X-Ray Identification of One-Layer Illite Varieties: Application to the Study of Illites around Uranium Deposits of Canada

V. A. Drits1, F. Weber2, A. L. Salyn1 and S. I. Tsipursky3
1 Geological Institute of the Russian Academy of Sciences, 7 Pyzhevsky per., 109017, Moscow, Russia
2 Centre de Geochimie de la Surface, 1 rue Blessing, 67084, Strasbourg, France
3 Department of Geology, Arizona State University, Tempe, Arizona 85287-1404

Abstract: Structural and diffraction criteria for distinguishing between t-1M, c-1M, m-1M, and 3T illite varieties are described. The t-1M illite corresponds to a one-layer monoclinic structure with vacant trans-sites. The c-1M illite has vacant cis-octahedra forming one of two symmetrically independent point systems; the other cis-octahedra as well as the trans-octahedra are occupied; and the m-1M illite corresponds to the structure in which cations are statistically distributed over available trans- and cis-sites. For t-1M, c-1M, and m-1M, the values of |c cos β/a| are equal to 0.39–0.41, 0.29–0.31, and 0.333, respectively. Application of these criteria demonstrates that illite samples described in the literature as the 3T polytype usually are c-1M instead. The relatively common occurrence of c-1M illite in association with t-1M and 2M1 polytypes has been recognized in illite from hydrothermal alterations around uranium deposits located in the Athabasca basement (Saskatchewan, Canada). The c-1M illite from these deposits was previously described as 3T one.

Key Words: Hydrothermal alteration • Illite • Octahedral cation distribution • Polytype • Uranium deposits • Vacant cis-sites • Vacant trans-sites

Clays and Clay Minerals; June 1993 v. 41; no. 3; p. 389-398; DOI: 10.1346/CCMN.1993.0410316
© 1993, The Clay Minerals Society
Clay Minerals Society (www.clays.org)