Ministère de l Environnement et de l Action en matière de changement climatique

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1 Ministry of the Environment and Climate Change 435 James Street South Suite 331 Thunder Bay ON P7E 6S7 Tel.: (807) Fax: (807) Ministère de l Environnement et de l Action en matière de changement climatique 435, rue James sud Bureau 331 Thunder Bay ON P7E 6S7 Tél. : (807) Téléc.: (807) July 23, 2015 M E M O R A N D U M TO: Monika Holenstein Gavin Battarino Senior Environmental Officer Project Officer Thunder Bay District Office Environmental Approvals FROM: RE: Shannon Heggie Regional Hydrogeologist Technical Support Section Thunder Bay Northern Region Office 2015 Geochemical Characterization, Environmental Baseline Data Report Premier Gold Mines Hardrock Inc. Hardrock Project Geraldton, Greenstone, ON Introduction and Purpose As requested, I have reviewed the groundwater-related portions of the report prepared by Stantec Consulting Ltd. (the consultant), entitled: Environmental Baseline Data Report Hardrock Project: Geochemical Characterization, dated May 8, The following three (3) documents were referenced for additional information: Greenstone Gold Mines/Stantec document: Welcome to the Hardrock Project Update Environmental Assessment, Results of Baseline Studies, dated July 2015; Premier Gold/Stantec document: Handout 1: Alternative Methods Screening Results, dated July 2015; and Page 1 of 8

2 Ministry of the Environment and Climate Change (MOECC) memo: RE: Baseline Hydrogeological and Geochemical Work Programs, Premier Gold Mines Ltd., Hardrock Property, Geraldton, Greenstone, Ontario, prepared by Shannon Heggie (Regional Hydrogeologist), dated May 23, The purpose of this review is to evaluate the baseline acid rock drainage and metal leaching (ARD/ML) assessment studies on overburden, bedrock and historic tailings materials representative of the Hardrock Project Development Area, with respect to geochemical characterisation of waste rock, ore and tailings, proposed site layout, seepage issues, and site closure considerations. These baseline studies will be included in the provincial Environmental Assessment (EA) submission. I have forwarded this review to the appropriate MOECC Surface Water Specialist and District Manager. Background The proposed open pit gold mine and associated infrastructure and facilities (Hardrock Project) are located within the Municipality of Greenstone, ~2 km south of the community of Geraldton, Ontario, adjacent to Kenogamisis Lake and Highway 11 (Trans-Canada Highway). The site includes the former underground MacLeod-Mosher Mine and Hardrock Mine, and associated historic tailings facilities. The development of the site would displace private residences and businesses in the MacLeod Townsite on Highway 11 and the Hardrock Townsite next to Kenogamisis Lake, and would result in the relocation of a portion of the MacLeod and Hardrock historic tailings to a new tailings management facility due to development of the main open pit and re-alignment of the highway. The anticipated mine life is fifteen (15) years, with ~12,000 tonnes per day of mineralised material processed in the mill during the first two (2) years, and ~30,000 tonnes per day processed during the remaining mine life. The conceptual project components include: open pit mine; overburden storage areas; waste rock storage areas; ore stockpiles; ore pad, crushing plant, crushed ore stockpile; mill; tailings management facility; access roads and pipelines; effluent treatment plant; sewage treatment plant (300 people); mine dry, assay lab, administration building, mine maintenance shop, warehouse; explosives plant and magazines; power plant, on-site substation and power distribution; water supply and distribution; fuel supply, conversion, storage and distribution; recycling and sort facility; aggregate quarries; Highway 11 realignment and relocation of Ministry of Transportation yard; watercourse realignments; relocation of a portion of the historic MacLeod and Hardrock tailings; relocation of Hydro One Networks Inc. substation; and natural gas pipeline. Page 2 of 8

3 Four (4) historic tailings piles are located in the vicinity of the Project Development Area and within the Local Study Area: MacLeod High Tailings (adjacent to Barton Bay East), MacLeod Low Tailings, Hardrock Tailings (adjacent to Kenogamisis Lake Central Basin and Southwest Arm), and Little Longlac Tailings (adjacent to Barton Bay West and East). Seepage and runoff from the MacLeod High Tailings is collected in ditches and is also channeled via two drainage ditches to Barton Bay East and Kenogamisis Lake Central Basin. Drainage from the MacLeod Low Tailings and the former plant site for the MacLeod-Mosher Mine flows east along Highway 11 and into the stope breakthrough ( Glory Hole /Stope B/T) at the adjacent former Hardrock mine. From the stope breakthrough, the drainage enters the flooded Hardrock underground workings, with discharge from the Hardrock No. 1 Shaft into Kenogamisis Lake Southwest Arm. Seepage from the Hardrock Tailings flows directly into Kenogamisis Lake Central Basin and Southwest Arm, and seepage from the Little Longlac Tailings flows into Barton Bay West and East. Site topography is relatively flat to gently rolling, with surface water drainage to several small lakes (Mosher Lake, Goldfield Lake, A-321, A-322) and ponds, creeks (SW Arm Tributary, Goldfield Creek) and streams, and into Kenogamisis Lake (Barton Bay, Central Basin, Southwest Arm). Groundwater flow is interpreted to generally follow topography and surface water drainage paths. Discussion Deposit Geology Overburden materials are composed of organics (peat, muck), glaciolacustrine deposits (silt to clay, fine sand), glacial till, and glaciofluvial ice contact deposits (sand and gravel) including esker deposits. Bedrock geology within the proposed open pit is defined by metamorphosed and folded, interlayered sequences of clastic sedimentary rocks (sandstone-argillite, conglomerate, greywacke, arenite, argillite), chemical sedimentary rocks (magnetite-rich chert, banded iron formation) and intrusive igneous rocks (Hardrock Porphyry, diorite, gabbro, diabase dikes). Minor metamorphic mica schists and extrusive igneous rocks (ultramafic, basalt, tuff) are also present. Mineralisation occurs within a zone of deformation immediately north of the Bankfield- Tombill Fault. Ore bodies and zones of mineralisation generally include: quartz veins and mineralised zones: lenses of semi-massive sulphides (pyrite, arsenopyrite, sphalerite, chalcopyrite) along contacts of intrusions and sedimentary rocks, disseminated in porphyry, or quartz-carbonate veins and stringers cutting porphyry and sedimentary rocks; massive sulphide quartz lenses in folded sandstone and banded iron formation (replacement ore/rocks), and sulphide (pyrite, arsenopyrite) replacement along fractures; and quartz stringer zones in sandstone, banded iron formation and quartz diorite, with pyrite and sub-ordinate arsenopyrite. Page 3 of 8

4 Sampling A range of static and kinetic testing methods were completed by the consultant on four hundred eighty-four (484) samples of ore, waste rock, and overburden. Of these samples, twelve (12) overburden samples were collected from test pits in the vicinity of the proposed open pit. Rock samples were collected from 1.5 m drill core intervals. Ten (10) composite ore samples were used for metallurgical testing, which resulted in samples of tailings slurry. In addition, fourteen (14) samples were also collected from 3 m drill core intervals of historic tailings. Static and Kinetic Testing Static testing methods included: acid base accounting (paste ph, total sulphur, total carbon, sulphate-sulphur and acid generation potential, HNO 3 leaching, total inorganic carbon, neutralisation potential, and siderite-corrected neutralisation potential), and total metal analysis following aqua-regia digestion. Leachate extraction testing included shake flask extraction and net acid generation. Kinetic testing methods included humidity cells and field bins, using composite samples of ore, overburden, and major waste rock lithologies (clastic sediments, intrusive rock, chemical sediments, metamorphic rock, extrusive rock, sulphide replacement zones, and veins) including samples with elevated sulphide content (potentially acid generating PAG). Humidity cell testing was completed in nine (9) weeks, and most field bin tests ran for twenty-nine (29) weeks. Samples of solid future tailings (tailings slurry generated from metallurgical testing) underwent humidity cell testing for weeks. Field bin samples were tested for: acid base accounting, net acid generation, shake flask extraction, whole rock analysis, particle size distribution, and mineralogical studies. Ageing tests were also completed to account for degradation of cyanide and ammonia, and trace element attenuation in tailings water (i.e. supernatant of tailings slurry). Quality control included a field bin blank, trip blanks, and internal laboratory procedures. Testing Results Summary The results of the acid rock drainage/metal leaching (ARD/ML) testing program have outlined several environmental concerns related to short-term and long-term leaching potential and acid generation from overburden materials, waste rock, future tailings, ore, and the historic MacLeod and Hardrock tailings. Leaching potential was based on the following criteria from the shake flask extraction tests: 50% of samples are below the Provincial Water Quality Objectives 1 (PWQO) = low potential; 50-75% of samples are above PWQO = moderate potential; and 75% of samples are above PWQO = high potential. ARD potential was based on generic criteria for neutralisation potential ratios (NPR), and site specific criteria for NPR and ratios of neutralisation potential (NP) to acid generation potential (AP) consumption rates. I have provided a summary of the results, following: Overburden: High leaching potential for As, Co, Cu 1 Queen s Printer for Ontario (1994). Table 2 - Table of PWQOs and Interim PWQOs, Appendix A, Provincial Water Quality Objectives, February 1999, Water Management Policies and Guidelines, Provincial Water Quality Objectives of the Ministry of Environment and Energy, July Page 4 of 8

5 ± Al leaching Waste Rock: o Clastic Sediments (WR-S) 72% of logged core Uncertain ARD potential due to some NPR Sid ratios of 1.9 High leaching potential for As, Al ± Sb, Co, U, Cr, Fe leaching o Intrusive Rock (WR-I) 15.6% of logged core High leaching potential for As Moderate leaching potential for Sb, Al ± V leaching o Chemical Sediments (WR-C) 11% of logged core ARD predicted in 3% of samples Moderate leaching potential for As, Sb, Al ± Cd, Co, Cu, Fe, Zn leaching o Metamorphic Rock (WR-M) 0.9% of logged core ARD predicted in 9% of samples Moderate leaching potential for As, Sb, Al ± Cd, Fe, V o Extrusive Rock (WR-E) 0.4% of logged core High leaching potential for As, Al Moderate leaching potential for V ± Cr, Fe leaching o Sulphide Replacement Zones (WR-R) 0.06% of logged core ARD predicted in 100% of samples, potential acid generation after 15 years High leaching potential for As after 15 years Moderate leaching potential for As, Sb, Co, Cu, Fe, Pb, Zn ± Al leaching o Non-Ore Veins (WR-V) 0.04% of logged core ARD predicted in 17% of samples High leaching potential for As, Al ± Co Page 5 of 8

6 Future Tailings: ARD predicted in samples with > 3 wt.% sulphide concentration, potential acid generation after 13 years High leaching potential for As, Co, Cu, Sb, Ag, ammonia, cyanade ± Fe, Pb, Ni Ore (0.38 g/t Au cutoff): ARD predicted in 34% of samples High leaching potential for As, Sb, Al ± Co, Ni MacLeod Tailings: Low ARD potential predicted; however, historic characterisation predicted ARD in 23% of samples High leaching potential for As, Fe, Co, Ni in groundwater; As and Co in surface water ± Pb, Cr, total cyanide Hardrock Tailings: ARD present in portions of reactive tailings area; high ARD potential predicted in reactive tailings High leaching potential for As, Ni, Zn, total cyanide in groundwater; As in surface water ± Al, B, Cd, Cr, Co, Cu, Fe, Pb, Ag, Tl, U, free cyanide Comments and Recommendations Following review of the Stantec Consulting Ltd. May 8, 2015 report Environmental Baseline Data Report Hardrock Project: Geochemical Characterization, it is my opinion that the consultant has completed an extensive and conservative analysis of the acid rock drainage/metal leaching (ARD/ML) properties of the overburden materials, waste rock, future tailings, ore, and the historic MacLeod and Hardrock tailings within the Project Development Area. Considering the results of the static and kinetic testing, I have serious concerns related to the long-term metal leaching potential of arsenic (As) and other heavy metals from: 1) stockpiles (waste rock, overburden, ore), 2) the tailings management facility (TMF), and 3) historic tailings. Between 1.8% and 4% of the total waste rock mass is estimated to be potentially acid generating (PAG) after 15 years, and 9.7% of the processed tailings materials will be PAG after 13 years. This ARD potential would result in enhanced metal leaching and high sulphate concentrations. It is my opinion that long-term metal leaching associated with development of the Hardrock Project will result in continued and additional contamination of the groundwater and surface water environments within the Local Study Area. Page 6 of 8

7 Based on these considerations, I have the following recommendations with respect to the provincial Environmental Assessment (EA) and Closure Plan: 1. Due to the predicted long-term metal leaching from waste materials associated with development of the Hardrock Project, it is recommended that the location of the waste rock piles, TMF, overburden and ore stockpiles must be set back a sufficient distance from surface waters to: a. ensure adequate attenuation of metals in groundwater, b. prevent seepage into surface waters, c. establish an appropriate monitoring network, d. install seepage collection measures (e.g. ditches), and e. develop appropriate seepage contingency plans. The currently proposed 30 m setback from surface waters is not sufficient. Predictive geochemical modelling must also be used in the EA to demonstrate metal attenuation and loading rates for setback distances. It is recommended that seepage collection measures (e.g. ditches) are installed as a preventative measure around waste rock disposal areas, TMF, overburden and ore stockpile areas prior to production. 2. Based on the high concentrations of sulphide minerals within some of the waste rock units, future tailings and ore associated with the Hardrock Project, and the predicted ARD, it is anticipated that high concentrations of sulphate will be generated from these materials. It is recommended that the EA includes calculations of sulphate loading to surface waters by long-term seepage from waste rock piles, TMF, and ore stockpiles. 3. Considering the long-term metal leaching concerns at the Hardrock Project site, it is recommended that a waste rock segregation study based on arsenic leaching potential is completed during the EA. Recent research has demonstrated potential for waste rock segregation during production, based on arsenic concentrations measured from pre-blast drill hole cuttings using an on-site desktop XRF (X-ray fluorescence) unit. 4. On-going ARD/ML to groundwater and seepage to surface water bodies from historic tailings within the Hardrock Project Development Area is a concern with respect to the currently proposed placement of waste rock piles on historic tailings. It is recommended that either waste rock is not placed on the historic MacLeod and Hardrock tailings, or that the affected portions of the MacLeod and Hardrock tailings are remediated with adequate multi-layer cover materials prior to any waste rock placement. 5. Based on the long-term metal leaching concerns at the Hardrock Project site, it is recommended that site closure activities must include placement of adequate multi-layer cover materials on all waste rock piles, TMF, and historic tailings (MacLeod, Hardrock, and Little Longlac tailings) within the Local Study Area (e.g. unsaturated covers, saturated covers, store-and-release covers). The currently proposed seeded soil/overburden covers are not sufficient to prevent long-term metal leaching. If you have any questions regarding the above comments and recommendations, do not hesitate to contact me. The purpose of the preceding review is to provide advice to the Ministry of the Page 7 of 8

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