Canada

Halfmile Project

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Overview

Mine TypeUnderground
StatusInactive / Suspended
Commodities
  • Zinc
  • Lead
  • Copper
  • Silver
  • Gold
Mining Method
  • Mechanized Cut & Fill
  • Avoca
  • Longitudinal retreat
  • Sub-level stoping
  • Sub-level Retreat
  • Post Pillar Cut & Fill
  • Undefined backfill
  • Cemented (undefined) backfill
Mine Life13 years (as of Jan 1, 2017)
ShapshotThe Halfmile-Stratmat integrated project is comprised of the Halfmile mine and the advanced exploration stage Stratmat project.

On Aug. 19, 2022, Trevali Mining Corporation announced that the Company had received an Initial Order for creditor protection from the British Columbia Supreme Court under the Companies' Creditors Arrangement Act (the "CCAA").

On June 30, 2023, Trevali Mining Corporation announced that the Supreme Court granted an order in the Company's ongoing CCAA proceedings pursuant to which FTI Consulting Canada Inc., the Court appointed "Monitor", has been granted enhanced powers in the CCAA Proceedings with respect to the Company's business and affairs.

The Monitor's powers to manage the Company, the Company's remaining employees have ceased their employment with the Company.

Please note that all data presented below is sourced from 2017 technical report prepared by SRK Consulting (Canada) Inc.
Related AssetHalfmile-Stratmat Project

Owners

SourceSource
CompanyInterestOwnership
Trevali Mining Corp. 100 % Indirect
The Halfmile-Stratmat integrated project is 100% held by Trevali Mining (Maritimes) Ltd., a 100% owned subsidiary of Trevali Mining Corporation.

On June 30, 2023, Trevali Mining Corporation announced that the Supreme Court of British Columbia granted an order in the Company's ongoing Companies' Creditors Arrangement Act proceedings (the "CCAAProceedings") pursuant to which FTI Consulting Canada Inc., the Court appointed "Monitor", has been granted enhanced powers in the CCAA Proceedings with respect to the Company's business and affairs.

Contractors

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Deposit type

  • VMS

Summary:

The Halfmile and Stratmat projectss are volcanic massive sulphide (VMS) deposits typical of the Bathurst Mining Camp (BMC). The BMC hosts 45 volcanic-sediment hosted massive sulphide deposits and 95 occurrences, including the world-class Brunswick 12 Mine. BMC deposits formed in a sediment-covered back-arc continental rift during periods when the basin was stratified with a lower anoxic water column. The basin was subsequently intensely deformed and metamorphosed during multiple collisional events related to east-dipping subduction of the basin.

The VMS deposits typically form lenses of polymetallic massive sulphide. Most deposits are zoned vertically and laterally from a high temperature, vent-proximal, copper-polonium bismuth-rich veined and brecciated core to vent-distal zinc-lead-silver-rich hydrothermal sediments. The vent complex is commonly underlain by a highly deformed sulphide stringer zone that extends hundreds of metres beneath deposits and consists of veins and impregnations of sulphides, silicates, and carbonates that cut chloritized and sericitized volcanic and sedimentary rocks.

The Halfmile project is underlain predominantly felsic volcanic rocks and lesser sedimentary rocks which are host to all massive sulphide deposits on the property. Provincial Government regional
mapping projects have classified the rocks as belonging to the Flat Landing Brook formation of the Middle Ordovician Tetagouche group and Nepisiguit Falls formation.

At Halfmile, the Flat Landing Brook formation consist mainly of rhyolite flows, quartz-feldspar porphyry and mafic volcanic rocks. The Nepisiguit Falls formation includes the massive sulphide mineralization, quartz-feldspar porphyry and clastic sedimentary rocks.

The stratigraphy for Halfmile is overturned. A stockwork of pyrrhotite-chalcopyrite mineralization occurs on top of the massive sulphides. Well-developed S1 foliation/cleavage is easily observed in most drill core samples. In general, the enveloping surface for this cleavage is oriented northeast with a dip of 40 to 60° to the northwest. An S2 crenulation cleavage accompanied by small parasitic kink folds is oriented at a high angle to the S1 foliation in the nose of folds.

Detailed interpretations are difficult to assess due to poor documentation in old holes and difficulty in assessing structure from drill data. Faulting is poorly documented in pre-1970 drilling. However, later interpretation suggests the influence that faults have on the sulphide horizon. A single thrust fault is readily observed immediately above or within the sulphide horizon. This fault occurs in about the same stratigraphic position on all of the Halfmile project. Local small-scale sheath folds may increase the thickness and grade within the hinge of the Lower Zone.

Reserves

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Mining Methods

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Comminution

Crushers and Mills

Milling equipment has not been reported.

Summary:

The RoM production will initially be subjected to primary and secondary crushing at the Stratmat mine site to reduce the rock size to a suitable feed for a dense media separation plant (DMS). This operation will reject barren material from the +3 mm size from the mill feed effectively increasing the mill head grade and reducing the overall operating costs of the concentrator. A Barely Autogenous Grinding (BAG) mill will be used for primary grinding followed by a conventional ball mill for secondary grinding to liberate the minerals to allow flotation to concentrate the metals to saleable concentrates.

Primary crushing, secondary crushing and screening will be contracted out. The crushed product will be fed to a covered stockpile with a live content of 4,000 tonnes and the DMS plant will be fed using two apron feeders in a tunnel under the stockpile at 175 tonnes per hour. The dense media process is expected to reject 22% of the mass of RoM material in a reject which will be suitable for producing backfill with the addition of the required amount of cement. As only the +3 mm fraction of the RoM material can be upgraded, the -3 mm fraction will be screened out on a wet screen, thickened and the thickener underflow pumped to the ball mill discharge pump box or to a lagoon if the DMS plant is operating and the main plant is down. DMS upgraded material will be conveyed to a second stockpile with a live content of 3,000 tonnes.

Design feed tonnage to the grinding circuit is 145 tonnes per hour. The BAG mill will operate in closed circuit with a vibrating screen recycling the +5 mm fraction back to the BAG mill. Screen undersize will flow to a secondary ball mill which will operate in closed circuit with 15-inch diameter cyclones and will grind the material to a P80 of 72 microns.

The upgraded mineralization stockpile will be an insulated structure with 3,000 tonnes of live capacity to allow for operation of the mill during maintenance of the DMS plant or vice versa. A dump point will allow crushed mineralization to be added to this stockpile to completely decouple the operation of the mill from the DMS plant

Primary grinding will be in a BAG mill with a 950 kW motor. A BAG mill is required as the -65 mm maximum size of the mineralization means that there will be no lumps that are large enough to act as media for a semi-autogenous grinding (SAG) mill. A ball mill will not be used because a higher aspect ratio mill is required to ensure that the balls have sufficient energy to break the largest particles at a size that will also provide highly efficient grinding. A double-deck vibrating screen in closed circuit with the BAG mill is included with a designed opening of 5 mm on the lower screen.

Sodium carbonate (soda ash) for pH control and depressants (sodium cyanide and zinc sulfate) will be added to the BAG mill feed to ensure that depression of sphalerite and pyrite occurs as soon as the surfaces are exposed.

A conventional ball mill with a 2 MW motor in closed circuit with a cyclopac having eight 12-inch cyclones will take the BAG mill screen undersize at a P80 in the order of 750 microns and reduce it to the size noted above (P80 of 72 microns) for flotation feed.

Regrinding of the lead/copper rougher and scavenger concentrates and the lead/copper first cleaner scavenger concentrate will be in a M4 (1MW) Isamill.

The zinc regrind mill will be an M4 (1MW) Isamill operated in closed circuit with a cyclopac having 10 five-inch diameter cyclones.

Processing

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Production

Combined production numbers are reported under Halfmile-Stratmat Project

Operational metrics

Metrics
Daily ore mining rate 2,600 t *
Annual ore mining rate 910,000 t *
Waste tonnes, LOM 2,472 kt *
Ore tonnes mined, LOM 9,376 kt *
Tonnes milled, LOM 9,376 kt *
* According to 2017 study.

Production Costs

Commodity production costs have not been reported.

Operating Costs

Currency2017
UG mining costs ($/t mined) CAD 38.2 *  
* According to 2017 study.

Project Costs

MetricsUnitsLOM Total
Pre-Production capital costs $M CAD  ......  Subscribe
Sustaining CapEx $M CAD  ......  Subscribe

Heavy Mobile Equipment

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Personnel

Mine Management

Source Source
Job TitleNamePhoneEmailProfileRef. Date
....................... Subscription required ....................... Subscription required ........... Subscription required ........... Subscription required Subscription required Aug 31, 2023

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