Gold definitions - "Alluvial", "Eluvial", "Colluvial" etc.

[Reg Wilson]

Flood gold is very fine. (Flour gold Mustard gold) Heavy gold can move quite some distance if locked up in boulders of conglomerate.
I have stood by streams in flood and could hear boulders bumping along in the torrent.

 

[WalnLiz]

Not sure why the sarcasm Reg ? No doubt your probably a knowledgeable chap on this matter, but then so are many more people and some that would possess even more of said knowledge I have no doubt? Your inputs appreciated Cheers

Sorry to hear that Reg as the intent of the thread was not to teach experts like yourself who probably already do very well in the hobby. The thread, as with most of my posts, is geared generally to those new to the hobby in an attempt to try and help them gain success. Cheers Wal.

 

[user 4386]

Eluvium - an accumulation ..... caused by the weathering and disintegration of rocks in place (Collins dictionary),
( Latin ēluere, to wash out)

This occurs in the immediate vicinity of the gold source (e.g. reef) – lighter material is washed away to leave the heavier gold in place – thus it accumulates as a residual accumulation = a residue)

Colluvium - rock detritus and soil accumulated at the foot of a slope. (Meriam Webster)
(Latin, a collection of washings)
The gold moves to the base of the slope under gravity and water flowing downhill

Alluvium - material deposited by rivers. (Britannica)
(Latin alluvius, from alluere, "to wash against")
The gold is concentrated by flowing water in a stream

Not a bad idea to check before disagreeing. I have been teaching this and discovering gold mines for more than half a century now. You will find many diagrams on Google that show the difference between the three.

 

[user 4386]

eluvial

 

[user 4386]

eluvial colluvial alluvial diagram figure - Bing images

This is colluvium

The distinction is that with an eluvial deposit, lighter material near the source (e.g. clay and sand), from the decomposing rock, is being washed away leaving heavy material like gold in situ at the source.

With a colluvial deposit some of the gold has now moved further down the slope (ultimately some will) and a thick accumulation concentrates towards the base of slope. Often lower grade than the eluvial deposit because it is mixed with more sand and clay, but derived from a larger area and dumped mostly towards the base of slope - so a larger volume of material available to hydraulic sluice etc.

Everyone understands alluvial - sorting of fine material in flowing water is a very efficient process. But a lot of people don't realize that a similar distinction occurs by sorting in a stream. Nearer the head where flow is turbulent and active, only coarse gold is efficiently dumped out - fine gold, sand and clay continue downstream. You could compare this with the eluvial situation on the hilltop. However ultimately downstream as the gradient of the stream decreases (and where it slows around bends) the velocity is insufficient to keep the finer gold in suspension in the water, and it drops out (which you could loosely compare with the colluvial deposit at the base of slope.

Understanding these things is not entirely academic - most things aren't (e,g, there will be a section of a stream where flow is still rapid but most coarse gold has already been dumped farther upstream - e.g. around the lake in Beechworth and Pennyweight flat and upstream towards Stanley and towards Hillsborough) - nugget country. So if you continue downstream to low velocity points you can find accumulations of finer gold (e,g at Eldorado). Eldorado is where the stream crosses the granite contact into a ridge of hornfelsed sedimentary rock, that dammed the flow naturally and slowed its velocity so it dumped fine gold.

 

[user 4386]

Just to stir the pot.
How about Diluvial gold.
Gold that is transported into place by flood waters.
Otherwise known as “flood gold”

Long time since I have seen diluvial Hawkear

-of or connected with a deluge, esp with the great Flood described in Genesis

You mostly see it on geological maps around the 1850s and earlier, when many geologists still thought in terms of rocks formed before and after Noah's flood. So they spoke of things like "pre-diluvial deposits"

Latin diluere ("to wash away"). I think the word deluge may come from the same source.

"English "diluvial" and its variant "diluvian" initially referred to the Biblical Flood. Geologists, archaeologists, fossilists, and the like used the words, beginning back in the mid-1600s, to mark a distinct geological turning point associated with the Flood" (Merriam Webster)

I have never seen a decent deposit formed that way - mainly just "poor mans diggings". The Chinese used to scratch out a living after floods on the Mitchell River in Gippsland - fine gold would be left on low spurs above normal river level.

 

[Hawkear]

Went panning with my FIL many years ago around the Kyneton area. He said that gold often got trapped in the roots of creek side grasses during times when the creeks flooded.
He then proceeded to rip up a few clumps, shake them off into the pan, and lo and behold!
Yes, agree that the origin of diluvial would be associated with the Noachian flood legend, as also words like “antediluvian“ to humorously describe people of my age as belonging to a period before the supposed time of Noah’s flood.
Getting back to the ”diluvial gold deposit”, it was only a few colours actually, but it’s presence however proved important to note, as many years later I returned with a small dredge and got about an ounce and a half of gold out of that small stretch of the little known creek.

 

[user 4386]

Went panning with my FIL many years ago around the Kyneton area. He said that gold often got trapped in the roots of creek side grasses during times when the creeks flooded.
He then proceeded to rip up a few clumps, shake them off into the pan, and lo and behold!
Yes, agree that the origin of diluvial would be associated with the Noachian flood legend, as also words like “antediluvian“ to humorously describe people of my age as belonging to a period before the supposed time of Noah’s flood.
Getting back to the ”diluvial gold deposit”, it was only a few colours actually, but it’s presence however proved important to note, as many years later I returned with a small dredge and got about an ounce and a half of gold out of that small stretch of the little known creek.

Yes, Howitt noted that the Chinese on the Mitchell River would get some rich patches after floods - he was intrigued because there was no gold in the rocks there, so the floods were bringing it down from up Dargo and Bullumwaal way.

 

[user 4386]

Long time since I have seen diluvial Hawkear

-of or connected with a deluge, esp with the great Flood described in Genesis

You mostly see it on geological maps around the 1850s and earlier, when many geologists still thought in terms of rocks formed before and after Noah's flood. So they spoke of things like "pre-diluvial deposits"

Latin diluere ("to wash away"). I think the word deluge may come from the same source.

"English "diluvial" and its variant "diluvian" initially referred to the Biblical Flood. Geologists, archaeologists, fossilists, and the like used the words, beginning back in the mid-1600s, to mark a distinct geological turning point associated with the Flood" (Merriam Webster)

I have never seen a decent deposit formed that way - mainly just "poor mans diggings". The Chinese used to scratch out a living after floods on the Mitchell River in Gippsland - fine gold would be left on low spurs above normal river level.

"Fossilists" - last time I quote Merriam Webster.

 

[user 4386]

Great to see "some" people picking at straws....Virtually all gold is derived from "Primary" gold and is then given a secondary name depending on where it ends up. Alluvial gold is given this term when it has been deposited and moved by water in streams and does not mean it originated within the watercourse.
Eluvial gold is disintegration of rock and gold at the site where it originates...not there through water movement alone but also other forces such as gravity. It's essentially primary gold which generally hasn't travelled far from its original source. I won' talk about Colluvial gold as it is not what is talked about in the thread.
If Goldierocks wishes to do a thread on Colluvial gold to enlighten us please do so. Cheers Wal.
Mod Edit: Posts split to new thread Wal where the definitions can now be discussed without cluttering up your thread.

I don't see any disagreement there Walnliz

 

[user 4386]

Is it possible then that alluvial, eluvial and colluvial gold can all be found in the one spot as terms such as those refer to the mechanism of transport and deposit not just how far gold is from its source.
Another thought is if you have a small quartz speci just broken off a reef and laying nearby on the surface is it eluvial? Then the next day it rolls down the slope into a flatter area is it colluvial? Could it be considered either one or the other or both like schrodingers cat.
Maybe we are splitting rabbits, or hares, actually I meant hairs.
The best of us will have a geologically informed instinct for how gold travels once it is released from a reef and the how can become the where.
A definition involving the mechanism of transport and deposit is best for that.

. One is a process of removing all except the gold and coarse rock fragments at the original site, the other of it then moving down the hill under gravity. It is really a continuum until it reaches the base of slope where it accumulates in colluvium. Colluvium does not really represent an efficient gold concentration process, just a way of accumualting a large volume of gold-bearing soil, So you don't see much discussion of colluvial gold deposits - it tends to be called eluvial much of the way down the slope even though you are transitioning into moving it away from its source by water and gravity. Sometimes the term residual is used for right on top of the original source area. All names - think processes as you say, that is what helps find gold.

 

[user 4386]

EVIE/BEE, A few years back James Beatty and I discovered an unworked area where we proved up gold over several thousand acres. There were only a couple of 'spec' holes in this whole area and no workings. The old timers obviously liked the look of some of this ground but could not prove it up. Before the secret got out we recovered quite a large amount of gold. No big nuggets turned up, the biggest being a little under five ounces.
The whole area was Permian and all the gold was very worn, some looking like worn soap. Some research revealed that a large boulder of granite was found in this location where there was no pluton or contact zone. This anomaly was particularly interesting due to the fact that the nearest granite of this type was located in northern Tasmania.
The nearest proven gold deposit was over twenty Ks away, so it is anyone's guess as to how far this gold may have travelled. (perhaps in glaciers)

PS This was in Victoria.

I think even granite experts would have trouble telling if a granite orignated in Tasmania or not - glacial action can do that but I have never seen an example. We did not get very big glaciers in the last glacial periods - it moved further in an earlier ice age (Permian). You will see giant granite boulders north of Queenstown (TAS) and around Heathcote (VIC) where there is no granite bedrock - because of glacial action. But the furthest distance I have found to source in that case is tens of km. Also around Bacchus Marsh.

 

[user 4386]

The burden of explanation or proof should be on the person who gives an opinion not someone else.
I see Dav79 has given another method of gold transportation which could be responsible for moving it considerable distances.
I am happy to accept any opinion provided it can be supported by facts. What would be needed is proof that gold found at a location is identical to gold from a source 35 Ks away.

The map I posted on the moved blog involves 26 km of transport. The reason is that there is no gold in the Pilot Batholith downstream of Beechworth - it is all derived from upstream of Beechworth although deposited as far downstream as Eldorado (where a dredge operated). however tin occurs in the granite and made the Eldorado gold economic.

 

[Reg Wilson]

Goldierocks, the granite to which you refer is indeed north of Heathcote on the fringe of the Permian deposits.
Slight correction Wal. My gold experience has not been a hobby but a profession for which I paid tax from the introduction of gold taxation in 89- 90.

 

[user 4386]

Goldierocks, the granite to which you refer is indeed north of Heathcote on the fringe of the Permian deposits.
Slight correction Wal. My gold experience has not been a hobby but a profession for which I paid tax from the introduction of gold taxation in 89- 90.

Yes, I think my distance of transport of the erratic is correct - from memory it is called the Cosbie granodiorite. But not from Tasmania to Victoria....

 

[user 4386]

Flood gold is very fine. (Flour gold Mustard gold) Heavy gold can move quite some distance if locked up in boulders of conglomerate.
I have stood by streams in flood and could hear boulders bumping along in the torrent.

Sure, it can be noisy - but that is bedload not the flood gold that gets caught up in the grassroots on the banks above normal water level - which is fine and not dragged along the bottom.

 

[Skip]

I think even granite experts would have trouble telling if a granite orignated in Tasmania or not - it moved further in an earlier ice age (Permian). You will see giant granite boulders north of Queenstown (TAS) and around Heathcote (VIC) where there is no granite bedrock .

I have indeed seen those granite boulders you speak of Goldie near Queenstown Tas and was wondering why/how they got there. It never occurred to me glacial movement is the likely cause.

 

[user 22230]

Could be just water also ? Never underestimate the power of water ie forces of nature. Interesting stuff indeed and when ages of 1.5 billion years are mentioned, explains well why I struggle many times trying to imagine what the landscape was were I'm standing ..





Wonder the size this was originally before weather and time had it's way

 

[WalnLiz]

Could be just water also ? Never underestimate the power of water ie forces of nature. Interesting stuff indeed and when ages of 1.5 billion years are mentioned, explains well why I struggle many times trying to imagine what the landscape was were I'm standing ..





Wonder the size this was originally before weather and time had it's way View attachment 2711

Some very good informative discussion happening on this thread and great work to all who are contributing.. Keep it up as we all benefit from such input...Cheers Wal.

 

[Reg Wilson]

The granodiorite erratic in Victoria is known as the Crosbie erratic north of Heathcote and is the only example in Victoria of that form of granodiorite. The nearest form is in northern Tasmania.