SILVER DEPOSITS AT BUTTE, MONTANA TERRITORY. 



211 



The matrix of the veins consists mainly of quartz, mixed witli 

 carbonate and silicate of manganese. These minerals give to 

 the mass a beautiful rose-coloured a23pearance. 



The silver minerals are principally native silver, silver-glance, 

 Fahlert, mixed with varying quantities of iron pyrites, zinc, 

 blende and galena. 



The veins vary much in width, from a few inches to 3 and 4 

 feet. The miner's estimate of the size of the lodes is greatly in 

 excess of what it really is, from the fact that they are accustomed 

 to regard the whole mass of rock which shews any signs of 

 mineralization, as part and parcel of the vein, and the natural 

 joint of the granite is often regarded as the true wall of the 

 fissure. 



The following is a rough sketch of a band of rock and small 

 veins as it appeared in the breast of one of the drifts in the 

 Moulton Mine, the total width being about 10 feet. 



{a) represents the i3ure unchanged granite, {h) altered granite 

 shewing kaolinized felspar, and sprinkled through with iron 

 pyrites, zinc, blende, &c., containing a little silver, the latter being 

 present to the extent of from 5 to 20 ounces per ton. {c) veins 

 of quartz, and carbonate of manganese, containing usually from 

 40 ounces to 100 ounces of silver per ton. 



The outcrop of the lodes frequently shew large continuous 

 masses of quartz and black oxide of manganese, principally 

 Psilomelane and Pyrolusite, and these highly oxidised minerals 

 extend in depth to about 40 feet. They are really manganous 

 gossans, and are formed by the conversion of the carbonate of 

 manganese into minerals having a liigher degree of oxidation- 



