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. 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.

DeGrussa commenced as an open-pit operation but now treats solely underground ore through its 1.5 Mtpa concentrator. The concentrator plant was built in 2011 and commenced commercial production in September 2012.

An underground mine is developed comprising over 19km of lateral development and 11km of vertical development. Underground mine development (to Q3 CY2012) is estimated at $56 million. Underground extraction will be undertaken using long-hole open stoping (both transverse and longitudinal). Open stopes will be up to 75m high (mostly 50m) by 25m long by the orebody width (up to 40m, but averaging 20m), with the proposed mining sequence aiming for maximum extraction of the resource using pastefill.

Monty Mine
The mining method selected is long-hole open stoping (LHOS) with fill. Primary fill material will be Cemented Aggregate Fill (CAF) with unconsolidated rock fill (RF) used where consolidated fill is not required. This method allows for total extraction where economic and provides good extraction flexibility with variable geometry and ground conditions.

An overhand mining sequence has been selected employing multiple mining panels. CAF sill pillars will be established to create mining panels. Strategic CAF rib pillars will be used to manage local stope and mining panel ground stability. The overhand sequence provides an opportunity to complete grade control drilling prior to accessing the orebody.

The selected mining method is considered appropriate for the nature of the defined Mineral Resources and surrounding host rock. Experienced gained at the nearby DeGrussa underground mine has been adopted where applicable as extraction is expected to occur under comparable conditions.

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.

Sandfire’s DeGrussa Copper-Gold operation in West Australia is a new high grade copper sulfide mine, which includes a 1.5 Mtpa concentrator which was completed in 2013.

Early after commissioning, it was identified that the flotation capacity in the all-mechanical cleaner circuit was not sufficient. In order to improve recovery, the tail from the cleaner scavenger was sent back to feed the rougher scavengers. Test-work was done on-site to evaluate the possibility of using a flotation column as a pre-cleaner. A CavTube™ sparging system was selected, which is especially ef ........