Josemaría Copper-Gold Technical Report (PFS) — 2018

The 2018 PFS defines a 150,000 tpd sulphide ore processing plant designed to produce copper concentrate using HPGR comminution and conventional flotation.

Report context

This technical report presents the results of a Pre-Feasibility Study (PFS) for the Josemaría copper-gold project, dated December 2018. The process facilities are designed to treat a nominal rate of 150,000 tpd of sulphide ore and produce copper concentrate. The process design is based on existing technologies and the largest available and proven equipment sizes.

Processing route

Comminution Circuit Selection

Ausenco undertook a comminution circuit review study for the Josemaría project as part of the PFS. This review included benchmarking the Josemaría ore against other operations, evaluating the previous comminution circuit design, providing a high-level design for SABC (semi-autogenous mill, ball mill, and pebble crushing) and HPGR-B plants, and updating the capital and operating cost estimates.

A conservative approach was adopted for sizing the HPGRs due to a limited number of HPGR laboratory and/or pilot trials completed and the absence of parameters obtained therefrom such as specific throughput rates (M-dot) and recycle rates. An HPGR motor power of 6,800 kW was considered to ensure that the installed power is sufficient to achieve nominal throughput rate.

The SABC circuit option is an established technological approach to comminution and generally results in smaller physical footprints than HPGR-based circuits. The capital cost estimate showed that installation of an SABC circuit resulted in 15% lower Capex than the HPGR-B circuit. However, the SABC circuit required higher energy and steel media consumption and the operating cost estimated for the HPGR-B circuit was 27% lower than that for the SABC circuit. The ore characteristics, net present cost (NPC) calculations and benchmarking against similar ores strongly support the use of HPGR technology over the life of the Josemaría project. The cumulative NPC was calculated for a 20-year period using an 8% discount rate.

Crushing and Screening

The crushing circuit will consist of two parallel trains of identical primary gyratory crushers (1,000 kW installed power), treating a total of 8,333 tph (dry). ROM material will be delivered to the primary crushers by mine trucks into a single dump pocket with a 500-t live capacity. The primary crusher will receive ROM (F100 of 1,200 mm) and reduce it to a P80 of 137 mm. The primary crusher will discharge into a 500-t live capacity surge pocket where a variable speed apron feeder will deliver ore to the coarse ore stockpile feed conveyor.

Dual reclaim tunnel systems will house a total of six reclaim apron feeders (three per train) that draw ore from the coarse ore stockpile (454,000 wet t) to two coarse ore reclaim conveyors. The coarse ore stockpile will have a total live capacity of 12 hours of mill feed at the nominal feed rate (91,000 wet t). Material will be reclaimed at an average rate of 3,676 tph (dry) per train.

There will be four secondary cone crushers (933 kW installed power), each operating in an independent line. The oversize (P100 = 365 mm) will be reduced to a product with a P80 of 41 mm. An allocation of space for two additional crushers will allow for possible future expansion.

Tertiary crushing will be performed by four independent HPGR lines (6,800 kW installed power). The HPGRs will be in closed circuit with wet screens, with the downstream fine ore screens providing a control on the particle size to the grinding circuit (F80 = 3.8 mm). Oversize (> 6 mm) from these screens will return to the HPGR surge bin.

Grinding

There will be four independent grinding lines, each consisting of a fine ore surge bin, two reclaim feeders, two screens, a pump box and cyclone feed pump, a cyclone cluster and a ball mill (7.9 m diameter x 12.5 m effective grinding length with 19,000 kW installed power). Cyclone overflow (P80 = 130 µm) will be sampled and analyzed for size and metal content as it passes to two banks of the rougher scavenger flotation circuit. Each grinding line will have a single (duty only) variable speed cyclone feed pump.

Flotation

The flotation circuit is designed to receive feed material grading 0.29% Cu and 0.21 g/t Au over the LOM. Nominal copper recovery to the flotation concentrate is 86.4%, with a gold recovery of 70.9%. Nominal copper concentrate grade is expected to be 25.1% Cu with 14.5 g/t Au.

Flotation comprises rougher scavenger flotation, regrinding of the rougher concentrate and three stages of cleaner flotation to produce a final copper concentrate. Rougher scavenger flotation will consist of two parallel lines of nine 630 m³ forced air tank flotation cells fed at a density of 35% w/w solids. The concentrate from the first two cells of each row, of higher copper grade, will be diverted directly to cleaner flotation, bypassing the regrind stage. The concentrate from the remaining seven cells will require regrind prior to further upgrading.

The regrind section will consist of three vertical stirred regrind mills (11,220 kW installed power), where size reduction to a P80 of 25 µm will be achieved in closed circuit with hydrocyclones.

The first cleaner flotation section will consist of six 300 m³ forced air tank flotation cells. The tailings from the first cleaner flotation will feed the cleaner scavenger flotation section consisting of seven 630 m³ forced air tank flotation cells. The second cleaner flotation section will consist of six 70 m³ forced air tank flotation cells. The third cleaner section will consist of six 30 m³ forced air tank flotation cells.

Copper flotation will be promoted using Potassium Amyl Xanthate (PAX), Sascol 95 and Matcol TC-123 collectors with Methyl Isobutyl Carbinol (MIBC) added as a frother. Lime will be used for pH modification, as required.

Concentrate Dewatering

The final copper concentrate will be thickened with flocculant to 65% solids in a high-rate thickener (35-m diameter). An agitated tank will have capacity to store six hours production of thickened concentrate ahead of the filtration stage. One pressure filter (61 plates, 2.5 m by 2.5 m plates) will reduce moisture content of the concentrate to approximately 9% for shipment.

Tailings Management

Flotation tailings will represent approximately 98% of the total plant feed tonnage. Tailings will initially be thickened in two high rate thickeners (85 m diameter) to approximately 62% solids and pumped to the TSF. The thickener overflow will be recycled to the process water system. The overall facility has no discharge to the surrounding environment other than water evaporation to the atmosphere.

Key reported parameters

Technical qualifications

The HPGR sizing adopted a conservative approach due to a limited number of HPGR laboratory and/or pilot trials completed, and the absence of parameters such as specific throughput rates (M-dot) and recycle rates. Process design criteria and equipment sizing are mainly based on the Phase II testwork completed by SGS, which included comminution and flotation tests on both composite and variability samples suitable for PFS level. Simplified flotation tests conducted by ALS, Kamloops in the late stage of the PFS showed potential to reduce the flotation circuit size and simplify reagent schemes relative to earlier testwork, and further testwork is recommended to evaluate the simplified flotation circuit and reagent schemes in the next phase of study.

Source: Josemaría Copper-Gold Technical Report (PFS), December 2018, Section 17 Recovery Methods.