Contributions to Mineralogy and Petrology

, Volume 91, Issue 2, pp 171–179

Mixed-layer illite/smectite as a paleotemperature indicator in the Amethyst vein system, Creede district, Colorado, USA

  • Duane G. Horton

DOI: 10.1007/BF00377764

Cite this article as:
Horton, D.G. Contr. Mineral. and Petrol. (1985) 91: 171. doi:10.1007/BF00377764


Ordered illite/smectite is the most abundant and widespread product of argillic alteration associated with the Oligocene, epithermal, Ag-Pb-Zn-Cu-Au Amethyst vein system, southwest Colorado. Hydrothermal illite/smectites exhibit all Reichweite from 1 to ≧3 and span the composition range from about 25% to about 3% illite.— The composition and Reichweite of illite/smectite vary smoothly with distance from the Amethyst vein. With increasing distance from the vein, percent illite and the Reichweite decrease. When composition-temperature relationships of illite/smectite from modern geothermal systems are applied to the fossil Amethyst system, isotherms describing the thermal regime at the time of argillization can be estimated. Temperatures near 240° C appear to have existed near the Amethyst vein; these temperatures agree with homogenization temperatures obtained from fluid inclusions in vein minerals. The most distal illite/smectites, sampled about 260 m from the vein, indicate temperatures near 110° C. Estimated thermal gradients are on the order of 0.4 to 1° C per meter. — Although illite/smectite composition and structure vary systematically with distance from the Amethyst vein, there are no systematic trends associated with the numerous, smaller veins and veinlets in the hanging wall of the system. This indicates that temperatures of both wallrock and the fluids in all but the major Amethyst vein were nearly the same during clay formation. Apparently, the hydrothermal system had reached a fairly steady, mature, thermal state at the time of argillization.

Copyright information

© Springer-Verlag 1985

Authors and Affiliations

  • Duane G. Horton
    • 1
  1. 1.University of IllinoisUrbanaUSA
  2. 2.Rockwell Hanford OperationsRichland