Mercury in Atjeh is the colonial-era geological record of the occurrence of native mercury and cinnabar in the gold-bearing alluvial deposits of the West coast of Atjeh — a record that comprises a single documented observation, that of De Groot in 1946, but that is nonetheless the only documented colonial-era occurrence of mercury minerals on Atjeh territory. The De Groot observation is recorded in Van Bemmelen’s *Geology of Indonesia* (1949) in the West Coast of Atjeh subsection of the mercury chapter, and it is the documentary basis for the inclusion of the West-Atjeh coast in the colonial mercury map of Sumatra.
The De Groot 1946 observation
Van Bemmelen’s record of the De Groot observation reads:
“DE GROOT (1946, p. 188) reports native mercury and fine grains of cinnabar to occur in the gold-bearing alluvial deposits on the West coast of Atjeh. In order to recover the finer gold during the exploitation by the M.A.E.M. in 1941 (see the subchapter on gold) 400 kg of mercury were used on the tables per bucket dredge and per clean-up. It appeared that after every clean-up the quantity of mercury had increased. Indeed, drilling samples occasionally sand contained native mercury and in the black sand very fine grains of cinnabar have been observed.”
The observation is remarkable on two counts. First, the M.A.E.M. dredges at Meulaboh were gaining mercury with each clean-up, which means that the alluvial deposits themselves were supplying native mercury and cinnabar to the gold-tables. The 400 kg of mercury that the M.A.E.M. used per bucket dredge per clean-up was accordingly being augmented, at each clean-up, by an unknown additional quantity of native mercury from the alluvial deposit itself. Second, the cinnabar grains in the black sand are “very fine” — implying that they are small enough to be recovered by the gold-tables’ amalgamation process, and that the cinnabar is accordingly a recoverable (rather than a merely mineralogical) component of the West-Atjeh alluvial deposits.
The geological context
The geological context of the West-Atjeh mercury occurrence is the same as that of the West-Atjeh gold-and-platinum placers: the pleistocene river terraces of the Meulaboh coastal basin, in which the alluvial gold, platinum and cinnabar are found together in the gold-bearing black sands. Van Bemmelen’s account of the Meulaboh placers records that “the gold-bearing black sands contain fine grains of cinnabar, besides considerable amounts of platinum”, and the primary sites of the gold — and, by implication, of the cinnabar — “have to be sought in the pre-tertiary Old Slates Formation and granite contacts of the interior”.
The cinnabar is accordingly interpreted as a derivative of the pre-tertiary mineralised belt of the West-Atjeh interior, with the cinnabar grains eroded from the primary deposits and concentrated, together with the gold and platinum, in the pleistocene river terraces of the coastal basin. The same interpretation is offered by Tobler for the cinnabar of the Sungei Glugur in the upper Merangin region of Djambi, where Tobler “considered that the cinnabar of Glugur Melipun probably originated from thermal springs, which ascended along a fault, adding silica and cinnabar to the gravel already present”. The West-Atjeh cinnabar may have had a similar thermal-spring origin, though De Groot’s 1946 report does not specify the genetic interpretation.
Place in the Sumatran mercury record
The West-Atjeh mercury occurrence is one of three mercury occurrences recorded for Sumatra in the colonial geological literature. The other two are:
- Sebalabu (in the Padang Highlands of the Westkust van Sumatra): cinnabar in a thin strip of alluvium at the foot of the isolated mountain Sombong, recorded by Fennema in 1876 and described in detail by Verbeek in 1883.
- Sungei Salak (in the upper Merangin region of Djambi): a few grains of cinnabar in river sands, recorded by Tobler (1922) and Zwierzycki (1930).
The West-Atjeh occurrence is, of the three, the only one for which native mercury (as opposed to cinnabar alone) has been documented, and the only one for which the mercury content of the alluvial deposits has been quantitatively observed (through the M.A.E.M. dredges’ gain of mercury with each clean-up). The West-Atjeh occurrence is accordingly the most substantial documented mercury occurrence in colonial-era Sumatra.
Significance
Mercury in Atjeh is significant for the encyclopedia of Acheh history because it is the only documented colonial-era occurrence of mercury minerals (native mercury and cinnabar) on Atjeh territory, and the most substantial documented mercury occurrence in colonial-era Sumatra. The De Groot 1946 observation of the M.A.E.M. dredges’ gain of mercury with each clean-up is the only quantitative record of mercury recovery from an Atjeh mineral deposit, and it accordingly provides the only documentary basis for any assessment of the mercury potential of the West-Atjeh alluvial deposits. The West-Atjeh mercury occurrence is also part of the wider mineral geography of the Meulaboh coastal basin — the only Atjeh locality for which colonial-era mineral production (gold, platinum, and the implicit mercury recovery) is recorded — and it accordingly belongs to the high-point of the colonial mineral economy of Atjeh.
See Also
- Acheh
- Atjeh’s Westkust
- Basin of Meulaboh
- C. de Groot
- Geudong Concession
- Gold and silver in Atjeh
- M.A.E.M.
- Meulaboh
- Ph. C. Fennema
- Platinum in Atjeh
- A. Tobler
- Van Bemmelen’s The Geology of Indonesia (1949)
- 1941
- 1946
Source
The Geology of Indonesia, by R. W. van Bemmelen, Vol. II: Economic Geology (The Hague: Government Printing Office; Martinus Nijhoff, 1949), p. 223 (West coast of Atjeh mercury, De Groot 1946 observation), p. 121 (Basin of Meulaboh, gold-bearing black sands with cinnabar and platinum).