FINAL BOTTLE ROLL LEACH TEST RESULTS
AND MINERALOGICAL ANALYSIS
FROM AFRICAN EAGLE'S DUTWA NICKEL PROJECT, TANZANIA
High nickel extraction and low acid consumption bodes well for
* Exceptionally low acid consumption and good nickel recovery
* High nickel extraction averaging 83% from solids
* Unique laterite mineralogy: high silica, low iron, low magnesium
account for the low acid and high recovery
* Low acid consumption will have a major impact on capital and
operating costs, favouring low cost heap or tank leach processing
* Scoping study contract to be awarded
African Eagle Resources plc has received the final results of acid
leach tests and mineralogical analyses on drill samples from its
Dutwa nickel laterite project in Tanzania. The tests were carried
out by Mintek in South Africa.
The leach test results show high nickel extractions, averaging 83% on
a solid basis, and very low sulphuric acid consumption, averaging 210
kilograms per tonne. These compare very favourably with laterite
deposits elsewhere in the world.
The mineralogical analyses show that Dutwa is a unique laterite,
dominated by silica and with very low iron and magnesium. These
characteristics account for the exceptionally low acid consumption
and high nickel recovery.
In November 2008, the Company announced a JORC compliant resource at
Dutwa of 31 million tonnes at 1.1% nickel and 0.034% cobalt,
containing 340,000 tonnes of nickel and 11,000 tonnes of cobalt.
Mark Parker, African Eagle's Managing Director comments: "We are
delighted with these results. Dutwa is a unique deposit, with
unusual mineralogy which results in high nickel recovery with
exceptionally low acid consumption. This bodes very well for
commercial development, as the ore should be amenable to tank or heap
leaching at atmospheric pressure. Either technology can be
implemented at relatively low capital cost.
"We will now commission a scoping study to assess the viability of
the project and indicate the best way to proceed. We are currently
evaluating bids and expect to award the contract in the next few
days. We then expect to commence a second phase of metallurgical test
work to evaluate the heap and tank leaching nickel-cobalt extraction
technology options in greater detail."
The table below shows the total acid consumption and nickel and
cobalt extractions from "bottle roll" leach tests on ten 500g
samples, five from diamond drill cores and five from reverse
circulation cuttings. Each sample was placed in a glass bottle with
two litres of dilute sulphuric acid and agitated continuously by
rolling on rotating rollers. Mintek completed the tests in
mid-February 2009 after 82 days rolling. The metal extractions
levelled off after 60 days; Mintek notes that similar results from
other laterite ores subsequently gave heap leach cycles of less than
Nickel extractions were between 70-90% averaging 83%, based on assays
of the samples prior to the test and of the solid residues at the end
of the test. Extractions calculated from the daily assays of the
liquid leachate were higher, at 80-95%, but are generally less
reliable. The acid consumptions, averaging 209kg/t, are very low
compared with other nickel laterite ores. The solids-based cobalt
extractions were mostly in the range 70 to 85%.
DH1 DH4 DH6 DH7 DH8 RC25 RC30 RC36 RC55 RC71 Average
Acid kg/t 352 196 233 114 200 159 207 304 190 138 209
Ni% 85 80 89 78 91 88 71 88 86 75 83
Co% 69 71 77 55 85 76 18 77 86 73 69
See our web site for day-by-day nickel extraction and acid
Mintek used X-ray Diffraction (XRD), and scanning electron microscope
(SEM) backscattered electron images to investigate the mineralogy of
the drill core and chips. Sixteen samples of drill core and five
samples of reverse circulation (RC) cuttings were submitted for XRD
analysis. The five RC samples and five composited drill core samples
were investigated by SEM.
The results showed two broad classes of material: a dominant class
composed largely of silica and a mixed class. The latter also
contains silica, together with variable amounts of the iron-chromium
oxides magnetite and chromite; the hydrated iron oxide goethite;
"manganese wad", (in which manganese, nickel, cobalt and other metals
replace some of the iron in amorphous goethite); and small quantities
of serpentine and clays.
The silica-rich nature of these samples and their low iron and
magnesium content, indicates that Dutwa is not a typical laterite
nickel deposit as the normal laterite mineralogy is diluted by the
high silica. The unusual mineralogy of the deposit is potentially
beneficial, as in heap leaching, the high silica and low iron should
help maintain the structural integrity of the heap and aid
percolation of fluids through the heap, reducing residence times,
while in tank leaching, the high silica should allow good
In addition, the low iron concentration will result in low impurity
levels in purification steps and potentially, lower capital and
operating costs. The lower iron will also result in commensurately
less iron residue for disposal.
Mintek believes that most of the nickel and cobalt occurs in the
manganese wad. The SEM work showed that this can have a manganese
content of 20-60%, a nickel content of up to 20% and a cobalt content
of up to 10%. The concentration of nickel and cobalt in the manganese
wad offers possibilities that mechanical selection of high-grade
material may allow reduced throughput and hence a lower cost
A glossary of technical terms used by African Eagle in this
announcement and other published material may be found at
For further information:
+44 20 7248 6059
+44 77 5640 6899
Seymour Pierce Limited, London
+ 44 20 7107 8000
Russell & Associates, Johannesburg
+ 27 11 8803924
+27 82 8928052
Ed Portman / Gareth Tredway
Conduit PR, London
+44 20 7429 6607
+44 (0) 7733 363 501
African Eagle has discovered a significant nickel laterite deposit
within the Dutwa project area, which lies in the Kilimafedha belt
(Swahili for "money hills") of the Lake Victoria Goldfield.
Operationally, the project is favourably situated, 100km east of the
railhead at Mwanza and close to the main Mwanza-Nairobi trunk road, a
major power line and the shore of Lake Victoria.
Greenstones and granites underlie the area. The greenstones, of
Archaean Nyanzian age, are mostly metamorphosed volcanic and
sedimentary rocks, with some banded iron formation in the east.
Several large ultramafic bodies intrude the greenstones and the
nickel laterites form a blanket up to 60m thick on top of these.
The Dutwa project area is composed of several prospecting licences
covering a total area of about 750km². The Company holds 90%
interests, with options to acquire 100%, over most of this ground,
including the area of the laterite discovery, and the remainder is
African Eagle acquired the Dutwa project for its gold potential, but
its exploration team quickly recognised that there was significant
nickel laterite potential. Geochemical soil surveys carried out by
African Eagle over the whole of the project area identified a
promising 5km-long nickel anomaly and a number of gold anomalies.
There is very little outcrop, so the Company conducted extensive
ground magnetic surveys to reveal the underlying structure and
geology. The Company has also compiled historical data, including
detailed geological maps and trench results dating from 1956, when
rock chip samples from the trenches over the ultramafic rocks were
reported as yielding up to 1.9% nickel and 10% chromium.
To investigate the nickel anomaly, the Company undertook trial
drilling in June 2008. The results were very encouraging and a
139-hole reverse circulation (RC) drilling programme was completed to
delineate the resource. African Eagle also undertook a 10-hole
diamond drill programme to obtain core samples for metallurgical
testing and density measurements.
In November 2008, African Eagle announced an initial Inferred Mineral
Resource estimate of 31 million tonnes at an average grade of 1.1%
nickel and 0.034% cobalt. At a cut-off grade of 0.5% nickel, this
gives Dutwa a contained metal endowment of some 340,000 tonnes of
nickel and 11,000 tonnes of cobalt. The estimate was prepared by
independent consultants SRK Consulting (UK) Ltd in line with the
Australasian Code for Reporting of Mineral Resources and Ore Reserves
(the JORC Code). SRK classified the estimate as an Inferred Mineral
Resource in terms of the JORC code, but noted that the deposit is a
continuous mineralised body of simple geometry, which has been well
delineated by the drilling, and could be promoted easily to Indicated
category with more density measurements and improved knowledge of the
The Company despatched 100 kilograms of mineralised drill core and RC
chip samples to Mintek Laboratories in Johannesburg for
investigations into the mineralogy and metallurgy of the deposit,
especially tests of the amenability of the material to sulphuric acid
leaching. Mintek carried out mineralogical characterisation by X-ray
diffraction (XRD), scanning electron microscopy (SEM) and polished
section work, to determine the nature of the ore body, and extended
'bottle roll' acid leach tests on ten samples, to investigate metal
recoveries and acid consumption.
The bottle roll test results show nickel extractions of 70-90% with
an average of 83%, based on assays of the samples prior to the test
and of the solid residues at the end of the test. Cobalt extractions
were mostly in the range 70 to 85%. The acid consumptions, averaging
209kg/t, are very low compared to other nickel laterite ores
The mineralogical investigations show that the laterite is extremely
silica-rich, with low iron and magnesium content, indicating that
Dutwa is not a typical laterite nickel deposit. Mintek believes that
much of the nickel and cobalt occurs in "wad" with manganese content
of 20-60%, nickel content of up to 20% and cobalt content of up to
The unusual mineralogy of the deposit is beneficial, as the low iron
concentration will result not only in lower acid consumption, but
also in commensurately less iron residue for disposal. In a heap
leach, the low iron and high silica should help maintain the
structural integrity of the heap and aid percolation of fluids
through the heap, reducing residence times. The concentration of
nickel and cobalt in the manganese wad offers possibilities that
mechanical selection of high-grade material may allow reduced
throughput and hence a lower cost processing plant.
As the next step in the process, African Eagle is commissioning a
Scoping Study to investigate the key operating parameters and to
assess the economic potential of the project.
The Company has also completed a trial programme of RC drilling to
test a laterite at its Zanzui project, 70km to the south of Dutwa.
Results included 42m at 1.05% nickel (including 6m at 2.80%) and 33m
at 0.91% nickel (including 9m at 1.41%).
About African Eagle
African Eagle is a diversified mineral exploration and development
company operating in eastern and central Africa. The Company's
principal advanced projects are the Dutwa nickel laterite discovery
in Tanzania, where the Company announced a significant resource at
the end of 2008, and the Mkushi Copper Mines project in Zambia, for
which a draft Feasibility Study was completed in Q4 2008.
African Eagle has also defined a gold resource estimated at half a
million ounces at the Miyabi gold project in Tanzania, and is
evaluating a second promising nickel laterite deposit which it
recently discovered in Tanzania. The Company holds a well-balanced
portfolio of promising earlier stage gold and base metal projects,
including the Ndola and Mokambo projects in the Zambian Copperbelt.
Zambia, Tanzania and Mozambique, the sites of African Eagle's
projects, are all countries which have highly prospective geology,
relatively low above-ground risks and track records of successful
major investments in the metals and minerals industries.
African Eagle specialises in project generation and exploration. To
take its discoveries into production, it seeks to sign up industry
partners with records of successful mine development. These joint
ventures and, in time, the revenue from advanced projects, will
finance future exploration and new discoveries.
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