by Grain Wyson Phillip Malunga FIMMM Mining and Environmental Management Expert
GRAPHITE IN MALAWI
Graphite is a form of carbon that easily conducts electricity. It occurs in form of flakes in metamorphic rocks, veins and pegmatites. Graphite deposits are mainly found in central Malawi in graphitic gneiss and Schist. Most of it is exposed in weathered rocks.
Sovereign Metals and Globe Metals and Mining are actively involved in evaluation of these deposits and may put Malawi on world map as one of the largest producers of medium to large flakes of graphite.
Graphite has several uses, some of which include;
- Being an excellent lubricant
- Its use in foundries gives a smooth facing to sand molds in which metal castings are made
- Crucibles with graphite components withstand very high heat
- It is also a component in break linings
- Graphite pencil manufacturing
- Its good electrical conductivity qualifies it to be used in electrotyping and electrical apparatus.
Main world producers are China, Brazil, Democratic People’s Republic of Korea and Canada.
- GRAPHITE OCCURRENCE
Graphite is common in central Malawi and occurs in biotite rich gneisses which have varying amounts of graphite and sometimes minor to moderate amounts of pyrite and/or pyrrhotite. The main ore bodies are weathered graphitic gneiss and schist. The ore body has partings of biotite gneiss, biotite and muscovite schists, amphibolites and mixed pegmatitic and syenitic veins. Graphite-rich zones have between 5 and 15 percent flake graphite of up to 5 millimeter long and generally exist aligned parallel to other platy minerals such as biotite.
Graphite is being mapped and evaluated in weathered and unweathered ore. Evaluation work is being undertaken at Katengeza, Chimutu, and Duwi. The average grade varies from 5% to about 11% carbon.
At Katengeza, 2.7 million tonnes with an average grade of 5.83% carbon was delineated by a consortium of Malawi Development Corporation and INDE Bank. The estimate was based on trenching, pitting and diamond drilling. Seven trenches totalling 900 meters were dug at a 100-meter interval and to a 2-meter depth. Eighteen diamond drill holes were sunk to a depth of 40 meters. The graphite deposit is more extensive.
The characteristics of the ore are given below:
- Coarse flake 39% @ 97% carbon
- Medium flake 26% @ 96% carbon
- Fine flake 35% @ 95% carbon
- Coarse flake 42% @ 98% carbon
- Medium flake 25% @ 98% carbon
- Fine flake 33% @ 95% carbon
Meanwhile Globe Metals and Mining is doing further exploration at Katengeza to confirm and increase the reserves.
Sovereign Metals has identified Duwi (Lilongwe), Nanzeka (Dowa) Malingunde belt (Lilongwe) and Dedza weathered ore as having potential for economic deposits of flake graphite, with grades exceeding 8% carbon within the medium to large flake graphite.
The company has estimated that Duwi Main and Duwi Bend deposits host 77.3-million tons of indicated and inferred resources at 7.2% carbon with 5% carbon cut-off grade.
Chimutu graphite is being evaluated by Globe Metals and Mining. Two main trends of mineralization were identified and the company has plans to do further evaluation of the deposit.
- MINING METHOD
As explained earlier, Malawi graphite occurs mainly as weathered ore and is exposed on the surface. The proposed mining method will be open cast with a standard vertical benched design. Pit planning will have to encompass whole lateral extent of the ore bodies and deepening by means of a single access ramp. The bench height will be 5 meters with an overall slope angle averaging 50%. Ramp gradients should not exceed 8% and the width has to be at least 15 m in order to include a safety berm and drainage ditch.
At Katengeza, mineable reserves have been put at 1 million tonnes. The production rate is put at 100,000 tonnes per month to a maximum depth of 30 meters. The production rate will be limited to 5,000 tonnes per annum. Selective mining is recommended due to inconsistency in ore grade. Grade control will be based on blast hole assays from dust/chipping collection during drilling.
At Duwi Main and Duwi Bend, the production rate is expected to be 1.5-million tonnes a year to produce 110 000 t/y of flake graphite concentrate over 20 years, or processing 11-million tons of Duwi Main ore at the rate of 0.55-million tons a year to produce about 40 000 t/y over 20 years.
The processing method for Malawi graphite will be through flotation. It is expected that the weathered ore has larger quantities of chlorite, sericite, smectite and kaolin. Iron oxides are also in abundance. The unweathered ore is composed largely of feldspar, quartz and micas. There are small occurrences of chlorite, kaolin and smectite.
Pilot plant studies were previously conducted, by MDM of South Africa, using 8 tonnes of weathered bulk sample and 5 tonnes of unweathered bulk sample from Katengeza graphite. The process flow sheet went through crushing, milling and floatation, and concentrate filtering, drying and screening.
The following product sizes were recovered:
+ 300 micron
– 300 + 180 micron
– 180 + 150 micron
– 150 + 75 micron.
Reagents to be used will be sodium silicate, frother and fuel oil. The following pilot plant results were considered to be optimum:
Head Grade 7.7
Mass Yield 6.9
Carbon Recovery 90 %
Concentrate % Mass % C
+ 300 micron 30 95 – 97
– 300 + 180 micron 30 95 – 97
– 180 + 150 micron 10 95 – 97
– 150 + 75 micron 20 90
Head Grade 10
Mass Yield 9
Carbon Recovery 90 %
Final Concentrate % Mass % C
+ 300 micron 30 97 – 98
– 300 + 180 micron 30 97 – 98
– 180 + 150 micron 10 97 – 98
– 150 + 75 micron 20 95
Processing of Duwi graphite using conventional techniques showed recovery of Jumbo flake concentrates grading up to 99.2% C(t) with combined coarse and jumbo flake categories (+150μm) averaging 97.5% C(t). Total graphite recovery was at 96.6% C(t).
It is envisaged that the graphite will mainly be sold to Europe and Far East Asia. Main world producers of graphite are China, India, Brazil, Democratic People’s Republic of Korea and Canada. The Malawi projects have the potential up to 50,000 tonnes per annum bringing Malawi into 4th or 5th largest world producer of graphite. The products will be within the upper quality range of top deposits.
- ENVIRONMENTAL STATEMENT
Displacement of a local people near mine sites will call for some compensation. At the same time the projects will employ about 120 people per project most of whom will be from the same area.
There will be no foreseeable toxic chemicals to contaminate ground water. The raw material has very little sulphides and there is no danger of acid leaching. Dust emanated from the operations will be suppressed by water spraying and mined out areas will be refilled by mine wastes.
- Malunga G. W. P. 2004. Katengeza Graphite Project, Project Profile
The Technical File with Grain Malunga “Graphite in Malawi” featured above was initially published in Malawi’s Mining & Trade Review Issue Number 40 that is circulating this August 2016.
The full edition is available for download here. This monthly publication is edited by Marcel Chimwala.