Highland Copper Announces Updated Process Plant Flow Sheet Demonstrating Increased Copper Recoveries of 87.6% and Reduced Processing Costs
September 4, 2025
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HIGHLAND COPPER ANNOUNCES UPDATED PROCESS PLANT FLOW SHEET
DEMONSTRATING INCREASED COPPER RECOVERIES OF 87.6% AND REDUCED
PROCESSING COSTS
Vancouver, Canada, September 4, 2025 – Highland Copper Company Inc. (TSXV: HI; OTCQB: HDRSF)
(“Highland” or the “Company”) is pleased to announce positive results from its 2025 metallurgical test work
program for the 100%-owned Copperwood Project (“Copperwood”), located in Michigan’s Upper Peninsula.
The test work was conducted by Base Metallurgical Laboratories Ltd. (“Base Met Labs”) in Kamloops, British
Columbia, with technical oversight provided by DRA Americas Inc. (“DRA”).
In Q1 2025, Highland initiated a metallurgical test program with the goal of improving the process plant
design, incorporating ultrafine flotation technology, and broadly reconsidering the operating cost structure
of the process plant. Highland is pleased to announce the process plant has been redesigned to reflect a
more effective comminution circuit, a simpler flotation circuit incorporating Jameson cell ultrafine flotation
technology, and an optimized reagent scheme. This is anticipated to deliver an increase in copper recoveries
to 87.6% at lower plant capital and processing costs. While more effective, the redesigned process plant is
smaller in scale and requires lower overall power consumption. Highland is pleased that Glencore
Technologies is prepared to offer a performance guarantee in relation to the improved copper recovery
estimate, providing confidence in the robust nature of the test program and its results.
This metallurgical update is an important component of Phase 1 detailed engineering , also initiated in Q1
2025. The goal of Phase 1 engineering is to finalize design criteria related to process plant, mine, tailings,
and water management. As demonstrated by the redesigned process plant, Phase 1 engineering represents
a significant re-evaluation by Highland Copper’s project team, overseen by Project Director, Dr. Wynand van
Dyk. Dr. van Dyk has a degree in Chemical Engineering/Extractive Metallurgy and a 30-year career in mine
design, construction and operations. Highland looks forward to providing further project design updates as
Phase 1 engineering concludes in September 2025.
Metallurgical Test Work Highlights:
• Comprehensive Testing Program: Conducted 45 kinetic rougher and cleaner flotation tests to
refine grind parameters and reagent schemes, along with locked-cycle tests and pilot-scale testing
on ultrafine flotation technology.
• Optimized Process Circuit: Adopted a mill-float-mill-float (“MF2”) flowsheet including a de-sliming
stage prior to the secondary milling stage. The addition of a de-sliming stage ahead of the secondary
milling and roughers allows for the rejection of up to 25% of the mass from the primary rougher
tailings. This configuration reduces over-grinding and offers potential comminution energy savings
of between 10 and 13.7%.
• Improved Reagent Scheme: Developed an o ptimized reagent suite that is expected to reduce
operating costs by up to $1.00 per tonne milled, while also improving environmental, health and
safety (“EH&S”) performance.
• MF2 Circuit and Improved Reagent Scheme Performance: Test work with the MF2 circuit and
optimized reagent scheme delivered kinetic rougher copper recoveries of up to 92.4% at the target
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rougher concentrate grade of 4.5% copper, a notable improvement over the 89.7% baseline from
2018 test work. Kinetic cleaner circuit recoveries were maintained at levels comparable to the 2018
baseline. Importantly, locked-cycle tests confirmed up to 85.8% recovery at a 25% copper
concentrate grade , demonstrating that the enhanced reagent scheme and MF2 configuration is
capable to deliver meaningful operating cost savings without compromising metallurgical
performance.
• Projected Ultrafine Flotation Performance Gains: Through the introduction of ultrafine flotation
technology, the adoption of an MF2 circuit, and the implementation of an optimized reagent scheme,
Copperwood is now expected to achieve average copper recovery of 87.6% at a concentrate grade
of 25% copper, all at lower operating costs. Glencore Technologies is prepared to offer a process
guarantee related to recovery and grade estim ates. This marks a significant step -change from the
2023 Feasibility Study 1, which reported 86% recovery at 25% copper grade, underscoring the
strength of the redesigned metallurgical flowsheet.
Dr Wynand van Dyk, Project Director for the Copperwood project, commented: “These results represent the
culmination of a complete re-evaluation and re-engineering of the Copperwood metallurgical flowsheet. The
outcome is a robust circuit design, firmly grounded in fundamental principles and tailored to the orebody
itself. I want to extend my sincere thanks to both the DRA and Base Met Labs teams for their dedication and
countless hours of effort throughout this test work program. Once we finalize the process design, we will be
well-positioned to advance confidently into the detailed engineering phase.”
Barry O’Shea, President and CEO of Highland Copper commented: “These metallurgical results represent
another key milestone as we advance toward a construction decision in 2026. The outcomes support a clear
pathway to lower processing costs, with projected recoveries exceeding those in our 2023 Feasibility Study.
As detailed engineering progresses with DRA, we are encouraged by the potential to enhance project
economics and reduce technical risk.”
Next Steps:
As announced in January 2025, Highland awarded the Front-End Engineering and Design (FEED) contracts
for both the mine and process plant to DRA. The 2025 metallurgical program has provided critical data to
finalize process plant design criteria under Phase 1 of the engineering program. The next steps will focus on:
• Variability Work: Completion of lock-cycle variability testing on the finalized flowsheet. This work
is expected to conclude in early Q4 2025.
• Design Criteria Finalization: Confirmation of the final process design criteria ahead of initiating
Phase 2 of the detailed engineering program.
SUPPORTING TECHNICAL DETAIL
Sample selection and spatial context
The 2025 metallurgical drilling campaign comprised 10 PQ -size drill holes , design ed to provide
representative material from the early mine years for metallurgical testing. These holes were twinned at
1 See “Feasibility Study Update Copperwood Project Michigan, USA” with an Effective Date of March 6, 2023, prepared
for the Company by G Mining Services Inc. available under the Company’s profile at www.sedarplus.com
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the five locations previously sampled during the 2017-2018 flotation test work campaign, which formed the
basis of the 2018 comprehensive metallurgical program conducted by SGS 2 (see Figure 1). The sampling
intervals, received sample masses, and assay values are summarized in Table 1.
To align with geotechnical recommendations for mine design, each metallurgical interval excluded the
uppermost 30cm of the Lower Copper Bearing Sequence (LCBS), as per the geotechnical recommendations
for the mine design. In total, 404 kg of core was collected and used to prepare the composite sample for the
current phase of test work, as well as to prepare variability samples for the forthcoming lock-cycle variability
testing.
One of the drill holes, CW -25-211, intersected the main Copperwood Fault, providing an additional 41.7kg
of mineralized fault -repeat material (sample CW -25-211FR). As this material is a structural repeat of the
LCBS, it was used in preliminary bench -scale tests to replicate the performance of the 2018 flotation
program. This strategy allowed Highland to preserve the primary composite material for the broader 2025
metallurgical testing campaign.
Table 1: 2025 test work sample detail
To confirm the representativeness of the 2025 composite sample, preliminary rougher bench-scale flotation
tests were done. The objective of these tests was to replicate the metallurgical performance observed
during the 2018 flotation program, thereby providing confidence in the validity of the new sample set.
Figure 2 presents the mass pull versus recovery curves from these preliminary tests, alongside historical
data from the 2018 campaign – specifically Test F19 and Test F71. Test F19 represented the optimal rougher
flotation conditions applied during the majority of the 2018 test work, while test F71 served as the baseline
for a campaign which employed excessive NaHS dosages exceeding 2,600 g/t.
2 The SGS report entitled “Optimization Flotation Testwork on Material from the Copperwood Deposit”, Project 16256 -002-Final
Report, August 28, 2018 forms the baseline used in the previous process design, and is discussed in the 2023 Feasibility Study (FSU)
for the Copperwood project.
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Figure 1: 2025 metallurgical test work sample locations corresponding with 2018 SGS metallurgical campaign.
As shown in Figure 2, the 2025 sample demonstrates a metallurgical response consistent with the 2018
baseline results. This correlation supports the representativeness of the new composite material. On this
basis an additional 19 rougher and 20 cleaner kinetic flotation tests were carried out to optimize the process
flowsheet and refine the reagent scheme.
Figure 2: Mass pull versus Recovery curves for preliminary rougher tests, confirming similar response to 2018 SGS baseline
Process flowsheet and reagent scheme optimization
Preliminary rougher flotation testing revealed that the Copperwood ore body contains bimodal
mineralogical fractions: a fast -floating component that responds quickly to flotation and a slower -floating
bulk fraction with more protracted kinetics. As shown in Figure 3, the fast-floating material generates a high-
grade initial froth characterized by well -loaded bubbles (Panel A). However, after approximately 7 minutes
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of flotation time, froth quality deteriorates, becoming brittle and poorly loaded (Panel B). While metallurgical
upgrading continues beyond this point, the recovery rate slows significantly, requiring extended flotation
residence times. An assay-by-size analysis of tailings confirmed the presence of a low -grade ultrafine (sub
20m) fraction, likely introduced through overgrinding in the previous single-stage milling setup.
Figure 3: Initial high-grade froth (panel A) and depleted brittle froth (panel B) after 7 minutes of flotation
Adoption of an MF2 circuit
To address these challenges, the flowsheet was revised to adopt a mill-float-mill-float (MF2) configuration,
incorporating a de -sliming stage between the primary and secondary milling circuits (see Figure 4). This
approach, widely established in metallurgical operations, helps mitigate overgrinding and the associated
fines losses. Grind optimization test work determined the optimal parameters as:
• Primary circuit grind P80: 80 µm
• Secondary circuit grind P80: 38 µm
Bench-scale de-sliming was performed via wet screening at 38 µm, while later pilot-scale testing employed
cyclone separation.
A
B
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Figure 4: Revised front-end of the circuit showing desliming and mill-float-mill-float (MF2) configuration
De-sliming Efficiency and Mass Rejection
Test work demonstrated a strong linear relationship (R² = 0.691) between the mass fraction and copper
grade in the de-slime fraction (see Figure 5). At a target grade of 0.3% Cu in the de-slime product, up to 25%
of the mass of the primary rougher tailings can be rejected ahead of secondary milling. This not only reduces
the size requirement for the secondary mill ing circuit but also prevents overgrinding and associated fine
particle losses.
Figure 5: Linear relationship between deslime mass fraction and Cu grade of deslime fraction
Comminution Circuit Power Saving
The 2023 FSU contemplated an MF1 circuit comprising a 5.5 MW SAG mill and a 5.5 MW ball mill in closed
circuit with cyclones, producing a flotation feed P80 of 45 µm and drawing 4.8 and 5.0 MW respectively. This
configuration included a single rougher stage with 50 minutes of residence time, followed by a 2.2 MW
regrind mill drawing 1.9 MW. In total, the circuit incorporated 13.2 MW of installed comminution power, with
a projected power draw of 11.7 MW.
Under the new configuration, designed for a coarser primary grind target of 80 µm, DRA’s mill sizing indicates
that a 3.8 MW SAG mill and 3.8 MW ball mill represent the optimal setup for the primary milling circuit, with
projected power draws of 3.3 MW and 3.4 MW, respectively. Following the de -slime step, a new secondary
milling circuit (3.0 MW installed, 2.0 MW power draw) will deliver the secondary grind target of 38 µm. In
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addition, a 1.5 MW regrind mill (1.4 MW projected draw) will regrind the rougher concentrate to a target P80
of 10 µm.
Altogether, the revised comminution circuit is projected to draw just 10.1 MW, representing between 10%
and 13.7% reduction in power requirements compared with the 2023 FSU design —highlighting both
improved operating efficiency and the potential for meaningful cost and energy savings.
Reagent Scheme Optimization
In parallel with flowsheet improvements, the flotation reagent suite was also optimized to improve both
performance and cost-efficiency (see Table 2). Key changes include:
• Replacement of SIBX collector with PAX
• Substitution of A-249 promoter with A-407
• Adjust pH and redox potential in the primary rougher conditioning stage, reducing NaHS dosage
• Elimination of Polypropylene glycol methyl ether (D-250)
• Elimination of n-Dodecyl Mercaptan (NDM)
In the 2023 FSU, flotation reagents accounted for $6.50 per tonne milled in operating costs. The revised 2025
reagent suite is projected to reduce this cost to $ 5.49 per tonne (at current reagent pricing), yielding a
savings of up to $ 1.00 per tonne. In addition to the cost reduction, the updated reagent scheme offers a
substantially improved environmental, health, and safety (EH&S) profile.
Table 2: Reagent regimes and contribution to operating costs (updated to 2025 reagent pricing)
Enhanced Rougher Recovery
Figure 6 presents the mass pull versus recovery curves from selected MF2 bench -scale flotation tests,
shown alongside the 2018 campaign baselines from Test F19 and Test F71. A notable step -change is
observed at approximately 20% mass pull, which reflects the transition between flotation products from the
primary and secondary milling stages. Data points below the 20% mass pull correspond to the primary
milling circuit and primary rougher flotation, while those above 20% represents recovery contributions from
the secondary milling circuit and roughers.
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Figure 6: Mass pull versus Recovery curves for MF2 bench tests compared with 2018 SGS baseline
Figure 7 presents linear grade-recovery curves fitted to the secondary rougher flotation data from both the
2018 and 2025 test programs. The fitted models yield R² values of 0.97 for both datasets, indicating a strong
correlation between grade and recovery in the secondary rougher stage. The shaded regions represent the
95% confidence intervals for each regression line.
Figure 7: Fitted Grade-Recovery curves for 2025 MF2 rougher tests compared with 2018 SGS baseline
At the target rougher concentrate grade of 4.5% copper, the updated reagent scheme and MF2 circuit
achieved a rougher recovery of up to 92.4%, compared to 89.7% in the 2018 baseline. Importantly, the non-
overlapping confidence intervals confirm that this improvement is statistically significant, underscoring the
technical merit of the revised flowsheet and reagent strategy.
Consistent Cleaner Recovery
Bench-scale cleaner optimisation focussed on refining reagent addition rates and evaluating the impact of
regrind size on performance . Figure 8 illustrates the grade versus recovery curves from selected 2025