## 2 RPEM Economic Evaluation Method
### Construction of RPEM Economic Evaluation Model  
#### 2.2.1 Evaluation Index System  
There are numerous and complex indicators that affect the economy of mining projects [32], which can be divided into three secondary indicators: reserve indicators, production indicators, and operational indicators. Then, the indicators are classified according to their attributes to form a three-level indicator. The established technical and economic evaluation index system is shown in Figure 2.  
2.2.2. Solving the Reliability of RPEM Economic Evaluation  
To study the applicability of RPEM to the economic evaluation of mining, taking the mining and selection production process of underground mines as an example, the commonly used technical and economic indicators are selected for mining economic evaluation and are used to establish a reliability model for economic evaluation of RPEM. The main indicators include mining cost, beneficiation cost, ore dilution rate, ore grade, concentrate grade, beneficiation recovery rate, concentrate sales price, etc. These indicators are all included in the indicator system shown in Figure 2.  
When establishing an RPEM economic evaluation reliability model based on the cash flow method, only the costs and benefits directly generated during the mining production process are considered, and the impact of its fluctuations on costs and profits is analyzed using the ore grade as a sensitivity indicator. When the mining and selection production balance and concentrate production and sales balance are achieved, the specific calculations are as follows:  
(1) Cash inflows from mines (only when calculating concentrate sales revenue) F:  
\[F=A\cdot\frac{g\cdot\varepsilon\cdot W}{\gamma} \tag{9}\]  
where A is the annual mining output of the mine, 10,000 t/year; G is the ore grade (i.e., the ore grade after beneficiation), %; \(\varepsilon\) is the recovery rate of mineral processing, %; \(W\) is the sales price of concentrate, CNV/t; \(\gamma\) is the concentrate grade, %. (2) Annual cash outflow from mines \(P\):  
When the production and sales of concentrate produced by the mine are balanced, the annual cash outflow \(P\) of the mine is:  
\[P=A\cdot\frac{g\cdot\varepsilon}{\gamma}\cdot C_{c}+C_{1}+C_{2} \tag{10}\]  
where Cc is the production cost of ton of ore concentrate, CNV/t; \(C_{1}\) represents various taxes and fees, in CNV 10,000; \(C_{2}\) refers to the annual average fixed assets investment and current asset investment of the enterprise, CNV 10,000. Figure 2: Technical and economic index system. (3) Net cash flow of mines \(I\):  
\[I=F-P=A\cdot\frac{g\cdot\varepsilon}{\gamma}\cdot(W-C_{c})-C_{1}-C_{2} \tag{11}\]  
(4) Construction of Objective State Function for Economic Reliability Evaluation  
Based on the basic principles of RPEM, the cash flow method is combined with RPEM to construct the objective state function of the RPEM economic reliability evaluation model, as shown in Equation (12). \[Z=\frac{F}{P}=\frac{A\cdot g\cdot\varepsilon\cdot W}{A\cdot g\cdot\varepsilon C _{c}+\gamma(C_{1}+C_{2})} \tag{12}\]  
The economic reliability evaluation target state function represented by Equation (12) reflects the level of benefits that can be achieved by mining projects. The higher the economic reliability, the higher the mining benefits, and vice versa. From Equation (12), it can also be seen that when the \(Z\) value is 1, it indicates that the cash inflow and outflow of the project are equal. At this point, the breakeven point of a certain technical and economic indicator can be determined by formula transformation. (5) Solution of Economic Reliability Based on RPEM  
First, Equation (12) is used as the objective state function, according to the RPEM calculation process shown in Figure 1; the sensitivity indicators for evaluation and their possible range of values are determined.