Justification the surface mining system parameters of amber pits with semi-mobile beneficiation plants

Research is aimed at establishing the dependence of the semi-mobile beneficiation plant productivity on the face width of the excavator at the developing amber deposits. Analytical research methods were used at the development of the methodology to determine the working time of excavator, taking into account the time for moving the enrichment plant. Appropriate calculation methods are relevant for determining the required amount of technical equipment that ensures the mining operation. The efficient parameters of the face width during the excavation of mining mass have been established, depending on the parameters of the excavator boom, taking into account its replacement. It was determined that the duration of the working cycle of working out the block with the corresponding face width of the pit is based on the time of loading and moving the semi-mobile beneficiation plant, as well as the time for reexcavation. The effective width of the working pit face was calculated with the appropriate choice of the excavator boom. The established parameters of the face width of the pit on the mining bench with the loading of mining mass to the semi-mobile concentrator were implemented in the pit at the development of the Galbin-24 amber deposit.


Introduction
After the adoption of Law of Ukraine No. 402-ХХ in 2019 on the improvement of the legislation on the extraction of amber and the intensive development of the amber extraction industry on "crosscutting" sites with an area of up to 10 hectares, there was a need to develop technology for short-term development of deposits within the validity period of special permits [1].Additional factors that complicate the development of small areas are the heterogeneity of amber deposits within the intermountain place, both in terms of strength and extent, and partially or completely extracted amber in previous periods during illegal artisanal mining [2].
The history of amber finds in Polissia in Ukraine dates back to the 18th century, as a number of Polish and European researchers were engaged in the research of these amber deposits for two centuries [3].The results of these studies became the basis for the beginning of exploration and evaluation work on amber starting in 1979.During their implementation, for the first time in the conditions of the Pripyat amber-bearing basin, the methodology of conducting work, laboratory testing of samples, as well as the calculation of reserves and estimation of forecast resources, which is mainly used to this day, was worked out [4].These studies were carried out on all previously established manifestations of amber: in the basins of the Horyn and Ubort rivers, in the area of Klesova, the villages of Barashi, Gulyanka, etc.In the process of these works in the area of the village Klesov discovered a number of sites with industrial amber content [5].The development of Ukrainian amber began in 1989 with the industrial development of the Klesiv deposit, and the extraction of the first batch of amber was carried out in 1993 [6].And in fact, until 2019, legal amber mining was carried out at two enterprises -State Enterprise "Burshtyn Ukrainy" and "Sonyachne Remeslo" LLC, which developed the Klesivske ("Pugach" site) and "Volodymyrets-Skhidny" deposits, respectively.Several enterprises were engaged in amber mining during the exploratory and industrial development of promising areas during the geological study [7].Most of the extraction (according to some estimates in the period 2015-2017 -up to 95% of the total volume) was carried out by prospectors illegally.

Methods
Today, the technologies of legal amber extraction do not make it possible to effectively develop small deposits with an area of up to 10 hectares, deposits with heterogeneous deposits of minerals and explored reserves of the C1 category, as well as deposits that were significantly affected by the work of prospectors in previous periods.For the development of such fields, the haulage scheme of development [8] is mainly used.
According to the technology, after removing overburden rocks, an excavator of the reverse shovel or dragline type is placed on the upper crest of the mining bench [9].Mining mass in the pit is loaded into dump trucks or into a bunker where it is washed by a hydraulic monitor with further haulage to the beneficiation plant [10].Mining mass is haulage to the beneficiation plant by road or hydraulic haulage, respectively [11].During enrichment at the plant, amber is separated on washing sieves into an over-sieve product on a sieve with a cell of 5 mm.The over-sieved product is separated from crushed stone, roots, pieces of clay, etc. on manual sampling conveyors.In areas where part of the reserves were removed during illegal mining by prospectors in previous periods and with heterogeneous content in the productive layer of the mineral [12], the classic amber development scheme had several main disadvantages that should be changed at the new technological solution: the impossibility of operational determination of the amber content to change the parameters of the extraction; the need for a sufficiently long advance of the demolition works in case of a change in the parameters of the pit or the mining area in the absence of amber deposits; financial costs and high complexity of work organization when haulage mining mass in the marshy areas of Polissia.

Results and discussion
The adoption of the Law of Ukraine No. 402-Х of 19.12.2019 on the improvement of the legislation on the extraction of amber and other minerals by subsoil users contributed to the development and implementation of new technological solutions [13] in the organization of amber extraction [14] on deposits that were partially involved in the illegal activities of prospectors in previous periods.During research and industrial development at the "Bila" site in Zhytomyr region and the "Galbin-24" site in Rivne region, a technology using a semi-mobile enrichment plant AmberWash-40 installed directly in the pit (Figure 1) was implemented.
Taking into account the mining and geological conditions of the individual amber sites mining, the physical and mechanical properties [15] and layer thickness of the mineral and overburden [16], as well as the technological features of the rock mass excavation with amber content, the full technological cycle includes a haulage system [17] of development with transverse movement of pits and longitudinal continuous movement of the mining front along the entire length of the section.
The full technological cycle involves: the surface of the overburden is preliminarily cleaned and planned with bulldozers, the removed rocks are piled up along the perimeter of the development site [18].In the future, it can be used for reclamation and planning on the spent part of the pit; the layer of overburden will be developed by excavator in sections.The overburden excavator, being on the roof of the overburden bench with the lower digging, develops the undercut of the specified bench with the movement of overburden rocks into the residual space of the pit, with their simultaneous use for the formation of demarcation dams of internal hydraulic dumps [19] in the residual space of the pit; excavation of mineral by excavator with loading directly to the beneficiation plant; beneficiation of minerals at the beneficiation plant with simultaneous storage of washing waste in sections [20] of internal hydraulic dumps, while recycled technical water for the beneficiation plant is used in a closed cycle.A JCB JS 220 excavator is used to load the enrichment plant, which can be equipped with both a standard and an extended boom (Table 1).When using an excavator with an extended boom, the width of the working bench increases from 20 meters to 40 meters and the downtime associated with moving the installation and shifting the slurry pipeline, respectively, decreases.The working scheme of the JCB JS 200 inverted shovel type excavator with standard boom length values is shown in (Figure 2).
where: H is the height of the bench, m; φ is the angle of the non-working slope of the bench, degrees; α is the angle of the working slope of the bench, degrees.
The width of the safety strip at the maximum height of the bench for the JCB 220 excavator, provided that the height of the bench is 2.4 m, the angle of the non-working slope of the bench is 30° and the angle of the working slope of the bench is 1.8 m.
The minimum working bench width on the mining horizon consists of the size of the collapse prism and the dimensions of the excavator and the safety distance from the counterweight of the excavator on the uphill side: where: Po is the width of the safety distance from the counterweight of the excavator on the uphill side of the bench, m; Rp.p is turning radius of the bench, m; Wx is the width of the undercarriage of the excavator, m; Pb is the width of the safety zone of the collapse prism (accepted for amber deposits), m.
Taking into account the initial parameters: the width of the safety distance from the counterweight of the excavator is 1.0 m, the turning radius of the bench is 2.9 m, the width of the excavator's undercarriage is 3.2 m, the width of the safety strip of the collapse prism is 1.8 m, the minimum width of the site will be 7.3 m.
Under the conditions of the safe location of the semi-mobile concentrator the width of the working bench is: WSMC is the width of the semi-mobile concentrator; Bb is safety berm; Wb is the distance from the edges of the semi-mobile concentrator for personnel access; Ws is the width of the protective shaft on bench.
At the carry out researches the width of the semi-mobile concentrator was 5.1 m, the safety berm -2 m, the distance from the edges of the semi-mobile concentrator for personnel access -1 m, the width of the protective shaft -2 m, the width of the safety zone of the collapse prism (accepted for amber deposits) -1.8 m.According to the established parameters the width of the working bench is 12.9 m.
During the sectoral movement of the excavator in the face (Fig. 1), the fulfilment of the relevant parameters is ensured.
When changing the parameters of the mining and haulage equipment, a corresponding adjustment of the width of the working bench.
Taking into account that the movement of the excavator will be carried out in a semicircle behind the bunker of the semi-mobile enrichment plant, the maximum width of the working bench for an excavator with a standard boom will be: where: Rcdigging radius of the excavator, m; Rp is the unloading radius of the excavator, m.For excavator with conventional boom Arp1 is determined according to the parameters of the excavator (Table 1), which with the standard parameters of the boom, the digging and unloading radius of 6.5 m is 26 m.
When using a JCB JS 200 excavator with an extended boom (Figure 3) the maximum width of the working bench will be 40 m, since the digging and unloading radius of the excavator is 10 m.
For the development conditions of the "Bila" site, in practice, the passport capacity of the AmberWash-40 semi-mobile beneficiation plant was achieved at 40 m 3 /h, regardless of the capacity of the bucket used to load the mining rock, but when the width of the working bench was increased, the time for moving the semi-mobile beneficiation plant was significantly reduced.It was also determined that the time required for shifting the sludge pipelines was reduced.It is necessary to calculate the volume of the rock mass that temporarily remains in its block under the semi-mobile concentrator at the working out the excavator cut: According to existent parameters the rock mass that temporarily remains in its block under the semi-mobile concentrator is 156.7 m 3 .
When working with an excavator with a standard boom (Figure 2) the radius of the upper crest of the mining face was: Thus, the radius to the upper crest of the mining face when using an excavator with a standard boom is 13 m.
Then the length of the top to the crest of the mining pit will be: For the initial operating parameters of the scheme using an excavator with a standard boom, the length to the upper crest of the mining pit will be 20.4 m.Accordingly, the volume of mining rock extracted from one pit will be: For the conditions of development of the "Bila" site with a JCB JS 200 excavator with a standard boom, the volume of rock extracted from one cut is 480 m 3 .
When developing a mining bench with an excavator with an extended boom, the radius to the upper crest of the mining pit was: where Rp2 is unloading radius of an excavator with an extended boom, m.JCB JS 200 excavator with an extended boom has the unloading radius 10 m, then the radius to the upper crest of the mining pit is 20 m.
The length to the upper crest of the mining face will be: For the scheme using the JCB JS 200 excavator with an extended boom, the length to the upper crest of the mining pit will be 31.4m.
The volume of mining rock extracted from one pit using an excavator with an extended boom is: If the bench with a height of 2.4 m is worked out using an excavator with an extended boom, the where: tsh is shift time, hours; Kpc is coefficient of working time use; nsh is the number of changes day; N is the number of working days per month.
During the studies, the shift time was assumed to be 12 hours, the number of working shifts per day was 2, and the number of working days per month was 30.The coefficient of working time use is 0.8.Under appropriate conditions, the duration of working hours at the enterprise is 576 hours/month.
The time for working one pit with an excavator with a standard boom (T1) and with an extended boom (T2) is determined as the sum of the working hours number when working the pit and the time for moving the semi-mobile beneficiation plant and relevant communications in the pit: where QSMB is the time productivity of a semi-mobile beneficiation plant by mining mass, m 3 /h; Tp1 and Tp2 are the time for replace the semi-mobile beneficiation plant and relevant communications for excavator with standard and extended boom, respectively.
According to the technical characteristics of the semi-mobile beneficiation plant AmberWash-40, which is used in the pit, the temporary productivity is 40 m 3 /h.The time taken to move the semimobile beneficiation plant and the relevant communications in the pit is 2 hours.According to it, it was determined that the time required to work one cut with a volume of 480 m 3 when using an excavator with a conventional boom is 14 hours, while when using an excavator with an extended boom, a pit with a volume of 1350 m 3 requires 35.8 hours.
Accordingly, the number of worked cuts per month will be (Nf1, Nf2): When using a JCB JS 200 excavator with a conventional boom, the number of working cuts per month will be 41, while the use of an excavator with an extended boom will allow only 16 cuts to be worked.
Monthly output of the production line when using an excavator with a conventional and extended boom (QM1, QM2) is set according to the formulas: According to the established parameters, the monthly output of the production line when using an excavator with a conventional boom is 19 749 m 3 /month, while the use of an excavator with an extended boom will allow to increase this indicator to 21,751 m 3 /month without the involvement of auxiliary equipment.
Given that the thickness of the mineral bench can vary from 1.5 m to 3.5 m (average 2.4 m), the dependence of the excavation volume from one cut on the height of the bench was determined (Figure 4).During the research, it was established that the width of the working bench of the excavator with a conventional and extended boom can be increased by reexcavating the rock.With an productivity of an excavator with a standard boom of 165.3 m 3 and at the an extended boom -89 m 3 /h the volume of mining mass reexcavated for one digging radius (6.5 m and 10 m) will be 480 m 3 and 1350 m 3 , respectively.When the width of the pit is increased to two digging radius, the volume of mining mass will increase by two times, and the time spent on reexcavation of the rock will increase by three times.The studies results allow to determined the impact of the cut width on the productivity of the loading and beneficiation equipment are shown in (Figure 5).

Figure 1 .
Figure 1.AmberWash-40 semi-mobile concentrator in the pit Excavation works are carried out according to haulage and non-haulage technological schemes with the internal location of overburden dumps.Minerals are moved using road and hydraulic haulage.A JCB JS 220 excavator is used to load the enrichment plant, which can be equipped with both a standard and an extended boom (Table1).When using an excavator with an extended boom, the width of the working bench increases from 20 meters to 40 meters and the downtime associated with moving the installation and shifting the slurry pipeline, respectively, decreases.

Figure 2 .
Figure 2. Working scheme of the JCB JS 200 excavator with a standard boom: 1semi-mobile beneficiary plant; 2axis of beneficiary plant; 3axis of excavator The minimum width of the safety lane (collapse prisms) is determined by the formula:

Figure 3 .
Figure 3. Working scheme of excavator JCB JS 200 excavator with an extended boom.

Figure. 4 .
Figure. 4. Dependence the volume of rock from cut pass on the height of the bench.

Figure 5 .
Figure 5. Dependence the monthly productivity of an excavator with different types of boom on the width of the working cut.

Table 1 .
Parameters of the excavator JCB JS 220 type inverted shovel.