Advertisement

Gemstones Concentrated by Surface Waters: The Gem Gravels of Sri Lanka

  • Peter C. Keller

Abstract

When gemstones are hard and tough enough to withstand mechanical breakdown, chemically resistant to attack by natural acids or bases, and dense enough to be concentrated, they can form secondary placer or alluvial deposits. Diamonds, rubies, sapphires, jades, tourmalines, topazes, spinels, aquamarines, and chrysoberyls are but a few of the minerals that may be freed from the softer parent rock by weathering, eroded and transported down a slope to the nearest stream, and further carried along by river currents and/or wave action. Moving stream water sweeps away the lighter minerals, and the heavier placer minerals, such as diamond and corundum, sink to the bottom or are moved downstream a relatively short distance. Waves and shore currents also separate heavy minerals from lighter ones and coarse grains from finer ones. From thousands of tons of debris, the few heavy mineral grains in each ton of rock are gradually concentrated in the stream or beach gravels until they accumulate in sufficient abundance to be worth mining.

Keywords

Source Rock Heavy Mineral Parent Rock Placer Deposit Diamond Deposit 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Adams, F. D. 1929. The geology of Ceylon. Can. Jour. Res., 1:425–511.CrossRefGoogle Scholar
  2. Bancroft, P. 1984. Gem and Crystal Treasures. Western Enterprises-Mineralogical Record, Fallbrook, Cal. 488 pages.Google Scholar
  3. Coates, J. S. 1935. The geology of Ceylon. Ceylon Jour. Sci. 19: (B) 101–187.Google Scholar
  4. Coomaraswamy, A. K. 1903. Occurrence of corundum in situ near Kandy, Ceylon. Geol. Mag. 59: 348–350.CrossRefGoogle Scholar
  5. Cooray, P.G. 1967. An Introduction to the Geology of Ceylon. National Museums of Ceylon, Colombo.Google Scholar
  6. Cooray, P. G., and P. S. Kumarapeli. 1960. Corundum in biotite sillimanite gneiss from near Polgahawela, Ceylon. Geol. Mag. 97: 480–487.CrossRefGoogle Scholar
  7. Dahanayake, K. 1980. Modes of occurrence and provenance of gemstones of Sri Lanka. Mineralium Deposita 15: 81–86.CrossRefGoogle Scholar
  8. Dahanayake, K., A. L. Liyanage, and A. P. Ranasinghe. 1980. Genesis of sedimentary gem deposits in Sri Lanka. Sedimentary Geology 25: 105–115.CrossRefGoogle Scholar
  9. Dissanayake, C. B. 1981. The mineral potential of Sri Lanka, prospects for the future. Indian Geology Assoc. Bull. 13(1) 23–36.Google Scholar
  10. Fernando, L. J. D. 1948. The geology and mineral deposits of Ceylon. Bull. Imperial Institute 46: 303–325.Google Scholar
  11. Gübelin, E. 1968. Die Edelsteine der Insel Ceylon. Edition Scriptar, S. A., Lausanne. 152 pages.Google Scholar
  12. Guilbert, J. M., and C. F. Park, Jr. 1986. The Geology of Ore Deposits. W. H. Freeman and Co., New York. 985 pages.Google Scholar
  13. Gunaratne, H. S. 1976. On the occurrence of gem corundum in Kolonne. Jour. of Gemmology 15(1):29–30.Google Scholar
  14. Gunawardene, M., and M. S. Rupasinghe. 1986. The Elahera gem field in central Sri Lanka. Gems & Gemology 22: 80–95.CrossRefGoogle Scholar
  15. Hapuarachehi, D. J. A. C. 1968. Cordierite and wollastonite-bearing rocks of Southwest Ceylon. Geol. Mag. 105: 317–324.CrossRefGoogle Scholar
  16. Herath, J. W. 1982. Mineral resources of Sri Lanka. Sri Lanka Geol. Surv. Dept. Econ. Bull. 2.Google Scholar
  17. Katz, M. B. 1969. Cordierite gneisses: Source rock for some gem deposits of Ceylon. Proc. Ceylon Assoc. Adv. Sci. 1 (abstr.):60–61.Google Scholar
  18. Katz, M. B. 1971. The Precambrian metamorphic rocks of Ceylon. Geol. Rundschau 60(4): 1523–1549.CrossRefGoogle Scholar
  19. Katz, M. B. 1972. On the origin of the Ratnapura-type gem deposits of Ceylon. Econ. Geol. 67:113–115.CrossRefGoogle Scholar
  20. Keller, P. C. 1983. The rubies of Burma: A review of the Mogok stone tract. Gems & Gemology 19(4) 209–219.CrossRefGoogle Scholar
  21. Lacroix, A. 1891. Gneissose rocks of Salem and Ceylon. Geol. Surv. India 24:157–200.Google Scholar
  22. Munasinghe, T., and C. B. Dissanayake. 1981. The origin of gemstones of Sri Lanka. Econ. Geol. 76(5):1216–1225.CrossRefGoogle Scholar
  23. Perera, N. M. 1939. Report of the Sub-committee of the Executive Committee of Labor, Industry and Commerce on the Marketing and Cutting of Ceylon Gems. Ceylon Government Press, Colombo. 34 pages.Google Scholar
  24. Proctor, K. 1984. Gem pegmatites of Minas Gerais, Brazil: Exploration, occurrence, and aquamarine deposits. Gems & Gemology 20(2): 78–100.CrossRefGoogle Scholar
  25. Scalisi, P., and D. Cook. 1983. Classic Mineral Localities of the World: Asia and Australia. Van Nostrand Rein-hold, New York. 226 pages.Google Scholar
  26. Silva, K. K. M. W. 1976. Some geological aspects of the Elahera gem field, Sri Lanka. 32d Ann. Sessions Sri Lanka Assoc. for the Advancement of Science.Google Scholar
  27. Spencer, L. K., S. D. Dikinis, P. C. Keller, and R. E. Kane. 1988. The diamond deposits of Kalimantan, Borneo. Gems & Gemology 24(2): 67–80.CrossRefGoogle Scholar
  28. Wadia, D. N. and L. J. D. Fernando. 1945. Gems and semiprecious stones of Ceylon. Ceylon Dept. Mineral Rec. Prof. Pap. 2:13–44.Google Scholar
  29. Webster, R. 1961. Corundum in Tanganyika. Gems & Gemology 10(7) 202–205.Google Scholar
  30. Webster, R. 1975. Gems: Their Sources, Descriptions, and Identification. 3rd ed. Butterworths, London, England.Google Scholar
  31. Wilson, N. W. 1948. The world’s diamond deposits. Mining Mag. 79:329–341.Google Scholar
  32. Wells, A. J. 1956. Corundum from Ceylon. Geol. Mag. 93:25–31.CrossRefGoogle Scholar
  33. Zwaan, P. 1974. Garnet, corundum, and other gem minerals from Umba, Tanzania. Scripta Geol. 20:41.Google Scholar
  34. Zwaan, P. 1982. Sri Lanka: The gem island. Gems & Gemology 18(2): 62–71.CrossRefGoogle Scholar

Copyright information

© Van Nostrand Reinhold 1990

Authors and Affiliations

  • Peter C. Keller
    • 1
  1. 1.Natural History Museum of Los Angeles CountyUSA

Personalised recommendations