Overview
Stage | Production |
Mine Type | Open Pit & Underground |
Commodities |
|
Mining Method |
- Truck & Shovel / Loader
- Sub-level caving
- Longhole open stoping
|
Processing |
- Carbon re-activation kiln
- Smelting
- INCO sulfur dioxide/air process
- Flotation
- Counter current decantation (CCD)
- Concentrate leach
- Agitated tank (VAT) leaching
- Pressure oxidation
- Carbon in leach (CIL)
- Carbon adsorption-desorption-recovery (ADR)
- AARL elution
- Solvent Extraction & Electrowinning
- Cyanide (reagent)
|
Mine Life | 10 years (as of Jan 1, 2021) |
The Macraes Operation includes the Coronation, Coronation North, Innes Mills, Deepdell and Frasers open pits, Frasers (FRUG) and Golden Point (GPUG) underground mines, and an adjacent processing plant including a pressure oxidation plant for the processing of sulphide ore.
OceanaGold achieved the first production from Golden Point Underground (GPUG) in the fourth quarter of 2021. GPUG will continue to ramp-up with future development and will initially supplement, then eventually fully replace the existing Frasers Underground gold production. |
Latest News | OceanaGold uses cable bolts and pumpable resin to help advance decline & begin production at new Golden Point Underground mine December 2, 2021 |
Source:
p. 10, 27
The Project is controlled by OceanaGold Corporation through its wholly owned subsidiary OceanaGold Limited
Deposit Type
- Orogenic
- Breccia pipe / Stockwork
- Vein / narrow vein
Summary:
The Coronation and Coronation North deposits are located 5 to 6 km to the northeast of the processing plant. Coronation consists of a 15 to 20 degrees dipping hangingwall shear that is between 3 and 10 metres thick. Immediately beneath (1 to 10 metres) the hangingwall shear is a thinner lode structure that parallels hangingwall. Unlike deposits to the south, there is very little development of stockwork mineralisation beneath the hangingwall. Mineralogically, the Coronation deposit is very similar to previously mined deposits to the south. Located 1km to the north of Coronation is the Coronation North deposit which was discovered in 2015. Coronation North differs from most of the previously mined ore bodies along the HMSZ. Pit mapping and grade control data have delineated a left-hand lateral bend in the strike of the HWS coincident with a high-grade zone of mineralisation that plunges to the ENE. Traversing along the shear from southeast to northwest the dip of the HWS gradually decreases whereas the strike bends towards the west. This bend coincides with a zone of steeply dipping en-echelon style mineralised splays beneath the HWS, whose dip steepens to near vertical as they approach the FWF. Zones of finely laminated mineralised quartz veins also form beneath this WSW-striking segment of the HWS, perpendicular to its strike. Compared to the other deposits in the goldfield, the WSW-strike of Coronation North, the relatively narrow approximately 100m width of the mineralised zone and its steep dip are currently unique in the goldfield.
At the Frasers open pit and FRUG, deposits are centred on mining the hangingwall shear. In outcrop, the shear typically dips at 15 to 20 degrees to the east and is approximately 5 metres thick. At depth, the dip of the shear flattens to approximately 5 to 10 degrees and develops into an approximately 20 to 30 metres thick mineralised high-grade zone of quartz cataclasite, and mineralised schist. Within the open pit, gold mineralisation comprises mineralised schist and cataclasite, shear-parallel quartz veins and arrays of sub-vertical quartz veins. hangingwall shear and arrays of subvertical quartz veins account for most of the mineralisation within the open pit, although there are a few shear-parallel quartz veins. These veins typically splay off the base of the hangingwall Shear and dip at between 5 and 10 degrees to the west.
A large amount of erratic mineralisation occurs between the base of the hangingwall shear and the footwall fault. At the resource drilling stage, this mineralisation manifests as poorly developed clusters of elevated gold grades, which often appear discontinuous. During mining however, these typically present as extensive zones of quartz vein arrays and mineralised shears. The footwall fault lies between 80 metres and 120 metres below the hangingwall shear and is identified as a cataclastic zone up to 10 metres thick. To date, no economic mineralisation has been located below the footwall fault.
FRUG encompasses the down-dip continuation of the hangingwall shear mined in the Frasers open pit, which is known to extend approximately 600 metres beyond the limit of the open pit design. The thickest, most mineralised part trends approximately northeast and tapers in length from approximately 350 metres at its western end to approximately 150 metres at the eastern limit of drilling, where it abuts the Macraes Fault zone. Mineralisation is contained within the intrashear schist which is generally 80 metres to 100 metres thick, with the higher gold grades confined to the upper part, which is dominated by cataclasite, lode schist and local stockwork pelite lithologies. Numerous drill holes have penetrated through the intrashear schist into the Footwall Psammite, particularly at the western end where the Footwall Fault is relatively shallow, at depths of less than 500 metres. Mineralisation is consistent with the ore delineated in the Frasers open pit. The highest gold grades are contained within the strongly developed and visually distinguishable zone within the upper hangingwall, characterised by quartz cataclasite and silicified breccias. This typically forms a well mineralised, continuous zone up to 15 metres thick, with a grade of approximately 3 g/t Au. Less intensely mineralised lode schist is typically developed lower in the hangingwall package.
GPUG encompasses the down-dip continuation of the hangingwall shear mined in the Round Hill and Golden Point open pits. Current drilling has shown this to extend more than 700 metres beyond the limit of the open pit design. The thickest, most mineralised part is a series of stacked lodes proximal to the Golden Point pit. Mineralisation continues as a single higher-grade lode down-dip to the north-northeast. Mineralisation is contained within the intrashear schist, which is generally 80 metres to 100 metres thick, with the higher gold grades confined to the upper part, which is dominated by cataclasite, lode schist and local stockwork pelite lithologies. Numerous drill holes have penetrated through the intrashear schist into the footwall psammite. Mineralisation is consistent with the ore delineated in the Golden Point and Round hill open pits, however down-dip of Golden Point this is constrained to a single lode. The highest gold grades are contained within the strongly developed and visually distinguishable zone within the upper hangingwall, characterised by quartz cataclasite, and mineralised schist. This typically forms a well mineralised, continuous zone up to 5-10 metres thick, with a grade of approximately 3 g/t Au.
Mineralisation
The Macraes deposit is a classic example of an orogenic style gold deposit, with mineralisation broadly synchronous with deformation, metamorphism, and magmatism during lithospheric-scale continental-margin orogeny. Most orogenic gold deposits like Macraes occur in greenschist facies rocks. Orogenic deposits typically formed on retrograde portions of pressure-temperature time paths during the last increments of crustal shortening, and thus postdate regional metamorphism of the host rocks. The following four types of mineralisation occur within the HMSZ at Macraes:
(a) Mineralised schist. This style of mineralisation involves hydrothermal replacement of schist minerals with sulphides and microcrystalline quartz. Mineralisation is accompanied by only minor deformation;
(b) Black sheared schist. This type of schist is pervaded by small scale anastomosing fine graphite, and sulphide bearing microshears. This type of mineralisation is typically proximal to the hangingwall shear;
(c) Shear-parallel quartz veins. These veins lie within, and/or, adjacent to the black sheared schist and have generally been deformed with the associated shears. The veins locally crosscut the foliation in the host schist at low to moderate angles. Veins are mainly massive quartz, with some internal lamination and localised brecciation. Sulphide minerals are scattered through the quartz, aligned along laminae and stylolitic seams. These veins range from 1 centimetre to more than 2 metres; and
(d) Stockworks. These veins occur in localised swarms that are confined to the intrashear schist. Individual swarms are up to 2,000 square metres in area and consist of numerous subparallel veins. Most of these veins formed sub perpendicular to the shallow east dipping shear fabric of the intrashear schist. Stockwork veins are typically traceable for 1 metre to 5 metres vertically with most filling fractures that are 5 centimetres to 10 centimetres thick but can be up to 1 metre thick.
Mining Methods
- Truck & Shovel / Loader
- Sub-level caving
- Longhole open stoping
Summary:
Open Pit:
Conventional open cut bench mining methods are used at the Macraes Goldfield. Pits are excavated on level benches 2.5m high within the ore zone (approx. 2.8m high after blasting) and 4m high within the waste zone.
Hydraulic backhoe excavators in the 250t and 360t class are used for mining ore and waste. Ore is mined with different techniques depending on the style of mineralisation.
- Hanging wall lode ore is mined by first removing the hanging-wall waste with an excavator under visual control of a geological technician, then mining the exposed ore. Footwall ore is selectively removed from the underlying footwall waste if it can be visually controlled, otherwise the footwall ore is diluted with the wedge of underlying waste; and
- Stockwork ore is generally mined within the defined ore blocks. Ore blocks are defined with the guidance from a conditionally simulated grade control model.
With this mining method and equipment, the smallest selective mining unit (SMU) used when defining ore blocks is 4m by 4m by 2.5m high (approximately 100t), but blocks are generally a minimum of 500t to minimise dilution.
Mining to date at Macraes has come from thirteen pits comprising (from north to south), Coronation North, Coronation, Deepdell North, Deepdell South, Golden Point, Northwest Pit, Round Hill, Southern Pit, Innes Mills, Innes Mills West, Frasers, Golden Ridge and Golden Bar. Current operations are based in Coronation North, Deepdell North, Gay Tan and Frasers West pits. The Round Hill, Innes Mills and Southern pits were mined to what were their economic limits. Round Hill and Innes Mills pits were subsequently backfilled, and Southern Pit was used for tailings disposal. Following updated geologic interpretation and economic analysis, as part of its ongoing program to convert Mineral Resources to Mineral Reserves at Macraes, the Company has added these deposits back to its Mineral Resources and Mineral Reserves.
The bulk of the future open pit tonnage from Macraes will be sourced from Frasers West, Gay Tan 3 and 4, Deepdell North, Innes Mills, Round Hill and Golden Bar deposits.
Mineralisation has also been outlined to the north at the Nunns/New Zealand Gold & Tungsten, Longdale, Mt Highlay and Mareburn deposits, and to the south at the Taylor’s, Wilson’s, Shaw’s and Ounce deposits. Further drilling programs are required to upgrade these deposits.
Open pit mining at Macraes is carried out by Company personnel using owned mining equipment. Ore concentration is carried out at the Macraes site by Company personnel. A standard refining contract is in place for the transportation and refining of the doré bullion into fine gold.
The current life of mine plan for the Macraes Mining operations ends in the fourth quarter of 2028 with processing completing in the fourth quarter of 2030. Based on the current drilling program, it is possible the Company will extend the LOM plan if additional Mineral Reserves are defined in the interim.
Underground :
The Frasers underground orebody encompasses the down dip continuation of the Hangingwall shear mined in the Frasers open pit. The orebody is relatively shallow dipping (15 – 20 degrees) to the east. The orebody is tabular with undulations and has a thickness varying between 5 to 30 metres.
The mining method used underground involves 15-metre-wide open stopes with 6 metre yielding pillars between stopes. Mining areas are separated by 20 metres to 60 metres wide regional pillars. The mining areas are generally restricted to about 120 metres width and 160 metres length. Mine production targets the high-grade ore at the top of the 30 metres thick mineralisation. Stope heights vary between drive height (5 metres) and up to 25 metres.
The most utilised mining method at FRUG is retreat long hole open stoping. In addition, sub-level caving is used to recover some of the regional pillars after they are no longer required. Declines and access drives are mined to a 5.0mW x 5.5mH arched profile. Ore drives are mined to a 5.0mWx5.0mH profile. This allows enough space for services, secondary fans, vent ducts and mobile equipment. Stoping panels were designed based on the main considerations below:
- Ore drives placed at 21m centres to allow for 15m wide stopes with 6m yielding pillars between them. There are no secondary stopes designed to be extracted following the mining of the primaries;
- Ore drives positioned such that they will have a gentle uphill gradient for water drainage but not orientated directly north-south, parallel to the strike of many of the faults present, to maintain drive stability;
- Regional pillars maintained between panels of 30m width if they contained no development and 60m wide if they contained development drives. In some cases, pillars containing access drives were reduced to a width of 40m if the contained drives were no longer needed following stoping of the surrounding areas;
- The stoping panels should be retreated towards a solid abutment rather than towards an internal regional pillar; and
- Panel accesses designed in conjunction with primary ventilation return loops and secondary egress routes and positioned such that they will stay intact following stoping of nearby areas.
Flow Sheet:
Crusher / Mill Type | Model | Size | Power | Quantity |
Jaw crusher
|
|
|
|
2
|
SAG mill
|
|
|
1500 kW
|
1
|
SAG mill
|
|
|
2300 kW
|
1
|
Ball mill
|
|
|
900 kW
|
1
|
Ball mill
|
|
|
2300 kW
|
2
|
Ball mill
|
|
|
2500 kW
|
1
|
Summary:
The plant's crushing and grinding comprises the following components and stages:
- Two single stage jaw crushing circuits, which reduce the ore to a top size of approximately 200mm; the products from these two circuits are directly fed to the two SAG mills and an emergency feeder on the conveyor system feeding the higher capacity circuit provides continuity of feed to the grinding
circuit if the jaw crusher feed is interrupted;
- A complex grinding circuit to reduce the particle size of the ore to 80% passing at 130 µm; the original, higher capacity crushing circuit feeds a 2,300kW SAG mill and the new crushing circuit feeds a 1,500kW SAG mill; discharge from the two SAG mills is combined with the discharge from one of the two ball mills (2,300kW) and directed to the primary cyclone cluster. Discharge from the higher capacity ball mill (2,500kW) is fed to the secondary cyclone cluster. The underflows from both cyclone clusters are combined and fed in parallel to the flash flotation circuit and two ball mills (2,300kW and 2,500kW);
- Regrind of the flotation concentrate is performed in a 900kW ball mill to 80% passing of 15 µm to improve pressure oxidation kinetics;
Processing
- Carbon re-activation kiln
- Smelting
- INCO sulfur dioxide/air process
- Flotation
- Counter current decantation (CCD)
- Concentrate leach
- Agitated tank (VAT) leaching
- Pressure oxidation
- Carbon in leach (CIL)
- Carbon adsorption-desorption-recovery (ADR)
- AARL elution
- Solvent Extraction & Electrowinning
- Cyanide (reagent)
Flow Sheet:
Summary:
The Macraes Process Plant recovers gold by concentrating the metal into a relatively small fraction of flotation concentrate, oxidising the reground concentrate in a pressure oxidation autoclave, washing the oxidised residue and then utilising a carbon-in-leach process to recover gold from the residue.
In detail the plant comprises:
- A flash flotation circuit made up of roughing and cleaning stages. The circuit is fed from the circulating load of the grinding circuit via cyclone underflows to recover the bulk of fast floating sulphide minerals containing high gold content in the coarser size fraction;
- The main flotation circuit made up of roughers, scavengers, cleaners, recleaners and cleaner scavenger flotation cell trains to produce a gold bearing sulphide concentrate at optimum sulphur grade for the downstream pressure oxidation circuit;
- Limestone is added to the regrind circuit discharge to control net acid generation in the pressure o ........

Recoveries & Grades:
Commodity | Parameter | 2021 | 2020 | 2019 | 2018 | 2017 | 2016 | 2015 |
Gold
|
Recovery Rate, %
| ......  | ......  | ......  | 86.1 | 81.2 | 83.7 | 80.4 |
Gold
|
Head Grade, g/t
| ......  | ......  | ......  | 1.24 | 1.04 | 0.94 | 0.98 |
Production:
Commodity | Units | 2022 | 2021 | 2020 | 2019 | 2018 | 2017 | 2016 |
Gold
|
koz
| ...... ^ | ......  | ......  | ......  | 203 | 160 | 149 |
Silver
|
koz
| | ......  | ......  | ......  | ......  | ......  | ......  |
All production numbers are expressed as metal in doré.
^ Guidance / Forecast.
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Operational Metrics:
Metrics | 2021 | 2020 | 2019 | 2018 | 2017 | 2016 |
Total tonnes mined
| ......  | ......  | 51,619 kt | 44,927 kt | 42.1 Mt | |
Ore tonnes mined
| ......  | ......  | 6,456 kt | 6,314 kt | 5,071,508 t | 4,971,248 t |
Waste
| ......  | ......  | 45,163 kt | 38,613 kt | 37,069,604 t | 27,052,932 t |
Tonnes milled
| ......  | ......  | 5,917 kt | 5,897 kt | 5,877,501 t | 5,866,286 t |
Plant annual capacity
| ......  | ......  | | 6 Mt | 6 Mt | |
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Reserves at December 31, 2021:
Mineral Reserves Cut-off grades are 0.4 g/t Au for Open pit, 1.61 g/t Au for Frasers Undeground and 1.44 g/t Au for Golden Point Underground.
Mineral Resources Cut-off grades are 0.3 g/t Au for Open pit, 1.25 g/t Au for Frasers Undeground and 1.34 g/t Au for Golden Point Underground.
Category | OreType | Tonnage | Commodity | Grade | Contained Metal |
Proven
|
In-Situ (OP)
|
15.6 Mt
|
Gold
|
0.87 g/t
|
|
Proven
|
In-Situ (UG)
|
0.33 Mt
|
Gold
|
2.23 g/t
|
|
Probable
|
In-Situ (OP)
|
19.9 Mt
|
Gold
|
0.85 g/t
|
|
Probable
|
In-Situ (UG)
|
3.21 Mt
|
Gold
|
1.88 g/t
|
|
Proven & Probable
|
In-Situ (OP)
|
35.5 Mt
|
Gold
|
0.86 g/t
|
0.98 M oz
|
Proven & Probable
|
In-Situ (UG)
|
3.54 Mt
|
Gold
|
1.91 g/t
|
0.22 M oz
|
Measured
|
In-Situ (OP)
|
21.7 Mt
|
Gold
|
0.88 g/t
|
|
Measured
|
In-Situ (UG)
|
0.7 Mt
|
Gold
|
2.98 g/t
|
|
Indicated
|
In-Situ (OP)
|
56 Mt
|
Gold
|
0.75 g/t
|
|
Indicated
|
In-Situ (UG)
|
6.1 Mt
|
Gold
|
2.48 g/t
|
|
Measured & Indicated
|
In-Situ (OP)
|
77.7 Mt
|
Gold
|
0.79 g/t
|
1.96 M oz
|
Measured & Indicated
|
In-Situ (UG)
|
6.9 Mt
|
Gold
|
2.53 g/t
|
0.56 M oz
|
Inferred
|
In-Situ (OP)
|
24 Mt
|
Gold
|
0.7 g/t
|
0.5 M oz
|
Inferred
|
In-Situ (UG)
|
0.3 Mt
|
Gold
|
2.1 g/t
|
|
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