508 



MINING INDUSTEY. 



shows parallel bands or lines of structure, or of varied mineral composition, 

 which usually dip flatly to the eastward. 



The walls of the vein are not very regular. Sometimes they are quite 

 smooth and well-defined, but usually there is little or no gouge or selvage, 

 and the removal of the vein-matter near the wall leaves a ragged and uneven 

 surface. Where the walls ha,ve been left standing sometimes they frequently 

 scale off and fall in large pieces ; sometimes belts of highly micaceous char- 

 acter occur, which soften on exposure to the air, rendering the walls very in- 

 secure and requiring substantial support. The width of the vein varies from 

 2 to 5 feet, sometimes expanding to 12 or 15. 



The vein-matter is like that already described in the Bobtail — ^quartzose 

 generally, sometimes a mixture of quartz and feldspar, much of which has a 

 softened, altered character, carrying a large percentage of finely-divided pyrites. 

 Sometimes masses of pure quartz are also densely impregnated with finely 

 crystallized iron pyrites. Crystallized quartz occurs sometimes. Free gold 

 is also found, lumps worth $50 being reported. 



As in the Bobtail, there is usually a seam of compact ore, consisting of 

 iron and copper gold-bearing pyrites, associated with the wider belt of vein- 

 matter carrying the ore in disseminated form, as just described. The value 

 of this compact ore-seam varies considerably, but is generally less per ton 

 than that of the Bobtail. Some of the richer lots are said to yield from $150 

 to $200 coin, per ton, but such are uncommon. In fact, the value of the lode 

 seems to be less concentrated than in the Bobtail, affording a smaller propor- 

 tion of smelting ore. In their favor, as compared with the Bobtail, the aver- 

 age width of the Grregory is greater. The yield per ton under the stamps 

 varies according to the proportion of compact and richer pyrites occurring 

 with the poorer vein-matter. The latter yields alone from 5 to 6 ounces per 

 cord, or $10 to $13, in coin, per ton, while the average yield of the Black 

 Hawk rock for six months, crushing everything together, is stated at from $20 

 to $25, coin, per ton. 



The same distinction observed in the Bobtail, that the fine-grained cop- 

 per pyrites is the richest gold-bearing mineral of the ore, prevails also in this 

 vein. But little galena, and less zincblende, is found associated with the ores 

 of the Grregory. 



