Subsurface Methods as Applied in Mining Geology 



973 



bodies are located near those channelways. In other veins no control or 

 localization other than the premineral host fracture is apparent. 



Folding represents another type of structural control. In competent 

 rocks, crests of folds are more open than the flanks; and, when aided by 

 an impermeable cap rock, deposits are restricted and localized near the 

 crests. In the saddle-reef deposits of Bendigo and Ballarat, Victoria, 

 Australia, ore occurs more abundantly near the crest line, but it also ex- 

 tends a short distance down the flanks. In tight, overturned folds, prin- 

 cipally in metamorphic rocks, deposits occur along the flanks of some 

 folds but the controls might be considered as faults developed because of 

 intense folding. 



Structural petrology ^^ is a newly applied tool, being used to help 



/o,ooo 



o too 



I I I I I 



200 



l_ 



300 ♦00 ft. 

 _J I 



EXPLANATION 



Ore 



Lean Ore 



Figure 522. Section showing ore in limestone below relatively unreplaceable and 

 impermeable porphyry, Oro La Plata mine. (After Emmons.) 



^ Fairbairn, H. W., in Newhouse, op. cit., pp. 265-267. 



