Constancia mine include the Constancia and Pampacancha deposits

CONSTANCIA
The Constancia deposit is a porphyry copper-molybdenum system which includes copper-bearing skarn mineralization. Multiple phases of monzonites and monzonite porphyry have intruded a sequence of sandstones, mudstones and micritic limestone of Cretaceous age.

The majority of the mineralization is associated with potassic alteration and quartz veining, occurring as chalcopyrite-(bornite)-molybdenite-pyrite mineralization in “A” and “B” type veinlets, and replacing ferromagnesian minerals or filling fractures. Copper grades are highest where fracture-filling style copper mineralization is superimposed on earlier disseminated copper mineralization. The higher-grade hypogene copper mineralization is hosted by a dense A-veinlet stockwork developed in an early porphyry phase. The pyrite/chalcopyrite ratio is typically below 2:1. Molybdenite commonly increases with depth in association to “B” veinlets. Bornite occurs sporadically especially at deeper levels, sometimes associated with some gold values.

Propylitic alteration is transitional to the potassic alteration and extends more than one kilometre from the porphyry intrusive contacts. The propylitic alteration mineral assemblage includes epidote-chlorite-calcitepyrite-rhodochrosite. Subordinate chalcopyrite is also present, filling fractures or replacing mafic minerals. Sphalerite-galena veinlets and veins are distributed as a halo to the copper-molybdenum mineralization within the propylitic alteration zone up to 3 km away from the porphyry copper system.

Phyllic alteration forms a pervasive carapace surrounding and sometimes overprinting potassic alteration. The phyllic alteration accompanies almost complete destruction of primary rock textures; the mineral assemblage includes sericite-quartz-pyrite, limited amounts of chalcopyrite and associated occasional “D” veins and veinlets.

At the contact between intrusions and limestones, a magnetite garnet skarn develops, while a pyroxene– diopside (garnet–epidote) association is more common in calcareous sandstones and arkoses of the Chilloroya formation. Skarn mineralization is volumetrically much smaller, but grades are normally higher.

Structural deformation has played a significant role in concentrating the hydrothermal alteration and the copper-molybdenum-silver-gold mineralization, including skarn formation. Major inter and post mineral fracture systems in the deposit area strike northeast and include the Barite fault system. This is represented by a number of nearly parallel vein-faults carrying base metal sulphides and barite which have been exploited by artisanal workings throughout the property. A second important system strikes northsouth. It appears to be more recent than the Barite system and controls part of mineralization and most of the silicified breccias (sometimes mineralized) in the system.

PAMPACANCHA
The Pampacancha deposit is a porphyry Cu-Mo-Au related Skarn system. Oligocene unmineralized basement diorite is intruded by the diorite porphyry cited as the source for skarn mineralization. This in turn is cut by intra-mineral monzonite intrusions which provide minor local increases in Cu-Au and also locally replaces skarn Cu-Au mineralization which is most developed at the upper and lower margins of the limestone body. Magnetite-chalcopyrite-pyrite skarn ranges to marginal less well mineralized garnet and pyroxene skarn, locally overprinted by epidote-bearing retrograde skarn.

Epithermal mineralization as low sulphidation quartz-sulphide Au + Cu style accounts for common supergene enriched Au anomalies along with other features such as hydrothermal alteration and veins typical of near porphyry locations.

The Constancia mine is an open pit mining operation relying on conventional trucks and shovels. The Constancia ultimate pit design will measure approximately 1.6 km east to west, 1.7 km north to south, and have a maximum depth of around 705 m. The Pampacancha ultimate pit design will measure approximately 0.6 km east to west, 1 km north to south, and have a maximum depth of about 300 m. A primary waste rock facility (WRF), which is located to the south and east of the Constancia pit, is intended to be used for both deposits.

The processing facility is located approximately 1 km west of the Constancia Pit. The NAG waste rock is deposited south of the Constancia pit, while the tailings management facility (TMF) is located 3.5 km southwest of the Constancia pit.

DESIGN CRITERIA
Constancia is mined in nine stages and a two stage pit is planned at Pampacancha. The minimum mining width for each phase is 60 meters; this will allow a shovel, trucks (in two lines) and a drill to work safely and simultaneously.

The haul roads at Constancia and Pampacancha have been designed with a 10% grade and 32 m width for double lane haul roads and 24 m for single lane haul roads.

The final design for waste rock facilyty facility incorporates 20 m high benches with 1.4H:1V (36°) of bench slopes and 32 m wide benches. The overall slope of the stockpile will be about 3.0H:1V (18°). The current remaining capacity of the WRF is estimated at 413 Mt.

The Constancia mine is planned to have four operational stockpiles, which will segregate the ROM material by ore type and grade range. The lift height of these stockpiles ranges between 12 and 20 meters.

The Tailings Management Facility (TMF) area is where mill tailings are placed behind waste rock containment buttresses. The buttresses' material will come throughout the life of the mine, from mining operations and quarries. The TMF area is located southwest of the mining facilities area. The design for the TMF includes ramps access to the lower and upper levels for the regular mining fleet (240 tonnes trucks) and a smaller fleet called HCW, which has been used since October 2015 to send NAG material from the Constancia pit to the TMF area.

MINE PHASES AND ULTIMATE PIT
The extraction sequence is defined by nine mining phases at Constancia and two mining phases at Pampacancha. In parallel, seven pushbacks are planned for ore exposure purposes and optimal sequencing at Constancia with one pushback for waste and construction purposes. The phase development strategy consists of extracting the highest metal grades along with minimum strip ratios during the initial years to maximize the economic benefits while enabling smooth transitions in wastestripping throughout the life of the mine to ensure sufficient ore exposure.

MINE OPERATIONS
Open pit mining at the Constancia operation is based on conventional open pit mining techniques. The Constancia operation consists of two pits, Constancia and Pampacancha. The Constancia pit operation started in 2014, while Pampacancha will begin in 2021.

The mine production plan contains 569.4 Mt of waste and 532.5 Mt of ore (from pit and stockpiles), yielding a stripping ratio (waste/ore) of 1.1 to 1. An average yearly mining rate of 77.0 Mtpy, through the first 13 years, with a maximum of 81 Mtpy, is required to provide a nominal ore process feed rate of 31.3 Mtpy based on a variable throughput by ore type (90 to 94ktpd and 94% available). LOM average grades are 0.311% Cu, 0.009% Mo, 0.065 g/t Au and 3.04 g/t Ag, where the mine's life is 17 years.

For primary drilling production, single-pass 270 mm diameter (or 10 5/8”) drills are used. After evaluating equipment dimensioning, three drill rigs PV-271 were selected to achieve the production rate. The drilling ratio of the drill rig is approximately 45 m/h. Pre-split drilling is done with a Smart Rock D65 drill (downhole). Equipment used to improve the stability of the slopes and optimize the design of the phases.

For wet holes, Heavy ANFO 73 (70% of Emulsion and 30% of ANFO) and dry hole, Heavy ANFO 55 (50% emulsion and 50% of ANFO) is used. Based on the evaluation of productivity, powder factors are estimated to be about 0.40 Kg/t for ore and 0.30 Kg/t for waste.

Two 27 m3 (Hitachi EX5600-6) shovels and a 19 m3 (CAT 994H) loader are used to excavate blasted materials. The loader provides flexibility for blending purposes. Pampacancha is expected to enter into production in 2019, and will require a loader at the start of the mining activities.

All phases have been designed to achieve high productivity, taking advantage of double-side loading and working at faces around ~60 meters in width.

For life of mine, ore and waste will be transported by 240-tonne capacity haul trucks (CAT 793F). The use of this class of trucks minimizes road congestion, labor requirements, and operating costs. 240-tonne trucks require a minimum haulage road width of 32 meters.

PRIMARY CRUSHING
A 63” x 118” gyratory crusher receives ROM of up to 1 m in size and reduces it to less than 125 mm. A variable speed belt feeder delivers ore from the crusher chamber to the coarse ore stockpile feed conveyor. The site mobile crane is used for major crusher maintenance. A drive-in dump pocket makes it possible to clear the crusher with a small FEL or bobcat.

The crusher is an FLSmidth 63” x 118” gyratory crusher with a 1000 kW motor. This is likely to be underutilized for most of the highly fractured ore, but will ensure throughput when processing an area of competent rock. The ROM bin and crusher surge pocket has the volume to hold 1.6 truck loads

CRUSHED ORE STOCKPILE AND RECLAIM SYSTEM
The grinding circuit requires two SAG mill feed conveyors. Dual reclaim chambers (nearparallel) are used to house a total of four apron feeders that draw ore from the crushed ore stockpile to the SAG mill feed conveyors. A secondary egress or emergency tunnel is provided through the connection of the two reclaim chambers.

GRINDING
The grinding circuit consists of two trains of grinding mills, each train identical, treating 1875 t/h. Each train consists of a single FLSmidth semi-autogenous grinding (SAG) mill, a ball mill and a potential addition of a pebble crusher (SABC). The ball mills are operated in closed circuit with a FLSmidth (Krebbs) cyclone cluster to produce a product from the grinding circuit of 80% passing until 130 µm.

The SAG mills are fitted with a dual pinion drive system and are driven by a variable-speed drive comprised of a SER hyper-synchronous drive. The SAG mills are 11 m (36’) dia, 7.3 m EGL (26.5’). Each SAG mill is driven by two 8 MW motors. The 16 MW, twin pinion, SAG mills were selected over the equivalent GMD to reduce both capital and commissioning costs.

The two 16 MW ball mills selected are fitted with twin pinion drives operated at fixed speed. The mills are 7.9 m (26.5’) dia, 12.4 m EGL (41’). Like the SAG mills, each ball mill is driven by two, 8 MW motors. Each of the eight mill motors are interchangeable, and started using conventional liquid resistant starter circuits (although once started, the SAG mill SER system takes over control enabling limited variable speed control). The commonality of motors reduces the number of maintenance spares required to be held on site.

The two 16 MW ball mills selected are fitted with twin pinion drives operated at fixed speed. The mills are 7.9 m (26.5’) dia, 12.4 m EGL (41’). Like the SAG mills, each ball mill is driven by two, 8 MW motors. Each of the eight mill motors are interchangeable, and started using conventional liquid resistant starter circuits (although once started, the SAG mill SER system takes over control enabling limited variable speed control). The commonality of motors reduces the number of maintenance spares required to be held on site.

Each grinding train was originally configured with a single (duty only), 1.5 MW Warman 650 MCR M200 variable speed cyclone feed pump but since commissioning a larger-capacity Excellence ESH-650MU was installed as a trial unit on grinding line 1. Pending successful results, the other line will be upgraded. A full spare assembly is held on site and changed out when required. The layout allows for the flexibility to recycle cyclone underflow to the SAG mills; a single “drive-on” grinding floor; a simple cyclone tower; clear access to the wet end pumps; and clear access to scats clean-up from the ball mill.

The capital cost was reduced by not installing standby cyclone feed pumps. Spare units can be installed in approximately six hours. Easy access by mobile cranes is provided and it is possible to only change the wet end of the pump which minimized downtime.

GENERAL
The processing plant has been laid out in accordance with established industry best practices for traditional grinding and flotation plants. The major objective was to make the best possible use of the natural ground contours to minimize pumping requirements by using gravity flows and to reduce the height of steel structures.

To optimize the cost of the major footings for the SAG mill, the height of the SAG mill above grade was minimized by situating the cyclone feed sump as low as possible. The mill cyclones have been located so that the cyclone overflow can gravitate into the rougher conditioning tank.

At the tailing end of the flotation bank, the copper tailings thickener has also been situated to facilitate gravity flow and eliminate the requirement for another large set of pumps.

Due consideration has been given to the layout of the molybdenum plant to facilitate good housekeeping and occupational health and safety requirements. ........