82 MINING INDUSTEY. 



bonanza, there was perhaps a shght mcrease over the present proportionate 

 yield of gold. In a part of the Bullion, however, and in the Virginia vein 

 back of the Ophir, and in the Sacramento, gold largely predominates. The 

 metal produced from these mines averages nine dollars to the ounce. With 

 these miimportant exceptions, the average proportion of gold is about thirty 

 per cent, of the whole value. Eight-tenths of all the bonanzas have occurred 

 in the ore-channel, or in fissures joining it and belonging to its system. 

 Within this zone there has been a general tendency to accumulate where the 

 convex face of the east wall invades the lode, as at Grold Hill, Grould and 

 Curry, and the Ophir. The chief developments have been within 600 feet of 

 the surface. The mineralogical characters of the ore vary very little from the 

 surface to the lowest depths, except that above 400 feet the "Colorados" have 

 reddened the veins, and oxide of iron in a measure replaces the sulphide of 

 that metal. 



Accidental minerals are horn silver, which in rare small crystals occurred 

 in the outcrop of the Gold Hill group ; and native copper, the latter in con- 

 nection with native gold and silver; and green carbonate of copper, in an 

 earthy, clay-like mass, occurred in the upper works of the Gould and Curry. 

 Native copper also, in minute but well defined crystals, is found in the clays 

 of the Sierra Nevada. This is interesting, since directly above it in the earlier 

 works an unusual predominance of copper pyrites was found. At a depth of 

 about 500 to 700 feet, in various parts of the lode, the ore not unfrequently 

 assumes a greenish hue, given it by an admixture of chlorite. On the 325- 

 foot level of the Chollar-Potosi, north of the Potosi shaft, this first made its 

 appearance. It has occurred largely in the Hale and Norcross, and now in 

 the 900-foot level of the Yellow Jacket is quite frequent. Together with the 

 chlorite is chloride of silver in thin scales. Perhaps the greatest variety of 

 unusual forms of the ore was found in the Ophir. In the back-stope of that 

 mine, in the midst of a very rich deposit, occurred considerable masses of 

 antimonial ore, and a singular association of rich galena and native silver. 

 Near the lower limits of the front body were unusual accumulations of zinc- 

 blende, which in depth associated itself more and more with galena and 

 copper pyrites, and finally gave out at the bottom of the bonanza, the quartz 

 there being stained with carbonates and a sulphate of copper, and the waters 



