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20INCREASING THE BOUNDARIES OF OPEN PIT DEPTHS BY APPLYING EFFECTIVE METHODS OF OPENING AND TRANSPORTATION SYSTEMS OF MINED ROCK FROM DEEP HORIZONS
T. E. Melnikova
Lecturer of the department "Mining" of the Almalyk branch of the Tashkent State Technical University named after Islam Karimov
ABSTRACT
This article discusses the prospects for increasing the boundaries of the open-pit method and the depth of open-pit mines, as well as the scheme of using heavy-duty skip hoists in the quarry, the scheme of opening and transporting rock mass from the quarry when using inclined or vertical hoists, shows the dependence of the reduced costs on the depth of the quarry for various options transportation schemes. The change in the productivity of the hoists depending on the depth of their introduction into the open pit, the change in the cost of mining 1 ton of ore at various stripping ratios, the change in the total, specific, total and discounted costs by technology type are shown.
Keywords: opening scheme, rock mass transportation scheme, changes in total, specific, total and discounted costs, steeply inclined conveyor, cyclic-flow technology.
INTRODUCTION
Quite a lot of both research and design works are devoted to the problem of opening and developing deep horizons of open pits [1]. By the beginning of the 90s, many researchers came to the conclusion that the most effective technological schemes that ensure the opening and transport of ore and overburden from the deep horizons of the quarry are the use of haul-offs in inclined shafts, steeply inclined conveyors in trenches, and vertical skip hoists. Least of all talked about steeply inclined and vertical conveyors installed on the benches of the sides of the quarries, although the feasibility of their use has already been worked out. At the same time, it was rightly believed that the implementation of such schemes and methods for delivering ore and overburden to the surface is mainly associated with the stability of the benches of the ledges themselves, of their sides in general.
REFERENCES AND METHODS
The method of delivering ore and rock to the surface with the use of inclined lifts at deposits with difficult mining and technical conditions will allow achieving minimum capital costs and operating costs when reworking reserves in the bottom zone of an open pit and timely transferring to an underground method of deposit development without reducing productivity enterprises.
In 1980-1981, a group of researchers and design workers published a work in which the most efficient and productive way of delivering ore and rock to the surface was considered to be the use of heavy (80 t) skip hoists [2].
Efficiency zone of road and rail transport
15 __L___
0 100 200 300 400 500
quarry depth, m
Figure 1. The dependenceof the reduced costs on the depth of the open pit for various options for transportation schemes.
According to the technical and economic calculations performed by them in relation to the conditions of open pit, it turned out that this option is characterized by the lowest reduced costs for mining ore in an open pit and transporting the rock mass to the surface, especially at a pit depth of more than 250-300 m. Minimum cost price extraction of 1 ton of ore during the development of the upper horizons is achieved using road and rail transport. However, when it is introduced to the middle, and even more deep horizons, due to the increase in the additional volume of overburden in the benches of the sides, when the routes fit in the sections of the exit, a sharp rise in the cost of mining occurs. The cost of extracting 1 ton of ore at deep pits of 300 and 500 m is, respectively, 13 and 35% higher than when using skip lifts with belt conveyors in the haulage adit. According to the data given in the work (graph. - Fig. 1), Technical and Economic Projects of this option are more preferable than for the option with inclined skip lifts on the side of the quarry.
However, this method of delivering ore and overburden to the surface also has some drawbacks that hinder its use in quarries. The main ones are considered to be a significant amount of capital mining operations associated with the vertical shaft, conveyor cross-ways and ore passes, as well as the presence of ore overloads under ore passes near the shaft and on the surface. If for the case of reloading ore on the surface to another mode of transport (for example, railway) this process is less complicated, then with the delivery of rock to the surface, its reloading into vehicles is difficult, as a rule, due to large volumes of overburden, the need for additional number of shafts and etc.
DISCUSSION AND RESULTS
In the last 5-10 years, both in our country and abroad, a number of scientific and design studies have been carried out to expand the field of application of delivery
vehicles for lifting loads, including cars, dump cars to the surface [3, 4]. This eliminates the overloading of ore and overburden in the quarry and on the surface during transportation, for example, of rocks to dumps, and ores to a factory or special warehouses. In addition, tests have been carried out abroad on the use of steeply inclined and vertical conveyors for delivering rock mass to the surface or to places of its reloading to another mode of transport.
Thus, the use of new methods of delivering goods to the surface, as well as lowering materials and equipment to deep horizons in the case of using inclined lifts in the coming period, will depend on the accounting and elaboration of a number of mining and geological, mining engineering, climatic and purely technical (design) factors.
It is quite understandable that the first attempts at the feasibility of their application in deep quarries were carried out for cases with difficult mining and technical conditions of field development (increasing depth of quarries, significant values of stripping ratios, ore bodies in shape close to kimberlites, etc.).
For the conditions of the kimberlite field in Yakutia (the Yubileiny quarry, an assessment was made of the possibility of using inclined automobile lifts on the board of the open pit [3]. In the considered variants, the calculations were carried out taking into account the lifting of dump trucks with a carrying capacity of 120-130 tons. The slope of the lift track is 35-600. Efficiency of application in the development of a deep quarry (up to 550 m) of road transport, inclined lifts and diesel-trolley transport. For diesel - trolley carriers, the smallest volume of rock mass removal from the quarry has the option with road transport.
The excess of overburden removal when using car lifts was 8.5, and with diesel-trolley transport - 15.4 million tons. This significantly worsened the indicators of the compared options, plus additional restrictions adopted, in particular, the conditions for gas contamination of the quarry. In all variants, the capital costs for the purchase of ventilation equipment are assumed to be the same, which may not correspond to real conditions. Nevertheless, when comparing the unit total costs for excavation and movement of 1 ton of rock mass from the quarry, the most preferable option is the use of automobile lifts.
With a strict comparison of the options, obviously, a geomechanical justification for the construction and safe operation of inclined lifts for 20 - 15 years, taking into account the influence of Arctic conditions and the relatively less stable enclosing rocks of the deposit, than purely rocky igneous solid rock massifs, should be provided. In addition, the reduction in operating costs for the enterprise in time since the commissioning of new, more efficient systems for delivering rock mass to the surface should be taken into account.
According to the design studies for the conditions of the quarry of the Vostochny mine of JSC "Apatit", carried out by the Institute "Giproruda", more obvious advantages over other options, which considered the use of railway transport in combination with automobile, cyclic-flow technology (CCT), have options with the use of inclined lifts.
In contrast to the Yubileiny quarry, this open pit has a more elongated shape, therefore, according to the conditions for fitting the lift routes into the contours of the open pit without additional stripping operations, it has some advantages. However, for a detailed consideration of the alternatives in the project, it is necessary to solve a number of geomechanical and technical issues for the construction of lifts on the side of the quarry before the design stage. These include, first of all, the substantiation of the angle of the elevator route, taking into account the stability of rock masses in the areas of their construction. The productivity of the hoists depends on the depth of their entry into the quarry and the bench (Fig. 2).
In fig. 2 shows the change in the productivity of the lifts depending on the depth of their entry and the carrying capacity of the dispensing vessels or the carrying capacity of dump trucks. In addition, the performance of the dispensing systems obviously depends on the lifting speed of the vessels (dump trucks). It follows from the graph that in the area of shallow depths (up to 250 m), vertical skip hoists are most productive (skip lifting capacity - 80 t), then the SIMAG inclined hoist system (dump trucks carrying capacity - 170 t) and the bench angle of the track - 530). Close to these data are the data given by prof. L.L. Kuleshov for lifts with an inclination angle of 400 (curve 1). Somewhat below is the curve constructed according to the data of prof. Yu.V. Demidov (curve 3) and even lower the data given in [4] (point A). Least of all, the performance of the inclined hoist changes with depth, according to the design studies of the Giproruda Institute (curves 4 and 5, respectively, for rock and ore).
P, min iyear
A'
0 200 400 600 H m
Figure 2. Changes in the productivity of lifts depending on the depth of their entry into the quarry: 1,2,3 - according to prof. A, A. Kuleshov, SIMAG Jinn, Prof, YilV. Demulov, respectively; 4,5 - according to design studies for ore and overburden (dump truck carrying capacity 120 tons); 6 - for vertical skip hoists (skip lifting capacity - SO t).
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The inclination angles of the lifts in the considered variants vary from 36 - 37 (taking into account the bulk) to 40-420 (in rock massifs). It should be noted that the filling of the base of rock with a height of 100 - 115 m is a complex structure, since it must exclude the sediment of rocks no more than 5-10 mm, otherwise at the joints of concrete slabs their displacement is possible with a high specific pressure on the rails (up to 300 t the absolute value of the load), and even a slight deformation can lead to serious violations of the structure's performance.
For other considered constructions, the bench angles of the lifts vary from 16 - 33 to 36 - 450 in [4], to 530 (SIMAG firm). With their different productivity, the capital costs for their construction in both versions are approximately the same (11 - 12 million dollars), although the risk of adopting the second option increases many times, and underestimation of the array's stability potential can also lead to significant damage.
In addition, in the project, it is necessary to resolve in more detail the issue of choosing the location of inclined lifts and their parameters, since this is related to the productivity of the open pit. In the previously considered design solutions, especially in the first design studies, the productivity of the Koashvinsky quarry was about 9 million tons/year. In the 1993 project, due to the use of CPT for ore and stripping and conservation of a part of the ore areas (in the north-western and south-eastern zones of the open pit), the productivity of the open pit was reduced to 8.0 million tons/year. In the latest pre-design solutions of the Giproruda Institute, related to the analysis of various options for transporting ore and overburden from the open pit, the open pit ore productivity has already reached 7 million tons/year. This is due to the additional decommissioning of a part of the ore areas. When compared with the original options, the total amount of ore excluded from the contour of the open pit will be 4.0 - 5.0 million tons.
According to research data, the depth of the open pit can be 700-800 m (the bottom level is 400-500 m instead of 290 m according to the project). It should also be taken into account that the content of P2O5 in the ore increases with depth, and the complexity of the occurrence of ore bodies increases; therefore, an early transition to underground mining will be associated with large losses of valuable ores. On the other hand, the choice of the location of transport and delivery systems to the surface without taking into account the prospects for the development of the open pit on a long-term basis will lead to the fact that most of the structures can fall into the contour of the open pit, and they are subject to relocation (Figure 3). Therefore, the project should analyze all promising options and select the most efficient one (including the use of vertical skip hoists for ore and inclined shafts with ore passes over the overburden).
In fig. 3 shows the contours of the quarry, taking into account the stages of development of the deposit in conditions when the lifts (1) introduced into the quarry lead to the conservation of ore areas and can fall into the contours of its prospective boundaries. For comparison, a variant with vertical skip hoists is shown (2), which allows achieving a greater depth of the open pit with differentiated benches of its sides (correspondingly, decreasing fracturing of the massif with depth), and also a gradual transition to an underground method of field development. Underestimation of the capabilities of the rock massif ultimately leads to an increase in the thickness of the open pit, in overburden and, accordingly, to an increase in the cost of 1 ton of ore (Fig.
4).
The graph (Fig. 5) shows the change in total costs by options for transport and delivery of ore to the surface for the Koashvinsky quarry mine (according to the Giproruda Institute).
In this regard, the method used in the development of the kimberlite deposit in South Africa requires attention, analysis and practical use. There, they not only achieved minimum capital expenditures and operating costs when reworking reserves in the bottom zone of the open pit, but also timely made the transition to an underground method of field development without reducing the productivity of the enterprise.
The essence of the method is that when a certain depth of the open pit is reached, when a sharp increase in operating and capital costs for maintaining the capacity of the open pit begins, further development of the ore body with the achieved development front for mining operations on ore is carried out without stripping. The resulting cost savings over a 10 to 15 - year period of the open pit operation allows performing most of the preparatory work to open the underlying ore horizons without borrowing and raising funds from outside, as usual under the program: separately construction and operation of the quarry, and then the mine.
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Figure 5. Change in total costs by options over time (a)> unit costs by technology type (b), and total and discounted costs for central heating and
flow technology (c): a - at the cyclical flow technology, motor transport and car lifts and additionally railway transport; b -1 - total costs for options, 2 - costs per 1 ton of production; c-1 - total costs for the options of cyclical flow technology and a/s and car lifts (flow technology), 2 - discounted costs for technologies.
Moreover, most of the capital investments can be repaid during the operation of the quarries.
CONCLUSION
In conclusion, it should be noted that at the present time, at the level of the Academy of Sciences, it is necessary to raise issues related to the need to conduct in-
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depth research for typing and identifying the possibilities of various rock massifs for geomechanical stability, which will allow domestic industry to timely create productive systems for lifting ore and overburden to the surface in in the form of steeply inclined vertical conveyors (prof. E.E. Sheshko and others), as well as container modes of transport, which can reduce the capacity of lifting equipment in quarries by 2-3 times or more.
REFERENCES
[1]. Eremin G.M. Increasing the boundaries of the open-cut method and the depth of open pits with the use of effective methods of opening and transport systems of rock mass from deep horizons // Mining information and analytical bulletin - 2001.-№ 7. - P. 68 - 72.
[2]. Kulbida P.N., Roizen V.V., Serbin V.I. and others. Heavy-duty skip hoists for mining deep quarries. Gornyi Zhurnal. - 1981. - No. 7. - Pp. 48-50.
[3]. Zotov A.A., Zyryanov Yu.V., Faiblit M.A. Efficiency of transport systems at the Yubileiny open pit of AK ALROSA // Mining journal. - 2000. - No. 3. - Pp. 37-40.
[4]. Epishov V.N., Petrichenko L.N., Kaplun A.S., Demidov Yu.V. Automobile inclined lift for the Koashvinsky quarry of JSC "Apatite" // Mining magazine - 2001, - No. 5. -Pp. 76-77.
[5]. Furem K.G., Druzhin V.G. Hoisting-and-transport system for ore delivery from working horizons // Gornyi Zhurnal. - 1999. - No. 2.
[6]. «Wall control and contour blasting to ensure the stability of the quarry boards when operating drilling and blasting works». Oriental Renaissance: Innovative, educational, natural and social sciences, Volume 1, Issue 4, ISSN: 2181-1784, SJIF 2021: 5,423, pp. 902-909.
