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Costerfield Community | Exploration News | Reserves and Resources | Operating stats| Costerfield Technical Report |
Costerfield Narrow Vein Case Study (AusIMM 2016 Mine Management Conference) | Exploration License Application Notice
Significant improvements in mining and processing methods since then has enabled production to grow to the 10,000-12,000 t/m range by early 2013 and has been sustained since then.
The Costerfield operation encompasses the underground Augusta Mine including the Augusta veins, Cuffley, Brunswick and Youle deposits, the Brunswick Processing Plant, Splitters Creek evaporation Facility, Bombay Tailings Storage Facility, Brunswick Tailings Storage Facility and associated infrastructure.
In 2018, Mandalay announced multiple high-grade drill intercepts defining the core of the emerging Youle vein beneath the historical Costerfield mine. The drill hole intercepts reported in this press release contained gold and antimony grades that were diluted to minable gold equivalent grades over the minimum mining width of 1.8 metres (“m”). Subsequent drilling defined a strike length (400 – 600 m) and depth extent (150 – 200 m) that was consistent with the dimensions of orebodies found beneath the other historic mines in the district.
In September 2019, Mandalay commenced on-vein development of the Youle vein, which lies approximately 800 m north of the Brunswick Lode. With the orebody accessed, the Company initiated its first stope in the final weeks of 2019 and expects a ramp-up of development and stoping over the next 12 – 18 months.
Costerfield has significant organic production growth with the Youle vein, and highly prospective targets in the mineral district within the 100%-owned Mandalay tenement.
Location, Property, and Permitting:
The Costerfield mine is centred on the small settlement of Costerfield in Central Victoria, Australia, located approximately 10 kilometres (“km”) northeast of Heathcote, 50 km southeast of the city of Bendigo and 100 km northwest of Melbourne, Victoria. The Costerfield tenements currently total 5,644.7 hectares (“Ha”), of which 1,249.7 Ha are held as the mining licenses and the balance in three exploration licenses. Further exploration licenses abutting the current tenements to the east and west are under application and total 3,960.0 Ha. The mine is fully permitted and operates year-round.
Ore Deposit Geology:
Veins of the Costerfield district are hosted by Silurian Costerfield Siltstone, exposed in the core of the Costerfield Anticline. The anticline strikes north-south, gently bowed toward the west and domal, plunging to the north and south.
Historically, Costerfield mineralization has been mined over a length of about 8 km north to south. The currently mined Brunswick and Youle deposits occur in the center and to the north of the field. Auriferous quartz-stibnite veins strike north-northwest and predominantly sub-vertical to west dipping. They occur either as discrete veins that range in thickness from a few millimeters (“mm”) up to 4 m, or in sheeted vein arrays of up to 10 m. Despite their narrow width, the veins tend to be persistent along strike and down dip. Individual ore shoots have been traced over 800 m strike length and have been worked down to 400 m depth within the Cuffley deposit. Mining of the Youle deposit is currently planned to extend to a depth of 450 m below surface.
The Youle deposit extends below the historical Costerfield, Minerva and Bombay group of mines located approximately 1.2 km northeast of Brunswick. Mineralization was identified in 2011 in drill hole MB012, which struck the down-dip continuation of the vertical Kendall Lode, offset westward over the west-dipping No. 3 thrust fault. In 2016, drill hole BC006W1 revealed the existence of a high-grade north–northwest striking, west-dipping lode structure. The Youle vein dips at a shallower angle to the lodes at Brunswick and Cuffley and has been identified as the down-dip continuation of the vertical Kendall Lode offset westward over the west-dipping No.3 thrust fault.
The Costerfield veins were discovered in the 1860’s by two prospectors named Coster and Field and together with further veins discovered in the mineral district were mined for both gold and antimony, most extensively during two periods: 1860 – 1883 and 1904 – 1925. Intermittent small scale production took place during the period 1934 – 1950.
Since 1975 the Costerfield district has undergone more extensive, modern exploration, mainly geochemical sampling of bedrock under shallow alluvial cover and drilling. This was met with early success with the discovery of the Augusta deposit in 1975. The construction of a processing plant in 1995 by AGD enabled the re-treatment of tailings and the oxide portion of the Brunswick deposit which was mined by open pit method. Resource definition drilling at Augusta resulted in the completion of a successful feasibility study and development of the Augusta underground mine in 2006, utilizing the Brunswick processing facility. The mine was shut for a few months during 2009.
Exploration and Mineral Resources and Reserves:
The drilling and resource/reserve estimation process are described in the independent technical report completed by SRK Consulting in February 2019, which was filed on this website and on the Company’s profile on SEDAR (click here to view Costerfield’s reserves and resources).
The Company published an updated Resources and Reserves on January 8, 2019, including the maiden Reserves and Resources estimate for the high-grade Youle lode. Numbers can be found here, and full details are included in the independent technical report completed by SRK Consulting in December 2018, which was filed on February 6, 2019.
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Costerfield currently produces ore from two veins Brunswick and the Youle. The mining method employed is long-hole stoping with cemented rock fill. Ore is accessed by a primary spiral ramp. Level spacing is at 10 meter centers and horizontal development is advanced in 1.8 m wide drives in both directions extents of the deposit. Levels are then retreated though production stopes drilled to a width of approximately 1.5 m. The stopes are subsequently backfilled with cemented rock fill to supply stability, reduce dilution and allow for mining above and below mined out levels. This mining method is used for both the Brunswick and Youle veins.
Processing and Sales:
Ore is trucked on the surface from the Augusta mine portal to the Brunswick plant, where it is stockpiled and blended into the crusher. The circuit includes: primary mobile crusher, primary and secondary ball mills; rougher, scavenger, cleaner flotation, and filtering. Gravity gold concentrate is sold to refinery in Melbourne, Victoria and Gold Antimony flotation concentrate is trucked to the port of Melbourne, from which it is shipped to smelters in China.
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Chris Gregory, General Manager of Australasian Corporate Development and Exploration for Mandalay Resources, a Member of Australian Institute of Geoscientists (AIG) and a Qualified Person as defined in NI 43-101, supervised the scientific and technical information relating to exploration reported here and has reviewed and approved such information contained in this website.