El Roble Mine — 2023 Technical Report

The El Roble Mine process plant uses conventional crushing, grinding, and flotation to produce a copper-gold concentrate, with a nominal throughput of 850 tonnes per day.

The El Roble Mine process plant is a conventional facility that extracts copper and gold from feed material through a series of sub-processes: crushing, grinding, flotation, concentrate thickening and filtering, and tailings disposal. The plant has a rated nominal throughput capacity of 850 tonnes per day. Before flotation, the ore is ground to 80 per cent passing 200 mesh. Process tailings are deposited in an impoundment facility along the banks of the Atrato River, downstream of the plant, with decanted process waste water released into the river at a pH between 7.48 and 8.45. Over the 12 months from January 2023 to December 2023, average process recovery was 91.67 per cent for copper and 59.74 per cent for gold. The only penalty metal known to the Qualified Person responsible for this portion of the Technical Report that occasionally exceeds maximum limits is mercury. Smelter charges are currently US$88 per dry metric tonne. The concentrate sales contract specifies payables of copper content minus 1.1 per cent, 95 per cent of contained gold, and 95 per cent of contained silver. Contract specifications require copper concentrate grades between 18 and 24 per cent Cu, gold grades between 4 and 20 grams per tonne, and silver grades between 30 and 60 grams per tonne.

Critical Data

Overview

The El Roble process plant is designed to treat copper-gold ore using crushing, grinding, and flotation. The plant uses a SAG mill and ball mill circuit followed by multiple flotation stages. Concentrate is thickened, filtered, dried, and stored on site before shipment by highway truck to the Pacific Coast port of Buenaventura. The flowsheet is considered suitable for the ore type, providing reasonable recoveries of copper and gold. Electrical energy is supplied from the national grid.

Key Process Stages

The crushing circuit comprises a series of bins, feeders, and conveyors. Coarse ore is fed via two coarse ore bins, each with 640 tons effective capacity, through apron feeders onto a conveyor belt system. A jaw crusher with a 24-inch by 36-inch opening is incorporated in the crushing stage. A conveyor feeds a 30-ton storage hopper, and subsequent conveyors feed the SAG mill. An electronic scale on the final conveyor records tonnage entering the SAG mill.

Grinding is performed by a SAG mill with dimensions of 18 feet diameter by 6 feet (200-ML-001), operating in closed circuit. The SAG mill discharge grate has openings of 19 mm by 50 mm, and the trommel screen mesh has 12 mm openings. Classification is completed by a nest of cyclones. Cyclone underflow reports to an Otsuka 5-foot by 5-foot ball mill for further grinding, while cyclone overflow reports to the flotation circuit.

The flotation circuit is a multi-stage arrangement of cells of various styles and sizes. The circuit begins with an OK-20-style flotation cell fed by cyclone overflow. The OK-30-style cell overflow reports to the concentrate thickener, while underflow reports to a bank of two OK-8-style flotation cells. The flotation overflow from these cells reports to the concentrate thickener, and the underflow reports to eight Denver 100-style flotation cells. Cell overflow feeds the final cleaner cells, with cleaner overflow reporting to the concentrate thickener and underflow to the tailings thickener. A flash cell (SK-240) is part of the circuit, with overflow transported by gravity to a 10-foot by 10-foot pulp conditioner and underflow returned to the SAG mill. The circuit also includes a bank of four OK-8 cells and an OK-14 flotation cell, with underflow transported to the concentrate conditioner. Sub-A 24 cells perform second fine cleaning, operating in a closed circuit. Concentrate from the second fine and coarse cleaning is sent to the concentrate conditioner.

Concentrate thickening and filtering remove water from the concentrate. Thickened material reports to a concentrate filter. The filtered material has a moisture content between 11 and 13 per cent water. A rotary dryer tank, operating with a gas burner, reduces moisture to around 10 per cent. Filtered and dried material is conveyed to a concentrate storage shed for secure storage before shipment.

Tailings are processed through a five-meter by ten-meter vertical thickener with a conical base. The thickener overflow is recycled to the ball mill and flotation circuits, while underflow reports to a pump box for pumping to the tailings impoundment. A tailings dewatering plant receives tailings pulps with solids content greater than 70 per cent from the vertical thickener. This plant produces a filtered cake for dry stack tailings disposal, reducing the need for a wet tailings storage facility. The filtered material passes through ceramic discs within the filter drum and is discharged into filter tanks. A filtration skid, comprising a filtration pump, turbidity sensor, and automatic valves, regulates filtration levels and monitors water quality in the process water tank, detecting issues such as broken or detached hoses or ceramic membranes.

Electrical energy is supplied as three-phase power from the national grid at a nominal voltage of 13,200 kVA. The high voltage line is split at the property boundary, with feeds to the process plant, mine, and smaller sub-stations across the property. Recorded electrical energy consumption for the period January to December 2023 includes 371,922 kW for SAG milling, 283,123 kW for flotation, 51,697 kW for tailings, 74,499 kW for filtration, and 86,218 kW for the filtrate dehydration plant.

Process water data from a mass balance at 815 dry metric tonnes throughput indicates total water consumption of 1,780.78 m³ per day, 44.52 m³ per hour, and a water consumption ratio of 2.16 m³ per dry metric tonne. Total water used in the plant, considering 60 per cent water reused from all processes, is 1,068.47 m³ per day, 30,172.15 m³ per month, and 362,065.80 m³ per year. Recirculated water consumption is 1.30 m³ per dry metric tonne.

Additional Interesting Data and Summary

Historical operating data from January to December 2023 provides insight into plant performance, including average copper recovery of 91.67 per cent and gold recovery of 59.74 per cent. The plant's tailings dewatering system enables dry stack disposal, significantly reducing reliance on wet storage capacity. The reported mass balance table provides a detailed breakdown of the processing parameters, highlighting water consumption and recirculation rates.

Key Processes

• Crushing using jaw crusher and conveyor system
• Grinding in SAG mill and ball mill circuit
• Flotation using multiple cell types
• Concentrate thickening, filtering, and drying
• Tailings dewatering for dry stack disposal

Source: El Roble Mine , 2023 Technical Report, 2023. Project website: [Not stated]

Editorial Note: The source text includes contradictory statements regarding the flotation cell configuration and the mass balance water consumption values. One passage describes the flotation circuit as beginning with an OK-20-style cell, while another passage describes a flash cell (SK-240) as the start of concentration. Additionally, the mass balance table in the source contains both formatted tables and raw text with unclear column structure, leading to potential inconsistencies in reported water consumption figures.

Project website: El Roble Mine, 2023 Technical Report