Condor Gold Project: Gravity, Cyanidation & Flotation Recovery

Source: SILVERCORP METALS INC (2026)
Website: https://silvercorpmetals.com/condor/

Critical Data

Overview

Silvercorp Metals Inc. operates the Condor Gold Project, a polymetallic gold-silver-lead-zinc deposit located in the Zamora Chinchipe Province of Ecuador. The project’s recovery methods are based on extensive metallurgical test work and a life-of-mine (LOM) plan that targets an average head grade of 2.15 g/t gold and 14.2 g/t silver. The processing facility, designed for a milling rate of 5,000 tonnes per day (tpd), integrates three complementary gold recovery methods: gravity concentration, cyanidation via a carbon-in-pulp (CIP) circuit, and differential flotation for by-product lead and zinc concentrates. The flowsheet is tailored to the unique mineralization of the Camp and Los Cuyes zones, where coarse free gold is first recovered by gravity, followed by cyanide leaching to extract fine gold and silver into doré, and finally cyanide detoxification before flotation recovers silver-lead and zinc concentrates. Overall metal recoveries are projected at 94% for gold, 64% for silver, 36% for lead, and 54% for zinc. The plant operates 24 hours per day, 365 days per year, with an availability of 92% for grinding, leaching, and flotation circuits. This comprehensive recovery approach maximizes value from a complex ore while incorporating environmental controls such as SO₂/air cyanide destruction and a tailings storage facility with water reclaim. The design life of the Condor process plant is approximately 13 years, reflecting a long-term commitment to sustainable gold mining in Ecuador.

Key Process Stages

• Stage 1: Primary Crushing – Run-of-mine (ROM) ore from underground mines is trucked to a ROM pad and fed into a jaw crusher via a vibrating grizzly feeder at 298 t/h. The jaw crusher (1,150 mm × 760 mm opening, 160 kW) reduces the feed to 80% passing 100–120 mm. Oversize material from the static grizzly (600 mm spacing) is broken by a rock breaker. Crushed product is conveyed to a 5,000 t live capacity stockpile.
• Stage 2: Grinding, Classification, and Gravity Concentration – A SAB circuit (SAG mill + ball mill) grinds the feed to P80 of 74 µm. The SAG mill (6,700 mm dia. x 3,350 mm, 2,500 kW VFD) discharges through 65 mm pebble grates and a 10 mm vibrating screen. Oversize is returned to the SAG. The ball mill (4,900 mm dia. x 8,500 mm, 3,000 kW) operates in closed circuit with eight 350 mm hydrocyclones (six operating). About 25% of the ball mill discharge is diverted to one centrifugal gravity concentrator (226 t/h capacity) to recover coarse gold. The gravity concentrate is batch leached in an intensive cyanide reactor; the solution goes to the gold room and residue returns to the ball mill. Circulating load is ~300%.
• Stage 3: Cyanide Leaching and Carbon Adsorption – The hydrocyclone overflow (P80 74 µm, 32% solids) is thickened in a 28-m diameter high-rate thickener to 40–45% solids. Thickener underflow feeds a CIP train: six leach tanks (10.7 m dia. x 13.4 m) and seven CIP tanks (7.5 m dia. x 9.4 m) offering >28 hours retention. Air is supplied by two oil-free compressors. Sodium cyanide and hydrated lime (pH ~10.5) are added. Activated carbon (15 g/L) is advanced counter-currently. Loaded carbon is screened and sent to stripping; leach residue passes through a carbon safety screen (0.6 mm apertures).
• Stage 4: Loaded Carbon Stripping and Gold-Silver Refining – Loaded carbon is eluted at high temperature (up to 150°C) and pressure (0.5 MPa) in a pressurized desorption column using NaOH. The pregnant solution is filtered and electrowon onto stainless steel cathodes. Gold-silver sludge is filtered, mixed with flux, and melted in an induction furnace at 1,150°C to produce doré bullion. The entire elution cycle is completed in approximately 12 hours. The gold room is secured with 24-hour CCTV and restricted access.
• Stage 5: Silver-Lead and Zinc Flotation – After cyanide detoxification (SO₂/air reducing WAD CN to <1 ppm), the residue is conditioned with lime, ZnSO₄, and collectors for silver-lead rougher/scavenger flotation (five 38 m³ cells). The rougher concentrate is cleaned in three stages (8 m³ and 3 m³ cells). Tailings are then conditioned with CuSO₄ and collectors for zinc rougher/scavenger flotation (four 38 m³ cells). Zinc rougher concentrate may be reground in a tower mill before three-stage cleaning. Final silver-lead and zinc concentrates are thickened to 60% solids, pressure-filtered to 9% moisture, and stored for shipment.

Additional Interesting Data and Summary

The Condor process plant incorporates several design features to handle the polymetallic nature of the ore while meeting environmental and economic targets. Primary crushing achieves a product of 80% passing 100–120 mm using a single-stage jaw crusher with a vibrating grizzly feeder. The SAG mill is designed without a pebble crusher based on current test work, but space is allocated for future installation if needed. Grinding media (steel balls) are added batchwise to the SAG and ball mills. The gravity circuit processes 25% of the circulating load, recovering coarse free gold that would otherwise report to tailings. The intensive cyanide leach reactor for gravity concentrate operates on a batch basis, with leach solution reporting to the gold room and washed solids returned to the ball mill. The CIP circuit uses six leach tanks and seven adsorption tanks, providing a total retention time exceeding 28 hours. Activated carbon concentration is maintained at 15 g/L, and loaded carbon is stripped using a high-temperature, high-pressure elution system (150°C, 0.5 MPa) with a 12-hour cycle. Sodium hydroxide is the eluant; the depleted solution is recycled to the leach circuit. The elution and electrowinning system is housed in a secure building with 24-hour CCTV. Stripped carbon is reactivated in an electrically fired kiln at 650°C under inert atmosphere, then quenched, sized, and returned to the CIP circuit. Make-up fresh carbon is treated by attrition and sizing before addition. Cyanide destruction is achieved via the SO₂/air process in two reactors (6 m dia. x 7 m), reducing weak acid dissociable (WAD) cyanide to below 1 ppm. This is critical before flotation to prevent cyanide interference with lead/zinc recovery and to meet environmental discharge standards. The flotation circuit includes silver-lead rougher/scavenger (five 38 m³ cells) and three stages of cleaning (8 m³ and 3 m³ cells), followed by zinc rougher/scavenger (four 38 m³ cells) with regrinding via a tower mill and three-stage cleaning. Flotation concentrates are dewatered by separate 4-m diameter thickeners and pressure filters to 9% moisture, then stored under cover for bulk shipment to overseas smelters. Tailings from zinc flotation are thickened in a 30-m diameter high-rate thickener to 60% solids and pumped to a conventional wet tailings storage facility (TSF). A reclaim water system recovers supernatant water from the TSF for reuse in the mill, reducing fresh water demand. An emergency discharge pond is available for process upset conditions. Economic impact: with a design life of 13 years and processing 5,000 tpd, the Condor project will produce doré gold-silver bullion plus marketable silver-lead and zinc concentrates. Sustainability initiatives include cyanide detoxification, water recycling, and dust suppression at transfer points (water-spray systems). Future studies will verify the need for pebble crushing and the regrinding stage for zinc. The project is located in the Zamora Chinchipe Province of Ecuador, a region with established mining infrastructure. The robust recovery methods—combining gravity, cyanidation, and flotation—ensure maximum value extraction from the complex polymetallic ore while adhering to modern environmental stewardship practices.

Key Processes: Flotation, CIP/CIL, Cyanidation, Gravity Separation, SAG Mill, Ball Mill, Crushing

Target Commodities: Gold, Silver, Copper, Zinc, Lead