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ANAGEMENTVolume 10, Number 2 (January 2023):4199-4207, doi:10.15243/jdmlm.2023.102.4199 ISSN: 2339-076X (p); 2502-2458 (e), www.jdmlm.ub.ac.id
Open Access 4199 Research Article
Dredging technology at placer gold deposits in the Far North
R.Z. Nafikov1*, V.E. Kislyakov1, A.K. Kirsanov1, U.R. Teshaev2
1 Siberian Federal University, Krasnoyarsk, Russian Federation
2 Tajik Technical University named after academician M.S. Osimi, Dushanbe, Republic of Tajikistan
*corresponding author: [email protected]
Abstract Article history:
Received 20 June 2022 Accepted 2 November 2022 Published 1 January 2023
The volumes of world gold mining were reviewed. As a result of the analysis, it was found that the proportion of placer gold is very insignificant. This is due to the fact that the most easily accessible reserves are substantially depleted, and the development of deposits with complex mining and geological conditions, including those located in the Far North, is economically impractical. To solve this problem, a method was proposed for isolating the dredging open-pit from the effects of negative temperatures by a hangar-type structure. Similar structures used in the mining industry were considered. Calculations of the dimensions of the structure that allow for safe manoeuvring of the dredge were presented. The data on the duration of the dredging season when implementing the proposed solution in the conditions of the Far North were provided. A method of protecting rocks from freezing when using this technology was proposed. The technical and economic indicators confirming the effectiveness of the implementation of the proposed solution were presented.
Keywords:
dredge hangar placer gold deposit productivity the Far North winter period
To cite this article: Nafikov, R.Z., Kislyakov, V.E., Kirsanov, A.K. and Teshaev, U.R. 2023. Dredging technology at placer gold deposits in the Far North. Journal of Degraded and Mining Lands Management 10(2):4199-4207, doi:10.15243/jdmlm.2023.102.4199.
Introduction
According to the annual World Mining Data analytical collection, gold production around the world has a pronounced tendency to increase, and over the past 10 years, the volume of production of this metal has increased by more than 40% (Reichl and Schatz, 2020). At present, various indigenous and placer gold deposits are being developed in 96 countries of the world, but most of them are produced only in 5 (Table 1). With the improvement of extraction technologies, as well as the discovery of new deposits, and, accordingly, with the appearance of new firms in this market, the structure of gold production has changed over time. For example, over the past 10 years, such producing countries as Rwanda (2.0 tons/year), North Macedonia (0.59 tons/year), Vietnam (0.54 tons/year), Cyprus, Germany, Taiwan and the Philippines (each with an extraction volume of less than 0.05 million tons/year) have entered the market. Gold production
for the same time period was stopped on the territory of Greenland, Guatemala, Oman, the Solomon Islands, Thailand, Uganda and Uruguay. Most of the world's extracted raw materials are accounted for by indigenous gold deposits, the share of placer deposits in this structure, according to various experts, is currently about 10% (Kosov, 2019; Maslovsky et al., 2020). A rather small share of the development of placer gold is associated with the depletion of mineral deposits located in favourable conditions (Russian Academy of Sciences, 2013). It is possible to increase the volume of gold extracted from placers due to the development of deposits with complex mining and geological conditions. For example, significant deposits of the Russian Federation, the United States and Canada occur in the regions of the Far North. It should be noted that the dredging method has the highest technical and economic indicators in the development of placers (Figure 1). Numerous data on the work of enterprises indicate that with the dredging
Open Access 4200 method of deposit development in harsh climatic
conditions, the duration of the dredging season can be from 4 to 8 months. This is due to the open-pit freezing, the formation of ice and sludge, which leads to a sharp decrease in the productivity of the dredging equipment and forced work stoppage. Also, a significant amount of frozen rocks affects the duration
of the season. This fact determines the relevance of a wide range of studies on the extension of the dredging season (Avdeev et al., 2005; Rashkin et al., 2007;
Kurilko et al., 2011; Johnson and MacKenzie, 2012;
Kostromin and Greshilov, 2012), and highlights an obvious problem-the low supply of deposits with thawed reserves during the year.
Table 1. 2015 to 2020 gold production by the leading countries.
Country Dynamics of world gold production by year, thousand tons/year
2015 2016 2017 2018 2019 2020
China 450 454 426 401 380 380
Australia 277 298 292 313 326 320
Russia 255 256 270 280 305 316
USA 214 228 237 226 200 194
Canada 163 164 179 194 183 170
Other countries 1,761 1,862 1,931 1,963 1,899 1,881
a) b)
c) d)
Figure 1. General view: a – dredge, b – deposit dredging development, c, d – open-pit icing in winter.
As practice shows, at the moment, quite a lot of experience has been accumulated in frozen rocks thawing and protecting them from seasonal freezing.
So, the main methods of frozen rocks thawing are:
– a natural method using the energy of solar radiation
– hydro-needle method, the essence of which is to supply heated water to steel pipes (needles) with a diameter of 34-42 mm, which further are driven to a depth equal to the capacity of the thawed layer;
– filtrating and drainage method, carried out due to the heat rejection by the filtration flow, which spreads from irrigation workings to drainage ones
(Ministry of Non-ferrous Metallurgy, 1975;
Kostromin et al., 2007; Ivashin, 2015;
Rosstandart, 2017; Churakova, 2020).
Protection against seasonal freezing of thawed reserves can be carried out by flooding the developed area for the winter period or by using artificial or natural thermal insulation materials as temporary protection. However, these methods are not widely used in practice due to various technological, environmental and economic reasons. It is also worth noting that today in some outlying regions of Russia, the United States and Canada, where placer deposits were previously developed, abandoned dredges and
Open Access 4201 dredgers can be found. These equipment disposals are
often found in such US states as California, Nevada and Idaho, in Canada (Yukon) and in the forests of Siberia (Spence, 1996; Garnett and Bassett, 2005;
Grayson, 2008; Grayson and Chimed-Erdene, 2008;
Grayson, 2009). At the same time, most of the equipment is operable or requires insignificant repair costs. Abandoned dredges are often the result of economic inefficiency of work in harsh climatic conditions. By introducing new methods and technologies, it is possible to more widely use a highly efficient dredging method of gold extraction, while it can be successfully used in deposits under the conditions of the Far North around the world (Pyatkov, 2005).
Methods
Thus, the authors proposed a method for extending the dredging season based on isolating the open-pit with a hangar-type structure made of modern building materials (Kislyakov et al., 2017; Nafikov and Kislyakov, 2020; Kislyakov and Nafikov, 2021). The idea was the use of similar structures in the mining industry. The existing structures are designed to protect the environment from dust, to store mineral dumps, fuel, hazardous materials and for other
purposes (Figure 2). Today, many companies around the world are engaged in the construction of structures of this type; however, we can distinguish Geometrica, which designs production buildings that do not contain columns for the smooth operation of equipment (Geometrica). For the proposed technology, light- transmitting materials should be used; this will eliminate the cost of artificial lighting since energy supply to areas with poor infrastructure and roads is a very difficult and expensive task. Also, transparent materials will increase the air temperature inside the hangar as a result of solar radiation. As a result of studies of the technical characteristics of transparent building materials, cellular polycarbonate was selected, the installation of which will be carried out on the metal structure (Figure 3). The saddles installed at the base of the hangar will allow it to be transported by a bulldozer upon dredge stepping. There are a number of conditions for the deposit development by dredging method, such as the compliance of the capacity and width of the industrial part of the placer with the structural parameters of the dredge; the presence of circulating water in the amount necessary for its safe manoeuvring and uninterrupted operation of the washing and processing equipment; size compliance of field stones with the capacity of digging buckets.
a)
b)
Figure 2. Mineral storage facilities: a – operating one, b – installation process.
The application of the proposed technology puts forward an additional condition: the compliance of the structural dimensions of the dredge with the parameters of the hangar, the main of which are height, length and width, which allow for safe manoeuvring of
the dredge when performing works. At the same time, in order to reduce the capital expenditures for the construction of a hangar and effectively maintain a positive air temperature inside it, the structural dimensions should be taken as minimally permissible.
Open Access 4202 Figure 3. Schematic diagram of the dredging open-pit isolation.
Results and Discussion
The length of the dredge hangar depends on the dredge model and the parameters of the deposit developed (Figure 4) and is determined by the following formula 𝐿а= 𝐿dr+ аdr⋅ 𝑛 + 𝐿 + 𝛿 + 𝜀, m, (1) where Ldr is the overall length of the dredge, m; аdr is the value of the dredge stepping, m;
n is the accepted number of stepping within the hangar units; Lc is the caving of the front bank, m; δ is the catch bench, m; ε is the safe gap, m.
The overall length of the dredge should be considered the distance measured in the horizontal plane between its extreme points. The amount of
stepping is determined by the structural dimensions of the dredge. With maximum stepping, the digging process becomes inefficient as the loss of minerals increases and productivity decreases. Therefore, for each model, a rational, according to the conditions of the excavating completeness, the value of stepping is established (Figure 5), at which the losses in the interstep pillars are minimal. The number of steps within the hangar affects its size and, accordingly, the cost. In addition to economic indicators, it should be taken into account that increasing the area of the structure reduces the efficiency of maintaining a positive air temperature inside the hangar and leads to a dredging season decrease. Therefore, it is advisable to accept one dredge moving up within the hangar.
Figure 4. Diagram for calculating the length of the hangar.
Open Access 4203 Figure 5. The dependence of the dredge stepping amount on the volumetric capacity of digging buckets.
During the development of the bedrock-adjacent part of the sands, mechanical effects occur on the upper layers, which lead to their caving. It can also occur naturally over time. Therefore, this indicator should be taken into account in the calculations of the length of the hangar. The values of the caving length of the front bank at different depths of dredge digging are given in the studies of V. G. Leshkov (Leshkov, 2007). The dependence derived from the initial data looks like this:
𝐿с= 0.22 ⋅ 𝐻 + 1.3 m, (2)
where Hs is the dredge digging depth, m.
For safe operation, it is also necessary to take into account the catch bench adopted in this method equal to 30% of the maximum digging depth. Horizontal distance from the dredge stacker to the rear wall of the hangar (safe gap) in all cases, 0.5 m should be taken.
This distance will allow you to safely manoeuvre and conduct the stacking process. Using the formula (1), we determine the value of the required hangar length, taking into account the capacity of digging buckets of different models. The results are given in Figure 6.
Figure 6. Dependence of the hangar length on the volumetric capacity of digging buckets
The height of the hangar should be taken in such a way that the dredge can freely manoeuvre during operation (Figure 7). This parameter depends on the dredge model, its characteristics, as well as on the conditions of placer occurrence and is determined by the formula
𝐻а= 𝐻dr− 𝐻 − 𝐻 + 𝜀, m, (3) where Нdr is the overall height of the dredge, m; Нd is the average draft of the dredge, m; Нb is the height of the freeboard of placer deposit, m.
The overall height changes over a wide range and varies from 9 m for 50-liter dredges to 39 m for 380- litre ones. Using the formula (3), we will determine the height of the hangar for different models. At the same time, for calculations, the height of the freeboard of the placer deposit is assumed to be minimal. This is necessary for a hangar construction that allows a safe deposit development during the entire period of operation of the insulating structure. The results are given in Figure 8.
аdr = 0.01·E + 1.75 R² = 0.99
1 2 3 4 5 6
0 50 100 150 200 250 300 350 400
Dredge stepping, m
Volumetric capacity of digging buckets, l
Lа = 0.39·Е + 21.8 R² = 0.97
20 40 60 80 100 120 140 160 180 200
0 50 100 150 200 250 300 350 400
Hangar length, m
Volumetric capacity of digging buckets, l
Open Access 4204 Figure 7. Diagram for calculating the height of the hangar.
Figure 8. Dependence of the hangar height on the volumetric capacity of digging buckets.
However, this parameter characterizes the size of the hangar at the points with the maximum dredge height (its rear gantry). Next, we will consider the height of the hangar at points that differ from the points with the maximum dredge height and also calculate the width of the hangar. The dredge model and the parameters of the deposit developed (Figure 9) affect the width. The face width (B) and the manoeuvring angle (β) will depend on the choice of the model.
The width of the hangar at the base is determined as follows:
Вa.f= В + 2 ⋅ 𝐿с+ 2 ⋅ 𝛿, m, (4) where Вb is the width of the front bank, m.
To determine the required width of the hangar at different elevations, we will use the graphoanalytic method. For dredges of different models in AutoCAD software environment, we will adjust the positions of the extreme points of some dredge units (rear gantry, superstructure, bow gantry, stacker, bucket chain) when manoeuvring them. The manoeuvring angles at this stage are assumed to be conditionally equal to 60,
100 and 140 degrees for dredges of all standard sizes, regardless of their technical capabilities.
Then we will determine the area of the hangars.
Let's draw an arc (the contour of the end wall of the hangar) with the minimum possible radius so that all points are located inside it. At the same time, we take into account the safe gap on each side, accepted as 0.5 m. Then, based on the obtained figures, we will build hangars and measure their areas. The results are given in Figure 10. Knowing the dimensions of the hangars, the dynamics of the air temperature inside them was predicted with different wall thicknesses made of cellular polycarbonate. At the same time, it is worth noting that the use of polycarbonate with a thickness of more than 12 mm is inefficient due to its high cost, complexity of installation and low light transmission coefficient. Further, according to the known methods (Leshkov, 2007), the duration of dredging operations during the season for dredges of different dimension- types is determined (Table 2). The data are calculated for deposits located in the area of 60° north latitude.
However, having increased the duration of the dredge operation inside the hangar, attention should also be Hа = 0.08·E + 7.1
R² = 0.95
5 10 15 20 25 30 35 40
0 50 100 150 200 250 300 350 400
Hangar height, m
Volumetric capacity of digging buckets, l
Open Access 4205 paid to the preparation of rocks for excavation, since
the length of the block worked out in winter can reach 300–500 m, the length of the hangar is on average 100 m (see Figure 6). The most effective and relatively inexpensive way to protect rocks from freezing, with
the current state of methods and technology, is to flood the dredging polygon for the winter period. However, with the proposed solution, this method is extremely difficult to implement, so the authors also suggest using cellular polycarbonate to protect rocks.
a)
b)
Figure 9. Diagrams for calculating the width of the hangar at the base: a – front view, b – top view.
Open Access 4206 Figure 10. Changing the hangar area for different types of dredges with their different manoeuvring angle.
Table 2. The duration of the dredging season during the dredging open-pit isolation.
The thickness of the hangar walls, mm Volumetric capacity of dredge digging buckets, l
50 80 150 250 380
Conventional technology 210 220 235 240 270
4 289 283 274 262 292
6 322 312 298 281 301
8 360 346 322 306 308
10 360 360 349 331 314
12 360 360 360 340 326
In the summer-autumn period, it is recommended to make a deep ripping of the prepared area. Then it is necessary to lay sheets of polycarbonate with a thickness of 10–12 mm over the entire area. The air layers of this material contribute to high thermal insulation. In this case, the joints must be sealed with solid aluminium self-adhesive tape.
Conclusion
Next, an economic assessment of the effectiveness of the proposed technological solution was calculated on the example of a placer gold deposit, also located in the area of 60° north latitude, which is developed with a 250-litre dredge. The results are given in Table 3.
Table 3. Technical and economic indicators.
Name of indicators If current technology
applied at the enterprise
If proposed technology applied
Duration of the dredging season, days 240 340
Volume of gold production per season, kg 42.8 68.48
Price per gram of gold, USD 58 58
Volume of products sold, USD million 2.48 3.74
Workers on pay-roll, people. 26 26
Average salary of a worker for a season, USD thousand 11.6 16.2
Capital expenditures (buildings and structures), USD million 0.91 1.13
Balance sheet profit, USD million 1.91 3.93
Capital expenditures payback period, years 1.7 1.08
Sa = 0.01·β + 4.35
Sa = 0.02·β + 4.37 Sa = 0.06·β + 4.17
Sa = 0.13·β + 5.95 Sa = 0.28·β + 21
0 10 20 30 40 50 60 70
60 70 80 90 100 110 120 130 140
Hangar area, thousand m2
Dredge maneuvering angle, deg
50 80 150 250 380
Volumetric capacity of digging buckets, l
Open Access 4207 As can be seen from the presented results, the
application of the proposed solution is economically feasible. At the same time, it is possible to increase the duration of the season by introducing additional heating elements into the dredge hangar, which will allow year-round development of placers in the Far North regions. Thus, the proposed technology is a very promising direction in the mining industry of most countries.
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