Golden Rivers: The mighty gorges
The veins with gold are eroded from the mountains by glaciers and flood waters, and carried into the rivers which drain to the west. The Southern Alps are rising at nearly 10 millimetres / year adjacent to the Alpine Fault, and the valleys are eroding down at the same rate. This means that about 20 vertical kilometres of rock have been removed over the past 2 million years, leaving spectacular schist gorges. Some gold is trapped in bedrock crevices and under house-sized boulders, and some gold is carried through the gorges every time the rivers flood. Thus the gorges resemble huge sluice boxes cleaned out occasionally by the giant hand of glaciation.
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The gorges of the Whataroa valley, with the Main Divide in the background. Photo by Ross Cullen.
Sample of gold from the Whataroa Gorge immediately upstream from the Alpine Fault. Gold grains are hammered into flat flakes by tumbling in the rivers. Some gold is released from boulders of quartz by the same tumbling action, and is angular in shape. |
