Block Caving Method, Mining, This is a case of block caving, where you can find infomation about this method of specif min, this extract is of a mining book
430 TABLE 52.7 Mining production costs Cost element Ground handling Labour Materials General expenses Working cost, miscellaneous Total Mining production Labour Materials General expenses Working cost, miscellaneous Vehicle maintenance Total Supervision and human resources Control and instrumentation Services Total mining cost Percentage of Cost, US$ (2000) total cost, % 1. 1 0.1 0.1 0.2 1.7 1.0 0.2 0.2 0.1 0.4 2.0 0.8 0.2 1.3 6.0 28 33 13 3.3 22 100 Mining production costs (expressed in year 2000 US dollars) are set out in Table 52. 7. Services include geology, survey, planning, salvage, shaft maintenance, and rock drill shop costs. 52.10 FUTURE PLANS Premier Mine has shown that modern caving methods using relatively widely spaced drawpoints, an advance undercut mining sequence, and LHps for ore extraction can be used to mine kimberlite ore in a cost-effective manner. The challenge posed by having to mine below the sill has been addressed and the mine has been able to meet tonnage and carat targets within budgeted cost in recent years. This has given the Premier Mine and the De Beers Group the confidence to embark on an expansion programme that could result in the establishment of a large cave at a mining depth in excess of 1,000 m, which could extend the life of operations by 17 or more years. The mine is currently engaged in an evaluation of the resource inferred to exist in the pipe below current mining levels. Twelve thousand metres of large-diameter drilling (318 mm) is being used to sample a resource of at least 120 million tonnes of kimberlite ore. A further 17,000 m of core drilling and fine- Panel Caving diamond sampling have been undertaken to delineate the geological model. The evaluation programme is planned to define the mineral resource at the confidence level of at least an indicated resource. The feasibility study being carried out in parallel with the evaluation programme suggests that it should be possible to mine the resource as a block cave at a rate of some 9 million tonnes per annum. The column height of the proposed cave would average 350 m. Total re-engineering of the mine, including development of new shafts and ground handling systems, could lower production costs considerably as a result of the economics of scale and by the judicious use of automation. A new treatment facility will be bui lt. The successful completion of the evaluation programme and feasibility study could lead to approval of the project by May 2001. Sinking a service shaſt to provide rapid access to the proposed production level and ore body could start soon thereafter. Production from the 1082-m level could start in 2005, building up to 9 mi llion tonnes per year by 2009. Re-engineering of the mine and treatment facility will aim at reducing working costs and exploiting the economies of scale as production increases from a current 3 million to 9 million tonnes per year. The skill levels of employees will be enhanced by training to meet the demands of a high-technology mine. The organisational design of the staffing structure will aim at a maximum of four levels of work. The total labour cost will be considerably reduced from the current high levels. 52.11 ACKNOWLEDGMENTS The author would like to thank the general manager of Premier Mine and the De Beers Consolidated Mines geotechnical engineer for permission to publish this paper. The work done by colleagues in preparing diagrams and providing details of the operations as set out in the paper is gratefully acknowledged. 52.12 REFERENCES Bartlett, P.J. 1992. The Design and Operation of a Mechanised Cave at Premier Diamond Mine. MASSMIN 92 SAIMM Publication Sympo- sium Series S12. Bartlett, P.J. 1994. Geology of the Premier Diamond Pipe. Twenty-Fifth CMMI Congress, Johannesburg, SA, SAIMM, H.W. Glen, ed. Vol. 3, pp. 201-213. Bartlett, P.J. 1992. Support in a Mechanised Cave at Premier Mine. MASSMIN 92. SAIMM Publication Symposium Series Sl2. Kirsten, H.A.D., and P.J. Bartlett. 1992. Rigorously Determined Support Characteristics and Support-Design Method for Tunnels Subject to Squeezing Conditions. SMM, Vol. 92, No. 7. CHAPTER 53 Block Caving the EESS Deposit at P. T Freeport Indonesia John Barber,* Suyono Dirdjosuwondo,* Tim Casten,* and Leon Thomas* 53.1 I NTRODUCTION PT Freeport Indonesia operates a copper and gold mmmg complex in the Ertsberg Mining District in the province of Irian Jaya, Indonesia (Figure 53.1) . The Ertsberg district is located in the Sudirman Mountains at elevations from 3,000 to 4,500 m above sea level. The topography is extremely rugged. Rainfall in the mine area averages 3,000 mm per year. Freeport began production in the district in 1972 when the mill began processing ore from the Ertsberg open pit. Underground mining began in 1980 when the GBT (Gunung Bijih Timur-Ertsberg East) was brought on line using block caving methods. The GBT reached a maximum production rate of 28,000 tonne/d in 1991 and was exhausted in 1994. The Intermediate Ore Zone (IOZ) was brought into production in 1994, also using block caving methods, with a design rate of 10,000 tonne/d. The IOZ is currently producing at a rate of 18,500 tonne/d. The Deep Ore Zone (DOZ) was discovered in the mid-1980s by deep drilling from the GBT. Portions of the DOZ were mined using open stoping methods from 1989 to 1992. In 1993, the first of several studies was completed indicating that portions of the DOZ could be successfully and economically mined using block caving methods. The DOZ is currently being developed and is scheduled to begin production in the second half of 2000. The DOZ is planned to produce 25,000 tonne/d of ore. A study is currently underway to determine if an ultimate production rate of 35,000 tonne/d is feasible. The GBT, IOZ, and DOZ mines are stacked vertically on the Ertsberg East Skarn System (EESS) . The EESS is open to depth and along strike (Figure 53.2) . The DOZ ore body is situated in the lower portion of the EESS. 53.2 GEOLOGY AND ORE RESERVES 53.2.1 Geology The EESS is hosted by Tertiary-age carbonates that have been altered to calcium-magnesium silicate skarn. The EESS is an essentially vertical tabular body with a vertical extent i excess of 1,200 m, a strike length of over 1,000 m, and an average width of 200 m. The northeast (hanging wall) contact of the EESS is a skarn reaction ont in sudden contact with barren marble. This contact coincides with a zone of localized faulting and brecciation. The EESS is bounded to the southwest (footwall) by the Ertsberg Diorite intrusive. The GBT ore bodies are dominated by calcium-magnesium skarn, such as monticellite and garnet. The GBT copper skarn ore bodies include magnetite and retrograde alteration, such as chlorite. The IOZ ore bodies are dominated by magnesium-calcium skarn, such as forsterite and diopside. The IOZ ore bodies include * PT Freeport Indonesia. 431 O TAIWAN �Km PA CIFIC OCEAN FIJI0 0 OUTH PA CIFIC OEAN FIGURE 53.1 Ertsberg Mining District location map magnetite and retrograde alteration, such as talc, serpentine, tremolite-actinolite, and chlorite. Moving across the strike of the EESS from the footwall to the hanging wall, the specific rock units encountered in the EESS are- • Ertsberg diorite. Generally a hard, competent rock unit with good ground conditions. Proximal to the skarn con- tact, the diorite has been locally altered and mineralized. • Forsterite skarn. A massive unit adjacent to the Ertsberg Diorite contact, averaging O.S copper. Generally a hard, competent rock unit with good ground conditions. • Magnetite-forsterite skarn. Grades vary between O.S to 2.0% copper. Often finely bedded. Generally a hard, competent rock unit with good ground conditions, but with localized zones exhibiting poor ground conditions • Massive magnetite. Occurs mainly along the marble con- tact. Often strongly bedded. High-grade ore with grades ranging from 2% to 10% copper. Generally a hard, com- petent rock unit with good ground conditions, but with localized zones exhibiting poor ground conditions. • BAS breccia. A contact breccia in the GBT and IOZ deposits that tends toward high copper grades (>3%) and very poor ground conditions. • DOZ breccia. A lenticular zone that plunges westerly across the lower half of the DOZ, cross cutting all other
Transcript
430
TABLE 52.7 Mining production costs
Cost element
Ground handling
Labour
Materials
General expenses
Working cost, miscellaneous
Total
Mining production
Labour
Materials
General expenses
Working cost, miscellaneous
Vehicle maintenance
Total
Supervision and human resources
Control and instrumentation
Services
Total mining cost
Percentage of
Cost, US$ (2000) total cost, %
1 . 1
0.1
0.1
0.2
1 . 7
1 .0
0.2
0.2
0.1
0.4
2.0
0.8
0.2
1.3
6.0
28
33
13
3.3
22
100
Mining production costs (expressed in year 2000 US dollars) are set out in Table 52. 7. Services include geology, survey, planning, salvage, shaft maintenance, and rock drill shop costs.
52.10 FUTURE PLANS Premier Mine has shown that modern caving methods using relatively widely spaced drawpoints, an advance undercut mining sequence, and LHps for ore extraction can be used to mine kimberlite ore in a cost-effective manner. The challenge posed by having to mine below the sill has been addressed and the mine has been able to meet tonnage and carat targets within budgeted cost in recent years. This has given the Premier Mine and the De Beers Group the confidence to embark on an expansion programme that could result in the establishment of a large cave at a mining depth in excess of 1,000 m, which could extend the life of operations by 17 or more years.
The mine is currently engaged in an evaluation of the resource inferred to exist in the pipe below current mining levels. Twelve thousand metres of large-diameter drilling (318 mm) is being used to sample a resource of at least 120 million tonnes of kimberlite ore. A further 17,000 m of core drilling and fine-
Panel Caving
diamond sampling have been undertaken to delineate the geological model. The evaluation programme is planned to define the mineral resource at the confidence level of at least an indicated resource.
The feasibility study being carried out in parallel with the evaluation programme suggests that it should be possible to mine the resource as a block cave at a rate of some 9 million tonnes per annum. The column height of the proposed cave would average 350 m. Total re-engineering of the mine, including development of new shafts and ground handling systems, could lower production costs considerably as a result of the economics of scale and by the judicious use of automation. A new treatment facility will be built.
The successful completion of the evaluation programme and feasibility study could lead to approval of the project by May 2001. Sinking a service shaft to provide rapid access to the proposed production level and ore body could start soon thereafter. Production from the 1082-m level could start in 2005, building up to 9 million tonnes per year by 2009. Re-engineering of the mine and treatment facility will aim at reducing working costs and exploiting the economies of scale as production increases from a current 3 million to 9 million tonnes per year. The skill levels of employees will be enhanced by training to meet the demands of a high-technology mine. The organisational design of the staffing structure will aim at a maximum of four levels of work. The total labour cost will be considerably reduced from the current high levels.
52.11 ACKNOWLEDGM ENTS
The author would like to thank the general manager of Premier Mine and the De Beers Consolidated Mines geotechnical engineer for permission to publish this paper. The work done by colleagues in preparing diagrams and providing details of the operations as set out in the paper is gratefully acknowledged.
52.12 REFERENCES Bartlett, P.J. 1992. The Design and Operation of a Mechanised Cave at
Premier Diamond Mine. MASSMIN 92 SAIMM Publication Symposium Series S 12.
Bartlett, P.J. 1994. Geology of the Premier Diamond Pipe. Twenty-Fifth CMMI Congress, Johannesburg, SA, SAIMM, H.W. Glen, ed. Vol. 3, pp. 201-213.
Bartlett, P.J. 1992. Support in a Mechanised Cave at Premier Mine. MASSMIN 92. SAIMM Publication Symposium Series Sl2.
Kirsten, H.A.D., and P.J. Bartlett. 1992. Rigorously Determined Support Characteristics and Support-Design Method for Tunnels Subject to Squeezing Conditions. SAIMM, Vol. 92, No. 7.
CHAPTER 53
Block Caving the EESS Deposit at P. T. Freeport Indonesia
John Barber,* Suyono Dirdjosuwondo, * Tim Casten, * and Leon Thomas*
53.1 I NTRODUCTION
PT Freeport Indonesia operates a copper and gold mmmg complex in the Ertsberg Mining District in the province of Irian Jaya, Indonesia (Figure 53 .1) . The Ertsberg district is located in the Sudirman Mountains at elevations from 3,000 to 4,500 m above sea level. The topography is extremely rugged. Rainfall in the mine area averages 3,000 mm per year.
Freeport began production in the district in 1972 when the mill began processing ore from the Ertsberg open pit. Underground mining began in 1980 when the GBT (Gunung Bijih Timur-Ertsberg East) was brought on line using block caving methods. The GBT reached a maximum production rate of 28,000 tonne/d in 1991 and was exhausted in 1994.
The Intermediate Ore Zone (IOZ) was brought into production in 1994, also using block caving methods, with a design rate of 10,000 tonne/d. The IOZ is currently producing at a rate of 18,500 tonne/d.
The Deep Ore Zone (DOZ) was discovered in the mid-1980s by deep drilling from the GBT. Portions of the DOZ were mined using open stoping methods from 1989 to 1992. In 1993, the first of several studies was completed indicating that portions of the DOZ could be successfully and economically mined using block caving methods. The DOZ is currently being developed and is scheduled to begin production in the second half of 2000. The DOZ is planned to produce 25,000 tonne/d of ore. A study is currently underway to determine if an ultimate production rate of 35,000 tonne/d is feasible.
The GBT, IOZ, and DOZ mines are stacked vertically on the Ertsberg East Skarn System (EESS) . The EESS is open to depth and along strike (Figure 53.2) . The DOZ ore body is situated in the lower portion of the EESS.
53.2 GEOLOGY AND ORE RESERVES
53.2.1 Geology
The EESS is hosted by Tertiary-age carbonates that have been altered to calcium-magnesium silicate skarn. The EESS is an essentially vertical tabular body with a vertical extent iri excess of 1,200 m, a strike length of over 1,000 m, and an average width of 200 m. The northeast (hanging wall) contact of the EESS is a skarn reaction front in sudden contact with barren marble. This contact coincides with a zone of localized faulting and brecciation. The EESS is bounded to the southwest (footwall) by the Ertsberg Diorite intrusive.
The GBT ore bodies are dominated by calcium-magnesium skarn, such as monticellite and garnet. The GBT copper skarn ore bodies include magnetite and retrograde alteration, such as chlorite.
The IOZ ore bodies are dominated by magnesium-calcium skarn, such as forsterite and diopside. The IOZ ore bodies include
* PT Freeport Indonesia.
431
O TAIWAN
�Km
PACIFIC OCEAN
FIJ I 0 0
OUTH PACIFIC O"CEAN
FIGURE 53.1. Ertsberg Mining District location map
magnetite and retrograde alteration, such as talc, serpentine, tremolite-actinolite, and chlorite.
Moving across the strike of the EESS from the footwall to the hanging wall, the specific rock units encountered in the EESS are-
• Ertsberg diorite. Generally a hard, competent rock unit with good ground conditions. Proximal to the skarn contact, the diorite has been locally altered and mineralized.
• Forsterite skarn. A massive unit adjacent to the Ertsberg Diorite contact, averaging O.So/o copper. Generally a hard, competent rock unit with good ground conditions.
• Magnetite-forsterite skarn. Grades vary between O.So/o to 2.0% copper. Often finely bedded. Generally a hard, competent rock unit with good ground conditions, but with localized zones exhibiting poor ground conditions
• Massive magnetite. Occurs mainly along the marble contact. Often strongly bedded. High-grade ore with grades ranging from 2% to 10% copper. Generally a hard, competent rock unit with good ground conditions, but with localized zones exhibiting poor ground conditions.
• BAS breccia. A contact breccia in the GBT and IOZ deposits that tends toward high copper grades (>3%) and very poor ground conditions.
• DOZ breccia. A lenticular zone that plunges westerly across the lower half of the DOZ, cross cutting all other
432
J600 car ACMT
1,1�! Level .l.dtt {IJLA)
ERTSBERG EAST SKARN SYSTEM.
SECTION LOOKING NORTH - EAST
,,, 1 3 1 t.I. I.I){;X Cu 0.8t PPioi A.U 7.4.9 PPI.I .I.G 1.66� Cu EOU-V
FIGURE 53.3 Geological plan of DOZ extraction level
units. Ore grades tend to be >2o/o copper and locally are greater than 4o/o copper. Almost without exception, ground conditions in this unit are very poor with a history of failure.
• Dolomite-marble. Alteration extends 250 to 300 m from the skarn into the hanging wall and is generally barren of mineralization. Rock quality and ground conditions are highly variable and locally very poor proximal to the skarn-marble contact. Ground conditions in the marble contact zone deteriorate with depth.
Figure 53 .3 shows a geological plan of the DOZ extraction level at 3,136 m.
Panel Caving
53.2.2 Ore Reserves
Ore reserves on the EESS have increased since 1980. This is partially due to increased geologic information and partially to economies of scale made possible by the increased throughput of the mill. Total GBT production was 59 .1 million tonnes at 1. 99o/o copper and 0 .67 ppm gold.
IOZ reserves (diluted) in 1994 were 21 million tonnes at l.SSo/o copper and 0.54 ppm gold. These were calculated at a cutoff grade of 0.98% copper. The IOZ production rate was calculated at 10,000 tonne/d to feed the concentrator operating at 60,000 tonne/d. During the fourth concentrator expansion project, economies of scale in the concentrator, open pit mines, and underground mining allowed P.T. Freeport Indonesia to reduce the cut-off grade at the IOZ to 0.90% copper equivalent. The copper equivalent calculations take into account copper grade, gold grade, silver grade, differences in metallurgical recovery, royalties, treatment charges, royalty charges, and overhead costs. The new expanded IOZ reserves were increased to 43 .55 million tonnes at 1.23o/o copper, 0.49 ppm gold, and 7.7 ppm silver at a cut-off grade of 0.90o/o copper equivalent. Production was increased from 10,000 to 18,000 tonne/d. The majority of the increased IOZ reserves are located in the footwall of the deposit in the forsterite skarn and mineralized diorite.
Current reserves (diluted) for the DOZ block cave ore body are 131 million tonnes grading 1.06% copper, 0.81 gm/tonne gold, and 7.49 gm/tonne silver, or 1 .66% copper equivalent, utilizing a cut-off grade of 0.90% copper equivalent.
53.2.3 Hydrogeology
The underground mines have a history of wet muck runs in the production areas. The problem first became serious in the IOZ production area. Wet muck runs as large as 2,000 m3 have occurred from individual drawpoints. These runs are a serious safety hazard and impediment to production.
Water enters the cave through rain, surface drainage, and groundwater. The water moves down through the cave and creates saturated conditions in the drawbells, which leads to the wet muck runs.
Two main sources of groundwater that must be intercepted have been identified.
:1.. Hanging wall water is impounded behind a sandstone aquaclude (Sirga Sandstone) . As the cave cracks intercept the sandstone, the impounded water flows into the cave. The impoundment is continually recharged by rainwater from the surface (Figure 53.4) .
2. Long-strike water flows into the cave along contacts and relict bedding in the skarn formations and along the skarn-diorite contacts. Some of the long strike water is perched water and some is recharge from the surface.
This situation is complicated by a series of high-angle crossstrike faults that provide some communication between the water sources and the cave. The model is further complicated by a number of karst features in the hanging wall.
Dewatering strategy is based on draining impounded water from behind the Sirga Sandstone so that the phreatic surface falls below the elevation at which the cave cracks intercept the sandstone. This will be accomplished by means of a drill gallery developed in the hanging wall outside the predicted ultimate crack line of the DOZ cave. Diamond drilling from the gallery will pierce the Sirga, allowing the impounded water to drain off through the drill holes. Continuous flows from the Sirga drainage drilling are predicted to be on the order of 315 L/s.
Long-strike water will be intercepted outside the predicted ultimate DOZ cave crack system by drilling from development in the hanging wall and footwall parallel to strike. The long-strike development will be on a number of different levels, utilizing existing workings as jumping off points. This method has been
Block Caving the EESS Deposit at P.T. Freeport Indonesia
successfully used in other areas of the EESS. Continuous flows from the long-strike drilling are also predicted to be on the order of 315 L/s.
53.2.4 Geophysical
Geophysical engineering and planning are based on diamonddrill holes, and on geological, scanline, and cell mapping of the workings. Until 1994, most drill holes were logged for rock quality designation (RQD) only; since then all drill holes have been logged for fracture frequency and rock mass rating (RMR) analysis.
Almost without exception, ground conditions in the EESS vary from very poor to very good as you proceed from hanging wall to footwall. Uniaxial compressive strength varies from a high of 219 MPa in some massive magnetite to less than 10 MPa in the DOZ breccia. RMR varies from a low of 25 in the poorest areas to a high of 65 in the most competent ground.
Cavability of these deposits was evaluated using a combination of RQD, RMR, and mining rock mass rating (MRMR) data. All cavability and fragmentation studies have been reviewed by outside geotechnical consultants. The hydraulic radius needed to sustain the cave ranges from a low of 10 m in the areas of poor ground to 30 m in the forsterite skarn. Footprints in the IOZ and DOZ have been in excess of the required hydraulic radius, so cave propagation has not been a problem in IOZ and will not be a problem in the DOZ.
Fragment size at the drawpoints has never been a problem in the IOZ until recently. Draw heights in the IOZ expanded reserve area are now reaching the elevation of the GBT mine. This is the footwall area of the GBT, where most of the
433
permanent facilities (shops, lunchroom, supply room, service facilities) were located.
As draw heights reached the GBT elevations, particle size at the IOZ drawpoints suddenly and unexpectedly increased. We think that as the cave front passes through the large pillars that protected the GBT facilities, the rock is not fragmenting on geological and geophysical controls, but rather the pillars are detaching from the intact ground and entering the cave as much larger masses. Comminution in the cave is not enough to reduce the large masses to manageable size before they reach the IOZ drawpoints.
For the DOZ mine, fragmentation s.tudies predict that less than 30o/o of the ore body will exceed 1 m. Comminution within the draw column will further reduce the material size reporting to the drawpoints. We will apply the lessons learned in the IOZ to ensure that the IOZ pillars over the DOZ draw columns will be weakened or destroyed before abandoning the IOZ workings.
53.3 M I N I N G METHOD
The mining method chosen for the IOZ, and later the DOZ mine, is mechanized block caving. The basic method is similar to the method successfully developed at the GBT mine .
The initial mining method used at the GBT, Area I, was block caving using slusher panels and rail haulage. Management soon realized that fragmentation was too coarse for this method to be used efficiently. An experimental panel using load-haul-dump (LHD) machines was opened. This proved so successful that all mucking since has been with LHDs.
Development of GBT Area II was started soon after Area I was put into production. Area II was designed using all LHD production and conveyor haulage. This was successful, and the GBT Area II layout and haulage system was used at the IOZ mine .
53.3.1 General Description, IOZ Mine
The IOZ mine footprint, expanded reserve, is 350 m long and 250 m across strike. Maximum draw height is 200 m. The draw columns have intercepted the production levels of GBT Area I and II .
Undercutting began in the northwest corner of the deposit, taking advantage of the weak, high-grade BAS. Cave propagation was sustained after a hydraulic radius of 10 m was achieved.
53.3.2 Extraction Level Design, IOZ
The extraction level of the IOZ mine is shown in Figure 53 .5 . Panels are transverse to the strike of the ore body on 30-m centers. Drawpoints are on 17.3-m centers. All mucking is done to the grizzly and rock breaker stations on the north and south fringe of the ore body (Figure 53 .6) .
Drawpoint Layout. Drawpoint layout has changed since the IOZ was first developed. The initial layout was the "El Teniente"-style layout. This was easy during the development of the mine, but created difficulties when the area entered production. The primary objection to the El Teniente layout is that mucker operators are forced to choose between a long (200-m) tram with the bucket behind the LHD and a shorter tram with loaded bucket in front of the operator. At times this has created difficulties with control of the draw.
A second objection to this layout is that a worker in one drawpoint is directly exposed to unanticipated muck slides from the drawpoint directly across the panel. This problem did not become apparent until the IOZ began experiencing severe wet muck problems.
We changed the drawpoint layout to an offset herringbone when the additional reserves were added. This eliminated the need to tram a loaded bucket ahead and provides a degree of protection to workers in a drawpoint from unanticipated slides in opposite drawpoints.
FIGURE 53.6 Typical panel layouts, IOZ and DOZ mines
Drawpoint Support. Drawpoint and panel support is a combination of mass concrete and cable bolts (Figures 53.7 and 53.8) . The IOZ support system was designed using empirical methods based on support used at the GBT. This method has been moderately successful. The success of such a system is highly dependent on the quality of the concrete used, which, in turn, requires that full-time quality assurance and control people be assigned to the work.
53.3.3 Panel Ventilation, IOZ
At the GBT and IOZ mines, fresh air is delivered at the south fringe and exhausted from the north fringe. This is illustrated in Figure 53.6 . The older method means that anyone working on the north side of the mine is always working in exhaust air, and that it is almost impossible to provide enough ventilation to operate two muckers in a single panel. This method was acceptable when using slushers and rail haulage, but was found to be inadequate when using diesel-powered LHDs.
H . . . .
DRAWPOINT ENTRY EXCAV'N !.: CONCR�;n;
IOZ 3456/L
Panel Caving
FIGURE 53.7 Concrete support in IOZ mine
Section B - B ------------------
Section C - C F1an View Section 0 - 0 3474/L-3456/L !OZ
PANEL AND DRAWPOINT CABLE GROUTING
FIGURE 53.8 Cable bolt support in IOZ mine
53.3.4 Haulage System, IOZ
The haulage system used at GBT and IOZ consists of a pocket under each grizzly on the north and south fringes of the ore body (Figure 53 .6) . Grizzly size is usually set at 500 mm, but the grizzly panels can be changed if desired. Pocket capacity is 400 tonnes.
Each pocket discharges on to a 60-in coarse ore conveyor, which dumps into a 1,067- by 1,219-mm jaw crusher. There is a crusher on the north side and one on the south side of the ore body (Figure 53.9) . Both crushers discharge on to a 48-in conveyor that delivers the ore to an ore pass in the footwall diorite. At the bottom of the ore pass, a hydraulic apron feeder directs ore onto a system of conveyor belts that deliver the ore to the surface and the mill stockpiles. Figure 53 .10 is a cross section of the IOZ mine and clearly shows the relationship of the conveyor system to the extraction level.
53.3.5 Undercutting, IOZ
The undercut level is 18 m above the extraction level. Drill drifts are situated directly over the panel drifts.
After the drill drifts are developed, the major apex pillar is supported with cable bolts. Figure 53.8 shows the bolt pattern used. As with the panel concrete, this method requires a full-time quality control presence while the holes are drilled and the cables installed and grouted.
Block Caving the EESS Deposit at P.T. Freeport Indonesia
Drawbell blasting at the IOZ precedes undercut blasting. The drawbell drill pattern is shown in Figure 53 .11 . After the drawbell is drilled, it is blasted in three stages.
3. Load blast 1 and preload blast 2. Blast the center of the pyramid. Muck out.
4. Preload blast 3. Blast the pyramid to full height. Muck out.
5. Blast the remainder of the draw bell. Undercut blasting follows the drawbell blast. The typical
undercut drill pattern is shown in Figure 53 .12. Drill patterns A and B are drilled over the drawbell and side walls of the drawbells. Pattern C is drilled over the minor apex between drawbells. Ring burden varies from 2 to 3 m and is adjusted to suit ground conditions.
Undercut rings are not blasted until swell muck has been pulled from the drawpoints, so that the ring is blasted into a lo�se muck pile, if not an open void. Rings are normally loaded wtth
.,. I � ! l _[_
Pnnel li7
OrawbeH Section A - A'
-'--=�::-�--�-r-��r:_: __
·-.. ,����l!I�Jl '\';: ·:; '!>''
Row t5 (83')
DRAW BELL PATIERN FOR BLAST HOLE P f 7 - P 18- 345611
FIGURE 53.11 Typical drawbell drilling pattern
435
Aowlt4 {72')
o i �i l
· · ---------- ·-·-···----- .,-
U ndercut Dri l l ing Pattern C
FIGURE 53.12 Typical undercut drill patterns
gl �j
! �� ·l
436
ANFO and a collar is left to mimmize brow damage on the under�ut level. It is occasionally necessary to repair the brow before the next rings are loaded and blasted. This is usually done with timber sets.
53.3.6 Wet Muck Operations, IOZ
The wet muck situation in the GBT was less severe than in the IOZ for a number of reasons.
• The GBT draw columns were shorter than those in the IOZ, resulting in less comminution in the draw columns. This resulted in coarser muck reporting to the drawpoints. Since coarse muck is more difficult to liquefy, there were not as many problems with wet muck runs.
• The GBT production levels are 150 to 200 m above the IOZ production level. The reduced depth results in reduced hydrostatic pressure, which results in lower water inflows into the cave.
• Production level geometry in the IOZ is different than in the GBT. The GBT used a "trench" undercut system. The trench was at the extraction level and connected all the drawpoints. This meant that water in the cave could not concentrate in a single drawpoint, but was distributed through all the drawpoints along the full length of the trench. The IOZ uses discrete drawbells that tend to concentrate water in a single draw bell. After the draw bell becomes saturated, the water spills over the minor apex into the adjacent drawbell.
• The IOZ is located directly below portions of the GBT. IOZ draw columns have broken into the GBT cave. The cut-off grade for the GBT was much higher than the IOZ (1.0% copper versus 0.90% copper equivalent), hence much of the "dilution" from the GBT cave is now classified as ore. As a result, production mucking continues long after most IOZ drawpoints are theoretically exhausted. In some instances, IOZ drawpoints have produced 175% of reserve tonnage. The GBT muck, saturated and drawn through an additional 150 to 200 m of draw column, is extremely fine grained when it reports to the IOZ drawpoints. The very fine muck is much more easily liquefied than the coarse muck from the GBT.
When the wet muck situation first appeared in the IOZ, operational controls were instituted that relied on rigid mucking schedules and close supervision. Conventional mucking equipment was used. This was not safe enough to meet the requirements of Free port Indonesia or of government authorities.
As soon as it became apparent that the wet muck situation in the IOZ was more serious than in the GBT, outside hydrology and rock mechanics consultants were commissioned to determine the causes of the problem and recommend solutions. They have developed recommendations for the dewatering situations discussed above and for operating practices to help control the problem.
Mine management decided that the safest method to adapt was a remote-control system that would completely remove the operator from any danger. Because it would take some time to develop, install, and commission a complete remote-control system, we elected to use an interim method for wet muck operations. The interim method required the use of specially built closed (armored) cab muckers. These machines were built in our shops to provide heavy steel protection for the operators while pulling wet muck. The "closed-cab" muckers were used to pull coarse wet muck in certain areas of the production panels. Some areas were deemed too dangerous to pull even with the closed-cab machines and were shut down until remotecontrolled equipment became available. The closed-cab
Panel Caving
machines are still used on isolated, coarse wet muck drawpoints and for cleaning up after a wet muck run.
The ultimate solution to safely pulling wet muck has been tele-remote operations. This system has been developed in stages since 1997. The muckers are equipped with video cameras and remote-control electronics and controls. The operator runs the machine from a console located in a special room near the lunchroom on the south fringe of the mine area. The rock breakers on the north fringe (wet area) of the IOZ are also equipped with remote controls. All areas under remotecontrolled operations are barricaded so that pedestrians cannot enter without stopping operations.
Remote-controlled operations give the IOZ mine the ability to safely pull wet muck, but at a price. Remote mucking is only about 75% as productive as manually operated mucking. Because of damage incurred by the remote muckers when they are involved in wet muck runs, availability of remote-controlled muckers is only 60% to 65%, compared to 80% for manually operated machines.
To minimize the problems of dealing with wet muck in the DOZ mine, an extensive dewatering program is underway. This will reduce the amount of wet muck reporting to the drawpoints in the DOZ.
53.3. 7 Cave Management
Original System. The cave management-draw control system used at the IOZ was developed at the GBT. Paper draw orders were issued twice a week to the production superintendent. The draw order told the operations supervisor how many buckets of muck to pull from each individual drawpoint on each shift. The shift supervisors issued the paper draw sheets to the mucker operators. The operators were to pull the muck as ordered and record the number of buckets from each drawpoint. It was the responsibility of the supervisors to correct the shift draw orders to account for hung-up drawpoints, panel repair, or other operations problems.
The primary method of checking the accuracy of the reports was reconciliation against belt scale tonnage reports. This allowed a good check of the total bucket count, but did not help check against the drawpoint report. Spot checks and field bucket counts showed that draw report accuracy was not good.
The production reporting and recording system was primarily a manual system utilizing spreadsheets to manage the data. This was labor intensive and prone to errors during data manipulation and transfer.
The difficulties with field reporting and office data manipulation prompted a review of available technology. As a result, major modifications have been made to the cave management-draw control systems.
Current System. Improvements to the cave management system have been made in two areas.
• Automation of data management • Dispatch system Improvements to the data management system have been
based on the development of a database, called Ubase, to manage all drawpoint data on a single platform. The database contains information on each drawpoint about daily draw order, actual reported draw, sampling data for copper and gold, drawpoint status, drawpoint condition, wet muck status, and initial drawpoint reserve. Ubase also records shift and daily production data and conveyor belt weightometer data.
Data are input only once, and the laboratory directly reports assay results over the Internet. These procedures minimize transposition errors. All daily, weekly, and monthly reports are generated from Ubase. Drawpoint history reports are much more readily run, which makes it much easier for the cave management
Block Caving the EESS Deposit at P.T. Freeport I ndonesia
engineers to analyze drawpoint grade trends, hang-up frequencies, etc. . . . A dispatch system from Modular Minmg was comm1ss
_wned
in December 1999. The system provides real-time reportmg of mucking activity to the dispatcher and allows the dispatcher to give draw orders to the mucker operators. The dispatcher can react to changing conditions in the productiOn area (hang-ups, closed grizzlies, equipment, etc.) and issue changes to draw orders as needed.
We have already seen improvements in the accuracy of production reports from the field and in compliance with draw orders. Direct data transfer from the dispatch database to Ubase has reduced data processing time and transposi�ion e�rors and given us the ability to update draw �r��rs on � dmly basis.
The dispatch system was Imtially mstalled to_
track production muckers only, but it is now being ex�anded �o mclude jumbos for secondary blastin� and
_other service eqmp
_ment m
production areas. The DOZ mme will have the system mstalled and operating when undercutting commences.
53.3.8 General Description, DOZ Mine
The production (extraction) level of the DOZ will ultimately be 900 m long and average more than 200 m wide, with the w�dest location being 350 m wide. The maximum height of draw will be 350 m. Production panels will be transverse to the ore body on 30-m centers. The undercut level will be 20 m above the extraction level. Drawpoints will be on 18-m centers along the panel drifts, yielding a draw column footprint of 15 by 18 m.
Undercutting will begin in the center of the ore body and progress eastward. This takes advantage of the extremely
_ weak
ground conditions and the higher-than-average grades m the DOZ breccia. After the IOZ has been depleted, undercutting in the DOZ will be advanced westward, underneath the IOZ.
53.3.9 Extraction Level Design
Extraction level design of the DOZ mine departs from previous Freeport Indonesia block caves (Figu�e 53.6). . .
Drawpoint Layout. Drawpomt layout IS hernngbone style. This was chosen because it allows us to use central muck raises, which is a major change from the IOZ and, GBT where grizzlies were located between pa�els at the
_north and south
fringe drift outside the ore body. This ch_ang� will reduce average
tramming distance by 40 m and mamtam preferred �uck�r orientation for most drawpoints. Right and left drawpomts m each panel are staggered to minimize open spans and to reduce exposure of workers in a drawpoint to muck slides from opposite drawpoints. .
Drawpoint Excavation and Support. Dra.v:rpo�nts . are excavated with long-term ground support and stab1l�ty
_m m�nd.
Each round is line drilled and trim blasted to mmimize pillar damage. After each round is advanced, the heading receives 125 mm of shotcrete as primary ground support before the heading is advanced another round. After the drav:rpoint has b�en excavated one round beyond the design lmtel locatiOn, permanent ground support (3.5-m-lon� groute
_d re?ar an
_d
monolithic concrete) is installed. This IS the first time this procedure has been used at Freeport Indonesia; we are pleased with the results and have started using it in other areas that previously would have been supported with timber or steel sets.
53.3.10 Panel Ventilation
The panel ventilation system implemented at DOZ i� designed �o that all personnel working in a panel will be . m fresh air. Ventilation in the panels is by means of fresh air delivered by both the north and south fringe drifts and exhausted through exhaust raises in the center of each panel. The exhaust raises discharge on a dedicated exhaust gallery that leads directly to the exhaust
437
UNDERCUT
11 sro 20, �.1 GRIZZLY l l I PANEL N�� 11:
---FRESH AIR I 1 �"'"" 'I'·
<0-50M GALLERY
L .,.----' '-n TRUCK HAULAGE
FIGURE 53.13 Typical cross section, DOZ mme
FIGURE 53.14 Truck haulage level
----FRESH AIR
mains (Figure 53.13). This means that two muckers can operate at the same time in a single panel, each in its own split of air.
53.3.11 Haulage System
The haulage system built for the DOZ mine is a major departure from the haulage systems used at the GBT and IOZ mines. The system at DOZ uses a combination of trucks and chutes to deliver ore to the crusher. . . Grizzly Muck Handling. Muck from the central gnzzly m each panel is stored in a muck raise 4 m in diameter and 40 to 50 m long. Average raise capacity is 1000 tonnes. All panel muck raises bottom at chutes on the 3076 haulage level. This level is a limited access, one-way, racetrack-type truck loop with a chute for each panel muck raise (Figure 53.14). All roadways will be paved. Fifty-tonne-capacity trucks haul ore from the chutes to the direct dump crusher station. .
Crushing and Conveying. The haul trucks will dump directly into the Fuller-Traylor 1372- by 19
_56-mm gyratory
crusher installed just below the haulage level. Discharge from the crusher falls into a 1800-tonne, live-capacity ore bin. The bottom of the bin is equipped with a Jaques 18.29-cm by �1-m apro� feeder that pulls the crushed ore from the bin and discharges It onto a 15.24-cm, 3,500-tonne/hr conveyor system that delivers the ore to the mill.
System Flexibility. The haulage system as installed at the DOZ is more flexible than the ones installed at IOZ and GBT. Th
_e
new system can be readily expande� or changed t? . smt modifications in the mine plan or discovery of additiOnal reserves. It can also easily support additional production froJ? other areas. A further advantage of the DOZ haulage system IS that it is sufficiently far below the extraction level that it will not be affected by mining-induced stresses and should be usable long after the DOZ is exhausted.
438
53.3.12 Ventilation Systems
The DOZ mine ventilation system includes a number of improvements over the ventilation systems built for the IOZ and GBT mines. All shops, storage facilities, conveyorways, crusher stations, ore dumps, compressor stations, powder magazines, etc., are ventilated from a fresh airway directly to a dedicated exhaust airway. All conveyor transfers and feeder stations are equipped with dust collection hoods and ducts to deliver the dust directly to dedicated exhaust airways. These two changes in design philosophy will result in a major improvement in the quality of the ventilation in the production areas.
The DOZ cave line will destroy the existing main fan installations. To ensure adequate mine ventilation throughout the life of the DOZ and beyond, two new ventilation shafts 800 m deep and 7 m in diameter are being excavated. Each shaft will be equipped with two centrifugal fans of 750 kW each. In addition, existing raises into the idle DOM mine have been converted into exhaust airways and equipped with a 450-kW centrifugal fan.
Overall ventilation of the DOZ is expected to be significantly better than that of the IOZ. Total ventilation throughput of the IOZ is currently 425 m3js for a production rate of 18,000 tonne/d, giving a ventilation rate of 24 m3/ktonne. The DOZ will have throughput of 920 m3/s for a production rate of 25,000 tonne/d, giving a ventilation rate of 37 m3/ktonne.
53.4 SUM MARY Since underground mining began at Freeport Indonesia in 1980, there has been a constant process of modifications and improvements to the mining methods and techniques used. This evolutionary process has resulted in improved safety, efficiency, and economics in the Underground Mines Division. We at
Panel Caving
Freeport Indonesia expect this process of continuous improvement to continue into the future as we meet the challenges of mining deeper, larger, and more complex ore bodies.
53.5 REFERENCES Barber et al. 2000. Development of the DOZ Mine at PT Freeport Indo
nesia. SME 2000. Coutts et al. 1999. Geology of the Deep Ore Zone, Ertsberg East Skarn
System, Irian Jaya. Paper presented at PacRim '99, Bali, Indonesia, October 1999.
Cas ten et al. 2000 Excavation Design and Ground Support of the Gyratory Crusher Installation at the DOZ Mine, PT Free port Indonesia. SME 2000.
Calizaya et al Commissioning of a 750-kW Centrifugal Fan at PT Freeport Indonesia's Deep Ore Zone Mine. SME 2000.
Calizaya et al New PT Freeport Mine Ventilation System-Basic Requirements (25 kt/day Plan) . Mining Engineering, August, 1999, pp 54.
Call & Nicholas, Inc. Impact on Facilities Due To Mining the GBT, IOZ, and DOZ Deposits. 199904.
Call & Nicholas, Inc. 1997. Update to DOZ Cavability Study. 199804 PT Freeport Indonesia. 1998. Feasibility Study of the DOZ Block Cave.
Wallace et al. June 1999. Ventilation System Review of PT Freeport Indonesia Company's DOZ Underground Mine. Mine Ventilation Services, Inc., 199907.
Wallace et al. Ventilation System Analyses of PT Freeport Indonesia Company's DOZ Underground Mine. Mine Ventilation Services, Inc. 199912.
CHAPTER 54
Finsch Mine: Open Pit to Open Stoping to Block Caving
Christopher Andrew Preece*
54.1 I NTRODUCTION
Since 1966, De Beers Consolidated Mines, Ltd. , has been exploiting a diamond-bearing kimberlite pipe. The pipe is known as the Finsch Mine after the prospectors who discovered it, Finscham and Schwabel. The mine is located in the Northern Cape in the Republic of South Africa (Figure 54. 1) . The pipe is elliptical and originally had an area of 17.9 ha on the surface, which is 1,590 m above mean sea level. The pipe is known to extend to more than 900 m below the surface.
Open-pit methods were first used to exploit the diamond pipe, but by 1976, it became apparent that the open-pit operation would reach its maximum economic depth toward the end of the 1980s. Planning and design of an underground mine were undertaken at that time to ensure continuity of operations, and sinking of the main shaft commenced in 1979. Two vertical shaft complexes, tunnels, and ground handling infrastructure were prepared for the continued exploitation of the diamond pipe with the use of highly mechanised underground methods.
The pipe has been divided into a series of blocks. Blocks 1 and 2 were mined by a combination of open-pit and blasthole open stoping methods. Block 3 is exclusively blasthole open stoping while block 4 will employ block caving. The reason behind the change in method is that significant failures are expected from the high, near-vertical faces of the country rock, and this would make the continuation of blasthole open stoping uneconomic. Block 5 has not as yet been fully delineated, but it is expected to be on the order of 200 m. The existence of further blocks has yet to be confirmed. Currently, each block consists of a drilling level and a loading level.
54.2 GEOLOGY
The Finsch kimberlite pipe is a near-vertical intrusion into the country rock, which consists of dolomite, dolomitic limestone with chert bands, and lenses of almost pure limestone. The pipe originally occupied 17.9 ha and was covered by rubble, infilling a topographic depression. It occurs on an external precursor dyke set striking approximately 50° east of north. Two minor pipes and two kimberlite dykes are known in the vicinity, making up the Lime Acres kimberlite cluster.
Eight different kimberlite types have been identified within the pipe. The most significant intrusion is designated F1 and is a diatreme-facies tuffisitic kimberlite breccia. It occupies 70% of the pipe area on the 350-m level (levels are designated by distance in metres below the surface) , decreasing to 60% on the 630-m level. Large masses of Drakensburg Basalt, which makes up about 20% of the pipe volume, occur within the F1 kimberlite (Figure 54.2) . A secretionary textured tuffistic kimberlite brecia, designated F8, is the second largest kimberlite type in the pipe. This kimberlite is similar to the F1 petrologically, but contains fewer inclusions of the country rock and may be part of the same
* De Beers Finsch Mine, South Africa.
439
100 200 JOO kilometre:�
Cope Town
Oanielskuil
F insch Mine ' Kimberle9 0 Bloemfontein
S O U T H AF R I C A Durban
Eost London Port Eliz<Jbeth
FIGURE 54.1 Location of Finsch Mine
major intrusive phase. In general, the F8 kimberlite is the highgrade area of the pipe.
An irregular, bulbous, satellite pipe is seen on the western side of the main pipe, giving rise to poor ground conditions in the area. Diamond content of this satellite pipe is moderate. Because its size is relatively small, mining has not been considered as a priority.
Proven ore reserves extend down to 630 m and will be exploited using the underground infrastructure. Below 680 m, there is an indicated resource over 200 m thick. Pre-1980 tailings, laid down before the modernisation of the treatment plant, are available for retreatment.
54.3 OPEN-PIT MINING
Production started in 1966 and had progressed to 364 m by the end of 1989. The final economic pit depth of 423 m was reached in September 1990. External waste stripping continued to approximately 244 m and was completed in 1986. After that time, benching was employed within the kimberlite, and only
