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Gold Prospecting
Alluvial Gold Prospecting
Confused about sudden change in deposition layers in creek
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<blockquote data-quote="user 4386" data-source="post: 481171" data-attributes="member: 4386"><p><strong>When you say the quartz hasn't traveled far due to how little erosion it has experienced, is there any way of quantifying that? </strong></p><p></p><p>Other than the fact that gravel pebbles tend to become more rounded with distance - no. It also depends on whether the rock is hard or soft, the turbulence of the river, the amount of flow, the water velocity, the gradient (slope) of the river downstream (since this affects velocity). Also, new rivers often erode the gravels left by old rivers (common in Victoria). So pebbles might have become rounded in an early large and vigorous river, perhaps 100 km long, but be eroded into a small and not very spectacular stream only a few km long. The shape of alluvial gold tends to be a more sensitive indicator, although the same applies (angular grains are usually close to the source, as are unrounded quartz crystals as someone else said). Gold tends to be coarser close to source, and really nuggety gold is usually only hundreds of metres from its source - medium-size is within kilometres, fine gold could be 30 km from the source.</p><p><strong></strong></p><p><strong>Very cool to have found some sapphire, I've looked a geological map of the area and there is isolated areas of basalt not far from where I was digging, does it stand to reason that if I was to look closer to these I could increase the likelihood of finding more sapphires?</strong></p><p></p><p>Possibly - I would give it a try. It is not a bad area for both blue sapphire and zircon (big zircon crystals can be seen in basalt in a quarry near Daylesford, and a few attempts have been made to mine blue sapphires near Trentham (Blue Hill or Mount?).</p></blockquote><p></p>
[QUOTE="user 4386, post: 481171, member: 4386"] [b]When you say the quartz hasn't traveled far due to how little erosion it has experienced, is there any way of quantifying that? [/b] Other than the fact that gravel pebbles tend to become more rounded with distance - no. It also depends on whether the rock is hard or soft, the turbulence of the river, the amount of flow, the water velocity, the gradient (slope) of the river downstream (since this affects velocity). Also, new rivers often erode the gravels left by old rivers (common in Victoria). So pebbles might have become rounded in an early large and vigorous river, perhaps 100 km long, but be eroded into a small and not very spectacular stream only a few km long. The shape of alluvial gold tends to be a more sensitive indicator, although the same applies (angular grains are usually close to the source, as are unrounded quartz crystals as someone else said). Gold tends to be coarser close to source, and really nuggety gold is usually only hundreds of metres from its source - medium-size is within kilometres, fine gold could be 30 km from the source. [b] Very cool to have found some sapphire, I've looked a geological map of the area and there is isolated areas of basalt not far from where I was digging, does it stand to reason that if I was to look closer to these I could increase the likelihood of finding more sapphires?[/b] Possibly - I would give it a try. It is not a bad area for both blue sapphire and zircon (big zircon crystals can be seen in basalt in a quarry near Daylesford, and a few attempts have been made to mine blue sapphires near Trentham (Blue Hill or Mount?). [/QUOTE]
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Gold Prospecting
Alluvial Gold Prospecting
Confused about sudden change in deposition layers in creek
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