- Gold recoveries to 99.3% and averaging 98.7% recorded for four metallurgical samples from the Baggy Green deposit, located in the wholly owned Wudinna Gold Camp.
- The samples comprise one supergene and three primary zone samples. A conventional gravity and cyanide leach flowsheet gave consistent gold recoveries across ore types.
- A minimum 40% of the gold reports to a gravity concentrate, while gravity tails leaching is achieved with only modest reagent additions.
- The Baggy Green results are equivalent to the excellent metallurgical results achieved for the nearby Barns deposit, where high gold recoveries averaging 97.9% were achieved using an identical gravity and cyanide leach flowsheet.
- Together Barns and Baggy Green contribute 95% of the Wudinna Gold Camp's total Mineral Resource of 200,300 ounces, and this work confirms that both deposits can be efficiently treated using a conventional flowsheet in a single processing plant.
- The next logical metallurgical test work for Barns and Baggy Green would involve coarsening the grind size to establish the optimum economic grind-recovery combination.
The Wudinna Gold Camp falls in the Company's Eyre Peninsula Gold Project which comprises seven tenements totalling 2,385 km2 in area on the Gawler Craton of South Australia (see Figure 1 in the link below).
Mineral Resources, estimated in accordance with the requirements of the JORC Code 2012, have been completed for the Barns, Baggy Green and White Tank deposits(see Note 1 below). The consolidated Mineral Resource for the Wudinna Gold Camp is 3.849 million tonnes grading 1.62g/t gold for 200,300 ounces of gold, using a 0.5g/t gold cut-off.
The Mineral Resource is classified into Indicated Resources of 380,000 tonnes at 1.40g/t gold (17,000 ounces), and Inferred Resources of 3.469 million tonnes at 1.64g/t gold (183,300 ounces).
Together Barns (107,000 ounces) and Baggy Green (82,400 ounces) comprise 95% of the total Wudinna Gold Camp Mineral Resource, and these two deposits will be critical to the development of the project.
In early 2017 the Company announced the results of metallurgical testwork on mineralisation from the Barns deposit(see Note 2 below), testing three potential processing options. A combination of gravity concentration and cyanide leaching of the gravity concentrate and tailings gave compelling results, with overall gold recoveries exceeding 97%.
The Barns gravity and cyanide leach results were achieved with low lime (~0.2kg/t) and modest cyanide (~1.0kg/t) additions for the primary mineralisation, presenting a viable conventional flowsheet option for the treatment of all identified Barns ore types.
Baggy Green metallurgical test work
The Company has now conducted metallurgical testing on gold mineralisation from Baggy Green to determine whether it can be successfully processed using an identical gravity concentration and cyanide leach flowsheet to that indicated for Barns.
Four composite samples were assembled from material retained following a reverse circulation drilling programme completed at Baggy Green in late 2016. The representative composites include:
- One sample of supergene gold hosted in weathered lower saprolite, and
- Three samples of primary gold hosted in fresh gneiss.
The testwork was completed by Bureau Veritas Minerals Pty Ltd metallurgical laboratories in Perth, Western Australia, the same laboratory that tested the Barns samples during the earlier study.
Representative sub-samples of each composite were submitted for gold, silver and copper analysis (see Table 1 in the link below).
Gold head grade assays showed variations implying the presence of coarse free gold, later borne out by the gravity test work.
Gravity and cyanide leach
2kg of each composite was ground in a stainless steel rod mill to a p80 nominally minus 75 microns.
The ground material was passed through a Knelson Concentrator to produce a gravity concentrate and gravity tailings. The gravity concentrate was then passed over a Mozely Table to reduce the mass to approximately 0.25% of the initial feed.
The Mozely Table concentrate was then subjected to 24 hours of intense cyanidation at 10% pulp density with a solution of 2.5% sodium cyanide. The pregnant solution was analysed for gold, silver and copper.
The leach residue was combined with both the Knelson Concentrator and Mozely Table tailings and subjected to 48 hours leaching at 45% pulp density with initial and minimum sodium cyanide solution strength of 500mg/l and 300mg/L respectively. Oxygen was sparged and lime was added to maintain a pH of 10 during the test.
The pulp was filtered and the liquid and solids submitted for gold, silver, and copper analysis to determine metal recoveries.
Gravity plus leach gold recoveries totaled 94.3% for the supergene sample, and ranged between 97.5% and 99.3%, averaging 98.7%, for the primary zone samples (see Table 2 in the link below).
Analysis of results
Excellent gold recoveries are achieved for Baggy Green mineralisation through gravity and cyanide leach with low lime additions (~0.2kg/t for primary ores) and modest cyanide additions (~1.1kg/t for all ores).
The same conclusions were drawn following the identical earlier test work for Barns, and confirmation that a conventional gravity and cyanide leach flowsheet can efficiently deliver exceptional gold recoveries for both deposits is a positive result.
The next logical metallurgical test work to be conducted on the Wudinna Gold Camp deposits would involve coarsening the grind size to establish the optimum economic grind-recovery combination.
The metallurgical results will also form important inputs into future studies investigating project economics.
Note 1: See ADN's ASX releases dated 19 July 2016 titled "Maiden 107,000 ounce gold resource estimated for Barns deposit" and dated 23 January 2017 titled "Wudinna Gold Camp Mineral Resource jumps to 200,000 ounces of gold" for full JORC information.
Note 2: See ADN's ASX release dated 16 January 2017 titled "Barns metallurgy results deliver 97% plus gold recovery with conventional flowsheet."
To view tables and figures, please visit:
About Andromeda Metals Ltd
Andromeda Metals Ltd (ASX:ADN) is an Australian Securities Exchange listed company focusing on mineral exploration for gold, copper and lithium deposits. The company has built a highly prospective exploration portfolio of projects covering 7,969 sq kms within 21 exploration licences located in South Australia, Queensland, Western Australia and the Northern Territory. Andromeda Metals was incorporated on 23 December 1993 and subsequently listed on the ASX on 11 September 1996. The company's head office is in Adelaide, South Australia.
Andromeda Metals' vision is to be a sustainable minerals exploration company providing shareholders with risk managed discovery, development and mining opportunities.
Executive Director and Company Secretary
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