T A M B A N G S A W A H

GEOLOGY

Gunung Seblat is 20 km to the NNW of Tambang Sawah while the town of Muara Aman is 8 km to the south. Most of the thermal features occur along the Air Putih river valley, Air Putih being a tributary of Air Ketuan. They emerge from a brecciated zone along the NW edge of a granite intrusive. It is not clear whether the brecciation occured during emplacement and cooling of the granite or is the result of more recent tectonic activity. However the linearity of Air Putih in this region and the alignment of the thermal features suggest fault control. The granite has intruded Mesozoic slates (with lenses of marble), which outcrop extensively to the north of Tambang Sawah, and also lower Tertiary intermediate and silicic volcanics which are mineralised at several locations. Plio-Pleistocene andesites and basalts are the youngest rocks in the immediate area.

High temperatures, with some above the boiling point (97^oC-100^oC), characterise the near neutral pH springs in this area. Outflows are generally small but the hottest spring has a flow of 7.5 l/s. Several of the springs are depositing travertine sinter and this may reflect the interaction of the thermal fluids with the Mesozoic Marbles at depth. An area of steaming ground about 200 m long at Suban Keramat releases the greatest amount of heat energy at Tambang Sawah which has been calculated to be about 10 MW (th).

Sumatra Fault zone faults cut the southern end of the Tambang Sawah thermal area and generally NNE trending faults cut these regional faults. As mentioned previously fault control of the thermal features is likely.

No young volcanic heat source is obvious for the field and the small aerial extent of the thermal features suggest a resource of limited value but the existence of temperatures above boiling point and the natural heat flow make this area interesting for further exploration.

REFERENCES

Akbar, N., 1984. Penyebaran Kenampakan panasbumi daerah Lebong Utara & Lebong Selatan, Kabupaten Rejang Labong, Propinsi Bengkulu. Unpublished Report, Direktorat Vulkanologi, Departemen Pertambangan Dan Energy, Bandung, Indonesia.

Bachri, S., 1972. Inventarisasi dan penyelidikan pendahuluan terhadap gejala-gejala panasbumi di Propinsi Bengkulu. Unpublished Report, Direktorat Vulkanologi, Departemen Pertambangan Dan Energi, Bandung Indonesia.

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