Do big Nuggets travel further from the source than small nuggets

[metaldetective]

I have been trying to understand if big nuggets travel further than smaller ones. In my experience I always seem to find the bigger ones further away from the source. Interested to know if this is your experience as well?

Gold on sloped ground will fan out from the source, small to big as it travels down (normally). A pediment will also catch gold - as the gradient changes.
The same as river gold, small to heavier from each edge of any obstruction....eg: fines will be around base, larger further away

 

[sand surfer]

a guide i found a few years ago , not sure how true it is
it was snipped from a old miners journal i was reading

 

[mbasko]

a guide i found a few years ago , not sure how true it is
it was snipped from a old miners journal i was reading

View attachment 11102

Maybe fairly general information for a specific area or primary reef gold in a general setting but wouldn't take as true to all areas.

One thing I don't think we've really covered is whether the source is primary or secondary.
This can change things too. Secondary source gold can be "gold is where you find it". Mixed up + deposited by huge geological or other forces thousands of years ago then unmoved where it lays i.e. capped by basalt, lead gold, ancient river terraces etc. so knowing your source is important in understanding how/why.

 

[Qmot]

My 2 cents worth is that it is important to remember that the ratio of surface area to volume decreases as mass gets bigger. I.e., a larger nugget has a proportionally smaller surface area than a smaller one. Assuming that (over a long period of time) that soil behaves as a fluid, than the drag experienced by a nugget is roughly proportional to its cross-sectional area. This means that a nugget that weighs twice as much will travel 1.26x faster (Over long periods of time) (calculation: 2/(2^(2/3)) (Assuming net force is roughly proportional to speed).

So my maths suggests big nuggets may travel slightly further! Although I'm well aware theoretical can be very different to actual experience!

 

[grubstake]

So my maths suggests big nuggets may travel slightly further! Although I'm well aware theoretical can be very different to actual experience!

Surely by that logic, a sluice box would catch the fines and small gold at its head, while the larger pieces would be at risk of washing away with the tailings? In my experience, that's the reverse of what happens.

 

[Mackka]

Larger nuggets = more weight, therefore less movement.

 

[Jaros]

Doesn't more mass equate to a larger object meaning that the larger object creates a larger resistance to the water flow initially and due to the fact that the larger object probably weighs less it will move as species do.

 

[Hawkear]

My 2 cents worth is that it is important to remember that the ratio of surface area to volume decreases as mass gets bigger. I.e., a larger nugget has a proportionally smaller surface area than a smaller one. Assuming that (over a long period of time) that soil behaves as a fluid, than the drag experienced by a nugget is roughly proportional to its cross-sectional area. This means that a nugget that weighs twice as much will travel 1.26x faster (Over long periods of time) (calculation: 2/(2^(2/3)) (Assuming net force is roughly proportional to speed).

So my maths suggests big nuggets may travel slightly further! Although I'm well aware theoretical can be very different to actual experience!

The maths there doesn’t take into account inertia. A nugget double the weight may well have 1.26 times more push force applied because of its greater cross section but it will have DOUBLE the inertia (the metric for mass and inertia are the same), which has an offsetting effect on its acceleration.
In any event the movement of an object freely suspended in a moving medium is not really a good model in considering the total amount of movement applied. This is because when that medium is not moving, the opposite effect comes into play acting on moving objects in that lighter objects will slow down faster than heavier objects. (think wind resistance)
What is missing in the model is the relevance of gravity. Nuggets and other objects that are held in contact with other surfaces apply friction to each other. The force necessary to allow movement between two objects in contact is measured by the factor known as the coefficient of friction times the pressure.
Pressure in this context is provided by gravity so the force that would be needed to allow movement is proportional to the weight of the nugget.
So whilst nugget double the weight of another would encounter a drag force of 1.26 times more, the frictional force that would have to be overcome for it to even start moving would double.

 

[Metabet]

The maths there doesn’t take into account inertia. A nugget double the weight may well have 1.26 times more push force applied because of its greater cross section but it will have DOUBLE the inertia (the metric for mass and inertia are the same), which has an offsetting effect on its acceleration.
In any event the movement of an object freely suspended in a moving medium is not really a good model in considering the total amount of movement applied. This is because when that medium is not moving, the opposite effect comes into play acting on moving objects in that lighter objects will slow down faster than heavier objects. (think wind resistance)
What is missing in the model is the relevance of gravity. Nuggets and other objects that are held in contact with other surfaces apply friction to each other. The force necessary to allow movement between two objects in contact is measured by the factor known as the coefficient of friction times the pressure.
Pressure in this context is provided by gravity so the force that would be needed to allow movement is proportional to the weight of the nugget.
So whilst nugget double the weight of another would encounter a drag force of 1.26 times more, the frictional force that would have to be overcome for it to even start moving would double.

If a large nugget embedded in quartz was jettisoned from the side of a mountain wouldn't its momentum (and gravity) keep it going just like a bomb skidding along the water did in the Dam Busters?

 

[Moneybox]

If a large nugget embedded in quartz was jettisoned from the side of a mountain wouldn't its momentum (and gravity) keep it going just like a bomb skidding along the water did in the Dam Busters?

A nugget of any size embeded in quartz will travel at a different rate and distance to a gold nugget due to its lighter specific gravity. Gold is heavy so if it gets deposited into a crevice or clay base it's likely to stay there. The smaller lighter or flakier nuggets are more easily moved by wind and water than solid chunky bits that have less surface area compared to their weight.

 

[Hawkear]

If a large nugget embedded in quartz was jettisoned from the side of a mountain wouldn't its momentum (and gravity) keep it going just like a bomb skidding along the water did in the Dam Busters?

Yes heavier objects have more momentum than lighter objects, and just as they are harder to get moving they are harder to stop moving.
The force necessary to bring an object travelling at a certain velocity to a halt is exactly equal to the force that was required to accelerate it to that velocity.
This opposing force can be provided in most natural situations by air or water resistance or in the case of a nugget imagined to be falling down the side of a hill, by friction against the surface.
Imagine an object on a 45 degree slope. The force of gravity will be split into two equal vectors. One vector will be parallel to the slope and provide for the motive force. The other vector will be vertical to the slope and provide for the frictional force opposing the motion.
There is an obvious point of balance where the angle of the slope will decide which vector wins out.
Once in motion if an object loses contact with a surface as by bouncing and spinning friction is almost completely overcome leaving the surface parallel gravity vector as the only force in play.
The situation with bouncing bombs or skipping stones may be a bit or even a lot more complicated as it would also involve fluid dynamics. Just happy we had men like Barnes-Wallis on our side.

 

[Jaros]

Ah the bouncing lake bombs--good show.

 

[Metabet]

Yes heavier objects have more momentum than lighter objects, and just as they are harder to get moving they are harder to stop moving.
The force necessary to bring an object travelling at a certain velocity to a halt is exactly equal to the force that was required to accelerate it to that velocity.
This opposing force can be provided in most natural situations by air or water resistance or in the case of a nugget imagined to be falling down the side of a hill, by friction against the surface.
Imagine an object on a 45 degree slope. The force of gravity will be split into two equal vectors. One vector will be parallel to the slope and provide for the motive force. The other vector will be vertical to the slope and provide for the frictional force opposing the motion.
There is an obvious point of balance where the angle of the slope will decide which vector wins out.
Once in motion if an object loses contact with a surface as by bouncing and spinning friction is almost completely overcome leaving the surface parallel gravity vector as the only force in play.
The situation with bouncing bombs or skipping stones may be a bit or even a lot more complicated as it would also involve fluid dynamics. Just happy we had men like Barnes-Wallis on our side.

So did the Welcome Stranger likely 'bounce' from a long gone mountain to where it was found or, did it 'grow' in the ground as is sometimes alleged? Apologies if this has been canvassed before.

 

[Moneybox]

So did the Welcome Stranger likely 'bounce' from a long gone mountain to where it was found or, did it 'grow' in the ground as is sometimes alleged? Apologies if this has been canvassed before.

Gold is quite dense so doesn't bounce very well....

 

[Hawkear]

The idea of large nuggets “growing” in the ground is largely discounted. Studies of the crystalline structure of large nuggets has shown that they form at hot temperatures 300 To 400 Celsius. This discounts the idea that they formed in a molten state and also that they formed in the ground where temperatures would be much cooler. It is consistent that gold was deposited in reefs from hot mineral and metal rich fluids simultaneously with quartz and other associate minerals.
Also the terrain in the goldfields over its geologic history been subjected to probably thousands of vertical feet of erosion to the gentler slopes we see today. Most of the gold we find today has been deposited in later epochs of that history so we would not likely see nuggets careening down steep hillsides.
Bradford in his memoirs has lots to say about the situation of nuggets at specific places in reefs when encountering indicators in the host rocks. Certainly some points of a reef are more nuggety than others and large masses of gold weighing up to 1000 ounces have been discovered by reef mining, so there is no argument that reefs would deposit large nuggets as well as fine gold Into their immediate environment.
It has also been noted that large nuggets have been found in gullies at the point where that gully crosses a gold bearing reef eg Shoots gully.
There was no reef line noted were the Welcome Stranger was found, the nearest, Black reef, being about one hundred meters away. But then not all gold is derived from vertical reefs, with much Nuggety gold coming from almost flat side reefs. Moliagul was noted for its flat reefs and the best recorded example was Snow and Liddells about 500 meters away and on a similar geologic line. Mining on that reef was conducted by following the indicator to where it encountered a flat cross reef where nuggety patches were encountered.
If the Welcome stranger was derived from a flat reef (evidenced by much quartz still attached to the big nugget when found), the reef would have long disappeared leaving the massive nugget to lay on a surface many feet, possibly hundreds, almost directly below its original position.

 

[Aries]

The idea of large nuggets “growing” in the ground is largely discounted. Studies of the crystalline structure of large nuggets has shown that they form at hot temperatures 300 To 400 Celsius. This discounts the idea that they formed in a molten state and also that they formed in the ground where temperatures would be much cooler. It is consistent that gold was deposited in reefs from hot mineral and metal rich fluids simultaneously with quartz and other associate minerals.
Also the terrain in the goldfields over its geologic history been subjected to probably thousands of vertical feet of erosion to the gentler slopes we see today. Most of the gold we find today has been deposited in later epochs of that history so we would not likely see nuggets careening down steep hillsides.
Bradford in his memoirs has lots to say about the situation of nuggets at specific places in reefs when encountering indicators in the host rocks. Certainly some points of a reef are more nuggety than others and large masses of gold weighing up to 1000 ounces have been discovered by reef mining, so there is no argument that reefs would deposit large nuggets as well as fine gold Into their immediate environment.
It has also been noted that large nuggets have been found in gullies at the point where that gully crosses a gold bearing reef eg Shoots gully.
There was no reef line noted were the Welcome Stranger was found, the nearest, Black reef, being about one hundred meters away. But then not all gold is derived from vertical reefs, with much Nuggety gold coming from almost flat side reefs. Moliagul was noted for its flat reefs and the best recorded example was Snow and Liddells about 500 meters away and on a similar geologic line. Mining on that reef was conducted by following the indicator to where it encountered a flat cross reef where nuggety patches were encountered.
If the Welcome stranger was derived from a flat reef (evidenced by much quartz still attached to the big nugget when found), the reef would have long disappeared leaving the massive nugget to lay on a surface many feet, possibly hundreds, almost directly below its original position.

Very well said,M. Creasy spent millions proving all those absurd theories about nuggets "growing" in soil and other weird ways to be false.

 

[Hawkear]

Very well said,M. Creasy spent millions proving all those absurd theories about nuggets "growing" in soil and other weird ways to be false.

Yes, it was reported that researchers cut an 8 kilo gold nugget among many in half to etch and examine the their internal crystalline structure. Ouch!
Sometimes sacrifices have to be made. At least we now know that nuggets form at temperatures too hot to be near the surface and not so hot as to be molten.

 

[grubstake]

Yes, it was reported that researchers cut an 8 kilo gold nugget among many in half to etch and examine the their internal crystalline structure. Ouch!
Sometimes sacrifices have to be made. At least we now know that nuggets form at temperatures too hot to be near the surface and not so hot as to be molten.

What about lateritic gold in WA? Originally deposited in quartz reefs, from which it is later slowly dissolved by hyper-saline groundwater and transported in that fluid until it precipitates out of solution when it comes in contact with iron-rich laterites.

 

[Hawkear]

Dissolution and redeposition of gold and redeposition in nugget form in a laterite or just incorporation of nugget shed from a reef in a laterite?
I prefer the least complex explanation, however I do not deny that the dissolution and redepostion process can occur, as have seen evidence of this process first hand in Vic.
Working on drilling the Loddon river deep lead, I saw pyrites crystals brought to the surface which had fine gold associated with them. They were apparently formed by slow moving aquifers moving through highly gold bearing ground (Poseidon area) and redepositing their dissolved gold, iron and sulphur under the right chemical conditions. The gold was extremely fine and could only be determined by assay.
The company we were working for had intended to commence a solution mining operation pumping cyanide down one bore and out another lower down the aquifer and precipitate the gold out of the recovered cyanide solution. It never got off the ground, I wonder why.
There was never any evidence of any more than microscopic particles gold and certainly nothing that even approached what could be called a nugget.
I think the real test would have to be an examination of the crystal structure of any suggested lateritic nuggets to determine whether they were indeed of cool temperature origin or perhaps of orogenic origin but deposited from a reef to be later incorporated in a laterite.

 

[Aries]

What about lateritic gold in WA? Originally deposited in quartz reefs, from which it is later slowly dissolved by hyper-saline groundwater and transported in that fluid until it precipitates out of solution when it comes in contact with iron-rich laterites.

Grubstake, do you have any scientific proof of this occurring ? If so could you please direct me to the source.
To the best of my knowledge all laterite gold nuggets in WA can be dated to the Archean period whilst all the laterites were deposited much later. ie they were deposited "whole" during the formation.
The weird one in WA is that our gold is much older than say the gold in Victoria, all Archean with only 3 geographically isolated mines that don't conform to this period (T, B and SoM).
The gold being so old there has been much more vertical erosion in WA (kilometres ) and what is now a laterite hill was once a river valley or floodplain.