Substantiation of the depth of the open pit employing the in-pit crushing and conveying technology as a determinant of the pit development at the subsequent stage of mining

The constant increase in the depth of open pits employing the in-pit crushing and conveying technology applied to mining steeply dipping deposits causes an increase in the height of the ore lifting and transportation distance, and results in an increase in the cost of ore transportation to the surface. This, in turn, affects the depth of the subsequent stage of reconstruction of the pit transportation system. The present research aimed to substantiate the depth of the subsequent stage of iron ore pit mining applying the in-pit crushing and conveying technology using a generalising estimation figure for various consecutive time intervals during the stage-by-stage mining, which should improve the quality of design operations. The article employed methods of statistical-logical, causal and comparative analysis and the method of system-structural approach to determine the generalising figure for estimating the subsequent stage of mining by the in-pit crushing and conveying technology. When substantiating the depth of the subsequent stage of open pit reconstruction, the dependency was proposed to determine the maximum operating stripping ratio. The dependency takes into account the increase in transportation costs caused by the increased lifting height and the extension of the distance of transporting ore to crushing and reloading points of conveyor lifts located in the pit as a result of its deepening. In addition, the dependency of the position of the mined ore mass centre on the open pit depth was used in calculations. Considering the fact that in modern deep open pits, the volume of ore mined and transported by the truck-conveyor complex can reach 30 Mt annually, the search for ways to improve cargo flows of the pit transport complexes becomes one of the important designer tasks. In this connection, an estimated figure was proposed to determine the depth of the subsequent stage of mining the open pit employing the in-pit crushing and conveying technology complex, which takes into account the increased cost of ore transportation, the cost of marketable mineral products, and the current stripping ratio. At the same time, the increase in costs caused by the increased height of ore lifting due to mining deepening is taken into account to consider the increase in transport costs when designing further development of the in-pit crushing and conveying technology complex. In the open pit, the depth of which is determined according to the proposed methodology, the value of the current stripping ratio will not exceed the maximum operational one at the subsequent stage. This approach allows quick estimation of the depth of an iron ore open pit that mines steep deposits when designing the subsequent stage of reconstruction to provide its breakeven finalisation