At Northparkes, the Goonumbla Volcanics are a folded sequence of trachyandesitic to trachytic volcanics and volcaniclastic sediments that are interpreted to have been deposited in a submarine environment.

In the Northparkes region the Goonumbla Volcanics have been intruded by equigranular monzonite stocks. Quartz monzonite porphyry pipes and dykes, some of which are associated with mineralisation, have intruded both the Goonumbla Volcanics and the equigranular monzonite stocks.

The Northparkes deposits are typical porphyry copper systems in that the mineralisation and alteration are zoned around quartz monzonite porphyries. The porphyries form narrow (typically less than 50 metres in diameter) but vertically extensive (greater than 900 metres) pipes. Mineralisation extends from the porphyries into their host lithology. The E26 and E48 deposits range from 60 to 400m in diameter (>0.4% copper) and extend vertically for more than 900m.

Sulphide mineralisation occurs in quartz stockwork veins, as disseminations and fracture coatings. Highest grades are generally associated with the most intense stockwork veining. Sulphide species in the systems are zoned from bornite dominant cores, centred on the quartz monzonite porphyries, outwards through a chalcopyrite dominant zone to distal pyrite. As the copper grade increases (approximately >1.2% Cu), the content of covellite, digenite and chalcocite associated with the bornite mineralisation also increases. Gold normally occurs as fine inclusions within the bornite.

The alteration zonation is complex but tends to be zoned around the quartz monzonite porphyries with a central K-feldspar altered zone surrounded by biotite magnetite alteration. The K-feldspar alteration zone at E26 is well developed and extends up to 100 metres outboard from the porphyry. This is in contrast to E22, E27 and E48 where K-feldspar alteration is generally less than 10 metres outboard from the porphyries. The biotite magnetite zone is strongly developed at the E22, E27 and E48 deposits, and forms a zone up to 200 metres from the porphyry. It is this biotite-magnetite zone that forms the distinctive annular magnetic features at E22 and E27.

A central white sericite-quartz +/- alunite alteration zone occurs at E26, and to a lesser extent at E48, and is generally associated with the high grade zones within the deposits. At E48, an alteration assemblage of hematitesericite+/ carbonate occurs both within and proximal to the mineralisation.

All of the Northparkes deposits are cross cut by late faults/veins filled with quartz-carbonate+/- gypsum, anhydrite, pyrite, chalcopyrite, sphalerite and galena. The associated sericite alteration extends up to 10 metres from the fault.

Oxide mineralisation blankets were well developed over the E22 and E27 deposits. The upper blanket was gold rich and copper poor. The lower blanket was enriched in copper by supergene processes. The dominant copper oxide minerals at E22 and E27 were copper carbonates (malachite and azurite) and phosphates (pseudomalachite and libethenite) with lesser chalcocite, native copper, cuprite and chrysocolla. A gold poor, less well developed, supergene copper blanket was also developed over the E26 deposit. At E26 the oxide copper minerals included atacamite, clinoatacamite and sampleite, in addition to those copper minerals observed in E22 and E27.

Underground mining activities are currently undertaken in ore body E48 using block caving methods and E26 using Sub Level Cave (SLC) methods. Block Caving is an underground hard rock mining method that involves undermining an ore body, allowing it to progressively collapse under its own weight. It is the underground version of open pit mining. SLC methods rely on the undercutting of an area of rock, and then gradual failure of the overlying rock due to gravity and stress, to minimise mining risk and supply production.

The operations at E26 orebody ceased in 2008 due to ingress of clay in the draw points. The E26 SLC was commissioned in 2016. The construction of E48 block cave mine was completed in 2010, with the first ore extracted from E48 Lift 1 block cave mine, and is currently in production.

The E26 SLC project commenced construction in April 2015. The mine design aims to extract a remnant wedge of high-grade material adjacent to the E26 Lift 2 Block Cave. The SLC mining method involves construction of the sub level horizon followed by retreat drill and blast of that horizon. The broken material from blasting is recovered as the main source of production. The second sub level horizon is then constructed, as the top down process continues. The E26 SLC Mine consists of three sublevels approximately 20m apart. The first production ring in the E26 SLC was extracted in July 2016.

Automation (remote operation of underground load, haul and dump machinery) continued in the reporting period (2019) to maintain full automation of underground mine loaders. In mid-October 2015, Northparkes confirmed its position as the most automated underground mine in the world and achieved 100 percent automation of underground mine loaders.

Six autonomous Sandvik LH514 loaders (five electric and one diesel) operate 500 metres below the surface, tramming ore from the draw bells and dropping 11- to 12-tonne loads in the ROM bin for crushing. [https://www.australianmining.com.au/news/automation-pays-off-for-northparkes/]

Currently Northparkes is developing a new block cave (E26 Lift 1 North). Construction started in January 2019 and during 2019 approximately 3,689 metres of new tunnels were developed. This new block cave is scheduled to start full production in 2023.

Mining Operations Plan 2020 to 2022
Underground Mining
Access to the underground operations is by a 1 in 7 grade, 5m wide by 5.5m high decline from surface. Access to the E48 ore body is via a 200m extension from the access decline. Mined ore is transported to surface via underground conveyors and a dedicated hoisting shaft. The hoisting shaft is 520m deep.

The E48 extraction level, beneath the ore body, is located approximately 580m below surface and consists of 13 extraction drives, 143 draw bells (connecting the extraction level to the block cave above) and 262 draw points through which the broken rock is drawn.

Production mining in the E48 Block Cave is primarily undertaken using electric powered load-hauldump units with up to 100% of mining using automated loaders. These loaders tram the broken ore from the extraction level draw points and haul it between 50-400m to the primary crusher. The rock is crushed to less than 150mm diameter, then conveyed and hoisted up the hoisting shaft to the surface for overland conveying to the processing plant. Current production tonnes from E48 is approximately 5.4Mtpa.

Mining is also occurring in the E26 Sub-level Cave mine. 1.3Mtpa of ore is extracted from a 4 level SLC mine using a fleet of diesel powered equipment consisting mainly of loaders, trucks and drill rigs. Mining occurs from the top of the ore body and is extracted in approximately 20m high lifts using conventional drill and blast techniques.

Blasted ore is loaded into mine trucks with capacities ranging from 50t to 60t. The ore is then hauled to the E26 Primary crusher where it is crushed and then conveyed to the hoisting shaft.

Average production rates from underground mining are between 18,000-20,000t per operating day resulting in an annual average production rate of 6.5-7.6Mtpa. Daily and annual production levels will reflect localised changes in mining conditions and the prevailing throughput of the processing plant.

Open Cut Operations
Active open cut mining ceased in 2010.
Open cut operations are scheduled to recommence during the Mining Operations Plan period. The E31 and E31N pits are located adjacent to the Rosedale TSF. The E31 and E31N open cuts will have an area of approximately 6.3ha and 5.4ha respectively, will be taken to a depth of approximately 100m each and will extract a combined 3Mt of ore.

The E28N open cut is located to the east of the existing E48 subsidence zone. The E28N open cut has an approximate area of 6.2ha, will be taken to a depth of approximately 60m and will extract approximately 3Mt of ore.

The open cut mining will be undertaken on a campaign basis using conventional mining methods. These conventional mining methods include drill and blast and load and haul, using excavators and trucks.

The grinding circuit comprises two separate modules (Mod 1 and Mod 2), each incorporating a Semi Autogenous Grinding (SAG) mill, oversize crushing technology, two stages of ball milling and froth floatation.

Operations at Northparkes primarily comprises underground mining from multiple ore sources that feed a processing plant with a capacity of 6½ million tonnes per annum (Mtpa).

Ore processing includes several defined stages including grinding, floatation and thickening. The grinding circuit comprises two separate modules (Mod 1 and Mod 2), each incorporating a Semi-Autogenous Grinding (SAG) mill, oversize crushing technology, two stages of ball milling and froth floatation.

The floatation process floats a sulphide concentrate to recover copper and gold bearing minerals. From the floatation, the concentrate is processed through the concentrate thickener and transferred to the storage shed.

The tailings component is pumped from the floatation stage to a tails thickener and then to the Tailings Storage Facility (TSF).

In 2019 the Company completed the construction of new floating pool of phase II construction and commissioning of the tailings pond, which formed a part of the construction expansion engineering and earthwork project for establishing new crushing facilities.

The project scope considers a range of modifications and upgrades to each of the operating facilities to achieve a throughput rate of nominal 7.6Mtpa.