TECHNICAL MEMORANDUM

Transcription

1 FOR INTERNAL DISCUSSION PURPOSES ONLY TECHNICAL MEMORANDUM TO: Augusta Resource Corp. ATTENTION: Jamie Sturgess FROM: Troy Meyer Project Manager, Vector Colorado LLC (Vector) DATE: June 5, 2006 SUBJECT: Conceptual Heap Leach Pad Design Layout PROJECT #: Rosemont Mine / General As requested by Augusta as part of the Preliminary Economic Assessment for the Rosemont Mine, this report presents conceptual design and cost estimates for the development of the Heap Leach Pad proposed for the Project. The conceptual design work for this report was requested by Augusta to determine the general level of pad layout for a +/-35% cost estimate. The preliminary general facilities arrangement for the project is presented on Figure 1. The leach pad layout is shown on Figure 2 with a typical section and details shown on Figure 3. An Excel spreadsheet of calculations for approximate pad tonnage limits and lift placement time for pad startup and expansion siting purposes is shown on Table Background The Rosemont project site lies in a high, sparsely populated intermountain area approximately 35 miles southeast of Tucson, Arizona on the east slope of the Santa Rita Mountains. Access to the site is via Highway 83 which connects Interstate 10 with the town of Sonoita. Augusta controls a large portion of the site including the Hidden Valley Ranch and Rosemont Ranch. The Coronado National Forrest is custodian of much of the slopes of the Santa Rita Mountains. Rosemont Heap Leach Conceptual Design Page 1

2 Vector Colorado Technical Memorandum Page 2 FOR INTERNAL DISCUSSION PURPOSES ONLY 1.2 Site Visit Troy Meyer, P.E. of Vector visited the Rosemont property March 8 through 9, 2006 to perform site reconnaissance and familiarize Vector with the proposed facility locations, site features, surficial geology and soils. Photographs taken during this site visit are presented in Attachment A. 2.0 Leach Pad Siting The general leach pad siting location was determined by Vector, Augusta and WLR Consulting as part of the overall mine and waste rock dump layout as shown on Figure 2. Ore production and process flows for conceptual siting purposes were discussed with Washington Group International (WGI) to be 11,000 tons per day (tpd) with 3,100 gpm flow to the PLS flow and recycle flow from a mid-grade PLS pond of 3,857 gpm. The preliminary design incorporates a raffinate bleed rate of 1,500 gpm to agitation leach and a raffinate pond flow of 4,600 gpm resulting in an overall total application rate of 6,957 gpm including recycle (see Table 1). Pad drainage toward the pit was preferred for optimizing waste rock layout around the pad and associated process ponds and for closure drainage planning. The total ultimate ore tonnage is currently planned at approximately 60 million tons. The pad site will require significant grading to achieve this configuration with initial grading via cut/fill operations and borrow from the nearby pit area. Subsequent expansion pad grading can then be performed by controlled waste rock placement. The drain fill for the pad overliner system likely will include selected durable crushed rock from the pit overburden supplemented with closely spaced 3 inch diameter perforated drain pipes. 3.0 Ore Stack Layout The ore stacking sequence assumed approximate 25 ft ore lifts stacked in 10 lifts to the 250 ft heap height at overall 2H:1V side slopes. A conceptual cross section of the pad and ore stack is shown on Figure 2. The ore tonnages and ore lift times are approximate and presented on Table 1 attached. The Phase I pad can accommodate approximately 17.3 mt (4.3 years of production at 11,000 tpd) to the 125 ft height. The Phase II pad will accommodate approximately 21.5 mt (5.3 years of production) to the 125 ft height with the remaining tonnage stacked over the entire pad area to the 250 Rosemont Heap Leach Conceptual Design

3 Vector Colorado Technical Memorandum Page 3 FOR INTERNAL DISCUSSION PURPOSES ONLY height. An ore density of 1.6 tons per cubic yard was assumed for the conceptual layout. 4.0 Conceptual Pad Design 4.1 General The startup pad construction will include the site grading fill for controlled drainage to the collection ditch and ponds, perimeter and interior pad cell berms as needed, the pad drain fill cover, the drain pipes within the drain fill, and the temporary diversion ditch uphill of the pad limits. The state of practice composite pad, collection ditch and pond liner systems are the major cost components for the startup pad. The intermediate Phase II expansion pad will require an additional downhill collection ditch but will not require additional pond liner. The ultimate heap stack above the startup and expansion pad heaps will require minimal additional pad costs. 4.2 Startup Pad The startup (Phase I) and Phase II pad areas are about 3.1 million sq. ft. each and will include 60 mil LLDPE pad liner. The downhill collection ditch tie-in to the pad toe berm is about 35 ft wide by 1390 ft long at about 48,000 sq ft of 80 mil HDPE liner. The liner system will include a geosynthetic clay liner (GCL) underlying the geomembrane to form a double lined pad. The process pond will be double lined and the storm overflow will be single lined with an 80 mil HDPE top liner and the process ponds (PLS and midgrade) bottom liner will be 60 mil LLDPE liner with geonet leak detection between liners. The process pond may include netting or bird balls for bird protection. The downhill toe site grading for the ultimate 250 ft ore stack will require about a 375 ft of textured geomembrane liner for adequate slope stability based on previous experience. The site grading volume for Phase I startup pad is about 1.7 million cubic yards (cy) of cut to fill and 630,000 cy of fill from borrow without considering any bulkage or shrinkage from borrow to fill conditions. Future design may allow optimization of the pad layout with respect to grading costs, however this is thought to represent a conservative estimate of the required grading. The temporary uphill diversion channel south of the pad is about 2100 ft long and could be eliminated once waste rock is placed in this area. The permanent uphill diversion Rosemont Heap Leach Conceptual Design

4 Vector Colorado Technical Memorandum Page 4 FOR INTERNAL DISCUSSION PURPOSES ONLY channel west of the pad is about 5900 ft long. The diversions are likely less than 3 ft in depth in a V ditch cut along a 0.5% contour grade. 4.3 Expansion Pad The Phase II expansion pad costing will include additional 10 million cy pad grading fill which was assumed to be waste rock placed and compacted by mine haul trucks. The downhill collection ditch tie-in to the pad toe berm is about 35 ft wide by 3640 ft long (including the northern ditch) for about 127,400 sq ft of 80 mil HDPE liner. The liner system will include a geosynthetic clay liner (GCL) underlying the geomembrane to form a double lined pad. Lump sump costs were estimated for diversion ditches, perimeter and interior berms, sumps, pumps and pipelines. Raffinate pond construction costs were not estimated and were assumed to be included in work by others for the SX/EW plant. Unit rate or lump sump cost assumptions for this conceptual design estimate are included in Table 2 attached. Attachments: Table 1 Ore Stack Tonnage Estimates Table 2 Quantities and Cost Estimate Figure 1 General Facilities Arrangement Figure 2 Leach Pad Layout Figure 3 Leach Pad Sections and Details Rosemont Heap Leach Conceptual Design

5 TABLE 1 - ORE STACK TONNAGE ESTIMATE PROJECT: ROSEMONT PROJECT DATE: APR 2006 PROJECT # ORE PRODUCTION: 11,000 TONS/DAY LEACH CYCLE TIME: 93 DAYS ORE HEAP SLOPE: 2 H TO 1 V ACTIVE AREA: 688,889 SQUARE FT ORE DRY DENSITY: 1.6 TONS/CUBIC YARD APPLICATION RATE: GPM/SF LEACH RATIO: 3.8 TON SOLUTION/TON ORE TOTAL APPLICATION FLOW: 6,957 GPM FLOW TO HIGH GRADE POND: 3,100 GPM (from WGI) RECYCLE FROM MID-GRADE POND: 3,857 GPM RAFFINATE BLEED TO AGITATION LEACH: 1,500 GPM (from WGI) RAFFINATE POND FLOW: 4,600 GPM ORE LIFT BOTTOM BOTTOM TOP TOP LIFT TOP LIFT LIFT ACCUM. ACCUM. LIFT ACCUM. ACCUM. NUMBER LENGTH1 LENGTH2 LENGTH1 LENGTH2 AREA HEIGHT VOLUME VOLUME TONNAGE TIME TIME TIME (#) (FT) (FT) (FT) (FT) (SQ FT) (FT) (CU FT) (CU FT) (TONS) (DAYS) (DAYS) (YRS) Starter Pad 1 2,300 1,410 2,200 1,310 2,882, ,562,500 76,562,500 4,537, ,200 1,310 2,100 1,210 2,541, ,787, ,350,000 8,554, ,100 1,210 2,000 1,110 2,220, ,512, ,862,500 12,080, , ,000 1,110 1,900 1,010 1,919, ,737, ,600,000 15,146, , ,900 1,010 1, ,638, ,462, ,062,500 17,781, , Expansion Pad(s) 1 Expansion Phases 1 2,300 1,410 2,200 1,410 3,102, ,312,500 79,312,500 4,700, , ,200 1,410 2,100 1,410 2,961, ,787, ,100,000 9,191, , ,100 1,410 2,000 1,410 2,820, ,262, ,362,500 13,473, , ,000 1,410 1,900 1,410 2,679, ,737, ,100,000 17,546, , ,900 1,410 1,800 1,410 2,538, ,212, ,312,500 21,411, , Ultimate Expansion Pad 1 1,800 2,320 1,700 2,220 3,774, ,332,624 99,332,624 5,886, , ,700 2,220 1,600 2,120 3,392, ,532, ,865,170 11,192, , ,600 2,120 1,500 2,020 3,030, ,232, ,097,625 15,946, , ,500 2,020 1,400 1,920 2,688, ,432, ,529,971 20,179, , ,400 1,920 1,300 1,820 2,366, ,132, ,662,188 23,920, , Total Tons 63,113,

6 TABLE 2 - QUANTITIES AND COST ESTIMATE Rosemont Heap Leach and Site Civil Estimated Costs based on Conceptual Designs FOR INTERNAL DISCUSSION ONLY Description Unit Quantity Unit Cost Cost Comments Phase I Leach Pad and Process Ponds Pond Pad Clearing and Grubbing Acre 259 $1,000 $259,412 Heap and Pond Foundation Preparation (Cut to Fill) yd 3 1,744,000 $0.80 $1,395,200 Includes estimate for perimeter fill to provide possitive drainage to diversion Heap and Pond Foundation Preparation (Fill from Borrow) yd 3 629,000 $1.20 $754,800 Assumes borrow source is within 1/2 mile of the pad Diversion Ditches lump sum 1 $250,000 $250,000 Approx. 8000' v-ditch 2' deep Perimeter & Interior Berms and Ditches lump sum 1 $150,000 $150,000 18' wide perimeter berms and 25' wide permiter ditches Heap Geomembrane Liner ft 2 3,243,000 $0.45 $1,459, mil LLDPE Perimeter Ditch Liner ft 2 49,000 $0.45 $22, mil HDPE Heap Liner Bedding (GCL) ft 3 3,243,000 $0.40 $1,297,200 Assumes fill can be compacted for suitable surface Pad Drain Piping ft 2 3,243,000 $0.10 $324,300 3" dia perforated secondary pipes and 6" perforated primary pipes Drain Cover Fill (2ft thickness crushed rock) yd 3 240,222 $5.00 $1,201,111 Assumes durable rock is available from pit Pregnant Solution Pond (PLS) Excavation yd 3 111,000 $2.20 $244,200 Assumes soil or rippable rock Pregnant Solution Pond Liner (Double) ft 2 135,000 $0.90 $121, mil HDPE top liner, 80 mil LLDPE bottom liner Pregnant Solution Pond Liner Bedding (GCL) ft 2 135,000 $0.40 $54,000 Assumes excavation can be compacted for suitable surface Mid Grade PLS Pond Excavation yd 3 100,000 $2.20 $220,000 Assumes soil or rippable rock Mid Grade PLS Pond Liner (Double) ft 2 125,000 $0.90 $112, mil HDPE top liner, 80 mil LLDPE bottom liner Mid Grade PLS Pond Liner Bedding (GCL) f t2 125,000 $0.40 $50,000 Assumes excavation can be compacted for suitable surface Leak Detection Geonet and Sumps lump sum 1 $100,000 $100,000 Pumps and Pipelines lump sum 1 $750,000 $750,000 Includes PLS and raffinate systems Stormwater Pond Excavation yd 3 268,000 $2.20 $589,600 Assumes soil or rippable rock Stormwater Pond Liner ft 2 298,000 $0.45 $134, mil HDPE liner Stormwater Pond Bedding (GCL) ft 2 298,000 $0.40 $119,200 Assumes excavation can be compacted for suitable surface Subtotal $9,608,523 Phase II Leach Pad Expansion Heap Foundation Preparation (Compaction Only) yd 3 9,963,000 $0.20 $1,992,600 Assumes waste rock fill will be supplied by the Mine and compacted by haul trucks Perimeter & Interior Berms lump sum 1 $150,000 $150,000 18' wide perimeter berms and 25' wide permiter ditches Heap Geomembrane Liner ft 2 3,243,000 $0.45 $1,459, mil LLDPE Perimeter Ditch Liner ft 2 127,400 $0.45 $57, mil HDPE Heap Liner Bedding (GCL) ft 3 3,243,000 $0.40 $1,297,200 Assumes fill can be compacted for suitable surface Pad Drain Piping ft 2 3,243,000 $0.10 $324,300 3" dia perforated secondary pipes and 6" perforated primary pipes Drain Cover Fill (2ft thickness crushed rock) yd 3 240,222 $5.00 $1,201,111 Assumes durable rock is available from pit Subtotal $6,481,891 TOTAL HEAP LEACH $16,090,415

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10 APPENDIX A SITE PHOTOS

11 Rosemont Project Appendix A - Page 1 Tailings Facility Siting Study A_Site Photos_Heap Leach.doc Barrel Canyon Area Near proposed heap leach site Barrel Canyon Basin near top of basin looking north

12 Rosemont Project Appendix A - Page 2 Tailings Facility Siting Study A_Site Photos_Heap Leach.doc Arcosic near surface soils in Barrel basin Typical rocky ground surface at Rosemont site