DeLamar Gold-Silver Heap Leach & Merrill Crowe Processing

Source: Unnamed_Company_70 (2026)
Website: https://integraresources.com/asset/delamar-project/

Critical Data

Overview

Integra Resources Corp. operates the DeLamar project in the Owyhee Mountains of Idaho, employing conventional cyanide heap leaching followed by Merrill Crowe processing to recover gold and silver from oxide and transitional mineralization. The project, which resumed exploration in 2017 after historical open-pit mines closed in 2003, includes two heap leach pads (Florida Mountain and DeLamar) and a centrally located Merrill Crowe plant. Ore is processed through a two-stage crushing circuit (mineral sizer and three roll crushers) to achieve a P80 of 19 mm at a rate of 35,000 tonnes per day. DeLamar ore, which contains higher clay content, is agglomerated with cement and cured before stacking via conveyor, while Florida Mountain ore is truck-stacked directly. Pregnant leach solution (PLS) is collected in in-heap process ponds and pumped to the Merrill Crowe plant for gold and silver precipitation. The resulting precipitate is transported 362 km to Integra’s Florida Canyon refinery for doré production. The life-of-mine plan estimates recovery of approximately 910,000 ounces of gold and 17.4 million ounces of silver from 119.9 million tonnes of ore, achieving an overall gold recovery of about 72%. This optimized recovery method balances ore variability, clay content, and seasonal conditions to maximize economic returns while maintaining environmental compliance.

Key Process Stages

• Stage 1: Two-Stage Crushing – Run-of-mine ore is dumped into apron plate feeders (MMD D7, 2 m x 14.5 m, 149 kW each) and fed to a primary mineral sizer (MMD 750 4-tooth x 8-ring, 522 kW) reducing ore to P80 133 mm. The crushed material discharges onto a conveyor (1.8 m x 40 m, 45 kW) and enters three secondary roll crushers (McLanahan 0.8 m diameter x 2.4 m, 186 kW each) achieving a final P80 of 19 mm at a design throughput of 1,724 tph. The circuit operates at 83% availability, processing 35,000 tpd.
• Stage 2: Agglomeration & Cure Stockpile (DeLamar-only) – Approximately 15-30% of DeLamar ore passing a 25.4 mm screen after primary crushing is conveyed to an agglomeration drum (3.6 m diameter x 10 m length, 260 kW motor). Portland cement is added at a controlled rate to bind fines and provide alkalinity, while raw water is injected via spray bars at 69.3-76.1 m³/h. The agglomerated ore is radial-stacked onto a 24-hour cure pile where cement solidifies. After curing, a CAT 988 loader reclaims the material onto the overland conveyor for blending with non-agglomerated crushed ore.
• Stage 3: Heap Leach Stacking – Florida Mountain ore is loaded by a CAT 993 loader into seven CAT 785 haul trucks and dumped onto the HLP, leveled by D10 dozers in 10 m lifts with 3:1 side slopes. DeLamar agglomerated ore is conveyed via three overland conveyors (731.5 m total length, 75 kW each), up to 36 grasshopper conveyors (36.6 m each, 30 kW), two horizontal index conveyors (45.7 m, 75 kW), and a radial stacker (48.2 m, 75 kW). Stacking rate for both pads is 35,000 tpd.
• Stage 4: Leaching Operations – Barren solution with sodium cyanide is applied by drip irrigation at a nominal rate of 1,360 m³/h (application rate 6.11 L/s/m²). The primary leach cycle is 90 days. PLS is collected via a network of 100 mm corrugated perforated pipes within a 0.9 m overliner layer over LLDPE geomembrane. During winter, irrigation lines are buried to prevent freezing. After Florida Mountain mining ceases, residual PLS from that pad is amended with cyanide and pumped to the DeLamar HLP to boost influent metal concentrations to the Merrill Crowe plant.
• Stage 5: Merrill Crowe Plant & Refinery – PLS is clarified through four diatomaceous earth pre-coated filters (three operating, one standby). Clarified solution enters a deaeration tower to remove dissolved oxygen, then powdered zinc and cyanide are added to precipitate gold and silver via redox reaction. The mixture passes through four recessed plate-and-frame filters (three operating, one standby) capturing the precious metal precipitate. Barren solution is recycled with added sodium cyanide. Filter cakes are shipped 362 km to Integra’s Florida Canyon refinery, where they are dried in a retort furnace, smelted in an induction furnace, and poured into doré bars. Off-gases pass through sulfur-impregnated carbon for mercury removal.

Additional Interesting Data and Summary

The DeLamar project’s recovery methods are underpinned by a robust technical design that adapts to ore variability. The two-stage crushing circuit, with a mineral sizer and three roll crushers, achieves a P80 of 19 mm at 1,724 tph, while the agglomeration system (drum sized at 3.6 m x 10 m with a 260 kW motor) treats up to 30% of DeLamar ore passing 25.4 mm, using Portland cement at target rates and water addition of 69.3-76.1 m³/h. The heap leach pads are designed as valley fills with LLDPE geomembrane liners, 0.9 m overliner, and 100 mm collection pipes. Leaching parameters include a 90-day cycle and a nominal barren solution flow of 1,360 m³/h applied at 6.11 L/s/m². Each HLP includes an in-heap process pond sized for 8 hours of operational solution plus 24-hour drain down, and an event pond storing the 100-year, 24-hour precipitation event with 1 m freeboard. The Merrill Crowe plant processes PLS from both pads via four clarifying filters and four precipitate filters, achieving gold and silver precipitation through zinc addition. The precipitate is transported 362 km to Integra’s Florida Canyon refinery, which will require a retrofit (parallel or larger equipment) to handle additional throughput. Environmental management is supported by reclamation bonds totaling over $4.3 million with IDL, IDEQ, and BLM for ongoing closure and exploration activities. Life-of-mine production estimates from dynamic 3D modeling indicate cumulative recovery of 910 koz gold and 17,392 koz silver over 12 years, with peak annual gold production of 109 koz in years 2–3. The project’s phased approach—starting at Florida Mountain and transitioning to DeLamar in year 4—optimizes capital deployment and allows Florida Mountain to continue residual leaching after mining ceases. This integration of crushing, agglomeration, heap leaching, and Merrill Crowe processing delivers a technically sound and economically viable recovery scheme for the DeLamar project’s gold-silver resources.

Key Processes: Heap Leaching, Cyanidation, Crushing

Target Commodities: Gold, Silver, Zinc