Further Metallurgical Testing on New Liberty Ore Confirms Gold Recovery and Reduces Reagent Consumption and CIL Residence Time
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TORONTO, Jan. 28, 2013 /CNW/ - Aureus Mining Inc. ("Aureus" or the "Company") is pleased to announce that the metallurgical optimization test work programme undertaken as part of the on-going New Liberty Project ("New Liberty" or the "Project") optimization phase confirms a substantial improvement on the results in the original Technical Report published in October 2012. Key highlights include:
Improved leach kinetics allows for halving the leach residence time
Cyanide consumption has been reduced to one-third
Potential gold recovery increase to over 93%
- Cyanide destruction process - sodium metabisulphite addition could be reduced from 2.0kg/t to 0.5kg/t
Metallurgical test work has shown encouraging results with improved leach kinetics indicating that the recovery of 93% modelled in the Technical Report is achievable at a reduced carbon in leach ("CIL") residence time of 24 hours (previously 48 hours), with significantly lower reagent consumption. These improvements will impact positively on both the capital and operating costs. Overall plant recovery will be defined when an economic trade-off has been completed to quantify the recovery benefit associated with the inclusion of a regrind mill.
The extensive optimization test work was completed on a 240kg representative bulk composite sample and six variability composite samples from the New Liberty deposit and has produced the following key results:
Improved leach kinetics allows for halving the leach residence time -
The inclusion of high shear and oxygen addition resulted in improved
leached kinetics. The improved leach kinetics allow for a reduction in
leach residence time to 24 hours.
Cyanide consumption has been reduced to one-third - CIL reagent
optimization test work indicated that cyanide consumption could be
reduced from 1.5kg/t to 0.5kg/t with the inclusion of lead nitrate
addition of 25g/t.
Potential gold recovery increase to over 93% - The evaluation of CIL
recovery as a function of grind size on the bulk master composite
sample at a head grade of 4.23g/t indicated that at a grind of 90%
passing 75 micron CIL recovery increased recovery to 91.7% as compared
to 91.2% for a mill grind of 80% passing 75 micron. A further increase
in mill grind to 95% passing 75 micron resulted in an increase in CIL
recovery to 94.5%.
Continuous tests using a Hybrid SO2/Air process indicated that a weak acid dissociable cyanide ("CN (WAD)")
concentration of less than 20ppm could be achieved in the effluent
stream. This CN (WAD) concentration is below the target level of 50ppm
as stipulated by the International Cyanide Code of Practice. This test
work also indicated that for the Hybrid SO2/Air process (cyanide destruction process) sodium metabisulphite
addition could be reduced from 2.0kg/t to 0.5kg/t.
Variability test work was conducted on five core samples with a head
grade value ranging from 4.26g/t - 10.44g/t at an average of 5.9g/t. It
was found that for a grind size of 93% passing 75 micron, the overall
gold extraction ranged from 92.6% - 97.9% of the gold present in the
feed sample as measured by screen fire assay, with an average test work
recovery of 94.3%.
- The results of the metallurgical test work is the first of a number of initiatives which are part of the re-optimization programme announced in November 2012 after completion of the feasibility study. Initiatives include remodelling the creek diversion, the optimum location of the processing plant, and further improvements in the infrastructure at New Liberty. The full results will be announced at the end of Q1 2013.
Commenting on the metallurgical test results, David Reading stated:
"These metallurgical results, which indicate significantly lower operating costs due to factors which include a shorter CIL residence time and lower consumption of reagents, further demonstrate the strong economics of New Liberty. This is the first set of results for what is an on-going optimization programme, the full results of which will be available towards the end of the first quarter of this year. We are confident the results of this programme will further enhance the returns for all stakeholders on what will be Liberia's first commercial gold mine."
Subsequent to the feasibility study the Company initiated optimization phase for the Project. The objective of the optimization phase test work was to finalize the flowsheet and optimize reagent consumption while achieving an overall test work recovery of 93%.
Metallurgical Testwork Programme
A metallurgical test work programme has been completed as part of the optimization phase. The test work programme was undertaken by the Australian, Perth based, ALS Laboratories ('ALS').
In October 2012, 800kg of pre-crushed (12.7mm) core sample material was delivered to ALS's mineral progressing facility for metallurgical characterization test work. This material was the product material from comminution test work conducted on core samples at JKtech in September 2012. The sample material received from JKtech was composited to produce a 240kg bulk master composite sample for test work aimed at finalizing the flowsheet and optimizing reagent consumption. This bulk sample was comprised of pre-crushed core samples from the western and central portions of the deposit at various depths. The master composite had a gold grade of 4.23g/t. In addition to the test work conducted on the master composite sample, further variability test work was conducted using the optimized flowsheet and reagent consumptions. Six (6) variability samples were prepared from the pre-crushed core samples as received from JKtech and four (4) additional ½ drill core samples which were delivered to ALS in December 2012. The four additional ½ drill core sample mass totalled 136kg. The variability samples had a measured gold grade ranging from 4.26 g/t - 10.44g/t.
The scope of work of the test work programme included:
Sample preparation, bulk mineralogy and chemical analysis
Evaluation of preg-robbing
Comparison of kinetic leach performance for the feasibility study
flowsheet which was based on a 24 hour leach followed by a 24 hour CIP
process as compared to an flowsheet that includes high shear
pre-oxidation followed by a 24 hour CIL process with oxygen addition
Gravity recoverable gold (GRG) test work and modelling by Consep for
further GRG verification
Grind on gravity tails to various target sizes namely; 80%,90%, 95% and
greater than 95% passing 75 micron
Optimization of reagent consumptions for the carbon in leach (CIL)
Continuous cyanide destruction test work to determine the most suitable
flowsheet and optimize reagent consumption
- Levin test work to determine energy requirements, for a regrind milling application
The test work schedule was designed with the objective of finalizing the process flowsheet and optimizing reagent consumption while achieving a test work recovery of 93%. The results received from the test work program will provide engineering data to be utilized for finalizing the process flowsheet and refining the process plant operating costs.
Flowsheet Finalization and Reagent Optimization Test work Outcomes
Flowsheet Finalization and Reagent Optimization Test work were carried out on the master bulk composite sample. The results of this test work are as follows:
Evaluation of Preg-robbing
The testwork showed that gold extraction was similar for tests conducted
with both carbon and diesel present as compared to leach tests
conducted with no carbon present
- Based on the similarity in overall extraction it can be inferred that there is no evidence of preg-robbing
Figure 1: Results for testing conducted to evaluate preg-robbing
Evaluation of Leach Kinetics with the Inclusion of High Shear
The testwork showed that a flowsheet with the inclusion of high shear
and oxygen addition at a dissolved oxygen level maintained above 16ppm
would allow for improved leached kinetics and improved overall recovery
- The improved leach kinetics allow for a reduction in leach residence time to 24 hours
Figure 2: Kinetic curves for testing conducted to evaluate the inclusion of high shear Pre-oxidation on CIL residence time requirements
Optimization of Reagent Consumption
- CIL Reagent optimization test work indicated that cyanide consumption could be reduced from 1.5kg/t to 0.5kg/t with the inclusion of lead nitrate addition at 25g/t without negatively impacting on overall recovery
Figure 3: Kinetic curves for testing conducted to determine optimum CIL Cyanide addition requirements
Evaluation of CIL recovery as a function of grind size
The evaluation of CIL recovery as a function of grind size indicated
that at a grind of 90% passing 75 micron CIL recovery improved by 0.48%
as compared to a mill grind of 80% passing 75 micron
Further evaluation of CIL recovery as a function of grind size indicated
that at a grind of 95% passing 75 micron CIL recovery improved by 2.69%
as compared to a mill grind of 90% passing 75 micron
It was found that a mill grind size in excess of 95% passing 75 micron
did not show any further recovery benefit when compared to a mill grind
of 95% passing 75 micron
- The target mill grind size of 95% passing 75 micron can be achieved with the inclusion of a regrind mill. Based on Levin test work, the regrind milling circuit has a power requirement of 6.8kwh/t and an estimated steel media consumption rate of 0.05kWh/t
Figure 4: Kinetic curves for testing conducted to evaluate CIL recovery as a function of grind size
Continuous Cyanide Destruction Testing
Continuous SO2/Air cyanide destruction test work revealed that the target CN (WAD)
concentration of less than 50ppm in the effluent stream could not be
achieved even at a reagent addition ratio of 4:1 or 2.0kg/t Sodium
- Continuous tests using a Hybrid SO2/Air process indicated that a CN (WAD) concentration of less than 20ppm could be achieved in the effluent stream with the addition of 0.5kg/t Sodium metabisulphite
Variability Test work Outcomes
Variability test work was carried out on five (5) variability core samples at a target grind of 90% passing 75 micron. Further variability test work was carried out on six (6) variability core samples at a target grind of 100% passing 75 micron. All variability test work was carried out using the optimized flowsheet configuration (as shown in Figure 1) and reagent consumptions in order to give an estimate of the expected range for recovery.
The results of the variability test work are as follows:
Variability test work was carried out on five (5) core samples with a
head grade value ranging from 4.26g/t - 10.44g/t at an average of
5.9g/t. These tests were carried out at a grind of 93% passing 75
micron and indicated that a CIL gold residue grade of 0.22g/t - 0.36g/t
could be achieved
For a grind size of 93% passing 75 micron, the overall gold extraction
ranged from 92.6% - 97.9% of the gold present in the feed sample as
measured by screen fire assay. At the time of publication the back
calculated feed grades based on the test work results were not yet
The average CIL residue grade for all variability tests conducted at 93%
passing 75 micron was 0.31g/t with an average test work recovery of
- Further variability test work was conducted on six (6) core samples at a grind size in excess of 96% passing 75 micron. These tests produced overall recoveries in excess of 95%. This test work is to be re-evaluated using a different regrind testing strategy with a target grind of 95% passing 75 micron in order to replicate the expected feed to the mill by scalping the coarse size fraction for regrind. This will eliminate overgrinding of finer size fractions
Summary of Test work Results
A summary of the test work results for testing conducted on the master bulk composite and all variability samples are presented in Table 1 and Table 2 below:
Table 1: Summary of results for testing conducted on the master bulk
composite sample (head grade of 4.23 g/t)
Table 2: Summary of results for testing conducted on the variability
New Liberty Flow Sheet
In the optimized flowsheet for New Liberty as presented in Figure 5, high shear oxygen addition has been added to the pre-oxidation tank and the leach tanks have been removed. The CIL circuit has been re-sized to allow for a 24 hour residence time. The optimized circuit also includes second stage cycloning and a regrind mill.
Figure 5: Optimized Process Flow Sheet
About Aureus Mining Inc.
The Company's assets include the New Liberty gold deposit in Liberia (the "New Liberty Gold Project" or the "Project"), which has an estimated proven and probable reserve of 910,000 ounces of gold grading 3.3 g/t and an estimated measured and indicated mineral resource of 1,143,000 ounces of gold grading 3.6 g/t and an estimated inferred mineral resource of 593,000 ounces of gold grading 3.2 g/t. A feasibility study has been completed on the Project and construction has commenced with initial earthworks. The Project is expected to have an eight and a half year mine life and annual production of 120,000 ounces for the first five years of production. The Company has financed the Project's equity funding requirement and is in advanced discussions with interested parties to fund the balance.
The New Liberty Gold Project is located within the Bea Mountain mining licence, which covers 457 km² and has a 25 year, renewable, mineral development agreement. The Bea Mountain mining license also hosts the proximal gold targets of Ndablama, Gondoja and Weaju, which are the focus of exploration programs during 2013. The contiguous Archaen Gold exploration licence, which covers 89 km², is also a focus of exploration for 2013, with Leopard Rock being the main target.
The Company also has gold exploration permits in Cameroon.
Information in this report that relates to Metallurgical Test Work Results is based on information compiled by Glenn Bezuidenhout of [DRA Mineral Projects. Glenn Bezuidenhout is a Fellow of SAIMM, and has sufficient experience, which is relevant to the style of mineralization and type of deposit under consideration, and to the activity which he is undertaking to qualify as a Competent Person as defined by the NI-43-101 (National Instrument Code for the TSX) . Glenn Bezuidenhout consents to the inclusion in this report of the statements based on his information in the form and context in which it appears.
This press release contains certain forward-looking information. All information, other than information regarding historical fact, that addresses activities, events or developments that Aureus Mining believes, expects or anticipates will or may occur in the future is forward-looking information. Forward-looking information contained in this press release includes, but may not be limited to, the future plans and objectives of Aureus Mining and their anticipated future growth, mineral resource estimates and the anticipated exploration and development activities of Aureus Mining. The foregoing and any other forward-looking information contained in this press release reflects the current expectations, assumptions or beliefs of Aureus Mining based on information currently available to Aureus Mining. With respect to the forward-looking information contained in this press release, Aureus Mining has made assumptions regarding, among other things: general business, economic and mining industry conditions; and it has also been assumed that no material adverse change in the price of precious and/or base metals occurs, no unusual geological or technical problems occur and no significant events occur outside of the normal course of Aureus Mining's respective business.
Such forward-looking information is subject to a number of risks and uncertainties that may cause actual results or events to differ materially from current expectations, including: risks normally incidental to exploration and development of mineral properties; uncertainties in the interpretation of results from drilling and test work; the possibility that future exploration, development or mining results will not be consistent with expectations; uncertainty of mineral resources estimates; adverse changes in precious and/or base metal prices; and future unforeseen liabilities and other factors including, but not limited to, those listed under "Risk Factors" in the Preliminary Prospectus of Aureus Mining Inc. dated April 20, 2011, a copy of which is available on SEDAR at www.sedar.com, and in the Aureus Mining Admission Document, a copy of which is available at www.aureus-mining.com.
Any mineral resource figures referred to in this press release are estimates and no assurances can be given that the indicated levels of minerals will be produced. Such estimates are expressions of judgment based on knowledge, mining experience, analysis of drilling results and industry practices. Valid estimates made at a given time may significantly change when new information becomes available. While Aureus Mining believes that the mineral resource estimates in respect of their respective properties are well established, by their nature mineral resource estimates are imprecise and depend, to a certain extent, upon statistical inferences which may ultimately prove unreliable. If such mineral resource estimates are inaccurate or are reduced in the future, this could have a material adverse impact on Aureus Mining, as applicable. Due to the uncertainty that may be attached to inferred mineral resources, it cannot be assumed that all or any part of an inferred mineral resource will be upgraded to an indicated or measured mineral resource as a result of continued exploration.
Forward-looking information speaks only as of the date on which it is made and, except as may be required by applicable law, Aureus Mining disclaims any obligation to update or modify such forward-looking information, either as a result of new information, future events or for any other reason.
SOURCE: Aureus Mining Inc.For further information:
Aureus Mining Inc.
David Reading / Jeremy Cave
Tel: +44(0) 20 7010 7690
Bobby Morse / Gordon Poole
Tel: +44 (0) 20 7466 5000
RBC Capital Markets (Nominated Adviser and Joint Broker)
Martin Eales / Richard Hughes
Tel: +44(0) 20 7653 4000
GMP Securities Europe LLP (Joint Broker)
Richard Greenfield / Alexandra Carse
Tel: +44(0) 20 7647 2800