8 Field Museum of Natural History 



final stage of blocking out the ore that lies between it 

 and the shaft. It will be seen that the block of ore 

 lying between the hundred and the fifty foot levels 

 and between the shaft and the raise has four of its 

 six faces open for examination. Experience has sho'w^l 

 that when four faces of a body of ore can be examined, 

 a very fair estimate may be made of the quantity and 

 value of the ore. Such ore is said to be BLOCKED 

 OUT or ORE IN SIGHT. On this model two such 

 blocks are shown, one from the surface to the fifty 

 foot level and the other from the fifty foot to the 

 hundred foot level. The mine workings described, 

 shafts, drifts, cross-cuts, raises, etc., constitute DE- 

 VELOPMENT WORK which must be done before the 

 extraction of the ore in a large way can be undertaken. 

 It is customary to carry development considerably 

 ahead of the mining proper so that it may be known 

 what may be expected of the mine for some time in 

 the future. 



Some ore is extracted during development but at 

 a cost much greater than that of the average cost of 

 mining. 



The larger part of the ore is taken from chambers 

 called STORES. 



The principle on which mining is carried out in 

 this mine and in the great majority of all metal mines, 

 is to so conduct the operations that the ore always 

 moves downward to the shaft and no lifting of the ore 

 is performed except at the shaft. Ore moves down- 

 ward by its own weight, but to raise it, effort, human 

 or mechanical, must be employed. It is economical 

 to concentrate all this application of power in one 

 operation at the shaft. Stopes worked along these 

 lines are called OVERHAND STOPES. 



The beginning of a stope is shown about midway 

 of the lower level, where a small opening appears 



t8] 



