Lead and zinc in Atjeh is the corpus of colonial-era geological observations that document the occurrence of lead-zinc mineralisation in the Residency of Atjeh, recorded in Van Bemmelen’s *Geology of Indonesia* (1949) and based on the field-work of Jansen, Lindberg and Wolvekamp (1922). Two Atjeh localities are recorded — Krueng Heureueng (76.1 % Pb, 920 gr/t Ag) and Krueng Isep (65.13 % Pb, 680 gr/t Ag) — together constituting the entire documented colonial-era lead-zinc record for Atjeh. The high silver contents (920 and 680 gr/ton respectively) make the Atjeh lead-zinc occurrences, on paper, among the most attractive lead-silver prospects recorded in the colonial geological literature on the East Indies.
The two Atjeh localities
The two Atjeh lead-zinc localities recorded in Van Bemmelen’s Fig. 35 key are:
- Krueng Heureueng: 76.1 % Pb, 2.2 % Zn, 0.5 % Fe, 0.15 % CaO, 1.1 % SiO₂, 920.0 gr/t Ag. Sample size: 1st sample, small.
- Krueng Isep: 65.13 % Pb, 8.30 % Zn, 10.2 % S, 0.89 % Fe, 0.94 % CaO, 0.94 % SiO₂, 680 gr/t Ag. Sample size: 2nd sample, 500 kilogr.
The contrast between the two assays is geologically significant. The Krueng Heureueng assay has the higher Pb and Ag grades but the lower Zn grade; the Krueng Isep assay has the lower Pb and Ag grades but the higher Zn grade (8.30 % vs 2.2 %) and a substantial sulphur content (10.2 %), indicating that the zinc is present as sphalerite (ZnS). The contrast suggests a paragenetic zonation within the Atjeh lead-zinc province, with the Krueng Heureueng occurrence representing the higher-temperature, more silver-rich end of the zonation and the Krueng Isep occurrence representing the lower-temperature, more zinc-rich end.
Place in the East-Indian lead-zinc record
Van Bemmelen’s general assessment of the East-Indian lead-zinc record is unambiguous: “No important deposits of lead and zinc are known in the Archipelago. The same can be said of zinc. Lead and zinc sulphides frequently occur in the young tertiary gold-silver veins, but only as accessory minerals.” The Atjeh lead-zinc occurrences are accordingly exceptional within the East-Indian context: they are among the few localities where the lead-zinc mineralisation is sufficiently concentrated to be assayed as a primary ore rather than as an accessory mineral, and the high silver contents (920 and 680 gr/ton) make them, on paper, more attractive than the average East-Indian lead-zinc occurrence.
The only other East-Indian lead-zinc locality with which the Atjeh occurrences can be compared is the Sungei Pagu deposit in the Westkust van Sumatra residency, which Van Bemmelen recommends for “a closer examination” of its “silver-containing lead-zinc deposits”. The Atjeh occurrences, however, have the higher Pb and Ag grades and are accordingly the most attractive lead-silver prospects recorded in the colonial geological literature on northern Sumatra.
Sample-size considerations
The sample-size difference between the two Atjeh lead-zinc assays is significant. The Krueng Heureueng assay is based on a “small” sample — i.e. a hand-sample rather than a systematic channel-sample or drill-core — and the actual tonnage and average grade of the occurrence are accordingly unknown. The Krueng Isep assay, by contrast, is based on a 500-kilogram bulk sample, which is a more substantial basis for the assay and accordingly provides a more reliable indication of the average grade of the occurrence. The Krueng Isep assay is accordingly the more reliable of the two, despite its lower Pb and Ag grades.
Significance
The Lead and zinc in Atjeh is significant for the encyclopedia of Acheh history because it is the corpus of colonial-era geological observations that document the occurrence of lead-zinc mineralisation in the Residency of Atjeh — a corpus that comprises only two localities but that records the highest-grade lead-silver assays of any Atjeh mineral occurrence in the colonial geological literature. The 920 gr/ton Ag content of the Krueng Heureueng assay is, in particular, the highest silver grade recorded for any Atjeh mineral occurrence, and it accordingly makes the Krueng Heureueng occurrence — despite its small sample size — the most attractive single lead-silver prospect recorded in the colonial geological literature on Atjeh. The fact that neither occurrence was ever developed is, like the non-development of the Kr. Geuenteuet iron-ore deposit, evidence of the colonial state’s unwillingness or inability to translate geological occurrences into productive mines.
See Also
- Acheh
- B. B. Lindberg
- H. Wolvekamp
- Krueng Heureueng
- Krueng Isep
- P. J. J. Jansen
- Van Bemmelen’s The Geology of Indonesia (1949)
- 1922
- 1949
Source
The Geology of Indonesia, by R. W. van Bemmelen, Vol. II: Economic Geology (The Hague: Government Printing Office; Martinus Nijhoff, 1949), pp. 161–163 (lead and zinc in Sumatra, Fig. 35 key and assay table).