MAGNESIUM-RICH CLAYS OF THE MEERSCHAUM MINES IN THE

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 (K /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 ~tsO values 4-6%0 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 6~sO 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 ubstantial AI and Fe (A1-Ke/S0. 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 ofkerolite-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 A1-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)