The Plutonic deposits are Archean Greenstone gold deposits. The gold mineralisation is predominantly structurally controlled occurring in a variety of stratigraphic settings, mainly associated with replacement-style lodes and stockwork veining within a wide variety of host rocks ranging from ultramafic and mafic volcanic rocks, metasediments, felsic intrusive, volcanoclastic units, and banded iron formations.

In the Hermes and Bryah JV Projects there are two broad mineralisation styles (Outhwaite, 2013) referred to here as the Peak Hill Type and the Bryah Type.

The Peak Hill Type gold deposits are hosted in rocks that are generally highly deformed (four or more fold events) and metamorphosed (up to amphibolite facies), generally represented by the Peak Hill Schist Formation. Mineralisation is early in the paragenesis, (syn- to post-D1 isoclinal folding) with folded mineralisation commonly observed. Previously mined examples include Peak Hill Main/Five-Ways, Mt Pleasant, Jubilee, Wilgeena and St Crispin. The Hermes deposits may be examples of unmined mineralisation that belongs in this category.

The Plutonic Resources mined and unmined lie with a surface area of approximately 10 km east-west by 5 km north-south. The historical Plutonic Main Pit is approximately 1.5 km long by 800 m wide by 200 m deep. Current Resources being mined underground at Plutonic including the Main Pit, Indian, Indian Extension, Baltic and Baltic Extension lies in a semi-continuous mineralised trend that extends from the base of the open pit 1.7 km down plunge (880 m in elevation) and mineralisation is 1-3 m thick but individual mineralised pods have a short range (generally <30 m).

The Cortez-Area 134-Timor zone extends approximately 1.2 km north-south, by 1.0 km east-west.

The main style of gold mineralisation (Plutonic brown-lode) typically occurs as thin (~1 - 3 m wide) lodes that consist predominantly of quartz-biotite-amphibole-titanite-epidote-carbonate- tourmaline-arsenopyritepyrrhotite ± chalcopyrite ± scheelite ± gold. Visible gold is considered to have occurred at a late-stage during the evolution of the deposit as it is largely undeformed and overprints most, if not all, of the minerals and fabrics. It is typically associated with thin, discontinuous quartz-calc-silicate veins within the brown-lodes. Where these gold-bearing zones are well developed, they tend to be near-parallel to the stratigraphy as marked by the rare metasedimentary horizons and to the dominant foliation, which is also typically parallel to metasediment horizons. Geochemistry suggests that these lodes developed on the boundary between mafic units or are focused along or adjacent to minor metasedimentary units within the Mine Mafic unit. Lodes may be rich in arsenopyrite or pyrrhotite, and while arsenopyrite is a good indicator of mineralisation, it may not be present in all mineralisation.

Mineralisation at Plutonic is separated into four distinct styles:
• Replacement “brown” or “Plutonic” lodes (which contain the bulk of the gold);
• Replacement “green lodes”;
• “Invisible lodes”;
• Dilational high angle quartz veins.

The Plutonic “Brown lodes” are characterised by a series of moderately-dipping to very flat- lying, stacked, banded replacement-style lodes, individually up to five metres wide, that are hosted within ductile mylonitic shear zones, oriented slightly oblique to the main stratigraphic contacts. Hydrothermal alteration during midto lower-amphibolite facies conditions has resulted in a zoned hydrothermal assemblage consisting of plagioclase–biotite-quartz-amphibole-titanite- carbonate-arsenopyrite-pyrrhotite-tourmaline-muscovite-pyritescheelite-gold-sphalerite. The replacement style lodes are restricted within the Mine Mafic unit, preferentially within the Upper Mine Mafic unit, sub-parallel to primary lithological contacts. Arsenopyrite associated with gold mineralisation at Plutonic is subtly zoned with respect to gold, antimony, and arsenic abundance. Within individual grains of arsenopyrite there is a negative correlation between gold (rims) and antimony (core). Arsenic abundance generally increases from core to rims, indicating increasing temperature. There is a conspicuous lack of quartz veining associated with mineralisation except where the ductile shear zones have intersected early quartz veins subsequently deforming them. Wall rock alteration adjacent to the lodes is very narrow, often confined to 20 cm to 30 cm. Mass balancing of the lodes against the host amphibolite indicates a general SiO2 loss of seven to ten percent and volume decreases of up to 30%.

The Plutonic “Green lodes” are characterised by an amphibole-quartz-titanite-plagioclase- arsenopyrite-pyritevisible gold-scheelite assemblage, generally confined to the upper portion of the Mine Mafic unit and commonly spatially associated with the Plutonic style “Brown” lodes. Both gold and arsenopyrite appear to overprint the layer parallel fabric where present. The morphology of lodes is similar to the Brown lodes, situated within mylonitic shear zones. Quartz is more abundant and is present as a fine-grained interstitial mineral, commonly recrystallised.

Plutonic “Invisible Lodes” are less common than the Plutonic Brown and Green lodes. There are more abundant in the Zone 19 area. They do not occur within ductile shear zones but are developed predominantly within the upper five metres of the Upper Mine Mafic unit within the hornblende amphibolite. Gold is finely disseminated throughout an apparently unaltered groundmass in which minor pyrrhotite and pyri te are associated. There is no biotite, albite or arsenopyrite alteration. In higher-grade examples, free gold is sited within quartz-carbonate veins oriented parallel to overprinting local penetrative fabrics with no associated sulphides or visible alteration halo.

Quartz vein hosted mineralisation is the least abundant form of mineralisation and is mainly located close to the Quartz Hill Thrust which separate the Overthrust mafic to the Hangingwall Ultramafic or proximal to high angle dolerite dykes where the dykes cut replacement lodes. Above the Quartz Hill Thrust, gold is associated with pyrrhotite-pyrite-sphalerite-galena in quartz veins and unlike the shear zone-related gold mineralisation at Plutonic there is an absence of arsenic. Immediately below the Quartz Hill Thrust, high grade gold mineralisation is present in close proximity to Brown lode mineralisation. Coarse gold is observed within quartz veining and silica flooding. The gold overprints the Brown lode layer parallel fabric, possibly indicating a remobilised origin for this coarse free gold. The mineralisation of the Plutonic Gold Mine is truncated to the south by a local structure called the MPS Fault, a minor fault splay off the major regional structure known as the MMR Fault.

Ore feed to the mill during 2019 was from mining operations at Plutonic Underground (underground mining methods) and the Hermes Open Pit which commenced in December 2017.

Plutonic Underground
Plutonic Underground is a mechanised access underground mine that has been in continuous operation since 1995. Historically the mine has produced at a rate of up to 1,400 ktpa ore, although in recent years’ production has stabilised at approximately 800 ktpa. The current constraint on underground production is not the infrastructure: the constraint is gathering the data to move the stopes through the planning process and into production.

The Plutonic Underground has eight active mining zones. Seven of these mining zones are well- established having been active for a number of years (Established Areas). The eighth zone, Baltic N1/N2 Extension, is a new mining zone (New Areas).

The underground mining operation covers an area of about three kilometres north-south and two kilometres east-west and currently extends over a 500 m vertical extent from approximately RL 150 m to RL 650 m. The Baltic Extension is a new mining area adjacent to existing workings and is planned to extend the depth of operation by a further 500 m vertical including Inferred Resources (total depth below surface 1,150 m). As the depth of mining increases, the ground stress also increases and can create significant mining issues. The mining studies to date have not considered stress as part of the Baltic Extension, however mining to this depth will occur gradually and the issue is not imminent or expected to materially impact successful extraction of the Mineral Reserves in this area.

Underground mining at Plutonic takes place from five declines, four of which are located in the Plutonic main operation and the fifth is located about five kilometres east of the main operation at Plutonic East. The underground workings are extensive with a number of internal ramps in place to access the mining zones.

There are three general mining methods used at Plutonic:
• Long hole retreat mining (the main method applied to the vast majority of stoping);
• Jumbo stripping (slashing); and
• Airleg (jackleg) mining.

The split of Mineral Reserves ore tonnage production by mining method is;
• Long hole stoping – 84%;
• Airleg stoping – 4%; and
• Ore development – 12%.

Open pit mining method
Open Pit Mining at Billabong is at Hermes Complex, which is about 65 kilometres from Plutonic. The Hermes Complex consists of two project areas –

• Hermes Project – It has following four open pit cutbacks –
o Trapper
o Klinger
o Hawkeye
o Winchester.

• Hermes South Project – It has following one open pit –
o Wilgeena.

The Hermes Project commenced being mined in December-2017 and paused in May-2019, as below –
• Trapper Pit started in December-2017 & paused in April-2019. Trapper was mined in four stages
• Hawkeye Pit started in December-2017 & paused in January-2019
• Klinger Pit started in April-2018 & paused in December-2018
• Winchester Pit ran for a month in May-2019, contour mining near surface deposit only.

The Hermes South Project is about 20 kilometres south of Hermes Project. Historically, prior to Billabong takeover, contour mining very near to surface is done in Wilgeena Pit.

All four pits in the Hermes Project area are mined as a conventional open pit excavator-truck mining operation. A mining contractor was engaged for drilling, blasting, loading, hauling, and dumping, as well as civil services for general site maintenance works. The material mined from each pit is being stockpiled adjacent to each pit exit before being loaded onto road trains for transport along the haul road to Plutonic for processing through the existing mineral processing configuration.

Crushing
Run of Mine (ROM) ore is trucked to the ROM pad from the underground mine. The ore is classified and stockpiled according to gold grade, arsenopyrite content, pyrrhotite content, and graphitic content so that blending can be undertaken to maintain an optimal feed to the processing plant. Oversize ore and tramp metal are sorted from stockpiles and broken on the ROM pad using a loader or excavator. Any oversize that cannot pass through the primary crusher grizzly is broken by a rock breaker mounted at the grizzly.

The PP1 crushing circuit has a nameplate capacity of 2.5 Mtpa and consists of three stages of crushing:
A 60 x 48 Jacques primary double-toggle jaw crusher,
A Symons 7’ SXHD secondary standard head cone crusher, and
Two Symons 7’ SXHD tertiary short-head cone crushers.

In addition, there are separate surge bins that are operated in closed circuit with two Nordberg 7.1 m x 2.4 m double deck vibrating banana screens. Crushed ore exits the pro duct screen with a top size of 10 mm and is stored in the fine ore bin. The fine ore bin has a live capacity of 3,000t.

PP1 crushing circuit contains 2 x Thermo Scientific Ramsey 10-17 belt scales (CV07 and CV13) for measuring mass of circuit ore.

The now decommissioned PP2 oxide crushing circuit consists of a 48 x 42 Kemco double toggle jaw crusher with a nameplate capacity of 1.2 Mtpa, a product conveyor and a coarse ore stockpile with a live capacity of 2,200 tonnes. Crushed oxide ore was transferred to PP2 grinding mills using two variable speed belt feeders.

Grinding
Crushed ore is withdrawn from the Fine Ore Bin via two belt feeders (CV 14/15), which transfer ore onto the mill feed conveyor (CV04) that feeds into the primary grinding mill (ML01). Mill feed can also be fed via an emergency feed hopper (CV02) which is fed via the oxide coarse ore feed slots. Quicklime is discharged onto CV04 via a variable speed, manually controlled rotary valve from a 200t lime silo. Liquid lead nitrate (40% w/w) is discharged directly into CV04 head chute into the grinding circuit.

The grinding circuit comprises a Svenson 4.5m diameter by 5.63m long primary mill and two Svenson 4.2m diameter by 5.63m long secondary ball mills. The primary mill has a grate discharge and is rubber lined. Its speed is fixed at 14.6 rev/min (72 per cent of critical) and the installed power is 1,600kW (1,350kW drawn). 78mm diameter forged steel grinding media is used in the primary mill.

The secondary mills are rubber lined overflow mills run at 15.8 rev/min (75% of critical), also with 1,600 kW power (1,450 kW drawn). The grinding circuit throughput is currently operated at 165 tph with a primary mill and one ball mill configuration; this however can be increased to 230 tph by running the stand-by ball mill. 40 mm High Chromium steel grinding media is used in the secondary mills.

The primary mill discharge slurry is screened on a 6 mm aperture scalping screen and oversize is returned to the primary mill. Screen undersize reports to the ball mill discharge hopper. ML01 mill undersize and ML02/ML03 mill discharge is pumped to a hydrocyclone cluster consisting of 18 x 250 mm Cavex cyclones. Operating pressure is 130 to 150 kPa. Each cyclone contains 90 mm ceramic vortex finders and 75 mm ceramic spigots. Coarser cyclone underflow is returned to the operating secondary ball mill for further size reduction. Cyclone overflow (approximately 80% passing 75µm) discharges over a trash screen (1mm) with screen undersize reporting to the leaching circuit.

The primary sections of the processing plant that are in use are:

• Crushing and conveying
• Ore reclaim and grinding
• Leaching and carbon adsorption
• Carbon stripping, electrowinning, refining and carbon regeneration
• Tailings thickening
• Tailings deposition and storage
• Reagent mixing and handling
• Plant services.

Leaching and adsorption
The leach and adsorption circuit consists of two leach tanks and six CIL carbon adsorption tanks, all with a 1,020m3 capacity. All tanks mechanically agitated with dual, open, down- pumping impellor systems powered by 55kW drives. Facilities are currently available to inject oxygen into tanks #1, #2, #3, #4 and #6, with a high shear MMS oxygen injector feeding into Tank #1. Gold in solution is recovered and concentrated by adsorption onto activated carbon in the adsorption tanks. Leach tank 1 is used as a pre-oxidation (oxygen sparged) conditioning tank, to oxidise reactive sulphides ........