june 2007 · a total of 10 boreholes totaling 877 feet of drilling, 33 test pits, and 18 miles of...

011-1110 -c,0

51,6 6,0`

Summary of Tetra Tech Reports Provided for the Feasibility Study And the Mine Plan of Operations

Rosemont Project

June 2007

CLEAR SOLUTIONS"

Summary of Tetra Tech Reports Provided for the Feasibility Study And the Mine Plan of Operations Rosemont Project

Prepared for:

Augusta Resource Corporation 4500 Cherry Creek South Drive, Suite #1040 Denver, Colorado 80246 (303) 300-0138 Fax (303) 300-0135

Prepared by:

TETRA TECH

3031 West Ina Road Tucson, Arizona 85741 (520) 297-7723 Fax (520) 297-7724

Tetra Tech Project No. 320614 June 2007

Tetra Tech Report Summaries Augusta Resource Corporation

TABLE OF CONTENTS 1.0 INTRODUTION 1

2.0 PROJECT DESCRIPTION 2 2.1 Location 2 2.2 Facilities and Operations 2

3.0 GEOLOGIC HAZARDS ASSESSMENT 3

4.0 GEOTECHNICAL STUDY 4 4.1 Geotechnical Program 4 4.2 Investigation Findings 5

5.0 GEOCHEMICAL STUDY 8

6.0 LEACHING FACILITY DESIGN 9 6.1 General 9 6.2 Location 9 6.3 Capacity 9 6.4 Solution Management 9 6.5 Site Conditions 10 6.6 Pad Liner System 10 6.7 Pond Liner Systems 11

7.0 DRY TAILINGS FACILITY DESIGN 12 7.1 General 12 7.2 Location and Design Criteria 12 7.3 Site Conditions and Geology 13 7.4 Tailings Properties 13 7.5 Dry Stack Stability 14 7.6 Hydrologic Modeling 14 7.7 Dry Stack Operations 15 7.8 Surface Water Control 16

8.0 SITE WATER MANAGEMENT 17 8.1 General 17 8.2 Site Conditions 17 8.3 Climatology 17 8.4 Project Facilities 18 8.5 Hydrology 18 8.6 Sediment Yields 18 8.7 Sediment Controls 18 8.8 Surface Water Management 19

Tetra Tech June 2007


9.0 RECLAMATION AND CLOSURE 21

9.1 General 21

9.2 Closure Concepts 21

9.3 Post-Closure Land Uses 21

9.4 Concurrent Reclamation Design 22

9.5 Operating Considerations 23

June 2007 ii Tetra Tech


1.0 INTRODUTION

This report presents the Tetra Tech Mining and Manufacturing (Tetra Tech) feasibility level studies and designs for the following aspects of the Augusta Resource Rosemont Copper Project (Project).

•Geologic Hazards

•Geotechnical Study

•Geochemical Study

•Leaching Facility

•Dry Tailings Facility

•Site Water Management

•Reclamation and Closure

In August 2006, Augusta authorized Tetra Tech to provide professional engineering services related to site-wide geotechnical and geochemical studies and feasibility-level design of the leach pad and associated ponds, tailings dry stack facilities and water management facilities, and development of reclamation and closure plans for the Rosemont Project.

This report provides an executive summary of the compendium of reports presenting the feasibility-level design of the above-mentioned Project aspects. The list of reports below present the results of field investigations, laboratory testing, and engineering analyses and design activities carried out in support of the Project. The detailed scope of work for each aspect of the Project is presented in their respective report.

•Leaching Facility Design (Tetra Tech, June 2007)

•Dry Tailings Facility Design (Tetra Tech, June 2007)

•Site Water Management Plan (Tetra Tech, June 2007)

•Geotechnical Study Report (Tetra Tech, June 2007)

•Geologic Hazards Assessment (Tetra Tech, June 2007)

•Baseline Geochemical Characterization (Tetra Tech, June 2007)

•Reclamation and Closure Plan (Tetra Tech, June 2007)



2.0 PROJECT DESCRIPTION

2.1 Location

The Project site is located approximately 30 miles southeast of Tucson, west of State Highway 83 on the east slope of the Santa Rita Mountains. In geographical terms, the coordinates of the Rosemont property are approximately 31° 50'N and 110° 45'W. Access to the property will be from Interstate 10 to State Highway 83 south, then west on Forest Road (FR) 231.

2.2 Facilities and Operations

The Project will be developed as an open pit mine with a milling and processing plant for approximately 493 million tons (Mt) of sulfide ore concurrent with copper leaching of approximately 50 Mt of oxide ore in an approximate 19-year mine life. Tailings from the milling process will be further dewatered before being transported to a designated dry stack storage facility. Waste rock quantities of up to 1,288 Mt will be generated as part of the mining operation.

Open pit mining techniques will be used to mine and access the ore, move overburden (barren material) and other non-ore, or waste, materials. Overburden and the waste materials will be transported by haul truck to the waste rock storage area. Sulfide ores will be hauled to a crusher, crushed, and subsequently conveyed to a mill for further processing. The rougher flotation tailing and the scavenger flotation tailing are combined in a tailings thickener for water recovery. The thickener underflow slurry is then pumped to a bank of connected large drum filters where moisture is reduced from 40 to 50 percent water to ten to 15 percent moisture. The tailings are then transported and placed by conveyor in a designated tailings "dry stack" area.

The deposition of dry tailings, waste rock, and overburden will be initiated with a series of perimeter buttresses that are designed to reduce visual impacts from State Highway 83 and surrounding areas, allowing reclamation to begin within the first year of operation. Topsoil will be salvaged from pit and waste rock/tailings storage areas for use as a vegetation growth medium as needed. Waste rock and tailings will be deposited behind, i.e. to the west of the perimeter buttresses during the life of the mine. The dry tailings deposition will incorporate staged waste rock buttresses or berms for screening and to improve mechanical and erosional stability of the tailings.

Current plans by Augusta include copper leaching of approximately 50 million tons (Mt) of oxide ore in an approximate 6 year leaching operation concurrent with milling operations. The leach pad is designed to accommodate the planned ore tonnage with a lined pad built in one construction phase. The lined leach pad, collection ditch and pond design, as well as the solution pumping systems and pipelines, will provide full containment of operational solutions, including a design storm event.

The primary Project facilities include a primary crusher and process plant, a tailings filter plant, leach pad and associated ponds located just east of the open pit, a Process Water Temporary Storage (PWTS) Pond located southeast of the plant, tailings dry stack and waste rock storage facilities, truck shop and administration buildings, supply water tank and pipelines, ancillary facilities, and access roads.

Tetra Tech June 2007 2


3.0 GEOLOGIC HAZARDS ASSESSMENT

A geologic hazards assessment was performed to identify potential hazards within the bounds of the Project site, estimate the risk associated with these hazards, and present possible mitigation techniques.

The primary hazards identified by this study are rockfall hazards and abandoned mine workings. A large rockfall zone, identified along the western wall of the proposed Rosemont open pit, presents a high rockfall risk to the proposed Project and will require engineered mitigation to prevent rockfalls into the pit. Additional small areas of localized rockfall, many insignificant on the map scale, exist particularly in steeply incised alluvial valleys. The source material of these rockfall areas is not generally bare rock as described above, but rather loosely consolidated deposits where rockfall results from differential weathering between cobbles or boulders and matrix material.

The Project site and the general Project area have been the subject of historic mining activities, although none of these previous activities has matched the scale of the proposed mining Project. Prior mining activities ranged from simple, shallow prospector borrow pits no more than a few feet in diameter and several feet in depth, to well developed mine adits that extend tens of feet or more into the subsurface. Additionally, one slag deposit and a historic ore leaching tank exist on the Project site. In order to inventory these previous mine workings, Tetra Tech researched the Abandoned Mine Lands (AML) database available on the World Wide Web through the USGS and conducted a ground survey. Six historic mine workings, absent from the USGS database, were discovered during field investigations. A geologist was also sent to the property to photographically document each AML site and provide a general description of the workings.

Many of the AML sites present negligible risks of mine subsidence hazards to the Project facilities. Other AML sites will require further investigations and possibly active engineered mitigation to reduce risks associated with mine subsidence. Possible mitigation efforts include backfilling, bridging, or complete avoidance of AML sites. Classifications of these mine workings, and the efforts necessary to reduce risks, should be handled during final design efforts.

The geologic hazards assessment also estimated the seismic hazard for the Rosemont site in accordance with the Arizona Department of Environmental Quality (ADEQ) published guidelines for mining project design criteria. Seismic hazards for the Project site are defined by the Maximum Probable Earthquake (MPE) and the Maximum Credible Earthquake (MCE) design events. These events are correlated to specific engineered structures based on the level of risk and life of a particular facility. The estimated ground acceleration for the MPE and MCE is 0.0458 and 0.3268, respectively. These values were used for design of the various engineered structures.



4.0 GEOTECHNICAL STUDY

Tetra Tech has performed site-wide geotechnical studies for the various proposed facilities. Initial site investigations were conducted between November 2006 and March 2007 at the Rosemont site. Additional site investigations are planned to support the feasibility designs of the Rosemont facilities. The site investigation included borehole drilling, test pit excavating, surface geology mapping, field penetration and hydraulic testing, geotechnical logging of condemnation boreholes, geophysical ground surveys, and laboratory testing of selected samples.

The main objectives of the site investigation work performed included:

•Determining foundation conditions beneath the dry tailings storage facility, leach pad and ponds, PWTS pond and dam, waste rock storage facility, crusher, plant, and other planned mine structures;

•Determining material and mass properties of the bedrock for foundations, including permeability to support hydrogeologic assessments;

•Determining the groundwater regime;

•Estimating quantities and quality of borrow materials for facilities construction, including granular soils and rock material;

•Determining distribution and material properties (including in-situ permeability) of the overburden soils for excavations and structure foundations; and

•Providing engineering properties for design of structure foundations.

4.1 Geotechnical Program

The fieldwork carried out by Tetra Tech included mapping of bedrock outcrops and the extent of superficial materials within the plant site and heap leach areas to supplement published mapping previously performed by others.

A total of 31 seismic refraction profiles were carried out across the site using refraction tomography methods in order to determine the substratum morphology in the proposed facility locations. Six shear wave sounding locations where completed using refraction microtremeter methods.

A total of 10 boreholes totaling 877 feet of drilling, 33 test pits, and 18 miles of geophysical survey lines were conducted during the initial phase of the work. An additional 17 boreholes and 14 test pits are planned to provide supplemental data. Field testing included packer and falling head testing within various lithologic units after completion of drilling, point load testing on rock core, and Standard Penetration Testing in soils.

Laboratory testing was conducted to analyze the suitability of local materials as foundation materials and in slope cuts and fills. Soil samples from selected test pits and boreholes were taken to several soils laboratories and a testing program, comprised of grain size distribution, Atterberg limits, modified Proctor, and direct shear tests, was carried out.

Data generated during the geotechnical program has been compiled in the geo-data management and reporting program and includes field and laboratory data. The database



included a total of 70 exploration/condemnation holes drilled by Augusta and previous owners in addition to the data gathered by Tetra Tech.

4.2 Investigation Findings

General

Due to the size of the Rosemont site, the overall Project area was broken up into four facility areas. The surficial geology for each area has been mapped and geological and geotechnical cross sections have been generated through each area, generally along the seismic survey lines, with lithological designations of soil, cemented soil/soft rock, rippable bedrock, and non-rippable bedrock estimated from seismic velocity zones correlated with borehole and test pit data.

Facility Area

This area includes the proposed plant facilities, ore conveyor, tailings filter plant, PWTS Dam, truck shops, and administration buildings. The majority of the site is underlain by a series of arkosic to tuffaceous siltstones, sandstones, and conglomerates within the Willow Canyon Formation. There is an andesitic mafic lava flow cutting through the southeast portion of the plant site and several deposits of alluvium are within the area.

Test pits completed to the west of the plant site show that there is a thin layer of soil, 1 to 2 feet thick, overlying bedrock. The soil ranges from silty sand with gravel to clay with sand. Rock mass calculations indicate the Willow Canyon Formation can be classified as "Fair Rock".

Several geological/geotechnical cross sections were developed by Tetra Tech throughout the plant site area. These cross sections show the anticipated geologic units, measured material velocities and building pad elevations proposed by M3 Engineering & Technology (M3). From the 6 seismic lines that intersect facilities in the plant site area, only one facility pad was found to be within non-rippable rock.

Facility Area 2

This area encompasses the leaching facility and associated ponds. The northern portion of the leach pad and process ponds are underlain by the Willow Canyon and Apache Canyon Formations. Rock mass calculations indicate the rock in these areas can be classified as "Fair Rock".

Although test pits excavated within the Apache Canyon indicate the rock will be rippable at the near surface, velocities from seismic data indicate that non-rippable rock may be present at 20 to 50 feet below the ground surface within the leach pad and at 10 feet deep near the northern most pond. The southern portion of the heap leach facility is underlain by the Gila Conglomerate formation. Several test pits completed within the Gila Conglomerate indicate it is well to moderately cemented clayey sand with gravel containing trace amounts of cobbles and boulders.

The alluvium in this area was found to be as thick as 50 feet. The material is predominantly a moderately to weakly cemented sand with silt and gravel. Field penetration testing indicates the overburden materials exhibit increased density with depth.

Facility Area 3

Facilities in this area include the primary crusher, north and south dry tailings storage facilities, and north diversion channel. The tailings facilities are mainly underlain by the Willow Canyon, Apache Canyon, and Mount Fagan Rhyolite Formations. There are smaller occurrences of an



andesitic porphyry, a mafic lava flow, an extrusive rhyolite, and alluvium deposits within the footprint. Apache Canyon and Willow Canyon rock mass values within the tailings area are believed to be similar those for the nearby heap leach pad and plant site area. Values are not yet available for the Mount Fagan Rhyolite due to the limited access for drilling.

The alluvium in this area was found to be as thick as 27 feet. The material is predominantly a moderately to weakly cemented sand with silt and gravel. Field penetration testing indicates the overburden materials exhibit increased density with depth.

Facility Area 4

This area comprises the waste rock storage facility area. The waste rock facility is mostly underlain by the Gila Conglomerate except for deposits of alluvium located within the drainages and associated floodplains. Although no test pits were completed within the waste rock facility area, test pits from the nearby heap leach pad indicate the Gila Conglomerate is well to moderately cemented clayey sand with gravel containing trace amounts cobbles and boulders.

The alluvium in this area was found to be as thick as 80 feet. The alluvium material is predominantly a moderately to weakly cemented sand with silt and gravel. Field penetration testing indicates the overburden materials exhibit increased density with depth.

Borrow Materials

The site investigation identified potential borrow materials for use as subgrade and drain rock in the construction of the heap leach pad. Samples of Gila Conglomerate were collected from test pits near the heap leach site and tested for subgrade suitability. Although the Gila Conglomerate is believed to be suitable subgrade material, it will need some processing to remove large cobbles and boulders prior to use as subgrade fill under the leach facility liner system.

Tetra Tech investigated the Concha limestone and Bolsa Quartzite within the pit limits for potential rock quarrying to provide aggregate material. It is currently anticipated that borrow materials for concrete aggregate required for the initial construction will primarily be from the Concha limestone based on accessibility of the material. A silica-rich arkose conglomeratic sandstone from the Willow Canyon Formation, located within the northern portion of the pit, was sampled and tested for suitability as drain rock for the leach pad. Testing results indicate the material will exhibit negligible degradation under the expected operational conditions, and it is suitable for drain rock fill on the leach pad.

Based on point load and laboratory strength testing, the three above-mentioned rock types would be suitable as drain rock for underdrains for the heap leach facility or for other high load applications. Processing may be necessary to produce the specified materials and may include crushing and screening depending on the rock type and conditions encountered in the field. Preliminary geochemical testing indicates the arkose material is inert and benign in terms of potential acid generation or seepage water quality. Additional geochemical testing is ongoing to characterize the rock types considered for construction.



Geotechnical Design Parameters and Analyses

Geotechnical parameters for surface soils and bedrock have been developed from the field investigation and laboratory testing program and include rock mass rating, shear strength, and foundation and earth pressure parameters.

Geotechnical analyses have been performed for the various facility foundations based on preliminary anticipated foundation types and loads. Recommendations have been developed for bearing capacity, settlement, slope stability, and foundation liquefaction.

General design recommendations are also given for cut and fill slopes, site preparation, structural and controlled fill, access roads, erosion and drainage, corrosive soils, and seismic design parameters.



5.0 GEOCHEMICAL STUDY

Tetra Tech has completed baseline geochemical characterization associated with the Rosemont Project. The scope of this study was to determine the baseline geochemical characteristics of the waste rock and tailings materials. The following tasks were performed in support of the baseline study:

•The creation of a database of static and kinetic geochemical tests of waste rock collected from core and tailings collected from metallurgical tests;

•The assessment of geochemical behavior and geochemical risks of the waste rock and tailings materials; and

•A preliminary mitigation plan for preventing and/or controlling drainage that shows the potential for environmental impacts.

This study is part of a phased approach to quantifying and mitigating geochemical risk that will be expanded and revised throughout the planning, construction, and operational life-cycles of the Project.

The waste rock characterization baseline study was based on coarse reject samples collected from site core. Where possible, samples were composited over a 50 foot interval to simulate the bench height of the pit wall and/or the waste rock storage area. In total, 94 static and 17 kinetic tests have been performed and 80 static tests are on-going. Acid-Base Accounting (ABA) testing performed on the waste rock samples showed that most (73%) of the material characterized to date meets the "inert" definition set forth in the Arizona Department of Environmental Quality draft policy. However, 28 of the 94 total samples had likely or uncertain acid generation behavior.

The waste rock samples are enriched in copper, antimony, molybdenum, selenium, cadmium, arsenic, zinc, gold, lead, and silver when compared to average concentrations in the earth's crust. The leachate from the waste rock was benign, with most metals below the detection limit. Kinetic testing was focused on uncertain and potentially acid generating materials. At 20 weeks, the kinetic testing has yet to show any significant geochemical risk from waste rock samples, either under controlled laboratory conditions or from on-site kinetic testing.

However, because the materials appear to come from distinct zones within the Arkose and Andesite formations, a waste rock placement strategy is required to properly blend waste rock containing abundant acid-neutralizing capacity with the uncertain acid generating materials to ensure long-term water quality protection.

Tailings characterization was performed on two samples that were available from metallurgical testing. ABA testing, leachate analysis, whole rock analysis, and on-going kinetic testing all strongly suggest that the tailings material will have a limited potential for leaching metals to groundwater or surface water and will have no significant risk of producing acid. Additional testing is currently being performed on a third test sample.



6.0 LEACHING FACILITY DESIGN

6.1 General

The Rosemont leaching facility will be constructed southeast of the proposed open pit within the Barrel drainage. The pad will be large enough to contain the currently-identified oxide ore reserve of 50 Mt's stacked to a maximum ore heap height of 300 feet.with an optional expansion pad was also designed with up to 50 Mt of additional storage, The lined leach pad will utilize gravity solution drainage via perforated drain pipelines to the downhill perimeter berm, including a collection ditch pipeline system to the pregnant solution pond and storm event pond. A raffinate pond will be located adjacent to the pregnant solution pond.

6.2 Location

The leach pad site was selected by Tetra Tech, Augusta, and M3 Engineering personnel during initial internal studies for the Project. The selected pad site provides sufficient slope for gravity solution flow. Additionally, the pad was sited outside of major drainages to minimize the impact from storm flows during operation. Temporary diversion ditches are not required as the heap layout utilizes the natural drainage boundaries to a large extent.

6.3 Capacity

The selected nominal ore stacking rate is 38,000 tons per day (tpd) of Run-of-Mine (ROM) ore to the leach pad with no ore stockpiling. The heap leach pad design is based on a nominal 13.9 Mt of leach material stacked per year on the pad. However, the heap leach ore production schedule indicates a variable leach ore production schedule with the maximum rate occurring in Year 1.

The Rosemont leach pad, as designed, will provide an ultimate ore capacity of approximately 100 Mt and would be constructed in two phases. Current oxide reserve estimates indicate that only 50 Mt of ore can be economically leached. Therefore, construction of the second phase of the leaching facility is not anticipated.

The pad capacity was based on an average stacked ore density of 125 pounds per cubic foot and a maximum heap height of 300 feet over the pad liner. ROM ore will be stacked on the pad through end dumping of haul trucks in approximately 30 foot lifts. The leach pad will be lined with a synthetic liner to maximize solution recovery and minimize the potential for impacting groundwater.

Lifts of ore will be stacked to provide benches between lifts around the perimeter of the heap, providing an average overall ore slope of 2H:1V (horizontal to vertical). The 2H:1V slopes will provide operational stability of the heap. The 2H:1V sideslopes were determined based on stability analyses with a design basis of achieving a static factor-of-safety against instability of at least 1.3 and a dynamic factor-of-safety of at least 1.1. Dynamic stability analyses modeled the effects of earthquake loading using a peak acceleration of 0.045g. This value was based on the results of a seismic hazard assessment performed for the site.

6.4 Solution Management

Solution will be applied to the ore at an average rate of about 0.004 gpm/ft2. Solution will be collected by a drainage system placed above the synthetic pad liner, which will in-turn direct pregnant solution flows to a pregnant leachate solution (PLS) pond located at the northeast corner of the leach pad. The Phase 1 leach pad and pond limits include approximately 522,000



cubic yards of site grading cut/fill to achieve positive drainage to the ponds, to provide suitable slopes and surfaces for geomembrane lining,and to allow for a relatively level surface for downstream heap stability.

The PLS pond was sized to accommodate 8 hours of operational flows plus 24 hour draindown of the ore heap. The PLS pond will be fitted with a sump and well riser pipe to pump pregnant solution to the plant at a normal rate of 2,500 gpm.

During upset conditions, such as a power or pump outage, or a severe storm event, solution can flow by gravity from the pregnant pond to a lined storm pond located adjacent to the PLS pond. The storm pond has been sized to a volume of 50 ac-ft developed from a 100-year, 24-hour storm event falling on the pad.

The water balance analyses indicate that the average year precipitation conditions result in a makeup water requirement throughout the operational year. The total makeup water required in an average year of precipitation is approximately 800 ac-ft of water corresponding to an average flow rate of about 500 gpm. The maximum makeup water rate occurs in the month of June at up to 600 gpm.

6.5 Site Conditions

Subsurface geology at the leach pad site was explored under the direction of Tetra Tech and included a total of 4 geotechnical borings, 13 test pits, and approximately 2.3 miles of geophysical survey completed within the vicinity of the leach pad and ponds.

The leach pad and process pond area is located southeast of the planned open pit within a tributary of the Barrel drainage basin and is characterized by terrain sloping generally north and east from the pit area to the Barrel drainage which runs generally north-south in this area. A network of small arroyos feed the main Barrel drainage. The leach pad limits follow the major ridgelines delineating several of the arroyo networks. Vegetation at the leach pad site consists of a poor coverage of native grasses and shrubs.

Surface soils within the proposed leach pad area are comprised primarily of alluvial deposits in the drainages and floodplains. The thickness of the alluvium ranges from 20 to 80 ft based on borehole and geophysical data. The two major rock units found within the area are the Willow Canyon and Apache Canyon Formation. Locally, the Willow Canyon Formation consists of a fine to coarse grained arkosic sandstone to conglomerate, and the Apache Canyon Formation is a series of calcareous siltstones and sandstones. Bedrock depth varies from 80 ft within the drainages and floodplains to at ground surface within the hills. Where topsoil is present, depths vary from 1 to 2 ft across the site based on test pit logs.

In-situ permeability testing was conducted in the boreholes using the double packer and falling head method at depths ranging from 19 feet to 63 feet. The results indicate fairly low permeability surficial soils (alluvium) with values between 2x10-4 to 5x10-5 cm/s and bedrock permeabilities in the 4x10-5 cm/s range.

6.6 Pad Liner System

The lining and solution collection system for the leach pad will include (from the bottom to the top): a layer of compacted bedding soil; a sodium bentonite geosynthetic clay liner (GCL); 1.5 millimeter (60 mil) thick linear low density polyethylene (LLDPE) geomembrane liner; and a 3-foot layer of crushed liner cover fill. The liner design considered the use of COL due to the low quantity of nearby clay borrow materials available for construction of a compacted soil layer.



The GCL liner provides an equivalent 1 foot minimum thickness of 1x10-6 cm/sec or lower permeability soil layer.

Liner cover fill used for the 3-foot layer placed over the geomembrane pad liner will be a high-permeability crushed gravel product produced on-site using a portable crushing plant. Feed material will be supplied from within the mine pit area.

The solution collection system will consist of pipes placed within the 3-foot liner cover fill layer above the geomembrane liner. Primary solution collection will be from 3-inch diameter perforated collector pipes placed at a spacing of about 30 feet across the entire lined pad. The collector pipes will convey flow to larger collector pipes which will convey pregnant solution flows to the PLS pond.

6.7 Pond Liner Systems

The PLS and raffinate pond lining system will consist of the following (from the bottom to the top): a layer of compacted bedding soil; a GCL; a 1.5 millimeter (60 mil) LLDPE secondary geomembrane liner; a leak detection layer consisting of a geonet; and a 2 millimeter (80 mil) HDPE primary geomembrane liner. The storm pond will be lined with a 2 millimeter (80 mil) HDPE primary liner placed on a GCL.



7.0 DRY TAILINGS FACILITY DESIGN

7.1 General

The Rosemont dry stack tailings facility will receive dry tailings from the sulfide ore processing plant at a nominal rate of 75,000 dry tons per day. This material will be stacked behind large containment buttresses constructed from pit run waste rock; consequently, this storage area will be active from late preproduction through the end of the mine's life (presently estimated at 19 years).

The deposition of dry tailings, waste rock, and overburden will be initiated with a series of perimeter buttresses that are designed to reduce visual impacts from State Highway 83 and surrounding areas. The staging of these buttresses will also allow reclamation to begin within the first year of operation. Topsoil will be salvaged from pit and waste rock/tailings storage areas for use as a vegetation growth medium. Waste rock and tailings will be deposited behind, i.e. to the west of the perimeter buttresses during the life of the mine. The dry tailings deposition will incorporate staged waste rock buttresses for screening and to improve mechanical and erosional stability of the tailings.

7.2 Location and Design Criteria

A siting study was conducted to evaluate alternative sites based on defined design and selection criteria, as well as estimated development costs, to identify the preferred tailings storage location and placement methods.

Design criteria and objectives for the dry tailings storage facility included:

•Provision of secure long-term storage of a minimum 500 million tons (Mt), which is sufficient for the ore to be mined and processed during about 19 years of Project life at a projected rate of 75,000 tons per day (tpd);

•Location within the immediate general area of the mine (approximately five-mile radius from the proposed mine pit);

•Prevention of airborne release of tailings solids to the environment by provision of dust suppression measures;

•Compliance with all applicable regulations including Arizona BADCT standards;

•Creation of a site-specific design that accounts for local factors including climate, geology, hydrogeology, seismicity, and vegetation; and

•Establishment of an effective and efficient reclamation program, with a focus on concurrent reclamation.

The results of the study indicated the dry tailings option as the most favorable placement method. Advantages of the dry tailings stack over conventional tailings is that it eliminates the need for an engineered embankment and seepage containment system, maximizes water conservation and minimizes water makeup requirements, results in a very compact site limiting disturbance to a single drainage, and allows opportunities for concurrent reclamation and provisions for dust control.

June 2007 12 Tetra Tech


7.3 Site Conditions and Geology

The selected dry tailings storage site is located just east of the proposed mill site in Barrel drainage. The tailings facility site is characterized by terrain sloping generally east from the plant area to the Barrel drainage which runs generally north south in this area. Vegetation at the tailings facility consists of a poor coverage of native grasses and shrubs.

A geotechnical investigation was performed under the direction of Tetra Tech to characterize the site soil and rock conditions and to provide engineering parameters for feasibility design. Site investigation work within the limits of the proposed tailings facility included two geotechnical borings, two test pits, and four miles of geophysical survey.

Surface soils within the proposed tailings facility area are comprised primarily of alluvial deposits in the drainages and floodplains. The thickness of the alluvium can range from 20 to 80 feet. Topsoil depths vary from a few inches to three feet across the site based on test pit logs. Bedrock depth varies from 80 feet within the drainages and floodplains to at ground surface within the hills.

The major rock units found within the area are the Mt. Fagan Rhyolite, the Willow Canyon Formation, and the Apache Canyon Formation. The Mt. Fagan Rhyolite ranges from a phenocryst-rich ash-flow tuff to a megabreccia. The Apache Canyon Formation is a medium- to thick-bedded sequence of shale, laminated siltstone and fine-grained sandstone. The Willow Canyon Formation is a succession of medium- to coarse-grained, locally granular to pebbly, feldspathic sandstone, argillaceous sandstone, and siltstone. A few moderate to small andestitc mafic lava flows flank the northwest edge of the tailings facility.

Insitu permeability testing was conducted in the boreholes using the double packer and falling head method at depths ranging from 19 to 63 feet. The results indicate fairly low permeability surficial soils with values generally ranging from 10-4 to 10-6 cm/s and bedrock permeabilities for the Apache Canyon Formation in the 10-6 to 10-7 cm/s range.

7.4 Tailings Properties

Laboratory testing of the tailings was performed to provide parameters for design and operation of the dry tailings storage facility. The testing program included index testing (gradation, moisture/density relationship, and specific gravity), capillary moisture retention tests, shear strength, consolidation, and permeability tests.

The objectives of the testing program were to provide input parameters for engineering analyses to include slope stability, liquefaction potential, seepage (unsaturated flow modeling), as well as operational parameters for handleability and trafficability during transport and placement of the dry tailings.

The proposed disposal method for the dry tailings involves transporting the dewatered tailings to a secure placement area via conveyor and stacking in relatively small lifts behind previously constructed waste rock buttresses. The dewatered tailings must be handleable for transfer and movement by conveyor. The placed tailings must also support the stacking system, with a dozer to be used for spreading the tailings where necessary. Therefore, it was necessary to understand the effective range of moisture contents that would be suitable for the proposed operation. Shear strength is the primary parameter for evaluation of bearing capacity and trafficability of a material. Based on laboratory testing results on an initial sample of the Rosemont tailings, it can be concluded that trafficability of the Rosemont tailings will be very



poor and likely impossible with the proposed stacking and operational equipment at moisture contents above 16 percent by dry weight. The tailings filter plant, therefore, must be capable of dewatering the tailings to moisture contents of 16 percent or lower.

7.5 Dry Stack Stability

The Rosemont tailings dry stack is designed as a low hazard facility with fully drained waste rock placed as buttressing material and low moisture tailings placed in relatively thin controlled lifts. The ultimate tailings mass will exhibit only partially saturated conditions with no excess pore pressure throughout the life of the facility and at closure. The tailings lifts will densify under successive controlled conveyor lift placement operations, which will result in an increase in the lower lift fill strength over time. The tailings facility stability analyses considered the maximum ultimate height at the maximum section through the facility for downstream and upstream stability.

The tailings will be placed in a relatively dry state for acceptable handleability during conveyance and trafficability of the tailings surface, which will limit susceptibility to liquefaction under dynamic loading. Based on a liquefaction assessment for fine grained soils, the Rosemont tailings are potentially liquefiable at a moisture contents greater than 19 percent by dry weight. Since the tailings will not be handleable or trafficable at moisture contents above 16 percent, placement of tailings in the storage facility at moisture contents approaching 19 percent is not expected. However, limited higher moisture zones within the tailings mass created by meteoric water may occur. This condition was considered in the stability modeling by applying reduced shear strength to thin layers within the tailings mass at various levels to simulate these higher moisture zones and to evaluate the subsequent earthquake resistance of the facility.

Adequate factors of safety at 1.5 static and 1.1 psueudo-static (OBE earthquake) were obtained from the stability analyses based on the selected parameters and proposed facility configuration.

The slope stability analyses indicate the dry tailings stack operations can be constructed with stable 3H:1V inter-bench slopes and an overall stable slope of approximately 3.5H:1V to a total maximum height of approximately 600 feet.

The potential for discrete liquefied tailings layers encapsulated in the tailings mass does not result in an unacceptable reduction of the factor of safety against slope failure. However, as an added measure against potential deformation of the outer waste rock buttresses constructed on tailings, compaction of the tailings below the waste rock buttress is recommended. This measure will result in a higher density material, thereby reducing the liquefaction susceptibility of the tailings that form the foundation for subsequent waste rock buttress lifts.

7.6 Hydrologic Modeling

Hydrologic steady-state and transient modeling of the tailings dry stack was performed to estimate the quantity of water flowing through the tailings and waste rock mass, the time water spends in contact with reactive rocks within the facilities, and the airflow in the pore spaces between soil particles.

Tailings and waste rock material properties and site climate parameters were used to simulate three scenarios: the facility during operations, a worst-case operational scenario, and a closure scenario. For the transient models, each was run for a one-year period using average climate data from the Santa Rita Experimental Range meteorological station.

June 2007 1 4 Tetra Tech


The balance between precipitation, evaporation, transpiration, runoff, storage, and percolation is a key output of the models. What percolates through the cover has the potential to become impacted leachate after traveling through the tailings. With average annual precipitation around 20 inches per year and about 100 inches of evaporation, there is a net negative atmospheric water balance. This factor was reflected in the results of the seepage modeling.

The operational model assumed that cover material would be placed along the surface of the waste rock buttresses and vegetated as part of the planned concurrent reclamation program. The results of the model indicate evaporation as the dominant component of the water balance. The infiltration and the storage of water in the tailings and waste rock mass were negative, suggesting that the precipitation that contacts the top of the facility is lost to evaporation. Modeled moisture contents within the tailings material decreased over time.

The worst-case operational scenario considered the impacts of depositing tailings with a moisture content greater than 15 percent or an increased moisture content of up to 25 percent following placement due to rainfall. The results of this simulation suggest that the presence of an isolated wet tailings layer does not mobilize moisture into the alluvial formation below the facility. This behavior is typical for unsaturated conditions because the matrix suction in the material exceeds the gravitational force.

The closure model results indicate negative storage and infiltration in the tailings mass upon closure - assuming a one foot thick cover composed of 10-5 cm/s material is placed over the tailings material. This suggests that evaporation is the controlling component of the water balance, and that infiltration is removed from the system through plant transpiration or evaporation. The resulting moisture content within the tailings was approximately five percent, which is consistent with the laboratory-measured values for alluvial material found at the site. Much of the water that does infiltrate and move through the facility is limited to the buttresses. The simulated moisture content of the buttress material was approximately ten percent.

7.7 Dry Stack Operations

The design developed for the tailings involves placement of an initial waste rock starter buttress in the lower portion of the waste rock storage area to provide a dry tailings buttress. Dry tailings will be delivered by conveyor and placed with a stacker. A dozer will be used to spread the dry tailings and provide sufficient compaction for trafficability of the conveyor and stacker as needed. Additional compaction will be conducted in specified areas to limit the possibility of dynamic (earthquake) liquefaction of the tailings material which may cause instability of the stack.

An initial starter buttress will be constructed with waste rock to accommodate approximately six months of tailings storage. Concurrent tailings and waste rock placement will occur throughout the life of the tailings facility. Waste rock will be advanced ahead of the tailings level in successive lifts using the upstream construction method. The waste rock buttresses will have top widths of 150 feet to accommodate two-way haul traffic and outer slopes of 3H:1V with benches to achieve an overall sloped facility of 3.5H:1V. This configuration will allow visual screening of the tailings placement activities from Highway 83 and concurrent reclamation of the lower waste rock buttress slopes.

Dry tailings will be delivered by conveyor from the filter plant down the drainage below the planned diversion ditch and placed with a stacker against the starter buttress. A dozer will be used to spread the dry tailings and provide sufficient compaction for trafficability of the conveyor and stacker, as necessary. A second conveyor will be constructed along the upper ridge area to



allow temporary placement of tailings into the upper drainage area using dozers while the primary conveyor is inactive for movement or maintenance.

The tailings material will generally be placed in 15- to 20-foot lifts by conveyor and trafficked with a dozer, as needed, to provide a suitable surface for the conveyor and stacking system. The outer perimeter of each tailings lift will be compacted with a smooth drum roller as necessary to achieve a higher density, thus providing a suitable foundation for subsequent waste rock buttress construction using the upstream construction method. This will limit the possibility of liquefaction of the tailings under dynamic (earthquake) loading.

The tailings facility consists of two separate areas referred to as the North Stack and the South Stack. The North Stack will be constructed in two phases and operated in Years 1 through 14 and can accommodate approximately 375 Mt of tailings. Phase 1 of the North stack will operate in Years 1 through 5 and Phase 2 will operate in Years 6 through 14. The South Stack will store the remaining 125 Mt of tailings and will be operated in Years 15 through 19.

7.8 Surface Water Control

Stormwater run-on to the North Stack will be limited by diverting the major drainage upstream of the stack area. Stormwater runoff sediments will be captured in a sediment pond located downstream of the tailings stack. During operations, the tailings surface will be sloped away from the waste rock buttresses constructed around the tailings stack to limit potential water impoundment against the buttresses. Ponded water will be pumped to the PWTS pond as necessary to limit infiltration of surface water into the tailings mass.

A waste rock drain (Central Drain) will be constructed starting in Year 6 between the North and South Stack to convey surface water from the drainage above the process plant area. An attenuation pond, designed to temporarily store flows from the 100-year, 24-hour storm event, will be designed to drain through this Central Drain within 30 days. Flows will exit the downstream toe of the tailings facility and pass through a final compliance pond prior to release. The Central Drain will extend to the top of the south tailings stack and allow surface water from the top of the stack to be conveyed through the drain following closure. Material to construct the drain will be from competent and inert waste rock sources.

Stormwater run-on to the South Stack tailings operation will be controlled by impounding the water behind the planned haul road which forms the south terminus of the tailings facility and the north terminus of the waste rock facility. Prior to placement of tailings in the South Stack area, the south face of the haul road fill will be sealed with a low permeability GCL and covered with drain rock for protection and to promote drainage to the low point in Barrel Drainage where a sump will be constructed. The sump will be covered by waste rock starting in Year 10, and the water level in the sump will be monitored over the life of the facility. As necessary to prevent water infiltration into the tailings mass, water collected in the sump will be removed by installing a well pump or by constructing a conduit bored horizontally from the sump area through the ridge east of Barrel Drainage. Preliminary seepage modeling suggests that sufficient water is not expected to infiltrate the waste rock to cause phreatic build-up behind the sealed haul road, and therefore removal of water from the sump is only considered for contingency purposes .

Tetra Tech 16 June 2007


8.0 SITE WATER MANAGEMENT

8.1 General

A Project Site Water Management Plan (SWMP) has been developed to identify appropriate hydrologic methodology and develop design storm events and flows for the Project site for use in the design of the storm water management, water retention, and milling and process facilities. The overall intent of the SWMP is to demonstrate how storm flows and sediment yield will be managed during the active mine life. The main tasks performed included:

•Development of the 2-year, 5-year, 10-year, 50-year, 100-year and probable maximum precipitation (PMP) events using a methodology suitable for the site conditions;

•Generation of basin runoff peaks and volumes for use in design of storm water and sediment control facilities;

•Sizing of sediment control facilities to handle the 10-year design flow event and maintain discharged total suspended solid concentrations equal to pre-mining levels; and

•Sizing of culverts for the access and haul roads and diversion canals with sufficient capacity to pass the design storm event without overtopping.

8.2 Site Conditions

The Project area is an arid region typical of the desert southwest. In general, the terrain is mountainous and rugged, and contributing basins primarily drain to the north and east. Elevations range from 4500 to 6300 feet above mean sea level. There are three main contributing basins in the Project area: Barrel, Wasp, and McCleary Canyons. A network of small arroyos from Wasp and McCleary Canyons feed the main Barrel Canyon drainage, which drains to Cienega Creek, the main downstream tributary.

Vegetation on the site generally consists of Madrean evergreen woodlands and semi-desert grassland. The evergreen woodlands cover the higher elevation portions of the site and are characterized as trees interspersed with grasses and forbs. The semi-desert grasslands are primarily located in the lower elevations and are characterized as open grasslands with widely scattered shrubs and cactuses.

8.3 Climatology

Meteorological records for the immediate vicinity of the Rosemont Project are of limited duration and are available for a period covering 56 to 75 years. More than half of the precipitation recorded at these stations fell during the summer months of July, August, and September. The months with the least recorded precipitation are April, May, and June. In general, annual precipitation has been less than average for the past 10 years, resulting in severe drought conditions. Annual average precipitation for Rosemont, estimated from various sources, ranges from approximately 16 inches to 22 inches. For feasibility design purposes, average climate data from the Western Regional Climate Center Canelo weather station were used for calculations.



8.4 Project Facilities

The SWMP includes storm water management provisions for the open pit, leaching facilities, dry stack tailings facility, plant areas, waste rock storage facility, access roads, diversions, PWTS pond, and compliance point dam. Many of the proposed site facilities will change with time as mining progresses. In order to account for the changes that occur over time, the SWMP considered the progression of the facilities at baseline conditions, Year 0 (pre-production), Year 5, Year 10, Year 16, and ultimate mine conditions.

8.5 Hydrology

Flood frequency precipitation totals and temporal distributions were taken from a published rainfall atlas. Published procedures were used to estimate the 72-Hour General and 6-Hour Local Storms probable maximum precipitation estimates. The United States Corps of Engineers' program HEC-1 was used to generate design flood events and route the flows through basins for each of the 6 scenarios.

8.6 Sediment Yields

The site water management facilities are intended to have sufficient capacity to handle runoff generated throughout the life of the site for a 100-year, 24-hour storm event. Sediment control facilities are designed to reduce the total suspended solids (TSS) load to the minimum practical level for the 10-year, 24-hour storm event. For this feasibility level study, the minimum practical level was defined as equal to a total suspended solids (TSS) concentration approximately equal to existing conditions. There are currently no site-specific TSS concentrations for the Rosemont Project. In order to estimate background TSS levels for the feasibility level study, suspended sediment concentrations from nearby gaging stations were examined and used as a proxy to develop a baseline condition. These stations reported suspended sediment concentrations of less than 10 percent solids, with the large majority of the available data indicating values between 0.1 — 10 percent. Although there is no indication of the level of development or typical conditions in the basins where sampling occurred, it is reasonable to assume the results are fairly representative of native conditions.

Hydraulic calculations related to sediment yield were performed using computer modeling software. Representative grain size distributions were taken from test results of soil and waste rock samples and used to simulate the material that would be displaced during a storm event for the sloped areas.

8.7 Sediment Controls

Based on the modeling results, sediment ponds were located and sized based on topography, available space, and the anticipated sediment generating capacity of the contributing basin. The unlined ponds are typically sized to be no more than 6 to 8 feet deep, utilizing small porous dams constructed of inert waste rock. The ponds are designed to be temporary structures that will collect stormwater flows and settle velocities so that the heavier wash load falls out. Water captured in the structure is then designed to slowly seep out through the rockfill. As the facilities progress, the sediment dams will be abandoned and another sediment dam constructed. Both upstream and downstream faces of the sediment structures will be armored and larger storm events will overtop the length of the dam crest.

Best management practices (BMPs) are recommended as a cost effective method to help reduce surface erosion and lower TSS levels. It is recommended that BMPs are employed

Tetra Tech June 2007 1 8


wherever construction activities will be occurring and soils are disturbed. For this study, it was assumed that the waste rock and dry tails storage areas will be terraced and graded inwards in order to decrease slopes and flow lengths. Silt fences or similar techniques were assumed to be applied whenever active construction occurs. It was also assumed that straw or equivalent will be applied to bare earth areas after construction was completed until revegetation can become established (assumed to be 6 months). Wherever possible, the existing desert shrubs and foliage should be left intact to decrease runoff and sediment loads.

8.8 Surface Water Management

The open pit will be treated like a closed system with all direct rainfall and local runoff being treated as contact water and collected in a sump in the pit bottom. During operations, the captured water will be used for dust suppression or incorporated into the process circuit. Like the open pit, the heap leach facility will be a closed system during the active life of the pad. All rainfall falling on the pad during the active life of the facility will be captured and collected by the solution collection and drainage system. The captured storm flows will be incorporated into the process flows. The plant site will also be a closed system with all precipitation and local runoff collected in the Process Water Tailings Storage (PWTS) Pond and treated as contact water. The PWTS is planned to be constructed in Year 0 and is designed to provide lined storage for the equivalent of 3 days of process flows (69 million gallons) plus the 100-year, 24-hour storm event. The 3 day time period is designed to allow some flexibility and emergency storage in case of a service interruption at the plant facilities. During the operational phase, the surface of the tailings area, which has a fairly impervious layer, will be sloped inward so that all precipitation that falls on top of the active area will remain on top and evaporate. Ponded water can be pumped to the PWTS Pond as needed to limit infiltration into the tailings mass.

The waste rock facilities will be handled in a similar way as the dry tailings storage facility. Initially, screening buttresses will be constructed and material will be stacked in uniform lifts. Concurrent reclamation will progress up the slope areas to limit the potential for erosion and diversion channels will be used to direct runoff to sediment ponds, as needed. The exterior toes of the waste rock buttresses are set back from basin divides by approximately 100 feet, allowing runoff from the sloped areas to infiltrate back into the facility area. The top areas will be sloped to drain towards the open pit or to internal basins, as needed.

A porous drain (Central Drain) constructed of inert waste rock will convey surface water from the drainages located upstream of the plant area through the tailings area and downstream, eventually to the Davidson Canyon confluence. An attenuation impoundment will be placed at the drain headwaters which is designed to store and release flows from the 100-year, 24-hour event within 30 days. Rosemont intends to use this Central Drain in Barrel Canyon to maintain the bulk of premining flows, as much as practicable, into Davidson Canyon during the operational phase and at closure. At closure, the top surfaces of the waste rock and the capped tailings areas will be sloped to direct stormwater runoff into the drain. The porous nature of the waste rock will allow flows to continue downstream, eventually to Davidson Canyon. Diversion of the flows upstream of the Project area will continue to allow pass-through via the attenuation pond into the downstream drainage area.

In the operational phase, runoff and seepage from the waste rock storage facility will be sampled and tested for water quality to verify modeling results. The sediment collection ponds will serve as a final control point for water quality testing prior to discharge to the environment. Suspended sediments will settle out in the collection pond located downstream of the waste rock facility, and the clarified water will be released. A small, porous dam constructed of large inert waste rock materials is planned to be constructed in Year 0 at the outlet of the Barrel



Canyon. Monitoring wells will be located downstream of the embankment. This is the final compliance point were groundwater and surface water flows can be monitored and tested prior to release to the downstream drainage.

Surface water quality will meet the standards required under either the Arizona Pollution Discharge Elimination System General Industrial Stormwater Permit or the National Pollution Discharge Elimination System General Industrial Stormwater Permit. The Arizona permit is currently being reviewed by the Supreme Court for validity and the National permit is expired so at this time it is impossible to determine what standards may apply. Augusta has designed the facilities to control the release of potential pollutants and to manage sediment loading. Any additional standards will be complied with first through engineering controls and secondly through treatment once known.



9.0 RECLAMATION AND CLOSURE

9.1 General

As a component of the overall environmental stewardship policy of Augusta Resource associated with the Rosemont Project, a reclamation plan has been designed to exceed regulatory requirements by creating a unique concurrent reclamation and closure approach. This approach provides a template for development of on-going mitigation measures that will be developed during the design and operations phases of the Project.

Major elements of the reclamation and closure plan are dictated by the regulatory requirements contained in the Arizona Mined Land Reclamation Act, the U.S. Department of Agriculture Forest Service Plan of Operations regulations, and the Arizona Aquifer Protection Program. Although other regulatory requirements may contribute mitigation elements, these three regulatory programs form the framework for the reclamation plan.

Applicable design criteria for the overall approach to mining, processing, and the sequencing of material placement within the final landform (Rosemont Ridge) for optimum reclamation and closure conditions are addressed. The plan contains provisions for protection of the environment during the operations phase via best management practices primarily guided by the protection of surface water and groundwater resources. Sediment transport is addressed through design of stormwater control features and dust control measures.

The proposed reclamation/closure mitigation elements for Rosemont include employment of concurrent reclamation of the facilities. Therefore, reclamation obligations will be incrementally reduced as the operation progresses.

9.2 Closure Concepts

The reclamation plan proposed for the Rosemont site has several key components, referred herein as initiatives. These initiatives provide the physical and philosophical foundation for the reclamation plan and will remain constant throughout the operational life of the facility. These initiatives include: beginning with the end in mind (i.e., design of facilities with closure goals in mind); concurrent reclamation practices; constraining disturbances to a single drainage; minimizing downstream hydrologic disturbances; preparing a comprehensive drainage plan; using modern technology to minimize the generation of impacted water; managing operations to minimize environmental impacts; reclaiming the facilities to blend with surrounding topography; construction of an outer facility shell to reduce visual impacts of the mining operations; salvaging soil resources; select vegetation removal; revegetating reclaimed surfaces; and preparing an estimated closure cost.

One of the major initiatives of the Plan will be to facilitate concurrent reclamation of the outer shell of the waste rock and tailings storage areas and to provide a perimeter buttress to mitigate the visual impact of the Project. Site revegetation will be based on work currently being performed by the University of Arizona, Department of Agriculture.

9.3 Post-Closure Land Uses

Post-mining reclamation objectives for the Rosemont property are expected to be consistent with typical rural values embodied in the use concepts associated with western open space. This is in alignment with currently existing patterns of use, such as dispersed recreation, wildlife habitat, and ranching.



Current and probable post-mine recreational activities include horseback riding, hunting, prospecting, all-terrain vehicle and motorcycle riding, four-wheeling, hiking and bird-watching. Because Augusta is planning concurrent reclamation for the facility, it is anticipated that wildlife disruption to wildlife habitat and use will be minimal. It is expected that by year 10 significant portions of the perimeter buttresses and waste rock facilities will be nearly completely reclaimed.

The Rosemont property is part of an existing ranching facility with over 15,000 acres of grazing rights. The post-mining use for a portion of this facility will include on-going ranching, and it is anticipated that cattle will be used throughout the life of the mine to assist in providing nutrients to the soil as well as a long-term post-mining use of the area.

9.4 Concurrent Reclamation Design

A unique concurrent reclamation plan will be initiated at the Rosemont facility from the initial topsoil stripping through conclusion of operations. Perimeter buttresses will be placed around the waste rock and dry tailings storage areas. Placement of the perimeter buttresses will allow for screening of the project facilities as well as facilitating early reclamation of these areas as they are constructed. Leaching activities will also take place early in the project life, allowing for early reclamation and closure of this portion of the facility. Finally, measures can also be taken to accelerate vegetation on the upper benches of the mine pit. Also illustrated in the reclamation plan are illustrations showing staged reclamation if the operation should cease prior to the currently planned mine life. This information was also used to develop interim reclamation cost estimates.

Potentially acid-generating materials will not be used for construction of the perimeter buttresses, required drains, or channel grading fills. These materials will be placed in the interior of the waste rock storage areas and isolated. .In the tailings areas, the buttresses will be placed so that approximately 50 feet (maximum) of waste rock will extend past the current tailings placement elevation. As the tailings are deposited behind the buttress and approach the buttress elevation, another lift of buttress material will be placed. Once the buttress is raised to a new level, the lower buttress can be contoured, capped, and reseeded as required.

The footprint of Rosemont Ridge will be wholly located within the Barrel Canyon drainage. The ultimate configuration of the waste rock storage area and capped tailings area will be a stable ridge with overall minimum slopes of 3H:1V to a total maximum height of approximately 600 ft. Once the tailings facility reaches its ultimate configuration, the top of the facility can be capped and seeded.

It is anticipated that leach materials will be available early in the process, during pre-production stripping activities. Most of the ore mined for the leaching operations will be placed on the pad by year 6. This will allow closure and reclamation of this facility early in the mine life. It is anticipated that by year 10, leaching and drain-down of the leach pad will have been completed. At that time, the ponds will be decommissioned and residual leach solutions will have been evaporated or processed. Once the ponds are decommissioned and have been deemed closed by ADEQ, the facility will be completely covered by run-of-mine rock. The surface above the heap leach facilities will be graded to drain.

During operations, Rosemont plans to encourage plant growth in the upper reaches of the pit by seeding the upper benches before mining restricts access. It is anticipated that reseeding these areas will provide a visual break on the upper benches. At closure, the open pit will be bermed and/or fenced to restrict access.



Following closure, the Central Drain will continue to act as a conduit for passing stormwater in the upstream Barrel Canyon drainage above the Project site to the lower Barrel drainage. The drain will also take stormwater flows from the top surface of the reclaimed Rosemont Ridge landform.

Operating facilities at the Rosemont site will be demolished at closure. All areas will be investigated for contaminants and any soils, reagents, fuels, etc. will be disposed of off-site. Currently plans call for removing all materials that are above-grade and recontouring for drainage. Sub-grade materials such as foundations will be buried in place and capped and the areas graded for drainage.

9.5 Operating Considerations

Operations and maintenance necessary to ensure the integrity of the Project facility and systems, whose failure could potentially endanger human health and the environment, are limited. The layout of the operating facilities is internal to the waste rock storage area and tailings facility. This ensures that opportunities do not exist for human health to become endangered due to process excursions. With this layout, simple facility security such as fencing can restrict access and ensure the human health is protected.

The facilities are designed to isolate hazardous substances either in tanks, ponds, or operational structures to keep them from being contaminated. The layout and design of the facilities also helps to protect the environment. Redundant sources for power are part of the overall design as needed to manage solutions. Process ponds associated with the leach facility are sized so that there is sufficient freeboard to contain operating volumes and storm water inflows.


woolpewile sm m

HD31V11131

june 2007 · a total of 10 boreholes totaling 877 feet of drilling, 33 test pits, and 18 miles of...

Documents