IRON ORES 77 



The known character, the apparent dimensions, the j^eneral 

 form, and the position of an iron ore deposit, with reference 

 to the surface and water, the physical structure or chemical 

 composition of the material to be extracted, the character of 

 the earth or rock inclosing or occurring in the ore body, the 

 stratification, dip, and strike, the simplicity or complexity of 

 the ore body, the convenience of the deposit to an available 

 market for its product, and the capital at command of those 

 who attempt the exploitation — all influence the methods fol- 

 lowed in mining iron ore. 



AVhere the ore body projects above or lies close to the 

 surface, or where in a large apparently well defined deposit the 

 cover can be stripped to advantage, the exploitation may be 

 carried on by open cut work, from which the ore is taken out 

 either by train or, after digging, lifted by steam power applied 

 to inclines or to vertical hoists. 



In the Mesabi range of Minnesota, in the Sunrise district 

 of Wyoming, and in a number of brown hematite deposits of 

 the south, large open cuts are worked by the use of the steam 

 shovel, these appliances removing the ore in successive benches 

 after large areas have been stripped by the same method. 



Wliere the body of ore is under considerable cover, if 

 the roof is firm, or if the vein matter is comparatively narrow 

 and the dip steep, it is removed through shafts, either vertical 

 or inclined, and through tunnels or adits. In a number of in- 

 stances open cut work has, after reaching a considerable depth, 

 been supplemented by underground exploitation, while in a 

 few cases this method has been reversed and a large open 

 cut has supplanted underground work. The shafts or adits, 

 which are generally expected to serve as long as the deposit 

 yields ore, are necessarily costly and need to be planned and 

 located with care, for through these the miners have access to 

 the underground workings, and the ore and water are carried 

 to the natural surface. 



Except when the strata penetrated are exceptionally com- 

 pact and hard, the shafts or adits must be substantially tim- 

 bered, so that they can be maintained until the deposit is ex- 

 hausted; they are excavated either in the ore or in inclosing 

 rock, and if in the ore large bodies are left adjacent to these 



