Gold & Silver Recovery: Flotation and Leaching at Lawyers-Ranch

Source: Thesis Gold Inc (2026)
Website: https://www.thesisgoldsilver.com/lawyers-ranch-project/

Critical Data

Overview

The Lawyers-Ranch Project, operated by Thesis Gold Inc., is a significant gold-silver mining venture located in British Columbia, Canada. The process plant, designed by Ausenco Engineering Canada ULC, is set to process 5 million tonnes of ore per year from both open pit and underground resources. The facility employs a two-phase recovery strategy: Phase 1 (Years 1–3) produces a saleable flotation concentrate plus gold-silver doré, while Phase 2 (Years 4–15) focuses solely on doré production. The flowsheet integrates primary crushing, SAG/ball mill grinding, gravity concentration, flotation, regrind, concentrate leaching, tailings leaching, counter-current decantation (CCD), and Merrill-Crowe precipitation. The plant is designed to handle nominal throughput of 13,700 t/d with high availability, ensuring robust gold and silver recovery. This project is significant for its adaptive flowsheet that responds to changing ore characteristics over the mine life, maximizing economic returns through conventional yet optimized technologies.

Key Process Stages

• Stage 1: Crushing and Stockpiling – Run-of-mine ore (F80 800 mm) is crushed by a jaw crusher to a P80 of 160 mm and conveyed to a covered coarse ore stockpile providing 12 hours of live storage. The circuit operates at 65% availability with a capacity of 878 t/h, using a vibrating grizzly feeder, rock breaker, and reclaim feeders.
• Stage 2: Grinding Circuit – A SAG mill (9.75 m dia. × 5 m EGL, 8.8 MW variable speed) reduces ore from F80 135 mm, with pebble crushing for oversize. The ball mill (6.4 m dia. × 9.8 m EGL, 7.1 MW) operates in closed circuit with hydrocyclones (500 mm dia.) to achieve a primary grind P80 of 125 µm. The circuit handles a 300–400% circulating load at 75% solids.
• Stage 3: Gravity Concentration and Intensive Leaching – 50% of cyclone feed is diverted to a gravity concentrator (45 kW) producing a concentrate (0.04% mass pull) that feeds an intensive cyanidation unit (ICU). The ICU leaches gold and silver into a rich eluate, which undergoes electrowinning to produce sludge for the refinery.
• Stage 4: Flotation, Regrind, and Cleaner Circuit – Rougher flotation (3 cells, 224 m³ each) and scavenger flotation (4 cells, 168 m³ each) produce a rougher concentrate that is reground to P80 40 µm using a 600 kW stirred mill, then upgraded through three stages of cleaner flotation (34.5, 23, 11.5 m³ cells). The final concentrate (1% of plant feed) is dewatered to 10% moisture via thickener and plate-and-frame filter (Phase 1 only).
• Stage 5: Concentrate Leaching and Tailings Leaching – Combined gravity tailings and cleaner scavenger concentrate are reground to P80 20 µm, then leached in three tanks (1,059 m³ each) for 36 hours at 19% solids with cyanide and oxygen. Scavenger flotation tailings are thickened to 50% solids and leached for 18 hours in four tanks (3,892 m³ each). Both leach circuits feed a 4-stage CCD system (30 m dia. thickeners) to recover pregnant solution, which is clarified and processed through Merrill-Crowe (zinc cementation) to produce doré.

Additional Interesting Data and Summary

The Lawyers-Ranch process plant is designed for a 15-year life of mine with two distinct operating phases. Phase 1 integrates flotation concentrate production (1% of feed) with concentrate leaching and doré production, achieving design recoveries of 65% Au and 57% Ag to concentrate, plus 29% Au and 30% Ag to doré. Phase 2 omits cleaner flotation and concentrate dewatering, routing all material through scavenger cleaner flotation and leaching, achieving 93% Au and 81% Ag recovery to doré. The plant’s total installed power demand is 19,535 kW, with grinding being the largest consumer (10,975 kW, 88.5 GWh/year). Reagent consumption includes sodium cyanide (3,611 t/a in Phase 1, 3,799 t/a in Phase 2), lime (9,511 t/a), and PAX (262 t/a). Cyanide detoxification uses the SO₂/air method with 90 minutes residence time in two 1,515 m³ tanks, reducing free cyanide to acceptable levels for tailings disposal. Tailings are thickened to 60% solids and sent to a tailings management facility (TMF), with final settled density of 80% solids. The process plant layout includes outdoor CCD thickeners (30 m dia.) covered with fiberglass to retain heat in British Columbia’s climate. The Merrill-Crowe circuit and refinery are secured with restricted access and CCTV for doré handling. The project’s sustainability is enhanced by recycling process water from thickener overflows and using conventional, low-risk technologies. Future outlook indicates the ability to switch back to concentrate production if market conditions favor, providing operational flexibility. This flowsheet represents a robust, standard approach for gold-silver recovery from a complex sulphide ore body, balancing throughput, recovery, and capital efficiency.

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

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