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Revista Minelor – Mining Revue ISSN-L 1220-2053 / ISSN 2247-8590 vol. 28, issue 4 / 2022, pp. 33-41 EXPLOITATION OF THE POLYMETALLIC ANTONIO ORE BODY, FROM BĂIȚA PLAI MINE 1 * 2 Dacian-Paul MARIAN , Ilie ONICA University of Petroșani, Petroșani, Romania, firstname.lastname@example.org University of Petroșani, Petroșani, Romania, email@example.com DOI: 10.2478/minrv-2022-0028 Abstract: The Antonio polymetallic ore body is part of the Baița Plai ore deposit. Below the XVIII horizon, it has a medium slope, a height of approx. 81 m, an average extension of 200 m and a thickness varying from 4 to 36 m. Above this horizon, the orebody was mined in horizontal slices with integral backfill and the first 9 m high sublevel with rooms and pillars. In depth, below this sublevel, 6 more sublevels with a height of 12 m are mined with sublevel caving mining method. The design of the opening, preparation and exploitation of the deposit was carried out for a production capacity of 100 k tonne/year. Keywords: polymetallic ore, mine, underground mining, opening workings, sublevel gallery, sublevel caving mining 1. Geology of the ore deposit The exploitation perimeter of the Baița Bihor deposit is located in the southeastern part of Bihor county, 4 km from the village of Baița, in the upper basin of the Crișul Baiței stream and is recognized as the oldest mining center in the region. From a morphological point of view, the exploitation perimeter is located in the Bihor Mountains, in the upper hydrographic basin of Crișul Negru, on the slopes of Criș Băița, upstream approx. 2.5 km northeast of its confluence with the Valea Plaiului. The geological structure of the Băița-Bihor deposit reflects, on a smaller scale, the structure of the Northern Apuseni mountains with the Bihor Unit at the base of the structure, with a paraautochthonous role, over which they follow each other the Codru Unit, the Arieșeni Nappe and the Highiș-Poiana Nappe . The perimeter of the Baița Mine is located in an extremely complicated area from a tectonic point of view. The entire structural ensemble is part of the Northern Apuseni Mountains region. From the structural analysis of the current tectonic configuration, it is very clear that the discontinuities arose at different moments of tectonization, being rejuvenated several times following the resumption of movements. Laramic magmatism played an important tectonic role, being accompanied by tectonic phenomena, generating rupture structures with faults showing a preferential orientation NW-SE, but also NE-SW. The entire nappes system present in the Baița Mine area was affected by the Upper Cretaceous magmatism processes that materialized by placing a granitic/granodioritic-dioritic batholith, as well as its vein derivatives. Thus, metamosaic products were generated (calcic, magnesian, chalco-magnesian skarn). The main metasomatic columns in the Carnian dolomites are Antonio, Sturzu, Baia Roșie, Marta, Bolfu -Toni and Hoanca Moțului, often accompanied by satellite bodies (small columns, lenses, metasomatic veins). o o The spatial distribution of the columns is controlled by the rift systems N60 -70°E and N50 - 60°W, the metasomatites being located along the fractures (Sturzu, Marta, Bolfu - Toni, Hoanca Moțului) or at their intersection (Antonio, Baia Roșie). The height of the columns varies between 100 and 530 m, and the thickness is limited to a few tens of meters. Corresponding author: Dacian-Paul Marian, Assoc.Prof. PhD. Eng., University of Petroșani, Petroșani, Romania, contact details (University st. no. 20, Petroșani, Romania firstname.lastname@example.org) 33 Revista Minelor – Mining Revue vol. 28, issue 4 / 2022 ISSN-L 1220-2053 / ISSN 2247-8590 pp. 33-41 One of the main metasomatic bodies within the deposit is represented by the Antonio ore body. This body is located in close proximity to the fault that separates the Carnian dolomites from the Norian limestones. He has a height of approx. 200 m and a diameter of 60-80 m; the vertical position is maintained for approx. 130 m, after which it curves towards the SW, to connect to the skarn mass on the contact of the dolomites with the hornets at their base. For the Antonio body, the location at the intersection of two fracture systems (N50-60W; N60E) is extremely characteristic; this aspect is evident in its median part, between elevations 520-560 m. 2. Opening of the deposit The basic object of the Baița Plai mine is the mining and processing of polymetallic ore. Due to the geomorphological configuration of the area, above horizon VI (approx. +576 m), the access to the mineralized structures was made through adits, and below this level the opening of the deposit was made through 3 shafts (including 2 blind ones) that serve horizons VI – XVIII, between levels +576 m and + 224 m. In general, up to approximately the level of the XIII horizon (approx. +417.7 ÷ 422 m), all the main mineralized areas are known. Below this level, the XV - XVI horizons also open the bodies of Terezia, Baia Roșie, Pregna and to a small extent or even not at all structural Marta, Nepomuk and Bolfu. These, basically, below the +317.4 m level are not explored, although according to the specialized literature they would have chances of expansion in depth, given the important metallogenetic potential they have. The exploitable reserves of the Antonio ore body are located below the XVIII horizon, at a depth estimated, from geological research drilling, of a maximum of 81 m (respectively, at the lower limit of the XVIII-81 horizon). The average extension per direction of the ore body is approx. 200 m, and the horizontal thickness is variable, from 4-16 m, in the western part, to 36 m, towards the west (measured at the level of the XVIII-9 horizon). The deposit has a lower thickness, in the first two thirds from the west, which becomes maximum in the southeast area, changing its orientation from the NE, to the NW-SE, with a narrowing towards the southeast limit. Horizon XVIII (located at +224 m above sea level) is the maximum level reached with the mine opening scheme, which requires the completion of opening and preparation mining workings to make it possible to exploit the Antonio ore body ”in eye-pit” , thus making up for the lack of the horizon XIX. Thus, during the exploitation of this ore body, horizon XVIII must function both as the main transport horizon and as a ventilation horizon, which complicates the configuration of the opening and preparation scheme. Below the XVIII horizon, the ore body is divided into 7 sublevels: the first sublevel (related to horizon XVIII-9) has a vertical height of 9 m, and the following 6 sublevels (related to horizons XVIII-21 XVIII-81) have a height of 12 m [2, 3, 4]. The sublevel caving mining method raises a series of problems regarding the location of the mining workings, which must be kept in a good condition for a longer period of time, as are some opening or preparation workings executed in the barren roof rocks, outside the mining area of influence. So, based on the calculation scheme of rock displacements on the sliding surface in fig.1, the condition for the location of the mining workings that must remain stable during the exploitation of a sublevel is obtained. From fig.1 it follows that the safety limit distance of mining workings from the roof of the deposit is: D = h⋅(ctgα + ctgδ) (1) where: h is the height of a sublevel, in m (for the XVIII-9 sublevel, h=9m, and for the other sublevels, h=12m); α-average inclination of the Antonio ore body; δ - the inclination of the weakened sliding surface / the caving angle (for the conditions of the Baița Plai deposit ). δ = 70 Therefore: - for the first sublevel, with h = 9 m, results D > 13 m; - for the lower sublevels, with h = 12 m, results D > 16 m. Taking into account the relative value of the angles α and δ, these safety distances, which adopted, they can grow properly. 34 Revista Minelor – Mining Revue vol. 28, issue 4 / 2022 ISSN-L 1220-2053 / ISSN 2247-8590 pp. 33-41 Figure 1. Calculation scheme for the safety distance of mine opening and preparation workings  The opening of the deposit in the perimeter of the Antonio ore body can be achieved through several opening schemes, which ensure: the operation of the production process at the sublevels; transport of the mined ore to the horizon XVIII; access/transfer of loading, transport and drilling equipment to/from the faces; staff movement; introduction of materials; ventilation of underground mining workings of opening, preparation and exploitation, etc. For the opening and preparation of the Antonio ore body, an opening scheme was approved for the entire height of the level (fig.2). In principle, this opening scheme develops over the entire level height of 81 m . Figure 2. Antonio ore body opening and preparation scheme  For the gravity transport of the ore, an ore chute is executed at the eastern extremity of the ore body, with o o an inclination of 70 -80 , with a length of 90-95 m, 8 m below the level of the XVIII-81 horizon (respectively at the -89 m level). The connection of the ore chute with the directional transport galleries, from each sublevel in operation, is made through a short cross sublevel gallery. 35 Revista Minelor – Mining Revue vol. 28, issue 4 / 2022 ISSN-L 1220-2053 / ISSN 2247-8590 pp. 33-41 The transport of the blasted ore to the XVIII horizon, starting from the XVIII-33 sublevel and ending with the XVIII-57 sublevel, is done on the belt conveyor inclined transport plane, with an inclination of 12 and a length of 274 m. The section of the inclined plane can be 7.5 m (with dimensions of 2.5 x 3 m), being furnished with a single rubber belt conveyor. The connection between the inclined transport plane, by means of a short 8m ore chute and the main transport ore chute (from level XVIII-49, to level XVIII -89) will be made with a new inclined plane equipped with a belt conveyor, with an inclination of 11 and a length of 210 m. The access of the loading and transport equipment to the sublevel galleries is achieved with a spiral inclined plane, located at the western limit of the ore body, which will be excavated at least up to the level of the XVIII-33 sublevel, when the belt conveyor inclined plane will be realized. The main disadvantage of this scheme results from not knowing the depth of the Antonio ore body. More precisely, the execution of the opening mining workings along their entire length is risky because, with the descent into the depth of the exploitation, the ore reserves may not justify the exploitation of the deposit, and the investment in these workings may be ineffective. In order to eliminate this risk and optimize the scheme of opening, preparation and exploitation of the deposit, the degree of knowledge of the Antonio body should be increased through geological research drilling and through geophysical research methods, such as the Georadar or GPR (Ground Penetrating Radar) method. This method can be considered effective, in the geological conditions of the Antonio ore body, because the deposit is clearly delimited from the surrounding rocks (dolomite, in the roof and limestone, in the floor), and the ore and the rocks have very different qualitative characteristics, which facilitates the spatial representation of the ore body by geophysical methods. 3. Exploitation of the Antonio ore body, under the XVIII horizon In order to choose an appropriate mining method for the Antonio ore body, within the Baița Plai deposit, the influencing factors were taken into account: geological, technical-mining and economic [2, 3, 4]. Thus, the mining method and technology with sublevel galleries and the caving of the ore and the surrounding rocks was proposed. This method is part of the class of methods with the caving ore and surrounding rocks, the variant with forced caving of the ore in sublevel galleries. The principle of the method consists in dividing the level with a vertical height of 81 m (related to the Antonio ore body), below the XVIII horizon, into 7 sublevels. The first sublevel from oriz. XVIII-9 has a height of 9 m, and the next 6 levels have a height of 12 m. The sublevels are delimited in two areas: the lower area with a height of 3 m, in which the sublevel galleries are executed, in the first phase and the upper area (the ore bank), which is exploited in retreat, in the second phase, with long drillholes of fan blast, by surfacing the ore and the surrounding rocks (with a height of 6 m - for horizon XVIII-9 and with a height of 9 m - for horizons XVIII-21÷ XVIII-81). It should be noted that the total estimated reserve of ore related to the XVIII-21 sublevel (fig. 3) is approximately 75,200 tonnes (8,200 tonnes – in the underground galleries dug in the deposit; 67,000 tonnes - total reserve in the pillars and the caved bank). Figure 3. Spatial scheme of the sublevel galleries at oriz. XVIII-21  36 Revista Minelor – Mining Revue vol. 28, issue 4 / 2022 ISSN-L 1220-2053 / ISSN 2247-8590 pp. 33-41 The two phases of exploitation of sublevels can be applied simultaneously, in the same sublevel or in different sublevels. Practically, the two phases of exploitation, in the same sublevel, is recommended for the case of thick ore bodies with a large extension, which is not the case of the Antonio ore body . That is why, in the case of the Antonio ore body, it is recommended to apply the two phases simultaneously, in two different sublevels. Moreover, the first sublevel, XVIII-9, will be exploited in the second phase, by caving the ore and the surrounding rocks, simultaneously with the execution of the sublevel galleries at level XVIII-21. Then, the XVIII-21 horizon will be in the 2nd phase of exploitation with the caving of the ore and the surrounding rocks and the XVIII-33 horizon, in the phase of digging the sublevel galleries. In the 1st phase (sublevel „n”), the sublevel galleries are executed using the following mining equipment: the mobile drilling rig Conax Mantis CMR-4; loading and transporting machine Diesel LHD WJ-0.6; Barford Hydrostatic SX3000 dump truck (fig.4.b). In the 2nd phase („n -1”), mining is carried out with long holes, drilling in the fan and surfacing of the ore and the surrounding rocks, equipped with the following equipment: the mobile drilling rig Conax Mantis CMR-4; loading and transporting machine Diesel LHD WJ-0.6 and WJ-1 (fig.4.a); Thwaites Mach 340 dump truck. a) b) Figure 4. Loading and transporting machines a) Diesel LHD WJ-1 b) Dumper Barford Hidrostatic SX3000 For the exploitation of the ore reserves related to the XVIII-9 sublevel, the mining method in sublevels, with caving of the ore and the surrounding rocks, adapted to the mining rooms from this horizon, was proposed, being the only mining method that can ensure the recovery of the ore from the sublevel horizon XVIII-9, with reduced costs. At the mining level of horizon XVIII-9, with a total area of about 2,400 m , the deposit was already 2 2 exploited with rooms (on an area of 1,400 m ) and abandoned pillars (1,000 m ), under an ore ceiling with an average thickness of 6.5 m, disposed below the backfill and broken rocks, from the upper levels. Both the mining rooms and the pillars have an irregular layout in the horizon plane, with different sizes. In general, the rooms have an average height of approx. 2.5 m, there being local situations where the rooms can exceed this height, reaching 3 m and even 4 - 5 m high. The width of the rooms is 3-4 m, the shape of the pillars is irregular and their horizontal dimensions are approx. 4÷ 6 x 9 m, in the eastern part, reaching 5÷ 7 x 16-19 m, in the western part. The layout of the rooms and pillars and their shape was influenced by the irregular configuration of the deposit, in a horizontal plane. The geological reserve related to the XVIII-9 level is approx. 59,200 tonnes, of which approx. (11,100 tonnes, leaving an abandoned reserve in the ceiling and in the pillars of 48,100 tonnes). Which means an extraction of the deposit of 18.79% and a total ore loss of 81.21%, values that are unacceptable for the exploitation of a polymetallic deposit of this type, such as the one in the Antonio body, at the Baița Plai mine. That is why the Baița Plai mine set out to design a mining method and technology that would ensure the most important recovery of the abandoned ore in the ceiling and pillars in the level of the XVIII-9 horizon, with as much economic efficiency as possible. At a production capacity of 100,000 t/year, the geological reserve of 134,400 tonnes, contained in the two sublevels (XVIII-9 and XVIII-21), at an extraction of about 85%, these sublevels cover the production capacity of the mine for about a year. The cross-section of the sublevel galleries of 3 x 4 m (12 m ) was determined taking into account their stability, the optimal evacuation of the crushed ore and the sizes of the drilling rigs and the loading and transport machinery. 37 Revista Minelor – Mining Revue vol. 28, issue 4 / 2022 ISSN-L 1220-2053 / ISSN 2247-8590 pp. 33-41 Also, the width of the pillars between the sublevel galleries was set at 6 m (correlated with the sublevel height of 12 m and the sublevel galleries width and height of 3 x 4 m), which is an optimal size to ensure an ore extraction of more than 90%, ore losses below 10% and a maximum dilution of 20%. These technical- economic indicators are influenced by the geometric parameters of the mining method, which were established according to the laws of the flow of the broken ore caved in the mining stope [4, 5, 6, 7]. From various experiments carried out in the laboratory and in situ, it is known that when the ratio between the height of the caved ore bank and the maximum size of the extraction opening (in this case, the width of the sublevel gallery) is between 2 and 30 or even more (in in the case of the XVIII-9 horizon it is 6.5 m /3 m=2.166 and in the case of the XVIII-21 m horizon and those from the depth it is 9 m / 4 m=2.25), and the caved ore bank was broken into non-cohesive pieces and inhomogeneous, the geometry of the broken ore, in motion, will approximately take the shape of an ellipsoid of revolution. Between the sublevel galleries there is a passive zone where the crushed ore can be recovered at the level of the lower sublevel (fig. 5). The thickness of the passive zone can be thinner or thicker, depending on the inclination of the outflow funnels formed in the massif, the width l of the gallery, the distance S between the g g sublevel galleries and the characteristics of the flow parameters of the granular material, which control the shape of the passive zone . Figure 5. The vertical location of the sublevel gallery, according to the gravity flow model [4, 6] Knowing the values of h and L , it is possible to determine, with approximation, the distance S between t t g the axis of the underground mining workings, at the end of which the broken ore evacuation operation is carried out. It is assumed that the loosening ellipsoid is 2.5 times larger than the extraction ellipsoid, and the width of the extraction ellipsoid is 40% of the width of the movement ellipsoid. In the design of the mining method with sublevel caving of the ore and the surrounding rocks, it is necessary to determine the width La of the loosening ellipsoid in horizontal section, right at the level where the extraction ellipsoid has the maximum size L (see fig.5). Assuming that the principles of idealized gravity flow can be applied under mining conditions with sublevel caving of the ore and surrounding rocks, the total width L of the extraction ellipsoid is approximately 60-65% of the width of the loosening ellipsoid, (at the level where the extraction ellipsoid has its maximum width L ). Therefore, the approximate horizontal distance between the outlets S is : t g - for an extraction height h ≤ 18 m: S < (2) 0.6 - for an extraction height h > 18 m: S < (3) 0.65 38 Revista Minelor – Mining Revue vol. 28, issue 4 / 2022 ISSN-L 1220-2053 / ISSN 2247-8590 pp. 33-41 The parameters L and d can be approximately calculated with the relations: t t L ≅ h + a− 1.8 (4) t t d ≤ L / 2 (5) t t Where a represents the effective width of the sublevel gallery into which the caved ore is discharged, which depends on the shape of the gallery ceiling. An approximate value of this parameter, for the sublevel galleries is: a = 0.7⋅ l (6) Regarding the design of the advance step (the thickness of blasted space or burden space), in order to reduce ore losses, it is recommended that this parameter be determined with the relationship: W ≤ (7) Taking into account the above relations, following calculations obtained the following values (Table 1): Table 1. Calculated geometric parameters of the mining method Horizon a, [m] L , [m] d , [m] S , [m] W, [m] t t g XVIII-9 2.1 9.3 <15.50 ≤ 4.65 ≤ 2.23 XVIII-21 2.8 13.0 ≤ 6.50 <21.66 ≤ 3.25 In order to determine the drilling, loading and transport equipment, in the endowment of the mine, meets the conditions imposed by the annual production capacity of 100,000 t/year, in the context of an opening and preparation scheme and the proposed mining technology, they have their productivities, which satisfy these conditions, have been calculated. The CONAX MANTIS CMR-4 drilling rig executes a fan of 25 drillholes, with a total length of 140 m, in 3 shifts of 6 hours each. The productivity of the drilling rig, for a 6 hour shift and an average drillhole length L , was calculated with the relation : P = , [m/shift] (8) 0,504⋅ L + + 1,45 1− exp(−0,186⋅ L ) L g g Figure 6. Conax Mantis CMR-4 drilling rig Also, the calculated productivities of the LHD WJ-0.6, LHD WJ-1 and LHD WJD -1 loading and transporting machines are 30, 38 and 47 t/h. Drilling-blasting parameters (number and length of drillholes, total and specific explosive consumption, etc.) were calculated for the execution of sublevel galleries and fan drillholes layout schemes [3, 8, 9], for the representative situations from horizons XVIII-9 and XVIII-21 (fig. 5). 39 Revista Minelor – Mining Revue vol. 28, issue 4 / 2022 ISSN-L 1220-2053 / ISSN 2247-8590 pp. 33-41 Figure 7. Schemes for the placement of the long drillholes in the fans, sublevel XVIII-21, for some representative sections through the ore deposit  As an example, table 2 summarizes the drilling-blasting parameters related to the fans A, B and C, in fig.7.c. The type of explosive used is Riomax HE 38/400 (MAXAM). Table 2. The value of the drilling-blasting parameters for the fans A, B and C - fig.7.c Value Specification UM Fan A Fan B Fan C Total number of drillholes 25,000 24,000 21,000 Total drillhole length m 147,210 141,390 126,210 m/m 0,953 0,887 0,860 Specific hole consumption m/t 0,352 0,327 0,317 Total stemming length m 48,410 46,590 42,210 Total volume of stemming m 0,067 0,065 0,058 Total number of cartridges 247,000 237,000 210,000 Total amount of explosive kg 129,922 124,662 110,460 kg/m 0,841 0,782 0,753 Explosive consumption kg/t 0,310 0,289 0,278 staples / m 0,162 0,151 0,143 Detonators consumption staples / t 0,060 0,056 0,053 Burden space m 1,400 1,400 1,400 Mining face surface m 110,310 113,860 104,800 Volume of ore m 154,434 159,404 146,720 Quantity of ore t 418,516 431,985 397,611 In order to optimize the parameters of the mining method and technology, which are the basis of the organization of the production system, the design of the production process in the mining faces with the sublevel caving of the ore from the XVIII-9 and XVIII-21 horizons and the digging of the sublevel galleries was carried out. In the same context, the calculation of the labor productivity in the mining face (15.5 t/man- shift - at horizon XVIII-9; 17.5t/man-shift – at horizon XVIII-21) and the consumption of materials, fuel and energy was carried out. The calculation of the unit cost of the tonne of ore extracted from the mining face included: electricity and fuel consumption; depreciation of machinery and means of transport; other consumables; maintenance and repair works of machinery and means of transport; personnel expenses, etc. 40 Revista Minelor – Mining Revue vol. 28, issue 4 / 2022 ISSN-L 1220-2053 / ISSN 2247-8590 pp. 33-41 4. Conclusions • The Antonio polymetallic ore body is one of the main metasomatic bodies within the Baița Plai deposit. This ore body contains Carnian dolomites in the roof and Norian limestones in the floor. • Starting from the upper limit, the ore body was opened with shafts and adits and was exploited in horizontal slices with the integral backfilling of the stopes, up to the XVIII horizon. • The opening and preparation of the deposit below the last horizon was carried out ”in eye-pit”, with a spiral inclined plane and a belt conveyor inclined plane, which connect with the directional sublevel galleries, through short cross galleries, raises and ore chutes. • Exploitation continued with rooms and pillars, at the XVIII-9 horizon and then with sublevel caving of the ore and the surrounding rocks, on the following 6 lower sublevels, with a height of 12 m. • The endowment with drilling machines and loading and transport equipment and the organization of the production process was carried out to ensure an ore production capacity of about 100 k tonnes/year, with minimal costs. References  Stoici S.D., 1983 The metalogenetic Băița Bihorului district (in romanian), Academic Publishing București.  Onica I., Cozma E., Georgescu M., Marian D., Cozma B., 2022 Study on the efficient exploitation of the polymetalic Antonio ore body, horizon XVIII, Băița Plai Mine, for the production capacity of 100 000 tonnes/year (in romanian), Contract no. 112/26.01.2022  Georgescu M., 1986 The optimization of the underground exploitation methods for metal ore deposits (in romanian), Technical Publishing, București  Onica I., 2016 Mining exploitation (in romanian), Universitas Publishing, Petroșani.  Richardson M.P., 1981 Area of draw influence and drawpoint spacing for block caving mines.  Kvapil R., 1982 The Mechanics and Design of Sublevel Caving Systems, Underground Mining Methods Handbook, W.A.Hustruild editor, A.I.M.M.P.E.I., New York.  Brady B.G.H., Brown E.T., 2005 Rock Mechanics for underground mining, Third edition, Kluwer Academic Publishers, New York, Springer Science + Business Media, Inc.  Fodor D., 2000 Industrial explosives (in romanian), Infomin Publishing, Deva  Fodor D., 2007 Blasting engineering (in romanian), Namaste Publishing, Timişoara. This article is an open access article distributed under the Creative Commons BY SA 4.0 license. Authors retain all copyrights and agree to the terms of the above-mentioned CC BY SA 4.0 license.
Mining Revue – de Gruyter
Published: Dec 1, 2022
Keywords: polymetallic ore; mine; underground mining; opening workings; sublevel gallery; sublevel caving mining
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