| 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.Scholars of domestic and foreign had made many valuable achievements about cutoff grade studies in the last 50 years,but it had the following insufficiencies:Cutoff grade which is defined by the profit and loss balance Method,is one static discrimination standard,which has nothing to do with the ore quality, the time and the position,and it don't considere the time value. Inconsequence of this method is obviously, therefore it is eliminated gradually. The Maximum NPV Method supposes that cutoff grade in entire optimization scope obediences identical statistics distribution, that is to say, this distribution is identical everywhere in this scope. Under this hypothesis, optimized result that make the total NPV maximum is that cutoff grade decreased year by year. But in practice, almost all deposits don't meet this hypothetical condition, and they generally have low-grade and high-grade areas. When the low-grade area was located at the upside of the deposit, mining process by a high cutoff grade is obviously unreasonable and even impossible to achieve. In order to obtain the optimal cutoff grade that accords with the actual practice, we must consider the actual grade distribution in the different sections of the deposit.Aiming at the insufficiencies of the cutoff grade optimization studies, basing on the research of underground mining technology, and according to the mineral deposit conditions and ore mining sequence, the optimization scope was divided into a series of sections, namely optimize units. On this basis, the mining process is divided into transition mining stage of the before and after,and a stage include a number of states.The state variable of a stage was showed by cumulate mining quantity from start to this stage mining finished. Mining quantity of a state in a stage is gained from cumulate mining quantity of the state in this stage and cumulate mining quantity of the transition state of preceding stage.The mining scheme begins from each states of the first stage. Cutoff grade of every state could be obtained from the graph of distribution and grade VS mine quantity of optimize unit-1.Profit of mining quantity could be calculated by the investment of mining process and the cost of mining by the corresponding mining method. Then, according to the annual production capacity of mine, the production life-span could be calculated, and the profit could convert into the NPV of initial stage. After the first stage, mining quantity, cutoff grade and NPV of each state of this stage could be obtained. Every state of the second stage was come from certain state of the first stage. Taking one state of the second stage as an example, supposing that this state could be transited by K states in the first stage and every transition has a mining quantity which is mined in optimize unit-2. So the cutoff grade, the profit and its NPV(discount to initial stage) can be obtained from the graph of distribution and grade VS mine quantity of optimize unit-2. NPV of this state is equal to that NPV of the former transition state add on NPV obtained by the mining quantity. NPV of this state was maximal one among the K-NPVs which come from the K-states of former stage. And the cutoff grade of this state was the one which corresponds with the maximum NPV.The cutoff grade and the NPV of each state were calculated to the final stage (final optimize unit) with similar method. Find 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-making) of every stage was obtained. The optimal result of this cutoff grade optimization problem was composed of all optimal decision-makings. According to the above optimization ideas, a new dynamic programming cutoff grade optimization model is established by the target function of NPV, and ore-body mining sequence, mine production capacity, and ore grade's spatial distribution in different area (optimization unit) were considered, and together combining with the actual mining method. The model achieves the cutoff grade dynamic optimization in underground min both in time and in space. This model makes a significant breakthrough on cutoff grade optimization method in underground mine.The dissertation also based on the Lane's method theory, I analyze the differences between underground mining and open-pit mining, and then deduce mathematics models of cutoff grade optimization of underground mining of the two phrases in mining and mill and the three phrases in mining, mill and smelting. These models add parameters as depletion rate and wall rock grade, and use the variable of ratio of wall rock grade and ore geological grade. Then it can fit for the underground mine.Based on the mathematic models of two optimizations method, relevant computer software system is explored, that is, Dynamic Programming Optimize System (DPOS1.0) and Mine Economy Decision-making System (MEDS1.0). DPOS1.0 not only can get each optimization unit's mining quantity, cutoff grade, accumulative production life and NPV, but also can get all the valid decision-makings and the best strategy of the optimization object directly through dynamic programming network diagram.MEDS1.0 not only can consider the whole ore-body as optimization object, but also can consider the arbitrarily selected ore-body scope between reconnoiter line and plane line as optimization object, and it can use many series of technical and economic parameter schemes, so that it can make up the traditional NPV optimization method shortcomings of supposing grade distribution to be unchangeable in optimization scope. Though MEDST1.0 is explored based on the Zambia Chambishi copper mine, it can be applied to other mines, so it is a relatively general mine economy decision-making software.The cutoff grade dynamic optimize method application on Zambia Chambishi copper mine, and the optimize scope is two mining phases with avalanche mining method. Dynamic programming method divides the optimization scope into 12 optimization units(the phase of dynamic programming) and each optimization unit has its grade distribution according to the defined mining sequence. The optimize result is:cutoff grade and mining quantity from optimization 1 to 12 are respectively:1.004% and 853823.852 ton,0.808% and 1333158.948 ton,0.905% and 913919.33 ton,1.002% and 883214.087 ton,1.015% and 906692.185 ton, 0.999% and 965396.035 ton,0.995% and 716111.732 ton,1.007% and 708986.005 ton, 0.993% and 710850.398 ton,0.993% and 759790.244 ton,0.993% and 709781.188 ton, 0.989% and 740540.653 ton, the total mining quantity is 10202264.66 ton, production life-span is about 10 years, the maximum NPV is 242816.8 thousand US dollars. The cutoff grade optimization is between 0.808% and 1,015%.According to cutoff grade 1% that was used by the mine now, the total mining quantity is 9719937.8 ton, production life-span is about 9 years and 5 months and the maximum NPV is 239817.6 thousand US dollars.
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