By Grain W. P. Malunga
Abstract
Lead in Malawi has been identified through regional geochemical survey and through prospecting by artisanal and small scale miners. It occurs in granitic pegmatites and in granitic schist.
INTRODUCTION
Lead is a soft heavy metal used in batteries, ammunition, and solder. It can be extracted from ores in different ways like leaching, concentrating, or smelting methods. The main source of lead are galena (Pb) and cerussite (Sn).
Table 1: Lead minerals
MINERAL | CHEMICAL FORMULA | COMPOSITION | APPLICATION |
Galena | PbS | Pb 86.6%; S 13.4% | Lead-acid battery, electrodes, ceramic glazes, stained glass, radiation shields, paints, power and telephone cables, chemicals, etc. |
Anglesite | PbSO4 | Pb 76.3%; SO4 23.6% | |
Cerussite | PbCO3 | PbO 83.5%; CO2 16.5% | |
Jamsonite | Pb4 FeSb6S14 | Pb 20 – 40% |
LEAD OCCURRENCES
Lead is a hydrothermal mineral that is formed by hydrothermal fluids circulating in Earth’s crust through fractures. The hydrothermal fluids are essentially water with less or variable amounts of CO2, H2S, SO2, CH4, N2, NaCl, and other salts.
Geological boundaries may also localize lead where they are cut by fractures that served as conduits for aqueous ore-bearing fluids. There may be a chemical reaction between rock and ore fluid, owing to the permeability of the host rock.
Lead in Malawi has been reported as a geochemical anomaly and minor occurrences. Small lead occurrences have been observed in pyrite and pyrrhotite bodies capped with gossan in the Nkhota Kota – Dowa area.
Lead anomalies were observed around Kamvula in Lilongwe and the Chitunda area in Mchinji. Walter, 1972, reports lead geochemical anomalies that were observed at Mulela Village near Lilongwe-Salima Lumbadzi Bridge and 3 km east-south-east of Chiponde Hill. A lead-zinc anomaly was observed near the Malindi stream at Chimtedza in Nsanje in nepheline biotite gneiss. A long niobium-zinc lead anomaly was found in Rumphi. Lake Malawi granites, in the southern end of the lake, have shown some interesting anomalies of lead. Narrow ferruginous veins of galena were observed at two localities near Dowa. Interesting anomalies seem to be associated with Dowa pegmatite complex. Worth pursuing are the Mzimba pegmatites, Chikangawa nepheline syenite and the Mphompha complex.
Galena is being mined by small-scale miners within the Dowa pegmatite complex and in granitic schist. The galena exists in cavities intermixed with quartz veins along fractures, in ferruginous veins and along geological boundaries. Some veins have shown silver-gold association. Figure 2 shows some galena pits excavated by artisanal and small scale miners in Dowa area.
Magnetic survey done by Graphite Africa (Pvt) Limited their tenement area shows that galena exists in the contact zones of less magnetic muscovite schist gneiss and a fairly magnetic amphibolite gneiss (2018)
LEAD MARKET
The demand for lead is being influenced by
- Increasing demand from the automobile and electronics industries
- There is growing demand for lead acid batteries in developing countries
- Rising prices of key substitutes such as copper and aluminum
- There are emerging new applications for lead.
REFERENCES
1. Carter, G. S., Haslam, H. W. and Smith, S. H. 1973. Regional geochemical reconnaissance of Malawi. Bull. Geol. Surv. Malawi, 43.
2. Walter, M. J. 1972. The geology of Salima-Mvera Mission area. Bull. Geol. Surv. Malawi, 30.
3. Walter, M. J. 1972. The geology of the Lilongwe-Dowa area. Bull. Geol. Surv. Malawi, 26
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