AIM RELEASE
31 August 2007
Bio-Ox metallurgical test enters final phase
for Dikoloti Nickel Project in Botswana
Metallurgical tests based on oxidation heap leaching of samples of
nickel-copper sulphide mineralisation from Discovery Metals Limited
(AIM:DME) Dikoloti Nickel Project, in northeast Botswana, are
progressing to their final phase of testing following positive
initial tests. Bio oxidation (Bio-Ox) processing has shown the most
promising results to date of a range of processing techniques being
trialled as part of an ongoing scoping study of Dikoloti. The project
work aims to define a cost effective method for processing Dikoloti's
nickel mineralisation.
Metallurgical Test Work Highlights
* Initial tests on the Dikoloti nickel sulphide mineralisation
indicated that high nickel extractions could potentially be
achieved using a bacterial leaching process;
* A column test, simulating the heap-leach bacterial process, has
achieved 50% nickel extraction to date with the nickel extraction
now accelerating rapidly, suggesting that a final high nickel
extraction value could be obtained at the conclusion of the test.
Discovery Metals' Managing Director, Mr Jeremy Read, said that due to
its fine grained nature, the Dikoloti nickel mineralisation presented
some challenges for conventional processing and as a consequence,
alternative methods of processing the nickel mineralisation are being
investigated.
"The first bacterial process test we undertook on the Dikoloti nickel
mineralisation was a stirred reactor test which showed that it should
be possible to achieve high nickel extractions using a bio-oxidation
process, as the reactor test achieved 97% nickel extraction," Mr Read
said.
"Following the successful reactor test, we moved to a 2m column test
which simulates the actual processes in a heap leach environment," he
said.
"The column test has highlighted several issues relating to the
release of iron into solution which has been slowing the nickel
extraction. In recent days, however, progress has been made on
controlling the iron and the rate of nickel extraction is now
increasing rapidly. We are optimistic of a successful final outcome
to the column test."
Dikoloti Bio-Oxidation Metallurgical Test
Previous testing by Discovery Metals on the Dikoloti nickel
mineralisation, indicated that a fine grind would be required in
order to liberate the nickel at acceptable recoveries using
traditional flotation processing techniques.
Consequently, Discovery Metals has been evaluating alternative
methods for processing the nickel mineralisation which would allow
Dikoloti to be developed as a standalone operation. The alternative
processing technique which has shown most promise to date is an
oxidation heap leach approach using bacteria to break down the
sulphide mineralisation and release the nickel into solution (Bio-Ox
Processing).
Preliminary stirred reactor testing demonstrated that the Dikoloti
ore is readily oxidised by bacterially regenerated ferric sulphate
chemistry, and that high nickel extractions (97%) can be achieved.
Following this successful initial test, a 2m column test was
initiated in order to simulate the processes which would occur in a
heap leach environment.
The early column testing indicated that due to large amounts of
pyrrhotite in the Dikoloti mineralisation, acid consumption was high
and breakdown of the pyrrhotite released a significant amount of iron
into solution. The release of the iron affected the ability of the
bacteria to break down the sulphides and release the nickel. As a
result of iron high concentrations in the column, nickel extraction
in the first 40 days of the test was low.
During the next 49 days of the test, a range of techniques was
trialled in order to control the iron release into the column such
that the bacteria would not be seriously affected. As a result of
these techniques nickel extraction has improved markedly from day
99. Nickel extraction now stands at approximately 50% and is
increasing steadily (Figure One).
The Bio-Ox test has now entered its final phase with this testing
expected to take another two months. Once the results of this final
test phase are available a decision on how to further progress the
Dikoloti Nickel Project will be made.
The information in this report that relates to Exploration Results is
based on information compiled by Mr. Jeremy Read who is a Member of
the Australasian Institute of Mining and Metallurgy. Mr Read is a
full-time employee of the Company. Mr. Read has sufficient experience
which is relevant to the style of mineralisation and type of deposit
under consideration and to the activity which he is undertaking to
qualify as a Competent Person as defined in the 2004 Edition of the
"Australasian Code for Reporting of Exploration Results, Mineral
Resources and Ore Reserves". Mr. Read consents to the inclusion in
the report of the matters based on information provided by him and in
the form and context in which it appears.
NOTE: For further information contact
Jeremy Read
Managing Director
Tel: +617 3218 0202
Mobile: 0409 484322
Email: jeremy@discoverymetals.com.au
Jamie Wright
RFC Corporate Finance Ltd (Nomad)
Tel: +618 9480 2508
Email: Jamie.Wright@rfc.com.au
Richard Hail
Fox-Davies Capital Ltd (AIM Broker)
Telephone: +44(0) 20 7936 5200
Email: Richard.Hail@fdcap.com
Further information on the Company is available on its website:
www.discoverymetals.com.au
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