Geochemical Review of the Eagle Project Mine Permit Application

Geochemical Review of the Eagle Project Mine Permit Application Prepared for: F. Michelle Halley National Wildlife Federation PO Box 914 Marquette, MI 49855

Geochemical Review of the Eagle Project Mine Permit Application

Prepared for:

F. Michelle Halley National Wildlife Federation

PO Box 914 Marquette, MI 49855

Prepared by:

Stratus Consulting Inc. PO Box 4059

Boulder, CO 80306-4059 303-381-8000

1920 L St. NW, Ste. 420 Washington, DC 20036

Contacts:

Ann S. Maest Kaylene Ritter

October 16, 2007 SC11227

Executive Summary Stratus Consulting conducted a review of the existing geochemical information for the Eagle Project, a proposed nickel-copper mine in northern Michigan. The aim of this review was to evaluate the water quality predictions presented in the mine permit application for the underground mine and the development rock stockpile, and to evaluate the implications of these findings for water quality treatment and discharge. We also compared existing water quality predictions to predictions based on alternate modeling assumptions. The following points summarize our conclusions with respect to water quality:

The Eagle deposit (a massive sulfide ultramafic ore body) is similar to other ore bodies that have produced acidic waters with high concentrations of base metals such as nickel and copper.

The ore and its host rock, which comprise the vast majority of the managed material at the Eagle Project, clearly have a moderate to high ability to produce acid and contaminants and a low ability to neutralize the acid produced. The surrounding sedimentary rocks also have a high ability to produce acid and leach metals, with somewhat more ability to neutralize the acid produced.

Results from geochemical kinetic tests underestimate long-term leachate concentrations of copper, cobalt, nickel, and sulfate because concentrations of these contaminants were still increasing at the end of the test periods. Therefore, the concentrations presented in the mine permit application for the underground mine and development rock stockpile are likely lower than what may actually exist if these areas are mined.

The high percentages of sulfides in the ore and waste rock, including acid-producing pyrrhotite that weathers rapidly, will cause the production of acid and metals early in the mining process. The type of neutralizing material present in the rocks is unlikely to counteract the acid produced over long periods of time. Therefore, if high-sulfur rock remains in the underground workings or waste rock pile, poor water quality could be produced rapidly and last for long periods of time.

The quantity and distribution of rocks and geochemical test units selected for geochemical kinetic testing are not representative of the quantity and distribution of rocks in the underground mine and waste rock. Specifically, the rock category “peridotite” can contain up to 30% sulfide (~10% sulfur), and samples used for geochemical testing (kinetic testing) contained a high of only 2.4% sulfur. Because leachate quality is highly dependent on the amount and type of sulfide present, using results from kinetic samples

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Stratus Consulting Executive Summary (10/16/2007)

with low sulfide content could grossly underestimate acidity and sulfate and metal concentrations in leachate from mined materials.

No information exists on leaching rates of material in what would become the crown pillar. Because of the potential of this rock to impact mine water quality, more sampling of the crown pillar must be conducted and analyzed to be able to predict water quality accurately.

Water quality modeling that uses leachate and surface area values more representative of the likely long-term conditions in the underground mine predicts that concentrations of sulfate, nickel, total dissolved solids, aluminum, arsenic, beryllium, boron, cadmium, cobalt, copper, iron, lead, nitrate, and manganese will exceed one or more relevant water quality standards in the underground mine at the end of mining.

The mine walls and development rock in the underground mine present potentially problems for the integrity of the cemented backfill and the crown pillar. The use of cemented backfill in a mine with such high sulfide percentages is a poorly proven technique. Kennecott should demonstrate, using examples from other highly acid-generating mines with similar mining methods, that the use of cemented aggregate backfill will not threaten the integrity of the crown pillar.

All of these considerations should be taken into account before a mine permit is granted.

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1. Introduction The Eagle Project is a proposed nickel-copper mine development in northern Michigan. This report presents a review of the geochemistry of this deposit and associated water quality conditions. The report is organized as follows. Section 2 provides a comparison to other base-metal ultramafic deposits. Section 3 contains an overview of the acid generation and metal-leaching potential of rocks in the Eagle deposit. In Section 4, we describe issues that affect predicted Eagle Project water quality, including representation of rock types selected for geochemical testing, length of kinetic tests, and model assumptions. Section 5 outlines water quality predictions for the underground mine during and after operations using recommended leachate concentrations and alternate assumptions. Section 6 addresses the chemical stability of the cemented mine backfill and the crown pillar. A summary of conclusions is contained in Section 7, and an Executive Summary precedes the report. References are included at the end of this review.

1.1 Geologic and Project Setting The Eagle Project is located in the Upper Peninsula of Michigan in Marquette County, approximately 25 miles northwest of the City of Marquette and 10 miles from Big Bay on Lake Superior (Figure 1). The property is on the watershed divide of Yellow Dog River and Salmon Trout River, and the Salmon Trout River mainstem goes through the project site (Kennecott Exploration, 2005). The project is owned and operated by Kennecott Eagle Minerals Company.

The Eagle ore body is a high-grade nickel-copper sulfide deposit with minor cobalt, platinum, palladium, and gold. Average ore grades are 3.57% nickel, 2.91% copper, 0.10% cobalt, 0.28 grams per ton gold, 0.73 grams per ton platinum, and 0.47 grams per ton palladium that is hosted by an ultramafic igneous plutonic intrusion containing peridotite with minor pyroxenite. Economic minerals are pentlandite [a nickel sulfide mineral (Fe,Ni)9S8] and chalcopyrite (a copper-iron sulfide mineral, CuFeS2) in pyrrhotite (iron sulfide, Fe1-xS) dominated massive, semi-massive, and disseminated sulfides. The geologic resource comprises the massive and semi-massive sulfides only (Kennecott Exploration, 2005). The ore grades for the massive sulfide unit are 6.11% nickel and 4.15% copper, and grades for the semi-massive unit are 2.11% nickel and 2.19% copper. The deposit intrudes local “country rock” (CR) that consists of sediments (siltstones and sandstones) that have been metamorphosed by the intrusion to form greywackes, slates, and hornfels (Foth & Van Dyke and Associates, 2006a). The nickel-copper ore is contained in the peridotite, but also abuts the metasedimentary rocks in places, and consists of massive and semi-massive sulfide layers that are surrounded by disseminated sulfide. The disseminated sulfide peridotite, and to a lesser extent the CR, comprise the waste rock (also called development rock).

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Stratus Consulting (10/16/2007)

Figure 1. Map of the Eagle Project location and surrounding area. Source: Foth & Van Dyke and Associates, 2006a, Figure 2-1.

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2. Comparison to Other Base-Metal Ultramafic Deposits

The Eagle deposit is similar in terms of geologic setting and mineralogic composition to other magmatic ultramafic sulfide deposits in the United States and elsewhere, including the Duluth deposit in Minnesota, the Stillwater Mine in Montana, and the Noril’sk Mine in Russia (Foose et al., 1995). Foose et al. (1995) separate magmatic sulfide deposits into two groups: platinum-group-element-rich deposits with low sulfide and total metal content and a relatively low capacity to generate acid or metal-rich drainage; and most other economic magmatic sulfide deposits, with greater than 14 to over 40 weight percent (wt%) sulfide and high metal content with much greater potential for generating acid or metal-rich drainage. Even though the Stillwater deposit also contains nickel and copper mineralization, it has much lower sulfide mineral percentages [highest sulfide is ~1 to 5 wt%; maximum percent sulfur (%S) in the J-M Reef in the Stillwater complex is 1.64%S] and has not produced acid drainage and poor water quality to date. The Eagle deposit is more similar to the Duluth and the Noril’sk deposits, with 50 to 100% sulfide or 32 to 38%S. The Noril’sk deposit has a maximum of 34 to 37%S, and has the same mineral assemblage as the Eagle deposit: pyrrhotite, pentlandite, and chalcopyrite. Mining and processing of the Noril’sk deposit have created severe environmental degradation (Foose et al., 1995). Mining and weathering of high-sulfur magmatic ultramafic sulfide deposits can produce waters with elevated concentrations of nickel, copper, zinc, and other metals. Ultramafic sulfide deposits can produce mine drainage with pH values as low as 2 to 3, and there are examples around the world where this has occurred. However, other deposits with high sulfide content can produce more neutral drainage (pH ~4.5 to 8), because the ultramafic minerals do supply some buffering capacity (Plumlee et al., 1999). These deposits tend to produce high concentrations of metals (tens to hundreds of mg/L of nickel and copper) (Foose et al., 1995; Accornero et al., 2005). For example, the Duluth deposit has produced drainage with pH values as low as 4.5 to 6.4 with copper, nickel, cobalt, and zinc concentrations as high as 22, 38, 2.4, and 2.4 mg/L, respectively (Foose et al., 1995).

Additional information indicates that water discharged from some bulk-ore sample sites in the Duluth Complex contains nickel, copper, cobalt, and zinc at concentrations as high as 400 times baseline abundances (Eger and Lapakko, 1989; Siegel and Ericson, 1980). Best- and worst-case water quality estimates were made for releases from test pits and ore stockpiles as part of a regional environmental study. Estimates for the combined concentrations of copper, nickel, cobalt, and zinc were between 107 and 6,610 μg/L for discharges from tailings basins, 2,534 to 46,310 μg/L for emissions from ore stock piles, and 125 to 46,840 μg/L for mine water (Ritchie, 1988). “Mine water” used to simulate environmental effects related to the Duluth Complex in remediation studies had a pH of 4.5 and contained 2,000 mg/L sulfate and between 50 and 1,000 μg/L nickel (Hammack and Edenborn, 1992).

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A laboratory study of Duluth Complex ore (Lapakko and Antonson, 1994) demonstrated a direct correlation between ore sulfur content and pH of associated drainage water. Drainage water associated with ore that contained 0.18 to 0.4 wt% sulfur had a pH of 6.1, water associated with ore that contained 0.41 to 0.71 wt% sulfur had a pH between 4.8 and 5.3, and water associated with ore that contained 1.12 to 1.64 wt% sulfur generated pH values between 4.3 and 4.9. By comparison, Eagle Project leach tests reached lower pH values. Over the course of 50-week Phase I humidity cell tests for the Eagle Project, the lowest pH reached in the CR samples was 3.67 (1.39%S), and the pH in the massive sulfide unit (MSU) sample (36.1%S) at 70 weeks was 3.88.

Finally, a study of Sudbury ore from the Nickel Rim nickel-copper tailings impoundment demonstrated a well-developed vertical gradient within the tailings facility. Water draining the uppermost part of the tailings had low pH (2.1 to 3.5), whereas that draining the basal part of the tailings, where acid-consuming minerals are more abundant, had a pH of about 6.5. The nickel concentration of tailings water was sensitive to pH; nickel concentrations decreased from 250,000 μg/L to less than 10,000 μg/L as pH increased from 4.5 to greater than 5.8 (Blowes and Ptacek, 1994). By comparison, a nickel concentration of 120,000 μg/L was reached in the leachate from Eagle’s semi-massive sulfide unit (SMSU) Phase I kinetic test at week 70 (pH = 4.56), and the highest nickel concentration in the MSU kinetic test was 427,000 μg/L, reached at week 4 (pH = 3.62). Like other similar mined deposits around the world, water quality characteristics from leached Eagle ore, host, and country rock show that high metal concentrations and low pH values are likely to result from mining of the Eagle deposit.

3. Overview of the Potential of the Eagle Project to Generate Acid and Leach Contaminants

The nickel and copper minerals in the Eagle ore body are primarily pentlandite (iron nickel sulfide) and chalcopyrite (copper iron sulfide) in pyrrhotite (iron sulfide) (Kennecott Exploration, 2005, Appendix C-1, p. 1). Mineralogic evaluation showed that sulfides are pervasive in all rock types, and that the main neutralizing minerals are the iron-magnesium and magnesium silicates olivine and lizardite, and to a lesser extent, carbonates (Geochimica, 2004). Acid-base accounting (ABA), short-term leach testing, and kinetic testing were conducted on samples of Eagle Project rock. Whole rock chemistry, paste pH, and mineralogy were also examined as part of the geochemical testing program. A total of 108 samples were tested for whole rock and ABA analysis, 68 samples were subjected to net acid generating (NAG) testing, and 30 samples were subjected to detailed mineralogic analysis. Ten short-term leach test samples and 15 kinetic test samples were included in the geochemical analysis. The methodology and descriptions of test conditions are contained in Geochimica (2005a, Section 2). The results of

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static testing are summarized in this section, and the results of kinetic testing are presented in Section 4.

The static ABA tests included the Sobek method and the NAG test. Both tests operationally define the net acid-generation potential of samples but do not provide information on the source of the acid or neutralizing potential (NP). The NAG test is helpful for screening and management purposes, but it does not distinguish between acid and NP and may overestimate the long-term neutralizing ability of a sample because the titration endpoint is low (White et al., 1999; Tremblay and Hogen, 2000; Stewart et al., 2003; Maest et al., 2005). Therefore, the ABA results from the Sobek method are more reliable than the NAG test results, and these results will be used to discuss the acid generation potential of rocks in the Eagle deposit.

Table 1 presents a comparison of %S, acid generation potential (using only the Sobek method results), and extent of geochemical units in Eagle deposit vs. samples used for geochemical testing. ABA results for Eagle Project samples showed that the acid generation potential exceeded the neutralization potential in nearly all samples of all rock types, and that all rock types need “active management” to control acid generation (Geochimica, 2004, p. 23). The ABA results are presented in Geochimica (2005a) and Appendix A for “country rock” and “intrusives.” However, it is impossible to discern the sample breakdown for different rock types in the “intrusive” category – for example, which are massive sulfide, semi-massive sulfide, or non-ore peridotite. The one exception to this is the results from Phase I ABA testing, which are shown in Table A-2 of Appendix A and summarized in Table 1 of this report. There were three massive sulfide samples, all with acid-generating potential (maximum potential acidity) far exceeding neutralizing potential (NP) (e.g., acid production potential, AP = 1,130 to 1,170 tonnes calcium carbonate per 1,000 tonnes of material vs. NP = -2 to 3 tonnes calcium carbonate per 1,000 tonnes of material). Results were similar for the SMSU, but maximum potential acidity ranged from 402 to 478 and NP from 33 to 41 tonnes calcium carbonate per 1,000 tonnes of material. Clearly, the massive sulfide and semi-massive sulfide ore are considered highly acid-generating.

The waste rock (CR and intrusive rock, which is peridotite that is not massive or semi-massive sulfide) also has a moderate to high ability to generate acid. For the CRs, results from the Sobek method predicted that 69% will be acid generating, 11% uncertain, and 20% non-acid generating (using an NP:AP ratio of 3:1 or more). Results for NAG testing of the CRs predicted a lower percentage will be acid generating (45%), with 43% of uncertain acid-generating ability, and 13% non-acid generating (Geochimica, 2005a, pp. 33, 35). Results from the Sobek method for intrusive rocks indicate that 61% will be acid generating, 16% uncertain, and 23% non-acid-generating. NAG test results again predicted a lower percentage would be acid generating (50%),

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Table 1. Percent sulfur (%S) or sulfide, acid generation potential, number of kinetic tests run per rock type, and % S of samples used for kinetic testing of the Eagle deposit

Rock type/geochemical unit %S or sulfide in unit

Acid generation potential

summarya

Number of kinetic tests

run %S of samples for kinetic tests Sedimentary units (sandstone/siltstone/ hornfels)

0.2-1.4%S 69% AG; 11% uncertain; 20% non-AG

Siltstone: 5 Sandstone: 1 Hornfels: 1

0.31 to 2.1%S

Peridotite/disseminated sulfide unit/ pyroxenite (along margins of the intrusions, above and below the upper sulfide zone and above the lower sulfide zone)

3-15% sulfide (disseminated sulfide) Disseminated sulfide =

< 30% sulfide

61% AG; 16% uncertain; 23% non-AG

Peridotite: 4 Pyroxenite: 1

Peridotite: 0.2 and 2.44%S Pyroxenite: 0.99%S

Massive sulfide unit > 80% sulfide 50-100% sulfide

32-38%S

3/3 Phase I samples AG 1 36.1%S

Semi-massive sulfide unit 30-50% sulfide 12-15%S

3/3 Phase I samples AG 2 12.9 and 8.13%S

a. Using 3:1 NP:AP and Sobek method. AG = acid-generating; S = sulfur. %S in most common sulfides (pyrrhotite, pentlandite, chalcopyrite) ranges from 33 to 42%. Sources: Geochimica, 2004 (for sulfur percentages); Kennecott Exploration, 2005 (for sulfide percentages).


with 41% in the uncertain category, and 9% non-acid-generating (Geochimica, 2005a, pp. 34, 36). Geochimica concluded that over three-quarters of the waste rock must be managed as special-handling material in order to manage risks of acid drainage and metal leaching (Geochimica, 2005a, p. 37).

The detailed mineralogic review found that neutralizing minerals are present in all rock types, but most neutralizing ability for the MSU, SMSU, peridotite, and pyroxenite was attributed to olivine and lizardite (or olivine and serpentine for pyroxenite). These minerals generally react at slower rates and lower pH values than carbonates and therefore do not contribute substantial amount of neutralizing ability, especially where sulfide percentages are high (such as in the massive and semi-massive units). The siltstone and hornfels CR samples had higher amounts of calcite and dolomite (low iron), and chlorite. Therefore, the acid neutralizing ability of the CR is higher than that of the intrusives.

The ability to leach metals, sulfate, and other constituents was tested by short-term leach tests (synthetic precipitation leaching procedure, or SPLP) and longer-term kinetic tests. The SPLP tests were conducted for 22 hours at a pH of 4.2, which is considered representative of acid rain (Geochimica, 2005a, p. 8). Geochimica (2005a, p. 8) states that the SPLP test results are of limited utility because unoxidized samples were used (unoxidized samples will generally not form soluble sulfates, which are the minerals that will react quickly under short-term leach testing conditions). Geochimica instead recommends the use of Week 0 kinetic test results from Phase II geochemical testing to estimate short-term leach concentrations. The massive sulfide samples leached the highest concentrations of metals in early kinetic testing results (e.g., 427 mg/L in week 4), and the semi-massive test samples took longer to develop high concentrations of contaminants. Some of the CR samples in Phase II had elevated concentrations of sulfate in early kinetic testing, indicating that weathering produces sulfate salts that dissolved readily when flushed with water. This suggests that salts that build up in the waste rock pile or the underground mine during winter months may result in very high concentrations of metals during the Upper Peninsula’s spring thaw.

In summary, the ore and the peridotite, which comprise the vast majority of the managed material at the Project, clearly have a moderate (peridotite) to high (ore) ability to produce acid and contaminants and a low ability to neutralize the acid produced. The sedimentary rocks also have a high ability to produce acid and leach metals, with somewhat more ability to neutralize the acid produced. However, low pH values were reached in CR kinetic tests with higher sulfide percentages, most likely because of the presence of pyrite. The high percentages of sulfides, including acid-producing pyrrhotite that weathers rapidly, will cause the production of acid and metals early, especially in the MSU. The type of neutralizing material present in the rocks is unlikely to counteract the acid produced over long periods of time. Therefore, if MSU or other high-sulfur rock remains in the underground workings or waste rock, poor water quality could be produced rapidly and last for long periods of time.

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4. Issues Affecting Predicted Mine Water Quality 4.1 Comparison of Rock Types Selected for Geochemical Testing

with Characteristics of the Eagle Deposit

4.1.1 Representativeness of rock types used in kinetic tests

The quantity and distribution of rocks and geochemical test units selected for kinetic testing are not representative of the quantity and distribution of rocks and mineralization in the underground mine and waste rock. This issue is one of the main reasons Geochimica’s predictions of water quality likely underestimate leachate concentrations in the waste rock and post-mining water quality. The only testing conducted for the Eagle Project that simulates the production of metals and other contaminants over time is the kinetic testing, and results from the kinetic testing are the only ones used in the water quality predictions. Therefore, it is imperative that the kinetic test samples are representative of the rocks in the mine during and after mining (including backfilled development rock), and that this representation is accounted for in the model for predicting mine water quality.

A generalized stratigraphic column for the Eagle Project is presented in the Mine Permit Application (MPA) (Foth & Van Dyke and Associates, 2006a). The area is overlain by 0 to more than 60 meters of glacial till, followed by siltstone with minor fine-grained greywacke sandstone beds and hornfels-altered siltstone at the intrusive contact. The underlying intrusion consists predominantly of peridotite with pyroxenite at the mineralized contacts and layers of sulfide zones. Disseminated sulfide is located above and below the sulfide zones, and all three contain pyrrhotite and lesser chalcopyrite and pentlandite as the major sulfide minerals. There is an upper and lower sulfide zone sandwiched between layers of peridotite, with relatively sharp contacts between the semi-massive sulfide and the surrounding disseminated sulfide. The massive sulfide ore is more common in the lower zone, and the semi-massive sulfide ore occurs in both the upper and lower zones. The deposit is underlain by more sedimentary and metasedimentary rocks, including slate, shale, siltstone, and sandstone. Olivine alteration to lizardite occurs locally in the peridotites.

Cross sections through the ore body and the surrounding peridotite and sediments are shown in Kennecott Exploration (2005). The peridotite-glacial till contact is located at the 415 m elevation level, and Sainsbury (2007) recommends that mining be limited to below the 327.5 m level, resulting in a crown pillar thickness of 87.5 m, or 287 ft. In the Mine Permit Application, mining was proposed to progress to the 353-m level (~85 m below ground surface), with selective mining at the 383-m level (~55 m below ground surface). In some locations, massive and semi-massive sulfide ore would remain in the underground mine after mining as part of the crown pillar. Cross sections from Kennecott Exploration (2005) with ore above the 327.5-m level are

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shown in Figure 2. Plan views for the 300-m, 350-m, and 400-m levels are shown in Figure 3. The dashed and solid black lines in Figure 2 show the elevation of mining proposed in the Mine Permit Application and Sainsbury, respectively. If Sainsbury’s recommendation is followed, substantially more acid-generating ore will be left in the underground mine after mining, and the ceiling of the mine will be more mineralized than the permit application evaluates. The implications of the increase in crown pillar thickness for post-mining water quality are discussed in Section 4.4, but include that post-mining water quality will likely be worse than predicted in the Mine Permit Application.

No information is presented on the percentages of different rock types in the underground mine. The amount of development rock for each year of mining is contained in Table 4-4 of the Mine Permit application, but the breakdown according to rock type is also not presented. Geochimica (2005b) assumes that half of the development rock is CR and half is intrusives, and that half of the intrusives are mineralized. No basis is presented for this assumption. Geochimica also assumes that no ore will be present in the development rock stockpile, and this assumption causes an underestimation of contaminant concentrations in stockpile leachate and post-mining concentrations in the backfilled underground mine.

Table 1 presents a comparison of percent sulfur or sulfide, acid generation potential, and percent sulfur in the samples used for kinetic testing of the Eagle deposit. Seven kinetic tests were conducted on the sedimentary units, and five on peridotite samples. Only two samples of semi-massive sulfide ore and a single sample of massive sulfide ore were subjected to kinetic testing. In the kinetic testing, a greater emphasis was placed on testing of sediments (sandstone, siltstones, and hornfels) because it is the most likely to be stored temporarily as waste on the surface (Geochimica, 2004, p. 3). However, it is likely that some ore will also remain in the underground mine and in the development rock. More samples of MSU and SMSU were used for ABA, whole rock/trace metals, and one short-term leach test each, but only three samples total were used for kinetic testing, which are the only results used in predicting water quality. The practical effect of this is that water quality predicted for the waste rock leachate and the mine are less acidic and lower in metals than the most likely scenario.

4.1.2 Representativeness of geochemical test samples to the crown pillar

Notwithstanding uncertainties in the representativeness of the characterization of the leaching characteristics of the ore body, there is insufficient characterization of the rock that will make up the crown pillar. The samples for Phase I of the kinetic testing were collected from locations shown in Figure 2-2 of Geochimica (2004). Phase I kinetic samples were collected in the Lower sulfide zone (three samples), above the eastern side of the Lower sulfide zone, and farther above and to the east of the upper sulfide zone. It is nearly impossible to tell the difference between the

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Stratus Consulting (10/16/2007) Stratus Consulting (10/16/2007)

Figure 2. Composition of the crown pillar for four cross sections (shown on two pages: 431500E, 431470E, 431440E, and 431410E) in the proposed underground mine, Eagle Project, for approximate previous (Mine Permit Application, dashed black line, 383 m) and recommended (Sainsbury, 2007, solid black line, 327.5 m) elevations of top of mining.Rock types are peridotite (magenta), semi-massive sulfide (tan), and massive sulfide (red).

Figure 2. Composition of the crown pillar for four cross sections (shown on two pages: 431500E, 431470E, 431440E, and 431410E) in the proposed underground mine, Eagle Project, for approximate previous (Mine Permit Application, dashed black line, 383 m) and recommended (Sainsbury, 2007, solid black line, 327.5 m) elevations of top of mining.Rock types are peridotite (magenta), semi-massive sulfide (tan), and massive sulfide (red). Source: Enlarged from Kennecott Exploration, 2005. Source: Enlarged from Kennecott Exploration, 2005.

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Figure 2. Composition of the crown pillar for four cross sections (shown on two pages: 431500E, 431470E, 431440E, and 431410E) in the proposed underground mine, Eagle Project, for approximate previous (Mine Permit Application, dashed black line, 383 m) and recommended (Sainsbury, 2007, solid black line, 327.5 m) elevations of top of mining (cont.). Rock types are peridotite (magenta), semi-massive sulfide (tan), and massive sulfide (red). Source: Enlarged from Kennecott Exploration, 2005.

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Figure 3. Exposure of peridotite (magenta), semi-massive sulfide (tan), and massive sulfide (red) at the 400-, 350-, and 300-m levels in the proposed underground mine, Eagle Project, shown in plan view through the ore body. Source: Enlarged from Kennecott Exploration, 2005.

peridotite and siltstone symbols, but the three samples in the lower sulfide zone appear to be massive sulfide and two siltstones; the sample above the lower sulfide zone is keyed as a semi-massive sulfide, and the one farthest away from the sulfide zone as peridotite. Therefore, at least in the Phase I geochemical testing, there were no kinetic samples from the upper sulfide zone or from peridotite between the upper and lower sulfide zone, and no samples of peridotite or siltstone above the upper sulfide zone in what would become the crown pillar.

The locations for geochemical testing for Phase II are shown in Figures 2-2 to 2-9 in Geochimica (2005a). However, it is impossible to tell where the kinetic samples for Phase II were collected from these figures or anywhere else in the text. In the Response to Comment No. 5 in Foth & Van Dyke and Associates (2006b), another attempt is made to show the location of the kinetic

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test samples. However, the maps show only 14 kinetic test sample locations (as best as we can tell, so one is missing): 5 green with a red box for Phase 0, and 9 blue with a red box for Phase I. In fact, there were no kinetic test samples in Phase 0, as far as we can discern, five in Phase I, and 10 in Phase II, so clearly the representation on the map is not correct. Subtle shades of purple, gray, pink and pink-brown on the same map show where the samples were collected: 8 are in purple designating peridotite, and 6 are in pink or pinky-brown for ore body. However, in total there were 5 kinetic tests for peridotite, 3 massive sulfide unit and semi-massive sulfide unit, and 7 sedimentary country rock samples, so the representation on the map is also not correct for rock type of the kinetic samples.

Regardless of the poor map, it appears that no kinetic test samples were collected from the upper portions of the ore body and overlying peridotite that would become the crown pillar. This is important because the crown pillar is a source of acidity and metals to mine water once it has been exposed to air and water. With the changes to the mine plan to thicken the crown pillar, more acid-generating ore will remain in the mine; the effects of this change need to be assessed by Kennecott before mining is given final approval.

4.1.3 Representativeness of sulfide content of test rock

Because sulfides are the source material for acid and metals in mined-material leachate, it is important to have a similar range of sulfide values in the kinetic test samples as in ore and host rock. The percent sulfide and sulfur in mine project rock types is presented in Table 1. Kennecott Exploration reports percent sulfide values, while Geochimica reports %S values. The main sulfide minerals present are pyrrhotite, pentlandite, and chalcopyrite, and the wt% sulfur values for these minerals (if pure) are 36 to 42%S for pyrrhotite [depending on the value of x in Fe(1-x)S], 33% for pentlandite, and 35% for chalcopyrite. Therefore, a sample that was 100% sulfide could have a %S from 33 to 42%. The percent sulfide for the semi-massive sulfide ore ranges from 30 to 50%, while values for the massive sulfide ore range from 50 to 100% (Kennecott Exploration, 2005 and Table 1). Kinetic test samples for semi-massive ore ranged from 8.13 to 12.9%S, and for massive ore were 32.4 to 36.1%S. These values fall within likely %S values of the ore and values reported by Geochimica in Table 1 for the massive sulfide ore, but are on the low end for the semi-massive sulfide ore. For the peridotite kinetic test samples, %S values ranged from 0.2 to 2.44%S, but % sulfide ranges from 3 to 30% (for disseminated sulfide material), according to Kennecott Exploration. Geochimica (2004, p. 14) states that the cutoff for mineralized peridotite is 1%S. Regardless of the cut-off, the higher percent sulfide or S values for the peridotite are not represented in the kinetic test samples. If mineralized peridotite varies from 3 to 30% sulfide, the likely range of %S is ~1 to 10%S, while the range of %S in samples used for kinetic testing varied from 0.2 to 2.4%. Therefore, a more reasonable approach for mineralized peridotite leachate concentrations should have been to use the high end of sulfate and metal concentrations from kinetic tests in any water quality model.

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In conclusion, presentation of the results and sampling locations make it impossible to evaluate whether the kinetic test locations are representative of the range of lithologies and mineralization in the ore body and the surrounding rocks, and therefore calls into serious question the water quality predictions that are based on the kinetic tests results. The low number of samples from the sulfide ore body (only one massive sulfide and only two semi-massive sulfide samples) makes it very unlikely that the upper range of contaminant leachate concentrations is known. The low %S values for the peridotite rock kinetic samples also makes it very unlikely that the upper ranges of contaminant concentrations are known. Finally, there is no information on leaching rates of material in what would become the crown pillar. If better information cannot be supplied on the locations of the kinetic samples and the true range of %S values for the peridotite, more sampling of the crown pillar and more highly mineralized peridotite must be conducted and analyzed before a permit is granted.

4.2 Issues with Kinetic Tests and Recommended Leachate Concentrations for Water Quality Predictions

Although the kinetic tests were conducted for 50 to 75 weeks, which is much longer than most in the industry, concentrations from a number of the humidity cell tests (HCTs, the kinetic testing method used for the Eagle samples) did not reach steady-state values. For samples with lower sulfide content and low neutralizing ability (which could include the sedimentary rocks and the peridotite), and for samples with higher NP and higher NP to acid production (AP) ratios, much longer test times are necessary to determine if the samples will produce acid.

For example, the Duluth Complex in Minnesota (mentioned in Section 2) is a large copper-nickel resource with elevated levels of platinum group metals. Duluth complex rocks become acidic after 155 weeks of kinetic testing (not before) and produced leachate in the 4-5 pH range for rocks with low %S (relevant for peridotite). Lapakko and Antonson (1994) observed that samples with %S values from 0.41 to 0.71% produced pH values from 4.8 to 5.3, and samples with %S values from 1.12 to 1.64% produced pH values of 4.3 to 4.9 after 150 weeks. Lapakko noted that a tailings sample with 1.3 wt% calcite and 6.6 wt% pyrite generated circumneutral drainage for 112 weeks before generating acidic drainage, and that a mixture of rotary kiln fines and rock with 2.1 wt% sulfur from the Duluth complex had a lag time of 581 weeks before it started producing acid (Lapakko, 2003). In another example, Nicholson and Rinker (2000) showed that sulfate and nickel concentrations in leachate from both humidity cell and column leach tests did not start to increase until after 20 weeks, and that peak concentrations of nickel in HCTs were not reached until over 60 weeks had passed. These results are similar to those found for the Eagle deposit, although Eagle’s test duration was in key instances for shorter periods of time. Nicholson and Rinker (2000) also showed that a substantial amount of nickel was leached

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from the wastes under neutral pH conditions. In the Phase I Eagle kinetic test for SMSU, 4.16 mg/L of nickel was leached in week 25 at a near-neutral pH of 6.8.

Rocks with low S and low neutralizing ability, such as some of the low-sulfur peridotite, which would be abundant in both waste rock and the underground mine workings, require special attention in geochemical testing. Li (2000) presents a method for predicting the acid drainage potential for wastes in this category. He defines low-sulfide, low-neutralization potential waste as those with sulfur contents < 1% and NP < 20 kg CaCO3 equivalents per ton (eq/t). These ranges are applicable to some of the CR and the unmineralized peridotite samples at Eagle (see Table 1). Li notes that there are many documented cases of acid generation by mine waste with a sulfide-sulfur content of 0.1 to 1.0%S. At these low S contents, the addition of NP by silicates (such as lizardite and certain feldspars) becomes more important. However, the common silicates do not yield alkalinity at appreciable rates until the pH falls to < 3 (Stumm, 1997). Scharer et al. (2000) note that wastes with neutral drainage (such as some in the low-S, low-NP category) will have slower sulfide oxidation rates (because sulfides oxidize more slowly at neutral pH values) but can produce elevated concentrations of sulfate, base cations, and metals. The implications of these finding for the Eagle project are that lower sulfur intrusive and country rocks may produce more acid than currently known because of the relatively short test durations.

4.2.1 Summary of kinetic results and selected leachate concentrations by rock type

The main sulfide mineral in the Eagle deposit, pyrrhotite, does produce less acid than pyrite on a mole-for-mole basis, but pyrrhotite weathers more rapidly than pyrite (Schwartz et al., 2006). The environmental implications of this are seen in the results of the kinetic tests for the MSU sample, where acid conditions and high metal concentrations are produced immediately, even in previously unoxidized samples. Some of the samples in Phase II testing also produced relatively high concentrations of sulfate and metals early in kinetic testing. Therefore, lag times for the production of acidic and metal-rich leachate, especially from the massive sulfide unit are expected to be low, and waste stored at the surface and mineralization remaining on the walls and pillars of the underground mine can be expected to be environmentally problematic early in the mining history of the deposit. This conclusion is in direct contradiction to one presented in the summary of the Phase II geochemistry report (Geochimica, 2005a, pp. ii-iii), that states, with the exception of the massive and SMSUs, kinetic tests have not generated acidic effluent or high concentrations of dissolved metals, and that development rock could be stored at the surface for extended periods of time without becoming acid-generating. Later, in the conclusions of the same report, Geochimica concludes that up to 80% of the development rock (including high-sulfur intrusive and CRs) could be acid generating with variable lag periods to the onset of acidification, but that sulfate and nickel leaching can begin quite early in the leaching process. Geochimica (2005a) expects leaching from the wall rocks in the mine to be limited because much of the intrusive rock has a substantial lag time before significant leaching occurs, but

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Geochimica also expects that nickel could be present at the part-per-million level (Geochimica, 2005a, p. 44).

Recommended HCT leachate input values for all major rock types [CR (representing siltstone, sandstone, and hornfels), intrusives (representing peridotite and pyroxenite), MSU, and SMSU] are presented in Table 2 and compared to values used by Geochimica (2006) for mine water quality at the end of mining with all development rock backfilled. Leachate concentrations and pH values for this evaluation were selected based on the longest test times (50 weeks for CR and intrusives, 70 weeks for SMSU, and 70 weeks for MSU for sulfate and pH and 40 weeks for metals. Values below detection were entered as one-half the detection limit. Using the values from earlier weeks underestimates that concentrations of metals and sulfate at the end of mining and is one of the key factors in Geochimica’s finding that post-mining water quality meets all water quality standards except for nickel. Using updated values, many more constituents are predicted to exceed relevant standards.

4.2.2 Massive sulfide unit

Only one sample of the massive sulfide unit was subjected to kinetic testing. Figure 4 shows sulfate, specific conductance (SC), pH, and nickel values over time in the HCT leachate from this single sample. Sulfate concentrations were not reported after 20 weeks, and total dissolved solids (TDS) and metals concentrations not reported after 40 weeks. However, SC values extended to 70 weeks, and SC, sulfate, and TDS values track each other. Longer-term results for SC show that sulfate concentrations did not continually decrease but instead most likely remained at ~350-500 mg/L. Sulfate and SC values from the same weeks (0 through 20) were plotted and fit using a linear regression (Figure 5). The R2 value of the fit was 0.95, indicating that the points fit the line well. The equation for the line was used to estimate the sulfate concentration at week 70 (474 mg/L). The highest measured sulfate value was 1,220 mg/L at week 3. The pH of the leachate dropped to about 4 after the first week and remained below 4 (3.88) at week 70. Metal concentrations in HCT leachate were measured weekly through week 20 and then at week 40. Nickel concentrations peaked at week 4 at 427 mg/L, but were still 39 mg/L at week 40. It is clear from the ABA and the kinetic test results that the MSU will produce unneutralized acid and high metal concentrations for long periods of time. What is less known is how high metal concentrations would be in the leachate; more than one sample must be tested to gain a more realistic understanding of acid generation and metal leaching potential in the MSU. A more reasonable approach, using the available data, would be to use the upper end of the metal and sulfate leachate concentrations for water quality predictions for predicting water quality during mining, and the concentrations at the end of kinetic testing [week 70 for sulfate (estimated using SC values) and pH, and week 40 for metals] for predicting post-mining water quality.

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Page 17 SC11227

Table 2. Recommended input leachate values for water quality prediction after mining compared to values used in Geochimica (2006) [all units are in mg/L except pH (SU) and alkalinity (mg/L as CaCO3)] Source Stratus Consulting, this study Geochimica, 2006 Rock/mineralization type CR Intrusives SMSU MSU Low-S peridotite

High-S peridotite SMSU MSU

HCT used Phase II column 4

Phase II column 5

Phase I column 4

Phase I column 2

Phase I column 3

Phase II column 5

Phase I column 4

Phase I column 2

Week(s) used 50 50 70

SO4 (estimated from SC) and pH: wk 70;

others: wk 40 40-50 20-25 40-50 SO4: wk 15-20; others: wk 40

SO4 161 135 585 474 3.09 57 426 368 pH 3.82 7.14 4.56 3.88 7.83 7.5 4.76 4.15 TDS 248 203 1560 391 55 78 772 391 Alk 0 7.5 0.5 -419 38.32 14.8 1 -419 Al 5.51 0.0069 0.01 0.005 0.005 0.0078 0.019 0.005 Sb 0.0001 0.00026 0.001 0.00005 0.00005 0.00005 0.00005 0.0003 As 0.001 0.00014 0.001 0.00013 0.00005 0.00018 0.00005 0.00013 Ba 0.0412 0.0135 0.023 0.002 0.03 0.0037 0.03 0.002 Be 0.0031 0.00025 0.001 0.00025 0.00025 0.00025 0.00025 0.00025 Bi 0.0005 0.00025 0.001 0.00025 0.00025 0.00025 0.00025 0.00025 B 0.058 0.1 0.725 0.012 0.12 0.119 0.66 0.012 Cd 0.0126 0.000025 0.006 0.00085 0.000025 0.000025 0.003 0.00085 Ca 4.39 29.4 6.68 0.43 7.35 10.9 8.93 0.43 Cr 0.0005 0.00025 0.001 0.00025 0.00025 0.00025 0.00025 0.00025 Co 0.245 0.0029 1.4 0.363 0.00005 0.00016 0.721 0.363 Cu 12.7 0.0112 0.0208 0.0048 0.0016 0.005 0.017 0.0048 Fe 26.4 0.015 2.16 89.3 0.015 0.015 0.36 89.3 Pb 0.15 0.00012 0.0005 0.002 0.00005 0.00005 0.00005 0.00005 Li 0.021 0.0057 0.05 0.0025 0.0025 0.0025 0.0025 0.0025


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Table 2. Recommended input leachate values for water quality prediction after mining compared to values used in Geochimica (2006) (cont.) Source Stratus Consulting, this study Geochimica, 2006 Rock/mineralization type CR Intrusives SMSU MSU Low-S peridotite

High-S peridotite SMSU MSU

HCT used Phase II column 4

Phase II column 5

Phase I column 4

Phase I column 2

Phase I column 3

Phase II column 5

Phase I column 4

Phase I column 2

Week(s) used 50 50 70

SO4 (estimated from SC) and pH: wk 70;

others: wk 40 40-50 20-25 40-50 SO4: wk 15-20; others: wk 40

Mg 8.08 13.8 86.8 1.56 5.24 7.8 1.2 1.59 Mn 0.336 0.0555 1.875 1.59 0.003 0.0035 0.0006 0.000055 Hg 0.000025 0.000064 0.0004 0.000055 0.000025 0.0011 0.006 0.000055 Mo 0.00005 0.000025 0.0005 0.000025 0.0002 0.0002 0.0002 0.000025 Ni 2.66 0.754 120 39.9 0.0023 0.0066 68.2 39.9 P 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 K 3.6 5.4 8.9 1.0 3.8 4.3 1.0 1.0 Se 0.0163 0.0024 0.01 0.0045 0.0005 0.0005 0.016 0.0045 Si 5.19 2.09 5.815 0.667 2.5 1.9 3.75 0.667 Ag 0.00001 0.000026 0.0001 0.000019 0.000005 0.000005 0.0002 0.000019 Na 1 1 2.3 1 2 3.4 3.3 1 Sr 0.0885 0.17 0.059 0.005 0.022 0.116 0.06 0.005 Tl 0.00027 0.00005 0.001 0.00005 0.00005 0.00005 0.00005 0.00005 Sn 0.001 0.00005 0.001 0.00005 0.00005 0.00005 0.00005 0.00005 Ti 0.005 0.005 0.005 0.005 0.01 0.005 0.005 0.005 U 0.011 0.000005 0.0001 0.000013 0.000005 0.000005 0.0002 0.000013 V 0.001 0.005 0.01 0.0005 0.0005 0.0005 0.0005 0.0005 Zn 1.22 0.0029 0.074 0.0127 0.0014 0.001 0.06 0.0127 CR = country rock; SMSU = semi-massive sulfide unit; MSU = massive sulfide unit; S = sulfur; SC = specific conductance; wk = week.


0200400600800

1,0001,2001,400

0 10 20 30 40 50 60 70

SO4 (

mg/

l)

02004006008001,0001,2001,4001,600

SC ( μ

S/cm

)

SO4/SC

0.00

2.00

4.00

6.00

8.00

10.00

0 10 20 30 40 50 60 70

pH

pH

0

100

200

300

400

500

0 10 20 30 4

Ni (

mg/

l)

0

Ni

Figure 4. Sulfate, SC, pH, and nickel values in HCT leachate over 70 or 40 weeks (x axes) from MSU sample (Phase I column 2, 36.1%S).

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y = 1.0796x - 399.37R2 = 0.9484

0200400600800

100012001400

0 500 1000 1500 2000

Specific Conductance (μS/cm)

Sulfa

te (m

g/L)

Figure 5. Relationship between sulfate and specific conductance in leachate from the massive sulfide unit kinetic sample, weeks 1 to 20. Data source: Geochimica, 2004.

Geochimica (2006) used earlier values for sulfate and pH (average of weeks 40 and 50) and week 40 values for metals (no later samples were analyzed for metals) (see Table 2). This approach underestimates the higher sulfate concentrations that continue to exist between weeks 40 and 70 and will underestimate concentrations of sulfate in the underground mine, where some MSU will remain.

4.2.3 Semi-massive sulfide unit

There were two samples of SMSU subjected to kinetic testing, one in Phase I and one in Phase II. The %S value for the Phase I sample (12.9%) is more representative of the SMSU than the Phase II sample (at 8.13%S). Geochimica reported the %S range for the SMSU was 12 to 15%S. Therefore, only leachate values from the Phase I sample should be used for water quality predictions. In addition, testing was continued for longer (70 weeks vs. 50 weeks) in Phase I. Sulfate, pH, and nickel values over time for the Phase I sample are shown in Figure 6. Sulfate concentrations in Phase I samples were still increasing at week 70 (585 mg/L). The pH for the Phase I sample started at 9.05 and continually decreased to ~4.5 by week 60 and remained at that low value through week 70. Calcium concentrations decreased with time, and magnesium concentrations leveled off after about week 30, indicating that even though some neutralizing ability exists (assuming that the only neutralizing mineral is lizardite or olivine and possibly a small amount of calcite), it isn’t keeping pace with acid production. This will eventually result in exhaustion of the neutralizing capacity, while acid generation and metal leaching will continue unabated.

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0

100

200

300

400

500

600

0 10 20 30 40 50 60 70

SO4 (

mg/

l)

SO4

0.00

2.00

4.00

6.00

8.00

10.00

0 10 20 30 40 50 60 70

pH

pH

0

20

40

60

80

100

120

0 10 20 30 40 50 60 70

Ni (

mg/

l)

Ni

Figure 6. Sulfate, pH, and nickel values over 70 weeks (x axes) in HCT leachate from SMSU sample (Phase I column 4, 12.85%S).

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Metals concentrations for the SMSU tests were reported to 70 weeks in Phase I and 50 weeks in Phase II. Nickel concentrations in the Phase I leachate began to increase dramatically after week 20 and reached 120 mg/L at week 70 with no sign of leveling off; the maximum levels are unknown with the currently available data and testing length. It is also clear from the ABA and kinetic test results that the SMSU will produce acid and metals for long periods of time, and produce only a small amount of neutralizing ability initially. Again, because only two samples were tested and the one with the higher sulfur value is still at the low end of the range for the SMSU, and because steady state concentrations were not reached for most constituents and concentrations were still increasing, a it is more supportable to use the upper end of the available metal and sulfate concentrations for the SMSU at the end of kinetic testing (week 70) from the Phase I column 4 sample for water quality predictions. Geochimica (2006) used earlier results (average of weeks 40 and 50) for all analytes, which had substantially lower concentrations (see Table 2). Again, the implication of this choice of input values is that the modeling results from Geochimica (2006) will underestimate concentrations in the underground mine, where some SMSU will remain after closure.

4.2.4 Intrusives

Five samples of peridotite were used for kinetic testing, one in Phase I and four in Phase II (including the pyroxenite sample). Phase I leachate samples were analyzed for 70 weeks for both major elements and metals, and Phase II for 50 weeks. The range in %S is shown in Table 1 as 0.2 to 2.4%S. Contaminant leachate concentrations varied from sample to sample, but the sample with the highest sulfur content (Phase II column 5) produced the highest sulfate concentrations (135 mg/L) and the lowest pH values (6.60), at least through week 50. Sulfate, pH, and nickel values for this sample in HCT leachate over time are shown in Figure 7. Sulfate concentrations began to increase after about week 20, and continued to increase to 135 mg/L by week 50 with no signs of reaching steady state conditions. Nickel concentrations didn’t increase above 2 to 3 μg/L until week 25, and by week 50 were 754 μg/L. Most metal concentrations peaked between 25 to 30 weeks and began to level off after that time. Because samples with low %S values and low neutralizing ability can take a long time to produce acid and metals in kinetic test leachate, and because of the uncertainty about representation of the peridotite rock mass (in particular the low %S values) in the kinetic tests, using values at the end of kinetic testing (week 50) from the “high S” (2.44%) peridotite sample in Phase II (column 5) for water quality modeling would be more representative of long-term leachate concentrations. In contrast, Geochimica (2006) used a lower-sulfur peridotite sample from Phase I of geochemical testing (column 3) and averages of week 40 and 50 values (see Table 2). Using the values chosen by Geochimica (2006) will underestimate long-term leachate concentrations in the underground mine and the development rock stockpile, where a large amount of peridotite will remain.

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0

50

100

150

200

0 10 20 30 40 50

SO4 (

mg/

l)

SO4

0.00

2.00

4.00

6.00

8.00

10.00

0 10 20 30 40 50

pH pH

0.0

0.2

0.4

0.6

0.8

0 10 20 30 40 50

Ni (

mg/

l)

Ni

Figure 7. Sulfate, pH, and nickel values over 50 weeks (x axes) in HCT leachate from the intrusive sample (peridotite, Phase II column 5, 2.44%S).

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4.2.5 Country rock

Seven samples of sedimentary rocks (including the hornfels) were included in the HCT tests. The %S values for the sedimentary rocks varied from 0.2 to 1.4%S, but the %S values for the kinetic tests ranged up to 2.71%S for the hornfels and 1.39 for the siltstone (column 4) in Phase II samples (Geochimica, 2004, 2005a). Using only the sedimentary samples with %S values of above 1, lowest pH values ranged from ~3.7 to 5.4, and highest sulfate values ranged from about 100 to 230 mg/L. Concentrations of cadmium, copper, cobalt, iron, manganese, nickel, and zinc did not begin to increase until week 70 in the Phase I high S hanging wall siltstone sample (column 1, 1.06%S). Although the location (hanging wall) implies that the sample may be representative of sedimentary rocks above the ore body, location maps for kinetic samples do not show samples in the crown pillar. Sulfate, pH, and copper values over time in HCT leachate from the siltstone sample from Phase II column 4 are shown in Figure 8. Copper is shown in Figure 8 instead of nickel because copper dominates heavy metal concentrations in this sample. However, at week 50, nickel concentrations in leachate from this sample were also high at 2.66 mg/L. Cobalt and nickel concentration trends were very similar to those shown in Figure 8 for copper, with all metal concentrations rising dramatically after about week 10. Arsenic concentrations were highest at week 1 (14 μg/L) and decreased to near detection limits (~1 μg/L) by week 50. The highest metal concentrations in the sedimentary rock HCT samples generally were in leachate from Phase II column 4 sample (siltstone with 1.39%S), with concentrations as high as 333 μg/L cobalt, 12.7 mg/L copper, 2.71 mg/L nickel, and 15 μg/L cadmium by the end of the 50-week period. The copper concentrations in this sample were higher than any from the ore itself. Arsenic concentrations reached only 3 μg/L in this sample but 10 μg/L in the hornfels sample (column 8, 2.71%S) in Phase II. Considering that many of the metal and sulfate concentrations were still increasing at the end of the kinetic testing, the highest sulfate and metal concentrations from the Phase II column 4 siltstone sample should be used for water quality predictions. Geochimica (2006) used values from a low-sulfur sample of peridotite rather than CR in his prediction of post-mining water quality (see Table 2). The exclusion of the sedimentary unit from the modeling of water quality in the underground mine after closure and backfilling will underestimate copper concentrations in the underground mine.

In summary, the leachate concentrations used by Geochimica (2006) to predict mine water quality were generally lower than those that are more representative of longer term conditions and rock types expected to be encountered in the underground mine after backfilling. The combination of using values from earlier weeks of kinetic testing and lower sulfur rocks resulted in values with substantially lower concentrations of sulfate and metals and higher pH values than those representative of conditions in the proposed mine or the development rock stockpile.

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0

100

200

300

400

500

0 10 20 30 40 50

SO4 (

mg/

l)

SO4

0.00

2.00

4.00

6.00

8.00

10.00

0 10 20 30 40 50

pH

pH

0.02.04.06.08.0

10.012.014.0

0 10 20 30 40 50

Cu

(mg/

l)

Cu

Figure 8. Sulfate, pH, and copper values over 50 weeks (x axes) in HCT leachate from CR sample (siltstone, Phase II column 4, 1.39%S).

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4.3 Model Assumptions/Conceptual Model

Several assumptions were made by Geochimica in predicting mine water quality that are not representative of conditions expected to be encountered in the underground mine or development rock. The conceptual model created by Geochimica resulted in lower predicted concentrations of metals and contaminants and higher pH values than would be considered representative of Eagle Project mine water quality. The assumptions used by Geochimica (in bold) are:

Essentially all massive sulfide ore will be removed from the underground mine as a result of mining. As shown in Figures 2 and 3, quantities of both massive sulfide and semi-massive sulfide ore will remain in the underground mine using the revised thicker crown pillar.

No massive or semi-massive sulfide ore will be contained in the development (waste) rock. Mining is not a surgical removal of material; it is a large-scale endeavor that cannot be as selective as the economics of the deposit would dictate.

The diameter of rock particles in the development rock pile is 10 cm on average. Smaller particles exist in all waste rock piles at hardrock mines, and it is these smaller particles that control concentrations and leaching rates of contaminants.

No contaminated infiltration will move through the crown pillar to the underground mine during or after mining. As soon as the water level is lowered for mining, infiltration will percolate downward through the crown pillar, and this hydrologic condition will last until water levels recover after mining. Much of the contaminant loading to underground mines comes from infiltrated rainwater and snowmelt moving through fractured rock and underground workings that lie above the main portions of the mine (see, e.g., Hazen et al., 2002; Desbarats and Dirom, 2004). No value for contaminant loading through this pathway is included in the water quality prediction model for the underground mine during or after operation.

The crown pillar is irrelevant to mine water composition because it is composed of rock with low ability to leach acid and contaminants. Especially with the new crown pillar configuration, substantial amounts of ore and mineralized peridotite will remain in the crown pillar during and after mining.

Concentrations during earlier weeks of kinetic testing are representative of concentrations leaching to the underground mine during and after mining. For most kinetic test samples, except for the massive sulfide unit, concentrations of sulfate and metals increased after the first 10, 20, or even up to 50 weeks of testing. Ignoring these higher values will underestimate the higher concentrations that will develop in the

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underground mine and the development rock stockpile over time as the rock oxidizes and leaches.

The amount of water entering the mine will be 180 gallons per minute (gpm). Section 4.3.12.2 of the mine permit application states that the expected groundwater inflow is 75 gpm. If this value is used in the model, predicted concentrations will be higher. Changes in the amount of inflow will dilute leachate concentrations more or less rapidly. Using a constant value also ignores the importance of pulses of infiltration from rain and snowmelt events. These pulses can carry large concentrations of metals and sulfate as a result of dissolving salts that accumulate on mine walls and in fractures above and around the mining cavity.

For some of these assumptions, modifications can be made to the spreadsheet models used by Geochimica (2006) to arrive at values more representative of the deposit, the mining approach, and potential water quality conditions, recalculations of surface areas of the modified underground mine and the fractures in the thicker crown pillar must be made and used in a new estimate of mine water quality. Blasting from the underground mine will increase fracturing in and around the mine, including the overlying crown pillar, which will promote faster leaching. The concentrations in mine water affect decisions about the water treatment system used by the mine and also affect the type of mitigation measures that should be put in place before mining begins. Therefore, new estimates of mine surface area and composition should be made and used in a revised modeling effort before a permit is granted.

5. Water Quality Predictions using Recommended Leachate Concentrations and Alternate Assumptions

Geochimica predicted water quality for the leachate from the development rock stockpile (Geochimica, 2005b), water in the underground mine during mining (Geochimica, 2005c), and water in the underground mine after mining, both with backfill (Geochimica, 2006) and without backfill (Geochimica, 2005a). The models used for each prediction are similar and in a number of cases rely on each other. As an example of the issues with the water quality predictions, Stratus Consulting reviewed the predictions for mine water quality after mining with all development tock backfilled (Geochimica, 2006).

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Geochimica’s general approach to modeling was as follows:

Using selected leachate chemistry of representative rock samples, concentrations from kinetic tests were converted to leach rates per unit surface area per unit time

The total surface area of exposed rock in the mine (of each rock type) and the development rock used as backfill was used to compute a mass leached

The mass of leached contaminants was divided by the total water inflow volume to arrive at concentrations in the underground mine after mining and backfilling.

5.1 Modifications to Modeling Assumptions and Inputs

Stratus Consulting made the following modifications to the spreadsheet model for water quality in the underground mine at the end of mining and to the assumptions listed in Section 4.3 to represent conditions more representative of the actual mining environment that should be planned for when designing the mining approach, mine water treatment, and mitigation measures:

Some higher-sulfur rock was included in the development rock stockpile and the mine wall rock. Five percent SMSU was added to the development rock pile, under the assumption that 100% of the ore could not be excluded from the waste rock. The remaining 95% was divided evenly between intrusives and CR. We also used 12% SMSU (Geochimica used 8%) and 3% MSU (Geochimica used 2%) for the wall rock. We assumed that intrusives (peridotite) and country rock made 65% and 20% of the wall rock.

Longer-timeframe leachate values from the HCT tests were used in modeling. We used leachate concentrations listed in Table 2 (values listed for Stratus Consulting) rather than original values in the Geochimica spreadsheet. These values are for the longest HCT leach times available. For several important parameters (e.g., sulfate and nickel), concentrations at the end of testing were not constant. For nickel in the SMSU and intrusive samples and copper in the CR sample, concentrations had been constant and just recently started increasing (see Figures 6, 7, and 8). For sulfate in the SMSU and the CR sample, concentrations were continually increasing from week 1 (see Figures 6 and 8). Therefore, concentrations of these (and other) contaminants may eventually get even higher that the values we chose in Table 2, and predicted water quality could be even worse than we predict in this review. Geochimica’s calculation of development rock storage pad water quality (Geochimica, 2005b) asserts that leachate chemistry was taken for a representative period over which chemistries are essentially constant (p. 3).

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However, if concentrations had not yet started to increase, those low constant values are obviously not representative of conditions over longer time periods in the underground mine or the development rock stockpile.

Higher surface area for the rocks in the development rock stockpile were used to reflect the smaller size fractions that will reasonably be present in the pile. Geochimica (2005b) stated that he used the total surface area for rock in the stockpile, based on a model of particle size distribution for the rock. However, only one size – 10 cm – was represented in the spreadsheet used to estimate water quality. It is the finer particles that control leachate chemistry because of their higher surface area, yet these are not represented in the model. Instead of using only 10-cm size particle, we used 90% at 10 cm and 10% at 1 cm. This leaves the vast majority at a larger size fraction but takes the important smaller sizes created by blasting and crushing into account and comes closer to doing what Geochimica proposed for prediction of development rock water quality. The surface area for the development rock is also used in the prediction of post-mining water quality, so changes in surface area of development rock affect both estimations of water quality.

The weight of development rock used to calculate waste rock and post-mining water quality with backfill was more than doubled to reflect all the development rock that will be backfilled. Several unfounded assumptions were used to calculate surface area of the development rock stockpile in Geochimica, 2005b (spreadsheet). [1] Instead of using the stockpile volume of 185,000 m3, Geochimica uses half of this value, “assumed as characteristic” (see cell K60 in HCT_analysis_NewPad3.xls), and then uses a porosity of 50%, thereby cutting down the volume even more. The resulting weight (rock mass, tones, cells O69 and O70) sums to only 126,000 tonnes, rather than the 379,000 tonne stockpile that is discussed in Geochimica (2005b). This dramatically reduces the amount of development rock that is considered in the prediction. [2] A density of 2.7 tonnes/m3 (= gm/cc) is used to calculate the weight of development rock in the modeling spreadsheet. These values are closer to the specific gravity of quartz, but are not representative of olivine, which is the major mineral in the peridotite and which has a density ranging from 3.3 to 4.4 (Klein et al., 1985). When the higher density is used and the pile volume isn’t cut in half twice, the weight of development rock is much closer to the value reported in Geochimica (2005b) (332,000 tonnes). We used densities of 4.4 for intrusive rock, 2.7 for CR, and 4.7 for semi-massive sulfide (to represent pyrrhotite, which has a specific gravity ranging from 4.6 to 4.7 gm/cc (Klein et al., 1985).

The surface area for the development rock backfilled into the underground mine was increased. When the surface area from the development rock stockpile was pulled into the model for prediction of post-mining water quality with all rock backfilled, only the value for the 379,000 tonne pile was used in Geochimica (2006 – spreadsheet). Instead, twice that amount should have been used to account for all of the development rock used

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as backfill. The 379,000 tonne pile is simply the weight of the pile during year 3; the full amount that will be backfilled at the end of year 7 is instead 647,279 tonnes, including rock used as roadbed in the underground mine (see Table 4-4, Foth & Van Dyke and Associates, 2006a). We assume mining will stop at the end of year 7 if a thicker crown pillar is required. Using the smaller tonnage (Geochimica, 2006) resulted in much lower predicted concentrations at the end of mining than predicted in this review. We also reduced the surface area of the walls to 95.8% of Geochimica’s value to account for the thicker crown pillar.

The amount of groundwater infiltration to the underground mine. The inflow value used by Geochimica for prediction of water quality in the backfilled underground mine was 180 gpm. In the recalculations, we used the expected groundwater inflow rate of 75 gpm as used in the water balances for the mine permit application.

5.2 Results of Revised Modeling Using Modifications

5.2.1 Development rock stockpile water quality

Using the modifications listed above, the results of our recalculations of development rock stockpile water quality (for important constituents) are contained in Table 3 and compared to predictions made by Geochimica (2005b). Three different approaches were used to estimating the size distribution (and thus the surface area) of the development rock stockpile: 90% at 10 cm and 10% at 1 cm; 95% at 10 cm and 5% at 1 cm; and 95% at 10 cm and 5% at 1 mm. Each option leaves the vast majority of the rock sizes at 10 cm, as used by Geochimica (2005b), but we added in 5% of a smaller rock size to represent the smaller sizes that are always presented in blasted rock. In addition, we added 2 to 5% of the SMSU material to the stockpile, under the assumption that not all ore will be successfully removed from the waste rock. Other changes included increasing the density for the rock types and increasing the weight of the pile to reflect tonnages listed in the mine permit application. The new estimates of development rock water quality were not subjected to a geochemical model to account for limestone addition. In Geochimica’s analysis (2005b), concentrations of the following constituents were not reduced by the inclusion of limestone: antimony, arsenic, boron, cadmium, cobalt, lead, mercury, molybdenum, nickel, potassium, selenium, sodium, sulfate, and zinc. In our analysis we also assume that these constituents would not be affected by the addition of limestone to development rock.

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Table 3. Comparison of development rock stockpile water quality using different inputs and assumptions − before modeling to include limestone. All units in mg/L unless noted.

Geochimica (2005b) 90% 10 cm, 10% 1 cm;

5% SMSU Sulfate 575 5,940 Nickel 8.33 102 pH (SU) 6.60 NC TDS 956 8,340 Aluminum 3.46 79.8 Arsenic 0.08 0.018 Beryllium 0.0019 0.051 Cadmium 0.0002 0.185 Calcium 79.3 804 Cobalt 0.0008 4.14 Copper 5.58 184 Iron 26.8 383 Lead 0.0004 2.17 Magnesium 88.3 496 Manganese 2.50 6.95 Selenium 0.0037 0.30 Zinc 1.90 17.7 NC = not calculated.

In Table 3, we compare concentrations to Geochimica (2005b) values before geochemical modeling that accounted for limestone addition. The results in Table 3 for these modifications show that sulfate, TDS, and all metal/metalloid concentrations are higher when smaller size fractions and more highly mineralized material is accounted for in the development rock. Because the modifications are a better reflection of conditions expected in the waste rock pile, we believe that substantially higher concentrations of contaminants are likely in development rock stockpile leachate. These higher concentrations will affect water reporting to the treatment plant, being discharged to groundwater at the treated water infiltration system (TWIS), and being released in the underground mine. Because the concentrations with the modified assumptions are so much higher than those used for mine design in the mine permit application, the permit for mining should not be granted until a complete reevaluation of potential water quality is conducted by Kennecott.

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5.2.2 Water quality in underground mine at the end of operations, with all development rock backfilled

Using the modifications listed in Section 5.1, the results of our recalculations of water quality in the backfilled underground mine are contained in Table 4 and compared to predictions made by Geochimica (2006) and state and federal water quality standards. For the Stratus Consulting analysis, more ore was assumed to be present in wall rock in the underground mine (12% SMSU and 3% MSU, compared to 8% SMSU and 2% MSU in Geochimica, 2005b). In addition, the proportion of waste rock at 10 cm was decreased to 90%, with the remaining 10% at 1 cm to account for small particles from blasting that will remain in the mine. The proportion of rock types used for development rock were 47.5% each of peridotite and metasedimentary rocks and 5% SMSU. For non-ore rock on mine walls, we used 65% peridotite and 20% metasedimentary rocks. Our values in Table 4 are the expected groundwater inflow of 75 gpm, while Geochimica used 180 gpm inflow, which will dilute concentrations by over a factor of two compared to the expected inflow condition. Neither analysis includes geochemical modeling to account for solubility controls and attenuation.

In our analysis, sulfate, metal, metalloid, and major ion concentrations are higher than those predicted by Kennecott (Geochimica, 2006). In Geochimica’s modeling results, only nickel and iron exceeded relevant standards. However, using the modifications discussed above, which more accurately reflect conditions in the underground mine and backfill, the following constituents exceed one or more relevant standard: sulfate, nickel, TDS, aluminum, arsenic (MCLG), beryllium, boron, cadmium, cobalt, copper, iron, lead, nitrate, and manganese. Relevant standards include Michigan Part 201 and 22 standards and U.S. EPA drinking water (MCL, SMCL, MCLG) and Lifetime Health Advisories (see Table 4). If Stratus Consulting values are reduced by 10 times to account for dilution in downgradient groundwater, the following constituents would still exceed relevant standards: aluminum, arsenic (MCLG), cobalt, copper, iron, lead, manganese, nickel, and nitrate. Reduction by 100 times would still result in exceedences for nickel in downgradient groundwater. In conclusion, our analysis shows that water quality in the underground mine after backfilling will likely be substantially worse than estimated in the mine permit application, using more realistic leachate concentrations and surface areas as inputs.

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Table 4. Incremental water quality (selected constituents) of backfilled mine at the end of mining, and comparison to Kennecott prediction and relevant standards (mg/L)

Units

Stratus Consulting

(75 gpm inflow)

Geochimicaa

(180 gpm inflow)

Part 201

Part 22 standards MCL SMCL MCLG

Lifetime health

advisory TDS mg/L 561 – 500 Aluminum mg/L 4,950 4.0 300 150 50 to

200

Antimony mg/L 0.54 0.03 6 3 6 6 6 Arsenic mg/L 1.18 0.06 50 25 10 0 Beryllium mg/L 3.22 – 4 2 4 4 Boron mg/L 254 70 500 250 1,000 Cadmium mg/L 11.9 0.08 5 2.5 5 5 5 Cobalt mg/L 362 18 40 20 Copper mg/L 11,400 2.1 1,400 500 1,300

(TT) 1,000

Iron mg/L 26,500 780 2,000 300 300 Lead mg/L 135 0.03 4 2 15 (TT) 0 Manganese mg/L 594 1.6 860 50 50 300 Nickel mg/L 15,500 1,770 100 50 100 Nitrate + nitrite

mg/L as N

50b – 10 5 10 10

Sulfate mg/L 394 28 250 250 250 Thallium mg/L 0.40 8 1 2 0.5 0.5 Zinc mg/L 1,100 1.9 2,400 1,200 5,000 2,000 Part 201: Residential Drinking Water Criteria, Table 1 R 299.5744. Part 22 Standards: Appendix G1, Eagle Project Groundwater Discharge Permit Application, Kennecott Eagle Minerals Company, February 2006 (Foth & Van Dyke and Associates, 2006c). MCL = maximum contaminant level; SMCL = Secondary MCL; MCLG: MCL Goal. TT = Treatment technique. See U.S. EPA, 2007. Lifetime Health Advisories: U.S. EPA, 2006. a. Geochimica, 2006, Table 2. b. Estimated; see Stratus Consulting, 2007. Values in bold exceed one or more relevant standard.

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6. Chemical Stability of Cemented Backfill The integrity of the cemented backfill proposed for primary stopes in the Eagle Project is threatened by both physical and chemical issues. Dr. Stan Vitton (Vitton and Parker, 2007) concludes that the crown pillar will not be stable under the current mine plan due to the highly fractured nature of the rock in the crown pillar. The main chemical issue that will threaten the integrity of the backfill, and hence the crown pillar, is the presence of highly acid-generating rock in the primary and secondary stopes. The ore has between 30 to nearly 100% sulfide, and the primary sulfide is pyrrhotite, which weathers more rapidly that pyrite to form acid drainage. The rate of pyrrhotite oxidation is important because the cemented backfill will be curing at the same time that the pyrrhotite is producing large volumes of acid drainage immediately adjacent to the backfill. Acid attack on the cement will make the backfill more porous starting on its edges. Benzaazoua et al. (2004) found that enhanced leaching of a paste backfill (using tailings and cement) increased the porosity of the edges of the backfill and caused the release of arsenic from the edge of the backfill.

Most of the studies on the effect of backfilling in mines with acid drainage are on paste backfill, where mine tailings are mixed with cement. The situation proposed for Eagle is not comparable: first, the sources of acid drainage are the walls of the workings and the development rock, neither of which will be encased in cement. Second, the small size of the tailings (sand size) ensures better coating of the surfaces and more contact between acid neutralizing material (cement) and acid generating material (tailings) – at the Eagle Project, small size fractions will exist from blasting and crushing, but they will not be covered in cement. Finally, the acid generation potential of the Eagle ore is much higher than that of tailings and will be in direct contact with the backfill. The ore will have between 30 and 100% sulfides, and some of it will remain in the stope walls. The peridotite and metasedimentary rocks close to the ore body are also high in acid-generating sulfides, and this will be the primary composition of the stopes that will be backfilled. The chemical and physical problems associated with the use of cemented backfill in the Eagle stopes require more investigation by Kennecott. Kennecott should demonstrate, using examples from other highly acid-generating mines with similar mining methods, that the use of cemented aggregate backfill will not threaten the integrity of the crown pillar.

7. Summary of Conclusions Our review of geochemical information for the Eagle Project indicates that because of the inherent characteristics of the mine, including unusually high metal sulfide content of the ore and associated wastes, high concentrations of contaminants such as nickel, copper, cobalt, sulfate, and acid can be expected to discharge to groundwater and potentially surface water from operation of the project.

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Overall, we conclude that geochemical characterization and modeling performed to date for the permit application underestimates the degree of acid and metal contamination that will result from project implementation. A list of conclusions is contained in the Executive Summary of this review. Based on the severity of the implications for water quality at the mine and potentially for treated water discharged to groundwater, we recommend a reevaluation of mine and treatment design, using the information and recommendations in this review, before a mining permit is granted.

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Foth & Van Dyke and Associates. 2006b. Response to Michigan Department of Environmental Quality Comments, dated June 21, 2006, on the Eagle Project Mining Permit Application. Foth & Van Dyke and Associates, Inc. October.

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http://www.epa.gov/waterscience/criteria/drinking/dwstandards.html

http://www.epa.gov/safewater/contaminants/index.html

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Geochemical Review of the Eagle Project Mine Permit Application