GEOTHERMAL ENERGY POTENTIAL FOR NKHOTAKOTA

BY

GRAIN WYSON PHILLIP MALUNGA

 

ABSTRACT

Malawi’s geothermal resources are undeveloped due to the lack of appropriate data required to analyze their economic potential. Most of the available data is scientific with few parameters necessary for economic interpretation.

The geothermal resources in the Nkhotakota district offer potential for geothermal energy, tourism, and domestic use. The Linga Geothermal field has the potential to supply hot water to the future Nkhotakota urban center.

1. INTRODUCTION

The western rift system of Lake Malawi is endowed with geothermal resources manifested by numerous hot springs. The rift system has also produced geothermal systems in the Kirk Range, Shire Valley, and Zomba-Phalombe-Mulanje districts.

These hot springs offer a geothermal resource that can generate electricity. A flash system will require temperatures greater than 150⁰C while a binary system will require temperatures from 80⁰C.

Nkhotakota area is bound with extensive faulting within the Ntchisi Mountains and major faulting along the lakeshore. Main faulting is manifested by the Liwaladzi, Mphalanyongo and the Sani faults along the lakeshore (Figure 1).

There are three known geothermal fields and a total of five sets of hot springs in the district. Brief descriptions of the fields and their related hot springs have been outlined below. Their locations are shown on the map in Figure 2.

1. GEOTHERMAL FIELDS

Geothermal fields of Nkhotakota District are shown in Figure 1.

KASITU GEOTHERMAL FIELD (UTM coordinates 612182, 8642482) 

There are two springs, one on the beach at the foot of a small Kalari hill at the shoreline of Lake Malawi and one is 10 m into the lake at Kasitu. The temperature recorded is 78°C (Peters, 1965) though lower values that can be obtained in some parts of the year. The intersection point of the Kaungozi fault and the Khuyu and Mkoma II faults host Kasitu hot spring.  This is at the foot of Kalari Hill and 10 metres into the lake

LINGA GEOTHERMAL FIELD (UTM Cooardinates 640000 8570000)

There are three sets of hot springs in the field within a radius of 5 km from the district headquarters. These are Mawira, Chombo and Ling’ona hot springs. The hot springs are of nearly same average temperature.

Mawira hot springs

Mawira hot springs are located 2 km south of Nkhotakota Boma to the west of M5 road. There are a series of 7 hot springs with the average temperature of 65°C. A cold spring is just 14 m from the hottest spring indicating a bounding structure between them. The hot Mawira stream flows into the cold Mchandilu stream just 8 m away. The springs are to the east of the Sani fault.

Chombo hot springs (UTM coordinates 0636515, 8575051)

Chombo hot springs are about 1.5 km south of Chombo primary school and about 4 km north – west of Nkhotakota boma. The hot springs have a temperature of 64°C. The springs are at the lower end of the Mphalanyongo fault close to its junction with the Sani fault towards the mouth of Kaombe River (Harrison and Chapusa, 1975).

Ling’ona hot spring (UTM coordinates 0639080, 8567454)

Ling’ona hot spring is about 1.5 km southwest of Mawira hot spring. It flows at the bank of Ling’ona River. The hot spring measures 61°C and lies the Sani fault.

Table 1: Nkhotakota hot springs

Hot spring	Surface temp.(°C)	Temp (°C)SiO2	Temp (°C)Na-K	Temp (°C)Na-K-Ca
Mawira	65	130.5	100.2	99.5
Chombo	64	–	–	–
Ling’ona	61	–	–	–
Chikwidzi	55	124.2	88.9	93.3
Chiwi	78	–	–	–

BENGA GEOTHERMAL FIELD (UTM coordinates 634251, 8514862)

There are two hot springs at Chikwidzi, 1.5 km apart. This is about 10 km south of Benga. The hot spring measures 55°C lies about 100 m to the west of M5 road at Chikwidzi Bridge. Water bubbles from several places. The second spring is 1.5 km east of the road and has a measured temperature of 42°C. Benga is one of the vegetable growing areas of Nkhotakota. Benga is the southernmost geothermal field in the district.

1. GEOCHEMICAL CHARACTERISTICS OF NKHOTAKOTA HOT SPRINGS

Nkhotakota hot springs are characterized by Na+, Ca+ and HCO3-, SO4-, and Cl- anions. The Na-Cl-SO4 water from Chipuze are related to geothermal fluids from deep aquifers with full or partial water-rock equilibrium. Elizondo et al 2015 indicates Chipuze (Chikwizi) hot spring is a result of mixing waters heated by steam due to boiling and/or volcanic waters heated by intrusions at depth. These hot springs are linked to rifting parallel normal faults, which have displaced crystalline Precambrian rocks.

In Figure 3, silica concentration against quartz geothermometer temperatures shows water cooled by heat conduction. Ternary diagram K-Mg-Na geothermometer by Giggenbach (1988) shows estimated reservoir temperatures and the immature or partial equilibrium in Linga Hot Field.

4.    RECOMMENDATIONS

Further work is required to characterize the economic potential of these hot springs. It is recommended to undertake geophysical surveys to delineate the precise orientations of the fault conduits bringing the geothermal waters to the surface and understand seasonal variation in together temperature, water discharge, and hydrochemical parameters. Chemical and isotopic analyses and geothermometry calculations need to be done in order to determine the temperatures and depth of the source reservoirs.

1. REFERENCE

1. Dulanya Z. (2006). Geothermal resources of Malawi – An overview. Proceedings of Stanford University. SGP-TR-179 
2. Harrison, D. R.; Chapusa, F.W.P. (1975). The Geology of the Nkhota-kota – Benga Area. Bull. Geol. Surv. Mw. 32
3. Elizondo E., A. Atekwana E, Atekwana E. A., Tsokonombwe G and Laó-Dávila D. 2015 Geothermometry of hot springs in the Malawi Rift.