Overview

Deposit type

• Epithermal
• Vein / narrow vein

Summary:

The Pueblo Viejo deposit consists of high sulfidation or acid sulfate epithermal gold, silver, copper and zinc mineralization that was formed during the Cretaceous Age island arc volcanism. Pueblo Viejo is situated in the Los Ranchos Formation, a series of volcanic and volcaniclastic rocks that extend across the eastern half of the Dominican Republic, generally striking northwest and dipping southwest.

The Hatillo Formation hosts the limestone, which has been historically mined from the Quemados quarry and currently from the active Lagunas and San Juan quarries. There is potential for other limestone quarries to be developed towards the west of the MNFR.

All the lithologies at the Pueblo Viejo deposit are expected to have some argillic alteration with quartz, pyrophyllite and pyrite as the primary sulfide, minor sphalerite, local enargite with minor amounts of barite, rutile, telluride, and lead-sulfides.

The other sulfides, sphalerite, and enargite (with some antimony replacing arsenic), are present with pyrite, mainly in veins and filling fractures.

Mineralization events are strongly related to the alteration sequence, with disseminated pyrite occurring in an early event and sulfide veinlets occurring in a later event. Mineralization has also been considered to have occurred during or close to the end of the sedimentation in the basin. The presence of typically centimetre scale subvertical mineralized veinlets cutting the bedding or hosted conformably in the deformed sediments (bedding plane continuity) are evidence of this. The density of these centimetre scale veinlets is directly related to gold grades, and form the trends required within the models. Sulfide veins can be found conformably hosted in the carbonaceous sediments experiencing post-deformation and others cutting across folded rocks.

Pueblo Viejo is composed of several deposits; Moore and Monte Negro represent the main deposits along with small satellite deposits including Cumba, Mejita, and ARD1.

Moore
Moore forms the depocenter basement located at the southeast margin of the Pueblo Viejo deposit. The carbonaceous sequence is well developed with a thickness of more than 150 m. Mineralization is pyrite- rich, gold-bearing veins with an average width of four cm, steeply dipping with a trend typically to the NNW. There is a secondary pyrite vein set that trends N-S and N-NE. The orientation of pyrite veins and steep faults is similar.

Thin bedded carbonaceous siltstones and dacitic ash tuffs in the West Flank dip shallowly to the west. Dip increases towards the west where north trending thrust faults displace the bedding. Quartz veins with gold trend NW, oblique to the pyrite veins, have a similar strike to the interpreted contact with the overlying Hatillo limestone. They also occur as tension gash arrays in cm-scale dextral shear zones that trend north-northwest.

Faults create cm-scale displacement of bedding and pyrite-sphalerite veins occur along steep northnortheast trending faults. Two main NNE faults were mapped across the West Flank, sub-parallel to the Moore dacite pyroclastic contact. Displacement of veins preserves the evidence of lateral, sinistral movement.

The hydrothermal alteration is well developed and shows the four assemblages typical from Pueblo Viejo deposit. The core is advanced alunite, surrounded by an advanced pyrophyllite halo; this transitions into a propylitic halo and finally into an intermediate argillic envelope, which is the most exterior alteration.

Monte Negro
Monte Negro is located at the northwest portion of the Pueblo Viejo deposit. It is the distal area of the basin where the carbonaceous sequence is thinner and not as developed as it is in Moore.

In the Monte Negro central area, pyrite-rich veins with gold mineralization are sub-vertical and have different trends creating conjugate sets; the average width is two centimetres. The north-northwest trending set is sub-parallel to the strike of the bedding and fold axes, indicating a possible genetic relationship between folding and mineralization. Enargite and sphalerite gold bearing veins trend dominantly to the north-northeast and have an average width of three centimetres. The combination of vein trends forms a high-grade gold zone which extends 500 m north-northwest, 150 m wide, and up to 100 m thick.

The fault pattern is dominated by steep NNW trending faults sub-parallel to the dominant pyrite vein set.

Mineralized veins in the south of Monte Negro are relatively pyrite-poor, sphalerite-rich, and show an average width of five centimetres. The veins are sub-vertical and trend NW. The episodic vein fill demonstrates a clear paragenesis (massive pyrite-enargite-sphalerite-grey silica).

Shallow-dipping bedding and sub-vertical sphalerite-silica veins on the southern margin of Monte Negro South are cut by a west-dipping thrust. The thrust has brought thinly bedded pyritic sedimentary rocks into contact with andesitic volcanic and volcaniclastic rocks.

The hydrothermal alteration is well developed and shows the same four assemblages typical for Pueblo Viejo, which are the same as those described in Moore.

Satellite Deposits

Cumba
The Cumba satellite orebody is located northeast of Monte Negro. The mineralization is hosted within an andesitic rock where a silicified orebody is developed and contains the main mineralization associated with pyrite, enargite, tetrahedrite and covellite with some sphalerite.

The structural trend is northwest to east-west and seems to control the mineralization. A major structure trending northeast is limiting the mineralization to the south. Hydrothermal alteration is predominantly silica-pyrophyllite with traces of dickite in the center and illite-chlorite as the exterior envelope.

Mejita
The Mejita satellite orebody is located southeast of Moore. It is an extension of Moore, where the mineralization is hosted in the carbonaceous sediments (the upper part of the sequence) with some levels of dacitic pyroclastic rocks and a basement of andesitic flows.

Mineralization occurs in the contacts between carbonaceous sediments/andesitic flows and pyroclastic dacitic/andesitic flows. Some deeper mineralization with high values of gold and silver is associated with a cruciform textured quartz vein with pyrite-sphalerite.

ARD1
The ARD1 orebody is located southwest of Moore. The mineralization is hosted in the carbonaceous sediments and the underneath polymictic volcaniclastics that are overlayed by the Hatillo limestone. The ore consists of pyrite and sphalerite veins that follow the bedding of the carbonaceous sediments. Hydrothermal alteration consists of a halo of advanced pyrophyllite with some dickite traces, surrounded by an intermediate argillic alteration.

Mining Methods

• Truck & Shovel / Loader

Summary:

The Pueblo Viejo mine is an open pit, conventional truck-and-shovel mining operation. It achieved commercial production in January 2013 and completed its ramp-up to full design capacity in 2014. Current mining operations will supplement fresh ore from the Monte Negro and Moore pits with stockpiled ore to deliver the increased throughput rates contemplated in the process plant expansion.

The pit stages have been designed to optimize the early extraction of the higher-grade ore. Notwithstanding, the sulfur grade is an important consideration because the metallurgical aspects of the processing operation, the recoveries achieved, and the processing costs strongly depend on sulfur content in the plant feed, with benefits from consistency and low variability.

PAG waste rock from the pits is hauled to dedicated waste dump locations (currently the Hondo dump). From 2025 onwards, a crushing, conveying, and stacking system will transport and place PAG waste mined from the pit directly into the new Naranjo TSF. The PAG waste material deposited in Hondo is intended to be rehandled into completed pit void locations when available, and the remainder will be rehandled into the PAG handling system to the Naranjo TSF after pit mining is completed.

Mineral processing requires a significant amount of limestone slurry and lime derived from high quality limestone. Limestone quarries, located adjacent to the mine, have been in production since 2009 to supply material for TSF construction and the process plant.

Pit Design parameters
The final pit design is based on the following parameters:
• Bench height is 10 m with single and double benching by sectors.
• Main haul roads are designed with 35 m width and maximum 10% gradient.
• Roads within the carbonaceous sediments geotechnical domain are designed with a width of 40 m to account for residual geotechnical risk.
• In-pit single-lane haul roads (typically to within 3 x 10 m benches of pit bottom) have a design width of 20 m and a maximum gradient of 12%.
• The minimum mining width for phase design is generally targeted to be 60 m; however, locally can be narrowed to 40 m.

Quarries
Pueblo Viejo operations require significant amounts of limestone to operate the processing facility and construct the TSF facilities. PV exploits limestone resources adjacent to the gold and silver bearing pits to meet these requirements. PV utilises a Whittle type optimisation for guidance on the quarry designs and extents to maximise the resource extraction and minimise the mining costs.

The predominate users of limestone are:
• Processing (MQ).
• TSF wall construction for the Lower Llagal and Naranjo TSF (LQ1 and LQ2).
• Construction, such as internal roads, diversion channels, and additional dams (LQ2 and LQ3).

Waste rock from the quarries is generally non-acid generating (NAG) and taken to dedicated NAG dumps.

Waste Dumps
As part of the closure requirements pertinent to environmental permitting, all PAG waste must be stored in anaerobic conditions to minimise the acid generating potential. This is typically achieved by co-disposing PAG and tailings in the TSF facilities but can also be achieved by backfilling the pits to an elevation below the natural water table level. Due to sequencing of the completion of the Lower Llagal TSF and the planned commissioning of the Naranjo TSF, there has been a necessity to store PAG in above-ground dumps temporarily. The PAG will be ultimately rehandled into in-pit voids and the Naranjo TSF.

Typical PAG waste dump design considers a 20 m bench height and a 14 m bench width. NAG waste dumps are designed considering final reclamation slopes and surface drainages for revegetation and closure.

The Hondo PAG dump has been designed to temporarily store over 150 Mt of PAG waste and low-grade ore. The key design considerations for this dump are ARD surface water runoff management and geotechnical constraints. NAG material is also stored onsite in conventional surface dumps and backfilled into mined-out quarries. NAG waste does not have the ARD considerations relevant to PAG waste.

Stockpiles
The mine design and scheduling strategy at Pueblo Viejo focuses on maximizing net present value. An levated cut-off grade strategy is employed where ore is mined at a faster rate than can be processed. The higher gold grade ore is preferentially fed to the process plant, while the lower grade ore is stockpiled.

Stockpiles are designed to be reclaimed in various phases throughout the LOM. A stockpile optimization was performed as guidance for the phase sequence. Typical stockpile design considers a 10 m bench height and a 7 m berm width.

Comminution

Crushers and Mills

Summary:

Existing Operation
The processing plant is designed to process approximately 24,000 tpd of ROM refractory ore.

The ROM ore is crushed to a P80 of 130 mm in a primary gyratory crusher which is reclaimed from the crushing station dump pocket by an apron feeder and conveyed directly to the coarse ore stockpile. Ore is reclaimed from the coarse ore stockpile using apron feeders located in a tunnel under the stockpile. The apron feeders discharge onto a conveyor belt feeding the SAG mill. The ore is ground to the optimum grind size of P80 of 80 µm in a SABC circuit. The SAG mill is in a closed circuit with a vibrating screen and a pebble crusher, while the ball mill is in a closed circuit with hydrocyclones.

The primary crushing circuit consists of a primary gyratory crusher equipped with a hydraulic rock breaker to reduce oversize rocks in the dump pocket. Water sprays are provided at the truck dump pocket and an ADS (fogging dust suppression) system is deployed at the feeder to conveyor transfer point to comply with the dust emission standards.

The ore is transferred from the gyratory crusher, by an apron feeder onto a stacking conveyor that discharges the ore onto a 16,000 t live capacity stockpile. A belt scale monitors the material flow rate from the crusher to the stockpile.

A dust control system positioned at the reclaim tunnel below the stockpile services the material transfer locations. Two variable speed apron feeders under the coarse ore stockpile reclaim the ore and feed a common SAG mill feed conveyor. The feed rate to the SAG mill is monitored by a belt scale installed along the SAG mill feed conveyor.

The limestone primary crusher is exactly the same size as the ore primary crusher, which is more than adequate for the 12,000 tpd rate.

Ore grinding consists of a 9.76 m x 4.90 m 9 MW (32’ x 16’ 12,000 hp) SAG mill with blended 4.5” and 5“ balls, and a 7.93 m x 12.40 m 16.4 MW (26’ x 40’ 22,000 hp) single ball mill with 2” balls.

To counteract critical size build-up in the mill, the SAG mill is equipped with pebble ports. Oversize pebbles are screened from the discharge and transferred onto a conveyor recirculation loop feeding the material to the pebble crusher, or alternatively bypassing the pebble crusher if it is not in service. The pebble crusher product is conveyed back to the SAG mill feed conveyor. The undersize material is pumped to the cyclone feed pump box.

The ball mill is operated in closed circuit with a cluster of fifteen cyclones, with ability to expand to eighteen. The cyclone underflow flows via gravity back to the ball mill feed chute. The cyclone overflow flows by gravity over two vibrating trash screens. The underflow from the trash screens is dewatered to approximately 50% solids in the 70 m diameter high rate grinding thickener. The thickener underflow is pumped to one of four autoclave feed storage tanks while the overflow is recycled to the grinding circuit.

Expansion Project
The Expansion Project is designed to both expand processing operations from 8.6 Mtpa to approximately 14 Mtpa to economically treat lower grade ore.

The process plant expansion includes a new primary crusher and single-stage SAG (SS-SAG) milling circuit that is being added parallel to the existing grinding circuit. The existing SABC circuit will have the capability to feed the flotation plant as required. A dedicated crushed ore stockpile will feed the new SS-SAG milling circuit. The overflow from the primary cyclones in the SS-SAG milling circuit will be fed into two parallel flotation trains.

The expanded plant will include the following:
• New gyratory crusher.
• Grinding (SS-SAG).
• Vertical regrind mill for the limestone plant.

Limestone and Lime Plant
The limestone plant consists of: primary crushing and screening, grinding, calcining, and lime slaking.

PRIMARY CRUSHING AND SCREENING
ROM limestone is crushed to minus 85 mm (P80) in a gyratory crusher (1,067 mm x 1,650 mm) that is equipped with a rock breaker to break oversize rocks in the dump pocket. A dust control system at the primary crushing station is provided to reduce fugitive dust emission. The configuration of the limestone crusher is similar to that for the ore. The crusher product is screened and the +50 mm -110 mm intermediate fraction is sent to the kiln circuit for calcination. The balance of the crusher product reports to the limestone SAG mill feed stockpile.

GRINDING
The limestone grinding circuit consists of a SAG mill (6.70 m dia. x 3.65 m effective grinding length, EGL) driven by a 2,610 kW synchronous motor with a variable frequency drive (VFD) and a ball mill (4.88 m dia x 9.80 m EGL) driven by a 3,540 kW synchronous motor. The SAG mill operates in open circuit while the ball mill will operate in closed circuit with a cluster of hydrocyclones. The limestone slurry is pumped to three agitated storage tanks holding approximately 6,500 t of limestone. This provides 22 hours of storage capacity at peak limestone demand.

Processing

• Dry Screening
• Crush & Screen plant
• INCO sulfur dioxide/air process
• Smelting
• Carbon re-activation kiln
• Flotation
• Agitated tank (VAT) leaching
• Counter current decantation (CCD)
• Pressure oxidation
• Carbon in leach (CIL)
• Elution
• Carbon adsorption-desorption-recovery (ADR)
• Solvent Extraction & Electrowinning
• Cyanide (reagent)

Summary:

Gold and silver are recovered through pressure oxidation (autoclave) of whole ore followed by hot cure and hot lime boil, prior to cyanidation of gold and silver in a CIL circuit.

Following completion of the plant expansion, the process plant is now designed to process approximately 30,000 tonnes per day of run-of-mine refractory ore. The primary unit operations are crushing, grinding, flotation, high-pressure oxidation, washing, neutralization and CIL circuits. The flotation circuit is used to increase sulfide grade from 6.85% to 9.8%, and the design basis for the oxygen plant is to provide the oxygen required to oxidize approximately 109 tonnes per hour of sulfides. This is equivalent to 1,110 tonnes per hour of autoclave feed containing 9.8% sulfide sulfur, assuming a design factor of 2.2 tonnes of oxygen per tonne of sulfides. Lower sulfide ores are often fed to the plant resulting in higher tonnage, often well over 30,000 tonnes per day.

Copper is a by-product from the processing plant which was produced as a copper sulfide concentrate through the injection of hydrogen sulfide gas into a solution containing copper ion.

The process plant expansion and mine life extension project is designed to increase throughput to approximately 14 million tonnes per annum, allowing the mine to maintain minimum average annual gold production of approximately 800,000 ounces after 2022.

The process plant expansion flowsheet includes an additional primary crusher, coarse ore stockpile and ore reclaim delivering to a new single stage semi-autogenous (“SAG”) mill, and a new flotation circuit that concentrates the bulk of the sulfide ore prior to oxidation. The concentrate is blended with fresh milled ore to feed the modified autoclave circuit, which has additional oxygen supplied from a new 3,000 tonnes-per-day facility. The existing autoclaves were upgraded to increase the sulfur processing capacity of each autoclave through additional high-pressure cooling water and recycle flash capability using additional slurry pumping and thickening.

The construction and commissioning activities for the plant expansion were substantially completed by the end of 2023, with both of the new oxygen plants as well as the fine grind mill (Vertimill) now operational. Premature equipment failures encountered early in commissioning were resolved in collaboration with the original equipment manufacturers, including a new agitator gearbox design installed on all the flotation cells. Ramp-up for the plant expansion is ongoing into early 2024.

At the start of the fourth quarter of 2023, Pueblo Viejo experienced a structural failure of the crushed ore stockpile feed conveyor. While the reconstruction work is underway, the new SAG mill is being fed through smaller mobile crushers and a temporary conveyor system running from the gyratory crusher, albeit at a reduced rate. This reconstruction is expected to be completed in the second quarter of 2024, which will allow the plant to reach full throughput. During the first quarter of 2024, the focus will be on the continued stability and optimization of the flotation circuit.

Pipelines and Water Supply

Summary:

The Hatillo and Hondo Reservoirs supply fresh water for the process plant. Reclaimed water from the El Llagal tailings containment pond is used as a supplementary water supply.

Three vertical turbine barge-mounted pumps at Hatillo Reservoir and three vertical turbine in-line booster pumps pump fresh water directly to the fresh water pond at a maximum rate of 3,200 m3/h. The pipeline total length is approximately 10.5 km and utilizes 24 in and 30 in diameter HDPE, and 24 in carbon steel for the high pressure inclined section after the booster pumps. The fresh water pond has 12 hrs of storage at normal consumption rates and is positioned at an elevation which is 60 m above the plant to achieve a reliable gravity discharge.

The reclaim water from El Llagal TSF has six barge pumps capable of pumping close to a maximum of 6,000 m3/h through two parallel pipelines made up of both 30 in carbon steel and 32 in high density polyethylene (HDPE). Under normal conditions, three to five pumps operate simultaneously. Reclaim water is pumped directly to both the ETP and the Expansion Process Water Tank.

The pipeline between Hatillo and the freshwater pond includes points where fresh water is drawn off for two additional purposes. The first is to feed the plant’s fire water tank and potable water treatment system and storage tank (Cumba tanks). The second is to provide make-up water to the new Taino Dam. The Taino Dam will provide three days of water supply to the process plant in the event of a long-term outage of the Hatillo pumping system. When called upon for service, three barge pumps can be activated to pump fresh water to the Fresh Water Pond. Taino Dam will replace the Hondo Reservoir that will be converted to an acid run-off collection pond for the expanded Hondo PAG waste dump.

The plant site is located on a ridge between two drainage catchments. Where possible, runoff from the process plant is directed to the Margajita drainage area to separate it from the storm water runoff from the old facilities. Otherwise, a collection pond captures the runoff before it is returned to the process plant to serve as make-up water.

Process Water
The source of process water is the POX feed thickener and the flotation tailings thickener overflows. Process water is used in milling and thickeners as top-up and is supplied by dedicated operating and standby process water pumps. Process water is also used as service water for flushing, hosing and screen spraying applications.

Spray water is used on the milling discharge vibrating screens, trommel screens, trash screens and FTCIL tails screen.

Spillage in the process water distribution area is collected in the area sump and pumped back into the process water tank using the process water spillage pump.

The averaged reclaim water pumped from TSF is 3,340m 3/h, 20% is reused in process and 80% is treated in the effluent treatment plant (ETP) before being discharged into the Margajita river.

Production

Operational metrics

Personnel

Job Title	Name	Profile	Ref. Date
Chemical Laboratory Manager	Kelvin Rafael Núñez Santana		Oct 4, 2024
Country Manager	Juana Barceló		Oct 4, 2024
Environmental Superintendent	Yelisa Cuevas Díaz		Oct 4, 2024
Fixed Plant Maintenance Superintendent	José Gabriel Terrero Alburquerque		Oct 4, 2024
Maintenance Planner	Juan Araujo		Oct 4, 2024
Maintenance Superintendent	Ludwig Alexander De los Santos Dipré		Oct 4, 2024
Manager Site General Services	Andrew Briggs		Oct 4, 2024
Mine Manager	José Recio Herrera		Oct 4, 2024
Mobile Equipment Maintenance Manager	David Hogg		Oct 4, 2024
Procurement Superintendent	Yamal Escaff		Oct 4, 2024
Supply Chain Manager	Gustavo Ahumada		Oct 4, 2024
Supply Chain Superintendent	Saul Naranjo Lopez		Oct 4, 2024
Tailings Storage Facility Superintendent	Yohan Emilio Mendez Beltre		Oct 4, 2024