Study of the impact of the open pit productivity on the economic indicators of mining development

The article studied the issue of improving the scientific and methodological base in the field of design and planning of open-pit mining by developing new and adjusting existing methods for determining the ore productivity of an open-pit, which should take into account the interconnection between the mining schedule and the productivity of an open-pit for ore, based on the condition for ensuring the standard volume of finished to the extraction of reserves. When choosing the production of an open-pit for ore, it is necessary to take into account the impact of the interconnection between the schedule of mining and production, based on the conditions of regulatory regulation of the volume of mining for the excavation of reserves, on the cost of ore mining and concentrate production. With an increase in ore productivity, the cost of ore mining, as well as the cost of production of concentrate reduction. At the same time, the very possible productivity of the open-pit for especially minerals is achieved, the economic efficiency of the development of deposits is achieved with the chosen direction of the open-pit. A decrease in productivity for a common mineral by 20 and 40% entails a decrease in profit from the development of the deposit by 10 and 20%, respectively. It has been determined that an increase in the slope angle of the working side of the open-pit significantly reduces the economic efficiency of the development of the deposit due to the fact that the operation of the open -pit with a large slope angle entails not only a decrease in the current stripping ratios as a result of an improvement in the mining schedule, but also a decrease in ore productivity, which reduces the present value of marketable products due to an increase in the period of development of the deposit. The results of the studies performed can be used by design organizations and mining enterprises in determining the ore productivity of an open-pit.


Introduction
To select the productivity of a open-pit, which ensures the maximum efficiency of field development, a comprehensive technical and economic analysis of the operation of the enterprise is required [1][2][3], taking into account, among other things [4,5], the influence of the time factor on the evaluation of the results of its work [6,7].
The existing relationship between the parameters of the development system [8,9], which provide the norm of reserves ready for excavation in a open-pit [10,11], determines, with a change in productivity for a mineral, a change in stripping ratios [12][13][14].In turn, the change in stripping ratio is reflected in the volumes of rock mass and their distribution over the years of operation, which ultimately is one of the main factors affecting the economic indicators of a open-pit mine [15][16][17].At the same time, the maximum productivity for ore also determines the maximum or close to maximum productivity for the rock mass, which leads to an increase in the cost of developing the deposit.Thus, an increase in the productivity of a open-pit for a mineral is accompanied by an increase not only in income, but also in costs [18,19].
In this regard, the question arises whether there will be profitability in terms of economic efficiency [20][21][22] of operating a open-pit with the maximum possible productivity for a mineral [23,24].

Object and methods of research
Most studies aimed at establishing the impact of open-pit productivity on the economic indicators of development, the existing relationship between the development of mining and mining operations in a open-pit [25][26][27], is considered only on the basis of the condition that a change in the angle of slope of the working side of the open-pit [28] leads to a change in the current stripping ratios [29][30][31].This does not take into account the need to ensure the standard volume of reserves ready for extraction [32][33][34].
It is known that as the production capacity of a open-pit increases and its lifetime decreases, with the same reserves, the specific semi-fixed costs change [35], which means that the cost of ore mining also changes [36].Therefore, it is necessary to investigate the change in the cost of ore mining and the production of final marketable products, taking into account changes in stripping ratios with an increase in ore productivity.
Therefore, the goal was set: to improve the scientific and methodological base in the field of design and planning of open pit mining by developing new and corrections existing methods for determining the productivity of a open-pit by ore, which should take into account the interconnection between the mining mode and the productivity of a open-pit by ore, based on the condition for ensuring the standard volume stocks ready for extraction.

Results
The creation of normal working conditions for a open-pit for various ore productivity options, within the maximum possible value, is possible by changing the width of working benches [37,38], which ensures the standard of reserves ready for excavation.At the same time, an increase in the width of working benches leads to a decrease in the number of working benches within the deposit and, accordingly, to a change in the length of the mining front, both in ore horizons and in overburden, which largely determines the distance of transporting the rock mass in the openpit.With an increase in the width of the working bench, the transportation distance increases both on ore horizons and on overburden.This is due to the fact that with an increase in the width of the working bench, the ore front is concentrated on a smaller number of benches in the lower part of the open pit.At the same time, the overburden front of mining operations increases due to an increase in the number of underlying overburden benches.Therefore, when determining the cost of ore mining and the production of final marketable products, it must be taken into account that with an increase in ore productivity, the width of working benches will increase, as well as the haulage arm from the faces to the opening working.Therefore, even a small increase in the distance of transportation with significant volumes of traffic will lead to a significant increase in costs.
For conditions close to the mining and processing plants of Krivbass, let us analyze the impact of the productivity of an open-pit on the cost of production of the final marketable product.We investigate the work of an open-pit developing a steeply dipping mineral deposit.Let's divide the open-pit field by depth into zones, within which the pattern of changes in the volume of rock mass with a decrease in mining operations remains constant.
The studies carried out allow us to establish the measure of the influence of various costs on the production cost of the concentrate when changing the productivity of the open pit for ore.Influence of open pit productivity in terms of ore on the production cost of ore mining and its components at the first stage of its operation: 1 -unit semi-fixed costs for ore mining; 2 -unit conditionally variable costs for ore mining without overburden costs; 3 -unit conditionally variable costs for the excavation of overburden; 4 -unit conditionally variable costs for ore mining; 5 -unit production cost of ore.
From figure 1 and figure 2, it can be seen that the unit semi-fixed costs for ore mining (line 1) are the same in both the first and second periods and decrease with an increase in ore productivity.
However, in the second period, due to a decrease in stripping ratios, the specific conditionally variable costs for ore mining with an increase in productivity slightly decrease (line 4, figure 2).
Curve 5 (figure 2, figure 2) shows the change in the production cost of ore depending on the ore productivity of the open pit with the already chosen direction of development of mining operations and indicates the presence of an optimal productivity value.On figure 3 shows the change in the cost of production of concentrate from the productivity of an open-pit for ore for the first (line 1) and second (line 2) periods of work.It can be seen from the figures that with an increase in ore productivity, the cost of ore mining, as well as the cost of concentrate production, decrease.
However, the cost cannot fully characterize the increase in production for which development is being carried out.The main purpose of the enterprise is to make a profit.Therefore, it is more rational to solve the problem of determining the optimal productivity of an open-pit based on the profit from the sale of commercial products of the mining and processing plant.Profit from the sale of marketable products (concentrate) was taken as an optimality criterion when comparing options.For the commensurability of costs and incomes at different times, they were brought to one moment of evaluation.
We calculate the costs and revenues from the development of a mineral deposit and the production of a concentrate when operating an open-pit with different productivity values and a price for a concentrate, while for each performance option we set certain rates of deepening of mining operations.At the same time, when changing the ore productivity of an open-pit, it is necessary to take into account a change in the angle of slope of the working side of the The calculation results are shown in figure 4. From the graphs of the function K=f(A p ), C o =f(A p ) it can be seen that the given total capital (K) and operating (C o ) costs increase with the increase in the production capacity of the open pit.
The curve PR p =f(A p ), which characterizes the change in the reduced profit depending on the productivity of the open pit, shows that the maximum possible productivity of the open pit for minerals ensures the maximum economic efficiency of the development of the deposit in the chosen direction of the deepening of the open pit.In this case, the maximum profit is provided with a productivity of 12 million m 3 /year.A decrease in productivity for minerals by 20 and 40% entails a decrease in profit from the development of the deposit by 10 and 20%, respectively.
On figure 5 shows the influence of the slope angle of the working side of the open pit on the reduced profit from the development of the deposit when the norm of reserves ready for excavation is provided in the open pit.It can be seen from the graph that an increase in the slope angle of the working side significantly reduces the economic efficiency of field development.This is explained by the fa ct that the operation of an open-pit with a large slope angle of the working side entails a decrease in productivity not only for waste rocks, but also for ore, which   reduces the present value of marketable products due to an increase in the development period of the deposit.

Conclusions
An increase in the slope angle of the working side significantly reduces the economic efficiency of the development of the deposit due to the fact that the operation of an open-pit with a large angle of slope entails not only a decrease in the current stripping ratios as a result of a change in the mining schedule, but also a decrease in ore productivity, which reduces the present value of marketable products due to an increase in the period of development of the field.
The maximum possible productivity of an open-pit in terms of minerals ensures the maximum economic efficiency of the development of a deposit in the chosen direction of deepening the open-pit.A decrease in productivity for minerals by 20 and 40% of the maximum value entails a decrease in profit from the development of the deposit by 10 and 20%, respectively.

Figure 1 .
Figure 1.Influence of open pit productivity in terms of ore on the production cost of ore mining and its components at the first stage of its operation: 1 -unit semi-fixed costs for ore mining; 2 -unit conditionally variable costs for ore mining without overburden costs; 3 -unit conditionally variable costs for the excavation of overburden; 4 -unit conditionally variable costs for ore mining; 5 -unit production cost of ore.

Figure 2 .
Figure 2.Influence of open pit ore productivity on the production cost of ore mining and its components at the second stage of its operation: 1 -unit semi-fixed costs for ore mining; 2unit conditionally variable costs for ore mining without overburden costs; 3 -unit conditionally variable costs for the excavation of overburden; 4 -unit conditionally variable costs for ore mining; 5 -unit production cost of ore.

Figure 3 .
Figure 3. Influence of open pit ore productivity on the production cost of the concentrate at the first (1) and second (2) stages of open pit operation.

Figure 4 .
Figure 4. Change in costs and income from the development of a mineral deposit and the production of a concentrate, depending on the ore productivity of an open-pit.

Figure 5 .
Figure 5. Graph of changes in profit from the development of the field, depending on the angle of slope of the working side of the open pit.