Australia

Wiluna Mining (Matilda-Wiluna) Operation

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Overview

Mine TypeTailings
StatusActive
Commodities
  • Gold
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SnapshotWiluna Mining Operation has long history of gold production since 1897. In mid-2016 the Wiluna Mining Corp. re-started mining at the Wiluna Mining Operation. Mining operations ceased on 14 December 2022 and the underground mine placed on care and maintenance.

On February 16, 2024, Wiluna Mining Corporation Limited reported on the outcomes of a Pre-feasibility Study on a potential restart of mining operations for Wiluna. This resulted in a PFS that supports a projected 9.5-year operation that would prioritise sulphide material and restart BIOX processing at Wiluna, supported by the existing operational CIL circuit. These processing circuits would be fed initially by an open pit mine, later transitioning to underground mining. Tailings mining and tailings retreatment through the Wiltails repulper would also continue throughout.
Related Asset

Owners

SourceSource
CompanyInterestOwnership
Wiluna Mining Corporation Ltd. (operator) 100 % Indirect
Wiluna Mining Corporation Limited (formerly Blackham Resources Limited) is a Western Australian based gold mining company that owns and operates the Wiluna Mining Operation.

On 20 July 2022, Michael Ryan, Kathryn Warwick, Daniel Woodhouse and Ian Francis, all Senior Managing Directors of FTI Consulting, were appointed as Voluntary Administrators of Wiluna Mining Corporation Limited.

The Deed of Company Arrangement (“DOCA”) was signed by the Company and each of its subsidiaries in the Annexure A (all subject to Deed of Company Arrangement) and the Deed Administrators on 28 July 2023. This agreement with creditors is an important milestone to advance the broader strategic turnaround plan and recapitalisation of the Group.

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Deposit type

  • Orogenic
  • Tailings
  • Vein / narrow vein

Summary:

Wiluna Mining Operation comprises four mining centers being Wiluna, Matilda, Lake Way and Regent.

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.

WILUNA TAILINGS
Wiltails Ore Reserve includes reclaimed tailings material in Tailings Storage Facilities C, H and Western Extension and backfilled pits at Adelaide, Golden Age, Moonlight and Squib.

Reserves

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Mining Methods

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Comminution

Crushers and Mills

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Processing

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Production

CommodityProductUnits2023202220212020201920182017
Gold Metal in conc./ doré oz  ....  Subscribe  ....  Subscribe
Gold Metal in doré oz  ....  Subscribe  ....  Subscribe65,40670,56539,413

Operational metrics

Metrics2023202220212020201920182017
Ore tonnes mined  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe1,938,606 t1,696,842 t1,323,616 t
Tonnes processed  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe1,807,931 t1,835,057 t965,300 t
Annual processing capacity  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe1.8 Mt1.8 Mt
Stripping / waste ratio  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe9.1 8.6 13.7

Production Costs

CommodityUnits20212020201920182017
Cash costs Gold AUD  ....  Subscribe 1,505 / oz  
All-in sustaining costs (AISC) Gold AUD  ....  Subscribe  ....  Subscribe 1,760 / oz **   1,629 / oz **   1,875 / oz **  
** Net of By-Product.

Financials

Units202220212020201920182017
Capital expenditures M AUD  ....  Subscribe
Revenue M AUD  ....  Subscribe  ....  Subscribe  ....  Subscribe 102.5   118.3   47.3  
Gross profit M AUD  ....  Subscribe  ....  Subscribe  ....  Subscribe -1   4.8   7.5  
After-tax Income M AUD  ....  Subscribe  ....  Subscribe  ....  Subscribe -73.2   -20   -6.8  
Operating Cash Flow M AUD  ....  Subscribe  ....  Subscribe  ....  Subscribe 0.2   6.2   24.7  

Heavy Mobile Equipment

Fleet data has not been reported.

Personnel

Mine Management

Job TitleNameProfileRef. Date
....................... Subscription required ....................... Subscription required Subscription required Nov 30, 2023
....................... Subscription required ....................... Subscription required Subscription required Nov 30, 2023
....................... Subscription required ....................... Subscription required Subscription required Nov 30, 2023

EmployeesContractorsYear
...... Subscription required 2022
...... Subscription required 2021
...... Subscription required 2017

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