Research On The Relationship Between The Cutoff Grade Of Metal Ore And Mining Plan

Cutoff grade is one of the most basic and important parameters in mining process. The selection of cutoff grade affects the shape of the enclosed ore-body and ore reserves directly, and then affects mine construction, scale of production, income of mine, facilities selection, and production life-span, and even utilization rate of non-renewable resource. Therefore, cutoff grade is a major impact on the technical and economic parameters both in mine economic benefits and social benefits. Cutoff grade optimization is also one of the core content in mine management parameters' optimization.In the research of the cutoff grade, there are three main methods, the profit and loss balance method, Lane method and dynamic programming optimization method. Scholars of domestic and foreign had made many valuable achievements about cutoff grade studies, but it still exist some insufficiencies. In these studies, whether the profit and loss balance method, Lane method or dynamic programming method does not take into account the impact of the change of the mining plan on the cutoff grade and the final profit. In this paper, the cutoff grade of the mining sequence of the different unit is optimized with dynamic programming method, and comparing the optimization results of each mining sequence with the Lane method. It reveals that the final cutoff grade of the different mining sequence is different, and it can't achieve the maximum economic benefits of the deposit mining (NPV) without consider mining sequence (Lane) boundary grade.According to the existing conditions and the mining order, the object researched is divided into six optimization units. In this paper, the two kinds of calculation methods are based on the six optimization units for the calculating. The Lane method will combine the distribution of the grade and ore of the 6 units as a table and optimize with the whole, then calculate the annual cutoff grade with the special model of the maximum of present value. Objecting with the single unit, the production life and ore quantity per unit can be determined in the grade and ore distribution list, and then the annual profit and value can be calculated according to the mining sequence and the cutoff grade. The dynamic programming method define the 6 units as 6 mining stages, every stage is before and after the transition. Each mining stage comprises several states. The mining plans contain all the plans from the each state of the first stage to the each state of the last stage. Finding out the having maximum NPV of the state in last stage and deduced by reverse sequence of the transition order, then the optimal transition (also called optimal decision) of every stage was obtained. The optimal result of this cutoff grade optimal problem was composed of all optimal decision-makings.Compute the optimal cutoff grade and maximum value with the Lane method and dynamic programming method on the conditions of the changing mining plan. Using Lane method obtaining annual cutoff grade is 2.09%,1.86%,1.63%,1.40%,1.18%, the cutoff grade keep the same even the mining plane changes. Under the mining plan of 1->2->3->4->5->6,getting the present value is 292539055. 1?.Changing the mining plan, then under the mining plan of 1->3->2->4->6->5, the present value is 291956644.9 ?.Under the mining plan of 3->2->1->6->5->4, the present value is 290146957.5$.Using the dynamic programming method, obtaining annual cutoff grade under the mining plan of 1_>2->3->4->5->6 is 1.99%,1.11%,1.62%,1.55%.1.29%,1.20%,the maximum value is 294801859.1$.The cutoff grade under the mining plan of 1->3->2->4->6->5 is 1.99%, 1.80%,1.70%,1.47%,1.30%,1.14%,the maximum value is 292365193.6$. The cutoff grade under the mining plan of 3->2->1->6->5->4 is 1.94%,1.69%,1.49%,1.32%,1.12%, the maximum value is 290864278.8$. When the mining plan changes, although the cutoff grade obtained by using Lane method doesn't change, the net present value is significant different, while the cutoff grade and the net present value obtained by using dynamic programming method obviously changes. Because of the limitations of the Lane method, the final results of the dynamic programming method will be applied to the actual production. It can be discovered through the above results that the net present value obtained by using the mining plan of 1->2->3->4->5->6 is the biggest, and it is more suitable for mines.