7/30/2019 MIN-019-RG-CS

1/16

TECHNOLOGICAL IMPROVEMENT OF SUBLEVEL CAVING

METHOD IN UNDERGROUND COPPER MINE JAMA - BOR

Dejan Bogdanovic - Dragan Strbac

Institut za Bakar Bor (Copper Institute Bor)

INTRODUCTION

Copper ore mining has been continuously performed in the underground copper

mine "Jama" - Bor since 1903. Three ore bodies are in exploitation today: the

ore body "Tilva Ros", the ore body "P2A" and the ore body "Brezonik". New ore

body "Borska Reka" is a stage of opening.

At this moment, the greatest part of exploitation is performed by the use of

sublevel caving method, and around 80% of annual underground mine "Jama" -

Bor production (up to 1.5 million tons) is realized. This method is applied in the

ore bodies "Tilva Ros" and "P2A". Room and - pillar method of stopping with

filling of excavated area with flotation tailings is applied in the ore body

"Brezonik".

Since excavation depth is constantly increased and copper content in the ore is

constantly decreased, the conditions for economic excavation of useful mineral

raw material are more and more difficult. When previously used method of

sublevel caving and its parameters are used at lower depths of excavation,

where the ore body "Borska Reka" is spreaded out, then it does not satisfy the

economic criteria, so it is necessary to carry out its modification. This

modification would enable continuous ore production in the underground mine

"Jama" Bor to k -315 m (up to total depth of 754 m), i.e. it would enable a

continuation of underground ore mining from the Bor deposit, upon ending of

exploitation of the current active ore bodies "Tilva Ros", "P2A" and "Brezonik" at

the peak elevation k -76 m.

1

7/30/2019 MIN-019-RG-CS

2/16

Modification of this method includes an increase of height between sublevels

from existing 15 m to 30 m, an increase of distance between drifts from 14 m to

18 m, what reduces a volume of preparation works. Also, a cross section of

drifts will be higher and it will be 23.57 m2 instead of the existing 12.70 m2. In

that way, more effective loading will be enabled with less losses and dilution of

ore quality. Drilling will be carried out by the use of long blast holes, diameter of

115 mm instead of present 76 mm, what enables effective blasting with more

higher ore volume.

The modified method will be used for mining in the ore body "Borska Reka"

from level k -205 m. Ore will be stoped from this working level to k -175 m, i.e.

in a belt of thickness of 30 m. The other working levels would be located by 30

m, i.e. at k -235 m, k -265 m and k -295 m.

MINING - GEOLOGICAL PARAMETERS OF DEPOSIT

The Bor copper deposit is located in east Serbia and it includes many ore

bodies. Some of the ore bodies are depleted, but some of them are mined by

open pit or underground mining.

The ore bodies "Tilva Ros" and P2A" are located in central part of the Bor

copper deposit. Low grade impregnated and stockwork ore with copper content

in ore under 1% appears in the ore bodies. These ore bodies are formed in

hydrothermally altered andesite. The most present hydrothermal alterations in

the ore body "Tilva Ros" are silicification, chloritization and kaolinization, and

kaolinization is the most present in the ore body "P2A". Both ore bodies are

spreaded to depth under k - 155 m. Mining reserves in boundary line of 0.4%

copper is 12.2 million tons in the ore body "Tilva Ros" with average copper

content of 0.791%, and 11.6 million tons in the ore body "P2A" with average

content of 0.75%.

The ore body "Tilva Ros" was long time stoped by open pit mining. By getting

down to level k -5 m, the parts of ore body, which are now mind by underground

2

7/30/2019 MIN-019-RG-CS

3/16

mining, were left on north, west and south part at the pit sides. Until now, about

50% of ore reserve was mined and now the mining is carried out at peak

elevation k -16 m. The ore body "P2A" is mined at peak elevation k + 30 m, and

about 65% of ore reserve was mined until now from this ore body. Mining of

both ore bodies will be carried out to peak elevation k -76 m until 2003 year.

The ore body "Borska Reka" is located on the outermost north - west parts of

the Bor ore field. It is situated in intensive hydrotheramally altered andesites

and their volcanites - silicified, chloritized, coalinized and pyritized andesite.

According to the scales, porphyritic mineralization of the ore body "Borska

Reka" belongs to a category of medium deposits with a little increased copper

content. Its strike of bed is NW-SE, and it dips to the west, i.e. south-west at

angle of 45o - 55o in general. Maximum length of ore body is 1410 m, measured

at k -395 m. Maximum width of 635 m was measured at the same level, and the

average one is about 360 m. Average ending thickness of ore body from the

ground surface is about 920 m. From the given data, it could be seen that the

ore body is situated deeply under ground surface. The first greater continuous

area of ore body is situated at k -75 m, and the last one is situated at k -715 m.

Mining of this ore body by the use of modified sublevel caving method will start

in 2003. In this way, the upper part of this ore body will be mined to peak

elevation k 315, and about 20.7 million tons of ore with average copper

content of 0.777%.

Figure 1 gives a schematic review of given ore bodies locations in the Bordeposit.

3

7/30/2019 MIN-019-RG-CS

4/16

Figure 1. Schematic review of ore bodies locations in the Bor deposit

EXISTING METHOD OF SUBLEVEL CAVING

As it was mentioned, the existing method is used for sublevel caving of the ore

bodies "Tilva Ros" and "P2A". Basic caving unit in those ore bodies includes

drifts and sublevel drifts. Sublevel drifts are driven in a counter of ore body

where the drifts are just driven in the ore body. The drift were driften at mutual

distance of 14 m, and in a chess order per height, and height distance between

sublevels is 15 m (Figure 2). Based on this, every two alternating sublevels

have the same schedule of drifts which are axially moved by 7 m regarding to

the located sublevels between, over and under of these sublevels. Connection

of those sublevels is carried out by incline. Average coefficient of preparation for

the ore body "Tilva Ros" is 3.42 mm/t, and for the ore body "P 2A" is 3.17 mm/t.

There, a coefficient of preparation presents relation between total length of all

preparation rooms, and ore reserves which is seized by given preparation. Drifts

and sublevel drifts have lowarched profile, width 4 m and height 3.5 m and they

are adopted to the used equipment, primarily to the drilling machines, why they

have relatively high height.

Selection of this sublevel caving method was a result of its possibility to realize

high productivity, use of modern equipment, but also because many methods

could not be successfully and safety used in caving conditions under of surface

4

7/30/2019 MIN-019-RG-CS

5/16

stope. Possibility of appearance the high stresses in rock and specific caving

conditions of open pit slope have both the influence on method selection and

definition of preparation conditions, stoping method, formation of caving fronts

and others.

Figure 2. Sublevel caving

5

7/30/2019 MIN-019-RG-CS

6/16

Drilling of boreholes is carried out independently of other operations upon

ending of preparation works, often at sublevel located under sublevel where ore

blasting, loading and transport are carried out Drilling is carried out by the use

of SIMBA H 253 rig with outer hammer drill COP 1238 ME - T38E07 and drill bit

f 76 mm.

Technological process of drilling-blasting works is based on the following:

drilling of boreholes in a fan shaped pattern of defined geometry and

parameters of each borehole (Figure 3).

charging of boreholes (machinized) is carried out by the use of AN-FO

explosive mixture, and blasting is carried out per "NONEL" system.

Number of boreholes in a fan is 6 and their length is from 11 m to 24 m. Total

drilling length of one fan is 110 m. Distance between fans is 2.5 m, and only one

fan is blasted.

Transport of explosive and charging of boreholes is carried out by the use of

charger Anol - CC 1000.

Blasting of one fan drops average 1,375 t of ore. Specific explosive

consumption is 0.55 kg/m3. Since the average value of ore volume mass is

about 2.8 t/m3, standard quantity of explosive consumption per ton is

approximately 0.2 kg/t. Burden is 2.50 m, and coefficient of ore dropping at one

blasting is 12.5 t/m3 (relation between quantity of dropped ore and total

borehole length of one fan).

Upon ending of ore blasting in caving block, the blasted ore is gravitationally

transported at a level of loading drift where, by the use of loading machines with

diesel drive "WAGNER ST GC", it is loaded and transported to the ore shafts

("P2A"), or it is transported at k 16 m of the ore body "Tilva Ros", where it is

reloaded over ramps of bulk material, directly into trains of 20 "OK" waggons.

6

7/30/2019 MIN-019-RG-CS

7/16

Ore is transported to the haulage shaft by the trains, where upon crushing, it is

hoisted on the surface.

Annual capacity of ore production is up to 1 million tons in the ore body "P2A",

and it is up to 0.5 million tons in the ore body "Tilva Ros".

Figure 3. Fan shaped pattern of longholes (sublevel caving)

MODIFIED SUBLEVEL CAVING METHOD

Methods of sublevel caving the overhand rock masses were adopted, as the

only possible techno-economically acceptable alternative for mining the ore

body "Borska Reka". The authors of this work was directed by this choice to the

selection of "Super scale sublevel caving", i.e. variant of sublevel caving by the

use of long boreholes, diameter 115 mm.

The greatest importance in determination the basic sizes of mining unit in

sublevel caving methods has a height of mining belt, which depends on

possibility of drilling the long boreholes. Also, width of drifts and distance

between them are important, what has an importance on possibility of obtaining

a distinct parallel arrangement of boreholes in fan. Mutual distance between

7

7/30/2019 MIN-019-RG-CS

8/16

drifts was also caused by conditions of blasted ore running out, i.e. width of run

out ellipsoid. Basic mining unit in the ore body "Borska Reka" includes drifts and

sublevel drifts. Distance between drifts will be 18 m with chess order per height

(Figure 4).

Figure 4. Super scale sublevel caving

Height distance between sublevels is 30 m. Preparation coefficient is

considerably minor than in sublevel caving method and it is 1.15 mm/t. Drifts will

have lowarched profile, width 6 m and height 4 m, until sublevel drifts will also

have lowarched profile, width 4 m and height 3.5 m.

8

7/30/2019 MIN-019-RG-CS

9/16

The mining will be started from level k -205 m. Ore will be sized from this caving

level to k -175 m, i.e. in a belt of thickness of 30 m. The other caving levels will

be by 30 m, i.e. at k -235 m, k -265 m and k -295 m.

The existing equipment, used in the existing process of ore mining, will be used

for ore body mining, as well as a new equipment. So, a drill rig with two

branches and hydraulic hammer drills will be used for drifting, loading will be

performed by the use of loaders with diesel engines, drilling of long boreholes in

fans will be performed by the use of drill rig Simba type, until charging of long

boreholes with ANFO explosive mixture will be carried out by the use of charger

with diesel-drive vehicle. Transport level will be located at level k 315 m.

One of the key technological work stages in the ore caving process, by the use

of adopted sublevel caving method, are drilling-blasting works. Control of

blasting process in method of sublevel caving, concretely the method of "Super

scale sublevel caving" will present a serious work, because the final effects of

successful method function will be caused by blasting effects.

Drilling rig SIMBA H 4356 class with outer hammer drill COP 4050 and drill bit

115 mm has been chosen.

Technological process of drilling-blasting works is based on the following:

drilling of boreholes in a fan shaped pattern of defined geometry and

parameters of each borehole (Figure 5);

charging of boreholes is carried out (mechanized) by the use of AN-FOexplosive mixture, and blasting is performed by "NONEL" system.

Number of boreholes in a fan is 8, and their length is 223 m. Distance between

fans is 4 m, and one per one fan is blasted.

One charger Anol-CC 1000 is used for explosive mixture transport to a site and

charging of boreholes.

9

7/30/2019 MIN-019-RG-CS

10/16

Figure 5. Fan shaped pattern of longholes (super scale sublevel caving)

By blasting of one fan, average of 5235 t ore is dropped. Standard quantity of

explosive consumption per ton is approximately 0.288 kg/t. Burden is 4 m, and

coefficient of ore droppage in one blasting is 23.5 t/m.

10

7/30/2019 MIN-019-RG-CS

11/16

Upon ending of ore blasting in a caving block, the blasted ore is gravitationally

transported to a level of caving (loading) drift, where the ore is loaded and

transported to the mine shaft by the use of loading machines with diesel drive

"WAGNER ST 8B".

Annual capacity of production by the use of this sublevel caving method will be

2.4 millions tons.

COMPARATIVE ANALYSIS OF SUBLEVEL CAVING METHODS

For the aim of comparison, the existing sublevel caving method with modified

method, a review of basic parameters of given sublevel caving methods is given

in Tables 1 - 7.

DevelopmentSublevel

caving

Super scale

sublevel

caving

Sublevel height, m 15 30

Axial distance between caving drifts, m 14 18

Surface of cross-section of caving drifts, m212.70

(4mx3.5m)

23.57

(6mx4m)

Surface of cross-section of sublevel drifts, m212.70

(4mx3.5m)

17.47

(5mx3.5m)

Preparation coefficient, mm/t 3.17-3.42 1.15

Table 1. Development parameters of analyzed sublevel caving methods

11

7/30/2019 MIN-019-RG-CS

12/16

Drilling parametersSublevel

caving

Super scale

sublevel

caving

Drilling machine typeSIMBA H 253

2 PCs

SIMBA H4356

2 PCs

Drilling bit diameter, mm 76 115

No. of boreholes in a fan 6 (110 m) 8 (223 m)

Distance between fans, m 2.5 4

Table 2. Drilling parameters of analyzed sublevel caving methods

Blasting parametersSublevel

caving

Super scale

sublevel

caving

Charging machine typeANOL CC

1000 2 PCs.

ANOL CC

1000 1 PCs.

Service vehicle

ATLAS

COPCO DC

90/11 2 PCs.

ATLAS

COPCO DC

90/11 1 PCs.

Explosive type AN-FO J1 AN-FO J1

Explosive quantity in blasting of one fan, kg 323 1507

Quantity of dropped ore per one blasting, t 1540 5235

Specific explosive consumption, kg/t 0.21 0.288

Coefficient of ore dropping (t/m) 12.5 23.5

Blasting system NONEL NONEL

Table 3. Blasting parameters of analyzed sublevel caving methods

12

7/30/2019 MIN-019-RG-CS

13/16

Parameters of ore loading and transportSublevel

caving

Super scale

sublevel

caving

Loader typeWagner ST

6C 6 PCs

Wagner ST

8B 4 PCs

Average transport length, m 150 200

Table 4. Parameters of ore loading and transport of analyzed sublevel caving

Methods

Parameters of labourSublevel

caving

Super scalesublevel

caving

No. of workers 62 41

Supervision 5 5

Caving efficiency, t/shift 75 174

Table 5. Parameters of labour in analyzed sublevel caving methods

Ore productionSublevel

caving

Super scale

sublevel

caving

Annual ore production, mt 1.5 2.4

Annual copper production in ore, t 10800 17280

Ore recovery, % 85 88-90

Ore quality dilution, % 15 12

Table 6. Ore production from analyzed sublevel caving methods

13

7/30/2019 MIN-019-RG-CS

14/16

Standard quantitiesSublevel

caving

Super scale

sublevel

caving

Explosive - ANFO J1, kg/t 0.21 0.288

NON-EL detonators, pcs/t 0.0039 0.0015

Amplifiers, pcs/t 0.0039 0.0015

Starting segment, pcs/t 0.0008 0.0004

Drill pipes, pcs/t 0.0008 0.0004

Drilling bits, pcs/t 0.0009 0.0005

Industrial water, m3/t 0.036 0.023

Plastic pipe for water and air, m/t 0.0010 0.0005

Hoses for air and water, m/t 0.003 0.002

Ventilation pipes, m/t 0.0007 0.0004

Tires for loader, pcs/t 0.00005 0.00003

Tires for drilling equipment, pcs/t 0.000018 0.000013

Fuel, l/t 0.39 0.28

Oil and lubrication, kg/t 0.04 0.028

Electric energy, kWh/t 0.0713 0.564

Table 7. Standard quantities for analyzed sublevel caving methods

Based on comparative analysis (Tables 1 - 7) it could be seen that the modified

sublevel caving has a range of advantages regarding to the existing sublevel

caving method.

Those advantages are reflected, first of all in considerable lower preparation

coefficient, higher quantity of dropped ore in blasting of one fan and lower

standard quantities, what would enable more economical caving by the of

modified method in the ore body "Borska Reka".

14

7/30/2019 MIN-019-RG-CS

15/16

CONCLUSION

Underground copper ore mining in Bor is greatly carried out by the use of

sublevel caving method. Due to an increase of mining depth low-grade copper

in ore, it is necessary to carry out a modification of the existing mining method

with the aim of satisfactory the economic criteria in caving.

Modification of the existing caving method includes a change of preparation

geometry (increase of height between sublevels from existing 15 m to 30 m,

increase of distance between drifts from 14 m to 18 m, increase of drift-section

from 13.70 m2 to 23.57m2) what decrease a volume of preparation works from

3.17 - 3.42 mm/t to 1.15 mm/t. Also, drilling will be carried out by the use long

boreholes, diameter 115 mm instead of existing 76 mm, what enables an

effective blasting of more higher ore volume.

Supply of new equipment with maximum use of the existing equipment is

required for successful use of modified Super Scale Sublevel Caving Method.

New equipment is necessary for drilling (new SIMBA with accompanied

equipment and drill bits, diameter 115 mm, due to a change of geometry and

drilling and blasting parameters) and for ore loading and transport (loaders

Wagner ST 8B). The other existing equipment could be applied in use of

modified method.

By the use of modified sublevel caving method, the standard quantities of

caving (Table 7) are considerably reduced, what makes possible the conditions

for economical caving, especially at higher depths and, in this way, a continuityof underground copper ore mining is provided in the Bor deposit.

15

7/30/2019 MIN-019-RG-CS

16/16

LITERATURE

1. H. Hamrin; Guide to underground mining-methods and applications, (1986),

Atlas Copco, Stockholm, Sweden, p.27-29.

2. D.Nenadic, D.Bojovic, R. Kojdic, Z. Milicevic; Development strategy in

mining in RTB Bor Holding, XXVII October Conference, (1995), Conference

Journal , p. 1-10.

3. S.O. Olofsson, Applied explosives technology for construction and mining,

(1988), APPLEX, Arla Sweden.

4. Documents of Mining Department in Copper Institute Bor, (1999).

16