PRECIPITATION OF GOLD. 1095 



masses of gold (often more than 100 ounces in one piece) have been 

 obtained, and the greater part of the gold extracted from this belt has 

 come from those parts of the quartz veins near some one of the indicators." 

 Furthermore, Rickard" describes experiments in which the black carbon- 

 aceous shale of Rico was placed in silver solutions and in solutions 

 containing Cripple Creek gold ore. Both metallic silver and gold were 

 abundantly precipitated upon the shale in a short time. In the instances 

 above mentioned it can hardly be doubted that the organic material was 

 an important or controlling factor in the reduction and precipitation of gold. 



The argillite with which many of the gold ores of the Sierra Nevada 

 are associated is carbonaceous, b but the chief influence of this carbonaceous 

 material may have been to assist in the production of the ous salts which 

 ultimately reached the trunk channels. But in some places, as for instance 

 where the pyrite occurs in a carbonaceous argillite, but not in quartz/ the 

 gold may have been precipitated directly by the carbonaceous material. 

 But since the gold in the Sierra Nevada is mainly deposited in open 

 fissures/ the suggestion already made of direct reduction of the major 

 portion of the gold by ous salts, and especially ferrous sulphate, is thought 

 to be the more plausible, although if the formation of the ferrous sulphate 

 be due to carbonaceous material in the country rock, the precipitation is 

 indirectly due to organic matter. 



The sulphides of the base metals also precipitate gold from its 

 solutions. Below the level of ground water the rocks most commonly 

 associated with gold are the sulphides of the base metals. Thus gold 

 occurs on a great scale associated with pyrite. Very often it is found also 

 with sulphides of the other metals, especially copper. In such occurrences, 

 where the sulphides are abundant, the gold is likely to be plentiful; where 

 the sulphides are present in small quantity, the gold also is likely to be 

 deficient. This relation is illustrated in both California and Australasia," 



a Rickard, T. A., The Enterprise mine, Rico, Colo.: Trans. Am. Inst. Min. Eng., vol. 26, 1897, 

 pp. 978-979. 



*Lindgren, Waldemar, The gold-quartz veins of Nevada City and Grass Valley, California: 

 Seventeenth Ann. Kept. U. S. Geol. Survey, pt. 2, 1896, p. 81. 



cLindgren, op. cit., p. 140, PI. VIII. 



''Lindgren, op. cit., p. 259. 



^Lindgren, Waldemar, The gold-quartz veins of Nevada City and Grass Valley, California: 

 Seventeenth Ann. Rept. U. S. Geol. Survey, pt. 2, 1896, pp. 124-126. Don, J. R., The genesis of certain 

 auriferous lodes: Trans. Am. Inst. Min. Eng., vol. 27, 1898, p. 567. 



