C. de Groot was a Dutch geologist whose 1946 report on the gold-bearing alluvial deposits of the West coast of Atjeh — cited in the standard form “DE GROOT, 1946” — is one of the principal sources for Van Bemmelen’s *Geology of Indonesia* (1949) in its treatment of the Atjeh gold placers and of the mercury content of the West-Atjeh gold-bearing alluvial deposits. De Groot’s report also appears, in the coal chapter of Van Bemmelen, as the source for an 1858/1859 communication on the occurrence of lignite at Passir Estate in the Westerkwartier der Ommelanden of Batavia — a reference that suggests De Groot was active in the Netherlands Indies Geological Survey over a long period, and that the 1946 Atjeh report was the work of a senior mining geologist drawing on a career’s worth of archival and field knowledge.
The 1946 Atjeh gold report
De Groot’s principal contribution to the Atjeh mineralogical record is his 1946 opinion that “the placers of the Meulaboh areas offer good prospects for the winning of gold and platinum.” Van Bemmelen cites this judgment in the Summary of the Explorations in Sumatra section of the gold-and-silver chapter, alongside the 1922 report of Jansen, Lindberg and Wolvekamp, and the two reports together constitute the entire printed basis for the colonial assessment of Atjeh’s gold potential. De Groot’s 1946 report is the more recent of the two, and his favourable opinion of the Meulaboh placers is significant because it post-dates — and partly reverses — the more cautious tone of the 1922 Jansen-Lindberg-Wolvekamp survey.
The West-Atjeh mercury occurrence
The same 1946 report is also the source for the only documented occurrence of native mercury and cinnabar in Atjeh. Van Bemmelen records, in the mercury chapter, that:
“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.”
This is a remarkable observation: the dredges of the M.A.E.M. 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 implication is that the West-Atjeh coastal alluvium contains, in addition to gold and platinum, a small but recoverable mercury content — a fact that De Groot was the first to record in print.
The 1858/1859 lignite reference
In the coal chapter of The Geology of Indonesia, Van Bemmelen lists in the literature references:
“GROOT, C. DE (1858/1859): Communication on the occurrence of lignite at Passir Estate in the ‘Westerkwartier der Ommelanden’ of Batavia. Natuurk. Tijdschr. XVI. 1858–1859, p. 388.”
This is presumably an earlier C. de Groot — possibly a father or other relative of the 1946 geologist, or simply the same man at the very start of a long colonial career (the dates 1858/1859 make the latter unlikely but not impossible). The reference is to a communication on a lignite occurrence near Batavia, not in Atjeh; it is included here only because the recurrence of the name “C. de Groot” in the colonial mining literature invites caution against assuming that the 1946 author of the West-Atjeh report is necessarily the same individual as the 1858/1859 communicator on Batavian lignite.
Significance
De Groot is significant for the encyclopedia of Acheh history because his 1946 report is, with the 1922 Jansen-Lindberg-Wolvekamp survey, one of only two printed colonial sources on the Atjeh gold placers, and because he is the only source for the documented occurrence of native mercury and cinnabar in the West-Atjeh alluvial deposits. His favourable opinion of the Meulaboh placers — expressed after the M.A.E.M. had begun dredge-mining in 1940 — also provides the historical link between the colonial mineralogical survey of Atjeh and the actual gold production of the residency on the eve of the Japanese occupation.
See Also
- Acheh
- Atjeh’s Westkust
- Gold and silver in Atjeh
- M.A.E.M.
- Meulaboh
- Mercury in Atjeh
- P. J. J. Jansen
- Van Bemmelen’s The Geology of Indonesia (1949)
- 1946
Source
The Geology of Indonesia, by R. W. van Bemmelen, Vol. II: Economic Geology (The Hague: Government Printing Office; Martinus Nijhoff, 1949), pp. 121–122 (Atjeh gold), p. 223 (West coast of Atjeh mercury), p. 246 (literature references). De Groot’s own report cited as: “DE GROOT, 1946” (with page reference 188 for the mercury observation); and “GROOT, C. DE (1858/1859)” for the earlier Passir Estate lignite communication in Natuurk. Tijdschr. XVI, pp. 388.