Hostname: page-component-cd9895bd7-gxg78 Total loading time: 0 Render date: 2024-12-27T10:47:16.720Z Has data issue: false hasContentIssue false
  • English
  • Français

Magnesium-Rich Clays of the Meerschaum Mines in the Amboseli Basin, Tanzania and Kenya

Published online by Cambridge University Press:  28 February 2024

R. L. Hay ,
R. E. Hughes ,
T. K. Kyser ,
H. D. Glass  and
J. Liu
R. L. Hay
Affiliation:
Department of Geology, University of Illinois, 1301 West Green St., Urbana, Illinois 61801
R. E. Hughes
Affiliation:
Illinois State Geological Survey, 615 E. Peabody Dr., Champaign, Illinois 61820
T. K. Kyser
Affiliation:
Department of Geology, University of Saskatchewan, Saskatoon Saskatchewan, Canada S7N 0W0
H. D. Glass
Affiliation:
Illinois State Geological Survey, 615 E. Peabody Dr., Champaign, Illinois 61820
J. Liu
Affiliation:
Department of Geology, University of Illinois, 1301 West Green St., Urbana, Illinois 61801
Rights & Permissions [Opens in a new window]

Abstract

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

The Sinya Beds of the Amboseli Basin in Tanzania and Kenya consist largely of carbonate rocks and Mg-rich clays that are intensely deformed where exposed in and near former meerschaum mines. The carbonate rocks consist of limestone and dolomite in Tanzania, but only dolomite has been identified in Kenya. Sepiolite and mixed-layered kerolite/stevensite (Ke/St) are subordinate constituents of the carbonate rocks. The carbonate rocks and overlying bedded sepiolite were deposited in a semiarid lake basin at the foot of the large volcano Kilimanjaro. Calcite and dolomite of the carbonate rocks have δ18O values 4–6‰ lower than calcite and dolomite of the late Pleistocene Amboseli Clays, suggesting that the Sinya Beds were deposited in the middle or early Pleistocene under a different climatic regime when meteoric water had lower δ18O values than at present.

Mg-rich clay minerals form veins and fill cavities in the Sinya Beds. The principal clay minerals are sepiolite and Ke/St, some of which contains substantial Al and Fe (Al-Ke/St). NEWMOD® modeling and other X-ray diffraction (XRD) data suggest that most of the Ke/St contains 25–50 percent kerolite layers, but minor amounts of kerolite-rich Ke/St are present in some samples. Illite with an inferred high content of Fe or Mg is a minor constituent of the samples with Al-Ke/St. The cavity-filling clays were chemically precipitated, as shown by field relationships and SEM study. The early-deposited clays of veins and cavities are principally Ke/St with minor sepiolite, and the latest clay is sepiolite (meerschaum), generally with minor Ke/St.

The δ18O values of cavity-filling Ke/St range from 22.5–25.6‰ and correlate with mineral composition, with the highest values associated with the highest content of stevensite and the lowest values with the highest content of kerolite. This relation suggests that high salinities favored stevensite and low salinities favored kerolite. δ18O values of sepiolite (meerschaum) fall in the middle of the range for Ke/St, suggesting that salinity was not the main control on sepiolite precipitation. High values of aSiO2/aMg2+ may have been a major factor in sepiolite precipitation.

Different mixtures of dilute ground water and saline, alkaline lake water in pore fluids may largely account for the differences in clay mineralogy of cavity-filling clays. Sepiolite is the dominant clay mineral in lacustrine sediments of the Amboseli Basin, and the cavity-filling sepiolite may reflect a high proportion of lake water. The low-Al Ke/St may have formed from fluids with a higher proportion of ground water. Detrital clay was very likely a factor in forming the Al-Ke/St, for which δ18O values suggest a saline environment.

Keywords

KeroliteMeerschaumMixed-layered kerolite/stevensiteOxygen isotope compositionSepioliteStevensite
Type
Research Article
Information
Clays and Clay Minerals , Volume 43 , Issue 4 , August 1995 , pp. 455 - 466
Copyright
Copyright © 1995, The Clay Minerals Society

References

Brindley, G. W., Bish, D. L., and Wan, H.-M., 1977. The nature of kerolite, its relation to talc and stevensite. Mineral. Mag. 41: 443–452.Google Scholar
Brindley, G. W., and Kao, C. C. 1980. Formation, composition, and properities of hydroxy-Al and hydroxy-Mg montmorillonite. Clays & Clay Miner. 28: 435–443.Google Scholar
Ceding, T. E., and Hay, R. L. 1986. An isotopic study of paleosol carbonates from Olduvai Gorge. Quat. Res. 25: 63–78.Google Scholar
Clayton, R. N., and Mayeda, T. K. 1963. The use of bromine pentafluoride in the extraction of oxides and silicates for isotopic analysis. Geochim. Cosmochim. Acta 27: 43–52.Google Scholar
Dawson, J. B., 1992. Neogene tectonics and volcanicity in the North Tanzanian sector of the Gregory Rift Valley: Constraints with the Kenya sectors. Tectonophysics 204: 81–92.Google Scholar
Downie, C., and Wilkinson, P. 1964. Kilimanjaro-Moshi Special Sheet, 1: 125,000, covering Quarter Degree Sheets 42, 56, and 57: Geol. Surv. of Tanzania.Google Scholar
Eberl, D. D., Jones, B. F., and Khoury, H. N. 1982. Mixedlayer kerolite/stevensite from the Amargosa Desert, Nevada. Clays & Clay Miner. 30: 321–326.Google Scholar
Friedman, G. M., 1959. Identification of carbonate minerals by staining methods. Jour. Sed. Petrol. 29: 87–97.Google Scholar
Fritz, P., and Smith, D. G. W. 1970. The isotopic composition of secondary dolomites. Geochim. Cosmochim. Acta. 34: 1161–1173.Google Scholar
Goldsmith, J. R., and Graf, D. L. 1958. Relation between lattice parameters and composition of the Ca-Mg carbonates. Amer. Mineral. 43: 84–101.Google Scholar
Harland, W. B., Armstrong, R. L., Cox, A. B., Craig, L. E., Smith, A. G., and Smith, D. G. 1990. A Geologic Time Scale 1989. Cambridge: Cambridge University Press, 263 pp.Google Scholar
Haymes, D. E., 1988. An Isotopic Study of East African and Canadian Carbonatites. Unpublished M.S. thesis. University of Illinois, Champaign-Urbana, Illinois, 86 pp.Google Scholar
Hardie, L. A., and Eugster, H. P. 1970. The evolution of closed-basin brines. In Special Paper 3, Fiftieth Anniversary Symposia: Mineralogy and Petrology of the Upper Mantle, Sulfides, Mineralogy and Geochemistry of Non-marine Evaporites. Morgan, B. A., ed. Washington, D.C.: Mineralogical Society of America, 273–290.Google Scholar
Hay, R. L., 1976. Geology of the Olduvai Gorge. Berkeley: University of California Press, 203 pp.Google Scholar
Hay, R. L., and Wiggins, B. 1980. Pellets, ooids, sepiolite and silica in three calcretes of the southwestern United States. Sedimentology 27: 559–576.Google Scholar
Hay, R. L., Pexton, R. E., Teague, T. T., and Kyser, T. K. 1986. Spring-related carbonate rocks, Mg clays, and associated minerals in Pliocene deposits of the Amargosa Desert, Nevada and California. Geol. Soc. Amer. Bull. 97: 1488–1503.Google Scholar
Hay, R. L., and Stoessell, R. K. 1984. Sepiolite in the Amboseli Basin of Kenya: A new interpretation. In Palygorskite-sepiolite Occurrences, Genesis, and Uses. Singer, A., and Galan, E., eds. Amsterdam: Elsevier, 125–136.Google Scholar
Hay, R. L., Guldman, S. G., Matthews, J. C., Lander, R. H., Duffin, M. E., and Kyser, T. K. 1991. Clay mineral diagenesis in Core KM-3 of Searles Lake, California. Clays & Clay Miner. 39: 84–96.Google Scholar
Jones, B. F., 1966. Geochemical evolution of closed basin water in the western Great Basin. In Second Symposium on Salt, Vol. 1, Geology, Geochemistry, Mining. Rau, J. L., ed. Cleveland, Ohio: The Northern Ohio Geological Society, 181–200.Google Scholar
Jones, B. F., 1986. Clay mineral diagenesis in lacustrine sediments. In Studies in Diagenesis. Mumpton, F. A., ed. U. S. Geol. Surv. Bull. 1578: 291–300.Google Scholar
Jones, B. F., and Galan, E. 1988. Sepiolite and palygorskite. In Reviews in Mineralogy. Vol. 19. Hydrous Phyllosilicates. Bailey, S. W., ed. Mineralogical Society of America, 631–674.Google Scholar
Jones, B. F., and Weir, A. H. 1983. Clay minerals of Lake Abert, an alkaline, saline lake. Clays & Clay Miner. 31: 161–172.Google Scholar
Mifsud, A., Huertas, F., Barahona, E., Linares, J., and Fornes, V. 1979. Test de couleur la sepiolite. Clay Miner. 14: 247–248.Google Scholar
Moore, D. M., and Reynolds, R. C. Jr. 1989. X-Ray Diffraction and the Identification and Analysis of Clay Minerals. Oxford: Oxford University Press, 332 pp.Google Scholar
O'Neill, J. R., Clayton, R. N., and Mayeda, T. K. 1969. Oxygen isotope fractionation in divalent metal carbonates. J. Chem. Physics 51: 5547–5558.Google Scholar
Reeves, C. C., 1976. Caliche: Origin, Classification, Morphology, and Uses. Lubbock, Texas: Estacado Books. 233 pp.Google Scholar
Reynolds, R. C. Jr. 1985. NEWMOD, a Computer Program for the Calibration of Basal Diffraction Intensities of Mixed-layered Clay Minerals. Hanover, New Hampshire: R. C. Reynolds, 24 pp.Google Scholar
Reynolds, R. C., 1989. Principles and techniques of quantitative analysis of clay minerals by X-ray powder diffraction. In Workshop Lectures, Vol. 1, Quantitative Mineral Analysis of Clays. Pevear, D. R., and Mumpton, F. A., eds. Clay Minerals Society, 4–36.Google Scholar
Rozanski, K., Araguás-Araguás, L., and Confiantini, R. 1993. Isotopic patterns in modern global precipitation. In Geophysical Monograph 78, Climate Change in Continental Isotopic Records. Swart, P. K., Lohmann, K. C., McKenzie, J., and Savin, S., eds. Washington, D.C.: American Geophysical Union, 1–36.Google Scholar
Sampson, D. N., 1966. Sinya meerschaum mine, northern Tanzania. Inst. Min. Met. Trans. 75: B23–B34.Google Scholar
Savin, S. M., and Lee, M. 1988. Isotopic studies of phyllosilicates. In Reviews in Mineralogy, Vol. 19, Hydrous Phyllosilicates. Bailey, S. W., ed. Washington, D.C.: Mineralogical Society of America, 189–223.Google Scholar
Stoessell, R. K., 1977. Geochemical Studies of Two Magnesium Silicates, Sepiolite and Kerolite: Ph.D. dissertation, University of California, Berkeley, 122 pp.Google Scholar
Stoessell, R. K., 1988. 25°C and 1 atm dissolution experiments of sepiolite and kerolite. Geochim. Cosmochim. Acta 52: 365–374.Google Scholar
Stoessell, R. K., and Hay, R. L. 1978. The geochemical origin of sepiolite and kerolite at Amboseli, Kenya. Contr. Mineral. Petrol. 65: 255–267.Google Scholar
Talbot, M. R., and Kelts, K. 1990. Paleolimnological signatures from carbon and oxygen isotopic ratios in carbonates from organic carbon-rich lacustrine sediments. In AAPG Memoir 50, Lacustrine Basin Exploration; Case Studies and Modern Analogs. Katz, B. J., ed. Tulsa, OK: American Association of Petroleum Geologists, 99–112.Google Scholar
Western, D., and Praet, C. Van. 1973. Cyclical changes in the habitat and climate of an East African ecosystem. Nature 241: 104–106.Google Scholar
Williams, L. A. J., 1972. Geology of the Amboseli Area. Geol. Surv. Kenya Report 90, 86 pp.Google Scholar
Wollast, R., Mackenzie, T. T., and Bricker, O. 1968. Experimental precipitation and genesis of sepiolite at earth-surface conditions. Amer. Mineral. 53: 1645–1662.Google Scholar