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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."
Introduction
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)
process and
-
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
http://aureus-mining.com/wp-content/uploads/2013/01/Evaluation-of-Pregrobbing.png
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
http://aureus-mining.com/wp-content/uploads/2013/01/Effect-of-Shear.png
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
http://aureus-mining.com/wp-content/uploads/2013/01/Cyanide-Consumption-Optimization.png
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
http://aureus-mining.com/wp-content/uploads/2013/01/Effect-of-Grind.png
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
metabisulphite
-
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
available
-
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
94.3%
-
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)
http://aureus-mining.com/wp-content/uploads/2013/01/Table-1.png
Table 2: Summary of results for testing conducted on the variability
samples
http://aureus-mining.com/wp-content/uploads/2013/01/Table-2.png
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
http://aureus-mining.com/wp-content/uploads/2013/01/Process-Flow-Sheet.png
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.
Qualified Person
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.
Forward-looking Statements
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.
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