CUT AND FILL MINING
Cut and fill mining the ore is excavated by drilling and blasting in horizontal slices, starting from the bottom of a stope and advancing upwards as in shrinkage stoping. A slice has a thickness of not more than 3 m. The broken ore is loaded and completely removed from the stope, when one slice of ore has been excavated, the corresponding volume is filled with waste material upto within 1-3 m of the back before the next slice is attacked. The filling serves both as support for the walsl and as a floor when serves both as support for the walls and as a floor when the next slice above is mined.
The fillings material may be waste rock excavated during development, crushed and distributed mechanically over the method is a normal practice. The filling material may be mill tailings from the ore dressing plant, sand, crushed rock, boilerplant ash or slag of smelter plants. The mill tailings should be of course sand size as fine tailings, available from the mills where the ore needs to be crushed very fine for treatment, are easily washed away by the following water. The filling material mixed with water, is transported into the mine and distributed through pipelines. When the water is drained off a solid consolidated fill with a smooth surface is produced. Sometimes the material in the last pour in a fill is mixed with cement to provide a hard working surface.
Cut and fill mining can be used with steeply dipping as well as mildly dipping orebodies with reasonably firm ore. Small as well as large deposits with irregular outline can be worked. It is thus a versatile method. The filling operations ae easier with steeper deposits. An important advantage of this method is the flexibility and high degree of extraction,. Compared to sub-level stoping and shrinkage, cut and fill method offers advantage of selectivity. High grade ore can be extracted leaving the low grade ore behind in the fill. Dilution of the ore is very little. It is therefore often used for ores with irregular boundaries, ores of rather high valure and unstable wall rocks. The method is preferred to other mining methods where ground surface is to be prevented from subsidence.
The ore block may be prepared in the same way as for shrinkage stoping but the chute raise are not funneled out at the top. The preparation consists of:
The ore slice in cut and fill can be drilled in two different ways, with horizontal shot holes or with upward, vertical holes. With the lateer method a certain headroom is required between the back and the fill surface, usually 2.5-3 m. After blasting and removal of the ore, this distance is increased to 6-7m, which means that a comparatively competent ore and hanging wall are required.