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Title:Argillic Alteration Associated With the Amethyst Vein System, Creede Mining District, Colorado (Illite, Smectite)
Author(s):Horton, Duane Gale
Department / Program:Geology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Abstract:The Amethyst Vein System is an epithermal Ag-Pb-Zn-Cu-Au deposit in the Creede mining district, southwest Colorado. Silicification and argillization are the two dominant facies of hydrothermal alteration associated with the deposit. Most silicification occurs in the intermediate and deep levels of the system and most argillized rock occurs high in the system.
Mixed-layer illite/smectite is the dominant product of argillic alteration at Creede. Illite/smectite spans the composition range from about 26% to about 3% expandable and exhibits all Reichweite from R = 1 to R > 3. The composition and structure of illite/smectite vary systematically with distance from the Amethyst vein. The Reichweite increases and the percent smectite decreases as the vein is approached. Using the composition of the illite/smectites and using average temperatures for which specific compositions of illite/smectite exist in nature, the thermal regime at the time of argillization can be mapped. The result shows that the hydrothermal system at Creede was similar in several respects to some modern geothermal systems. Also, the temperatures indicated by the clays agree very well with temperatures obtained by other workers from fluid inclusion studies at Creede.
In addition to systematic variations of composition and structure, illite/smectite from the Amethyst system shows systematic zoning with respect to position in the deposit of polytypes, layer-charge density, the composition of expandable interlayers and the composition of 2:1 octahedral sheets. Illite/smectite from intermediate levels in the mine has the 1M polytype. Higher in the system, illite/smectites are either physical mixtures of both 1M and 3T polytypes or, for a few samples from the shallowest level, are solely 3T. In general, illite/smectite from the deeper parts of the system is Al-rich and has a higher layer-charge density relative to clays collected from shallower levels in the mine. Illite/smectite from Bachelor Mountain tuff is generally illite/1-H(,2)O smectite (presumably with Na('+) or K('+) as exchangeable cations) whereas illite/smectite from the volcaniclastic sediment is illite/1 = H(,2)O smectite (with Mg('2+) or Ca('2+) as the exchangeable cations).
Issue Date:1983
Description:463 p.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1983.
Other Identifier(s):(UMI)AAI8409955
Date Available in IDEALS:2014-12-16
Date Deposited:1983

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