Gekko Systems IPJs make a significant contribution to copper recovery at New Afton

The New Afton Mine is wholly owned by New Gold. The mine site is located in Kamloops, British Columbia. The mining method is block cave with the primary copper-bearing mineral in the original cave being primarily chalcopyrite. However, the New Afton Mine has more recently processed large quantities of metallic native copper from the upper oxide (supergene) and transition ores which do not recover as well in the conventional flotation circuit. According to Senior Metallurgist, Jennifer Katchen, this put at risk an average of 4.5% copper recovery in supergene ore and potentially more on individual days depending on the amount of native copper in the plant feed.

The project justification utilised an overall Cu recovery increase of 1.4% between October 2018-2021 with a payback period of two years. Because of the nature of the block cave, which draws ore down from the bottom and creates a cone of depression, it is difficult to control the feed blend to the mill. As a result, there was no option to batch run this ore separately from the main hypogene ore type. Supergene ore samples taken for metallurgical test- work were highly variable in their proportion of copper as native copper, ranging from 11% to 95% based on QEMSCAN mineralogical analyses. Analysis of tailings from testing indicated that the majority of the losses were due to native copper in the coarser size fractions (>200 micron).

Supergene ore copper recovery was expected to be in the low 70%s versus 82-84% for the hypogene and mesogene ore types. In order to de-risk the recovery, the New Afton team researched options for native copper recovery. While gold recovery benefit was considered, it was a lower priority due to relatively low gold head grades in the supergene ore.

Several gravity options were reviewed for the secondary (ball mill), tertiary and regrind grinding circuits. Due to the coarse nature of the native copper and the feed size to the gravity circuit required in the ball mill circuit (up to 10 mm), there were only two gravity options reviewed for this circuit. The first was Dense Media Separation but this was deemed to have too high a CAPEX and OPEX and was rejected on its inability to process ore finer than 500 microns. The Gekko IPJ was selected for the ball mill circuit over centrifugal concentration and coarse flotation technology due to its capability to process the widest range of particle sizes present in the ball mill grinding circuit (from <100 micron to ~8 mm size).

The flowsheet consists of a rougher IPJ3500, which is the first unit of its type in operation in the world. This is fed with cyclone feed from the cyclone distributor, due to its lower solids density no further feed dilution is required.

This was important in allowing the ball mill circuit water balance to be maintained while still operating the existing Flash flotation cell. The feed is approximately 200 cm3/h @ 50% solids by weight (Cw). The rougher typically provides a 3-5x upgrade of the feed grade. The unexpected outcome at this point was the gold recovery, which is higher than anticipated. The rougher provides about a four-time upgrade on the Au grade. Mineralogical analysis has shown 96% of this gold is present as native gold, primarily in -300 μm particles.

The proposed flowsheet by New Afton required the installation of the world first high-volume InLine Pressure Jig IPJ3500. This unit treats nominal throughout put rates of 200 t/h-250 t/h depending on the application and has been recently developed by Gekko Systems particularly for base metal and larger throughput operations. Due to potential demand an even larger sized unit is on the drawing board.

In order to optimise the circuit, the team at New Afton have worked with Gekko to control mass pull, manage water consumption and balance the circuit. Due to the coarse nature of the feed to the circuit the New Afton team have progressively addressed the issues of pipe and orifice wear with ceramic and tungsten inserts in the areas of low service life.

A novel approach to reducing mass pull was utilised by the New Afton team by reducing open screen area in the IPJs which has helped stabilise the circuit. The outcome has been a gravity recovery circuit which operates with very little operator input and achieves consistently high-grade concentrate. The performance of the operating circuit is achieving better outcomes than the test work suggested. The circuit has been de-risked and has the capability of maintaining high recoveries even in high native copper environment.

The overall recovery benefit in the justification was estimated at 1.4% whilst the native copper ore is present in the feed, which is projected to end Q1 2021.

The IPJs have made a significant contribution to copper recovery – approximately 9% of total copper – and have helped maintain the overall high copper recoveries in the New Afton plant. Overall native copper recovery from the gravity circuit is in the order of 50%. This reduces the mill circulating load and reduces coarse native copper (>200 micron) reporting to the tertiary circuit and subsequently the flotation circuit and potentially to the flotation tails. In addition, very high-grade concentrate is produced for both gold and copper which is sent directly to final concentrate.

Other benefits include financial returns from higher than expected gold recovery. Low water addition from the new circuit minimised any water balance issues and the IPJ’s are a low cost per tonne technology.

Jennifer Katchen states: “The IPJs are removing native copper and gold from the circuit in line with the original design parameters. Once optimised the jigs require very little day to day operational input. Theyare producing higher copper and gold grade concentrates than design, consistently meeting the grade required for reporting to final concentrate.”