several 



1 Geyser Mine, Silver Cliff, Colo. See S. F. Emmons, Seventeenth Annual Report, 

 U.S. Geological Survey, Part II, 462 (1895-96). 



2 Bulletin of the Department of Geology, University of California, IV, No. 10, 192 

 (1904-6). 



