Principles of mining : valuation, organization and administration; copper, gold, lead, silver, tin and zinc . Fig. 40. — Longitudinal section. Ore-pillar support in narrow stopes. Support by Pillars of Ore. — As a method of mining metalsof the sort under discussion, the use of ore-»pillars except inconjunction with some other means of support has no generalapplication. To use them without assistance implies wallssufficiently strong to hold between pillars; to leave them per-manently anywhere implies that the ore abandoned would notrepay the labor and the material of a substitute. There arecase
Principles of mining : valuation, organization and administration; copper, gold, lead, silver, tin and zinc . Fig. 40. — Longitudinal section. Ore-pillar support in narrow stopes. Support by Pillars of Ore. — As a method of mining metalsof the sort under discussion, the use of ore-»pillars except inconjunction with some other means of support has no generalapplication. To use them without assistance implies wallssufficiently strong to hold between pillars; to leave them per-manently anywhere implies that the ore abandoned would notrepay the labor and the material of a substitute. There arecases of large, very low-grade mines where to abandon one-halfthe ore as pillars is more profitable than total extraction, butthe margin of payability in such ore must be very, very spots are always left as j^illars, for obvious reasons. METHODS OF SUPPORTING EXCAVATION. 119 Permanent ore-pillars as an adjunct to other methods of supi:»ortarc in use. Such are the rib-pillars in the Alaska Treadwell, theform of which is indicated by the upward extension of the. Fig. 41. Horizontal plan at levels of Broken Hill. Method of alternate stopesand ore-pillars. pillars adjacent to the winzes, shown in Figure 37. Always acareful balance must be cast as to the value of the ore left, andas to the cost of a substitute, because every ore-pillar can be re-moved at some outlay. Temporaiy pillars are not unusual, par-ticularly to protect roadways and shafts. They are, when leftfor these purposes, removed ultimately, usually by beginning atthe farther end and working back to the final exit.
Size: 2511px × 995px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, bookpublishernewyorkmcgrawhillb
