by Grain Wyson Phillip Malunga FIMMM Mining and Environmental Management Expert
Malowa Limestone Group
Malowa limestone, in Malawi, has been a subject of research for a long time due to its potential for chemical grade lime making to support Viphya Pulp Wood Project for paper making. The project did not materialize and now it is a subject for cement manufacturing.
The demand for lime is there for application in agriculture, construction and chemical applications. This paper tries to give an account of its economic potential.
Bwanje Valley marble deposit lies to the South of the south-western arm of Lake Malawi. The nearest Trading Centre to the deposit is Golomoti and is about 7 Kilometres to the West.
The deposit is about 165 kilometres from Lilongwe using Dedza – Monkey Bay Road. Access to the deposit from the Lake Shore road is difficult during the rainy season because it is surrounded by a seasonal swamp within the Bwanje valley.
A Lake shore road (M17) and a rail line are about six kilometres from the deposit. The road starts from the Blantyre – Lilongwe road, near Balaka, and joins to the Northern Corridor road at Mzuzu. The rail line goes as far as Lilongwe and Mchinji near Zambian Border and provides access to Nacala Port in Mozambique. There is also a 132 Kv electricity sub-station at Golomoti.
Two “islands” form Malowa hill and Khungule hill limestone (Figure 1). These have been a subject of geological investigation for source of high grade chemical line for industrial use.
HISTORY OF EXPLORATION
Andrew and Bailey (1908) first located the Bwanje Valley marbles. Between 1965 and 1966 there was a sampling program that culminated into mapping and systematic sampling in 1970. Samples they collected from here showed very low magnesia contents.
Further work was done by Dawson and Kirkpatrick during regional mapping. They did surface resampling of Malowa and Khungule hills from whose analysis they concluded that large quantity of low magnesia (<3% MgO) marble at Khungule Hill could be economic. The deposits seem to be connected and exist over a large area.
Between 1970 and 1971, Charsley carried out geological mapping, sampling and drilling from which he came up with an estimation of 500,000 tonnes of low magnesia limestone in the central part of Malowa Hill. He also estimated that there could be 3 million tonnes of low magnesia marble on both hills.
A VIPCOR drilling project executed by Phiri (1975) on the central part of Malowa Hill indicated 330,000 tons of low magnesia marble suitable for use in pulp production. These reserves were calculated using a 15 % factor to take care of solution cavities.
Sobek (1979) and Bhutta (1980), through UNIDO consultancy, recommended more work on the limestones to delineate and increase reserves of fine grained low magnesia marble suitable for calcium carbide manufacture. They recommended the need to delineate recoverable reserves of 1 million tonnes for a mine life of 20 years.
Chatupa (1981) estimated that such detailed work would cost about MK 371,100.00.
Morsley (1981) carried out drilling on the two hills. He came up with demonstrated reserves of 560,000 tonnes on Malowa Hill and inferred reserves in excess of 1,000,000 tonnes at Khungule Hill.
Morsley recommended that the existence of low magnesia marble beneath colluvium to the West of Malowa Hill be tested by drilling or pitting and trenching before a decision to site a plant is made. He also noted that so far none of the marble from surface outcrops or from core could be suitable for calcium carbide manufacturing because of their grain size.
In 1996 Met-Chem Canada Inc was subcontracted by Mining Investment and Development Corporation (MIDCOR) to undertake an assessment study of the deposit. MET-CHEM’s assessment comprised technical, financial, environmental and economic viability of establishing a limestone mining and lime works.
A total of 79 holes were drilled between October 1995 and December 1996 representing a meterage of 2483 meters. The overall undiluted carbonate rocks resources for the Malowa hill proper amount to 14.85 million tons @ 46.83% CaO, 1.36% MgO inside the calcitic rock bands and 17.53 million tons @ 36.61% CaO, 7.14% MgO inside the dolomitic and impure rock bands.
Bwanje Cement Company has an Exclusive Prospecting Licence (EPL) for the deposit and has done further drilling between Malowa and Khungule. The purpose of this feasibility study is to establish cement works. Financial and Technical partner is being sort to develop this deposit.
Apart from construction and agriculture applications, limestone is used in chemical and metallurgical industries.
Limestone is a wonderful mineral. It has unlimited industrial applications including iron and steel, non-ferrous metallurgy, environment control, manufacture of chemicals, bleach power, sugar industry, agriculture, water treatment, sewage treatment, building and construction, and glass industry.
In sugar refining, lime removes the phosphate and organic acid compounds from the sugar cane juice. Between 2 and 8 kg of lime is required to refine 1 tonne of sugar.
Ground limestone and lime is used for improving soil fertility through neutralisation of soil acidity.
Lime is also used as detergent in white washing dairy barns and for composting manure.
Chemical lime or high grade lime is used in the treatment of municipal potable water and industrial process water. Lime removes temporary bicarbonate hardness from the water.
The high pH of 11.5 from lime in water acts as a sterilising agent to destroy most bacteria and viruses. The pH is lowered to accepted levels by introduction of CO2 to precipitate lime solution as carbonate sludge.
Kayelekera mine currently uses 300 tonnes per month in its water treatment process. The figure below shows the possible uses of lime.
CAPITAL COST ESTIMATE FOR LIME WORKS
In 1997, a study sanctioned by Mining Investment and Development Corporation (MIDCOR) and done by Met-Chem Canada Inc. proposed a manufacturing facility that would produce a rated capacity of 33,750 tonnes per year with a product mix indicated as follows:
- Hydrated lime: 18,750 tonnes;
- Agricultural limestone: 9,000 tonnes;
- Pulverised limestone: 6,000 tonnes.
The total capital cost for the project was put at $US 11.85 million dollars. The technology to be used was to be Fluidised Bed.
- Mine equipment: $US 678,029;
- Crushing/screening plant: $US 1,173,358;
- Calcination plant: $US 5,075,746;
- MHydration/Bagging plant: $US 1,374,900;
- Indirect expenditures: $US 3,541,927.
Another study done in 2003 by Centre for Development of Enterprise (CDE) reduced the lime works to produce 11,000 tonnes per year of hydrated lime and 3,000 tonnes of agriculture lime per year. The total cost of the project was put at €2.2 million.
OPPORTUNITY LIMIESTONE MINING
It is undisputable that the demand for cement in Malawi is higher than what is currently produced. About 100,000 tonnes of limestone is being used annually for cement production. This is mainly by Shayona Cement Company and Cement Products Limited. About 300,000 tonnes of limestone will be used for cement production in 2017.
Most lime is used for sugar refinery, construction, soil conditioning and water treatment. Current consumption is above 95,000 tonnes. Kayelekera mine is currently using about 2,000 tonnes per year for water treatment. During uranium production, up to 6,000 tonnes per annum is needed for uranium leaching sand tailing neutralization. Illovo Sugar spends about 3,000 tonnes of lime for sugar refining.
The capacity for limestone mining or quarrying can reach up to 300,000 tonnes.
Therefore there exist an opportunity for lime production too in Malawi.
The growth in demand of lime is mainly from agro-processing industries, particularly sugar and tobacco, fertilizer and chemical manufacture. The growth of the agriculture sector will trigger the rise in demand for lime and pulverized limestone. Limestone, dolomite and lime products are associated with the agricultural sector and hence their potential for growth.
The mining industry offers hope for increased usage of lime in beneficiation and environmental management. This growth in demand is expected to come from uranium, niobium and rare earths processing.
- Charsley T. J. 1972. The Limestone Resources of Malawi. Mem. Geol. Surv. No. 6. Malawi
- Mineral Resources Services Limited. 1995. Feasibility study for Bwanje Valley Limestone Deposits: A project background report. Prepared for Met Chem Canada Inc.
- Met Chem Canada Inc. 1997. Fesibility Study for Bwanje Valley Limestone Project in Malawi.
The piece “French expert calls for more gov’t investment in mining in Malawi” featured above was initially published in Malawi’s Mining & Trade Review Issue Number 39 that is circulating this July 2016.
The full edition is available for download here. This monthly publication is edited by Marcel Chimwala.