OCCURRENCE OF THE PROUSTITE 95 



different solutions. This explanation would account for the variation of 

 silver and lead values shown in the assays. 



Occurrence op the Proustitb 



In September, 1902, the largest pay streak of the vein widened to about 

 21 inches and assumed a distinctly banded structure, with galena and 

 sphalerite irregularly mixed on each side ; these were followed by siderite, 

 also symmetrical, while in the center was a streak of massive proustite 

 with finely intermingled quartz which was more or less drusy. This 

 streak was usually about 2 inches in width, but in one instance amounted 

 to 14 inches. The proustite possesses all its usual mineralogical charac- 

 teristics, which require no further description. For a very short distance 

 the central portion consisted of argentite and finely disseminated quartz 

 or a mixture of the two with proustite. When the latter predominated 

 along the vein, no argentite could be observed, whereas in many of the 

 argentite specimens proustite was detected. The proustite ore was fol- 

 lowed along the strike for a distance of 30 feet with an upward stope of 

 20 feet, at which point it disappeared. By means of a winze and cross- 

 cut, it was also followed downward 15 feet until mining operations 

 were siispended in the winter. The average specific gravity of four speci- 

 mens of the proustite-quartz ore was found to be 4.17 as compared with 

 5.60 for the pure proustite. Several quantitative blowpipe determina- 

 tions showed an average of about 20 per cent silver or about 6,000 

 ounces to the ton for the specimens examined. This would indicate about 

 33 per cent of the ruby silver, while the average specific gravity obtained 

 would indicate a little over 50 per cent proustite. 



Mr J. C. Sharp made two quantitative analyses of carefully selected 

 proustite, the average of which gave as follows : 



-i?„„„A Theoretical 



round / . „ . „a ■, 



(AgsAsSg) 



Ag 67.60 65.5 



As 13.85 15.1 



Sb 93 



S 17.40 19.4 



99.78 100.0 



The analysis shows that a small amount of the pyrargyrite molecule 

 (AggSbSg) is present, as is the case with certain proustites from Chile 

 and Germany. That the percentage of silver found is apparently too 

 high, while the sulphur comes lower than the theoretical amount, is prob- 

 ably due to an imperfect analysis, but might have been caused by the 



