Pulacayo Project Feasibility Study - Apogee Silver

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Pulacayo 1 000 t/d Phase I Feasibility Study - NI 43-101 Technical Report 090644-3-0000-20-IFI-100 16.2.2 Long Hole Stoping The long hole stopes will have an average length of 10 m, a stope width that varies between 3 m and 6 m depending on the payable vein thickness and an average stoping height of 23.4 m. The level spacing of the old mine has been maintained, and as a result, the spacing varies from 21.5 m to 32.5 m. Figure 16.2 shows a typical layout of a long hole stope. Figure 16.2: Top and Bottom Stope Accesses in Long Hole Stoping The bottom access will be used as a drilling and mucking level. Stoping will be done on retreat using parallel hole, long hole drilling techniques. A trackless drill rig will be used to drill 64 mm diameter blast holes into the hangingwall of the stope and the blast holes will be charged with Anfex. Remote-controlled LHDs (load-haul-dumper), each with a 3.1 m 3 bucket, will be used to tram broken ore from the stopes to the mucking bays. The mucking bays will be located along the haulage drive and they will be spaced at a maximum distance of 120 m. The LHDs will also be used to load rock at the mucking bays into trucks. The trucks will haul the ore out of the mine via the decline ramp system and tip at the stockpile at the process plant. Due to the tonnages involved, a 20 tonne haul truck has been recommended for this operation. The 20 tonne truck will be required to supplement the 15 tonne haul truck that the mine already TWP Sudamérica S.A. Av. Encalada 1257 Of. 801, Santiago de Surco Lima 33, Perú (51-1) 4377473 Page 147
Pulacayo 1 000 t/d Phase I Feasibility Study - NI 43-101 Technical Report 090644-3-0000-20-IFI-100 owns. Once all the broken ore has been removed from the stope, it will be filled with cemented backfill, as recommended in the Backfill Section of this report. Historic mining has left voids throughout the planned operation. The voids that have been identified are flagged in the block model and tend to be located along the high grade portions of the ore body. This risk of encountering them will be mitigated by implementing an exploratory drilling program (cover drilling) ahead of production. This will allow for evaluation of ground conditions and the quality of the deposit prior to mining. The information obtained from this exercise will: verify and identify the location and width of the previously mined areas (voids); determine if the voids are filled with old waste material; allow an economic estimation of the mineralization in each block to ensure that the area is profitable to mine; allow planning for the extraction of each stoping block to be made based on ground conditions; allow planning to prevent ore losses by backfilling voids that are located adjacent to stoping blocks; and put in suitable measures to minimize dilution and ensure the safety of people in the case where stoping blocks are located next to voids that are filled. There are several possibilities of void condition that could be encountered: They could be completely empty, or partially filled with material that has caved from the sidewalls of the stope. If such a void is encountered, it would need to be filled with cemented backfill in order to safely mine adjacent areas. They could be filled with water and mud. In such a case, it is almost certain that the mud would have settled and solidified at the bottom of the void. In such a case, the water would need to be drained through cover drilling holes. Once this has been achieved, the void would need to be filled with cemented backfill as recommended in the Backfill Section of this report. If the void is filled with loose material, it will not be safe to remove the waste due to the risk of losing equipment. In such a case, a pillar would need to be left around the void before mining adjacent areas. A potential risk to the project is a deficit in backfill material in the early years on the mine. The problem will worsen if a large number of unplanned and unfilled voids are encountered. To reduce the risk of having a deficit of fill material, the mine will have to use development waste and/or waste rock from a borrow pit on surface. The waste rock will have to be combined with cement as recommended in the Backfill Section of this report. 16.2.3 Mine Access The shrinkage stopes will be accessed via the San Leon tunnel, which is an existing haulage that was holed through the mountain during historic mining. The tunnel has a width and height of 2.5 m and a total length of about 1.57 km. The long hole stopes will be accessed via a 4 m (h) x 4 m (w) decline ramp system that will be developed from surface to allow rock to be trucked out of the mine. The ramp system will be developed at an inclination of 8 degrees from the horizontal and it will comprise the east decline ramp and the west spiral ramp. Figure 16.3 shows the decline ramp system and Figure 16.4 shows the designed mine layout. TWP Sudamérica S.A. Av. Encalada 1257 Of. 801, Santiago de Surco Lima 33, Perú (51-1) 4377473 Page 148
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