Cobre Panamá Project — 2015 Technical Report

This technical report details the proposed conventional mineral processing route for the Cobre Panamá copper-molybdenum project, including crushing, grinding, flotation, and tailings disposal.

Report context

This June 2015 technical report for the Cobre Panamá Project describes the proposed mineral processing facilities for treating ore from multiple open pits to produce copper and molybdenum concentrates. The processing plant is designed with a staged expansion capability, starting at 190,000 t/day in 2018 and increasing to a nominal 246,575 t/day from 2023 onwards, with a design capacity up to 274,000 t/day allowing for 10% day-to-day fluctuations.

Processing route

Crushing and grinding

The processing route begins with semi-mobile in-pit primary gyratory crushers. Crushed ore is conveyed out of the pit to a surface transfer point, then via an overland conveyor to either secondary crusher feed bins or directly to a coarse ore stockpile at the concentrator. The coarse ore stockpile is designed to hold a 2½-day supply for the mill, with 16 hours available to reclaim feeders without bulldozer assistance.

Two trains of feeders and conveyors draw ore from below the coarse ore stockpile to feed two parallel wet-grinding lines, each comprising one semi-autogenous grinding (SAG) mill and two ball mills, all with gearless drives. A third train feeds a third SAG mill linked to the other ball mill trains, enabling maintenance of treatment rate and independent operation.

SAG mill circuits are closed by trommel screens followed by washing screens, with oversize conveyed to pebble crushers. The pebble crushing circuits include pebble bins, cone crushers, and a bypass arrangement, with crushed pebbles returned to SAG mills via stockpile feed conveyors. Discharge from each SAG mill is cycloned; finished product gravitates to a surge tank for pumping to flotation, while unfinished product splits evenly between two ball-mill circuits closed by hydrocyclones.

A gravity gold recovery plant is linked to the ball mill circuit. A proportion of ball mill discharge is pumped to a gravity gold circuit comprising scalping screens and centrifugal gravity concentrators, which recover free gold for upgrading to bullion. Tails from the gravity concentrators return to the milling circuit.

Flotation

Ground slurry proceeds to a flotation circuit where a bulk sulphide concentrate containing copper, molybdenum, and gold values is collected and concentrated in rougher followed by cleaner flotation. A primary high-grade concentrate from the first rougher cell is cleaned directly in columns to produce a final product. The balance from remaining rougher cells is fed into regrind mills, then cleaned in two stages of mechanical cells followed by one column stage to produce a final bulk concentrate.

From 2025, an increase in rougher capacity is required to accommodate higher throughput, but no change to existing downstream regrind and cleaning capacity is needed since copper quantity remains the same. The bulk concentrate is thickened in conventional thickeners (with no flocculant) and pumped to a differential flotation plant, where copper minerals are depressed and molybdenite floated into a molybdenum concentrate.

Concentrates

Molybdenum concentrate is filtered, dried, and packaged in bulk bags for shipment to offshore roasters. Tailings from the molybdenum flotation circuit constitute the copper concentrate, which is thickened and pumped approximately 25 km to a filter plant at the port site. If molybdenum head grade is very low, the molybdenum separation plant can be bypassed.

Copper/gold concentrate piped from the plant site is filtered in automatic filter presses, reclaimed using a mechanical reclaimer, and loaded by closed conveyors onto bulk ore carriers. The dried concentrate (8% to 9% moisture) is stored in a covered building with a capacity of 140,000 t. Filtrate water is pumped through a return pipeline to the tailings management facility (TMF).

Tailings disposal and process water reclaim

For the first twenty years of operation, tailings from rougher and cleaning steps are deposited in the TMF located north of the mine and plant. The majority of rougher tailings are processed through cyclones, with the coarse fraction used to construct TMF embankments. The finer fraction and unused cyclone coarser tailings are deposited within the TMF on beaches upstream of the embankments. Cleaner circuit tailings are deposited underwater to prevent acid drainage generation.

In the original Inmet concepts, after twenty years the depleted Botija Pit would receive cleaner tailings deposited underwater, while rougher tailings would continue to the TMF for a period sufficient to form a cover, after which rougher tailings would also be diverted to the depleted Botija Pit and then ultimately to the depleted Colina Pit. Timeframes for tailings backfill will be revised as a function of new mining and processing schedules when production commences.

Reclaim water is pumped from the TMF to the process water pond north of the plant site, with a tee off providing water for the tailings cyclone plant. From the process water pond, water is used in the milling plant or boosted for general in-plant use. Excess water from the TMF overflows via a decant tower into the Del Medio River.

Key reported parameters

Technical qualifications

The report notes that these processing descriptions largely reproduce information from a 2013 source with updates, and that the information shows proposed design parameters rather than operational results. The design head grades (0.65% Cu and 0.023% Mo) are stated to be higher than the highest sustained head grades scheduled in the mine plan (0.48% Cu in 2027 and 0.008% Mo in 2021), providing flexibility to accommodate a wide range of head grades over the project life. The original Inmet tailings concept timeframes are noted as subject to revision based on new mining and processing schedules produced when production commences.

Source: Cobre Panamá Project Technical Report, June 2015, Section 17 – Recovery Methods.