Golden Rivers: Temporary storage
Once across the Alpine Fault, the gold is stored in gravels on the coastal plains. These gravels may be deposited by rivers emerging from the gorges, or as chaotic piles of material (moraine) left by glaciers which occasionally reached to the sea. Gold in these gravels may be flaky if it has been transported by a river at any time, or may be angular if it is very small or has been carried all the way from the Southern Alps by ice.
Once on the Australian Plate, the stored gold and gravels move northwards away from the source valley at 20-30 mm / year. The gravels are also carried upward as hills such as Mt Greenland are pushed up. Gold is reconcentrated in creeks draining these hills. Some of these hills also have gold in quartz veins which are eroded and contribute to nearby gold deposits. The Honourable Roddy nugget (99 ounce) from Ross comes from the slopes of Mt Greenland.
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A 90m deep alluvial gold mine in gravels on the Australian Plate at Ross. (photograph courtesy Crown Minerals) |
