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Australia
Wiluna Gold Operation

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 Location:
3 km SE from Wiluna, Western Australia, Australia

  Regional Office:
Level 3 1 Altona Street
PO Box 1412
West Perth
Western Australia, Australia
6005
Phone  ...  Subscription required
Fax+61-8-9322-6429
WebsiteWeb
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  • Overview
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  • Geology
  • Mining
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Overview

StageProduction
Mine TypeOpen Pit / Underground
Commodities
  • Gold
Mining Method
  • Airleg stoping
  • Truck & Shovel / Loader
  • Longhole open stoping
Processing
  • Gravity separation
  • Smelting
  • Agitated tank (VAT) leaching
  • Carbon in leach (CIL)
  • Elution
  • Carbon adsorption
  • Solvent Extraction & Electrowinning
  • Cyanide (reagent)
Mine Life12 years (as of Jan 1, 2020)
Wiluna Gold Operation comprises 20 open pits and 3 underground mines across four mining centers being Wiluna, Matilda, Lake Way and Regent.

Wiluna Gold Operation has long history of gold production and produced over 4.4 million ounces since 1897. In mid-2016 the Wiluna Mining Corporation (formely Blackham Resources Limited) re-started mining at the Wiluna Gold Operation.

Current Operations - Williamson open pit at Lake Way Centre and Golden Age underground mine at Wiluna Mining Centre.


Owners

Source: p. 5, 9
CompanyInterestOwnership
Wiluna Mining Corporation Ltd. 100 % Indirect

Deposit Type

  • Vein / narrow vein
  • Orogenic


Summary:

WILUNA MINING CENTRE
The Wiluna gold deposits are categorised as orogenic gold deposits, with similarities to many other gold deposits in the Yilgarn region. The deposits are hosted within the Wiluna Domain of the Wiluna Greenstone Belt. Rocks in the Wiluna Domain have experienced greenschist-facies regional metamorphism and brittle and ductile deformation. The Wiluna Domain is comprised of a sequence of basalts and high-magnesian basalts, with intercalated felsic intrusions, lamprophyre dykes, metasediments, and dolerites.

Mineralisation is structurally controlled by the Wiluna strike-slip fault system. Gold occurrences are predominantly associated with north or northeast trending dextral strike-slip faults. Gold mineralisation is localised at dilational bends or jogs along the faults, at fault intersections, horsetail splays and in later stage cross-cutting structures.

Post mineralisation reactivation on the main structures has offset ore bodies by a few hundred metres. Lodes are generally associated with silica-sericite-carbonate-sulphide alteration and comprise quartz lodes, cataclastic breccias and narrow veins associated with splay structures.

Depending upon the nature of the host rock and structural control, the ore zones generally form steeply dipping and southerly plunging lenses from 2 m to 25 m in thickness and extending up to 600 m down dip. Laterally they may extend from 50 m to 300 m.

The ore zones are weathered to an average depth of 45 m to 70 m below surface. In this zone the sulphides have been oxidised and the gold liberated, allowing the ore to be treated using conventional carbon in pulp technology. In the sulphide zone the gold occurs almost entirely locked within the arsenopyrite and pyrite sulphide crystal lattice - hence the refractory nature of the primary ores.

Free gold is noted only rarely in primary ore. The arsenopyrite and pyrite are finely disseminated through the rock with lesser amounts in quartz carbonate network veins and wispy sulphide veinlets and clots. Massive stibnite veins, of restricted extent and often with high grade gold contents, occur in West Lode, Happy Jack, Moonlight and Lone Hand deposits.

The major structure in the mine area is the north-south striking, steeply east dipping Graphite Shear Zone which controls the West Lode and Happy Jack South deposits. It splits in the Happy Jack South area into the north trending Creek shear and the north-east trending Bulletin shear. Several major splays from the main shear system also act as important mineralisation controls. These include the East Lode, Squib and Adelaide Shears. The cumulative displacement on the Graphitic Shear system in the mine area is about 1.3 km. A set of stratigraphically parallel shear zones (e.g. Lawless and Golden Age) are also important influences on the development of both lode and reef style mineralisation.

Within the Wiluna mine environment gold-related hydrothermal activity occurred in two main stages, each with a distinct mineralogical association. Wiluna fresh ores are refractory, with most gold occurring in either solid solution or as submicroscopic particles within fine-grained sulphides.

MATILDA MINING CENTRE
The Matilda domain is a greenschist to lower amphibolite facies metamorphic terrain with predominantly ductile deformation. It comprises a volcano-sedimentary sequence in an interpreted major north-west trending synclinal structure, with the axis close to the Perseverance Fault. The sequence comprises basal banded iron formation in the west, overlain by komatiitic volcanics with limited basal peridotite members, grading upwards into high-magnesium basalt and basalt with interflow chert and graphitic sediments. Metabasalt predominates in the project area. Felsic volcanic rocks and sediments are interpreted to form the core of the syncline.

The Matilda deposit is comprised of a number of domains; M1, M2, M3, M4, M5, M6, M8, M10 and Coles Find. These combined zones extend almost 5km along a strike of 330° and cover a width of approximately 1km. The deepest vertical interval is 395m at the M1 prospect.

LAKE WAY MINING CENTRE
At Lake Way, stratigraphy is concealed by shallow (0 to 4m deep) lake sediments, and comprises westerly younging, steep-to-vertically dipping lateral variants of the Wiluna Mining Centre stratigraphy. From footwall to hangingwall, the sequence consists of Unit3 basalt, Wiluna Mine komatiite marker, Unit2 tholeiite, Unit1 high Mg basalt and Unit4 basalts/interflow sediments, overlain by a thick sequence of volcaniclastics. All units are intruded by differentiated dolerite and minor felsic porphyry or monzogranite.

At Williamson and Williamson South, gold mineralisation occurs as weakly disseminated sulphides within a broad anomalous envelope around a north striking/east dipping monzogranite. Higher grade sulphide and visible gold mineralisation is associated with the shearing on the contacts of the granite and also within the main west dipping shear that intersects the monzogranite.

Mineralisation within the monzogranite body varies from broad, low grade, disseminated sulphides in the monzogranite to high grade veins formed within fractures (possibly conjugate) containing visible gold. Alteration ranges from weak carbonate chlorite alteration distal to the main structure to strong hematitecarbonate-silica-pyrite-sericite alteration associated with high grade mineralisation.

REGENT MINING CENTRE
The Regent Prospect is located within a package of felsic-intermediate volcanics west of the Wiluna Mine Sequence and Madji Fault, and east of the Perseverance Ultramafic. Stratigraphy at Regent is dominated by intermediate volcanic and volcaniclastic rock intruded by the Regent Dolerite. A graphitic shale unit occurs above the hanging wall of the dolerite in the southern area of the prospect. The sequence strikes to the northwest, and dips moderately to the northeast.

The Regent deposit is overlain by 30m of transported cover. This material consists of 20m of lacustrine clay overlain by ferruginous sand and clay, then up to 9m of calcrete to surface. The underlying residual profile is deeply weathered, with the base of complete oxidation (BOCO) encountered between 60-80m below surface. The BOCO has been the focus of supergene enrichment of gold. A depletion zone occurs in the overlying pallid clay zone. The first significant mineralisation of the Regent deposit occurs 45m below surface.

Gold mineralisation within the dolerite is hosted within intense silica-white mica- carbonate+-haematite alteration. Sulphides are abundant, and include pyrite (10-20%), arsenopyrite (1-5%) and rare stibnite. Pyrite is generally disseminated but also occurs as bands or stringers. Quartz veining abundance is variable, from 3- 50%. High-grade mineralisation is generally associated with quartz veinlets or quartz vein breccias. Visible gold is rare. Chlorite- leucoxene+-carbonate alteration is distal to the mineralisation. The presence of hematite alteration is variable, associated with both proximal and distal alteration.


Mining Methods

  • Airleg stoping
  • Truck & Shovel / Loader
  • Longhole open stoping


Summary:

Operations sites came out of Care and Maintenance in mid-2016 with the recommencement of mining at the Matilda and Wiluna mine sites.

Various approvals were obtained during 2016 to 2018 to commence mining at brownfields Wiluna, and Williamson mine sites and greenfields Galaxy mine site. Open cut mining commenced at Galaxy in April 2017 and was completed in 2018. In 2016 was commenced underground mining of the high grade Golden Age orebody.

OPEN PIT OPERATIONS 2020
- Open pit mining completed at Matilda and Wiluna subsidiary pits;
- In the month of June 2020 pre-stripping activities at Williamson were completed. Williamson is now the main free milling ore source and will continue to be mined at low strip ratios with the lower cost base to be maintained for the financial year 2021.

UNDERGROUND OPERATIONS 2020
Underground operations continue to provide valuable high grade, free milling feed from the Golden Age orebody to the process plant, whilst rehabilitation of existing development and new development commence to open stoping blocks for initial sulphide mining areas.

The Golden Age Underground mine is accessed via the Bulletin portal located only 2.5km from the Wiluna Gold Plant. Mining method - combination of top-down mechanised longhole open stoping method, with in-situ pillars left unmined for support, and airleg stoping in areas with a dip less than 35 degrees.

Murray Engineering have been contracted to supply and maintain mine fleet for current production associated development and stoping.

Byrnecut Contractors have been engaged to provide equipment and personnel for existing development rehabilitation and new development for resource-reserve drill out programmes and production from new mine areas.

SULPHIDE DEVELOPMENT PLAN
The Wiluna Mining Centre is divided into four geographical areas, centred on underground mine portals and planned mining areas of the Stage 1 Sulphides Development plan. Mining is planned to commence at the Wiluna North Mine area via the existing Bulletin Decline, and at the Wiluna Central Mine area via three existing declines, and then extend to the Wiluna South Mine area via three existing declines in Eats Pit.

Development will focus initially in the first 600 vertical metres in the Bulletin, Happy Jack, and Essex areas. These areas are dewatered and close to existing development leading to low cost, low risk and rapid ramp up in production. Production from these readily available areas will underpin the staged sulphide development and provide early access to future production areas.

Stage 1 Progress
- Five existing declines into orebodies – Bulletin, East Lode South, East Lode North, Happy Jack South, Happy Jack North
- One new portal (Essex)
- Mining to commence at the northern end of the Wiluna Mining Centre at Bulletin Upper, continuing south through Bulletin South, Essex, Calvert, East Lode North and East Lode South.

According to the Pre-Feasibility Study (2017), underground production at the Bulletin and East-West underground mines will be predominately extracted via top-down mechanised long hole open stoping and a smaller amount of a bottom-up modified Avoca mining method using unconsolidated backfill. Suitable pillars is left behind to ensure ground stability during the mining process.


Crushing and Grinding
Crusher / Mill TypeModelSizePowerQuantity
Jaw crusher 1
Cone crusher 2
Ball mill 2
Regrind 1
Rod mill 1

Summary:

The Wiluna Operations processing plant consists of a single crushing circuit for sulphide and oxide ores. Oxide and free-milling ores are sized through a three-stage crushing and two stage milling process, then processed in a CIL-OA (Carbon in Leach) cyanidation circuit.

Given the elevated hardness of the Wiluna ores, the existing Sulphide circuit throughput is limited by the grinding capacity of the existing circuit at approximately 750ktpa. The existing mill setup has two ball mills, a rod mill and a regrind mill post flotation that were used to treat the hard underground ores.

Stage 1 Sulphide expansion - Crusher and mill refurbishment
The first stage in the sulphide development plan will utilise the existing crushing and grinding circuits to provide feed to the new flotation circuit. Considerable work has been completed to prepare the crushing circuit for processing of a 100% underground fresh ore feed. This includes the replacement of the secondary cone crusher with a near identical crusher to the current tertiary cone crusher. The rod mill was refurbished and brought online in January 2020 (see ASX announcement 12 February 2020) to provide additional grinding capacity. These changes to the comminution circuit have recently been tested on fresh ore feed to confirm their performance on harder ore at the desired plant throughput rate.

The mill would use the existing 2 ball mills and a refurbished rod mill to process 750,000 tonnes of sulphide ore, to produce 46ktpa of gold concentrate at approximately 70 g/t gold, based on 90% flotation recovery.


Processing

  • Gravity separation
  • Smelting
  • Agitated tank (VAT) leaching
  • Carbon in leach (CIL)
  • Elution
  • Carbon adsorption
  • Solvent Extraction & Electrowinning
  • Cyanide (reagent)

Flow Sheet: Subscription required

Summary:

The Wiluna Gold Plant has run under several incarnations in the last three decades of operation, including Carbon in Pulp (CIP) and Carbon in Leach (CIL), to process free-milling (oxide) ores and more recently as a BIOX® CIL to process refractory (sulphide) ore.

Currently operating a CIL plant, processing free milling ore producing approximately 62kzopa.

The 2016 Restart
The strategy to re-start production focused on free-milling (oxide) resources which Wiluna Mining (formely Blackham Resources) intended to process through the relatively straight-forward Carbon in Leach (CIL) circuit at Wiluna. This involved crushing, grinding, gravity and CIL.

After successfully financing the project, first gold was poured in October 2016.

Over the last two years, the free-milling circuit has achieved steady throughput of 1.8 million tonnes per annum. The rod-mill refurbishment was completed in December 2019, offering ‘an approximate 20% increase in g ........

Recoveries & Grades:

CommodityParameter2020201920182017
Gold Recovery Rate, %  ......  Subscription required  ......  Subscription required  ......  Subscription required  ......  Subscription required
Gold Head Grade, g/t 1.41.31.41.4
Subscription required - Subscription is required.

Production:

CommodityUnits2020201920182017
Gold oz  ......  Subscription required  ......  Subscription required  ......  Subscription required39,413
All production numbers are expressed as metal in doré. ^ Guidance / Forecast.
Subscription required - Subscription is required.

Operational Metrics:

Metrics2020201920182017
Ore tonnes mined  ......  Subscription required  ......  Subscription required  ......  Subscription required  ......  Subscription required
Stripping / waste ratio  ......  Subscription required  ......  Subscription required  ......  Subscription required  ......  Subscription required
Tonnes processed  ......  Subscription required  ......  Subscription required  ......  Subscription required  ......  Subscription required
Annual processing capacity  ......  Subscription required  ......  Subscription required  ......  Subscription required  ......  Subscription required
Subscription required - Subscription is required.

Reserves at November 5, 2020:

CategoryTonnage CommodityGradeContained Metal
Proven 0.55 Mt Gold 0.8 g/t 15 koz
Probable 24.1 Mt Gold 1.8 g/t 1,366 koz
Proven & Probable 24.7 Mt Gold 1.7 g/t 1,381 koz
Measured 2.59 Mt Gold 1.42 g/t 118 koz
Indicated 62.59 Mt Gold 1.74 g/t 3,495 koz
Inferred 42.44 Mt Gold 2.49 g/t 3,401 koz
Total Resource 107.61 Mt Gold 2.03 g/t 7,015 koz

Commodity Production Costs:

CommodityUnits2020201920182017
Cash costs Gold AUD  ......  Subscription required  ......  Subscription required
All-in sustaining costs (AISC) Gold AUD  ......  Subscription required†  ......  Subscription required†  ......  Subscription required† 1,875 / oz†
^ Guidance / Forecast.
† Net of By-Product.
Subscription required - Subscription is required.

Financials:

Units2020201920182017
Revenue M AUD  ......  Subscription required  ......  Subscription required  ......  Subscription required  ......  Subscription required
Gross profit M AUD  ......  Subscription required  ......  Subscription required  ......  Subscription required  ......  Subscription required
After-tax Income M AUD  ......  Subscription required  ......  Subscription required  ......  Subscription required  ......  Subscription required
Operating Cash Flow M AUD  ......  Subscription required  ......  Subscription required  ......  Subscription required  ......  Subscription required
Subscription required - Subscription is required


Heavy Mobile Equipment as of December 31, 2020:
HME TypeModelQuantityLeased or
Contractor
Drill (long hole) ....................... Subscription required 2 Leased
Drill jumbo (two boom) ....................... Subscription required 3 Leased
Explosives Charger ....................... Subscription required 1 Leased
Loader ....................... Subscription required 3 Leased
Truck (underground) ....................... Subscription required 4 Leased
Subscription required - Subscription is required.

Mine Management:

Job TitleNameProfileRef. Date
....................... Subscription required ....................... Subscription required Subscription required Feb 11, 2021
....................... Subscription required ....................... Subscription required Subscription required Feb 11, 2021
....................... Subscription required ....................... Subscription required Subscription required Feb 11, 2021
....................... Subscription required ....................... Subscription required Subscription required Feb 11, 2021
....................... Subscription required ....................... Subscription required Subscription required Feb 11, 2021
....................... Subscription required ....................... Subscription required Subscription required Feb 11, 2021
....................... Subscription required ....................... Subscription required Subscription required Feb 11, 2021
....................... Subscription required ....................... Subscription required Subscription required Feb 11, 2021
Subscription required - Subscription is required.

Staff:

EmployeesYear
Subscription required 2017

Corporate Filings & Presentations:

DocumentYear
................................... Subscription required 2020
................................... Subscription required 2020
................................... Subscription required 2020
................................... Subscription required 2020
................................... Subscription required 2020
................................... Subscription required 2020
................................... Subscription required 2020
................................... Subscription required 2020
................................... Subscription required 2019
................................... Subscription required 2019
................................... Subscription required 2019
................................... Subscription required 2019
................................... Subscription required 2019
................................... Subscription required 2018
................................... Subscription required 2018
................................... Subscription required 2018
Annual Report 2017
Fact Sheet 2017
Feasibility Study Report 2017
Annual Report 2016
Annual Report 2015
Pre-Feasibility Study Report 2015
Subscription required - Subscription is required.

Aerial view:

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