Kwala Boe and Tjot Plaj (modern Kuala Bue and Cot Plaj) are two bog-iron localities on the West coast of Atjeh, respectively 30 and 12 km NW of Meulaboh, recorded by Jansen, Lindberg and Wolvekamp in 1922 and reproduced in Van Bemmelen’s *Geology of Indonesia* (1949). The Kwala Boe and Tjot Plaj localities are Nos. 6/7 in Van Bemmelen’s Fig. 41 key, and are the only Atjeh localities classified in the colonial geological literature as bog-iron (swamp-ore) deposits rather than as contact-metamorphic magnetite-hematite deposits.
The 1922 Jansen-Lindberg-Wolvekamp observation
The 1922 report of Jansen, Lindberg and Wolvekamp, as reproduced by Van Bemmelen, records:
“Locality: resp. 30 and 12 km NW of Meulaboh. Beach deposits: Scattered fragments of ore at the surface. Below 40 cm reddish-yellow sand, containing lumps of ore; only magnetiferous sea-sand has been found. According to a rough estimate only 10–15 % of ore-fragments are present in these 40 cm. These swamp ores were also found on the Tjot Seumeureueng, Tjot Meuseugit, Tjot Regan, Tjot Darat and Tjot Mane (not indicated on the map). The total area with ore lumps is ± 2 sq km; thickness 0.40 m, with ± 15 % lumps. Assuming a sp. gr. of 3 for the ore, 300,000–400,000 tons of lump-ore should be available.”
The detailed description is significant because it records, in addition to the Kwala Boe and Tjot Plaj localities themselves, a further five localities (Tjot Seumeureueng, Tjot Meuseugit, Tjot Regan, Tjot Darat and Tjot Mane) that were not indicated on Van Bemmelen’s map. The total area of bog-iron occurrences — about 2 sq km, with a thickness of 0.40 m and an ore-content of about 15 % — gives a reserve estimate of 300,000–400,000 tons of lump-ore, which is the only quantitative bog-iron reserve estimate for Atjeh in the colonial geological literature.
Philippi’s thermal-origin hypothesis
The Kwala Boe and Tjot Plaj bog-iron deposits are also the only Atjeh iron-ore occurrences for which a non-contact-metamorphic origin has been proposed. Van Bemmelen records:
“According to PHILIPPI these deposits are of thermal origin. His conclusions, however, are based upon a few samples from one pit. The peculiar structure and the comparatively high Zn content (3–4 %) are indeed in favour of a hydrothermal origin of the metal-bearing solutions. Precipitation of the ore must have happened under marshy conditions.”
Philippi’s thermal-origin hypothesis — proposed on the basis of a few samples from a single pit — is supported, in Van Bemmelen’s judgment, by the “peculiar structure and the comparatively high Zn content (3–4 %)” of the deposits, which are indeed more consistent with a hydrothermal than with a purely surficial bog-iron origin. The hypothesis is, however, tentative: Van Bemmelen notes that Philippi’s “conclusions are only based upon a few samples from one pit; consequently, not too much value can be attached to them.”
Significance
Kwala Boe and Tjot Plaj are significant for the encyclopedia of Acheh history because they are the only Atjeh iron-ore localities classified in the colonial geological literature as bog-iron (swamp-ore) deposits rather than as contact-metamorphic magnetite-hematite deposits. The 300,000–400,000-ton lump-ore reserve estimate is the only quantitative bog-iron reserve estimate for Atjeh in the colonial geological literature. The Philippi thermal-origin hypothesis is the only published non-contact-metamorphic interpretation of an Atjeh iron-ore occurrence, and the high Zn content (3–4 %) that supports it is the only recorded zinc anomaly in the Atjeh iron-ore record.
See Also
- Acheh
- Alu Talu
- B. B. Lindberg
- H. Wolvekamp
- Iron ores in Atjeh
- Kr. Ligan (Babah Loh)
- Kr. Rigaih
- Meulaboh
- P. J. J. Jansen
- Philippi
- Van Bemmelen’s The Geology of Indonesia (1949)
- 1922
Source
The Geology of Indonesia, by R. W. van Bemmelen, Vol. II: Economic Geology (The Hague: Government Printing Office; Martinus Nijhoff, 1949), pp. 207–208 (key to Fig. 41, Nos. 6/7, with detailed locality description and Philippi thermal-origin hypothesis).