The DeGrussa VMS deposit is high in copper and gold mineralisation with minor zinc and minor lead. There are varying amounts of the dominant iron sulphides which comprise chalcopyrite and pyrite, in abundance with minor pyrrohtite, magnetite, sphalerite and galena. There is little evidence of a pervasive stringer zone beneath the deposit although minor zones have been detected in drilling. The alteration at DeGrussa is primarily chlorite, quartz, and sericite that is more pervasive in the footwall contacts.

In the near surface parts of the DeGrussa and Conductor 1 lodes there is a zone of enriched supergene chalcocite mineralisation (containing direct shipping copper – gold ore in the DeGrussa lode) which transitions into a complex zone of copper oxide “plume” mineralisation. The oxide copper minerals noted to date include major chrysocolla, malachite, azurite, cuprite, native copper and minor tenorite, cuprous neotercite and other exotic copper oxide species.

The host rocks are a sequence of sediments, mafic volcaniclastics, dolerites, gabbros and minor local quartz carbonate breccias (mineralised), jasper beds and banded iron formation. The setting is structurally complex and dominated by the Shiraz Fault zone which offsets the ore bodies and is a significant local structure with varying widths of highly broken material. The Merlot and Pinot faults also have a local interaction with the massive sulphide lenses though are of a lesser impact than the Shiraz Fault.

Monty Mine
The Monty orebody is a volcanogenic massive sulphide similar in composition to the nearby DeGrussa orebodies.

Production was sourced from all lenses at DeGrussa and Monty throughout the reporting period (2020 financial year). The ramp-up of the Monty mine was completed during the year along with grade control drilling, defining the geometry of the deposit and underpinning an updated Ore Reserve estimate.

The mining operations strategy adopted for the DeGrussa and Monty operations targets the blending of the material from both mines and scheduling to have both life of mine plans completed as close to the same time as practicable. The updated underground Ore Reserve continues to support this strategy with DeGrussa producing approximately 1.2Mtpa and Monty producing approximately 0.4Mtpa.

DeGrussa Mine
Primary mining methods employed are sub-level open stoping (SLOS) and long-hole open stoping (LHOS) with fill. Cut and fill techniques are also employed in remnant areas. Primary fill material is paste with minor use of cemented rock fill and rock fill when appropriate.

Monty Mine
The underground mining method is long-hole open stoping (both transverse and longitudinal) with minor areas of jumbo cut and fill or uphole benching in some of the narrower areas. The primary method of backfill is paste fill. The sequence aims for 100% extraction of the orebody.

The DeGrussa Copper Mine commenced commissioning of its 1.5Mtpa concentrator in September 2012. During its first 18 months of operation, the milling circuit experienced numerous issues. The majority of these problems originated from the very fine feed particle size distribution fed into the processing plant.

Mill throughput increased following primary screen and pebble crusher installations, and SAG mill optimisation in FY15.

Currently the DeGrussa processing plant has a capacity of 1.6Mtpa.

Initiall design (2012)
The processing plant includes primary crushing, primary closed circuit milling, secondary closed circuit milling, conventional three stage flotation including concentrate regrind and tailings disposal.

The design of the DeGrussa grinding circuit is a typical SAG and ball mill (SAB) type. A single Metso C140 jaw crusher operating with a closed side setting of 125mm crushes pre-blended run of mine (ROM) material to 80% passing (P80) 146mm which is then conveyed to a 4,200t primary crushed ore storage bin. The material is reclaimed via one of three vibrating feeders which deliver ore to the primary mill. The installed primary mill is an Outotec 7.30m x 3.35m effective grinding length (EGL) grate discharge SAG mill with 3.4MW installed power. The mill is also installed with Turbo Pulp Lifters (TPL) in lieu of standard radial pulp lifters.

Once material is discharged from the primary mill the slurry is pumped to a cluster of four CVX500 cyclones which are designed to achieve a P80 of 180µm. The cyclone underflow gravitates to the SAG mill feed chute via the primary flash flotation cell and the cyclone overflow gravitates to the ball mill discharge hopper. This slurry, along with the ball mill discharge, is pumped to the secondary cyclone cluster including twelve 250CVX cyclones which are designed to achieve a P80 of 45µm. Secondary cyclone underflow gravitates to the ball mill feed chute via the secondary flash flotation cell whilst secondary cyclone overflow gravitates to the flotation circuit.

The installed secondary mill is an Outotec 4.7m x 7.5m grate discharge ball mill with 2.6MW installed power. The ball mill is also installed with Turbo Pulp Lifters (TPL) in lieu of standard pulp lifters.

Grinding Improvement (2015)
• Primary cyclones replaced with screen to improve mass transfer to secondary milling circuit for particle size distribution control and optimal chalcopyrite liberation for flotation;
• Pebble crusher installed for breakage of critical size particles in the primary milling circuit;
• Wear improvement initiatives to push out maintenance shutdown frequency.

Mill throughput for the 2020 financial year was as planned at around 1.6Mtpa, with copper recoveries in line with forecasts at 92.9% and gold recoveries at 45.9%. Mill throughput rates and recoveries were impacted slightly during the reporting period by the introduction of transitional ore from the DeGrussa crown pillar, which was successfully addressed by close management of blending strategies.

The DeGrussa processing plant has a capacity of 1.6Mtpa. The mining operations strategy adopted for the DeGrussa and Monty operations targets the blending of the material from both mines and scheduling to have both life of mine plans completed as close to the same time as practicable.

Testwork on the Monty ore has shown that flotation and comminution characteristics of the ores are similar to DeGrussa ore and Monty can be treated at DeGrussa with high recoveries.

The DeGrussa concentrator is designed for ultimate performance. Outotec had previously partnered ........