4 FiF.i.D Museum of Natural History 



time to leave as much as possible of the worthless 

 material behind, for it costs as much to mine and 

 raise gangue as it does to mine and raise ore. 



If the sulphides are worth forty dollars a ton 

 and it is necessary to mine three tons of quartz with 

 each ton of ore, then the material mined is worth only 

 ten dollars a ton, a value that in so small a mine in 

 so remote a region will barely pay expenses of mining 

 and treatment, although larger mines find such ore 

 very profitable. 



When, as is the case here, the ore can be so mined 

 that with each ton of sulphide only one ton of quartz 

 must be mined, the material hoisted is worth twenty 

 dollars a ton and yields a good profit. 



As the ore is not distributed equally in all parts 

 of the vein, there must be certain areas where the ore 

 is richer than elsewhere. These areas are likely to 

 have some regularity of form and distribution. The 

 laws controlling their distribution are frequently very 

 obscure, so that in many mines the discovery of these 

 enriched areas before the workings actually cut them 

 is very difficult and often impossible. They frequently 

 assume very elongated forms, and are then called 

 CHUTES or SHOOTS or sometimes CHIMNEYS. 

 These may run in any direction in the veins. In some 

 mines the richer portions take the form of patches of 

 limited area called POCKETS. A very rich pocket in 

 a gold mine is usually called a GLORY HOLE. Often 

 ore chutes cannot be distinguished by appearance from 

 the rest of the vein and their location and limits can 

 be determined by assay only. There may be one such 

 chute or a number of them in a mine. 



When the segregations of rich ore take an elong- 

 ated form, thick at the center and tapering toward 

 each end, they are called LENSES. 



[4] 



