Institute of Applied Geoscience (IAG)

Towards a generic model for localized, highly-enriched orogenic gold deposits

CASE project sponsored by Klondike Gold Corporation.

The PhD project aims to inform development of deposit models for orogenic gold mineralisation in the Klondike Gold District, Yukon, Canada. Current models which describe the genesis of gold deposits in metamorphic belts have focused on regions where mining is established, such as the large deposits in Western Australia and the Canadian Shield. Even recent literature makes little or no distinction between the genesis of Archaean age orogenic mineralization, and the more recent, (often smaller, but sometimes very rich) Phanerozoic orogenic gold occurrences.

The Klondike Gold district is located in north-west Yukon and is part of the Tintina Gold belt which extends through the Yukon and into Alaska. The discovery of economically significant in situ mineralization in the White Gold District in 2004 precipitated an exploration boom accompanied by studies of regional metallogeny. Subsequently both the Klondike and White goldfields were ascribed to a major period of orogenic mineralisation in the Mid-Late Jurassic. The Klondike District is of interest because of the huge amount of placer gold won from a relatively small area. The richest placer drainages were those of the Eldorado and Bonanza creeks, separated by the ‘Lone Star’ Ridge, which has been the focus of considerable exploration and small scale lode mining. Auriferous quartz veins have traditionally been assumed to be the source of the extensive placer deposits of the Klondike District, but exploration has proved challenging because of a lack of outcrop and the discontinuous nature of the veins, which are hosted in complex units of polydeformed (‘Klondike’) schist. The discovery of a schist unit greatly enriched disseminated gold has raised the possibility that quartz veins may not be the sole source of the detrital gold. A major element of this study has been the characterization of gold and associated mineralogy in both vein and schist environments to evaluate their genetic relationship and relative importance as gold sources for exceedingly rich placers in adjacent drainages.

The project has included multiple stages of field work with various analytical approaches:

1. Detailed petrography of auriferous vein and schist samples (optical microscopy, XRF mapping, EDS mapping).

2. Quartz paragenesis determination by CL.

3. Establishing the stage of Au influx in relation to quartz paragenesis

4. Compositional studies of vein and schist hosted gold.

5. Crystallographic studies of in situ, eluvial and placer gold and links to Au composition using EBSD.

6. Compositional studies of local placer gold.

Key findings to date 

1. Gold mineralization in the schist is not syngenetic, but is compositionally and mineralogically equivalent to that in the veins. 

2. Much of the quartz is barren, but nevertheless these veins have historically comprised the sole exploration target. 

3. Crystallographic studies have established that vein hosted Au and placer gold exhibit the same crystal textures

Main outcomes

1. A major stage of gold mineralization exploited permeability in both established quartz veins and a specific  unit of the Klondike Schists 

2. The Au mineralization in the schist both constitutes a plausible potential reservoir for local placers and explains the apparent discrepancy between Au inventories of placer and vein- hosted gold

3. The outcome raises the possibility that similar scenarios exist elsewhere which may explain generic placer-lode inventory discrepancy

4. The outcome has wide ranging implications for exploration targeting.