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Mexico
La Bolsa Project

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 Location:
27 km W from Nogales, Sonora, Mexico

  Project Contacts:
Ave. Ferrocarril No. 99 Piso 1, Local 1 Col. Bellavista
Durango
Durango, Mexico
34047
Phone  ...  Subscription required
Fax+52-618-128-0692
WebsiteWeb
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  • Filings & News

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Overview

StatusCare and Maintenance
Mine TypeOpen Pit
Commodities
  • Silver
  • Gold
Mining Method
  • Truck & Shovel / Loader
Processing
  • Dewatering
  • Filter press plant
  • Smelting
  • Hydrochloric acid (reagent)
  • Heap leach
  • Carbon in column (CIC)
  • Carbon adsorption-desorption-recovery (ADR)
  • Elution
  • Solvent Extraction & Electrowinning
  • Cyanide (reagent)
Mine Life5.3 years (as of Jan 1, 2011)
La Bolsa is a non-core asset that Pan American Silver Corp. intends to divest.


Owners

Source: p. 13
CompanyInterestOwnership
Pan American Silver Corp. 100 % Indirect
Ownership Tree

Deposit Type

  • Volcanic hosted
  • Epithermal
  • Breccia pipe / Stockwork


Summary:

The mineralized system at La Bolsa represents a low sulfidation, volcanic hosted, epithermal precious metal deposit.

The gold-silver mineralization at La Bolsa occurs within stockwork and disseminations that are generally located within a low-angle north-south trending structural zone that dips moderately eastward from its exposure along a north-south-trending ridge. Mineralization is in the form of an oxidized blanket that is sub-parallel to topography and dips shallowly below surface from the base of the ridge. Mineralization has been traced for approximately 1,100 meters (3,600 feet) in length and up to 800 meters (2,600 feet) in width with thicknesses that range from 10 to 60 meters (30 to 200 feet). Recent drilling at La Bolsa continues to extend that zone, and the known mineralization remains open both down-dip and along strike.

Most of the precious metals mineralization at La Bolsa occurs within a series of regionally propylitized andesite flows and flow breccias interbedded with varying amounts of conglomerates, arkosic sandstones, and minor siltstone. While the finer sedimentary material is regionally sourced, the coarser conglomeratic clasts are almost exclusively derived from the andesite flows. Andesite flows are moderately porphyritic and can range from less than one meter up to 100 meters thick. Post depositional faulting and folding as well as the lateral discontinuity of individual beds makes determination of strike and dip difficult. Within this package there is a general transition from sedimentary dominant at the north end of the deposit to volcanic dominant at the south.

While the northwest structural fabric plays a major role at La Bolsa, northeast conjugate sets as well as a range of other orientations possibly associated with emplacement of the intrusives also dissect the area and control mineralization. The main structure and the host to the majority of the mineralization at La Bolsa is the north - northwest trending La Bolsa structure. While moderate to high angle to the northwest, the structure shallows to approximately a 15 to 20 degree east dip at La Bolsa, forming a continuous 10 to 40 meter thick brecciated and fractured zone. Approaching the flow dome the low angle structure forms a series of en-echelon, stair- stepped to the south, flat-lying gashes that eventually die out in the vicinity of the dome.

High angle structures that cut the low angle zone are dominantly north – northwest or northeast in orientation although additional subordinate orientations do occur. High angle structures have at least three observed effects on the low angle zone and mineralization: 1) select structures acted as mineralizing feeders to the low angle zone; 2) intersection of select high-angle structures and the low-angle zone promoted greater fracturing and brecciation resulting in thicker and higher grade pockets of mineralization; 3) post–mineral structures offset the low- angle mineralized zone. Feeder structures tend to be north–northwest or northeast in orientation and have been identified on the north end of La Bolsa hill and extending to the central portion of the project. Typically these feeder structures have also developed increased fracturing at the intersection. Post- mineral high angle faulting is dominantly west–northwest or east-northeast in orientation with limited offsets of up to several tens of meters.


Mining Methods

  • Truck & Shovel / Loader


Summary:

The proposed open pit mining rate for this deposit is based upon a production rate of 8500 ore t/d yielding a mine life of 5.3 years.

The lowest bench mined is at an elevation of 966 m. The highest pit wall elevation is 1,176 m, measured from the highest point of the pit rim. Total vertical depth of mining is 210m.

A bench height of 6 m has been selected for the pit design based on the relatively low production rate and medium size mine equipment used in this study. The block model was initially constructed with a block height of 3 m for a more accurate gold grade estimating procedure. A reblocking exercise was completed resulting in 6m high blocks which were used in mine planning.

Ramp and Haul Road Design
The width of the travelling surface of the mine haul roads inside the pit is 21 m. In addition, there is a requirement for a 1 .5 m high safety berm which will occupy a width of 3 m. Allowance is also made for a 1 m wide drainage ditch. The total required width of the haul road is, therefore, 25 m. The grade of the haul road is generally at the gradient of 10%. The last four segments of the haul road close to the pit floor are designed for single lane only with a total road width of 13.5 m.

The pit haul ramp is constructed over the west wall of the pit with two switch-backs, one in the north and one in the south, thereby taking advantage of the low angle of mineralization.

Waste Dump Design
The western and eastern waste dump designs accommodate 18M and 11M tonnes capacity respectively.
Dumps were designed to receive waste rock material in 18m lifts with 20m catch benches, resulting in an overall slope of 22 degrees. Future re-contouring and reclamation efforts will be simpler and lower cost as the permitted 2.5:1 slope requirements are created. Final design details including berms should be completed prior to a production decision.

The waste dumps will be located east and west of the open pit, within 50 and 20m respectively, from the crest of the pit. The dumps will hold 29.6Mt of waste at completion of mining. The valleys in which the dumps are located, however, have a considerably higher capacity suitable for storing waste from any potential mine expansions.


Crushing and Grinding
Flow Sheet: Source
Crusher / Mill TypeModelSizePowerQuantity
Jaw crusher 1
Cone crusher ....................... Subscription required 240 kW 2

Summary:

Crushing
All ore is classified as oxide and will be campaigned through the crushing circuit. For the purpose of this study it was assumed, based on column tests at this size, that no permeability issues will occur and that the ore should not require any agglomeration pretreatment when crushed to p80% -25mm and stacked to lift heights in excess of 30 m. All ore will be crushed to p80% -25 mm. Lime and barren solution will be added to the ore accordingly, at rates defined through column test results.

Ore will be delivered to the primary crusher by 100-tonne haul trucks and direct dumped through a 900 mm stationary grizzly into a dump pocket, allowing capacity for approximately two truckloads. A rock breaker will be installed to break oversized material, lt will be necessary to sort large boulders in the pit to prevent excessive oversize material from reaching the crusher.

The ore will be fed to a primary jaw crusher at a rate of about 415 t/h, using a vibrating grizzly feeder. The bars on the grizzly decks of the feeder will have a spacing of 88 mm. Based on preliminary process modeling, approximately 46% of the feed material or 188t/h will bypass the crusher. The primary jaw crusher will operate with closed side setting of approximately 88 mm and produce a product with a p80% of approximately 170 mm. The mechanical utilization of the primary crusher has been projected to be 88%, which is typical for this type of crushing circuit.

The secondary crushing circuits will operate seven days per week, 20 hours per day with an average production rate of approximately 415 t/h. Ore will be reclaimed from the crushed ore stockpile using one 1,524 mm x 7,315 mm apron feeders and transferred to the secondary crusher feed bin by a 1,200 mm belt conveyor. Ore will be transferred from the feed bin to a double secondary crusher via a 1,200 mm belt feeder with a pant leg divider. The secondary crushers will be HP300 standard cone crushers or equivalent with 240kW drives and will operate in close circuit. The crusher closed side setting will be 32 mm and will produce a product of approximately 100% passing 32 mm. The crusher product will be transported to the two screen double decks where the oversize will be conveyed to a 50 Ton transfer box to feed back to the secondary crushers and the undersize will be conveyed to a weigh station, lime addition and sampler before the product stockpile at p80% -25mm. The two double screen decks will be 6’x16’ with upper deck at 44mm opening and lower deck at 32mm opening designed to work at 90% capacity with 415 t/h.

High pressure, low volume spray fogging systems will be used for dust suppression at the dump pocket and at conveyor transfer points throughout the crushing facilities.


Processing

  • Dewatering
  • Filter press plant
  • Smelting
  • Hydrochloric acid (reagent)
  • Heap leach
  • Carbon in column (CIC)
  • Carbon adsorption-desorption-recovery (ADR)
  • Elution
  • Solvent Extraction & Electrowinning
  • Cyanide (reagent)

Flow Sheet: Subscription required

Summary:

It was determined to begin the Project with a 3 million t/y crushing and heap leaching facility to process La Bolsa ores. The mine will continue at this production rate for approximately five years. The plant has been designed to produce the specified production rate. Preliminary crushing plant design work indicated that the equipment necessary to produce 3Mt/y would have a maximum capability of processing up to 3.38Mt/y.

Heap Leach Pad Loading
The crushed ore will be conveyed to the heap leach pad via grasshopper conveyors and a radial stacker system. Sufficient room to store 8 hours of normal operation will be provided at the stockpile in front of Crushing circuit.

The heap will be loaded in 6 m high lifts to a maximum height of 50 m. The total leaching cycle will be approximately 70 days so the total ore under leach at any one time will be 70 days production or approximately 560,000 t.

Heap Leach Pad Layout
The pad will be constructed i ........

Recoveries & Grades:

CommodityParameterAvg. LOM
Silver Recovery Rate, % 7
Silver Head Grade, g/t 9
Gold Recovery Rate, % 72
Gold Head Grade, g/t 0.63

Projected Production:

CommodityUnitsLOM
Silver oz 315,108
Gold oz  ......  Subscription required
All production numbers are expressed as metal in doré.

* According to 2011 study.

Reserves at June 30, 2021:

CategoryTonnage CommodityGradeContained Metal
Measured 10.8 Mt Silver 10 g/t 3.5 M oz
Measured 10.8 Mt Gold 0.7 g/t 242.8 koz
Indicated 10.6 Mt Silver 8 g/t 2.7 M oz
Indicated 10.6 Mt Gold 0.54 g/t 184.3 koz
Inferred 13.7 Mt Silver 8 g/t 3.3 M oz
Inferred 13.7 Mt Gold 0.51 g/t 224.6 koz

Commodity Production Costs:

CommodityUnits2021
Cash costs Gold USD 516 / oz *†
Assumed price Silver USD 14 / oz *
Assumed price Gold USD 850 / oz *
* According to 2011 study / presentation.
† Net of By-Product.
Subscription required - Subscription is required.

Operating Costs:

Units2021
OP mining costs ($/t milled) USD 7.51 *
Processing costs ($/t milled) USD  ......  Subscription required
G&A ($/t milled) USD  ......  Subscription required
* According to 2011 study.
Subscription required - Subscription is required.

2011 Study Costs and Valuation Metrics :

MetricsUnitsLOM Total
Initial CapEx $M USD  ......  Subscription required
Sustaining CapEx $M USD  ......  Subscription required
Closure costs $M USD  ......  Subscription required
Total CapEx $M USD  ......  Subscription required
OP OpEx $M USD  ......  Subscription required
Processing OpEx $M USD 54.9
G&A costs $M USD 0
Total OpEx $M USD  ......  Subscription required
Gross revenue (LOM) $M USD  ......  Subscription required
Net revenue (LOM) $M USD  ......  Subscription required
Pre-tax Cash Flow (LOM) $M USD  ......  Subscription required
Pre-tax NPV @ 0% $M USD  ......  Subscription required
Pre-tax IRR, %  ......  Subscription required
Subscription required - Subscription is required.

Proposed Heavy Mobile Equipment as of January 10, 2011:
HME TypeModelSizeQuantity
Backhoe 100 HP ....................... Subscription required
....................... Subscription required ....................... Subscription required ....................... Subscription required
....................... Subscription required ....................... Subscription required ....................... Subscription required
....................... Subscription required ....................... Subscription required ....................... Subscription required
....................... Subscription required ....................... Subscription required ....................... Subscription required
....................... Subscription required ....................... Subscription required ....................... Subscription required
....................... Subscription required ....................... Subscription required ....................... Subscription required
....................... Subscription required ....................... Subscription required ....................... Subscription required ....................... Subscription required
....................... Subscription required ....................... Subscription required ....................... Subscription required ....................... Subscription required
....................... Subscription required ....................... Subscription required ....................... Subscription required
Subscription required - Subscription is required.

Mine Management:

Job TitleNameProfileRef. Date
....................... Subscription required ....................... Subscription required Subscription required Oct 8, 2021
Subscription required - Subscription is required.

Staff:

EmployeesYear
Subscription required 2011

Corporate Filings & Presentations:

DocumentYear
................................... Subscription required 2021
................................... Subscription required 2020
Year-end Mineral Reserves 2018
Annual Information Form 2014
Pre-Feasibility Study Report 2011
Subscription required - Subscription is required.

Subscription required - Subscription is required.

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