Canada

Minto Mine

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Overview

Mine TypeUnderground
Commodities
  • Copper
  • Gold
  • Silver
Mining Method
  • Longhole upper cut retreat
Production Start2007
ShapshotThe Minto Mine Property includes underground mining operations, a processing plant that produces a high-grade copper, gold and silver concentrate.

In May 2023, the Minto Metals ceased all operations at the Minto Mine and the Government of Yukon assumed care and control of the Minto Mine.

The Yukon Supreme Court appointed PricewaterhouseCoopers (PwC) as the receiver in charge the mine's assets.

PwC is now (March 2024) seeking court approval for a plan to liquidate the abandoned mine's assets and pay back creditors.

Owners

SourceSource
CompanyInterestOwnership
Pembridge Resources PLC. 11.2 % Indirect
Cedro Holdings I, LLC. 27.7 % Indirect
Copper Holdings, LLC 37 % Indirect
Minto Metals Corp. (operator) 100 % Direct
The Minto Metal Corp. was incorporated on November 23, 2021, as a result of an amalgamation performed through a reverse-take-over of 1246778 B.C. Ltd. by Minto Explorations Ltd. Minto Metals operates the Minto mine.

Copper Holdings, Cedro Holdings and Pembridge, the Minto’s principal shareholders, own, or exercise direction or control over, directly or indirectly, approximately 37.0%, 27.7% and 11.2% respectively, of the Minto’s total issued and outstanding Common Shares on a non-diluted basis.

On June 29, 2023, the Supreme Court of British Columbia appointed PricewaterhouseCoopers Inc., (PwC) as receiver and manager without security, over certain assets of Minto Metals.

PwC has put the mine up for sale in the summer of 2023. In a submission to Yukon Supreme Court March 27, 2024, PwC said a plan to sell the mine project has failed, and it's now proposing to liquidate all the assets.

Contractors

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Deposit type

  • Porphyry

Summary:

Mineralization
The primary hypogene minerals are chalcopyrite, bornite, chalcocite, and minor pyrite. Copper sulphide minerals occur mainly as disseminations, foliaform stringers and as net-textured copper sulphides. The intensity of copper sulphide minerals increases with ductile deformation. The highest-grade mineralization occurs as semi-massive net-textured intergrowths of bornite and chalcopyrite. Typical bornite-chalcopyrite ratios are 3:1, and net-textured bornite is especially abundant in melanosome (mafic sections), where it forms higher grade (1 - 2% Cu) domains. Covellite locally occurs rimming bornite. Both bornite and chalcopyrite are commonly replaced by secondary digenite. Molybdenite locally occurs intergrown with net-textured copper sulfides.

Hessite (a gold telluride), native gold, and electrum occur as inclusions in bornite, accounting for high gold recoveries in copper concentrate. Coarse free gold has also been identified in late chloritic fractures, which may be the result of secondary hydrothermal enrichment. Copper sulphide mineralization is almost always associated with elevated biotite and magnetite.

At the Area 2, Area 118, Copper Keel, and Minto East deposits, mineralization occurs mainly as
disseminated and foliaform grains, and the net-textured domains are generally absent. The
mineralogical assemblage consists mainly of chalcopyrite-bornite-magnetite and minor pyrite.

The mineralogy of the Minto North deposit differs from the other deposits. At Minto North bornite is dominant over chalcopyrite and occurs as net-textured domains to massive lenses up to 2 m thick. Precious metal grades are elevated, and rare visible gold also occurs.

At the Minto North 2 deposit the dominant copper assemblage is chalcopyrite-bornite-chalcocite. Chalcocite commonly occurs as disseminated or local intergrowths with magnetite.

At the Ridgetop and Copper Keel South deposits, mineralization is subdivided into a near-surface horizon of supergene oxide, and a lower zone of more typical sulphide mineralization. The supergene copper oxide mineralization is characterized by malachite, chrysocolla, and local azurite. Oxidized magnetite and pyrite are also common. The mixture of oxide material with sulphides is commonly referred to as ‘POX’ (partially oxidized material). The lower zone is marked by an assemblage of chalcopyrite, magnetite, minor pyrite, and only minor amounts of bornite. Chalcopyrite occurs as disseminations and foliaform stringers. Magnetite is present as disseminated grains, local stringers and bands up to 0.3 m in thickness.

Copper grades increase progressively northwards from the lower grade material found at the Ridgetop towards the highest-grade material at the Minto North deposit (Mercer and Sagman, 2012). This trend is also observed on a regional scale, indicated by lower grade (chalcopyritedominant) mineralization of the Carmacks Copper deposit, progressively increasing northwestward in grade towards the bornite dominant higher-grade Minto deposits. This change in grade is likely caused by the increasing northward metamorphic gradient responsible for higher copper grades.

DEPOSIT TYPES
Since discovery of the Carmacks Copper and Minto deposits in the 1970s, several models have been proposed for their genesis, including (1) copper mineralization in digested Triassic volcanic rocks (A. Archer, pers. comm., in Sinclair,1977), (2) metamorphosed red-bed copper (Kirkham, 1974), (3) deformed and metamorphosed porphyry copper-gold (Pearson and Clark, 1979; Tafti, 2005), (4) iron-oxide copper gold (IOCG; Mercer and Sagman, 2012), and (5) a shear-hosted hydrothermal system generated in the ductile root zones of a porphyry system (Hood, 2012).

The most current geologic and geochronologic constraints require that mineralization was an inherited feature of a Late Triassic protolith, which was subsequently metamorphosed in the latest Triassic and texturally modified during subsequent magmatism in the Early Jurassic. For this reason, a syn-metamorphic or syn-intrusion model for mineralized material formation is unsupported. Furthermore, deep emplacement of the Minto pluton cannot be used as a proxy for the emplacement depth of mineralization at the Minto mine, as the emplacement of the Minto pluton postdates mineralization by >10 Ma. Similarly, the oxidation state of the pluton and the widespread presence of alteration hematite (Tafti, 2005; Hood et al., 2008) is irrelevant to the deposit that formed >10 Ma prior to the emplacement of the pluton. Lastly, the structurally controlled distribution of mineralized material is also not a demonstrably primary feature of either of the deposits, as material was melted and remobilized during the emplacement of the Minto pluton. In addition, the intensity and extent of alteration that is common in IOCG deposits is not well-developed at Minto and mineralized zones are not breccia hosted. As such the IOCG deposit model is not considered viable for the Minto deposit.

The recognition that the least deformed and migmatized host rocks at the Carmacks Copper deposit contain low-grade, disseminated Cu as a chalcopyrite-pyrite assemblage hosted in biotite-bearing and K-enriched host rocks is consistent with a porphyry copper deposit model. Hypogene grades from ~0.2 to 1% Cu and ~0.1 to 1 g/t Au at the Carmacks Copper, Minto, and Stu systems are within the range of typical porphyry copper grades globally (e.g., Kesler et al., 1992). The caveat to this is that post processes may have affected grade. Copper to gold ratios of 23,000 to 34,000 are also typical of gold-bearing porphyry copper deposits. Although no intrusive phases related to the pre-metamorphic hydrothermal system are recognized at Carmacks Copper, it is permissible that the population of 217.53 ± 0.16 Ma igneous zircons represents magmatic activity temporally and genetically related to >212.5 ± 1.0 Ma copper mineralization.

Hydrothermal features such as veins, alteration halos, or hydrothermal breccias are not recognized through the overprinting effects of metamorphism, penetrative deformation, and partial melting. However, the general lack of quartz rich domains within metamorphic rocks suggests that quartz-sulphide veins were likely absent from the protolith. It is therefore likely that protolith mineralization was introduced as disseminations or as sulfide dominant veinlets in conjunction with widespread biotite - magnetite alteration. Together, these observations suggest that the Carmacks Copper and Minto deposits each preserve the high-temperature potassic core of a porphyry copper system. Several features listed above are also consistent with alkalic porphyry affinity:
1. Low abundance of pyrite;
2. Association with alkaline intrusions;
3. Low volume or absence of hydrothermal quartz; and
4. Cu-Au metal tenor (compared to Cu-Au - Mo in calc alkalic porphyry systems).

The interpretation of the Carmacks Copper and Minto deposits as metamorphosed porphyry copper systems is further supported by their temporal and lithotectonic affinity with porphyry belts in British Columbia. First, correlation of metavolcanic host rocks at Carmacks Copper with Stikinia arc equivalents in Yukon (Kovacs, 2018) supports a similar tectonic and geodynamic setting to porphyry systems in British Columbia. Second, the ~217 to 213 Ma age of mineralization at Carmacks Copper constrains the system to within the prolific 227 to 178 Ma epoch of porphyry Cu mineralization in the Stikinia and Quesnellia arcs of British Columbia, and broadly coincident with peak productivity in Stikinia (e.g., Schaft Creek ~222 Ma, Galore Creek ~210–205 Ma, Red Chris ~204 Ma; Logan and Mihalynuk, 2014, and references therein).

Reserves

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Mining Methods

  • Longhole upper cut retreat

Summary:

MINING METHODS Minto utilizes both underground and open pit mining methods to extract the mineralized material for processing. In the past, the operation performed mostly open pit mining using a standard truck and shovel fleet, which was contractor operated. Since the restart of operations in 2019, Minto has undertaken only underground mining, using a ramp access system with longhole upper cut retreat mining with standard rib and pillar support. The longhole stopes are left open when completed. Underground mining is planned for Copper Keel, Minto East, Area 2 Minto North and Ridgetop. Open pit mining is planned for both Ridgetop and 118 deposits. 2023 Mining Plan: Next phase of mining will include Area 2, Minto North 2 and the development of Ridge Top pit to optimize the camp footprint and open Mill capacity. Underground Mining Methods All the underground mineralized zones can be described as lenses of foliated metamorphic rocks bounded at their hanging wall and footwall contacts by under formed granodiorite host rock. The metamorphic zones are typically 5 m to 30 m thick. These zones typically dip at 20° to 35°. Typical depths are 200 m to 250 m below surface, with vertical thickness of 5 m to 25 m. The mineralized zones bifurcate, which means that a mineralized zone can contain a significant amount of waste, or that thinner zones can merge with larger zones. A bifurcating geometry complicates geological modelling and may increase internal dilution. In Copper Keel, the footwall can undulate, and the operation has undertaken drilling to better delineate the footwall contact. The width and dip of mineralized zones are locally variable. The change in thickness might be as much as an order of magnitude over less than 30m in horizontal distance. At least some of the irregularity in the geometry and thickness of the mineralized zones is due to small-scale and large-scale structural displacements. This study utilizes the current method of underground extraction of longhole upper cut retreat mining with rib pillars. This method is considered appropriate for the modelled geology. Mine Design Historically the M-zone, Area 118, Area 2 and Minto East zones were all mined using a longhole upper cut retreat mining method. The currently active Copper Keel zone is mined in the same manner. The mining method requires a series of parallel sill drifts to be developed along the strike of the deposit, following the footwall contact. From these 6 m wide and 4.3 m high sill drifts, a top hammer longhole machine drills rings of 3” diameter up-holes into the deposit, drilling to the hanging wall contact. To provide adequate void space for blasted muck when initiating a new stope, a 1.8 m x 1.8 m inverse raise is drilled. The raise is composed of six 6-inch diameter reamed holes, which are left unloaded, surrounded by a pattern of eleven 3½-inch diameter blast holes. Generally, each stope is initiated with one or more rings of blast holes on either side of the inverse raise; subsequent blasts increase the number of rings fired simultaneously to take advantage of the void space in each block. Production drift centerlines are spaced 20 m apart. From each 6 m wide sill drift, drill holes are fanned out to blast a 14 m wide stope. Rib pillars with 6 m width separate neighboring stopes and support the hanging wall. For the Area 2 zone, production drift centerlines were 20 m apart and stope and pillar widths were varied based on the thickness (stope and pillar height). Historically typical stope widths were 15 m and pillar widths were 5 m. The mining method does not use backfill. Small quantities of development waste are sometimes placed in completed stopes to reduce waste haulage requirements to surface. For purposes of this study all excavated material is assumed to be hauled to surface. Underground Access The main ramp of the Minto Underground extends to the currently active Copper Keel zone. The upper ramp is 5.0 m wide and 5.0 m high; the ramp below the 690 level has been driven at dimensions of 5.0 m wide and 5.5 m high to provide additional clearance between vent ducting and haul trucks. This access is currently used for all mineralized material and waste haulage, personnel/equipment access, and services. It is also used as an exhaust airway. Additional ramps to surface have been proposed for both Copper Keel and Ridgetop. This will assist with both haulage and ventilation of the mine. Minto North will be accessed via a single ramp collared from the Minto North eastern pit wall. Ramps and access development will be driven at a maximum +/- 15% grade. Stope Layout The 6.0 m(w) x 4.3 m(h) crosscut drift has typically been designed on the down-dip side of the stope to better manage dilution and increase mining recovery. Longhole stopes have been designed at 14 m wide with a 6 m rib pillar between stopes. Open Pit Mining Methods In the past, open pit mine development and production was performed by contractor (Pelly Construction Ltd.). Engineering and planning were completed internally by Minto personnel. Open pit development of the Ridgetop and 118 deposits consider a similar arrangement; mining will be conducted using contract equipment, under the guidance of Minto technical staff. Deposit Characteristics for Open Pit Mining The Ridgetop pit shares a similar geological setting to the deposits previously mined at Minto. Copper mineralization is contained in a series of sub-horizontal stacked, foliated migmatitic lenses. These lenses are characterized by sharp contacts with the surrounding host rock. These deformed and migmatized metamorphic zones are highly variable in the content of their mineralization. The western regions of the proposed Ridgetop pits are anticipated to contain 1 m to 5 m of soil overburden, deepening to the east to from 5 m to 15 m on the east side and with a maximum depth of 12 m at the northeast portion of the Ridgetop pit. The bedrock at Ridgetop is generally weathered to a depth of approximately 45 m to 70 m below current ground surface. Open Pit Geotechnical Characterization and Design Parameters Geotechnical characterization and open pit design criteria for the Area 2, Area 118 and Ridgetop open pits were initially characterized by SRK (2009). Additional geotechnical characterization was carried out for the Ridgetop pit by JDS (2018). Mining of the Area 2 and Area 118 open pits has been completed with no significant geotechnical issues. No mining has occurred to date at Ridgetop.

Comminution

Crushers and Mills

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Processing

  • Flotation
  • Dewatering

Summary:

Introduction
The processing plant at the Minto Mine was constructed in 2006-2007 and commercial production was declared in October 2007, after a four-month long commissioning period. The processing plant operated continuously until it was placed on care and maintenance in October 2018, following discontinuation of mining operations. The operation was acquired by the current owners, Pembridge Resources, and the processing plant was recommissioned in October 2019.

The Minto process plant design incorporates standard industry comminution, flotation and dewatering circuits to produce a final copper concentrate product. The plant was designed to achieve an availability of 92% and has demonstrated the capacity to process an average of 4,000 dry metric tpd with a peak operation at 4,400 tpd sustained over a few days.

Flotation
The flotation circuit is comprised of 4 groups of flotation cells: Rougher, Scavenger, Cleaner and Re-cleaner.

Rougher flotation is conducted using three 1,350 ft3 tank cells each powered by a 75 HP motor. The rougher concentrate is pumped to the Cleaner circuit.

The rougher tailing is pumped to the Rougher-Scavenger circuit, a bank of four 500 ft3 flotation cells, each powered by a 40 HP motor. The Rougher-Scavenger concentrate is pumped to the cleaner circuit. The Rougher-Scavenger tailing is the final tailing from the flotation plant and is pumped to the tailings building.

The Cleaner circuit consists of a bank of four 350 ft3 tank cells each powered by a 25 HP motor. The Rougher concentrate, Rougher-Scavenger concentrate, and the Re-Cleaner tailings are combined in the Cleaner circuit feed. The cleaner concentrate is pumped to the Re-cleaner circuit. The Cleaner circuit tailings are gravity fed to the Rougher-scavenger circuit.

The Cleaner concentrate is pumped to a series of six 100 ft3 Re-Cleaner cells, each with a 15 HP motor. The re-cleaner concentrate is gravity fed to the concentrate thickener and dewatering circuit. The Re-Cleaner tailings are pumped to the Cleaner circuit.

Precious Metals Recovery
Currently, precious metals are recovered to the flotation concentrate as a by-product of flotation.

The Minto milling circuit includes a centrifugal “Knelson” concentrator which is currently not operational. The centrifugal concentrator works to concentrate gold by the difference in density between gold and the host rock, typically referred to as gravity separation. When operating, the Knelson concentrator will discharge a gold concentrate which will be pumped to the concentrate thickener.

The Knelson concentrator is located in the circulating load of the ball mill as is typical for this type of recovery device.

Concentrate Dewatering
The concentrate travels by gravity to an Outotec 9.4 m diameter Supaflo high-rate thickener. The concentrate is thickened to approximately 70% solids density.

The concentrate is pumped to a 55 m3 stock tank prior to filtering. The concentrate is pumped from the concentrate stock tank to a Larox 30 m2 ceramic filter with 10 discs for a total filter area of 300 m2. The dewatering rate averages 25-30 t/h with a typical product moisture content of 7 - 8 %.

The filter cake is transported to a concentrate storage shed via a 24” by 38’ long concentrate discharge conveyor powered by a 15 HP motor. The concentrate storage shed has a capacity for storing 18,000 t of flotation concentrate.

The concentrate is loaded into 25 or 50 t trucks and transported to Skagway, Alaska from which it is shipped to market. The road to access site crosses the Yukon river and concentrate transport is halted 2x per year for approximately 6 weeks each while the crossing is switched from summer to winter operation and vice versa.

Recoveries & Grades:

CommodityParameter2022202120202019201820172016
Copper Recovery Rate, % 94.193.293.495.187.582.695.2
Copper Head Grade, % 1.581.41.382.271.311.372.21
Copper Concentrate Grade, % 38.43835.538.143.744.7
Gold Recovery Rate, % 61.159.367
Gold Head Grade, g/t 0.440.791.23
Gold Concentrate Grade, g/t 8.81817.5
Silver Recovery Rate, % 77.377.687.8
Silver Head Grade, g/t 4.34.88
Silver Concentrate Grade, g/t 111142157

Production

CommodityProductUnits2022202120202019201820172016
Copper Payable metal M lbs 000000
Copper Concentrate kt 00000000273770
Gold Metal in concentrate oz 0000000000000000009,25125,20539,506
Silver Metal in concentrate koz 000000000098171355
Copper Metal in concentrate M lbs 000233669

Operational metrics

Metrics202220212020201920182017
Daily mining rate 3,000 t3,000 t
Daily milling capacity 4,200 t4,000 t4,000 t4,000 t
Ore tonnes mined 904,066 t866,805 t651,945 t841 kt1,269 kt
Waste 134,900 t128,166 t181,513 t1,315 kt7,890 kt
Total tonnes mined 1,038,966 t994,971 t833,458 t2,146 kt9,156 kt
Tonnes processed 878,380 dmt903,498 dmt629,078 t104,005 t
Daily milling rate 2,983 t3,943 t
Tonnes milled 907 kt1,439 kt

Production Costs

CommodityUnits202220212020201920182017
Credits (by-product) Copper USD -0.14 / lb   -0.24 / lb  
Cash costs (sold) Copper USD 0000000 0000000 0000000 4.15 / lb  
All-in sustaining costs (sold) Copper USD 0000000 0000000 0000000 5.26 / lb  
All-in sustaining costs (AISC) Copper USD 3.44 / lb   2.75 / lb  
C1 cash costs Copper USD 3.12 / lb   2.6 / lb  
All-in costs Copper USD 2.75 / lb  
Net of By-Product.

Operating Costs

Currency20182017
Total operating costs ($/t milled) USD 69.8  61.1  

Financials

Units202220212020201920182017
Growth Capital M CAD 7.8  4.8  
Sustaining costs M CAD 15.6  6.3  1.8   2.5  
Capital expenditures M 23.4  CAD6.3  CAD6.6  CAD 7  USD 2.7  USD
Revenue M 153.2  CAD138.3  CAD58.3  USD 12.4  USD 70  USD 111.5  USD
Operating Income M -0.4  CAD12.1  CAD-13.3  USD -6.3  USD -25.2  USD 31.7  USD
Pre-tax Income M -16  USD -7.6  USD
After-tax Income M -11.1  CAD-2  CAD-16.1  USD -7.5  USD -31  USD 12.7  USD
EBIT M 25  USD
EBITDA M 10  CAD14.7  CAD-5.2  CAD -21.7  CAD
Operating Cash Flow M 27.9  CAD12.2  CAD9.5  USD -6.9  USD

Heavy Mobile Equipment

HME TypeModelSizeQuantityStatusLeased or
Contractor
Backhoe Minecat MC100 1 Existing Leased
Bolter MacLean 982 3 Existing Leased
Dozer Caterpillar D10 600 HP 2 Required Leased
Drill Sandvik D50KS 152 mm 1 Required Leased
Drill Sandvik DX800 64 mm 1 Required Leased
Drill (long hole) Boart Longyear StopeMaster 3 Existing Leased
Drill jumbo (two boom) Epiroc Boomer 282 1 Required Leased
Drill jumbo (two boom) Epiroc Boomer 282 2 Existing Leased
Feeder Breaker MacLean RB3 1 Required Leased
Grader Caterpillar 16M 4.9 m 1 Required Leased
Grader Caterpillar M135H 1 Existing Leased
Loader (FEL) Caterpillar 993K 13 m3 1 Required Leased
Load-Haul-Dump (LHD) Caterpillar R1700G 14 t 5 Existing Leased
Load-Haul-Dump (LHD) Caterpillar R1700G 14 t 1 Required Leased
Personnel Carrier Minecat UT99D 8 Existing Leased
Scissor Lift MacLean SL2 2 Existing Leased
Shovel Komatsu PC2000 11 m3 1 Required Leased
Trans Mixer MacLean TM3 6 m3 1 Existing Leased
Truck (boom) Getman A64 Ex-C 2-500 1 Existing Leased
Truck (boom) Getman A64 1 Existing Leased
Truck (boom) Getman A64 Ex-C 2-500 1 Required Leased
Truck (fuel / lube) Getman A64 1 Required Leased
Truck (haul) Caterpillar 777G 90.7 t 4 Required Leased
Truck (underground) Caterpillar AD45B 45 t 1 Required Leased
Truck (underground) Caterpillar AD45B 45 t 6 Existing Leased
Truck (water) Caterpillar 773 1 Required Leased

Personnel

Mine Management

Source Source
Job TitleNameProfileRef. Date
Maintenance Superintendent Matt Campbell LinkedIn Apr 29, 2024

EmployeesContractorsTotal WorkforceYear
237 81 318 2022
177 2021
100 2019
201 2017
307 2016

Aerial view:

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