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Show toward ladderway. The down holes on the second level are, of course, drilled on to the underhanging floor. When the ladder- way is reached a new ladderway and set of sub-levels will have been prepared and made ready for mining. Men on each sub-level work under solid ore, and far enough back from the open stope to be safe from falling slabs. In long ore bodies, it is usual to make stopes about 250 ft • .long, separated by pillars containing the ladderway. Length of slope is adjusted to prevent premature caving of walls; horizontal pillars can also be left underneath main level. Ore in pillars may be mined later by top slicing or by sub-level caving provided stopes are first filled. Filling of stopes between 2 levels may be drawn down and re-used in lift below allowing walls above to cave. Advantages of method are its safety and small timber consumption in suitable ore bodies. Because of numerous points of attack, a large tonnage can be broken in a small stope. charges .break large tonnages from benches and backs. Small Chief dis- advantage is the large a.mount of narrow in preliminary development. The Flin Flon ore body having an average width of 50-75 ft. naturally will have a 25-35 foot of ore on each side of the sub-level· drifts, which is important when considering the same amount of development would be required for a much narrower vein. The Flin Flon ore body would undoubtedly allow the adoption of the shrinkage methods, but the fire hazards and oxidation of ore in stopes prevent the possible use of this method. are many other i mportant reasons. -23- There |
