Optimization of deep transportation plan for a large open pit mine

Transportation is one of the major open pit surface mining production processes, the basic task is to open pit mined ore is transported to the beneficiation plant, crushing plant or mine reservoir, the release of soil (i.e., waste rock) transported to the discharge In the soil field, the transportation network that completes such tasks constitutes an open-pit mine transportation system. Mine rock road transportation is the most common mode of transportation for open pit mines. Automobile transportation is not only flexible, but also has the advantages of large climbing ability and small turning radius, which makes automobile transportation become the main transportation mode of modern open pit mines [1-4]. However, with the increase of mining depth and the increase of waste rock discharge steps, the ore transport distance has gradually increased, and the cost of open-pit mine transportation has been rising. When the ore-rock transportation distance increases to a certain critical value (the economic transportation distance of open-pit mine automobile transportation), it is uneconomical to adopt the automobile transportation scheme, and the transportation system needs to be modified to achieve the purpose of reducing transportation costs. According to a large number of open-pit mine operations experience to develop the production of transport systems, most of the foreign metal surface mine car transport distance is 1.0 ~ 5.5km, an average of 2.5 ~ 3.0km to allow economical transportation distance of 5 ~7km, the domestic open-pit mine car transportation distance is generally 2km, the maximum is 6km. The economic distance of a car varies with transportation conditions and is closely related to the type of mine. Due to the advantages of large climbing ability, high automation level, large transportation capacity and low transportation cost, the belt conveyor has become more and more popular in deep open pit mines at home and abroad. In terms of slope and long-distance transport, tape transport can significantly reduce production costs compared to car transport. To this end, this study takes an open pit mine as an example to optimize the deep transportation plan of the mine.
1 transportation plan
An open-pit mine is located in the northern border of China. It is a large-scale copper- molybdenum associated deposit that has been proved in China. The comprehensive capacity of mining and selection has reached 75,000 t/d. At present, the ore in the stope is transported to the dumping site and the ore coarse crushing station respectively. With the downward extension of the open pit and the rising of the dumping steps of the dumping site, the car transport distance increases year by year, and the mining cost gradually increases. Increase. With the gradual reduction of the deep resource grade of the mine, the current price of copper and molybdenum metal is at a low market, it is necessary to optimize the transportation plan and compress the production cost.
1.1 All-car transportation plan (Scheme I)
During the mine service period, the mine (waste) stone is still all transported by automobile. The annual transportation cost is calculated according to the amount of mine (waste) stone, transportation distance and transportation unit price. At present, the mine mining adopts the outsourcing operation mode, and the outsourced unit rock transportation cost is 1.8 yuan/(m3·km).
1.2 Automobile-tape joint transportation plan (Scheme II)
In general, the unit transportation cost of tape transportation is lower than that of automobile transportation. However, according to the current mining situation, the 5a of the mine service period should be transported by car, the 5a construction tape system, and the 6th beginning of the car-tape joint transport. The transportation cost of automobiles is calculated according to the amount of ore, transportation and transportation unit price. The transportation cost of the belt is calculated according to the labor, electricity and repair costs consumed by the investment and operation of the belt transportation system.
The crushed ore is transported to the south side of the stope by two belt conveyors arranged in parallel with 1# and 2#. One transfer station is set up at 805m, and six sets of drive units are arranged in the station, and one bridge crane is arranged. Set 3#, 4# tape machine, respectively transfer the ore in the transfer station to the first and second stage crushing stations, and unload the upper part to the mining bin. The relevant parameters are shown in Table 1.

Install a fixed tape machine (1# tape machine) to transport the ore from the coarse crushing station to the dumping site, and transfer it to the on-site displacement belt conveyor for disposal through the earth-moving machine. After dumping, the dumping site has an elevation of 855m and a dumping depth of 55m. The working time of the waste rock coarse conveying system is 13.4h/d. The parameters of the tape machine are shown in Table 2.

2 comparison analysis of transportation plans
2.1 Mine (waste) stone transportation volume and car transportation distance
Scheme I and Scheme II have the same amount of ore transportation per year, but the vehicle transportation distance is different. The ore transportation volume and vehicle transportation distance of the two are shown in Figure 1.

2.2 New investment and transportation costs

Compared with Option I, the new investment in Option II is 41.092 million yuan, as shown in Table 3.

According to the tape configuration, the calculated operating cost of the mine (waste) stone tape is 0.71, 0.64 yuan / t, respectively, and the transportation cost of the tape with investment depreciation is 1.13, 1.16 yuan / t, see table 4.

2.3 Comparable and comparable present value
The comparison of annual transportation costs and accumulated transportation costs of Scheme I and Scheme II is shown in Figure 2. Under the condition that the transportation volume of mine (waste) stone is constant, with the increase of open pit mining depth, the transportation cost of mine (waste) stone of scheme I increases almost linearly, and the increase of transportation cost of scheme II is obviously lower than that of scheme I.

The comparison of the annual comparable cost and the comparable present value of the scheme I and the scheme II is shown in Fig. 3.

See Table 5 for a comparison of comparable investments in Scheme I, Option II, comparable costs, transportation costs during the service period and current values.

It can be seen from Table 5 that Scheme II needs to increase investment of 41.092 million yuan for the construction of the tape system in the 5th, but the annual operating cost is 55.56 million yuan lower than the operating cost. The total transportation cost plan during the mine service period is lower than the plan I. 94.453 million yuan; calculate the present value of comparable expenses after considering the discount rate of 8%, and reduce 79.04 million compared with scheme I
yuan. It can be seen that Scheme II is superior to Scheme I, indicating that it is reasonable to use the automobile-tape joint transportation scheme for the deep transportation system of the mine.
3 further analysis
3.1 unit ore car transportation costs
At present, the mine mining production operation adopts the mode of outsourcing operation. According to the outsourcing contract, the transportation cost of the mine rock is 1.844 yuan/(m3·km), which is affected by many factors such as diesel price, road condition and mine operation conditions. For the time being, there has been a significant decline in market oil prices, and the cost of outsourcing transportation has declined to some extent. When the outsourcing transportation cost decreases, the present value of the comparable cost of the scheme I will decrease. When the outsourcing transportation cost is reduced to a certain critical point, the present value of the comparable cost of the scheme I will be lower than that of the scheme II. At this time, the deep development of the mine will be carried out. Option II is not economical. The comparison of the present value of comparable expenses of Scheme I and Scheme II under different outsourcing cost levels is shown in Figure 4.

It is calculated that when the unit price of outsourced automobile transportation is reduced by more than 19%, that is, when the transportation unit price is lower than 1.46 yuan/(m3·km), the adoption scheme is more reasonable.
3.2 Discount rate
The comparison of the present value of the comparable costs of Option I and Scheme II under different discount rates is shown in Figure 5.

Due to the need to invest in the construction of the tape transportation system in the early stage of the program II, with the increase of the discount rate, the economic advantage of the automobile-tape joint transportation scheme is gradually reduced. When the discount rate is increased to 14.2%, the present value of the comparable costs of Option I and Option II are equal. When the discount rate is lower than 14.2%, it is economically reasonable to construct the belt transportation system and adopt the automobile-tape joint transportation scheme. . In general, the discount rate is higher than 14.2%, so the mine development plan II is more reasonable.
3.3 Mine remaining service years
A comparison of the present value of comparable costs for Option I and Option II is shown in Figure 6. It can be seen from Figure 6 that the present value of the comparable costs of the two schemes before the 5th is the same, the present value of the cost of the 5a scheme II is higher than that of the scheme I, and the present value of the costs of the two schemes after the 6th is gradually approaching. At the end of the 13th, the scheme I The present value of the comparable cost of Scheme II is almost equal. After considering the discount, the two transport schemes at that point in time have the same economic effect. After the 13a, the present value of the comparable cost of the scheme II begins to be smaller than that of the scheme I, and As the service life of the tape system increases, the difference in the present value of the cost of the two programs gradually increases, and the advantages of the program II become more and more obvious.

The remaining service life of the mine is 17a based on the amount of resources based on the scale of production and current market conditions. During the operation period of 17a, the present value of the comparable cost of the scheme II is 120 million less than that of the scheme I, indicating that the scheme II of the deep mining of the mine is more reasonable. If the future of mine service is increased due to the impact of the external economic environment, the advantages of Option II will be even greater. If the remaining service life of the mine is reduced to less than 13a, then Option I is more reasonable.
4 Conclusion
Taking a mine as an example, a detailed comparative analysis of the whole vehicle transportation plan (Scheme I) and the automobile-tape joint transportation plan (Scheme II) shows that the solution II requires a construction tape in the early stage. The transportation system has a large investment, and the operating cost will be gradually reduced. The advantage is more prominent. If the mining service period of the mine is too short (less than 13a), the plan I is more reasonable. In addition, the choice of the deep development of the mine should be Considering the impact of outsourcing vehicle transportation unit price, if the outsourcing unit price declines, the advantages of Scheme II will be reduced, especially when the outsourcing transportation unit price decreases by a large margin, Scheme II does not help to improve the economic benefits of the mine.
references
[1] Ma Chuanwei, Wang Xianfeng, Yang Weijing, et al. Research on economical rational transportation distance of mine automobile transportation [J]. Metal Mine, 2015 (7): 48-51.
[2] Yang Xiaoyun. Comparison of open pit ore development and transportation schemes [J]. Nonferrous Metallurgy Design and Research, 2014(2): 12-14.
[3] Wang Huilai, Han Ruijun. Large-scale open-pit mine transportation system program research [J]. China Mining Engineering, 2014(1): 20-22.
[4] Yan Jialong, Gao Zhongmin, Li Shoushan, et al. Transformation of a phosphate ore transport system [J]. Modern Mining, 2015 (6): 42-43.