Optimization of open-pit mining boundary in a copper mine

Fu exist between exploration lines 12 to 19 porphyry copper ore in a deposit, more than 2770m elevation, depth 25 ~ 220m, south, east depth is small, north, west greater depth. The ore body is 590m long from north to south, 265-613m wide from east to west, with an average of 391m. It has a layered output, and the bottom boundary of the ore body is slightly inclined to the west, and the inclination angle is generally 0°-30°. The overall shape is “W” shaped in the north and south and low in the middle. The I-1, I-2 and I-3 ore bodies are in order from top to bottom. The weight of the ore is 2.51t/m3, the looseness coefficient is 1.3, the f coefficient is 6-8; the rock weight is 2.62t/m3, the looseness coefficient is 1.5~1.7, and the f coefficient is 6~12; the natural rest angle of the rock It is 41.2 ° ~ 43.8 °.
According to the characteristics of the ore body and the technical conditions of mining, when selecting the mining method, open-pit mining shows obvious advantages such as economic rationality, small stripping, small depletion, small loss and low production cost. Therefore, the above 2794m elevation is determined. A total of 3 ore bodies of I-1, I-2 and I-3 are open-pit mining, and the copper ore grade between 2770 and 2794m is relatively low. Due to the low mining value under the current market conditions, it will be reserved for future development and utilization.
1 Determination of economically reasonable stripping ratio
There are many factors that affect the determination of open-pit mining. The influencing factors and influence levels of different deposits are also different [1-10]. Therefore, the determination of open-pit mining boundary needs to comprehensively consider many factors such as deposit conditions, technical organization and economy. The common stripping ratio is used to determine the open-pit mining boundary. The economic reasonable stripping ratio is an important basis for determining the open-pit mining boundary. 4].
This paper uses the profit comparison method to determine the economic reasonable stripping ratio Nj [3-4, 8]. Calculated as follows:

Where: γ—the average weight of the ore, 2.51 t/m3;
b———Opening mining stripping cost, 20 yuan/m3;
Ηl, ηd—the actual recovery rate of open-pit and underground mining is 95% and 88% respectively;
Η'l, η'd—the apparent recovery rate of open-pit and underground mining, 100% and 100% respectively;
Dl, Dd—the mining and processing fees for the mining and mining of the original mining are 82 yuan/t and 133.5 yuan/t respectively;
Α1, α2———The geological grades of Cu and Mo in the ore are 0.44% and 0.01%, respectively;
Ε1, ε2———Cu and Mo beneficiation recovery rates were 79% and 83%, respectively;
P1, p2———The price of useful components in Cu and Mo concentrates were respectively 50,900 yuan/t and 140,000 yuan/t.
The calculation result is: Nj=8.48t/t, that is, the economical reasonable stripping ratio is 8.48t/t.

2 Determination of the open-air boundary

2.1 The principle of open-air boundary delineation [1-2, 9-10]

(1) Ensure that the ore mined in the open-air boundary is profitable, that is, the open-pit boundary stripping ratio is not more than 8.48t/t.

(2) Considering the conditions for the occurrence of ore bodies in the mining area, the principle of using the average stripping ratio is not greater than the economically reasonable stripping ratio.

(3) Taking into account the advantages of open mining operations, high production efficiency and low loss and depletion rate, under economic and reasonable conditions, the mining boundary should be as much as possible in order to fully exploit the superiority of the mining.

(4) The final slope angle formed by the bound open pit boundary
Less than or equal to the angle allowed by the stability of the open slope to ensure exposure
The production of the day mine is safe.
2.2 Determination of open pit parameters
(1) Determination of mining depth. The mining depth of the stope is mainly determined according to the mining technical conditions. According to the principle that the stripping ratio of the boundary is less than the economic reasonable stripping ratio, the reasonable mining depth of the open boundary is determined [3-8].
Combined with the occurrence conditions of a copper deposit and the technical conditions of mining, it is determined that the mining height is between 2794 and 3178 m, that is, the mining depth is 384 m.
(2) Determination of the bottom plane. On the basis of determining the mining depth, consider the following four factors to determine the bottom plane of the open mining boundary: first, according to the determined mining depth, 2794m is the lowest elevation of the design, and second, the boundary of the bottom plane remains straight, meeting the curve of the transportation line. The requirements of the semi-menstrual, the third is that the length of the bottom plane meets the requirements of automobile transportation, and the fourth is that the minimum width of the bottom plane satisfies the requirements of the shovel handling equipment, and is calculated to take 32m.
2.3 Optimization and determination of mining boundary scheme
According to the actual situation of the mine, analogous to the same type of mines in China [9], the designed slope parameters of the stope are: step height 12m, step slope angle α=65°, sweeping platform width 14m, transport road width 15m, final slope The angle is 37.69°~44.46° (the final slope angle of the south side slope is 42.57°, the final slope angle of the north side slope is 44.46°, and the final slope angle of the east side slope is 37. .69°, the final slope angle of the west side slope is 43.88°).
According to the needs of the mine, in order to determine the optimal open-pit mining boundary, the design selects three boundary program parameters for comparison [10]:
(1) Scheme I, step height 12m, one cleaning platform for each of the two safety platforms, the safety platform width is 6m, and the cleaning platform width is 14m;
(2) Scheme II, the height of the step is 12m, every 2 steps are parallel, 24m after the section, and one cleaning platform is left after each section, and the width of the cleaning platform is 14m;
(3) Scheme III, the step height is 12m, and one cleaning platform is reserved for every two safety platforms. The width of the safety platform is 4m and the width of the cleaning platform is 14m.
Through calculation, the comparison results of each boundary scheme are shown in Table 1.

It can be seen from Table 1 that although Scheme I and Scheme III have more mines than Scheme II, the stripping comparison scheme II is large, and the amount of stripping during the infrastructure period is large. By comparison, it is determined that the scheme II boundary is optimal.
2.4 Determination of open-air boundaries
In order to accurately define the open-air boundary and make up for the shortcomings of the three-dimensional software, the combination of manual and three-dimensional optimization is used to adjust the open-air boundary. Within the allowable range of economically reasonable stripping, it is appropriate to adjust the end of the mining step on the flat section map, and at the same time, the on-street road and step design are carried out according to the parameters of the stop slope determined above. The final open-air boundary length × width = 1035m × 685m, the open-pit mining area covers 68.67 × 104m2, the perspective and plan view of the mine open-end boundary are shown in Figure 1, Figure 2.

3 conclusions
According to the ore occurrence characteristics and mining technical conditions of a copper mine, the economic reasonable stripping ratio is determined by the profit comparison method, and then combined with the actual production of the mine, the height of the step is determined by the comparison of the open-pit mining boundary, and the height of each step is 12m. In the parallel section, 24m after the section, a cleaning platform is set after each section, and the width of the platform is 14m, which is the optimal scheme. The combination of manual and three-dimensional optimization is used to delineate and optimize the mining boundary. The open-pit mining boundary suitable for mine production has important guiding significance for the actual production of the mine.
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[6] Cui Can, Yuan Feng, Li Xiaohui, et al. Optimization of open-pit mining boundary of Tongling Xinqiao deposit based on Surpac [J]. Metal mines, 2012 (10): 15-18.
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Author: Jiang Hu Chan; 内蒙古维拉斯托 Mines Ltd., Chifeng City, Inner Mongolia 025 372;
Source: Mining Technology: 2016, 16(2);

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