A member recently posted the comment "puddlers are a huge bonus to an amateur prospector because they indicate regions where the gold was trapped in clay and was difficult to wash, so the chances of finding a piece or two around those particular gullies is probably pretty high"
I feel that there is a misconception here (and not only because I see puddlers all over the place). Water sorts material according to size and density (the mass of grains - so water will concentrate coarse gold, nuggets, ironstone, dense gems like sapphire and diamonds etc within coarse, gravelly wash, especially towards its base, and not with clay - for clay to settle out of water directly very low flow velocities are required, and coarse gold will have already been dumped before such slow velocities are reached). Gold nuggets are as different in density and mass to clay as one can get. Some nuggets in clay formed in the clay of soils in laterite profiles, as in Western Australia, but that is not common in southeastern Australia (where we mostly see puddlers). However puddlers were used to get gold out of clay in alluvial gold leads in the main. I question "they indicate regions where the gold was trapped in clay and was difficult to wash" - instead they indicate a device used to separate from the clay component of gold-bearing alluvials (not usually a 'region", but "one component" of the wash).
So why do nuggets often occur in clay in alluvial gold deposits? Because it is commonly not alluvial clay but decomposed bedrock beneath gravelly wash.
One needs to look at how gold occurs in wash to understand why it occurs in clay. Most gold including nuggets occurs in a gravel layer that overlies weathered bedrock. However being heavy and concentrated towards the base of deposits, coarse gold including nuggets will penetrate downwards to some depth in cracks in clay bedrock. The miners would commonly sluice the easily separated gold from the overlying quartz gravel but treat the underlying clay (decomposed but in situ bedrock) separately. The nuggets are in clay, but it is commonly not alluvial clay but decomposed bedrock that is still in situ.
"Placer gold was mostly produced from within 2 m of the unconformity between the gravel and underlying Paleozoic rocks (Hunter, 1909). The basal gravels were typically 0.15 to 1 m thick, with thicknesses as great as 10 m being very rare.......... Commonly, decimeters of the top of the Paleozoic bedrock were also mined because of the presence of gold in mechanical traps". Up to a third of the alluvial gold production was recovered from this weathered bedrock below the gravel.
Commonly the "sticky" clay of this bedrock could not be sluiced like the gravel overlying it but was scraped up separately after shoveling off the gravel. It was treated separately in puddlers. So the presence of puddlers commonly only indicates devices used to treat the basal part of the alluvials in any area, and do not indicate some special nature of the alluvials in an area. Some areas did lack the decomposed bedrock clay base, with the gravels resting on fresh bedrock, but this was more common in the highlands where nuggets are relatively rare (and one only has to use ones eyes to see the different nature of bedrock). The common situation throughout the goldfields of central Victoria for example, where most Victorian nuggets come from, is that the puddlers were simply treating the sticky decomposed clay bedrock at the base of MOST alluvial gravels in MOST goldfields. As such, I would not consider puddlers usually to be a useful indicator of areas or regions for detecting, any more than any alluvial workings in such an area are indicators.
I feel that there is a misconception here (and not only because I see puddlers all over the place). Water sorts material according to size and density (the mass of grains - so water will concentrate coarse gold, nuggets, ironstone, dense gems like sapphire and diamonds etc within coarse, gravelly wash, especially towards its base, and not with clay - for clay to settle out of water directly very low flow velocities are required, and coarse gold will have already been dumped before such slow velocities are reached). Gold nuggets are as different in density and mass to clay as one can get. Some nuggets in clay formed in the clay of soils in laterite profiles, as in Western Australia, but that is not common in southeastern Australia (where we mostly see puddlers). However puddlers were used to get gold out of clay in alluvial gold leads in the main. I question "they indicate regions where the gold was trapped in clay and was difficult to wash" - instead they indicate a device used to separate from the clay component of gold-bearing alluvials (not usually a 'region", but "one component" of the wash).
So why do nuggets often occur in clay in alluvial gold deposits? Because it is commonly not alluvial clay but decomposed bedrock beneath gravelly wash.
One needs to look at how gold occurs in wash to understand why it occurs in clay. Most gold including nuggets occurs in a gravel layer that overlies weathered bedrock. However being heavy and concentrated towards the base of deposits, coarse gold including nuggets will penetrate downwards to some depth in cracks in clay bedrock. The miners would commonly sluice the easily separated gold from the overlying quartz gravel but treat the underlying clay (decomposed but in situ bedrock) separately. The nuggets are in clay, but it is commonly not alluvial clay but decomposed bedrock that is still in situ.
"Placer gold was mostly produced from within 2 m of the unconformity between the gravel and underlying Paleozoic rocks (Hunter, 1909). The basal gravels were typically 0.15 to 1 m thick, with thicknesses as great as 10 m being very rare.......... Commonly, decimeters of the top of the Paleozoic bedrock were also mined because of the presence of gold in mechanical traps". Up to a third of the alluvial gold production was recovered from this weathered bedrock below the gravel.
Commonly the "sticky" clay of this bedrock could not be sluiced like the gravel overlying it but was scraped up separately after shoveling off the gravel. It was treated separately in puddlers. So the presence of puddlers commonly only indicates devices used to treat the basal part of the alluvials in any area, and do not indicate some special nature of the alluvials in an area. Some areas did lack the decomposed bedrock clay base, with the gravels resting on fresh bedrock, but this was more common in the highlands where nuggets are relatively rare (and one only has to use ones eyes to see the different nature of bedrock). The common situation throughout the goldfields of central Victoria for example, where most Victorian nuggets come from, is that the puddlers were simply treating the sticky decomposed clay bedrock at the base of MOST alluvial gravels in MOST goldfields. As such, I would not consider puddlers usually to be a useful indicator of areas or regions for detecting, any more than any alluvial workings in such an area are indicators.
