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Klondike placer gold : new tools for examining morphology, composition and crystallinity Crawford, Evan Cameron

Abstract

This work focuses on developing and expanding the utility of several new and previously used methods for examining the morphology, composition and crystallinity of placer gold. Several studies using samples from the Klondike District and surrounding areas in west-central Yukon investigating each of these properties are presented, along with potential future applications for the methods, and implications of the results already obtained. The new method for examination of the morphology of placer gold is centered around semi-automated digital image analysis. Automating morphological analysis allows more accurate and reproducible measurement of much larger number of grains as compared to manual methods, allowing for improved statistical analyses of placer gold morphology. Combining results from these new methods of morphological analysis with conventional electron microprobe analysis of composition has produced a detailed model relating placer gold grain morphology to the distance it has been alluvially transported. This model was developed with regard to geology and gold composition and is significantly superior to previous models. A new method using laser ablation - inductively coupled plasma - mass spectroscopy (LA-ICP-MS) has been developed to examine minor and trace element composition of placer gold. This new method allows for compositional fingerprints to be defined, and spatial variations in trace and minor elements to be measured within individual grains. Placer gold crystallinity has been observed, however remains poorly examined. We have utilized X-ray diffraction to study the internal crystallographic texture of placer gold, and confirm that several other methods previously used for this purpose do probe internal crystallinity. These new methods have significantly broadened the range of techniques available to investigate placer gold. Examination of the results from these methods has yielded new insights into the potential genesis of gold deposits in the Klondike, the nature of gold crystallinity, and the changes in morphology that occur during alluvial transport. These early studies also indicate that there is still significant work to be done, and that these new methods have significant potential in the study of placer gold.

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