Australia

Costerfield Operation

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Categories

Overview

Mine TypeUnderground
StatusActive
Commodities
  • Gold
  • Antimony
Mining Method
  • Longhole stoping
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SnapshotCosterfield Operation includes encompasses the underground Augusta Mine including the Augusta, Cuffley, Brunswick, Youle and Shepherd Deposits; the Brunswick Processing Plant; Splitters Creek Evaporation Facility; Brunswick and Bombay Tailings Storage Facilities (TSF) and associated infrastructure.
Related Asset

Owners

SourceSource
CompanyInterestOwnership
Mandalay Resources Corp. 100 % Indirect
Mandalay Resources Australia Pty (“MRA”), formerly Australian Gold Development, is a private Australian Corporation that operates Costerfield. MRA owns 100% of the voting securities of its sole subsidiary, Mandalay Resources Costerfield Operations Pty.

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Deposit type

  • Vein / narrow vein
  • Mesothermal

Summary:

The Costerfield Property lies within a broad gold-antimony province mainly confined to the Siluro-Devonian Melbourne Zone of Victoria. The narrow quartz-stibnite-gold veins of the Melbourne Zone are mesothermal to orogenic in nature and are a product of a 380 Ma to 370 Ma tectonic event. Gold in Central Victoria is believed to have been derived from the Cambrian greenstones that underlie the entire province at depth, however the origin of the associated antimony has been less studied.

The mineralisation at Costerfield occurs as narrow veins or lodes, typically less than 50 cm wide and hosted within unmetamorphosed (anchizone) mudstone and siltstone of the Lower Silurian Costerfield Formation.

Typical lode material at Costerfield consists of gold-bearing quartz and carbonate with massive stibnite either as the latest stage vein fill or segregated to one contact of the vein. The average grade of this material is approximately 9 g/t Au (often greater than 20 g/t) and 4% antimony (Fromhold et. al. 2017). A variety of accessory minerals are associated with the mineralisation, including pyrite, arsenopyrite, aurostibite, pyrrhotite, muscovite, sphalerite and galena within the vein. Wallrock alteration minerals are dominantly pyrite, arsenopyrite and ferroan carbonate spotting, surrounded by a broader, visually cryptic halo of muscovite replacing phengite. Small crystals of barite and bournonite are often seen in chlorite-coated joints near the lodes.

The character of the ore material does vary between the different Costerfield lodes in a broad sense. For example, the Augusta C, D, E Lodes, N Lode, Cuffley and Youle generally contain the ‘typical’ quartz-stibnite material described above. The Brunswick Lode is notable for containing proportionally less quartz than usual and the lode material usually comprising sheared host rock with massive stibnite as either solid vein fill or as breccia matrix with lesser quartz infill.

The Shepherd veins are unusual in a local context for containing relatively little stibnite and the mineralisation encountered to date has comprised simple coarse gold in quartz-carbonate veining. The southern portions of the Shepherd veins have displayed a more consistent stibnite component in the completed exploration drilling.

Notable west to northwest dipping thrust faults typically bound the mineralisation packages at the Costerfield Property but can become significantly mineralised themselves along the fault planes. Shallower and dominantly west dipping thrust faults, typically at very low angles or even parallel to bedding with a laminated quartz component, link between the larger order thrust faults. The link faults can also offset the vertical lode structures up to 50 m in an eastwest sense.

These flat dipping structures have influenced the lifespan of some historic mining at Costerfield. The Alison Mine, where lodes were initially discovered in 1863, ceased mining a depth extension in 1871 because the lodes were truncated against a flat west-dipping fault. A crosscut established below the ‘slide’ unsuccessfully passed back into the hangingwall of the fault before any lode continuation was located. Intermittent mining finally ceased at the Alison mine in 1922 after strike extensions were finally exhausted.

Drilling of the Allison Lodes in 2011 successfully intersected a westerly-displaced lode below the truncating fault. This continuation was named Cuffley Lode and became a major source of ore for the Costerfield mine for several years, no doubt eclipsing the production of the overlying historic mine by a significant margin.

Property Mineralisation
Significant portions of the local area are obscured by alluvium and colluvium deposits, which have been washed over the surrounding flood plains by braided streams flowing east off the uplifted Heathcote Fault Zone. Some of this alluvial material has been worked for gold but workings are small-scale and limited in extent. Most of the previously mined hard rock deposits were found either out-cropping or discovered by trenching within a few metres of the surface.

The Augusta Deposit was discovered late in the history of the field (1970) by bedrock geochemistry, buried less than 2 m to 6 m below the alluvium, which was deposited at the meandering Mountain Creek/Wapentake Creek confluence.

The mineralised structures in the Costerfield Zone, which typically dip steeply east or west (Augusta, Brunswick, Kendall), or moderately west (Youle) are likely to be related to the formation of the Costerfield Dome and the subsequent development of the Moormbool Fault. The main reef system(s) appear to be developed in proximity to the axial planar region of the Costerfield Dome or hosted in reactivated west-dipping thrust faults.

The economic mineralisation at the Costerfield Property occurs in a north-south corridor that includes the Costerfield, Brunswick and Augusta zones. The moderately west to steeplydipping quartz-stibnite-gold lodes have thicknesses ranging from several millimetres to one metre, and extend over a strike of at least four kilometres. The lode system is centred in the core of the doubly-plunging Costerfield Anticline and is hosted by Costerfield siltstones. Individual lodes can persist for up to 800 m along-strike and 300 m down-dip.

The mineralogy of the vein contents and mineral proportions differ from vein to vein throughout the Augusta, Cuffley, Brunswick and Youle lodes. However, the texture and chronological order of each vein/mineral generation remains remarkably consistent across all lodes.

The Costerfield Property lodes are typically anastomosing, en-echelon style, narrow-vein systems, which dip from 25° to 70° west to 70° to 90° east. Mineralised shoots are observed to plunge to the north, when structurally controlled, and south when bedding controlled.

The mineralisation occurs as single lodes and vein stockworks associated with brittle fault zones. These bedding and cleavage parallel faults, that influence the lode structures, range from sharp breaks of less than 1 mm to dilated shears up 3 m wide that locally contain fault gouge, quartz, carbonate and stibnite.

Cross faults, such as those seen offsetting other Costerfield Property lodes, have been identified in both open-pit and underground workings.

The mineralised lodes vary from massive stibnite with microscopic gold to quartz-stibnite, with minor visible gold, pyrite, and arsenopyrite. The stibnite is clearly seen to replace quartz, and gold can also be hosted by quartz.

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

In August 2020, work commenced on developing the Brunswick Portal, which is used primarily for trucking of ore to the ROM pad. The first haulage of ore took place via the Brunswick Portal in November 2020.
CommodityProductUnits202320222021202020192018201720162015
Gold Payable metal koz  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe1522324142
Antimony Payable metal t  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe2,0322,1733,1153,5973,712
Gold Equivalent Payable metal oz  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe25,16135,84952,13860,07665,675
^ Guidance / Forecast.

Operational metrics

Metrics20222021202020192018201720162015
Ore tonnes mined  ....  Subscribe  ....  Subscribe  ....  Subscribe137,536 t151,557 t140,638 t158,351 t153,649 t
Tonnes processed  ....  Subscribe  ....  Subscribe  ....  Subscribe141,090 t155,744 t151,759 t154,409 t153,869 t
Annual processing capacity  ....  Subscribe  ....  Subscribe  ....  Subscribe150,000 t150,000 t
Waste  ....  Subscribe  ....  Subscribe  ....  Subscribe229,257 t171,064 t
Daily processing rate  ....  Subscribe  ....  Subscribe  ....  Subscribe420 t

Production Costs

CommodityUnits2023202220212020201920182017
Cash costs Gold Equivalent USD  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe 1,313 / oz   961 / oz   701 / oz  
All-in sustaining costs (AISC) Gold Equivalent USD  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe
All-in costs Gold Equivalent USD 1,742 / oz   1,407 / oz   991 / oz  
^ Guidance / Forecast.

Operating Costs

Currency2022202120202019201820172016
UG mining costs ($/t milled) USD 167  142  143  148  145  169  152  
Processing costs ($/t milled) USD  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe
Total operating costs ($/t milled) USD  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe

Financials

Units2023202220212020201920182017
Capital expenditures (planned) M USD  ....  Subscribe
Capital expenditures M USD  ....  Subscribe  ....  Subscribe  ....  Subscribe 19.2   22.4   10.9  
Revenue M USD  ....  Subscribe  ....  Subscribe  ....  Subscribe 33.9   48   63.2  
Operating Income M USD  ....  Subscribe  ....  Subscribe  ....  Subscribe 1.1   -5.3   10.4  
Pre-tax Income M USD  ....  Subscribe  ....  Subscribe  ....  Subscribe -10.6   -5.3   7  
After-tax Income M USD  ....  Subscribe  ....  Subscribe  ....  Subscribe -8.4   -3.8   5.4  
EBIT M USD  ....  Subscribe  ....  Subscribe  ....  Subscribe -10.1   -5.7  
EBITDA M USD  ....  Subscribe  ....  Subscribe  ....  Subscribe 0.9   10.4   24.6  

Heavy Mobile Equipment

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Personnel

Mine Management

Job TitleNameProfileRef. Date
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EmployeesContractorsTotal WorkforceYear
...... Subscription required ...... Subscription required ...... Subscription required 2022
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Aerial view:

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