Undergraduate Honors Theses

Thesis Defended

Spring 2011

Document Type

Thesis

Department

Geological Sciences

Abstract

The primary gold telluride minerals are represented by three distinct species: calaverite (Au0.85Ag0.15Te2), krennerite (Au0.75Ag0.25Te2), and sylvanite (AuAgTe4). All three of these mineral species are historically important ores of gold (and to a lesser extent silver), and are found in relative abundance within several of the world’s major telluride districts. Detailed studies on the atomic structure of the gold telluride minerals began in 1935 with work on calaverite. Additional research on krennerite and sylvanite was conducted in the following years. The mineral class was then revisited in 1984, yielding several redeterminations of crystal structure. Through technological advancements in both analytical technique and structure refinement algorithms, the author sought to again revisit the determination of crystal structure in an attempt to both verify the results of previous investigations, and to attempt to better resolve the atomic structure parameters in the literature. In the course of this research, several structure determinations were performed on euhedral sub-millimeter crystals of calaverite, krennerite, and sylvanite that were harvested from specimens within the University of Colorado’s mineral collection. Structurally, krennerite is the most ordered of these three species. Single crystal structural studies yielded several datasets, including a refinement of the krennerite structure with a reliability factor of 0.024- a significantly lower value than was attained in any of the previous studies. Atomic position coordinates derived from this dataset were resolved to a precision of nearly one order of magnitude over that of previous work. In addition to the primary structural studies, research into both crystal chemistry and paragenesis were performed using the specimen which provided the krennerite refinement discussed above. These latter studies provided information as to the specific crystal chemistries of the ore minerals found in the specimen, and also allowed for the determination of the mineralizing sequence of the hydrothermal fluids responsible for producing the krennerite used in the structural refinement. By combining the data derived in the structural study with observations made during these studies, a more coherent picture of the mineralizing system has emerged. Other original work contained in this thesis include the redetermination of the calaverite unit cell, as well as reanalysis of the crystal chemistry of an indeterminate gold telluride phase that contains silver concentrations which lie between the accepted values for either calaverite or krennerite.

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