AIM RELEASE
12th November 2007
* Successful new nickel recovery tests for the Dikoloti
Nickel Project in North-east Botswana
* Snowden to prepare new scoping study financial model for
project
Discovery Metals Limited (AIM: "DME") has completed a comprehensive
new study into the most cost effective way to process ore from its
Dikoloti nickel deposit in north-east Botswana, using a
state-of-the-art heap leach bio-oxidation process. The study was
based on GeoBiotics LLC's proprietary GEOLEACHTM process, which has
been developed as a method to recover base metals from sulphide ores
as an alternative to stirred tank leaching and other competing
technologies.
Following the positive results of the study, Discovery has contracted
Snowden Mining Industry Consultants to revise the Dikoloti scoping
study financial model as the bio-oxidation process has the potential
to lower capital and operating costs for development of the project,
in comparison to traditional flotation processing techniques.
Highlights from new metallurgical test work
* The Dikoloti nickel mineralisation is amenable to heap
leach bio-oxidation processing using the GEOLEACHTM process;
* Greater than 74% nickel extraction from the ore was
achieved after 160 days;
* 99% of the extracted nickel can be recovered from the
bio-oxidation solution as a nickel sulphide, by use of sodium
sulphide precipitation;
* The heap leach approach using GEOLEACHTM should have
capital and operating costs which are significantly lower than
conventional flotation processing.
Discovery Metals' Managing Director, Mr Jeremy Read, said today that
the metallurgical test work using the GEOLEACHTM process had shown
that bio-oxidation was a technically feasible method for processing
the Dikoloti nickel-copper mineralisation.
"The positive results from the GEOLEACHTM bio-oxidation test work are
a big step forward for the project. We have now identified a
processing technique which could lead to Dikoloti being developed as
a stand-alone operation," Mr Read said.
"We are currently having the scoping study financial model for
Dikoloti revised, based upon a bio-oxidation heap leap operation.
Once the results of this financial review are known, we will make a
final decision on how to progress Dikoloti to the next project
development phase," he said.
Dikoloti Mineral Resources
The Dikoloti mineral resource is situated 12km from Africa's largest
nickel processing facility at Selebi-Phikwe in NE Botswana. The
Dikoloti resource is currently 4.1 million tonnes at 0.7% nickel,
0.5% copper and 1.2 grams per tonne of Platinum Group Elements at a
cut-off of 0.5% nickel and has been classified as Inferred under the
guidelines of the 2004 JORC Code.
Dikoloti Bio-Oxidation Metallurgical Test
Previous testing by Discovery Metals on the Dikoloti nickel
mineralisation indicated that a costly fine grind would be required
in order to liberate the nickel at acceptable recoveries using
traditional flotation processing techniques. Consequently, the
Company evaluated several alternative methods for processing the
nickel mineralisation and determined that the technique with the most
promise was bio-oxidation heap leaching using the GEOLEACHTM process
developed by GeoBiotics LLC from Lakewood, Colorado. Discovery
contracted GeoBiotics to conduct scoping study tests in order to
determine if the GEOLEACHTM process was a viable process route for
the Dikoloti nickel-copper mineralisation and would allow Dikoloti to
be developed as a stand-alone operation. The scoping study test has
recently been concluded. The initial results from the test work were
reported on 31st August, 2007.
Discovery provided to GeoBiotics a 55kg sample of representative
nickel-copper mineralisation from Dikoloti. A 2kg sample of this
material was crushed and used for the bacterial amenability test,
while the remainder of the sample was crushed, screened and used for
2m column tests. The representative samples assayed 0.64% Ni, 31.2%
Fe and 11.4% Si. The test procedure comprised the following:
1. Acid consumption test
2. Bacterial Amenability Test (BAT)
3. 2m column test simulating the conditions of a heap
4. Nickel sulphide recovery test
Acid Consumption Test
Prior to column testing, an acid consumption test was conducted on a
pulverised sample to determine the maximum acid consumption expected
from the material. The observed acid consumption was 385 kg/t after
60 days. The high acid usage was largely due to the acid consumption
of the pyrrhotite component of the ore sample. It was expected that
the acid consumption of the ore in the column test would be lower
than this value.
Bacterial Amenability Test
The Bacterial Amenability Test (BAT) investigated the ability of the
bacterial culture to break down the nickel-copper mineralisation and
release the nickel and copper in to solution. The BAT was carried
out in a stirred tank using an adapted thermophile bacterial culture
on a pulverised ore sample.
The optimum pH value for bacterial culture growth is generally
between 1.4 and 1.8 and therefore acid is added to the system for the
BAT. In addition the system needs to operate under high oxidising
conditions (Eh levels above 500 mV) for adequate mineral oxidation
and release of the nickel and copper in solution to take place.
The BAT showed that nickel rapidly leached out of the mineral within
a period of 10 days and that rapid leaching was achieved using a
thermophile bacterial regime. Based upon solution analysis 98% of
the nickel was extracted after 10 days.
Column Test
A GEOLEACHTM 2m column test on whole Dikoloti nickel-copper ore was
conducted over a period of 160 days in order to simulate the
processes which would occur within a heap leach operation.
The initial part of the test was a simple acid leach to evaluate acid
consumption and this test indicated that pyrrhotite consumed a
significant amount of acid with a subsequent rapid release of iron
into solution. The column was initially started with thermophile
bacteria which generally operate at a higher temperate, but was
re-inoculated with mesophile bacteria (which operate in the temperate
range 30-45oC) at day 42. Between days 42 and 66 it became apparent
that due to the rapid build up of iron in the column, as the
pyrrhotite was broken down, the bacteria in the column lacked the
capacity to convert the rapidly increasing ferrous iron in the column
to ferric iron.
After 70 days of operation, a separate bacterial ferric generator
column was instituted with the aim of providing externally additional
culture and surface area for converting the ferrous iron, being
produced from the leaching of pyrrhotite, to ferric iron in order to
allow the oxidation of the nickel mineralisation and subsequent
release of nickel in to solution. After 120 days a fully active 2m
ferric generator column was used and connected directly to the 2m
leach column in order to provide more surface area and residence for
bacteria culture growth. This increased the ability of the entire
system to convert ferrous iron to ferric iron as needed in order to
liberate the nickel. Following the installation of the separate
bacterial ferric generator column iron and nickel leach rates
significantly increased.
After running the column for 150 days the maximum nickel extraction
was estimated to be 75% and the maximum iron extraction 50%. The net
acid consumed to achieve these extractions was 300 kg/t. Therefore,
given that both the BAT and column tests demonstrated that nickel
extraction is achievable, the economic viability of the project will
be largely determined by the acid consumption.
Nickel Sulphide Recovery Test
A procedure was developed for the precipitation of nickel as nickel
sulphide from the fluid generated from the column test. Sodium
sulphide was used as the reactant and 99% of the nickel in solution
was precipitated as nickel sulphide.
Conclusions
The conclusions from the bacterial amenability tests and the
GEOLEACHTM 2m column test are:
* The Dikoloti nickel-copper ore is amenable to
bio-oxidation
* Nickel extraction indicates that at least 74% of nickel
can be extracted
* The fundamental challenge for the successful bio-oxidation
of the Dikoloti nickel mineralisation was the high iron levels in
the solution and managing the conversion of ferrous to ferric iron.
* The use of a separate ferric generator column coupled to
the leach column was successful with the required ferrous to ferric
iron conversion
* The acid consumption of the Dikoloti mineralisation was
high due to the predominance of pyrrhotite in the mineralisation
* It is possible to successfully recover 99% of the nickel
from the bio-oxidation solution as nickel sulphide by using sodium
sulphide precipitation.
Following the successful conclusion to the scoping bio-oxidation
tests Discovery has contracted Snowden Mining Industry Consultants to
revise the scoping study economic model for Dikoloti, based upon a
heap leach bio-oxidation processing scenario.
Further information on the Company is available on its website:
www.discoverymetals.com.au
The information in this report as it relates to Mineral Resources was
compiled by Mr. Stefan Mujdrica, who is a Member of The Australasian
Institute of Mining and Metallurgy. Mr Mujdrica is a full time
employee of Snowden Mining Industry Consultants. Mr Mujdrica 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". 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 and Mr Mujdrica consent to the
inclusion in the report of the matters based on information provided
by them 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
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