El Porvenir is situated in the Pasco region of the Western Cordillera of the Andes, within the Eocene-Miocene Polymetallic and Miocene Au-Ag Epithermal Belts.

Three types of mineral deposits are recognized at El Porvenir:
• Skarn (exoskarn and endoskarn),
• Intermediate sulphidation epithermal veins and breccias, and
• Stratabound.

Within the property area, the stratigraphic units of primary interest are the Pucará and the Goyllarisquizga groups. The Goyllarisquizga Group outcrops in the area of the deposit comprising quartz rich sandstone, corresponding to the Goyllarisquizga Formation. Sandstones may vary from quartz arenite to arkose. The matrix is argillaceous to siliceous. Above the 4000 Level, the lithology and stratification are well defined and easy to recognize. Below the 4000 Level, strong alteration has obliterated the original rock intensity forming siliceous breccias and massive silica where it is still possible to recognize quartz grains and in few places the stratification.

Intrusive rocks within the property are variably porphyritic dacite to quartz diorite with hornblende and biotite phenocrysts. The Milpo-Atacocha fault is a major structural feature in the region, which can be traced for nearly 15 km from Yarusyacán in the north to Carmen Chico in the south.

Mineralization is characterized as a skarn, intermediate sulphidation epithermal vein/brecciastyle, or stratabound mineralization in the Goyllarisquizga Formation:

• Skarn-related mineralization is commonly associated with the garnet and silica-skarnchlorite assemblages, comprising pyrite, chalcopyrite, sphalerite, galena and minor pyrrhotite, pyrite, bornite, covellite, orpiment, and realgar within the Pucará Group sediments around the Milpo stock.

• The silica breccia consists of sub-rounded to sub-angular white to milky grey opaline silica clasts, millimetres to centimetres in size, and to a lesser extent, sandstone, and limestone clasts. The silica breccia clasts are cemented by white granular silica, with occasional cross-cutting veins of white silica. Breccias include massive (siliceous) breccias, granular (siliceous) breccias, and Ag-Pb-Zn breccias sub-divided into calcareous, polymictic-monomictic, and karst (collapse). Breccia clasts include limestone, marble, silica (massive), and skarn; the composition of the clasts indicates that brecciation occurred later than skarn development.

• The stratabound Pb-Ag-Zn mineralization occurs in the sandstone strata (mantos) at the base of the Goyllarizquisga Formation (near the contact with the Pucará Group). Several disseminated sulphide mantos have recently been identified at Sara and Porvenir 2W within the quartz sandstone, generally in contact with layers of silt and microconglomerates. The minerals include galena with silver content, sphalerite, and pyrite. Gold is also present.

El Porvenir is one of the deepest underground mines in South America, extending more than 1,800 m below the main access level. El Porvenir produces approximately 2.1 Mtpa of zinclead-copper ore using two mining methods, with the predominant method being mechanized overhand cut & fill (C&F). C&F has been used at El Porvenir for many decades and accounts for over 80% of its production. The remainder of the output comes from sub-level stoping (SLS), which was introduced at the operation in 2018. El Porvenir uses a version of this method called Avoca, also referred to as longitudinal longhole retreat mining.

Mine production is presently underway in the Upper Zone, the Intermediate Zone, the Lower North Zone, and the Lower West (El Porvenir 9) Zone.

MINE DESIGN AND MINING METHODS
C&F and SLS have similar development requirements as they both involve dividing a mining zone into horizons between sublevels and excavating the ore in an ascending fashion. Sublevels are typically spaced at 20 m vertical intervals and accessed via spiral ramps. The development on each sublevel includes an access drift, a footwall drive, and crosscuts or attack ramps, which provide access to the orebody. For SLS, the footwall drive can be as close as 15 m from the footwall contact, whereas for C&F, they have to be offset from it by 60 m to provide sufficient distance for fanning the attack ramps.

C&F’s mining cycle: drilling, blasting, mucking, and ground support. Backfilling is carried out after completing a cut and before initiating the next higherup one. With C&F, ore in an ore block is mined from bottom to top in five metre thick horizontal slices or cuts. The first cut of the stope is mined as a drift through the orebody, which is slashed out between the footwall and hanging wall contacts. The subsequent cuts are mined by breasting, which involves slashing the ore by drilling horizontal holes with the jumbo and blasting the ore downwards to the previous cut’s free face. Following each breast, the broken ore is mucked and transported out of the stope with an LHD.

Attack ramps driven from the sublevels provide access to a C&F stope. An attack ramp is initially driven with a -15% inclination to access a cut below the sublevel’s elevation. The attack ramp is then back-slashed in a fan-like fashion with some muck left on the floor to access each subsequent cut. The ramp to the highest cut will have a continuous positive grade over its entire 60 m length. The next cut must be accessed with a new attack ramp, driven at -15% from the next higher-up sublevel. An attack ramp at El Porvenir permits accessing four cuts from a sublevel.

After mining the complete cut or horizontal slice of a C&F stope, the open space must be backfilled from floor to back. Besides supporting the stope walls, the backfill provides the floor for mining the next higher-up cut. Hydraulic backfill is the principal backfill used for C&F at the Mine, and consists of classified mill tailings sent underground via a pipeline as slurry. Up to 70% of the stope is filled with rockfill, which is waste from development headings. This material is dumped on the stope floor, after which hydraulic backfill is placed to tight-fill the remaining opening. The stope then sits inactive for several days until the water drains out of the hydraulic backfill, leaving it with a consistency similar to fine sand.

While C&F is the predominant mining method at El Porvenir, SLS accounts for a small but growing proportion of the production. The Mine uses a version of SLS called Avoca, which is used instead of C&F when the configuration of the orebody and the ground conditions are suitable for the method and when development waste is available for backfilling.

As previously stated, the SLS Avoca method is similar to C&F in terms of its bottom-up mining sequence and development requirements. The main difference between the methods is how they excavate the ore horizons between sublevels. C&F mines the ore in horizontal slices by breasting, while Avoca mines vertical slices by benching.

Avoca benches the ore in a retreating fashion. The benches retreat towards the middle of the vein, starting from the opposite ends of the vein. The ore between two sublevels is completely mined-out once the final bench is blasted at the middle of the vein. Backfilling is an integral part of the mining cycle. The stope is progressively backfilled as the ore is extracted. The rockfill pile advances behind the bench.

TRANSPORT AND MATERIAL HANDLING
The underground transportation and materials handling system at El Porvenir has the following components:
• Ramps;
• Orepasses;
• Track haulage level;
• Picasso Shaft (1,732 m);
• Conveyor.

The ore produced in the C&F and SLS stopes is transported to and dumped in orepasses by LHDs. These orepasses extend to the 2,900 track haulage level (-1170), where the ore is pulled from chutes and loaded onto mine cars. The mine cars dump at an orepass grizzly, and the ore is transferred to the Picasso Shaft's loading pocket on the 2,500 level. From there, the ore is loaded onto skips and hoisted via the shaft to the ore dump. After being discharged at the dump, the ore is transferred to the underground crushing plant. Crushed ore is transported to the surface and the processing plant via a conveyor in an inclined drift.

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El Porvenir operates a conventional concentration processing plant with a nominal capacity of 6,500 tpd of ore (approximately 2.2 Mtpa). The concentrator plant processes on average approximately 5,800 tpd to 5,900 tpd. The processing flowsheet includes a multistage crushing plant, a conventional ball mill grinding stage, and sequential differential flotation to produce three final mineral concentrates: a zinc concentrate, a lead concentrate, and a copper concentrate.

Zinc concentrate accounts for the largest production from El Porvenir at approximately 77% of the total tonnage, lead concentrate accounts for approximately 21% of the tonnage, and copper concentrate for the remaining 2% approximately.

PROCESS DESCRIPTION
The bulk flotation circuit consisting of bulk rougher, scavenger, and cleaner cells produces a copper and lead concentrate. Bulk scavenger concentrate is reground before being returned to the roughers. Bulk flotation is followed by copper-lead ........