2352-0000-25RP-001 - Process Description Rev 0

Minera Yanacocha SRL Process Description 2352-0000-25RP-001 Gold Mill Project – Cajamarca Peru 6 December 2006 Contract 53235200 Page 1 of 48 Rev 0

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PROCESS DESCRIPTION

2352-0000-25RP-001 Rev 0 Process Description

This specification has been revised as indicated below. Please destroy all previous revisions.

Rev. No.

Date Originator's Name & Initials

Reviewed /Checked By

Name & Initials

Description / Issue

A 22 Nov 05 Andy Briggs

APWB

Alfonso Videgain

AV

Internal Review,

For Information

B 30 March

06

Andy Briggs

APWB

Alfonso Videgain

AV

Issued for Approval

0 6 Dec 06 Andy Briggs Issued for Design

APPROVALS SIGNATURES DATE

Lead Engineer: Andy Briggs 6 Dec 06

Engineering Manager: Freddie Colon

Project Manager: F. M. Caichac

Client Representative Kim Hackney

ISSUED FOR : Design Construction Other


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PROCESS DESCRIPTION


Table of Contents

1 INTRODUCTION............................................................................................................... 3

2 PROCESS SUMMARY ..................................................................................................... 6

3 DETAILED PROCESS DESCRIPTION ............................................................................ 9

3.1 Crushing…………………………………………………………………………..………….9 3.2 Milling Circuit…………………………………………………………………….……….…11 3.3 Pre-Leach Thickener…………………………………………………………….…………14 3.4 Leach Circuit……………………………………………………………………….…….....15 3.5 Counter Current Decantation…………..………………………………………….………16

3.6 Mill Sands Disposal……………………………………………………………..……….…18 3.7 SART…………………………………………………………………………………….…..20 3.8 AVR…………………………………………………………………………………………..27 3.9 Carbon Adsorption and Carbon Handling………………………………………………..31 3.10 Reagents…………………………………………………………………………………….33 3.11 Water Circuits…………………………………………………………………………….....41 3.12 Air Systems………………………………………………………………………………….46 3.13 Consumables………………………………………………………………………………..47


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PROCESS DESCRIPTION


1.0 INTRODUCTION A block process flowsheet for the Yanacocha Gold Mill is presented below. The overall process will comprise the following unit operations:

• Primary crushing in the existing agglomeration area • Conveying from primary crushing to crushed ore stockpile • Crushed ore storage in an open stockpile • Reclamation and conveying from the crushed ore stockpile to SAG milling • SAG milling in a single stage mill with wraparound motor • SAG mill pebbles rejects recycle by conveyors (no crusher) • Pre-leach thickening • Leach circuit with 24 hours residence time in 6 tanks arranged in series. • CCD circuit comprising 5 stages of thickening and wash • Mill sands pumping, pipeline and disposal (Knight Piésold’s scope) • Mill sands storage facility, and reclaim water systems (Knight Piésold’s scope) • SART circuit for copper removal • Copper precipitate handling • AVR circuit for cyanide recovery from SART solutions (used to balance cyanide

demand at LQ). • Neutralization of SART and AVR effluent solutions with lime. • Gold recovery from solution using existing carbon columns at La Quinua. • Carbon stripping and regeneration circuit at La Quinua • Eluate treatment in the existing Merrill-Crowe circuit at Yanacocha • Retorting and smelting in the existing refinery at Yanacocha • Reagents - mixing & addition systems for the following:

• Lime Supply – using existing storage silo at Agglomeration, and the LQ AWTP lime slaking plant.

• Flocculant – a large system for the CCD circuit, and a second system for the SART thickeners.

• Cyanide • Caustic soda • Sodium hydrosulfide • Sulfuric acid • Diatomaceous earth


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PROCESS DESCRIPTION


• Water services comprising: • Low cyanide process water and CCD wash water, using barren solution from

the carbon columns at La Quinua. • Raw water from La Quinua AWTP plant • Mill dilution water from pre-leach thickener overflow plus make-up from LQ

barren solution. • Fire water reticulation using raw water • Gland seal water using raw water

• Air Services Comprising • Plant and instrument air • Low pressure compressed air for the gold leach

• Diesel fuel - required only for emergency power generation.

Auxiliary Facilities The project will include the following infrastructure.

• Site access roads • Emergency drainage pond • Site drainage system • Main electrical substation • Power distribution • Reagent storage buildings • Covered area for the air compressors • A new dedicated sewage plant • Toilet facilities around the plant • Control room, lunch room, meeting room • Metallurgical lab within the plant for titrations, AAS, sample preparation, etc • Security fencing around the plant, guard house, and security systems • Offices – extension to existing facilities at the LQ Agglomeration plant • Workshops - extension to existing facilities at the LQ Agglomeration plant • Existing warehouse extension at La Quinua


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PROCESS DESCRIPTION


Figure 1 Yanacocha Gold Mill Block Flowsheet

Flocculant

Crusher(existing)

Milling(SS SAG)

Pre-LeachThickener

Leach(24 hrs)

CCD(5 Stages)

SARTPrecipitation

Mill SandsDisposal (LQ Pad)

Gold Recovery(at La Quinua)

Water From La QuinuaAWTP for Gland Seal, Raw Water, etc

Flocculant, Cyanide

NaHS, Sulfuric Acid, Flocculant

Lime

Cyanide, Lime

AVR (1 Train)(2 Trains Future)

SARTNeutralization

Caustic Soda

Precip FiltrationDispatch - Smelter

Caustic, DE

Mill Water Make-up -From La Quinua Barren Solutions

Conc NaCNRecycle to Mill

CCD Wash from LQ Barren Solutions

Lime, Flocculant

Barren Solution toLa Quinua Leach Pad

SART & AVRBypass

Raw Water

LimeLime From LQ LimeSlaking Plant at AWTP

Water for pump glandseals, sprays, etc

Lime to Mill, Gold Leach, SART

Mill DilutionWater

AVR Bypass

Ore

Water Make-Up

Mill Sands forGypsum Seed

Gypsum Recycleto CCD

PregnantSolution

PregnantSolution

Solution Drainto LQ Ponds

Main Ore StreamSolution & ReagentsOre Stream for Gypsum Seeding

Last CCD Stageunderflow


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PROCESS DESCRIPTION


2.0 PROCESS SUMMARY The circuit will be designed to treat 5mtpa of ore, which is equivalent to 620tph at 92% (8,059hrs per year) availability. Ore will be crushed in the existing crushing circuit at the La Quinua agglomeration plant and conveyed to a new crushed ore stockpile. Crushed ore will be milled in the presence of cyanide solutions using a single stage SAG mill. Equipped with a 16.5MW gearless drive. Mill discharge will gravitate through a trommel, with oversize material being recycled to the mill feed by conveyors. Trommel undersize will be pumped by a single pump to hydrocyclones, with underflow being recycled to the mill. Cyclone overflow slurry will gravitate to a pre-leach thickener, and thickener underflow, at a density of 60 to 65% solids will be pumped to the gold leach circuit. Gold leaching will start in the mill because of the cyanide present, and will be completed in the leach circuit, which will comprise 6 tanks arranged in series. 24 hours leach residence time at 60% solids will be provided. Gold leach slurries will gravitate to a 5 stage CCD thickening circuit for solid/liquid separation. High wash efficiencies on the CCD thickeners lead to high recoveries of Au, Ag, Cu, and CN- to the pregnant solution overflow, and thus the final stage underflow slurry will be suitable for discharge to the mill sands storage facility without the need for cyanide destruction. Wash solutions will comprise barren solution from the La Quinua carbon column circuit. When transition ores are treated the resulting solutions will contain copper cyanide complexes, and a copper removal stage will be necessary. A SART – Sulfidization, Acidification, Recycle, Thickening - circuit will thus be included in the circuit to precipitate copper (and silver, plus mercury and other base metals) as sulfides. The sulfide precipitate will be collected, dewatered, bagged and sold to local smelters for copper and silver revenues. Treated solutions from the SART circuit will contain a gold cyanide complex and cyanide as the free radical, which can be re-used for gold leaching on the La Quinua leach pad, after gold recovery in the carbon columns. However there may be some years when the cyanide released by the SART circuit will be in excess of that required by La Quinua. When this occurs, excess cyanide will be recovered in an AVR (Acidification, Volatilization and Re-adsorption circuit) where the acidic solution from the SART circuit will be subject to cyanide stripping by a high flow of air in sealed stripping and re-adsorption towers. Air containing cyanide will be recycled to re-adsorption towers where the cyanide will be adsorbed into a concentrated solution of caustic soda. A solution of 10 to 15% NaCN will be formed, which will be recycled to the milling circuit.


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PROCESS DESCRIPTION


Three parallel trains of stripping and re-adsorption columns will ultimately be required for the Gold Mill circuit. Initially only a single train will be installed, since La Quinua will be able to handle all the cyanide added at the gold mill. The solutions from SART or AVR will contain low levels of free cyanide together with the gold cyanide complex at a low pH. These solutions will be neutralized with lime, and gypsum will be precipitated and collected in a thickener and recycled to the CCD circuit. The resultant solution at a ph of 10 or greater, containing cyanide and gold, will be pumped to the La Quinua carbon adsorption columns for gold recovery. Tonnage treatment rates on the leach pads at La Quinua will be reduced in 2008, compared to current rates, thereby providing spare solution treatment capacity at La Quinua. Thus, no new carbon adsorption facilities will be required for the Yanacocha Gold Mill. It is also assumed that all the loaded carbon generated from treatment of YGM solutions can be treated in the La Quinua carbon stripping circuit. All areas of the plant will be installed on individual bunded concrete pads. The volume of storage within each bunded area will be greater than the volume of the largest tank within that area. The cyanide, lime, and flocculant bund areas will also overflow into the CCD bund area, which has a large storage volume of over 6,000m3. A spillway and drain connects the mill bund area to a lined emergency spillage pond. Solutions can be reclaimed to the process from this pond by a floating vertical spindle pump installed on a barge. Piperacks running between bunded areas will be provided with double containment for cyanide solutions. Each bunded process area will be served by spillage pumps that can return any spillage directly into the process, as and where it occurs. Hosing services will be available to wash down the concrete pads. Chemicals will be made-up in dedicated mixing and storage tanks – these will be located in bunded areas designed to take 110% of the largest tank contents, or to allow overflow into adjacent containment areas. Care will be taken to ensure that chemicals that are incompatible will not be stored or mixed in close proximity to each other. All gaseous emissions will be scrubbed prior to discharge to the atmosphere through a stack. Emissions will meet the applicable environmental regulations. The circuit is described in more detail in section 3 of this report, with special emphasis on the SART and AVR circuits.


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PROCESS DESCRIPTION


2.1 Plant Location The YGM will be located to the north of the La Quinua agglomeration plant, and just to the west of the La Quinua Mine Water Pond. It will be bordered on the west and north sides by the Tual Canal. All process spills will be retained within the concrete bunds provided for unit process, as described previously. Sediment control ponds will be installed prior to construction, and all run-off water within the plant (outside the process areas) will be directed away from the Tual canal. The plant will be fully fenced with one or two points of entry and exit only, one of which will be provided with a security guard house for entry control. The fence will ensure that unauthorized persons and animals do not come into contact with process solutions. 2.2 Cyanide Recycle Several processes are included in the process flowsheet that are not commonly utilized in Peru – CCD, SART and AVR. These are described in more detail in section 3 of this document. The purpose of CCD is to wash the process slurries with large quantities of barren heap leach solutions from La Quinua to extract all the dissolved gold, silver, copper, other metals and cyanide into process solutions for further treatment. The resultant slurries from CCD will contain cyanide levels similar to the present heap leach barren solutions, and these slurries (at a high density) will be deposited in a lined area of the existing heap leach pad at La Quinua. SART is a process for precipitating copper as a sulfide – this can then be sold to smelters for further processing for copper (and silver) credits. Cyanide associated with the copper is retained in solution in the YGM circuit AVR recovers cyanide from plant solutions into a small volume of concentrated cyanide solution for recycle to the milling circuit. Treated solutions containing low levels of weak acid dissociable (WAD) and free cyanide are returned to the La Quinua circuit for gold recovery in existing carbon columns, followed by re-use as irrigation solutions for the heap leach.


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PROCESS DESCRIPTION


3.0 DETAILED PROCESS DESCRIPTION 3.1 Crushing The crushing circuit will utilize the crusher feed bin, jaw crushers, and apron feeders at the agglomeration circuit at La Quinua. Both of the existing lines will be used, one at a time, thereby providing full standby capabilities in this circuit. This is important given the high abrasion index for the gold mill ore. Ore will be transported from the mine by truck and deposited on the ROM ore stockpile ahead of the crusher circuit. This stockpile will have a large capacity to cater for the typical Yanacocha mining rate, and will allow blending of different ore types if found desirable for efficient plant operations. It is anticipated that tonnage delivery may be at a high rate (up to 50,000tpd), but sporadic as each high grade block is mined and hauled. The stockpile capacity will thus be dictated by the mining schedules. Ore will be fed to the crushing circuit by two CAT 992 front-end loaders, delivering rock at minus 750mm in size to the existing ROM Ore Bin [3281-BN-09602]. The CAT 992s may need to be augmented by a small truck, or tractor dozer when handling the further reaches of the stockpile. A new static grizzly may be installed over the ROM ore bin to protect the apron feeders from over-large material. The rock breaker [3281-BK-09611], currently located between the two vibrating grizzlies, will also be relocated to the ROM ore bin. Variable speed apron feeders [3281-FE-09603, 04] regulate the feed to each crusher; spillage from the feeders is collected on the primary crusher feeder dribble conveyors [3281-CV-09647, 48], which discharge to the crusher discharge conveyors [3281-CV-09621, 22]. The crushers installed in the agglomeration circuit [3281-CR-09614, 16] are Jaques C160 single toggle jaw crushers, each crushing up to 585tph of ore at a closed side setting of 165mm. The crushers will be fed from apron feeders feeding material onto vibrating grizzlies [3281-FE-09609, 10]. Grizzly undersize will bypass the crushers onto the crusher discharge conveyors. The existing vibrating grizzlies will be refurbished for the YGM project. The crusher discharge conveyors will also require modifications at their head chutes. These conveyors will transfer ore to the new crushed ore stockpile feed conveyor [1100-CV-12001] which will deliver the crushed ore to the crushed ore stockpile [1300-SL-12001]. The conveyor is designed for a capacity of 1,613 tph (at 8% moisture) and will run at 3m/s. The belt width will be 1,200mm, and it will have a lift of 32m – it will be equipped with a 185kW fixed speed drive. The crusher discharge conveyors are fitted with tramp iron magnets [3281-MA-09625, 26] to protect the downstream conveying system from large pieces of tramp metal. Crusher weigh scales [3281-SL-09623, 24] are also installed on the crusher discharge feed conveyors, and will totalize the ore sent to the stockpile.


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PROCESS DESCRIPTION


The existing agglomeration circuit provides for cement addition to the crusher discharge conveyor belts from the existing cement silo [3340-BN-09804]. This system will be retained and used for lime to provide addition of a significant proportion of the lime required in the mill, and to reduce the requirement of slaked lime slurry. Some modifications to the silo and feeders may be required (eg a bin activator below the bin, slow down the feeders) to enable the system to operate satisfactorily. Because the lime will be added prior to the stockpile, there will be poor control of addition, and lime slurry will still be required in the mill for pH control. The crushed ore stockpile [1300-SL-12001] will have a live capacity of approximately 9,100 dry tonnes, providing 14.7 hours of ore storage. The stockpile will have a total capacity of 35,693 tonnes, and assuming an angle of repose for the ore of 37o, it will be 63.7m in diameter and 24m high at the apex. Ore will be withdrawn from the stockpile using 3 variable speed feeders [1300-Fe-12001, 02, 03]. Each feeder can provide the design tonnage at maximum speed, however it has been recommended by Jenike and Johanson that all three feeders operate together to provide an even flow of material through the stockpile to minimize segregation. The feeders will be 7m long, and equipped with 15kW drives, and will discharge the ore onto the mill feed conveyor [1300-CV-12001]; the mill feed weigh scale [1300-WS-12001] on this conveyor will control the speed of the feeders, and will totalize the mill feed tonnage. The mill feed conveyor will be fixed speed, 1066mm (42 inch) wide, running at 2.3m/s and equipped with a 55kW drive. A particle size monitor [2100-SA-12001]will be installed above this conveyor. This instrument scans the ore feed on the conveyor belt, either by digital camera, and provides a continuous read-out of particle size. Initially the data produced will not be used for mill control, but this might be feasible during future operations. Dust generated at the crusher feed area will be controlled by the use of the existing dust suppression sprays. A wet scrubbing system [1300-SK-12001, 1300-FA-12002] will be provided at the mill feeders to remove dust from the stockpile tunnel. Raw water will be used for the scrubber, to maintain cyanide free conditions in the area. The resulting dilute slurry will be pumped by the stockpile scrubber discharge pump [1300-PU-12002] to the mill discharge sump. High pressure compressed air will be generated for the crushing circuit by existing compressors [3550-CP-09680, 01]. The compressed air will be filtered through an in-line filter and stored in an air receiver [3500-VE-09682] to ensure a continuous air pressure in the system. Instrument air will be derived from plant air, dried in an air dryer [3500-DR-09683] and collected in the instrument air receiver [3500-VE-09684]. A ball feeder [1300-FE-12005], located at the exit of the stockpile tunnel, will feed balls onto the SAG mill feed conveyor belt. The ball feeding system will be similar to that installed at Tarkwa in Ghana, and will comprise a hydraulic ram and sliding plate pushing balls up and out of the ball bin and over into a chute feeding the mill feed conveyor belt. The mill ball feed bin [1300-BN-12002] will be sized for several days’ ball requirements and will be designed to receive ball deliveries in bulk by truck.


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PROCESS DESCRIPTION


A strategic stockpile of balls equivalent to 30 day’s requirements will be held on site. These balls will probably be stored in bags stacked in an area adjacent to the stockpile. A front end loader or front-end loader will transfer balls to the ball feeder when necessary (should normal deliveries be interrupted). 100mm balls will be used for the SAG mill. It is important that these balls be added continuously throughout the day, say once per hour, to reduce large fluctuations in ball load within the mill. The ball feeder will operate on a timed basis, adding the required number of balls from the day bin – frequency of operation, and amount of balls added will be adjustable, set by the operating staff. A spillage pump [1300-PU-12001] will also be provided at the entrance to the tunnel, to collect rain water run-off and discharge it to the mill discharge sump. Raw water will be provided for hose supply, but the majority of clean-up requirements will be met by a small front-end loader or bob cat. 3.2 Milling Circuit The grinding circuit will grind the crushed ore to a nominal grind size of 80% passing 75μm. The circuit will consist of a single stage semi-autogenous grinding (SAG) mill [2100-ML-12001] in closed circuit with hydrocyclones [2100-CY-12001]. The SAG mill will be 9.75m diameter by 9.75m EGL (effective grinding length) and will be equipped with a 16.5MW gearless drive providing full variable speed capabilities. Crushed ore will be discharged from the mill feed conveyor into the SAG mill feed chute [2100-ST-12001]. This chute will be designed as a rock box, and it will be supplied on a hydraulically operated trolley for ease of removal. A spare chute will be provided for maintenance (chute re-lining) flexibility. The feed rate to the mill will be controlled to a value set by the operator, by variation of the apron feeder speeds. Mill dilution water will be added to the feed chute using a ratio controller to maintain a constant slurry density within the SAG mill. The mill is expected to operate at a slurry density of 70 to 75% solids, with a 9 to 15% ball loading and a total charge volume of 25 to 28%. Lime slurry will also be added to the SAG mill feed chute to adjust the slurry pH in the circuit to 10.5 for corrosion protection and to reduce the hydrolysis of NaCN in the circuit. SAG mill discharge will pass through a trommel screen [2100-SC-12001], with oversize (plus 10mm material) being recycled back onto the mill feed conveyor using the 610mm wide pebble recycle conveyors [2200-CV-12001, 02, 03]. The quantity of pebble generation is not known at this stage, and the conveyors have been designed for a pebble production rate of about 35% of the feed tonnage, or 220tph. Real estate will be allowed in the layout for a pebble crusher to be installed, should the pebble generation rate warrant such an installation in the future.


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PROCESS DESCRIPTION


The first pebble recycle conveyor will be fitted with a tramp iron magnet [22100-MG-12001] to remove broken or worn balls from the mill circulating load, and a weigh scale [2100-WS-12001] to provide a measure of the circulating load of pebbles. Discharge slurry from the mill will flow through the trommel screen and gravitate to the mill discharge sump [2100-SU-12001], where it will be diluted with mill dilution water to a density of approximately 45% solids and pumped to the hydrocyclones. The cyclone feed pump [2100-PU-12001] will be variable speed, equipped with a 932kW motor. A single pump will be installed. Pump speed will be controlled by the level in the mill discharge sump; dilution water will be added to maintain a constant cyclone feed density, which will be measured using a nuclear density gauge. An alternative control philosophy of constant flow (and hence pressure) to the cyclones can be instituted with the same instrumentation and control circuitry. The classification circuit will operate in closed circuit with the mill and will consist of a nest of ten 660mm (26”) diameter cyclones arranged in a circle, a feed distributor [2100-DB-12001], cyclone feed isolation valves and overflow and underflow collection launders [2100-LN-12001, 02]. The number of operating cyclones will be adjusted manually to maintain a steady distributor feed pressure, and will normally be 8, with 2 standby. The distributor and cyclone arrangement will allow for a maximum of 12 cyclones to be installed. Dilution water to the circuit will contain cyanide recycled from the SART and AVR circuits. Fresh cyanide will be added to the pre-leach thickener feed, and recycled to the mill in the dilution water, to ensure rapid leaching of gold and silver. Some time prior to stopping the mill for re-lining or internal inspection, cyanide addition to the pre-leach thickener, and recycle of cyanide from the AVR circuit should be discontinued to reduce cyanide levels in the mill to safe levels. Cyclone underflow slurry at a density of 75% solids will be returned to the mill, and overflow slurry at approximately 21% solids will gravitate via trash removal screens [2100-SC-12002, 03] to the pre-leach thickener. The trash screens will comprise two 25m2 linear screens equipped with a monofilament polyester cloth with an aperture of 0.5 mm, to remove entrained trash (woodchips, plastic etc.). The screen oversize will be discharged off the end of the screens using high pressure sprays, and will be dewatered on sieve bends [2100-SC-12004, 05] prior to falling into trash skips [2100-BN-12001 to 04] for later disposal by fork lift truck. The screen sprays will be low cyanide process water because of the quantity required, but the trash will need to be rinsed with raw water prior to leaving the plant site, to allow it to be safely disposed of.


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PROCESS DESCRIPTION


A 16.5MW gearless motor will be installed to drive the mill. This drive will be variable speed across its entire speed range – and can vary the mill speed up to a maximum of 85% critical speed. The drive will have inching capabilities for relining and maintenance purposes, and frozen charge protection. An independent braking system will be provided for the mill. The mill will be trunnion supported with 4 bearing pads per trunnion. A hydrostatic lubrication system will be provided, comprising an oil reservoir and high and low pressure lubrication systems. The high pressure module will comprise three hydrostatic lube pumps, two hydrostatic thrust pumps, two pad piston pumps, two accumulator pumps and four accumulators. The low pressure module will consist of two low pressure pumps, two oil filters and two heat exchangers. Cooling water will also be required for oil cooling, and for the wraparound drive. The cooling water circuit will be a closed system utilizing high quality water. Cooling will be through two air cooled chiller units [2100-CT-12001, 02] operated in series, and the cool solution will be circulated through the vendor supplied heat exchangers using one of two available cooling water pumps [2100-PU-12005, 06]. Water flow, pressure and temperature requirements will be defined by the mill and motor vendors. A single overhead crane [2100-HI-12001] will be installed in the mill building for mill, trommel screen, cyclone feed pump and cyclone maintenance. This crane will also be used to unload liners and lift them up to the mill re-lining floor. A liner handling machine [2100-LH-12001] will assist in mill relining, and a thunderbolt machine, [2100-ME-12001] supported from a monorail around the mill, will assist in liner bolt removal. The milling area will be bunded for spillage retention. Mill area spillage will be handled by 2 spillage pumps [2100-PU-12003, 04], one located near the mill discharge sump, and the second beneath the cyclones and trash screens. Both pumps will pump spillage to the mill discharge sump, and the trash screen spillage pump will also have the option of returning spillage to the cyclone overflow launder. The spillage sump located by the mill discharge sump will receive a large volume of spillage whenever the mill is tripped, and should be sized for 3 sump volumes. The sump will be equipped with high pressure hosing points, permanently mounted, to re-slurry the settled material and prevent the spillage pump from becoming blocked. The sump will be provided with drive in facilities to remove coarse material by front end loader or bobcat, should the need arise. Excess spillage in the mill area (due to frequent stoppages) will overflow this sump to the emergency spillage pond [0200-PO-12001]. This pond will have a useful volume of 783m3 (plus 0.5m freeboard), and will be lined with a single HDPE liner. Hosing facilities will be provided to assist in removing any solids from the pond, and a submersible pump [0200-PU-12001] will be installed to return spillage to the milling circuit. As noted above, milling will occur in the presence of cyanide solutions. Thus cyanide will be present in solutions in the milling, thickening, leach, CCD, SART, and AVR circuits within the overall process.


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Any vehicle entering the area may be contaminated with cyanide solutions on its tires, and vehicles should be washed by hosing the tires with raw water as they leave the area. All of the above circuits will be equipped with cyanide monitors and alarms near all operating locations adjacent to tanks so that any hazardous situations may be immediately identified. Emergency showers and eye wash facilities will be provided in the process areas where hazard solutions are present. 3.3 Pre-Leach Thickener A single hi-rate thickener [3100-TH-12001] will dewater the cyclone overflow slurry prior to the leach circuit, thereby reducing the leach tankage and the cyanide addition required. Trash screen undersize slurry (cyclone overflow) will gravitate down a launder through the thickener feed launder sampler [3100-SA-12001] to the pre-leach thickener feed box. The sample will gravitate to a secondary sampler [3100-SA-12002], which will produce a shift sample for sizing and chemical analyses. The discarded slurry sample will discharge into the thickener spillage area and be returned to the thickener feed box by a small Sala-type sump and pump [3100-PU-12004]. The main slurry stream passing through the launder sampler will enter the thickener feed box [3100-BNI-12001] where flocculant will be added to assist in settling the solids in the thickener. Concentrated flocculant from the flocculant make-up system will be diluted with low cyanide process water in an in-line mixer [3100-MX-12001] prior to addition to the feed box. Settling rates for this material have been measured by Pocock Industrial, and show a fast settling slurry, providing high underflow densities with low residence times in the thickener. A 32m thickener is recommended based on a conservative use of the testwork data. The solids will be settled within the thickener and will be pumped as a thickened slurry at a density of 60 to 65% solids from the cone of the thickener by one of the two thickener underflow pumps [3100-PU-12001, 02] to the first leach tank. These pumps will be equipped with 150kW variable speed drives. The thickener underflow density will be controlled from a nuclear density gauge on the discharge pipeline, by varying the thickener underflow pump speed. Gland seal water will be provided to the underflow pumps from the gland service water reticulation header. Flocculant addition to the thickener will be controlled by the thickener bed level in order to maintain a clear thickener overflow.


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PROCESS DESCRIPTION


The slurry feed to gold leaching will be sampled for metallurgical accounting and plant control using a linear cross-cut sampler [3100-SA-12003]. This sample will gravitate to the leach feed secondary sampler [3100-SA-12004], which will be a rotary (Vezin-type) sampler. Sample discard will fall directly into the first or second leach tank. Clear solution from the thickener will overflow to the mill dilution water tank [6500-TKI-12002], from where it will be returned to the feed and discharge end of the mill for slurry density control. The thickener will be installed in the CCD bund area, together with the mill dilution and low cyanide process water tanks, and the cyanide mixing and storage facilities. The bund volume to the top of the bund wall will be able to contain the entire contents of the largest thickener in this area (the hi-compression thickener for CCD stage 5). Spillage from the pre-leach thickener area will be returned to the pre-leach thickener feed box by the thickener area spillage pump [3100-PU-12003]. This pump will also be able to discharge spillage directly to the final CCD thickener, and then on to disposal as mill sands, in the event of a major process upset. 3.4 Leach Circuit Leaching will be accomplished in 6 leach tanks [3200-TK-12001 to 06] providing a total residence time of 24 hours - 4 hours per tank. The tank volumes will be designed for a slurry density of 60% solids, giving an average tank volume of 2,600m3. Agitation will be provide by 150kW mechanical agitators [3200-AG-12001 to 06]. There will be a step down of 300mm between adjacent tanks to allow for gravity flow of the slurry. The ground slope in the area provides this drop, without the need for adjustment in individual tank sizes, and thus the average tank volume of about 2,600m3 will actually occur in all tanks, which will be 14.9m in diameter with a height, including freeboard and allowance for the overflow launders of 15.9m. Feed streams to the circuit will comprise thickener underflow slurry, cyanide as a 20% solution, and lime as a 25% solids (w/w) slurry. All of these flows can also be directed to the second leach tank in the event that the first leach stage is off line. The level of cyanide in the leach slurry will be controlled by a WAD cyanide analyzer [3200-SA-12003] which will measure cyanide levels in the feed, discharge and inter-tank flows within the circuit. Mill dilution water will contain cyanide, and cyanide will normally be added to the pre-leach thickener. Addition of cyanide (and lime) to leach tanks 1, 2, 3, and 5 will be for “top-up” purposes. Lime slurry addition will be controlled to maintain a pH in the circuit of between 10.0 and 10.5 to prevent the hydrolysis of cyanide. The majority of the lime addition to the circuit will normally be on the stockpile feed conveyor as dry lime, and as lime slurry to the SAG mill feed chute.


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PROCESS DESCRIPTION


Low pressure air will be added to the leach from the leach air compressors [6600-CM-12005, 06]. The air pipe will enter the top of the leach tanks, and pass down the inside of the tank, behind a baffle, to a single air sparge point (a “chinese hat”) at the center of the tank. Slurry will flow through each leach tank in series, and onto the next tank through connecting launders. The launder system will be designed to allow any tank in the circuit to be bypassed. Slurry will enter each tank into a “downcomer” which will direct the slurry into the body of the tank, and prevent it flowing across the leach tank directly into the overflow launder. Leach discharge will be sampled for metallurgical accounting and plant control. The leach tails primary sampler [3200-SA-12001] will cut a slurry sample from the final leach stage overflow stream. This sample will gravitate to the leach tails secondary sampler [3200-SA-12002]. The final sample will be collected at the end of each shift, and dispatched to the laboratory. Sample discard will report to the leach area sample return pump [3200-PU-12004], a Sala-type integrated sump and pump, and will be pumped back to the head of the leach. The leach tanks will be installed in a dedicated bund area equipped with two spillage pumps [3200-PU-12001, 02]. A portable drain pump [3200-PU-12003] will also be provided in this area for emergency drainage of the leach tanks to limit the need to drain tanks to the floor space. This pump can be connected to any leach tank, and the pump discharge connected to pipes installed up the side of each tank – slurry transfer will normally be to the adjacent leach tank. The leach area will be equipped with cyanide monitors to warn if there are abnormal concentrations of cyanide gas in the area. 3.5 Counter Current Decantation - CCD Leached slurry will be washed in a CCD circuit for solid/liquid separation and recovery of dissolved species into a solution for further treatment. Gypsum sludge and return seed slurry will also be returned to the feed end of the CCD circuit because entrained solution with the slurry will be at PLS grade. The circuit will comprise 5 thickening stages with a wash ratio of 1.4 – i.e. 1.4 tons of wash solution – 868m3/h - will be added per tonne of solids feed. Wash solutions will be barren solution from the La Quinua carbon columns.


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PROCESS DESCRIPTION


Underflow from each thickener [3300-TH-12001 to 05] will be pumped to the next stage downstream, with underflow from stage 5 being pumped to the mill sands management circuit. Solution overflowing each thickener will be directed to the previous stage upstream. Between each thickening stage a mixing tank will receive slurry from the previous stage upstream and overflow from the next stage downstream. For example # 3 thickener feed tank [3300-TK-12009] will receive underflow from the # 2 stage underflow pump [3200-PU-12003, 04] and overflow from # 4 thickener [3300-TH-12004]. These flows will be thoroughly mixed in the mixing tank and will overflow to the third stage thickener [3300-TH-12003]. The CCD thickeners will be identical to the pre-leach thickener – being 32m in diameter, but will be operated at slightly higher underflow densities. Settled solids will be pumped at a slurry density of 65 to 68% solids from the cone of each thickener by one of the two installed thickener underflow pumps [3300-PU-12001 to 10] to the next CCD stage mix tank. Thickener underflow density will be controlled from a nuclear density gauge by varying the thickener underflow pump speed. Gland seal water will be provided to these pumps from the gland service supply header. Flocculant addition to the thickener will be provided from the central make-up facility by a dedicated pump (one per thickener), and will be controlled by the thickener bed level in order to maintain a clear thickener overflow solution. Flocculant solution will be diluted to 0.1% strength using low cyanide process water in in-line mixers [3300-MX-12001 to 05] prior to addition to the thickener feed launders. CCD wash solutions (and process water make-up) will be obtained from carbon column barren solution at La Quinua. A total of 1,500m3/h will be required of which 870m3/h of solution will be required for the CCD circuit (a wash ratio of 1.4). Three pumps [6520-PU-12016 to 18] will be installed for the water transfer, with two pumps operating in parallel and one pump as standby. These pumps are rated at 750m3/h each, at 173m head – they will be equipped with 500kW fixed speed drives. Wash solution will be added directly to the 5th CCD stage mix tank [3300-TK-12011], (or the 4th

stage tank if the 5th stage is off-line). Thereafter, thickener overflow from each stage will gravitate to the next mixing tank upstream – stage 5 overflow to stage 4 mix tank, (or stage 3, if 4 is off-line), etc. The mix tanks [3300-TK-12007 to 11] are sized for a mixed slurry residence time of approximately 45 seconds, and will be 20m3 in size. Each will be equipped with a 2.2kW agitator [3300-AG-12001 to 05] to ensure underflow and overflow streams are thoroughly mixed, so that high washing efficiencies can be obtained. The tanks will be equipped with baffles and down-comers to ensure that there is no short-circuiting of slurry within the tank.


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PROCESS DESCRIPTION


Pregnant solution from the first stage thickener overflow will be collected in the pregnant solution tank [3300-TK-12013] and pumped to the SART circuit if it contains high levels of copper, or to the gypsum thickener overflow tank (from where it is pumped directly to the carbon columns at La Quinua for gold recovery) if no copper is present. The pregnant solution tank will be sized for 30 minutes surge capacity – 600m3, and will be 10.8m in diameter and 7.1m tall to enable thickener overflow to gravitate to the tank. Two pregnant solution pumps [3300-PU-12013, 14] will be installed, with one running and one standby. The pumps will be variable speed, equipped with 75kW drives. Overflow from all thickener stages will be automatically sampled [3300-SA-12001 to 05] through a solenoid valve on a timer, followed by a wire sampler. Solution samples will provide a guide to plant control in the CCD circuit, and will be important for metallurgical accounting. The CCD circuit will be installed in a large bunded area, together with the pre-leach thickener, the mill dilution and low cyanide process water tanks, the pregnant solution tank, the thickener mix tanks, and the flocculant make-up system. The bund volume can easily accommodate the contents of a thickener, due to the size of the circuit – over 5,000m2 in area. Five CCD spillage pumps [3300-PU-12015 to 19] (one per thickener) will return spillage to the respective thickener feed tanks. 3.6 Mill Sands Disposal Mill sands from the gold plant (the 5th stage CCD thickener underflow) will be deposited in a dedicated Mill Sands Storage Facility (MSSF), designed by Knight Piésold. The MSSF will be in a dedicated area of the La Quinua Leach Pad. The last stage of the CCD circuit will also serve as the mill sands thickener [3300-TH-12005], and will be run to as high a density as possible. Thickener underflow at approximately 71% by weight solids will be collected in the mill sands surge tank [5100-TK-12001], which will be sized for approximately 30 minutes surge capacity plus time to stop and start the mainline residue pumps. The tank will have a total volume of 505m3, and will be 8.2m in diameter by 9.2m tall, and will be equipped with a 75kW agitator [5100-AG-12001]. Slurry feeding the mill sands management system will be sampled for metallurgical accounting and plant control, using a primary and secondary sampler [3300-SA-12007, 08] located on top of the mill sands surge tank. The final sample will be collected at the end of each shift, and dispatched to the laboratory. Sample discard will drop into the tank. Dilution water will be added to the mill sands surge tank to reduce the slurry density to below 69% solids, at which density it can be transported to the mill sands storage facility by centrifugal pumps. Dilution water addition will be controlled by a nuclear density gauge measuring the slurry density in the CCD #5 underflow delivery line.


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PROCESS DESCRIPTION


The mainline mill sands pumps [5110-PU-12001 to 08] will be centrifugal pumps, installed as two trains, each with 4 pumps in series. One train will be operating, and the other will provide a complete standby system. The pumps will pump the slurry at below 69% solids (67.9% including gland seal water) approximately 3.2km to the MSSF. All pumps will be equipped with 300kW variable speed drives – mainly to provide soft start capabilities. The pumps will be supplied with gland seal water (at the correct pressure for each stage) from a dedicated gland seal water tank [5110-TK-12002] through multistage gland seal water pumps [5110-PU-12012, 13] – one pump operating and one standby. Two pipelines will be installed, with the ability for each pump train to discharge into either line. The lines will be 12” diameter unlined schedule 40 mild steel, with a wall thickness of 10.3mm, to allow for corrosion and abrasion during the life of the project. The lines will be in 100m welded sections between flanges that will allow the line to be broken in the unlikely event of a line failure or blockage. The rheological data suggests that the gold mill slurries are fast settling (>90% quartz), and it is believed that the material will settle quickly and may block the pipeline if the flow stops. Hence a sophisticated flushing system has been incorporated into the design. A flushing water pump [5110-PU-12010] will pump water into the suction pipes of the mill sands mainline pumps for pump and pipeline flushing. This will be required when mill sands delivery pipelines are changed over (when the delivery point on the MSSF is changed), or in the event of a power failure. Flushing will be to the MSSF, or into an emergency drainage area on the leach pad at a low spot in the pipeline (just prior to the riser pipe onto the MSSF). The flushing water pump and the mainline pumps will be supplied with power from the emergency power generators in the event of a failure of the main power supply. The mill sands pumping system will be located within a separate bund area separated from the CCD area by a roadway and located such that the pumps discharge into a straight pipeline without any immediate bends. The area will be provided with a spillage sump and pump [5110-PU-12009], which will return spillage to the last stage CCD thickener feed box [3300-TK-12011]. The MSSF will be part of the La Quinua leach pad system. It will be surrounded by ore that has been previously leached, and will be designed with a similar (and contiguous) liner and drainage system to that provided for the leach pads at Yanacocha. The mill sands are expected to bleed extraneous water when compressed on the dam. This water will pass to the drainage system at the base of the dam and enter the La Quinua leach pad solution system. The construction method employed for the MSSF will ensure any supernatant liquor on top of the sands is located against the upper side of the facility, adjacent to the drainage pipes. No solution return pumps will be provided for the system, and no power supply to the MSSF will be required.


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PROCESS DESCRIPTION


Two additional pumps will be located in the mill sands management area. These pumps [5110-PU-12015, 16] will provide seed material for the SART gypsum neutralization circuit, and will pump between 30 and 40tph of mill sands from the mill sands surge tank [5100-TK-12001] to the first SART neutralization tank [3400-TK-12004]. The pumps will be equipped with fixed speed drives, and will be arranged in series because of the onerous pumping duty – high slurry density, low flow, small pipeline. The pumps will be supplied with gland seal water from the plant GSW system, or from the mill sands GSW pumps if the pressure required is higher than the standard plant GSW supply pressure. 3.7 Sulfidization, Acidification, Recycle and Thickening Circuit (SART) Pregnant solutions from the CCD circuit containing high copper concentrations will be directed to the SART circuit, which will recover silver and copper into a sulfide precipitate, and convert CNWAD into free cyanide for later recovery and recycle. Pregnant solution from the CCD circuit will be pumped by one of two installed variable speed pumps [3300-PU-12013, 14] to the SART circuit. Solution will be directed to the gypsum thickener overflow tank [3410-TK-12009], if low copper ores are being treated, and the SART circuit is to be bypassed. From there solutions will be directed to La Quinua for gold recovery. A simplified flowsheet for the SART circuit is presented in Figure 2, below. 3.7.1 SART Precipitation Circuit When SART operates, the solutions will be pumped to the SART precipitation tank [3410-TK-12001]. Addition of sodium hydrogen sulfide (NaHS) and sulfuric acid (H2SO4) into the feed pipe in-line mixers [3410-MX-12001, 02] will react with the copper cyanide complexes in solution to form:

• copper sulfide precipitate (Cu2S), • hydrogen cyanide (HCN) dissolved in solution, • a small amount of hydrogen cyanide gas (HCN)

Silver and any base metals will also precipitate as sulfides, but gold will remain in solution and will not be precipitated, even in small quantities. The main reaction is shown below:

2 Na3Cu(CN)4 + 3.5 H2SO4 + NaHS → Cu2S (s) + 3.5 Na2SO4 + 8 HCN (aq) A copper sulfide "seed" from the precipitate thickener [3410-TH-12003] will also be added to the circuit feed stream to assist in precipitate crystal growth.


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PROCESS DESCRIPTION


Figure 2 Simplified CCD and SART Flowsheet

Underflow at 65% solids

Wash water( LQ barren)

Leach Slurry

Flocculant

Flocculant

Recycle for Seed (80% of forward flow)

Cu2S, etcto bagging

& sales

Wash Water

Metal Precipitate Filter(Belt or filter press)

Filtrate Recycle

Lime

HCN Solution

Neutralization tanks(res time - 60 mins in 3 tanks

H2SO4

NaSH

Precipitation tanks (10 mins in 2 tanks)

CCD Thickener

Note: CCD Circuit will comprise 5 thickeners in counter-current mode.Only 2 are shown below

Flocculant

Gypsum slurryto Mill

Neutralized SolutionTo Gold recovery

(Carbon Columns)

CCD

SART

5th Stage Underflow to Tailings

lid

The sulfide precipitation reactions occur in the feed pipe and the nucleation tank, which will be maintained at pH 4. Solution residence time in the precipitation (nucleation) tank [3410-TK-12001] will be a total of approximately 10 minutes, and the tank will be 233m3 in volume, with a


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PROCESS DESCRIPTION


diameter of 6.7m and a height of 7.2m. The tank will be equipped with an 11kW agitator [3410-AG-12001], and will be sealed and ventilated to the SART area scrubber [3410-SK-12001]. The SART process will be conducted in closed vessels kept under a negative pressure and any HCN or H2S gas that forms will be extracted to the scrubber and removed from the air into a re-circulating caustic solution. Caustic will convert the HCN to NaCN in solution, and this will be periodically bled from the scrubber to the mill dilution water tank [6510-TK-12002], and the scrubber replenished with fresh caustic solution. The copper sulfide that forms will be thickened in the precipitate thickener [3410-TH-12003], which will be equipped with an internal underflow recycle pump and a precipitate recycle (seed) pump [3410-PU-12004], in addition to conventional underflow pumps [3410-PU-12001, 02]. A portion (approximately 300%) of the precipitate generated will be recycled back to the feed to assist with nucleation and growth of sulfide particles. A bleed stream of precipitate from the thickener will be collected in the precipitate filter feed tank [3420-TK-12001], partially neutralized with caustic, dewatered in a filter press, and bagged for later dispatch to a smelter. This precipitate will contain values of copper and silver as sulfides, plus mercury and base metals. The precipitate thickener will be 22m in diameter, based on a conservative hydraulic load of 3m3/h/m2, based on data from Telfer supplied by Rob Dunne. Because the solutions treated will be at a pH of 4, and will contain HCN, the thickener will be sealed and vented to the SART area scrubber. Flocculant addition to the precipitate thickener will be provided from a central make-up facility. This flocculant type will be different from that used in the CCD thickeners because the operating pHs are different. (It is expected that the gypsum thickener will require the same flocculant as that used in the CCD circuit). The dedicated make-up system will be installed adjacent to the SART circuit, and a dedicated pump plus a standby [6440-PU-12014, 15] will dose concentrated flocculant to the thickener through an in-line mixer [3410-MX-12003] for dilution purposes. The copper precipitate thickener overflow will contain cyanide in low pH solutions. This solution will be collected in the SART precipitate thickener overflow tank [3410-TK-12010], which will be sealed and vented to the scrubber. The tank will provide approximately 15 minutes residence time (350m3) at design throughputs. Two solution transfer pumps [3410-PU-12014, 15] on this tank will transfer solution to the AVR circuit for cyanide recovery, or to the SART neutralization tanks. Only one variable speed pump will operate at a time, and a pressure control valve on the off-take to neutralization will ensure the flow to the AVR circuit (at a higher head) is satisfied, with the excess solution being directed to neutralization.


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PROCESS DESCRIPTION


3.7.2 SART NeutralizationThe SART neutralization circuit will receive feed from either the copper precipitate thickener [3410-TH-12003] overflow (when AVR is not operational), from the AVR solution stripping circuit through the stripped solution discharge pumps [4100-PU-12017 to 19], or from a mixture of the two flows. Solutions will be neutralized with lime slurry to pH 10 - 10.5. At high pH, the HCN is converted to free cyanide in solution:

2 HCN (aq) + Ca(OH)2 → Ca(CN)2 + 2 H2O

A gypsum precipitate also forms during neutralization:

Ca2+ + SO42- +2 H2O → CaSO4•2H2O (s)

The circuit will also receive a seed slurry of mill sands from the mill sands surge tank [5110-TK-12001], and a recycle of gypsum thickener underflow from the thickener recycle pumps [3410-PU-12011, 12]. These slurry flows have been included in the circuit design to enable the neutralization circuit to operate at over 10% solids to promote nucleation, to provide enough surface area for gypsum to precipitate out on, and to minimize scale build up on tank walls, agitator impellers and shaft, and the associated pipework. Once gypsum precipitation has been initiated it may be feasible to stop the addition of fresh seed from the mill sands circuit, and maintain a slurry density of 10 to 15% solids within the circuit by recycle of thickener underflow slurry alone. Neutralization will comprise 4 tanks in series [3410-TK-12004 to 07], with allowance for 1 tank always off-line for de-scaling. Three neutralization tanks will provide a total of 60 minutes residence time at a design solution flowrate of 1,400m3/h, plus 240m3/h of underflow recycle and new seed addition. The tanks will have a volume of 547m3 each and will be 8.9m in diameter and an average of 9.4 m tall. The tanks will be equipped with 30kW agitators [3410-AG-12004 to 07] for slurry suspension and to assist in reagent dispersion. The first two neutralization tanks may possibly operate in slightly acidic conditions, and thus these two stages will be sealed and vented to the SART area scrubber, [3410-SK-12001]. A gypsum thickener [3410-TH-12008] will separate the resultant gypsum sludge from solutions. The thickener will be identical in size to the precipitate thickener - 22m in diameter, based on a conservative hydraulic load of 3m3/h/m2. Flocculant addition to the gypsum thickener will be provided from the central make-up facility used to provide flocculant to the CCD circuit. A dedicated pump plus a standby [6440-PU-12010, 11] will dose flocculant to the thickener through an in-line mixer [3410-MX-12004] for dilution.


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PROCESS DESCRIPTION


Gypsum sludge from the thickener underflow will be partially recycled for “seeding” the neutralization circuit and will also be bled out of the circuit and returned to the to the CCD circuit – either CCD #1 or #2. The reason for this is that the solutions entrained in the underflow slurry will be at PLS grade, and need to be recovered. Two underflow pumps [3410-PU-12005, 06] will be installed, equipped with 30kW variable speed drives to discharge seed and gypsum to the CCD circuit. A second set of pumps [3410-PU-12011, 12] will be install for slurry recycle to the head of the neutralization circuit to maintain slurry densities within the circuit. Thickener overflow solutions will gravitate to the gypsum thickener overflow surge tank [3410-TK-12009] and will be pumped by one of two installed overflow pumps [3410-PU-12007, 08] to carbon columns at La Quinua for gold recovery. These pumps will be equipped with 110kW variable speed drives, and are sized to handle 1,400m3/h of solution transfer to La Quinua. The thickener overflow tank will also receive solutions directly from the CCD pregnant solution tank during periods when the operation of the SART circuit is unnecessary. The tank will be identical in size to the precipitate thickener overflow tank, but will not be sealed and vented. It will provide 350m3 (15 minutes) surge capacity, and will be 8m diameter by 7.5m tall. The tank height will be dictated by the elevation of the gypsum thickener overflow launder. The SART circuit will be controlled by flow and pH – the chemistry is extremely pH dependant. The process will be heavily instrumented for process control, with the inclusion of an on-line Cu analyzer [3410-SA-12003, 04] for control of reagent additions. Solution samplers will also be provided on the feed [3300-SA-12001] (the CCD pregnant solution sampler) and discharge lines of the acidification [3410-SA-12005] and re-neutralization circuits [3410-SA-12002] for plant control. A significant amount of instrumentation will also be installed for safety reasons. In all areas where cyanide solutions at low pH are encountered, cyanide monitors will be installed to warn of high levels of cyanide in the gas phase. 10ppm of HCN in air is tolerable over an entire shift, 30ppm could cause some people to feel ill, whilst 100ppm HCN could be tolerated for possibly up to 60 minutes depending upon the person, but would be hazardous. The cyanide monitors will be set to alarm at 5ppm HCN. It should be emphasized that all areas of the process containing acid cyanide solutions will be in sealed and ventilated tanks. These tanks will be maintained at a negative pressure so that any areas where the seal is not perfect will lead to air leaking into the tank rather than process gases leaking out of the tanks. As noted previously, the tanks will be vented to a scrubber [3410-SK-12001], where a high flow of circulating NaOH solution will scrub any HCN in the vented gases, and form NaCN which will be returned to the mill dilution water tank.


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PROCESS DESCRIPTION


The scrubber will be equipped with two (one operating and one standby) circulating pumps [3410-PU-12011, 12], and the negative pressure in the area will be maintained by one of two installed SART circuit scrubber fans, which will be sized for a gas flow of about 10,000Nm3/h. The SART circuit will be located in a dedicated bund area equipped with two spillage pumps [3410-PU-12009, 10] for solution return to the circuit. This circuit is a solution treatment circuit, and any spillage can be readily cleaned up. The sulfide precipitate and gypsum thickeners will be the largest tanks in this area, and the bund wall height will be designed to provide full containment of material from these thickeners. 3.7.3 SART Precipitate HandlingFiltration and bagging of SART precipitates will occur on a day shift basis only, during the first years of plant operation. When deep transition ores containing high copper levels are treated in 2015 and 2016, precipitate handling will move to a 24 hour per day operation. One of two precipitate thickener underflow pumps [3410-PU-12005, 06] equipped with 2.2kW variable speed drives will pump thickened precipitate to the filter feed surge tank [3420-TK-12001]. The precipitate is expected to be very fine, and will not easily settle – the underflow density to filtration is estimated to be only 10% solids by weight. The circuit is designed for a precipitate generation rate of 1,500kg/h, but 898kg/h (in 2016) is expected to be the maximum average production rate. This will comprise 140kg/h of carry-over solids from the CCD circuit (100ppm suspended solids in the overflow solutions), and 758kg/h of metal sulfides. Precipitate production is variable and depends on the copper grade of the ore feed; the 754kg/h noted above is based on a feed grade of 2,789ppm Cu in the feed, 35% Cu recovery in leaching, and precipitation of Cu2S in SART. The filter feed tank will have a total volume of 237m3 and will provide 20 hours surge capacity at 70% live volume. This surge capacity is necessary because of the batch operation of the filter, and because the filter will only operate during day shift. The tank will be 6.7m in diameter by 7.2m tall and will be equipped with a 7.5kW agitator [3420-AG-12001]. The tank will be sealed and vented to the SART area scrubber because of the acidic cyanide solutions present. Sodium hydroxide will be added to the filter feed surge tank to partially neutralize solutions prior to filtration. Additions must be carefully controlled to minimize re-solubilization of copper. This addition may not be required, as filter cake washing will be accomplished using high pH water. A horizontal centrifugal pump [3420-PU-12001] equipped with a 75kW variable speed drive will pump thickened precipitate from the surge tank to the precipitate filter press [3420-FL-12001]. The pump will have a pressure relief line back to the tank, to cater for the batch filtration operation without switching the pump off and on.


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PROCESS DESCRIPTION


Discharge solutions from the filter – pre-coat water and filtrate – will be collected in the filtrate return tank [3420-TK-12002], and will be pumped by the filtrate return pump [3420-PU-12007] to the precipitation circuit. The filtration cycle will comprise 7 stages, with an expected cycle time allowance of 20 minutes. The filtration cycle is expected to be:

• At the start of each cycle the pressure filter plate pack will be closed and locked under high pressure by the high-pressure hydraulic pump.

• Addition of pre-coat to the filter - Pre-coat (10% diatomaceous earth (DE) in water) will be added, and the residual water will be recycled to the precipitation thickener via the filtrate return pump.

• Filtration -. Feed slurry will be pumped into the filter chambers by one of the filter feed pumps. Solids will be retained by the filter and filtrate will pass through the filter and be returned to the precipitation circuit.

• Wash – After the filter chambers have been filled with cake, low cyanide process water will be injected into the filter at the same rate as the filter feed slurry, to wash remaining filtrate out of the cake. A booster pump will be installed on the offtake from the water header, to supply the 6 bar pressure required. It is assumed that 1 replacement wash with be required. Wash solutions will also return to the precipitation circuit with the filtrate.

• Compression - After washing, the cake will be stabilised by inflating a rubber membrane on one side of each cake. (Note that there may also be a cake squeeze sequence after filtration and prior to cake washing).

• Air Drying - Compressed air will be supplied from the plant compressed air system for several minutes to displace the water in the filter cake to the filtrate discharge on the opposite side of the cake.

• Cake Discharge - The pressure filter will be opened and the dried filter cake dropped into the filter discharge chute [3420-ST-12002] and moved by a screw feeder [3420-FE-12001] directly into bags. The cloths will be vibrated to ensure release of any sticky cake residue.

• Close Filter Press – the filter plate pack will be closed and pressurized ready for the next filtration cycle.

“Bomb bay” doors below the filter will prevent drippings and wash water from entering the filter cake discharge chute, and will only be opened during cake discharge. Filter drippings will flow to the filtration area floor sump and pump [3420-PU-12004], which will return any spillage to the precipitate thickener feed box [3410-BN-12001].


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PROCESS DESCRIPTION


The filtration characteristics of the copper sulphide precipitate are not known at present but, based on other operations, are expected to be difficult. Provision has thus been made for the addition of diatomaceous earth for pre-coat of the filter and for body feed during filtration. Addition of DE for pre-coat has been designed for 1.0kg/m2 of filter area – a filter area of 20m2 has been assumed, with 36 cycles per day allowed for. Body feed addition is expected to be 100g/m3 of filter feed. Pre-coat will be 10% DE, supplied by the pre-coat transfer pump [6480-PU-12001], whilst body feed will be 5% DE, and will be injected into the filter feed pump suction line by a small progressive cavity pump [6480-PU-12005] at the rate of about 180L/h. The hydraulic system for the filter will be a single system comprising a hydraulic fluid tank and a low and high pressure pump system. The filter discharge screw conveyor will feed precipitate to the bagging plant. The precipitate will be damp and probably sticky, and thus the bagging plant will consist of a chute delivering the screw discharge directly into bulk bags, which will hold about 1.0 tonnes of wet precipitate at a bulk density of about 950kg/m3. At a design rate of 1,500kg/h of precipitate generation about 103 bags will be required per day, however during initial operations, with low copper levels in the ore, this number drops to 9 bags per day. Bags will be loaded and weighed on a weigh scale [3420-WS-12001]; a sampler [3420-SA-12001] located on the base of the screw feeder will provide a sample for metallurgical accounting and control purposes. Precipitate samples will also be taken from each bag. Bagged precipitate will be sold to local or overseas smelters for further treatment. At present, the smelters to be used, and the shipping quantities and methods have not been finalized. It is envisaged that the precipitate will be shipped in containers, or on trucks delivering material to the mine which would otherwise return empty to Callao or Salaverry. Generation of about 100t of wet precipitate per day would require 5 trucks a day to deliver the material to port. An area adjacent to the SART precipitate filter has been set aside for storage of full bags of precipitate, should it be necessary to retain shipments on site. 3.8 Acidification, Volatilization, and Re-Adsorption Circuit (AVR) Solutions from SART precipitation will contain free cyanide as hydrogen cyanide, HCN, and as strong acid dissociable cyanide in species such as gold cyanide and iron cyanide complexes. Under most circumstances the free cyanide can be used for leaching in the La Quinua heap leach circuit, and thus the SART solutions can be neutralized and pumped to La Quinua for gold recovery, followed by discharge to the La Quinua leach pad as irrigation solutions.


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PROCESS DESCRIPTION


However, in some years, due to an increased amount of cyanide added to the YGM circuit to cater for copper dissolution, and a reduced demand for cyanide at La Quinua (low tonnage treatment rate) an excess of cyanide may be present in these solutions. Under these circumstances, cyanide will be recovered from SART discharge solutions (prior to neutralization) in the AVR circuit. Stripped solutions from AVR will be returned to the SART neutralization circuit prior to discharge to the La Quinua carbon columns. The mine plan indicates that the AVR circuit will not be required until later in the project life, and the complete circuit will not be installed initially. However, there is a possibility of transition ore treatment during the early years, and a single train of stripping and re-adsorption columns will be constructed immediately. HCN is released into the gas phase by blowing large quantities of air into the acidic solutions (at pH 4 from SART) in packed beds. These gases are then passed to adsorption towers where NaOH solutions are circulated, and a concentrated solution of NaCN is formed, which can be recycled to the process.

Figure 3 Simplified Flowsheet for the AVR Circuit


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PROCESS DESCRIPTION


A general process flow diagram for the AVR circuit is presented in the Figure 3, above. Only one stripping-absorption tower system is shown on this flowsheet – this represent the initial installation. Ultimately three stripping-absorption towers will be installed, with each stripping-adsorption tower combination treating 400m3/h of solution. Trains can then be switched on and off as required to satisfy the cyanide balance across the La Quinua leach pads. The three main reactions involved with the cyanide recovery process are. 1. In the YGM flowsheet, the acidification step of the AVR process has been accomplished in the SART circuit. Copper precipitate thickener overflow solutions will be at a pH of approximately 4, and these solutions can be fed directly into the AVR stripping circuit. During acidification free and weak acid dissociable (WAD) cyanides are converted into molecular hydrogen cyanide (HCN). The HCN at this point remains in solution.

2 CN- + H2SO4 → 2 HCN(aq) + 2SO42-

It should be appreciated that the gold cyanide complex is unaffected by acidification, being a strong acid dissociable species. Hence gold will remain as a cyanide complex in solution through the AVR circuit, and will remain amenable to recovery using activated carbon. 2. Acidified solution will be directed to stripping towers where it will be contacted in a counter-current flow with large volumes of air to strip HCN as a gas. The stripping towers provide the environment for rapid transfer of HCN from the aqueous to the gas phase, and include high surface area packing for turbulent gas-liquid contact.

HCN (aq) → HCN (g)

Stripped solution at the base of the towers will be transferred to neutralization. 3. Stripped HCN gas will be absorbed into a high pH solution of sodium hydroxide (NaOH) to generate a concentrated solution of recovered sodium cyanide (NaCN) in the adsorption towers.

HCN (g) + NaOH → NaCN + H2O Flow through the column will be counter-current, with the air flow upwards through a downflow of caustic solution. Solution flow will be broken up through packing material installed in the column. Overflow solutions from the copper precipitate thickener [3410-TH-12003] will gravitate to the thickener overflow tank [3410-TK-12010], and from there will be pumped to the AVR stripping columns or directly to the SART neutralization circuit.


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PROCESS DESCRIPTION


Three AVR circuits will ultimately be installed, running in parallel, with each circuit capable of handling 400m3/h of solution. One operating and one standby feed pump will be installed [3410-PU-12014, 15], equipped with a 132kW variable speed drive. The pump capacity will be 1,400m3/h of solution, with the excess (not required to be treated in AVR) being transferred directly to neutralization. The columns will be fabricated from mild steel, epoxy lined and will be 5.8m in diameter by 15m tall. The stripping columns will contain about 7.5m of random plastic packing to break up the solution and gas flows, and each adsorption column will have 3m of packing. Each stripping tower [4100-VS-12001-03] will be fed at a rate of up to 400m3/h – 3 towers in parallel will be required for a maximum design flow of 1,200m3/h. Barren solution at the base of the towers will be collected into a main header, and pumped to the SART neutralization circuit using the stripped solution transfer pumps [4100-PU-12017, 18, 21]. Two pumps will initially be installed – one running and one standby, each rated for 467m3/h and equipped with 37kW variable speed drives. The third pump will only be required in 2015; it will be sized for 1,000m3/h and will be equipped with a 75kW drive. An individual adsorption tower [4100-VS-12006-08] will be installed for each stripping tower, and the air flow circulated through the pair of columns with a dedicated fan [4100-BL-12001 to 03] – the total pressure drop in the system will be approximately 5.5kPa. The system will be run under a slightly negative pressure, ensuring air ingress to the system rather than gas egress. The air flow to solution volumetric ratios are related to solution temperatures. For 95% stripping efficiency, with solution temperatures of about 10oC, the air flow required is approximately 850 times the solution flow - necessitating a circulating air flow of 340,000m3/h (at ambient temperature and pressure) through each stripping and adsorption tower. Each fan will be equipped with a 1,000kW fixed speed drive. Sodium hydroxide solution will be circulated around the adsorption columns by recycle pumps [4100-PU-12006 to 08], one installed per column, at a design rate of 430m3/h, and concentrated NaCN (at 10 to 15% strength) will be bled off the recirculation line and discharged to the recovered NaCN surge tank [4100-TK-12011] for recycle to the circuit. This tank will provide 24 hours of concentrated cyanide storage, to enable any fluctuations in cyanide demand to be catered for. A 206m3 tank, 6.4m diameter by 6.9m tall will be provided. Cyanide will be pumped to the mill dilution water tank [6510-TK-12002] by one of two 4kW variable speed recovered cyanide discharge pumps [4100-PU-12013, 14], at an estimated rate of 11m3/h. Cyanide addition to the circuit will be taken from the AVR circuit in preference to new cyanide from the make-up facility. Stripped solution will contain up to 100ppm NaCN and HCN at a pH of 4 to 5. This solution will be discharged to the SART neutralization circuit, to bring the pH up to 10.5 prior to transfer to the La Quinua carbon columns for gold recovery


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PROCESS DESCRIPTION


The AVR circuit will be instrumented in much the same way as the SART circuit, with process control consisting of flow measurement and control and pH control. Solution samplers on the feed [3410-SA-12005] (on the precipitate thickener overflow stream) and discharge streams [4100-SA-12002] of the AVR circuit will provide a guide to circuit efficiencies and assist in maintaining the cyanide balance around the mill and the La Quinua leach circuit. All areas of the process containing acid cyanide solutions will be in sealed and ventilated tanks. These tanks will be maintained at a negative pressure so that any areas where the seal is not perfect will lead to air leaking into the tank rather than process gases leaking out of the tanks. The adsorption towers act as large cyanide scrubbers, and a bleed stream of air will be taken of the gas stream leaving these towers to maintain the negative pressure in the system. The bleed air flow will be controlled by one of two installed fans [4100-FA-12001, 02] sized for an air flow of 4,800m3/h, and equipped with 4kW variable speed drives. In all areas where cyanide solutions at low pH are encountered, cyanide monitors will be installed to warn of high levels of cyanide in the gas phase. The cyanide monitors will be set to alarm at 5ppm HCN. Emergency power will be provided to critical equipment (eg the bleed air fans) to maintain operations in the event of the loss of the normal power supply. The AVR circuit will be located in a dedicated bund area equipped with a spillage pump [4100-PU-12019] for solution return to the circuit. This circuit is a solution treatment circuit, and any spillage can be readily cleaned up. 3.9 Carbon Adsorption Columns and Carbon Handling at La Quinua Pregnant solutions from the CCD circuit containing low copper concentrations, or neutralized solutions from the SART and AVR circuits (when treating high copper ores) will be pumped to the carbon adsorption columns at La Quinua for recovery of the gold values (and silver values if the SART circuit is being bypassed). Solutions will be collected in the gypsum thickener overflow surge tank [3410-TK-12009], and pumped to La Quinua by one of two available gypsum thickener overflow pumps [3410-PU-12007, 08] rated at 1,400m3/h and 15m head, and equipped with 110kW variable speed drives. Seven carbon adsorption trains are currently installed at La Quinua in 2 separate circuits. One circuit contains 3 trains of columns, each with 5 adsorption stages, and the second circuit comprises 4 trains of 6 columns each. Gold mill solutions will be treated in the set of 4 adsorption trains (Carbon Adsorption Circuits 4 to 7).


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PROCESS DESCRIPTION


Tie-ins will allow YGM solutions to be added to each of the trains in this circuit, at a rate of 300 to 350m3/h per train, along with an additional 350 to 400m3/h per train (to achieve a total flow of 700m3/h/train) of PLS from the La Quinua leach pads. This will provide each column with the same solution feed grade, and thus carbon movement will be the same for each train. Additionally, if the YGM solutions are saturated in gypsum, dilution with LQ solutions will eliminate the possibility of further gypsum precipitation. A bypass line will be installed around the carbon columns to the La Quinua pregnant solution sump [3215-SU-11601] to provide the ability to transfer YGM solutions directly to the Yanacocha Merrill-Crowe circuit. Similarly, a bypass line will also be installed to the La Quinua operating pond to ensure that operating interruptions at the carbon columns do not affect the Gold Mill operation. After adsorption, solutions with low cyanide levels (LQ leach pad barren solutions) will be required for CCD wash at the gold mill – the barren solutions from the YGM solution treatment will contain higher cyanide concentrations making them unsuitable for CCD wash. Thus barren solutions from the circuit comprising three trains of adsorption columns will be used for transfer to the YGM for CCD wash and for process water make up. These solutions will be clarified in the existing reactor clarifier [3210-CL-08212] for fine carbon removal, and transferred to YGM using new pumps [6520-PU-12016 to 18] installed on the clarifier overflow tank [3210-TK-11638]. New facilities required at La Quinua for YGM solution treatment will be:

• Solution delivery lines to the carbon columns feed, plus a pressure reducing valve • Tie-ins to the feed to each of the carbon columns, plus a flow meter and flow control valve. • Bypass lines around the columns to the operating pond and the pregnant solution sump. • Re-installation of pipework to allow the barren solution from the set of 3 trains of carbon

columns to be directed to the reactor clarifier • Addition of a new pump system for transfer of approximately 1,500m3/h of solution to the gold

mill from the clarifier overflow tank. Loaded carbon generated from the treatment of YGM solutions will be mixed with other loaded carbons and stripped in the La Quinua carbon stripping circuit. It is envisaged that no modifications will be required to the existing stripping and regeneration circuit to allow treatment of YGM loaded carbon.


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PROCESS DESCRIPTION


3.10 Reagents The reagent systems for the treatment plant include all the reagent handling, mixing, storage and distribution facilities. Reagents are added in the following plant areas:

• Conveying Dry Lime

• Milling Circuit Lime slurry

• Pre-Leach Thickener Flocculant Sodium cyanide

• Gold Leaching Lime slurry Sodium cyanide

• CCD Thickeners Flocculant

• SART Circuit NaHS Sulfuric Acid Lime Flocculant (2 types) Antiscalent DE for the precipitate filter Caustic Soda (for scrubbers, and filtration pH control)

• AVR Circuit Antiscalent Sodium Hydroxide

In addition to the above, several reagents will be required for treatment of carbon and precipitation and smelting of precious metals at other (existing) facilities on the site.

• Activated carbon for carbon adsorption • Hydrochloric acid, sodium hydroxide, cyanide, diesel fuel and carbon for carbon

stripping • Diatomaceous earth and zinc dust for Merrill-Crowe of eluate solutions from

carbon stripping • Fluxes for smelting of Merrill-Crowe precipitates

These reagents will require no new make-up facilities or modifications to existing equipment as part of the YGM project.


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PROCESS DESCRIPTION


3.10.1 Lime, CaO, Ca(OH)2Lime will be used to control the pH of the ore slurry in the thickening and leach circuits, and for neutralization of SART and AVR discharge solutions. It is estimated that between about 26 to 35t/day of lime will be required, depending on the copper grade in the feed, and the amount of cyanide present in solution. A 10tph lime slaking system has been installed at the La Quinua AWTP plant, and this facility will have spare capacity in 2008, when the Gold Mill is started up. In addition, the existing cement silo [3340-BN-09814] at the La Quinua Agglomeration circuit will be used for lime storage, and dry lime will be added to the crusher discharge conveyors [3281-CV-09621, 22] using the existing weigh belt feeders [3340-FE-09826, 27]. It may be necessary to add a bin activator to the existing silo to enable it to handle lime satisfactorily. The dry lime addition to the stockpile feed material will be controlled to provide the majority of the lime required in the milling circuit, thereby reducing the quantity of slaked lime required. However, the slaked lime handling system will be sized on the premise that no dry lime is added to the crushed ore. Lime slurry will be transferred from the slaking facility to a lime storage tank located in the CCD area of the Gold Mill through a double contained transfer pipeline, using one of two installed pumps [6410-PU-12001, 02]. Transfer will take place once per day, and the line will subsequently be flushed with water into the lime storage tank. The lime storage tank [6410-TK-12001] will provide 36 hours surge capacity of the lime for the circuit, based on the worst case assumption that no dry lime is added to the stockpile feed. The tank size will be 333m3 in volume with a diameter of 7.6m and a height of 8.1m; it will be equipped with a mechanical agitator [6410-AG-12001]. Lime will be pumped from this tank to addition points around the plant by ring main fed by one of two lime distribution pumps [6410-PU-12003, 04]. Lime off-takes will be:

• SAG mill feed • Leach tanks 1, 2, 3 & 5. • SART neutralization circuit.

The lime storage tank will be located within the CCD bund area, but will be separately bunded, with a dedicated spillage pump [6410-PU-12005], which will return any washdown to the storage tank, or into the CCD circuit. In the event that the bund area is flooded, it will overflow into the CCD area. 3.10.2 Sodium Cyanide, NaCN Sodium cyanide will be used for gold leaching, and will be added to the pre-leach thickener feed box [3100-BN-12001] and the leach circuit. Consumption will be variable, depending on copper grades in the ore feed, and is expected to be between 7 and 20tpd of 100% NaCN. It will be delivered to site as a solid in 22 tonne trucks.


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PROCESS DESCRIPTION


Because of the new sparging system for cyanide off-loading, the majority of cyanide consumed in the La Quinua heap leach circuit will also be supplied by the gold mill cyanide make-up system. Up to 14 tonnes of 100% NaCN will be required per day at La Quinua, of which about 5tpd will be transferred in YGM PLS to the La Quinua carbon columns. The remainder will be transferred to La Quinua cyanide storage tank by a dedicated transfer pump [6420-PU-12005]. This eliminates the need for a new off-loading facility at La Quinua for handling the trucks. By installing a new cyanide transfer pump [6420-PU-12006] at La Quinua to enable cyanide to be transferred to the gold mill, a facility for handling bags of cyanide at the Gold Mill (in case of an interruption in tanker supply) can be eliminated, since a bag handling system exists at La Quinua. Bags of cyanide will be held on site, as a strategic stockpile, and these will have to be “turned over” on a routine basis. The La Quinua facility can perform that function. Sodium cyanide solution will be made up to a 20% solution by circulating low cyanide process water through the tanker and into the cyanide offloading tank [6420-TK-12001]. Once dissolved, the cyanide solution will be transferred into the cyanide storage tank [6420-TK-12002] using the cyanide transfer pump [6420-PU-12001]. This pump also serves as the circulation pump for offloading the tanker. Cyanide solution will be circulated in a ring main to the pre-leach thickener and leach by one of two cyanide distribution pumps [6420-PU-12002, 03]. Cyanide will be dosed to the circuit with the cyanide concentration being automatically controlled by a cyanide analyzer. Manual titrations will provide a back-up for the analyzer. The cyanide transfer pumps between LQ and YGM will pump about 30m3/h of solution – transfer of 14t of 100% NaCN at 20% strength will thus take approximately 2 hours per day. The line will be double contained, and flowmeters at both ends of the line will warn of a line failure. Both the make-up and storage tanks in the make up area will be sealed, and tank vents and overflow lines will be connected to the cyanide seal pot [6420-TK-12003]. The cyanide bund area will be provided with a spillage pump [6420-PU-12004], which will return spillage to the pre-leach thickener feed box. This bund area will overflow into the CCD thickener area in the event of major spillages. Regenerated cyanide from the AVR circuit will be recycled to the mill dilution water tank [6510-TK-12002] from the recovered cyanide surge tank [4100-TK-12011] located in the AVR circuit using one of two installed recovered cyanide discharge pumps [4100-PU-12013, 14]. The cyanide storage area will be equipped with cyanide monitors to warn if there are abnormal concentrations of cyanide gas in the area.


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PROCESS DESCRIPTION


3.10.3 Sodium Hydroxide (Caustic Soda), NaOHLarge quantities of sodium hydroxide will be required for re-adsorption of HCN to form NaCN solution in the AVR circuit. The peak demand (in 2016) will be 40tpd of 100% NaOH, which equates to 79tpd (4 tankers) of 45% solution. However, NaOH requirements will depend on the amount of cyanide recycled in AVR – requirements may be zero until 2015. Sodium hydroxide will also be required in small quantities for the SART scrubber - requirements are anticipated to be 2tpa (5.5kg/day) in 2008, and 14kg/day in 2009. A single train of AVR will be installed initially to cater for short periods of transition ore treatment, and thus a sodium hydroxide make-up and storage system will also be installed at the same time. This system will comprise a 2 tonne per batch mixing system, based on bags of sodium hydroxide, but with a storage tank sized for 1.5 days of liquid reagent at peak demand. Sodium hydroxide will be delivered as a solid in either 1 tonne bulk bags (preferred) or in 25kg bags. Solution will be made up using raw water, to a strength of 20% in an agitated mixing tank [6430-TK-12001] & [6430-AG-12001]. Bags will be hoisted [6430-HT-12001] up to the bag breaker [6430-ME-12001], and the pellets of sodium hydroxide dropped into the mixing tank. The make-up batch size will be 2t of NaOH, or 9m3 of solution at an SG of 1.22. The mix tank will have a diameter of 2.3m and a height of 2.8m. Mixed solutions will be transferred to the storage tank on a daily basis by the caustic soda transfer pump [6430-PU-12005]. The NaOH storage tank [6430-TK-12003] will have a capacity of 1.5 days at peak demand, sized for a solution strength of 45% (solution SG 1.48). The required volume will be 80m3, and the tank will have a diameter of 4.7m and a height of 5.2m. From the storage tank, sodium hydroxide will be dosed to the SART scrubber and AVR re-adsorption columns by one of two installed caustic soda circulating pumps [6430-PU-12002, 03] via a ring-main. When making up 20% caustic soda solution using anhydrous NaOH, the heat of dilution is such that solution temperatures will reach between 60 and 80oC. For this reason the mixing and storage tanks and the interconnecting pipeline should be insulated for safety reasons. 20% caustic soda freezes at minus 27.5oC, but 45% NaOH freezes at plus 10oC. Thus the storage tank should be equipped with facilities for installing an electric heating element [6430-HE-12001] at a later stage, when bulk deliveries are initiated. Nozzles should be provided in the initial design to allow for this heating element. Similarly, the caustic soda delivery lines will require heat tracing and insulation when bulk deliveries commence. Sodium hydroxide storage will be adjacent to the AVR circuit. It will be separately bunded and spillage will be pumped [6430-PU-12004] to the SART neutralization circuit where any excess NaOH can be utilized for pH control.


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PROCESS DESCRIPTION


3.10.4 FlocculantFlocculant will be made-up to a solution strength of 0.5% in a packaged plant - make-up will be automatically controlled by tank levels and timers. Two flocculant systems will be installed - one large one for the pre-leach and CCD thickeners (3.6tpd), and a much smaller unit (173kg/d) for the SART circuit. Both circuits will be identical (except in size) to those already in use at Yanacocha. Pre-leach and CCD thickener flocculant, and the flocculant required for the gypsum thickener in the SART circuit will be delivered to site as a powder in 1000 kg bulk bags. Flocculant powder will be loaded from the bags into the flocculant storage bin [6440-BN-12001] using the flocculant area hoist [6440-HT-12001] and bag breaker [6440-ME-12001]. Powder will be metered by the flocculant screw feeder [6440-FE-12001] into the flocculant mixer [6440-MX-12001] were it will be wetted by low cyanide process water, and diluted to a strength of 0.5% in the flocculant mix tank [6440-TK-12001], equipped with an agitator [6440-AG-12001]. A make-up batch of flocculant will be equivalent to approximately 3 hours requirements, or 450kg, and the make-up tank size will thus be 90m3. Made-up flocculant solution will be transferred to the flocculant storage tank [6440-TK-12002] by the flocculant transfer pump [6440-PU-12009], once that tank level has dropped below a pre-determined set point. The storage tank will have a total capacity of 3 make-up batches (9 hours) in 270m3 and will be 7.0m in diameter by 7.5m tall. Flocculant solution will be pumped to each application by dedicated flocculant dosing pumps [6440-PU-12001 to 08]; eight will be installed with six operating and two as common standbys for the pre-leach and CCD thickeners. These pumps will be variable speed positive displacement pumps, and will deliver up to 5m3/h per thickener. Two different sized pumps [6440-PU-12010, 11] will be installed for the gypsum thickener flocculant supply, with one operating and one standby. Delivery rate of 0.5% flocculant for this service will be up to 600L/h. Flocculant solution will be further diluted to a strength of 0.1% prior to addition to each of the thickeners, by injection of low cyanide process water into static mixers installed in the delivery lines. The CCD thickener flocculant make-up system will be installed adjacent to the CCD bund area, and will also be bunded with a dedicated spillage pump. Spillage from the area will be discharged to the mill sands surge tank [5110-TK-12001] for discard to the mill sands storage facility.


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PROCESS DESCRIPTION


The SART flocculant make-up system will be identical but smaller to the CCD flocculant system. Flocculant will be supplied in 25kg bags, and these will be manually fed to the flocculant feed hopper [6440-BN-12002]. Only 2 flocculant dosing pumps [6440-PU-12014, 15] will be installed – one operating and one standby – dosing 0.5% flocculant at a rate of up to 600L/h. These pumps will be identical to the gypsum thickener flocculant feed pumps. SART flocculant make-up facilities will be installed in the SART circuit, and any flocculant spillage will be picked up by the SART filtration area spillage pump [3420-PU-12004] and added to the precipitate thickener [3420-TH-12003]. 3.10.5 Sulfuric Acid, H2SO4Sulfuric acid will be required for acidification of solutions prior to SART, and to donate protons to CN-, producing HCN. Sulfuric acid consumption will depend on copper grades feeding the plant, since these determine the amount of WAD (weak acid dissociable) cyanide in solution, and on whether the SART and AVR circuits are operating. Up to 60 tonnes of 98% acid will be required daily (peak demand in 2016) – a delivery of 3 tankers per day. However, requirements in 2008 and 2009 will be less than 7tpd. Acid will be offloaded by pump [6450-PU-12001] into a mild steel storage tanks [6450-TK-12001], and from there metered to the SART precipitation circuit by one of two installed sulfuric acid distribution pumps [6450-PU-12002, 03]. These pumps will be magnetic driven gear pumps with VFD drives, controlled by the pH in the SART circuit. The storage tank will be sized to hold about 857t of acid (14 days at the peak demand) and will be 8.5m in diameter and 9.0m tall, with a volume of 470m3. The tank will be sealed, with vents and overflow lines leading to a seal pot filled with glycol. This is required in moist ambient conditions to prevent corrosion at the liquid/air interface in the tank. Acid delivered to site could have a concentration of between 93 and 98% acid. 93% acid starts to freeze at minus 32oC, but this rises to plus 4oC for 98% acid. The acid storage tank and pipelines will thus require heat tracing and insulation. The sulfuric acid off-loading and storage area will be adjacent to the SART circuit, and will be fully bunded with acid resistant concrete. The volume of the bund area will be greater than 110% of the acid tank, and will ensure no solution escape from the circuit. Acid spillage will not be returned to the storage tanks (in case of water dilution), but will be pumped to the SART circuit, by an air operated pump [6450-PU-12004]. 3.10.6 Sodium Hydrosulfide, NaHSSodium hydrosulfide will be required for sulfide precipitation in the SART circuit. The highest demand will be in 2016 when approximately 6.5tpd of NaHS will be required.


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PROCESS DESCRIPTION


Sodium hydrosulfide will be delivered as a solid in 1 tonne bulk bags. Solution will be made up to a strength of 20% using raw water. The NaHS bag breaker [6460-ME-12001] will deposit solid NaHS into an agitated mixing tank [6460-TK-12001] & [6460-AG-12001], where water will be added. The make-up batch size will be 7t of NaHS, or 32m3 of solution at an SG of 1.1. The mix tank will have a diameter of 3.5m and a height of 4.0m. Mixed solutions will be transferred to the storage tank on a daily basis by the NaHS transfer pump [6460-PU-12001]. The NaHS storage tank will have a capacity of 1.5 days, with a volume of 48m3, a diameter of 4.0m and a height of 4.5m. The mixing and storage tanks will be sealed and vented through the SART area scrubber [3410-SK-12001]. and the tank overflows will be sealed through a seal pot [6460-TK-12003]. 20% solution will be dosed to the SART feed by one of two installed NaHS metering pumps [6460-PU-12002, 03] which will be magnetic driven gear pumps with variable speed drive, similar to the sulfuric acid metering pumps. Sodium hydrosulfide mixing and storage will be accomplished within the SART bund area, but will also be separately bunded with a dedicated spillage pump [6460-PU-12004]. Spillage from NaHS make-up will be returned to the NaHS storage tank. Gas monitors in the area will detect the presence of abnormal levels of H2S gas in the area and warn of potentially hazardous conditions. 3.10.7 Diatomaceous Earth, DEDE will be required for pre-coat and body feed for the precipitate filter in the SART circuit. Initial estimates suggest 5,000kg/day of DE will be required and a make-up facility handling 1 tonne bulk bags will be installed. The make-up facility will comprise the typical arrangement of bag breaker [6480-ME-12001] and mixing tank [6480-TK12001] with agitator [6480-AG-12001]. DE will be made up to a 10% solution strength using low cyanide process water (since it will be injected into slurries containing cyanide). 10% slurry will be suitable for pre-coat, but this will require dilution to 5% DE for use as body feed. Thus, the mixed DE will be transferred with a transfer pump [6480-PU-12001] to a separate body feed tank [6480-TK-12002], also equipped with an agitator [6480-AG-12002] where it will be further diluted with low cyanide process water. The mixing tank will be 14m3 in volume, being 2.7m in diameter by 3.2m tall, and the DE body feed tank will be only 1.7m3 in capacity.


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PROCESS DESCRIPTION


The DE transfer pump will also be used as the pre-coat pump, delivering pre-coat to the filter at the same rate as the filter feed slurry. DE will deposit on the filter cloth and excess water will pass through the filter and be returned to the gypsum thickener overflow tank. Body feed will be injected into the filter feed slurry pump inlet during the filtration cycle using a small positive displacement pump [6480-PU-12005]. DE is basically inert. The make up facility will be located within the SART bund area, and any spillage generated during make-up will be handled by the SART filtration area spillage pump [3420-PU-12004]. 3.10.8 Antiscalant/Water Treatment ChemicalsWater treatment chemicals will be required to prevent gypsum scale formation after the neutralization circuit, and in the feed to the AVR circuit to limit scale build up in the stripping towers. It is assumed that a concentration of 3ppm of antiscalent will be required in solution – on 1,400m3/h of solution flow that is 100kg/day. The expected locations for antiscalent addition are:

• SART precipitation thickener overflow tank [3410-TK-12010] for feed to the AVR circuit • Gypsum thickener overflow tank [3410-TK-12009] for feed to the La Quinua carbon

columns. However, MYSRL will define the final locations, on the basis of operating experience. Antiscalant will be supplied in drums, or 1m3 tote containers and individual drum mounted metering pumps will be used to dose the reagent into the various feed locations. The metering pumps will be operated from the locally mounted power sockets.


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PROCESS DESCRIPTION


3.11 Water Circuits Water Supply Two separate sources of water will be required for the Yanacocha Gold Mill:

• Low cyanide process water from the La Quinua carbon column circuit barren solution

• Raw water from the La Quinua AWTP plant (acid water treatment plant) In addition, there will be an initial fill of potable or de-ionized water for the cooling water circuit. This circuit is a closed loop without bleed or make-up, and should require only infrequent “top-up” 3.11.1 Low Cyanide Process WaterApproximately 870m3/h will be required for efficient wash on the CCD thickeners. This wash water will contain low levels of cyanide, and can contain suspended solids, as it will be fed to the thickening circuit. In addition, it is estimated that up to 680m3/h of make-up water to the process water circuits will be required. Thus, a total of 1,550m3/h of water will be required from La Quinua for these duties. This water will be supplied by the addition of pumps and a pipeline from La Quinua. Carbon column barren solution will be used for the application, but it cannot be derived from the set of carbon columns to which the gold mill pregnant solution has been fed, as this solution is high in cyanide and the solution transferred to the mill should be low in cyanide. The barren solution will be taken from the set of 3 trains of carbon columns – barren solution from these columns will be routed to the barren solution clarifier [3210-CL-08212] for removal of fine carbon, and the take off will be from the barren solution clarifier overflow tank [3210-TK-11638]. . Three pumps [6520-PU-12016 to 18] will be installed for the water transfer, with two pumps operating in parallel and one pump as standby. These pumps are rated at 750m3/h each, at 173m head – they will be equipped with 500kW fixed speed drives. Water for CCD wash solutions will be added directly to the CCD # 5 feed tank [3300-TK-12011], or to the #4 feed tank [3300-TK-12010] if the 5th stage thickener is off-line. Barren solution will also be added to the low cyanide process water tank [6510-TK-12012] for make-up. This tank will provide 30 minutes solution storage for process requirements and a further 300m3 of storage dedicated to mill sands pipeline flushing. The tank will have a total capacity of 839m3 and will be 10.2m in diameter and 10.7m tall. The dedicate storage for mill sands pipeline flushing will be provided by installing the off-take nozzle for process water 3.8m up the tank wall.


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PROCESS DESCRIPTION


The low cyanide process water tank will always be full, and water will overflow the tank into the mill dilution water tank [6510-TK-12002] for make-up. The solution level in the mill dilution water tank will control the water feed to the low cyanide process water tank. Low cyanide water will be pumped to the process by one of two installed fixed speed process water pumps [6510-PU-12005, 06], each designed for a maximum flow of 272m3/h. These pumps will have a small recycle line back to the tank for pump protection in the event that all off-takes on the system are closed. An off-take at the base of the tank provides water to the mill sands flush pump [5110-PU-12010], which will be used to inject water into the suction lines of the mill sands pumps for pipeline flushing. This will be a dedicated supply, and the 300m3 dedicated storage volume represents 120% of the pipeline volume. 3.11.2 Raw Water Raw water will be clean water containing no cyanide or suspended solids, and will be supplied from the La Quinua acid water treatment plant (AWTP). An average requirement of 81m3/h will be required when treating oxide ores, and 128m3/h when operating the SART and AVR circuits. This water will be used for:

• Dust suppression sprays in the crusher circuit • Mill flushing prior to stoppage for liner inspection or changes • SART precipitate thickener flocculant dilution • Precipitate filter wash • SART scrubbers • SART flocculant preparation • NaOH make-up • NaSH make-up • Gland seal water for slurry pumps • Safety showers (through a treatment circuit), bathrooms, etc • Fire water make-up • All hosing within the plant

Raw water will be used for hosing supply within the plant as an environmental protection measure, to avoid cyanide solutions splashing onto unprotected ground outside bunded areas. Water is currently pumped from the AWTP to an existing water tank [3510-TK-12001-MY] located adjacent to the YGM stockpile area. This tank is now dedicated to raw and fire water supply to the laboratories, new office complex at La Quinua and the new warehouse.


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PROCESS DESCRIPTION


A new raw and fire water tank [6510-TK-12001] will be installed next to the existing tank, and will be supplied with water from a tie-in to the supply line to the existing tank The tank has a capacity of approximately 540m3, of which 140m3 is required for fire water, and 400m3 is available for raw water surge capacity. At this capacity, the tank will have about 4 hours’ storage capacity for raw water for the plant. Two new raw water pumps [6510-PU-12001, 02] will be installed on this tank, with one operating and one on standby. A small return line will recycle water back to the tank to protect these pumps in the event that all off-takes are closed. Water Reticulation In addition to the above supplies, several water systems around the Gold Mill will provide water for various uses:

• Mill dilution water from the pre-leach thickener overflow • Gland seal water using raw water. • Fire water reticulation using raw water • Water for safety showers and offices • Cooling water for the mill drives and the air compressors

3.11.3 Mill Dilution WaterProcess water will be used only for mill dilution water. Cyanide levels in this water will be higher than in the low process cyanide water and hence this water will be inappropriate for other uses. The water will comprise overflow solutions from the pre-leach thickener, where cyanide additions will be made, and this will be augmented by barren solutions from La Quinua, (overflowing the low cyanide process water tank), and recovered cyanide solutions from AVR. The mill dilution water tank [6510-TK-12002] will be sized for approximately 400m3 of solution storage, which is equivalent to about 10 minutes capacity based on outflow volumes, but an hour of solution lost from the circuit in pre-leach thickener underflow slurry. This is due to the recirculation of solution from the pre-leach thickener back to the tank – water will always be returned to the tank whenever the pumps are supplying water to the mill. The tank size will be 9.8m in diameter by 5.5m tall, the low height being dictated by the elevation of the overflow pipe from the pre-leach thickener. Process water will be pumped to the mill for water addition to the ore feed, and for dilution of the cyclone feed slurry to 45% solids. Three pumps [6510-PU-12011 to 13] (one standby) will be installed for this duty, which will be high volume low pressure pumps each delivering 1,320m3/h of solution to a head of 10m, and equipped with 90kW drives.


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PROCESS DESCRIPTION


3.11.4 Gland Seal WaterGland seal water will be supplied from raw water to a dedicated gland seal water tank [6510-TK-12003]. The design requirements for gland seal water are 140m3/h (balance 81m3/h with SART operating), and the tank will provide just over an hour’s requirement in 171m3. The tank will be 6.0m diameter by 6.5m tall. One of two installed fixed speed pumps [6510-PU-12003,04] will supply gland seal water to the slurry pumps around the plant. A small return line will recycle water back to the tank to protect these pumps in the event that all off-takes are closed. 3.11.5 Fire WaterRaw water will be drawn from a dedicated supply in the bottom portion of the raw and fire water tank [6510-TK-12001]. This dedicated supply will be guaranteed by installing the fire water off-takes at the base of the tank, and all other off-takes part way up the tank wall. Fire water will be supplied to the plant by pump – an electric pump [6800-PU-12001] will be installed, with a jockey pump [6800-PU-12002] operated to maintain pressure in the line at all times. A diesel driven pump [6800-PU-12003] will also be installed in case of a power failure. The main pumps will be sized to provide 170m3/h (750gpm) of water under pressure, and 1,000gpm at low pressure to fill a fire truck. The fire water pumps will be controlled by a local control panel which will start and stop pumps as required by the demand on the fire water system, as measured by the pressure in the system. 3.11.6 Safety Shower WaterRaw water will be provided throughout the plant to the safety showers and the plant buildings. Water to the showers requires heating to about 20oC and thus the raw water will require some treatment for this duty. Raw water will be treated through a water treatment system, which will comprise a strainer and chlorination unit only, and will be sized for a production capacity of 10m3/h. Raw water will be stored in the treated water supply tank [6510-TK-12004], which will provide a capacity of 20m3 of water in a tank 3.0m in diameter by 3.5m tall. The tank will be equipped with an electric heating element [6510-HE-12001], and the tank and pipelines will be insulated (but not heat traced), to maintain the water temperature. Raw water will be distributed throughout the plant by one of two installed treated water pumps [6510-PU-12009, 10] at a rate of 10m3/h through the chlorinating unit [6510-WT-12001], and ring main and back to the storage tank. Twenty three safety showers will be installed initially, with a further 4 being installed in the future with the expanded AVR circuit. These showers will be fed from the treated water header.


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PROCESS DESCRIPTION


3.11.7 Mill Sands Storage Facility Return Water As discussed previously, the MSSF will be managed in such a way that any water collected in the facility will be discharged directly through the drainage pipes into the La Quinua leach pad solution circuit. There will be no requirement for solution decant pumps at the MSSF, and no solutions will be returned to the Gold Mill from the MSSF. The drain systems will be designed for a maximum solution flow of 400m3/h, which covers water reclaimed from tailings, plus a 1 in 100 year storm event. 3.11.8 Cooling Water Cooling water will be required for the cycloconverter, the mill gearless drive, the mill lubrication system, and the plant and leach air compressors. The total water flowrate for these duties will be approximately 220m3/h, and the total heat load will be about 1,800kW. Cool water at 25oC will be generated by two chillers in series [2100-CT-12001, 02] and delivered to the equipment to be cooled by one of two pumps [2100-PU-12005, 06], one operating and one standby. These pumps will pump through an air separator [2100-SP-12001] and into a ringmain. Warm water will be returned at about 32oC through a ring main and expansion tank [2100-TK-12001] into the chillers. The operating temperatures and flows around the chillers and the mill ancillaries are subject to final approval by the respective vendors. The system is a closed system, and after initial fill with de-ionized or potable water, will not require water additions except after maintenance. The water quality required for the circuit is not available elsewhere within the Gold Mill, and top-up will be provided from bottles.


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PROCESS DESCRIPTION


3.12 Air Systems Three air systems will be provided throughout the plant:

• Plant air • Instrument Air • Aeration Air for the leach circuit

In addition, because of its remote location, a dedicated compressor and air receiver will be required in the crusher circuit – the existing units installed for the agglomeration plant will be utilized for this duty. 3.12.1 Plant AirHigh pressure compressed air (500Nm3/h at 690kPa) will be used for general use around the plant. It will be generated by 2 of 3 compressors [6600-CM-12001 to 03] running in lead-lag mode, and held in the plant air receiver [6600-VS-12001] before filtration and distribution to the milling circuit and for instrument air supply. The compressed air will be filtered through a set of oil removal filters [6600-FL-12001, 02] prior to reticulation around the plant. In addition to the plant air receiver, a SART precipitate filter air receiver will be located in the SART area to provide the surge requirements for air drying the filter cake. 3.12.2 Instrument Air800Nm3/h of instrument air will be used for actuation of valves around the plant and by several of the instrument systems. It will be generated by the plant air compressors, and will be filtered and dried prior to usage. The plant compressed air will be cleaned in a series of dryers [6600-DR-12001] and filters [6600-FL-12003] to produce compressed air of instrument air quality for the plant: Instrument air will be stored in the instrument air receiver [6600-VS-12002] to ensure a continuous pressure in the instrument air supply to the plant. 3.12.3 Aeration AirLow pressure air (390kPa) will be added to the leach reactors to satisfy the oxygen demand of the slurry and the gold dissolution reactions. This air will be supplied by one of two installed dedicated low pressure compressors [6600-CM-12004, 05] – air from the high pressure air system will not be used for this duty because of the high volumes and lower pressures required. It is estimated that 1,500Nm3/h of air will be required for the leach circuit, and this air will be sparged at the base of the tanks through an “Chinese hat” arrangement.


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PROCESS DESCRIPTION


3.13 Consumables There are a number of consumables on the plant that need to be replaced or made up as specified by the plant operations personnel. The following are the main consumables required by the process:

• Steel balls - SAG Mill • Diesel for the emergency generators and diesel fire water pump

Other consumable requirements for the gold mill include carbon for the carbon adsorption and treatment circuits, and fluxes for smelting. These consumables will not be added at the Gold Mill site, and no new facilities will be constructed to store or handle them. 3.13.1 Steel BallsSteel balls will be used in the SAG mill as grinding media. The SAG mill is expected to use 100mm (4 inch) balls at a consumption of 1.4kg/t, or nearly 20tpd. Steel balls will be delivered to site in trucks. A month’s storage of balls will be provided at the Gold Mill area, near the crushed ore stockpile. This storage may be achieved using containers or bulk bags. Care must be taken to prevent the balls rusting during long term storage. Balls will be added to the SAG mill via the mill feed conveyor, and will be loaded onto the belt as it exits the stockpile tunnel. A mill ball feed bin [1300-BN-12002] will be provided by the conveyor, and this will be filled on a daily basis directly by the delivery truck. Balls will be added to the mill on an almost continuous basis to keep the mill load constant. An automatic ball feeding system [1300-FE-12005] will be provided for this duty, comprising a timer as part of the DCS system, and a feeding mechanism. The ball feeding system will comprise a hydraulic ram and sliding plate pushing balls up and out of the ball bin and over into a chute feeding the mill feed conveyor belt. 3.13.2 DieselDiesel fuel will be used in the gold mill for emergency power generation and for the diesel fire pump [6800-PU-12003]. Emergency flushing of the mill sands pipeline will be accomplished using electric pumps supplied with emergency power in the event of a power failure. Annual consumption of diesel will be minimal, and a separate diesel off-loading and storage facility is not warranted. Each emergency generator [6140-GE-12001 to 03] will be equipped with a diesel storage tank and diesel will be delivered to these tanks by truck from the La Quinua diesel storage facility. Similarly, the diesel fire water pump will be supplied with an integral diesel tank, and the diesel level will be checked on a weekly basis, and topped up if necessary by tanker.


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PROCESS DESCRIPTION


End of Process Description

Documents

2352-0000-25RP-001 - Process Description Rev 0