The Northparkes deposits occur within the Ordovician Goonumbla Volcanics of the Goonumbla Volcanic Complex and Wombin Volcanics. The Goonumbla Volcanics form part of the Junee-Narromine Volcanic Belt of the Lachlan Orogen and consist of a folded sequence of trachyandesitic to trachytic volcanics and volcaniclastic sediments that are interpreted to have been deposited in a submarine environment.

The Goonumbla Volcanics at Northparkes have undergone little deformation, with gentle to moderate bedding dips as a result of regional folding. The dominant structure observed to date in the Northparkes area is the Altona Fault, an east-dipping thrust fault, which truncates the top of E48 and GRP314 and is known to extend from east of E26 north through E27.

The porphyries form narrow, typically less than 50 m in diameter, but vertically extensive (greater than 1,000 m) pipes. Mineralisation extends from the porphyries into their host lithology. The current life of mine plan is focused on five porphyries, referred to as E26, E48, E22, E31 and GRP314; in addition to these zones numerous other mineralised porphyries exist across the district. The deposits are hosted within both the Goonumbla and Wombin Volcanics, with mineralisation related intrusive rocks effectively forming part of the latter.

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 per cent copper), the content of covellite, digenite and chalcocite associated with the bornite mineralisation also increases. Gold normally occurs as fine inclusions within the bornite; due to the intimate relationship with bornite, visible gold tends to occur within the highest-grade zones of the central portion of the deposit. A small portion of gold mineralisation does not appear to be directly associated with copper sulphide minerals. Silver is associated with copper sulphide minerals and is present in solid solution and as inclusions of silver-bearing tellurides and electrum. Copper-to-gold ratios differ between the different deposits and within individual deposits.

All of the Northparkes deposits are cross-cut by late faults/veins filled with quartz carbonate and minor gypsum, anhydrite, pyrite, tennantite chalcopyrite, sphalerite and galena, the associated sericite alteration can extend up to 10 m from the faults. Tennantite, which contributes arsenic to the final copper concentrate, is present in higher concentrations in the E48 deposit.

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.

The Northparkes deposits are typical porphyry copper systems, in that the mineralisation and alteration are zoned around multiphase quartz monzonite porphyries. As described by Pacey et al (2019) mineralization was caused by the forcible, periodic escape of low-viscosity, crystal and volatile-rich magmas. These exploited pre-existing structural intersections and focused the discharge of large quantities of magmatic fluids from the underlying chamber. The fluids circulated in intricate fracture networks to produce K-feldspar-sulphide veinlets and quartz sulphide stockwork veins, surrounded by K-feldspar–dominated alteration. Ore grades are exclusively located within the potassic alteration zones, although some have been sericitically overprinted.

During 2022 year saw the planned decline of the E48 Block Cave with E26L1N now having replaced E48 as the primary ore source. Planning to extract ore from E26L1N SLC 5 and 6, E31 and E31 Open Pits progressed through the year, as supplementary ore sources to E26L1N in the years to come.

Underground Operations
Block cave mining accounts for the majority of ore production at Northparkes, with minor contributions from surface stockpile reclamation and open pit mining. Preproduction mining development work consists of establishing two working levels, the undercut level and extraction level, at the base of each ore block, as well as the development to support the associated material handling system. Northparkes has developed its own unique extraction level layout that locates the material handling system, including crusher, to the side of the extraction level, thereby alleviating the need to construct a third level dedicated to haulage. Similarly, it has established the extraction level as the primary ventilation level, thereby eliminating development to support mine ventilation. The undercut level, which is used to initiate caving, is 14 - 20 m vertically above the extraction level, the height being dependent on the undercutting method. Undercutting, which involves sequential firings of overlapping fans of blastholes to create the initial void for caving, is the rate controlling step for production ramp-up, controlling both the rate of undercutting ore and the start of production from drawpoints.

The Northparkes rock mass, including the E48 and E26 deposits, is a highly jointed rock mass with fracture frequencies of between three and 20/m and fracture density that increases with copper grade.

Mine access for all personnel and equipment is provided by surface portal and decline. The decline has a standard 5 m wide by 5.5 m high arched profile. The hoisting shaft represents the second means of egress and the ore skips can be fitted with a man-riding cage in the event that personnel cannot egress the mine via the decline. The mining process involves recovery of broken rock from the drawpoints by 14 t capacity electric LHDs, which tram the ore to a primary crushing station, consisting of plate feeder and jaw gyratory crusher, located on the margin of the extraction level. Typically, four to five LHDs operate on a continuous basis. E48 Lift 1 is highly automated, utilising driverless loaders. Crushed ore is fed onto high-speed inclined conveyors via an ore pass that also provides storage capacity. Ore is conveyed to the underground loading station, which consists of three ore passes feeding the hoisting system. The hoisting system consists of a ground mounted friction winder with integrated drum and rotor, servicing two 18 t payload skips in counterbalance, running on rope guides in the 6 m diameter concrete lined shaft. Hoisted ore is transferred via an overland conveyor to crushing cicuit.

Northparkes has developed a comprehensive cave management system based on its experiences with operating the E26 block caves. These management systems are designed to manage the specific catastrophic safety risks particular to block caves; namely airblast, surface subsidence and inrush and large-scale rock falls. The system is also designed to support maximising reserve recovery and optimising mine production. The system is based on a large number of monitoring systems, including real-time microseismic event monitoring, open hole surveys using probes and video cameras, time domain reflectometers installed in grouted boreholes, convergence monitoring using extensometers and manual measurements of mine openings on the extraction level and in key underground infrastructure, drawpoint fragmentation and geology mapping, drawpoint grade sampling, subsidence zone volume surveys and water inflow measurements.

The mine ventilation system consists of two primary exhaust shafts (E26 and E48) each with two fans mounted on surface above a system of vertical and lateral return airways. The primary air intakes are the main decline, the hoisting shaft and E48 intake shaft. The ventilation system typically operates at airflows of 600 - 650 m3 per second, which are shared across the various work areas.

In the first quarter of 2022 year the E26 L1N Block Cave development project was successfully completed, 5 months ahead of schedule. Throughout the year work has continued to successfully and safely managed the early establishment of the cave.

Underground mining activities are undertaken in the E48 and E26 ore bodies. The E26 L1N mine and the E48 ore bodies are operated as block caves as the primary method of resource extraction. Block Caving is an underground hard rock mining method that involves undermining an ore body, allowing it to progressively collapse under its own weight. The E26 SLC mine is a sublevel caving operation involving construction of the sub level horizon followed by retreat drill and blast of that horizon, with the material above allowed to freely cave to fill the opened voids.

The E26 SLC project commenced construction in April 2015 and went into production in 2016. The mine design aimed to extract a remnant wedge of high-grade material adjacent to the E26 Lift 2 Block Cave. The operations at E26 SLC had ceased in 2021, having completed production from the first four levels at approximately 20m vertical spacing. The remaining two levels were deferred due to less favourable economics. The development of the remaining levels commenced in 2023 with 25m vertical spacings. Production is planned from the remaining levels from 2023 until early 2026.

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. Automation (remote and autonomous operation of underground load, haul and dump machinery) continued in the 2022 year to maintain full automation of underground mine loaders in E48. E26 L1N operations began with loaders operating manually, with automated operations under consideration for 2023 implementation.

Open cut
Open-pit mining operations re-commenced at Northparkes in late 2022, following a period of only underground mining for more than ten years. Resumption of open-pit mining is providing waste concurrently for the continuing construction of the adjacent Rosedale Tailings Storage Facility.

Whilst there was no significant ore mining undertaken within the year, the approved production plan has scheduled more than 7.5 million tonnes of ore to be mined from the two small open pits over their two year lifespan.

Preparation is underway to also commence open-pit mining at the nearby E31N project. With E31N similar in size to E31, the two pits combined will see more than 14 million tonnes of material mined as either waste or ore.

As part of surface mining recommencing, drill and blast activities were undertaken during the period.

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Ore processing includes several defined stages that include crushing, grinding, flotation and dewatering. The plant was designed to process both copper gold oxide and sulphide ore; the cyanide / oxide processing circuity was decommissioned.

Ore is fed to the plant from two sources; via the underground operations and the winder, or from open cut material via a surface primary crusher.

From grinding, the material flows through a single line flotation circuit; initially through a series of rougher/scavenger flotation cells, before entering the cleaner circuit, comprised of Jameson Cells and mechanical cleaner-scavengers. Copper and Gold bearing sulfide minerals are recovered using Hostaflot 26293 as the primary flotation collector and Flotanol 16319 as the frother as well as Sodium.

Hydrosulphide (NaHS) as a sulphidizing agent. Concentrate produced from the flotation circuit is thickened and filtered to produce a final concentrate, with a moisture content of 8-10%.

Air and agitation to produce bubbles in combination with a suite of regents, to enable attachment of particles (minerals) are captured and recovered in the flotation process to produce a sulphide-rich concentrate containing Copper and Gold bearing minerals. After flotation, the concentrate is first thickened through thickeners and filtered through ceramic disc filters to produce a low moisture concentrate ready for loading and transportation to the port.

The recent expansion project comprised of: (1) the installation of a closed loop secondary & tertiary crushing circuit to replace the existing open circuit secondary crusher; (2) upgrading of the feed conveyors, discharge screens, hoppers, cyclone clusters and pumps; and (3) Relocation of existing pre flotation cell, installing a new flotation cell and refurbishing the cleaner scavenger cells.

Commissioning of the new secondary and tertiary crushing facility was completed in 2021 allowing the concentrator to achieve a nominal throughput rate of 7.6Mtpa.

The tailings component is pumped from the final flotation stage to a tails thickener for dewatering followed by additional pumping to the tailing’s storage facilities.

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