190 



University of California Publications. [Geology 



The analysis of the water showed it to be an alkaline sulphate 

 and carbonate solution containing a large amount of lime. The 

 presence of chlorine is important as affecting the gold in solution. 

 The C0 2 determined is low, for on standing, some of this gas is 

 given off and the silica separates out in sufficient amount to ren- 

 der the water milky. The writer has been unable, for stated rea- 

 sons, to test the water in the mine. The jugs of water stood 

 for from 48 to 64 hours before testing, hence the figures for the 

 carbon dioxide need considerable correction. On evaporating the 

 water and moistening the residue, a strong alkaline reaction is 

 obtained by litmus paper. 



SURFACE ORES AND WATERS. 



The ores are moving downward by the leaching action of the 

 acid surface waters. In this way they are extracted from their 

 containing rocks and redeposited below. This process in the past 

 has produced the striking "nodular" ores of the Andes mine, 

 noted by King * as occurring just below the level of ground 

 water. These ores are now in their turn being attacked and 

 again being carried below. A striking example of the ore depos- 

 ited by the vadose waters was exposed on one of the levels of 

 the Andes mine. The presence of east-west slips has already 

 been noted as occurring here, and one of these, dipping south 60°, 

 had opened sufficiently to allow the free circulation of water. 

 The slip had cut across all other rocks, vein and country, and 

 was filled with about two inches of solid coarse black sulphides of 

 lead and silver. This small sheet of ore pinched out toward the 

 bottom of the drift, but broadened above. The grain of the ore, 

 and general characteristics of ratio of lead to silver, etc., were 

 all different from the ore which occurs below, deposited from the 

 deep circulation. The nodular ores consist typically of nodules 

 ranging in size from that of a pea up to a foot in diameter, and 

 composed of rich black sulphide ore in a matrix of fine crystals of 

 quartz. Each nodule is completely surrounded by barren quartz, 

 which at times may penetrate the nodule along later cracks. 

 These quartz crystals are built upon the nodules as centers, giv- 

 ing them a radial arrangement. 



* Clarence King, "Survey of Fortieth Parallel," Vol. III. 



