Slide 1: Tulsequah Chief Mine Information Webinar on Remediation Planning Efforts
TULSEQUAH CHIEF MINE INFORMATION WEBINAR ON REMEDIATION PLANNING EFFORTS May 6, 2026
Slide 2: Teck – TRTFN Steering Committee
TECK – TRTFN STEERING COMMITTEE Rodger Gideon Jackie Dr. Chris Thorlakson Kyei Serbeh Caldwell Sergeant Lands and Mining Consultant Research Scientist, Resources Coordinator, for TRTFN U. of Washington, Manager, TRTFN Consultant for TRTFN TRTFN Dr. Deborah Stephanie Carolyn Read Tissot Holmes Tulseq
Slide 3: About Teck
ABOUT TECK Teck is a leading Canadian critical minerals company focused on responsibly providing metals essential for global economic growth and the energy transition. 110+ years of history as a Canadian company headquartered in Vancouver, B.C. 6 total operations in Canada, the U.S., Chile and Peru
Slide 4: About Taku River Tlingit First Nation
ABOUT TAKU RIVER TLINGIT FIRST NATION • Located in Atlin, BC - a remote community of approximately 400 people. • Territory covers over 40,000 km2 • Represent TRT Citizens on all matters that could affect Territory • TRTFN Lands, Mining Division has been involved in the active planning for the reclam
Slide 5: Collaborative Governance & Engagement
COLLABORATIVE GOVERNANCE & ENGAGEMENT Teck and TRTFN meet regularly to plan and Memorandum of Understanding (MOU) discuss field activities. between TRTFN, Teck, and BC: Steering Committee: Signed: • Guides decision-making. September 17, 2024 • Supports alignment on priorities and progress. Purpose:
Slide 6: Tulsequah Chief Site Location
TULSEQUAH CHIEF SITE LOCATION The mine is located approximately 100 km south of Atlin, British Columbia, on the Taaltsux̱éi Héen. The mine is approximately: • 10 km upstream of confluence of Taaltsux̱éi Héen (Tulsequah River) and T'aakú Héeni (Taku River) • 30 km from the U.S. border • 50 km NE of J
Slide 7: Timeline of the Tulsequah Chief Mine
TIMELINE OF THE TULSEQUAH CHIEF MINE Objective: Teck and TRTFN developing a final remediation plan for the site Province of BC Redfern conducted work purchase with some funding the mine. Redfern and from Teck, including Cominco Chieftain development of an ownership attempted to early Closure & cease
Slide 8: Site Layout
SITE LAYOUT airstrip, camp, lime sludge pit upper and lower mine workings waste rock, water treatment plant (not functional), lime sludge pit, exfiltration pond barge landing, barge camp, fuel storage 8
Slide 9: 5400 Level
2025 Teck Temporary Camp 5400 Level Taaltsuxéi Héen ~ (Tulsequah River) ~ Teck - Internal/Interno 9
Slide 10: Mine Workings Cross Section
MINE WORKINGS CROSS SECTION Current remediation concept • Plug 5200, 5400 to limit acid mine drainage leaving underground • Secure all portals to prevent human entry ground surface 6500 Level Upper 6400 Level workings 5900 Level tunnels Lower mined out 5400 Level workings cavity 5200 Level 10
Slide 11: Site photo 2019
2019 Teck Ore Storage Fuel Storage Hazardous Wastes Exdiltration Pond and Spillway Teck - Internal/Interno *———— __ 5400 Level PAG.Bedrock Waste,Rock 11
Slide 12: Past Water Treatment Efforts: Passive Water Treatment
PAST WATER TREATMENT EFFORTS PASSIVE WATER TREATMENT Passive water treatment system • Constructed by Redfern in the 5200 L in around 2005 • Consisted of 4 treatment cells (5 dams) • Contained limestone, mulch, and glycol • Aimed to encourage bacterial activity to mitigate acid production and remove
Slide 13: Past Water Treatment Efforts: Active Water Treatment
PAST WATER TREATMENT EFFORTS ACTIVE WATER TREATMENT Water treatment plant constructed in 2011 by Chieftan. Design: • Neutralize acid mine drainage and remove heavy metals and suspended solids. • Aimed to treat 40 m³/h with the peak flow rate of 100 m³/h. Operated: • March to July 2012 (4 months) • N
Slide 14: Progress Made During 2024 and 2025 Field Seasons
PROGRESS MADE DURING 2024 AND 2025 FIELD SEASONS Safe Access Underground (U/G) Water Management Mined Rock Environment Waste • Maintained safe, • Commenced and Monitoring • Quantified waste • Cleaned up and • Removed reliable access securing • Installed temporary rock and ore assess existing some hi
Slide 15: 2026 Objectives
2026 OBJECTIVES • Collection of geotechnical, geochemical, and environmental information needed to select and design effective remediation options for acid rock drainage at the Tulsequah Chief Mine. • Develop a Draft Remediation Plan outlining preferred acid rock drainage remediation options, with a
Slide 16: 2026 Proposed Plans
2026 PROPOSED PLANS Safe Access Underground (U/G) Water Management Mined Rock Environment Remediation • Maintained safe, • Secure and Monitoring • Quantify the • Adult salmon tissue Planning reliable access underground • Collect water quality, geochemistry of metals • Draft to site workings sediment
Slide 17: Safe Access
SAFE ACCESS Access to Site Remote access via fixed-wing airplane and helicopter supported by seasonal camp (May-Sept). • Annual/seasonal maintenance required for roads and airstrip • Re-armouring or northern corner of airstrip • Install a weather station and camera at airstrip. 17
Slide 18: Safe Access: Temporary Camp
SAFE ACCESS Temporary Camp • Camp Construction - temporary 22-bed camp will be re-established • Lower hillslope scaling planned to reduce rockfall risk. • Permanent weather station to be installed at mine area. 18
Slide 19: Bridge 8 Repairs
BRIDGE 8 Bridge Repairs Teck - Internal/Interno
Slide 20: Bridge 10 Repairs
BRIDGE 10 Bridge Repairs • Bridge and culvert repair • Bridge 10 (Rogers Creek) reinforcement • Other culverts 20
Slide 21: Underground - 2026: Secure Underground Workings
UNDERGROUND - 2026 Secure Underground Workings • Drone surveys – all levels • Ground Stabilization − 5400 Level − Remove sludge to allow access and stabilization activities. − Ongoing stabilization work to access deeper into mine 5400 Level July 2025 21
Slide 22: Underground - 2026: 5200 Level
UNDERGROUND - 2026 Secure Underground Workings • Ground Stabilization − 5200 Level (lowest mine level) − Replace portal timbers − Stabilization work to access mine − Remove sludge to allow access and stabilization activities. − Dam break safety management 5200 Level Portal May 2025 22
Slide 23: Sludge depth estimated to be 1.5 ft
Sludge depth estimated to be 1.5 ft 23
Slide 24: 5200 L Portal Dam at 392m
5200 L Portal Dam at 392m IFucHT | upTivE oS a 58% 224V | Ear | cae FLIGHT 15D 2873, EXP Vigo = @E2.'.' a
Slide 25: Underground - 2026: Accelerating Plug Design
UNDERGROUND - 2026 Accelerating Plug Design Remediation Concept • Construct plugs in the lowest two levels to flood the mine. • Reduce chemical reaction that causes poor water quality emerging from mine. Preliminary engineering design based on drone survey information. Plugs Will need to be updated
Slide 26: Mined Rock Remediation Options
MINED ROCK Remediation Options Geochemistry study • Assess potential cover materials and how they may affect runoff water quality • Confirm and validate earlier geochemistry findings for the mined rock Conceptual options development • Identify and document environmental impacts, logistics and future
Slide 27: Water Management and Monitoring: Water Monitoring
WATER MANAGEMENT AND MONITORING Water Monitoring 2026 Sampling • Monthly water quality • Sediment in May and September • Benthic invertebrates in September • Salmon tissue early August Studies • Water quality data review − Update baseline (last done 2021) − Trend analysis 27
Slide 28: Water Management and Monitoring: Water Studies
WATER MANAGEMENT AND MONITORING Water Studies Water quality prediction for remediation scenarios • How options will potentially impact water quality leaving site • Inform selection of remediation options Aquatic risk assessment for remediation scenarios • How options will potentially impact aquatic
Slide 29: Water Management and Monitoring: Sediment Control
WATER MANAGEMENT AND MONITORING Sediment Control • Install fencing and straw wattle at portals to reduce sediment load to river while underground work occurring. • Fencing will be removed post- season to prevent spring runoff impact. 29
Slide 30: Environment: Adult Salmon Tissue
ENVIRONMENT Adult Salmon Tissue Goal Analyze the concentrations of metals from fillets of Taku River coho and sockeye salmon Methods • During summer 2026, collect ten individuals of each species from the commercial in-river fishery • Remove a portion of the fillet for metals analysis at a certified
Slide 31: Environment: Bat Monitoring
ENVIRONMENT Bat Monitoring • Equipment installed at portals in 2025 to detect bat roosting/hibernation. • Monitoring to continue for about 18 months to inform planning for closure of underground. • Will check data in spring and fall of 2026. 31
Slide 32: Remediation Planning: Draft Remediation Plan
REMEDIATION PLANNING Draft Remediation Plan • Remediation of acid rock drainage: − U/G water discharge − Waste rock − Resulting surface water management • Focus on source control • Include preferred options for remediation and outline other potential options • Will not include: − Demolition of build
Slide 33: Next Steps
NEXT STEPS • Safety training and induction completed (May 1) with Atlin Tling Economic Limited Partnership (ATELP) team. • Public webinar to be held May 6 for other interested parties, including Alaskans. • Field work May 19 to September 24, 2026. • Continuous collaboration between Teck and TRT to a
Slide 34: Thank You
Teck THANK YOU
Slide 35: Stay Connected
STAY We Want To Hear From You CONNECTED You can ask us questions, share concerns or provide feedback at any time by leaving us a voice message at 1.888.767.7706 or emailing legacyproperties@teck.com and our team will respond in a timely manner. Learn more about us at Teck.com You can also reach us a