greenstone gold mines tailings management facility

GREENSTONE GOLD MINES TAILINGS MANAGEMENT FACILITY DESIGN

HARDROCK FEASIBILITY STUDY GERALDTON, ONTARIO

Submitted to:

Greenstone Gold Mines

365 Bay Street, Suite 500 Toronto, Ontario

Submitted by:

Amec Foster Wheeler Environment & Infrastructure a Division of Amec Foster Wheeler Americas Limited

160 Traders Blvd., Suite 110 Mississauga, Ontario

L4Z 3K7

September 2015 TC140307

Distribution: Greenstone 2 copies G-Mining Services e-copy Amec Foster Wheeler 1 copy

Greenstone Gold Mines Tailings Management Facility Design Hardrock Feasibility Study, Geraldton September 2015

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EXECUTIVE SUMMARY

Greenstone Gold Mines has retained Amec Foster Wheeler Environment & Infrastructure, a Division of Amec Foster Wheeler Americas Limited (Amec Foster Wheeler) to provide feasibility level geotechnical and hydrologic design of the tailings management facility (TMF) for the Hardrock Project located near Geraldton in northwestern Ontario (Figure 1). This report describes the background and planning studies, geotechnical field investigations, construction materials and the design basis of the TMF. The design is shown on drawings appended to this report.

The Hardrock Project involves the production of approximately 128 Mt of gold-bearing ore through open pit mining methods with gold extraction using cyanide leaching followed by in-plant cyanide destruction to treat process water. An allowance for 17 Mt of additional tailings has been included in the design of the TMF. The TMF is formed mostly using perimeter embankment dams raised in stages using mine rock with relatively low-permeability till forming an upstream core.

The gold extraction process for the project was designed by Soutex, with WSP providing design of the plant facilities. Stantec carried out the baseline environmental studies, geochemical evaluation of the mine waste and tailings, the site water balance, closure planning and the environmental impact assessment. Mine planning, site infrastructure, cost estimating and the overall feasibility study are the responsibility of G-Mining Services Ltd. (G-Mining).

The TMF site was selected to minimize the disturbance to fish bearing water bodies, maximize the use of natural containment and optimize project economics. Prior to construction of the TMF, Goldfield Creek will be diverted around the north side of the ultimate TMF into a permanent channel designed to provide fisheries compensation. The TMF is set back from other waterbodies by an environmental buffer width of approximately 125 m.

The site-wide water balance by Stantec has determined a positive water balance for the site. As such, the TMF will be developed initially with only one of two cells capturing runoff to minimize the surplus water requiring treatment. Similarly, efforts will be taken to complete tailings deposition early in one cell to allow for progressive rehabilitation and shedding of runoff from the system.

The TMF dams have been designed to meet the requirements of the Lakes and River Improvement Act (MNR, 2011) and the Canadian Dam Association guidelines with a relatively low permeability core along with filters and transition zones upstream of the main embankment constructed of mine rock. The core will be constructed contiguously with cutoffs to intercept sandy foundation soils. Foundation filters are provided under the rockfill to prevent piping of fines out of the foundation soils. Consolidation grouting of the upper fractured bedrock will be carried out where outcropping on shallow bedrock is encountered along the east side of the TMF. Geotechnical investigations at the site have been reported under separate cover.


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The TMF dams have been classified as Very High hazard potential based on the potential environmental impacts in the event of a failure. Dam design criteria include maintaining storage to contain the Environmental Design Flood (EDF), a 100-year return hydrologic event (24-hour storm or freshet), with no discharge through the spillway. An emergency spillway will be maintained to safely pass the Inflow Design Flood (IDF) consisting of a routed Probable Maximum Flood (PMF). The maximum starter dam section is about 10 m high with the ultimate dams raised to a maximum section height of about 35 m.

The tailings deposition plan involves spigotting tailings from the crest of the embankment dams to produce a wide beach to enhance dam safety and minimize seepage under or through the dams. The TMF South Cell has been designed with capacity to hold the tailings for the initial two years of operations. During this period a temporary diversion channel will be maintained to divert freshwater from the North Cell around the TMF. Thereafter tailings deposition will alternate between the North and South Cells with deposition into the North Cell targeted for early completion to facilitate early reclamation and closure. A key objective of the deposition plan is to maintain the TMF pond against natural ground on the northwest side of the TMF. This design will help to mitigate dam safety risks during operations, reduce dam seepage rates, and facilitate the ultimate closure design for the TMF.

Runoff and seepage from the dams will be collected in ditches downstream of the dams and pumped back to the TMF via three collection ponds. The ponds have been sized to contain runoff from a 100-year 24-hour storm with sufficient pumping capacity to drain down the ponds within about 14 days of the design storm.

Closure of the TMF involves lowering of the spillways and re-vegetation of the exposed beaches. Runoff will be directed through overflow spillways constructed in natural ground when deemed suitable for discharge to the environment.

Future work recommendations include:

Supplemental geotechnical investigations including a pump test(s) to better characterize the permeability of the overburden soils along the Southwest Dam alignment to support the design of the cut-off.

Deformation modelling of critical dam sections to confirm sufficiently robust protection against core cracking.

Detailed tailings deposition planning to optimize the dam raising schedule and inner dam construction requirements.

Detailed water balance modelling should be carried out to confirm design assumptions and set operating guidelines and restrictions for the TMF pond. Adequate mill make-up water supply storage will be required before winter.


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TABLE OF CONTENTS PAGE

EXECUTIVE SUMMARY ............................................................................................................... i 1.0 INTRODUCTION ................................................................................................................ 1

2.0 BACKGROUND ................................................................................................................. 2

2.1 Previous Studies ...................................................................................................... 22.2 Tailings Site Selection Re-evaluation ...................................................................... 22.3 Site Plan Development ............................................................................................ 3

3.0 SITE DESCRIPTION .......................................................................................................... 4

3.1 Climate and Hydrology ............................................................................................ 43.2 Geology ................................................................................................................... 4

4.0 GEOTECHNICAL SUBSURFACE INVESTIGATIONS ..................................................... 6

4.1 2014 TMF Investigations ......................................................................................... 64.2 Subsurface Conditions - Dams and Channels ......................................................... 64.3 Construction Borrow Materials ................................................................................. 8

5.0 TAILINGS CHARACTERISTICS ....................................................................................... 9

5.1 Physical Properties of the Tailings ........................................................................... 95.2 Tailings Geochemistry ............................................................................................. 9

6.0 TAILINGS MANAGEMENT ALTERNATIVES ................................................................. 10

6.1 Tailings Dewatering Technologies Considered ..................................................... 106.2 Recommendations for the Feasibility Study .......................................................... 11

7.0 DESIGN CRITERIA .......................................................................................................... 13

7.1 Tailings Deposition Criteria .................................................................................... 137.2 Dam Design Criteria .............................................................................................. 137.3 Environmental Design Criteria ............................................................................... 14

8.0 TAILINGS DEPOSITION PLAN ....................................................................................... 15

8.1 Guidelines and Assumptions for Deposition Planning ........................................... 158.2 Deposition Plan Overview ...................................................................................... 16

9.0 WATER BALANCE MODELLING ................................................................................... 17


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PAGE

10.0 HYDROLOGIC AND HYDRAULIC DESIGN ................................................................... 1910.1 Runoff Diversion Channels .................................................................................... 19

10.1.1 Goldfield Creek Diversion ........................................................................ 1910.1.2 Temporary Diversion ............................................................................... 19

10.2 Emergency Spillway Design .................................................................................. 19

11.0 DAM AND SEEPAGE COLLECTION DESIGN ............................................................... 2011.1 Typical Dam Section .............................................................................................. 2011.2 Dam Crest Level Determination ............................................................................. 2011.3 Dam Foundation Preparation ................................................................................. 21

11.3.1 Overburden Cut-off Trenches .................................................................. 2111.3.2 Bedrock Foundation Grouting .................................................................. 21

11.4 Seepage and Runoff Collection System ................................................................ 22

12.0 CONSTRUCTION QUANTITY ESTIMATES.................................................................... 23

13.0 OPERATIONAL AND CLOSURE CONSIDERATIONS .................................................. 2413.1 Monitoring and Surveillance .................................................................................. 24

13.1.1 TMF Water Balance ................................................................................. 25

14.0 RECOMMENDATIONS .................................................................................................... 26

15.0 REFERENCES ................................................................................................................. 27

16.0 QUALIFICATIONS AND LIMITATIONS .......................................................................... 29


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LIST OF TABLES PAGE

Table 1: Site and Project Characteristics .......................................................................... 30Table 2: Subsurface Conditions Encountered in Boreholes and Test Pits ........................ 31Table 3: Characteristics of Dam Foundation Soils ............................................................ 32Table 4: Till Borrow Characteristics ................................................................................... 33Table 5: Tailings Operational Data .................................................................................... 34Table 6: Dam and Environmental Design Criteria ............................................................. 35Table 7: TMF Water Balance Summary Years 2 and 7 .................................................. 36Table 8: TMF Pond Variation Considerations ................................................................... 37Table 9: Tailings Deposition Plan Overview ...................................................................... 38Table 10: Dam Crest Level Determination .......................................................................... 39Table 11: TMF Dam Construction Sequence and Staging .................................................. 40Table 12: Construction Quantity Estimates ......................................................................... 41

LIST OF FIGURES Figure 1: Site Location Map ................................................................................................ 42Figure 2: General Arrangement Plan .................................................................................. 43Figure 3: Watershed Map ................................................................................................... 44Figure 4: Site Investigations Plan ....................................................................................... 45Figure 5: Tailings Characteristics ....................................................................................... 46Figure 6: TMF Struck-Level Capacity Curve & Dam Staging ............................................. 47Figure 7: Typical Dam Section Alternatives Considered .................................................... 48Figure 8: Dam Seepage Analyses ...................................................................................... 49Figure 9: Dam Stability Analyses ........................................................................................ 50

LIST OF APPENDICIES

Appendix A Design Drawings Appendix B Hydrologic and Hydraulic Calculations Appendix C Dam Stability Assessment Appendix D Dam Seepage Assessment P:\2014\Projects\TC140307_Hardrock_Tailings_FS\08_Eng_Design\TMF Design Report\FINAL ISSUE\Report from DGR\Hardrock FS TSF design (sept.29.2015).docx


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1.0 INTRODUCTION

Greenstone Gold Mines has retained Amec Foster Wheeler Environment & Infrastructure, a Division of Amec Foster Wheeler Americas Limited (Amec Foster Wheeler) to provide specialized geotechnical and hydrologic engineering services for design of the Tailings Management Facility (TMF) for the Hardrock Project feasibility study near Geraldton, Ontario. Services include geotechnical site investigations, tailings deposition planning and design of the tailings dams and ancillary hydraulic structures.

The process design is being carried out by Soutex and design of the plant infrastructure is by WSP. Mine planning, site infrastructure, cost estimating and the overall feasibility study are the responsibility of G-Mining Services Ltd. (G-Mining). The environmental assessment and impact studies for the project are being carried out by Stantec.

This report presents the geotechnical design of the TMF and ancillary water management structures. Construction quantity estimates are provided. Calculation records and design drawings are appended.


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2.0 BACKGROUND

The Project site includes surface features and underground workings from the two former operations, MacLeod-Mosher and the Hardrock mines, that were actively mined between the 1930s and 1970s. The site was subsequently rehabilitated in the late 1990s.

The total tailings tonnage is 128 Million tonnes (Mt) with 550 Mt of mine waste rock produced with strip ratio of about 4.5.

Water management is a key project design driver, as presented in Stantec (2014). The progressively increasing footprint of the open pit and waste dumps results in a high effluent discharge requirement and corresponding increasing water treatment plant costs. Options for progressive closure and rehabilitation of the tailings facility are being examined as ways to reduce the net inflow to the system.

A large inventory of water will have to be maintained before the onset of winter to ensure mill make-up water can be accessed below the ice.

2.1 Previous Studies

The Preliminary Economic Assessment (PEA) Technical Report (Stantec, 2014a) documents earlier stages of planning for the project.

2.2 Tailings Site Selection Re-evaluation

A re-evaluation of the PEA tailings site selection was carried out in light of significant increase in the project resource and comments received during consultation. The tailings site selected for the PEA overprinted a fishery resource, Lake A-322, which we understand is environmentally and socio-economically significant. The site was relatively far from plant site and very close to Goldfield Creek. Further, the east dam was located in a wetland posing potential dam foundation problems. As such, a re-consideration of the TMF site selection was carried out (Amec Foster Wheeler, 2015a) and used to support the alternatives assessment completed by Stantec.

Following a full comparison of all sites identified, four candidate sites were selected for a detailed comparison involving environmental, social, and economic and risks considerations. The preferred site identified, TMF-8, had the highest storage efficiency in terms of dam construction volumes, low risk due to modest dam heights, relatively close proximity to the plant site and low potential environmental impacts, along with the flexibility to flood the tailings for closure if required.

A relatively long diversion channel is required for TMF 8 development but synergies with regard to fishery compensation were identified in coordination with the environmental assessment following consultation. The site also has good potential for expansion by creating cells to east of the current location.


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2.3 Site Plan Development

Figure 2 presents a general layout plan of the project. The mining is by excavation of an open pit. The processing plant will be constructed southwest of the open pit.

Four waste rock storage areas (A, B, C and D) will be developed progressively, of which three areas dumps will be located immediately northeast, southwest and southeast of the perimeter of the open pit. Waste rock storage area D will be located southwest of the plant site.

The TMF is located about 5 km southwest of the processing plant site. The dams will be largely constructed using mine rock. Diversion of Goldfield Creek will be required to develop the TMF. The permanent diversion channel located north of the TMF will be completed prior to mill start-up and will be constructed to meet fishery compensation objectives. Start-up water for the milling operations will be sourced from the flooded historic underground mines.


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3.0 SITE DESCRIPTION

The Hardrock project is located immediately south of the town of Geraldton in Northern Ontario, Canada, approximately 250 km northeast of the city of Thunder Bay, Ontario. Figure 1 presents the site location. The project site is well accessible by Highway 11 as well as local roads in the area such as Lahtis Road and Hardrock Road.

The Hardrock site is characterized by low-lying gently sloping outwash plains and numerous lakes and rivers. Higher grounds exist at the western side of the mine site. The site has a positive water balance, receiving approximately 765 mm of precipitation a year with only 515 mm of lake evaporation. Table 1 presents the site and project characteristics.

3.1 Climate and Hydrology

The climate at the site is characterized by moderate summers, cold and snowy winters. The mean annual temperature at site is 0.6oC with a high of 17.2oC and a low of -18.6oC. The site experiences a mean annual precipitation of 764.7 mm. Mean annual rainfall is 556.1 mm and mean annual snowfall is 242.6 cm. The mean annual evaporation is 515 mm (Environment Canada Climate Normals for 1981 to 2010 Geraldton).

3.2 Geology

The surficial geology in the area is generally dominated by soils derived from proglacial and glacial environments. Surficial post glacial organic and alluvial deposits are present in the area. In accordance with the surficial geology map of the Beardmore-Geraldton area, the Quaternary surficial geology units identified in the project area are outlined as follows (Kristjansson and Thorleifson, 1991):

Organic deposits; Alluvial Deposits; Subaqueous outwash and associated glaciolacustrine sediment; Outwash; Glaciofluvial sediments: and Till.

The Beardmore-Geraldton belt, which parallels and flanks Highway 11, is a predominantly metasedimentary sequence intercalated with mafic to intermediate metavolcanic rocks. Late Precambrian diabase dykes and, large tabular sills intrude the older rocks (Kristjansson and Thorleifson, 1991).

Two faults have been identified in the project area (Stantec 2014b). The Bankfield-Tombill Fault south of the proposed open pit strikes in an east-west direction with a surface trace cross-cutting WRA C and the north limit of WRA B. The Marron Lake Fault also strikes in an east-west


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direction, nearly parallel to and south of the Bankfield-Tombill Fault with a surface trace extending from Marron Lake to Lahtis Road.

As part of the EA, Hydro-Resources investigated the potential for the Bankfield-Tombill Fault to influence groundwater flow in the bedrock through hydraulic conductivity testing of three boreholes in proximity to the fault. The test results reportedly did not indicate differentiation in the hydraulic conductivity of the area adjacent to the fault compared to bedrock in other boreholes.


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4.0 GEOTECHNICAL SUBSURFACE INVESTIGATIONS

Geotechnical investigations carried out in the area of the TMF include 2013 and 2014 (Stantec) for environmental baseline data hydrogeological and geotechnical components.

4.1 2014 TMF Investigations

Amec Foster Wheeler carried out a geotechnical investigation program in 2014 to supplement the previous investigation data and further understand the geotechnical conditions of the TMF site. Seven boreholes and 28 test pits were advanced at locations along the TMF perimeter dam footprints. Generally, the boreholes penetrated 15 m into bedrock before termination. Piezometers/monitoring wells were installed in the boreholes at various depths to facilitate groundwater monitoring and testing. Standard Penetration Tests (SPT) were carried out in the overburden at regular depth intervals in the boreholes. Soil samples were collected from the boreholes and test pits and tested in our geotechnical laboratory for various index properties such as particle size distribution, Atterberg limits and moisture content. Consolidated drained direct shear testing was completed on select samples of the overburden.

Overburden hydraulic conductivity values were estimated using rising head slug testing from screened intervals of select piezometer/monitoring wells in the TMF area. Bedrock hydraulic conductivity values were estimated using rising and falling head slug and constant head test methods from continuous single packer testing in the TMF area. The bedrock core was logged by a technical member of our staff, stored in wooden core boxes, and handed over to Greenstone Gold Mines geology staff.

4.2 Subsurface Conditions - Dams and Channels

The general subsurface conditions encountered along the TMF dam alignments are summarized below. A standalone geotechnical investigation report outlining the factual findings in detail was prepared and submitted to Greenstone Gold Mines (Amec Foster Wheeler, 2015b).

Southwest Dam: Outwash deposits of very loose to compact sand and silty sand ranging in thickness from about 1 m to 10 m along with compact interbedded silts (at the southeast end and approximately 2.5 m thick) were encountered overlying dense to very dense, low permeability till. Average hydraulic conductivities were estimated to be 2 x 10-4 cm/sec and 5.5 x 10-6 cm/s in the upper sand and silty sand layer and till material, respectively.

Southeast and East Dams: Outwash deposits ranging in composition from very loose to compact sands to silts, as well as compact interbedded silt deposits generally 4 m to 5 m thick were encountered overlying dense to very dense low permeability till. Isolated deposits of glaciofluvial, compact sand and gravel overlying the till were also encountered. Average hydraulic conductivities for the till were estimated to be between 1.8 x 10-6 to 5.5 x 10-6 cm/s. The East dam alignment passes over a 7 m high and 300 m wide sand dune and a highly permeable bedrock outcrop about 100 m wide at the north end. The


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near surface bedrock here was found to be highly fractured near the bedrock surface but otherwise was of good quality.

North Dam: Generally, thin outwash deposits (up to about 1 m thick) ranging in composition from sands to silts and glaciofluvial deposits of sand and gravel overlying shallow bedrock were encountered along much of the alignment. The northwest end of the alignment encountered thicker overburden (more than 4.5 m thick). Minor till was encountered at the southeast portion of the alignment.

West Dam: Outwash deposits ranging in composition from compact sands to silts, as well as loose glaciofluvial sand and gravel deposits up to about 5 m thick were encountered along the alignment overlying a thin, compact till deposit and bedrock.

Inner Dam: Outwash deposits of sand to sandy silt underlain by, and interlayered with, interbedded silts generally 1 m to 3 m thick were encountered in the alignment area. Till is inferred underlying these layers. Bedrock was not encountered in the test pits in this area.

Organics/peat up to a maximum thickness of 2.5 m were encountered at surface at the majority of investigation locations.

Peak friction angles determined by laboratory consolidated drained direct shear tests were 32 for sand deposits, 34 for silt and 36 for till.

The groundwater table was found to vary from near surface to about 3.5 m below ground surface in the TMF area.

Bedrock encountered was generally good to excellent quality based on RQD measurements. The following estimated bedrock hydraulic conductivity values for the upper 15 m were assessed.

Southwest dam: 3.9 x 10-6 cm/s to 5.8 x 10-8 cm/s Southeast dam: 7.4 x 10-5 cm/s near Goldfield Creek to 5.8 x 10-8 cm/s East dam: 1.5 x 10-5 cm/s to 7.8 x10-5 cm/s North end of East dam: 1.5 x 10-2 cm/s to 1.4 x 10-3 cm/s West dam: 4.8 x 10-5 cm/s to 5.4 x 10-5 cm/s

Although not explicitly investigated, the expected subsurface conditions along the proposed Goldfield Creek diversion channel alignment (up to the watershed divide near the corner of the North and West dams) are up to 2 m of peat/organics underlain by outwash deposits of sands to silts in excess of 4 m.

Table 2 presents the location of boreholes and thickness of various stratigraphic units encountered at the investigation locations. Table 3 presents characteristics of dam foundation overburden soils and bedrock. In general, the subsurface conditions comprise relatively high


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overburden soils and bedrock. In general, the subsurface conditions comprise relatively high permeability outwash sands and silts overlying low permeability till and bedrock. The permeability of the shallow or outcropping bedrock at the northeast corner of the TMF was found to be of relatively high near the surface, but decreasing with depth (Amec Foster Wheeler, 2015b)

4.3 Construction Borrow Materials

Two locations of till construction borrow source areas have been identified. One area is located in the high ground south of Goldfield Lake and the other in the high ground north of Goldfield Lake off of Goldfield Road. Both glacial till deposits underlay a thin organics layer (0.1 m to 0.5 m thick) and are predominantly fine grained till varying in composition from silty sand to sandy clayey silt. The till contains trace gravel with cobbles and boulders. The indicated maximum thicknesses of the areas south and north of Goldfield Lake are 21 m and at least 6 m, respectively. The area north of Goldfield Lake has only been investigated with test pits and information for the thickness of the deposit is limited.

Standard Proctor Compaction tests for both areas yielded a maximum dry density ranging from about 2 t/m3 to 2,100 kg/m3, with optimum moisture contents ranging from about 8% to 10%, which is very close to the natural moisture content of the till. The groundwater table was encountered at a depth of 2.5 m to 4 m below ground surface.

The till is suitable for dam core construction. Additional investigations will be necessary to further characterize and quantify the till.

Table 4 presents the characteristics of till borrow.


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5.0 TAILINGS CHARACTERISTICS

5.1 Physical Properties of the Tailings

Particle size distribution tests for two tailings samples were provided by Greenstone Gold Mines. The tailings are non-plastic hard rock particles and are predominantly silt and sand sized with approximately 75% to 82% of the particles by mass finer than 0.075 mm diameter (silt and clay sized), out of which 11% to 16% are clay sized by mass.

Figure 5 presents the grain size distribution of two tailings samples determined by Soutex.

5.2 Tailings Geochemistry

Tailings geochemistry has been evaluated by Stantec who indicate that less than 10% of the ore is considered potentially acid generating (PAG) and will be further oxidized by up to 26% during processing, reducing the overall ARD potential for the tailings. As the ARD on-set time for the tailings is estimated at 13 years, on-going deposition of tailings will reduce the ARD potential. Prior to rehabilitation of the TMF, testing of tailings beaches is recommended to determine if localized areas or pockets of PAG tailings exist due to preferential settling of sulphide minerals near final deposition locations. If required, remedial measures will be undertaken to mitigate ARD conditions during closure.


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6.0 TAILINGS MANAGEMENT ALTERNATIVES

The design of any new tailings facility should consider the range of possible tailings management alternatives available, including various degrees of dewatering of the dilute tailings slurry produced in the mill, classifying the tailings into two streams using cyclones, co-deposition with the mine rock and in-pit disposal. A credible comparison of alternatives should consider the mining life cycle costs from development through operations and into closure, and also the potential risks.

In-pit tailings disposal has not been considered because the pit is not completed until mining ceases. Similarly, there is insufficient space to consider tailings and mine rock co-disposal as the sole tailings management solution.

6.1 Tailings Dewatering Technologies Considered

The potential benefits of dewatering include increased water recovery, lower dam volumes and often reduced consequence from a potential dam failure since the pond is smaller. Offsetting factors include potentially higher capital costs and operational challenges related to equipment performance.

The range of tailings dewatering in terms of increased dewatering includes conventional, thickened, paste and filtered. Cyclones are also used to dewater the tailings by separating the flow into two streams. An overview level description of the technologies includes:

Conventional tailings are produced at typically 30% to 45% solids by mass in standard or high-rate thickeners and transported by pipeline to the tailings impoundment. A relatively flat deposited slope is produced after deposition with the coarse tailings fraction of the tailings settling near the discharge location and the slimes migrating towards the pond. A relatively large pond is required to ensure solid-liquid separation.

Thickened (high-density) tailings slurries are produced by further dewatering the tailings to between 55% and 60% solids using high-compression thickeners to a higher viscosity slurry that does not segregate after being deposited. This allows flexibility to increase the deposited tailings slope through thin-lift deposition to reduce the size and volume of the dams. A small pond can be maintained since the bleed water is clear, with surge capacity to handle storm runoff.

Paste tailings are dewatered to say 65% to 70% solids, or the limit of pumpability. Paste or deep cone thickeners, and require positive displacement (PD) pumps to convey the paste by plug flow. Paste tailings deposit as a homogeneous mass with only minor bleed water produced, so the dams and pond only need to handle runoff.

Filtered tailings are produced using high capacity vacuum or pressure belt filters to further dewater the tailings to the point that they can be stacked by placing, spreading, and compacting them to form an unsaturated, dense and stable mound. No containment


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structures are required to retain the tailings; dams are required only to manage runoff from precipitation. The filtered tailings cannot be pumped to the tailings impoundment site. Instead they are transported by dump trucks or conveyor systems.

Cycloning tailings involves the use of gravity-based separation units (cyclones) to segregate the tailings into coarse and fine fractions. The coarse stream (underflow) is typically free-draining sand that can be used to build the dams, while the fines stream (overflow) contained most of the water discharged.

Cycloning, paste, and filtered tailings are not considered practical for Hardrock because:

Effective cycloning requires at least 40% sand sized particles by mass and is therefore not considered to be practical for Hardrock since the tailings contain less than 20% sand.

Paste tailings involve relatively expensive thickeners, higher power demand and operating costs considering booster stations would be required in at least two locations to keep pumping distances less than about 2 km, the technology is relatively unproven for surface deposition in cold, wet climates, and there is an unacceptably high risk of equipment failure or malfunction for a new mine development.

Filtered tailings involve the highest plant capital and operating costs and are best suited to arid climates where there is a shortage of water. At Hardrock the water surplus would actually increase with the use of filtered tailings. Further, a filtered tailings stack would introduce a long-term water quality risk given that a portion of the tailings is considered potentially acid generating.

Co-disposal of tailings and mine rock and in-pit tailings deposition are best management practices with lower risk than conventional tailings impoundments, but they are not suitable for Hardrock on their own. The open pit resource is not exhausted until late in the project life, so in-pit storage capacity is not available when required, and tailings and mine rock co-disposal is considered operationally challenging given the low topographic relief and high mill production rate. That said, the relatively high strip ratio presents an opportunity to explore tailings and mine rock co-disposal as the project develops.

6.2 Recommendations for the Feasibility Study

Conventional slurry is recommended for the project. It is proven cost-effective and allows flexibility for flooding of the tailings for closure should it be required.

Opportunities introduced by dewatered tailings that should be explored in the future include:

Co-disposal of tailings and mine rock in the same facility, with dewatered tailings (i.e., filtered or paste) to reduce water management requirements. Partially filling the rock voids


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with tailings would reduce the overall space requirements and possibly benefit by reducing the flow through the rock dumps (i.e., a potential water quality benefit for closure).

Thickened, high-density tailings discharge on a slope, possibly from a mine rock pile to reduce dam construction requirements. The geochemistry of the tailings (i.e., metal leaching and acid rock drainage characteristics) should be considered.

Use of thickened non-acid generating tailings to cap non-active tailings cells to promote runoff and ultimately produce more stable land masses for closure.


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7.0 DESIGN CRITERIA

The design criteria for the TMF include:

Site conditions climate (precipitation, temperature) and seismic risk (Table 1);

Tailings operating data production rate and discharge slurry density (Table 5); and

Dam design criteria MNR (2011) and the Canadian Dam Association (CDA, 2007)

7.1 Tailings Deposition Criteria

Operating data:

Nominal residue production 1,125 t/hour (9,855,058 t /year) Design Life 16 years Residue slurry discharge density 29.6% solids for first 2 years and 53.7%

solids until end of mine life (mass solids/total mass)

Specific gravity of residue solids 2.81 Void ratio of deposited residue 1.1 (volume of voids / volume of solids)

Derived or calculated operating data are:

Total tailings production 145 M t Dry density of deposited tailings 1.34 t/m3 (for short-term planning) Total deposited tailings volume 108 Mm3

7.2 Dam Design Criteria

The Hazard Potential Classification (HPC) for the TMF dams is Very High in accordance with the Ministry of Natural Resources (MNR) Lakes and Rivers Improvement Act Technical Bulletin entitled Classification and Inflow Design Flood Criteria (August 2011).

Dams classified as Very High hazard potential are those dams where one or more of the following incremental loses may occur:

Loss of life of 11 or more persons; Extensive third party losses exceeding 30 million dollars; and Environmental losses with extensive loss of fish and/or wildlife habitat.

In view of the anticipated extensive environmental losses a very high HPC was selected.


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Environmental criteria that drive the dam and spillway design include:

Minimum pond volume prior to winter 2 Mm3 considering 1 Mm3 ice losses Environmental design flood (contained) 1:100-year snowmelt or daily rainfall Inflow design flood for spillway design Probable Maximum Flood (PMF)

7.3 Environmental Design Criteria

Environmental criteria include:

Geochemical considerations Maintain flexibility for closure to reduce oxidation of sulphide minerals

Environmental design flood 1:100-year hydrologic event (contained) Seepage and dam runoff collection 1:100-year 24-hour storm (contained) Closure Passive drainage from TMF via spillway(s)


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8.0 TAILINGS DEPOSITION PLAN

The plan has been developed to provide flexibility during operations and facilitate progressive closure.

8.1 Guidelines and Assumptions for Deposition Planning

The TMF will be developed in stages for better water management and water balance. The TMF will be divided into two cells, namely the South Cell and North Cell. The following sequence of TMF development is planned.

Commence in South Cell with runoff from the North Cell diverted to Kenogamisis Lake via a temporary North Cell diversion ditch (Section 10);

Alternate deposition into the North and South Cells to optimize dam raising and tailings deposition;

Complete deposition into the North Cell early and commence progressive closure; and

Final deposition in South Cell until the end of the design life.

The perimeter dams and inner dam for TMF cell division will be raised in stages depending upon the capacity requirements. Dam foundation preparation, till core, filter construction and approximately 10 m width of mine rock abutting the till core will be executed by the Contractors, with the mine rock embankment raised using the mine fleet.

Guidelines and assumptions used for developing the deposition plan include:

Deposited tailings slope above pond 1% Deposited tailings slope below pond 4% Nominal spigot spacing 100 m (non-winter months) Minimum water level before deposition 3 m (to float the barge) Plant production start-up date 2017 Tailing production rate 12,000 then 27,000 tpd Provide winter discharge flexibility Avoid discharge relocation in winter

A target pond volume of 2 Mm3 should be maintained before winter to allow about 1 Mm3 of available water below an assumed 1 m ice cover.

The key drivers for the deposition plan is pushing the pond away from the perimeter dams, establishing the permanent pond against natural ground, where the closure spillway will be located.


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8.2 Deposition Plan Overview

Figure 6 shows the struck-level capacity curve for the TMF. Table 9 provides tailings levels at various stages of operation, deposited tailings tonnage, dry tailings beach areas, pond areas and normal pond operating levels.

Tailings deposition plans are presented on Drawings appended to this report.


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9.0 WATER BALANCE MODELLING

A site-wide water balance model was developed by Stantec for evaluation of the water management requirements for the project and support the feasibility level design and prediction of potential environmental effects in the Environmental Assessment (EA). Mill make-up water supply is sourced from the TMF, mine ponds and underground. The TMF pond volume was allowed to vary between 1 and 2 Mm3 (Stantec (2014d, e). The results of the modelling are presented in the EA report.

To support the design for the TMF and ensure a robust tailings deposition plan coupled with dam raising schedule, an operational water balance was used to determine TMF pond storage and dam crest elevation requirements. This was done to confirm that the TMF design has the ability to accommodate changes in water volumes under management due to varying climatic conditions and changes in reclaim water demands.

The following assumptions were included in the operational water balance:

The pond inflows and outflows are:

Direct precipitation on the pond; Runoff from the tailings beach; and Water discharged with the tailings.

Water outflows or losses:

Evaporation from the pond surface and wet beach; Water trapped in the void spaces of the residue; and Decanted water (i.e., from the closed north cell).

Dam seepage is not considered a loss in the model as it will be collected by the seepage collection system and pumped back to the TMF during operations. This is conservative from a TMF operations and dam safety perspective.

Table 7 shows the annual water balance for Years 2 and 7, assuming maximum recirculation to the mill. Years 2 and 3 are representative of early period with the South Cell only and the later period with both cells, respectively. Average, dry and wet annual runoff conditions were evaluated to determine the impact on the maximum pond volume.

Table 8 shows the potential variation (increase/decrease) in the annual pond volume should the recirculation rate to the mill decrease.

Table 9 summarizes the tailings deposition plan and demonstrates there is adequate containment capacity to handle the potential pond increases.


TC140307 Page 18

Dam design accommodates the pond fluctuation as shown on Table 10. The maximum operating pond volume has been assumed to be between 4.7 Mm3 in the Phase 1 (years 1 to 2) and 5.4 Mm3 thereafter, corresponding to scenarios with 80% and 65% recirculation from the TMF, respectively. The Maximum Operating Water Level (MOWL) varies accordingly. The emergency spillway invert levels will be maintained at least 1.5 m below the dam crest levels at all stages of operation to ensure capacity to contain the EDF.


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10.0 HYDROLOGIC AND HYDRAULIC DESIGN

Design of the spillway and diversion channels was performed using intensity-duration-frequency (IDF) curves obtained from Atmospheric Environment Service Rainfall Intensity-Duration Frequency Values Data Integration Division Geraldton, Ontario.

Hydraulic calculations are summarized in Appendix B.

10.1 Runoff Diversion Channels

Diversions include Goldfield Creek and the North Cell in the early period prior to start of TMF.

10.1.1 Goldfield Creek Diversion

Alternatives were examined and the preferred case selected by Stantec and Greenstone Gold Mines was taken to be diversion to southwest arm tributary to Kenogamisis Lake.

The pond between the diversion and the TMF West Dam will be pumped to the TMF with the level maintained below the diversion pond elevation to provide positive hydraulic containment.

10.1.2 Temporary Diversion

North Cell diversion through a small ditch to a creek, requires a small head pond against the north side of the Inner Dam which also serves to provide hydraulic containment to prevent seepage.

10.2 Emergency Spillway Design

Emergency spillways will be provided in the south cell during operations. The spillways are designed to pass the probable maximum flood with a minimum 0.3 m freeboard to dam crest.

At closure the spillway invert elevations will be lowered.


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11.0 DAM AND SEEPAGE COLLECTION DESIGN

11.1 Typical Dam Section

Figure 7 shows alternative dam sections evaluated. The following alternative sections were considered.

Central low permeability till core abutting compacted waste rock buttresses; Compacted waste rock with upstream low permeability liner; and Compacted waste rock with upstream inclined low permeability till core.

The compacted waste rock with upstream inclined till core was judged to be the preferred section.

The dam zonation is:

Zone 1: Core - till Zone 2 : Filter and transition - sand to sand and gravel Zone 3 : Bedding sand - sand Zone 4 : Frost protection - sand and gravel Zone 5 : Erosion protection - riprap/armour stone Zone 6 : Rockfill shell - mine rock Zone 7 : Road surface - gravel

11.2 Dam Crest Level Determination

Rationale for the crest level are provided in Table 10.

The South Cell by virtue of its topography has significantly large storage potential compared to the North Cell. Therefore, a nominal capacity pond of about 0.5 Mm3 will be maintained in the North Cell and the reclaim pond will essentially be in the South Cell. To facilitate this, the inner dam will have a spillway arrangement with invert 1 m below its crest level at each stage of deposition for passage of water to the South Cell pond.

Maximum operating pond storage required at any stage varies corresponding to the potential reduced recirculation rate for a year (Table 7). The EDF volume can be contained above the maximum operating pond.

The crest level of the dam is determined from required tailings capacity. The tailings discharge elevations at each stage of TMF operation will be 0.3 to 0.5 m below the dam crest at each stage. The emergency spillway invert level for each stage dam is set 1.5 m below the dam crest for passage of the IDF.


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11.3 Dam Foundation Preparation

The objectives of dam foundation preparation are to ensure stability of dams, control and mitigate foundation seepage. For dam safety, foundation filters are provided under the full width of the downstream dam shells to prevent piping of fine soil particles into the rockfill.

Foundation treatment in addition to removal of organics involves provision of seepage cut-off trenches in overburden soils and bedrock grouting. The following cases of foundation treatment were studied for comparison purposes:

No cut-offs in soils and no foundation bedrock treatment (Base case);

Partially penetrating cut-offs (southwest dam) in soils and foundation bedrock treatment in east and north dams; and

Fully penetrating cut-offs in soils with foundation bedrock treatment in east and north dams.

An evaluation of the effects of the above dam construction methods, cutoffs, and foundation treatments on dam seepage was completed and is provided in Appendix D. The seepage estimates were prepared for the final dam conditions at the end of mining using conservative assumptions. A total seepage rate of up to 3,000 m3/day was predicted based on the current understanding of site conditions. This estimate will be refined during the detailed design stage of the project.

The following cut-offs in overburden soils and bedrock were adopted based on the findings of the study.

11.3.1 Overburden Cut-off Trenches

A deep cut-off (i.e., a slurry wall) along the Southwest Dam is recommended for the feasibility study. The deep cut-off envisages a slurry trench through the sand layer to the underlying low permeability till layer. The slurry trench will be backfilled with a soil-bentonite mixture prepared using the excavated soil. The cut-offs are keyed into underlying low permeability till material.

For the Southeast Dam the cut-off trenches will penetrate shallow sand silt and interbedded silts to underlying low permeability till. In case of West Dam the cut-off will extend to bedrock after removal of shallow overburden soils. The cut-off trench will be backfilled with compacted till.

11.3.2 Bedrock Foundation Grouting

Bedrock foundation grouting is required to reduce the hydraulic conductivity of the upper, fractured portion of the bedrock that daylights along the east side of the TMF. As shown on Figure 3, the hydraulic conductivity of the rock mass is in the order of 10-6 cm/s below about 20 m


TC140307 Page 22

into the bedrock. Near surface fracturing of the rock due to post-glacial rebound is indicated by occasional hydraulic conductivity values of 10-3 cm/s.

A seepage analyses were carried out on representative sections to understand the implications of a locally deeper fractured upper bedrock zone. Scenarios were run with the grout curtain partially and fully penetrating the fractured upper bedrock.

Figure 8 shows the parameters adopted for the seepage analyses. The pond was assigned a constant head boundary and modelling was done for the worst case with tailings beach and pond. Consolidation grouting of the near surface high hydraulic conductivity bedrock along the East Dam and North Dam.

Additional boreholes along the TMF dam alignments are recommended to further advance knowledge on depth of overburden soils, foundation bedrock type and hydraulic response. This will facilitate further refinement to the cut-offs in soil and extent of foundation bedrock treatment to reduce the overall seepage losses.

11.4 Seepage and Runoff Collection System

The seepage collection arrangement for the TMF features perimeter collection ditches beyond the downstream toe of the ultimate dam configuration. The ditches were located to capture a high percentage of the seepage passing under the dam. In addition to the seepage, the ditches will also intercept the surface runoff from the downstream slopes of the dam and direct it to collection ponds.

Based on the topography in the downstream of the TMF area, the following three ponds will be provided at the low lying points along the ditch alignment.

Pond T1 collects seepage from the TMF southwest, southeast and part of east dams; Pond T2 collects seepage from the TMF west dam; and Pond T3 collects seepage from the TMF north dam and part of east dam.

The design criterion for runoff collection was to contain runoff corresponding to a 1:100 year, 24 hour storm event.

During operations the collected seepage and runoff will be pumped back to the TMF. The design capacity of the ponds and the pumping capacity were optimized for evacuating the ponds in 14 days after a design storm. This criteria harmonizes with that used in the other runoff collection ponds in the project. The required pond capacities are included in the drawing CAHR-A1-340-C-9310. Pumping capacities required at Ponds T1, T2 and T3 were 208 m3/h, 67 m3/h and 88 m3/h, respectively.


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12.0 CONSTRUCTION QUANTITY ESTIMATES

The quantity estimates provided are based upon the most recent feasibility level designs and drawings.

The accuracy of the estimated quantities is considered to be +/-15%. Bulk fill and excavation volumes for the dams, diversions, ditches and spillways were calculated using ground profiles extracted (Civil3D) from topographic data. Investigation data was utilized to infer the depth and extent of stripping below original ground required at all dams. Various material breakdowns (fill zones) for dams and diversion/seepage collection channels were estimated based on the feasibility design.

Table 12 presents the quantity estimates.


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13.0 OPERATIONAL AND CLOSURE CONSIDERATIONS

The principal operational considerations for the TMF include the following.

Freshwater diversion during construction and operation;

TMF ponds away from the perimeter dams abutting the natural ground on the western perimeter;

Wide tailings beaches abutting the perimeter dams for dam stability and to mitigate seepage;

Adequate spillway capacity for passage of IDF with required freeboard;

Flexibility in pond operation with considerations to upset /reduced reclaim rates resulting in higher capacity pond requirement;

Progressive closure opportunities by creation of two cells and completing deposition in one cell for shedding water from this cell;

Flexibility in pond operation by transferring water from north cell pond to south cell pond in case reclaim rate to the mill is significantly reduced;

Start rehabilitating the beach as soon as North Cell deposition is complete to allow time to optimize beach covering; and

Dewatering/water management during construction of the staged raises.

Closure of the TMF involves lowering of the spillways and re-vegetation of the exposed beaches. Runoff will be directed through emergency spillways constructed in natural ground when deemed suitable for discharge to the environment.

Early completion of deposition into the North Cell allows time for vegetation trials and water quality assessments prior to planned release to the environment.

The long term dam safety risks are reduced with the closure pond located against natural ground per the design. The final invert elevation of the closure spillway can be adjusted to optimize closure rehabilitation, i.e., the requirements for flooding or covering the tailings.

13.1 Monitoring and Surveillance

Observations and surveillance of deposition will be required during operations to ensure optimal performance. Periodic bathymetry of the pond should be carried out and followed by review and updating of the deposition plan, as required.


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13.1.1 TMF Water Balance

Close monitoring of the TMF pond volume is required during operation to ensure the pond is under control and does not grow significantly year over year This could happen if reclaim rates to the mill are significantly reduced resulting in increased TMF pond volume. The reclaim rate to the mill could be reduced if more runoff from waste rock areas is utilized or additional pit runoff is used as mill makeup water.

The TMF design allows flexibility for additional water storage by transferring of water from north pond to the south pond in the event of excess water in north cell due to a reduced reclaim rate. For example, Table 10 shows that the maximum operating pond volume that can be handled in the South Cell is significant larger than the normal pond (Table 9). Key Performance Indicators

Pond bathymetric surveys should be carried out annually to determine the pond volume to demonstrate the water balance reasonably tracks pumped flows. The pond levels and annual mill recirculation rates should be used to corroborate the water balance to demonstrate the facility can be operated as predicted.

Maintenance of a minimum tailings beach width of 150 m is targeted for dam safety.

Freeboard from the normal pond to the perimeter dam crest of 2 m is required during all operating periods.


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14.0 RECOMMENDATIONS

Future work recommendations include:

Supplemental geotechnical investigations including a pump test(s) to better characterize the permeability of the overburden soils along the Southwest Dam alignment to support the design of the cut-off;

Deformation modelling of critical dam sections to confirm sufficiently robust protection against core cracking;

Detailed tailings deposition planning to optimize the dam raising schedule and inner dam construction requirements; and

Detailed water balance modelling to confirm design assumptions and set operating guidelines for the TMF pond. Adequate mill make-up water supply storage will be required before winter.


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15.0 REFERENCES

Amec Foster Wheeler, 2015a. Hardrock Tailings Disposal Feasibility Study, Geraldton Tailings Management Facility (TMF) Site Selection Considerations. Final memo submitted to Premier Gold Mines Limited, January 28, 2015.

Amec Foster Wheeler, 2015b. Hardrock Mine Feasibility Study, Geraldton, Ontario Geotechnical Investigations for Tailings Management Facility and Waste Rock Areas. Final report submitted to Premier Gold Mines Limited, April 1, 2015.

Amec Foster Wheeler, 2015c. Hardrock Tailings Disposal Feasibility Study Goldfield Creek Diversion Options. Final memo revision 2 submitted to Premier Gold Mines Limited, April 3, 2015.

CDA, 2007. Technical Bulletin Geotechnical Considerations for Dam Safety. Canadian Dam Safety Association.

MNR, 2011. Lakes and Rivers Improvement Act Technical Guidelines. Ontario Ministry of Natural Resources.

Stantec, 2013. Preliminary Tailings Management Facility and Waste Rock Storage Site Selection Study. Report submitted to Premier Gold Mines Limited, July 9, 2013.

Stantec, 2014a. Trans-Canada Property - Hardrock and Brookbank Projects Preliminary Economic Assessment NI 43-101 Technical Report. Final report submitted to Premier Gold Mines Limited, March 13, 2014.

Stantec, 2014b. Environmental Baseline Data Report Hydrogeological and Geotechnical Components. Draft report submitted to Premier Gold Mines Limited, July 17, 2014.

Stantec, 2014c. ARD/ML Potential of Future Tailings of Hardrock Project. Draft memo submitted to Premier Gold Limited, July 21, 2014.

Stantec, 2014d. Hardrock Water Management and Water Balance for Tailings Management Facility, Open Pit, Mill and Waste Rock Storage Areas. Memo submitted to Premier Gold Mines Limited, October 17, 2014.

Stantec, 2014e. Updates to Site Water Balance for Mill and TMF. Memo submitted to Premier Gold Mines Limited, December 16, 2014.

Stantec, 2015. Hardrock Gold Mine Water Management Plan and Water Balance. Revised draft memo for discussion submitted to Premier Gold Mines Limited, February 2, 2015.


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Kristjansson and Thorleifson, 1991. Surficial Geology, Beardmore-Geraldton, Ontario. Geological Survey of Canada Map 1768A; Ontario Geological Survey, Map 2535, scale 1:100,000.


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16.0 QUALIFICATIONS AND LIMITATIONS

This report was prepared exclusively for Premier by Amec Foster Wheeler for specific application addressed herein. The quality of information, conclusions and recommendations contained herein is consistent with the level of effort involved in Amec Foster Wheeler services and based on: i) information available at the time of preparation, ii) data supplied by outside sources, and iii) the assumptions, conditions and qualifications set forth in the report. This report is intended to be used by Vale only, subject to the terms and conditions of its contract with Amec Foster Wheeler. Any other use of, or reliance on, this report by any third party is at that partys sole risk.

Amec Foster Wheeler Environment & Infrastructure a Division of Amec Foster Wheeler Americas Limited Prepared by: Prepared by: David G. Ritchie, M.Eng., P.Eng. Prabhat Habbu, M.Tech., P.Eng. Principal Engineer Associate Geotechnical Engineer Reviewed by: David E. Bleiker, M.A.Sc., P.Eng. Principal Engineer

Greenstone Gold MinesTailings Management Facility DesignHardrock Feasibility Study, GeraldtonSeptember 2015

Source or Calculation Value Unit

Mean 0.6 oCLow (February) -18.6 oCHigh (August) 17.2 oCPeriod of freezing 5 months (Nov - Mar) -

Mean annual precipitation 764.7 mmMean annual rainfall 556.1 mmMean annual snowfall 242.6 cmMean annual evaporation Amec Foster Wheeler (Note 3) 515 mm

1:100 year rainfall (24-hr) Atmospheric Environment Service (Note 4) 106.7 mmProbable maximum precipitation (PMP) (24-hr) Atmospheric Environment Service (Note 5) 360.7 mm1:100 year 30 day rain-on-snow Atmospheric Environment Service (Note 6) 352.6 mm

NRC/Amec Foster Wheeler 0.065 g multiple of gravity acceleration

slurry via pipelinessub-aerial

spigotting/end discharge from pipelines on dam crest

sub-aerial 1 %sub-aqueous 4 %

North Cell 162 haSouth Cell 356 haTotal 520 ha

North Cell 172 haSouth Cell 366 haTotal 538 ha

Pond T1 45.5 haPond T2 9.2 haPond T3 11.8 ha

Amec Foster Wheeler barge-mounted pumps -G Mining/Stantec fixed pumps discharging to TMF -

Notes:1.

2.

3.

4.

5.

6.

7.

8.

Storm events

Environment Canada (Note 2)

CAHR-A1-340-G-9302-0A

Amec Foster Wheeler

SITE CONDITIONS

Meteorlogical

Tailings Disposal Concept

Disposal type

TMF surface areas (Note 8)Basin Characteristics

Method of discharge

Contributing watershed and TMF surface areas vary with downstream raise. Ultimate configuration attributes are listed

PROJECT DESCRIPTION

From Ponds T1, T2, T3

Transport type

Seepage collection pond catchment areas

CAHR-A1-340-C-9310-0A

CAHR-A1-340-G-9304-0A

The 1:10,000 yr earthquake was extrapolated from 1:100 yr, 1:475 yr, 1:1000 yr, and 1:2475 yr events (2010 NBCC, NRCAN, 2015) and is considered equivalent to the maximum credible earthquake

Decant Strategy

Contributing watershed areas (Note 8)

From TMF

Table 1: Site and Project Characteristics

Criterion

Climatic dataTemperature

Design Criteria - Hardrock Mine Tailings Management Facility

Seismicity

1:10,000 year peak ground acceleration (pga) (Note 7)

Estimated talings beach slopes

Lake evaporation determined using average of Rawson Lake 1969-1999 (ID 6036904), Kemptville 1968-1995(ID 6104025), and Ottawa CDA 1962-1998 (ID 6105976) stations

TMF = Tailings Management Facility

Environment Canada Climate Normals for 1981 - 2010 Geraldton A 6042716

Atmospheric Environment Service Rainfall Intensity-Duration Frequency Values Data Integration Division Geraldton A Ont (Composite) 6042716

Hershfield Method using Atmospheric Environment Service Rainfall Intensity-Duration Frequency Values Data

Snow Melt Model 1. Atmospheric Environment Service Rain+Snowmelt Intensity, Duration, Frequency Values prepared by the Hydrometeorology Division, Canadian Climate Centre for Station 6042716 Geraldton A

TC140307 Page 30


Top Depth Thickness

Top Depth Thickness Top Depth Thickness

Top Depth Thickness

Top Depth Thickness

Top Depth Penetration

(m) (m) (m) (m) (m) (m) (m) (m) (m) (m) (m) (m) (m) (m)TP14-20 339.4 0.0 0.2 0.2 3.0 - - 3.1 0.9 4.0 1.5 - - 5.5BH14-06 337.5 0.0 0.1 0.1 10.2 - - - - 10.3 4.6 14.9 15.9 30.8TP14-19 337.0 0.0 0.6 0.6 4.5 - - - - - - - - 5.1TP14-18 334.4 0.0 0.4 0.4 4.2 - - - - - - - - 4.6TP14-17 333.9 0.0 0.5 0.5 4.0 - - - - - - - - 4.5TP14-16 334.8 0.0 0.1 0.1 3.0 3.1 2.4 - - - - - - 5.5BH14-05 332.2 0.0 0.9 0.9 0.6 1.5 2.6 - - 4.1 2.3 6.4 16.4 22.8TP14-15 336.1 - - 0.0 4.0 - - 4.0 2.0 - - - - 6.0TP14-14 338.3 0.0 0.1 0.1 2.6 - - - - 2.7 2.8 - - 5.5BH14-04 335.3 0.0 0.1 0.1 3.3 3.4 1.8 - - 5.2 19.0 24.2 15.6 39.8TP14-13 331.2 0.0 0.3 0.3 3.7 4.0 2.0 - - - - - - 6.0

0.1 1.42.7 0.8

TP14-11 331.1 0.0 1.0 1.0 0.4 1.4 3.5 - - 4.9 1.1 - - 6.0BH14-03 333.3 0.0 0.8 0.8 0.8 1.6 2.1 - - 3.7 18.5 22.2 15.6 37.8TP14-10 334.0 0.0 0.9 0.9 3.7 4.6 0.5 - - - - - - 5.1TP14-09 335.0 0.0 1.1 1.1 2.5 - - - - 3.6 2.4 - - 6.0TP14-08 338.1 0.0 0.1 0.1 3.3 - - - - 3.4 1.4 - - 4.8TP14-07 337.0 0.0 2.6 - - - - - - 2.6 1.4 - - 4.0TP14-06 337.3 0.0 0.1 - - - - 0.1 0.5 - - 0.6 - 0.6BH14-02 336.7 0.0 0.9 0.9 0.6 - - - - - - 1.5 15.5 17.0TP14-59 337.1 0.0 0.7 0.7 0.3 - - - - 1.0 0.6 1.6 - 1.6TP14-60 340.9 0.0 0.1 0.1 0.2 - - - - - - 0.2 - 0.2TP14-61 339.5 0.0 0.5 0.5 0.1 - - - - - - 0.6 - 0.6TP14-62 341.7 0.0 0.1 0.7 4.7 - - 0.1 0.6 - - - - 5.4

BH14-01A 338.4 0.0 1.6 1.6 0.6 - - 2.2 0.8 3.0 0.8 3.8 16.0 19.81.0 0.23.6 0.1

TP14-55 339.2 0.0 0.2 0.2 0.5 - - 0.6 2.6 3.2 0.4 3.6 - 3.6TP14-01 345.0 0.0 0.2 0.2 0.6 - - - - - - 0.8 - 0.8TP14-57 336.3 0.0 0.9 0.9 1.1 2.0 3.0 - - 5.0 0.5 - - 5.5

0.3 1.22.5 1.0

TMF-Inner Dam

Location Description

TP14-12 330.9

Table 2 : Subsurface Conditions encountered in Boreholes and Test Pits

Borehole Number

Ground Elevation

Glaciofluvial (Sand and TillTotal Depth

Subaqeous Outwash and Organics Outwash (Sand to Bedrock

-0.0 0.1 1.5 1.2

TP14-58 335.2

TP14-56 337 0.0 1.0 - - 1.2

0.0 0.3 3.5 1.0 - - - -

-

-

-

3.5 1.5

2.4 - -

-

-

-

- 5.0

3.7

3.5

TMF Southwest Dam

TMF Southeast Dam

TMF East Dam

TMF North Dam

TMF West Dam

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Foundation Strata Description Variability Permeability

Outwash (Sands to Silts) Silt to gravelly sand

Thick and prevalent at Southwest dam (up to 10 m thick), elsewhere thinner (less than 5 m thick), more silty at Southwest, Southeast and East dams

Hydraulic condiutcitvity: range from 1 x10-2 to 2.5 x10-5 cm/s (inferred from Hazens formula from grain size); (slug test result, 2 x10-4 cm/s)

Subaqueous Outwash and Associated Glaciolacustrine (Interbedded Silts)

Silt with thin clay interlayers

Encountered only at Southwest (east limit only), Southeast, East and Inner dams, ~1 m to 4 m thick. No clayey soils encountered in dam footprint areas.

Hydraulic condiutcitvity: range from 1 x10-5 to 1x10-6 cm/s (inferred from Hazens formula from grain size); (slug test result, 4.4 x10-3 cm/s)

Glaciofluvial (Sand and Gravel) Sand and gravel

Thin layers (~1 to 2 m thick) encountered in isolated portions of the Southwest, Southeast and East dams. More prevalent at the West dam (up to ~2.5m thick).

Hydrulic condcutivity: range from 3.5 x10-1 to 4x10-4 cm/s (inferred from Hazens formula from grain size); (slug test results, 1.4x10-1 to 5.4 x10-3 cm/s)

Till Clayey silt till to silty sand till

Prevalent underlying other strata and overlying bedrock at the Southwest, Southeast, East and Inner dams (~1.5 m to 19 m thick), thinner and less prevalent at the North and West dams (


Till Borrow Source Location Description Area/Depth Depth

Maximum Dry Density (kg/m3)

Optimum Moisture Content (%)

Natural Moisture Content (%)

North of Goldfield Lake Gravelly silty sand, gravelly sandy silt, sandy silt, sand and silt, and sandy clayey silt (PI = 5) ~50 Ha1 m to greater than 6 m (limited data from test pit investigations only) ~2100 8 to 9 8

South of Goldfield Lake Silty sand, sand and silt, sandy silt, and sandy clayey silt (PI = 4) ~50 Ha 2.5 m to 21 m (as encountered in one borehole and test pits) ~2000 8 to 10 9 to 10

Notes Cobbles and boulders are present within till deposits.

PI = Plasticity Index

Table 4 : Till Borrow Characteristics

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Symbol Source Total Phase 1 Phase 2 UnitsOperating data provided (design criteria)Ore production

A 145.0 Mt Open Pit A1 Gmining 127.9 11.4 116.5 Mt Contingency A2 Premier 17.1 - - Mt

Design production rate (when operating) B Gmining 13,043 29,348 t/dayMill availability (% of the year the mill operates) C Plant designer 92.0 %Production rate (nominal daily) D B/C 12,000 27,000 t/day

Tailings production & propertiesTailings / ore ratio E Plant designer 1.0Discharge slurry density (mass solids / mass solids + mass water) s m Soutex 29.6 53.7 % solidsSpecific gravity of tailings solids G st Plant designer 2.81 2.81 -Void ratio of deposited tailings (vol. of voids / vol. of solids) e t Amec FW 1.1 1.1 -

Mine rock production & propertiesStrip ratio (mine rock / ore) F Gmining 4.52Specific gravity of rock particles G sr Plant desinger 2.81 2.81 -Void ratio of deposited rock (vol. of voids / vol. of solids) e r Amec FW 0.40 0.40 -

Calculated data (design parameters)Project design life G A1 / (B x 365) 14.4 2.6 11.8 yearsTailings production

daily D x E 12,000 27,000 t/dmonthly D x E x 30 359,987 810,005 t/moannual D x E x 365 4,379,839 9,855,058 t/ytotal H x 365 x G 127.9 11.4 116.5 Mttotal with contingency H1 H x 365 x G + A2 145.0 - - Mt

Deposited tailings- Dry density dt Gst / (1+et) 1.34 1.34 t/m3

- Saturated water content of deposited tailings sat (et / Gst) x 100 39.15 39.15 %daily 8,968 20,178 m3/dmonthly 269,029 605,342 m3/moannual 3.3 7.4 Mm3/ytotal 95.6 8.5 87.1 M-m3

total with contingency 108.2 - - M-m3

Water retained in voids daily J H xsat 4,698 10,569 m3/dDeposited mine rock

- Dry density dr Gsr / (1+er) 2.0 2.0 t/m3

Flows affecting the mill water balanceMoisture content of the ore entering the mill K Soutex 4 4 %Fresh water for glands & reagent mixing (per ton of ore) L Soutex 0.02 0.02 m3/ tEvaporation and spillage losses in the mill (per ton of ore) M assumed 0.01 0.01 m3/t

Mill water balanceWater in ore entering the mill N D x K 480 1080 m3/dFreshwater for glands and reagent mixing O D L 240 540 m3/dWater leaving the mill with the tailings P I / sm - I 28,541 23,279 m3/dLosses in the mill Q D M 120 270 m3/dMake-up water required R N + O - P - Q 27,941 21,929 m3/d

- Maximum recirculation (% of slurry water) S Amec FW 98.0 94.0 %

Notes:1. Production rates shown are at the end of the relevant period.2. Partial saturation of tailings on the beach is not explicitly accounted for.3. The "nominal" tailings production is averaged over a year. Equipment design should consider the availibility of the plant and appropriate factors of safety.4. The contigency for historical tailings is for the Macleod High and Hardrock tailings.

Resource

H

Description

Table 5 - Tailings Operational Data

H / dt- Volume I

- Nominal tailings production

TC140307 Page 34


Source Value

MNR (LRIA) Very HighMNR (LRIA) 24-hour Probable Maximum Flood (PMF)

CDA MCE (1:10,000 year AEP)Amec Foster Wheeler 10 mAmec Foster Wheeler rockfill embankment with an upstream inclined coreAmec Foster Wheeler staged, downstream raisesAmec Foster Wheeler Till and transition fills in summer/fall, no restirctions on rockfill

CDA 1.3CDA 1.5CDA 1.1

Amec Foster Wheeler 100 m

MNR No overtopping of dam by 1:1000 year wind wavesMNR No overtopping of dam by 1:100 year waves

Amec Foster Wheeler 125 m

Amec Foster Wheeler 1:100 year event (storm run-off or freshet)

Amec Foster Wheeler inhibit seepage by cut-off keyed into till (key trench and slurry wall) or bedrock treatment (slush grouting and consolidation grouting and/or curtain installation)Stantec 1:100 year storm runoff plus dam seepage in ditches and ponds

Amec Foster Wheeler open channel spillway with concrete sill for level controlAmec Foster Wheeler none

MNR peak flows during routed IDF

Amec Foster Wheeler maximize diversion of freshwater (Goldfield Creek)Amec Foster Wheeler PMF (for dam safety)Amec Foster Wheeler to be determined based on routing in Goldfield Lake

Stantec Non acid generating, potentially metal leaching (arsenic)Amec Foster Wheeler sample monitoring wells

Stantec cover and re-vegetate exposed beaches to inhibit infiltrationStantec passive drainage

Notes:

1.

TMF closure concept

Target tailings beach width (exposed above pond)

Groundwater monitoring

Long term drainage / water management

The pond level will fluctuate during the year. The maximumum operating water level (MOWL) is set to ensure the environmental design storm (EDF) can be contained with no discharge through the spillway.

Objective

Peak flow in diversion channel

Freshwater Diversion

TMF Operation & Closure

Design flood

Tailings geochemistry

Structure typeFlow controlDesign flow

ENVIRONMENTAL PERFORMANCE AND CLOSURE

Short term (end of construction, before filling)

Pseudo-static for MDE

Weather restriction for construction

Table 6: Dam and Environmental Design Criteria

CriterionDAM DESIGN

Dam Hazard Classification CategoryInflow Design Flood (IDF) - for spillway design

Maximum Design Earthquake (MDE)

Minimum factor of safety for various load factors

Minimum crest width

Long term (during operation and post-closure)

Emergency Spillway

Environmental Criteria

Environmental Design Flood (EDF) - contained below spillway

1) At MOWL

Dam seepage control measures

Dam seepage & runoff collection system

Minimum freeboard above pond to dam crest

Dam TypeConstruction method

2) At IDF flood level

Setback of the dam toe from creeks and water bodies

TC140307 Page 35


Year 2 Reclaim Ratio 98%

Net Inflow Pond

Runoff Slurry Water Total InflowPorewater retained

in the voids of deposited tailings

Evaporation Recirculation Total Losses Net Inflow Volume

Oct 221,323 884,757 1,106,080 145,623 0 867,062 1,012,684 93,395 2,093,395Nov 123,229 856,216 979,446 140,925 0 839,092 980,017 -572 2,092,824Dec 72,626 884,757 957,383 145,623 0 867,062 1,012,684 -55,301 2,037,523Jan 63,266 884,757 948,023 145,623 0 867,062 1,012,684 -64,662 1,972,861Feb 56,335 806,270 862,605 132,705 0 790,145 922,849 -60,245 1,912,616

March 125,056 884,757 1,009,812 145,623 0 867,062 1,012,684 -2,872 1,909,744April 192,386 856,216 1,048,602 140,925 0 839,092 980,017 68,585 1,978,329May 200,651 884,757 1,085,408 145,623 139,200 867,062 1,151,884 -66,476 1,911,853June 230,685 856,216 1,086,901 140,925 185,600 839,092 1,165,617 -78,716 1,833,137July 296,478 884,757 1,181,235 145,623 201,067 867,062 1,213,751 -32,516 1,800,620Aug 228,228 884,757 1,112,985 145,623 167,040 867,062 1,179,724 -66,740 1,733,881Sept 277,368 856,216 1,133,584 140,925 103,627 839,092 1,083,644 49,940 1,783,821

TOTAL 2,087,631 10,424,432 12,512,063 1,715,765 796,533 10,215,944 12,728,242 -216,179 2,000,000

Year 7Reclaim Ratio 94%

Net Inflow Pond

Runoff Slurry Water Total InflowPorewater retained

in the voids of deposited tailings

Evaporation Recirculation Total Losses Net Inflow Volume

Oct 373,444 721,659 1,095,103 327,651 0 678,360 1,006,011 89,092 2,089,092Nov 207,928 698,380 906,308 317,082 0 656,477 973,559 -67,251 2,021,841Dec 122,545 721,659 844,204 327,651 0 678,360 1,006,011 -161,807 1,860,034Jan 106,750 721,659 828,409 327,651 0 678,360 1,006,011 -177,602 1,682,433Feb 95,055 657,641 752,696 298,585 0 618,183 916,768 -164,072 1,518,361

March 211,010 721,659 932,669 327,651 0 678,360 1,006,011 -73,342 1,445,019April 324,618 698,380 1,022,997 317,082 0 656,477 973,559 49,439 1,494,457May 338,564 721,659 1,060,223 327,651 193,560 678,360 1,199,571 -139,348 1,355,109June 389,241 698,380 1,087,621 317,082 258,080 656,477 1,231,639 -144,018 1,211,091July 500,255 721,659 1,221,914 327,651 279,587 678,360 1,285,598 -63,683 1,147,408Aug 385,095 721,659 1,106,754 327,651 232,272 678,360 1,238,283 -131,529 1,015,879Sept 468,010 698,380 1,166,390 317,082 144,095 656,477 1,117,654 48,737 1,064,616

TOTAL 3,522,514 8,502,775 12,025,289 3,860,472 1,107,593 7,992,609 12,960,673 -935,384 2,000,000

Notes:

Table 7 - TMF Annual Water Balance Summary - Years 2 and 7

Month

Inflows Outflows & Losses

Recirculation rate to Mill @ 98% to year 2 and 94% in subesequent years

Month

Inflows Outflows & Losses

TC140307 Page 36

Greenstone Gold MinesTailigns Management Facility DesignHardrock Feasibility Study, GeraldtonSeptember 2015

Year Climate Recirculation Month with Max. PondNet Inflow

(Mm3)

0.98 Oct -0.220.8 Sept 1.66

0.65 Sept 3.220.98 Sept 0.860.8 Sept 2.74

0.65 Sept 4.30.94 Oct -0.940.8 Sept 0.26

0.65 Sept 1.530.94 Sept 0.880.8 Sept 2.07

0.65 Sept 3.35

Table 8: TMF Pond Variation Considerations

2

7

normal

100 year wet

normal

100 year wet

TC140307 Page 37


Volume (Mm3)

Elevation (m)

Volume (Mm3)

Elevation(m)

Volume (Mm3)

Elevation (m)

1 341.0 4.39 338.7 2.3 336.2 - - - 0.3 336.0* 9.2 339.52 341.0 4.39 340.8 2.3 337.1 - - - 0.3 336.0* 6.3 339.53 341.0 - - 2.3 337.1 349.0 9.86 348.2 0.5 340.5 6.3 339.54 345.0 9.86 344.3 2.3 339.0 349.0 - - 0.5 340.5 11.3 343.5

5 to 8End of North Cell 345.0 81.26 - 2.3 339.0 365.0 35.04 364.5 0.5 359.7 11.3 343.5

8 to 16End of South Cell 365.0 99.90 364.5 2.3 357.5 365.0 44.90 - 0.5 359.7 11.4 363.5

* Freshwater pond. Goldfield Creek will be diverted to Kenogamisis Lake via a temporary diversion channel during first two years of operation.

Tailings Discharge

EL.Beach Area Pond Area

(m) (Ha) (Ha)1 South 338.7 84.4 129.82 South 340.8 128.1 112.13 North 348.2 120.9 102.84 South 344.3 195.7 78.9

5-6 North 356.5 148.9 20.6(N)7-8 North 364.5 137.7 20.7(N)

8-16End of South Cell South 364.5 296.3 42.1

Total

Pond Storage Available at Spillway Invert

South Cell

End of YearActive

Deposition Cell

Table 9: Tailings Deposition Plan Overview

End of YearTailings

Discharge EL.(m)

Tailings Discharge EL.

(m)

Normal Pond Normal Pond

South Cell North Cell

Tailings Tonnage

(Mt)

Dam Crest EL.(m)

Tailings Tonnage

(Mt)

Dam Crest EL. (m)

TC140307 Page 38

Greenstone Gold MinesTailings Management Facility DesignHardrock Feasibility Study, GeraldonSeptember 2015

1 South 341 4.7 337.6 0.55 338.0 339.5 9.2 1.2 340.7 0.3

2 South 341 4.7 338.7 0.55 339.0 339.5 6.3 1.2 340.7 0.3

3 North 341 5.4 339.1 0.55 339.4 339.5 6.3 1.2 340.7 0.3

4 South 345 5.4 341.2 0.55 341.5 343.5 11.3 1.2 344.7 0.3

5, 6 ,7 and 8End of North Cell North 345 5.4 341.2 0.55 341.5 343.5 11.3 1.2 344.7 0.3

Years 8 to 16End of South Cell South 365 5.4 361.1 0.55 361.2 363.5 11.4 1.2 364.7 0.3

Maximum pond storage volume required for dead storage, pre-winter inventory, upset storage for reduced reclaim rate

Recirculation rate for maximum pond volumes assumed at 80% of slurry water in a 1:100 wey year for years 1 and 2

Recirculation rate for maximum pond volumes assumed at 65% of slurry water in a 1:100 wet year for years 4 onwards

Pond Level(m)

Spillway Invert(m)

Total Pond Volume(Mm3)

Head above Spillway Invert

(m)

Peak Pond Elevation

(m)

Freeboard to Crest(m)

Table 10: Dam Crest Level Determination

Operational YearsEmergency SpillwayEnvironmental Design FloodMaximum Operating Pond IDF Routing

South CellSouth Dam

Crest Elevation

(m)

Active Cell Depostion Volume

(Mm3)Pond Level

(m)Volume (Mm3)

TC140307 Page 39


South Cell(m)

North Cell(m)

Inner Dam(m)

Till Core(Mm3)

Mine Rock(Mm3)

Till Core(Mm3)

Mine Rock(Mm3)

1 1 South 341 - 341 0.5 0.7 - -

2 1 South 341 - 341 - - 0.3 0.7 North Cells dams raised to EL 349 m by end of year 2 (13 m height)

3 2 North 341 349 342 0.2 1.2 - - South Cell dams raised to EL 345 m by end of year 3 (4 m raise)

4 3 South 345 349 349 - - - 0.9 North Cell dams raised to EL 355 m by end of year 4 (6 m raise)

5 to 6 4 North 345 355 355 - - - - North Cell dam raising continues in these two years while deposition of tailings continues in North Cell

7 and 8End of North Cell 4 North 355 365 365 0.6 3.1 0.3 1.4

North Cell dams raised to EL 365 m during these two years while deposition of tailings continues in North Cell

South Cell dams should be raised progressively as the North cell depostion is ongoing

Years 8 to 16End of South Cell 5 South 365 365 365 0.4 2.9 - - South Cell dam raising while deposition of tailings continues in South Cell

Total 1.7 7.9 0.8 3.0

Table 11 - Dam Construction Sequence and Staging

TMF Dam Crest ElevationsConstruction

Stages CommentsOperational

YearsPerimeter Dam QuantitiesActive Cell

Deposition

South Cell North CellPerimeter Dam Quantities

TC140307 Page 40

GreenstoneGoldMinesTailings Management Facility DesignHardrock Feasibility Study, GeraldtonSeptember 2015

Unit Goldfield Creek Diversion

Construction Period

South Cell Start Up - Crest EL - 341 m (Year -1)

North Cell Start Up - Crest EL - 349 m (Year +2)

Ultimate - Crest EL - 365

m (EOM)

Start Up - Crest EL - 341 m

Inner Dam - Crest EL - 347



Ultimate - Crest EL -

365 m

Start Up - Crest EL - 342 m

1 Clearing & grubbing - dam site ha 32.7 21.1 57.8 2.3 - - - - 1.72 Clearing - basin ha 270.5 93.9 69.2 33.3 - - - - 7.7

3 Stripping of unsuitable soils m3 215,022 137,573 189,644 17,112 - - - - 13,498

4Consolidation grouting (plan area) m

2 - 8,400 - - - - - - -

5 Slurry wall (profile area) m2 10,400 - - - - - - - -6 Cut-off trench excavation m3 141,825 54,000 49,500

greenstone gold mines tailings management facility

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