Where are the alluvial gold bonanzas of the past?

[user 4386]

OK goldie, I've this thread 6 times and understood 12.36 % of it!! If I understand you correctly, firstly, if you don't know geology you're wasting a lot of time, secondly, there's not much river gold that originates from the stream itself, and thirdly, most alluvial gold comes from paleoplacers through the action of geological uplift (of ancients layers) and the work of erosion, whether rain or river. Fourthly, if you want serious gold, you've got to dig deep and in the right spot. Few of us are in a position to dig a mine shaft, so alluvial gold by detection seems to be the best bet. Question is; how to find the likely place of a paleoplacer "lift" and its "downhill" region where there might be surface gold? Is this possible for the amateur? Can you do it on Geovic? Do you have to be able to read a detailed geological map? Any guidance on this would be greatly appreciated.

A few questions here.....

1. Have a higher chance of success (not quite the same as wasting time)
2. Most may have been palaeoplacer in the past, but for the reasons you state most that is AVAILABLE to you now is in modern rivers or near exposed and uplifted older river gravels. Not only is digging a shaft hard work, but in wet ground it was extremely dangerous with up to a death per day on some goldfields. Also, almost the entire Victorian forestry industry up to 1900s was devoted to timber for mines and to a lesser extents ports - they did not know how to season hardwood so it was not a choice for housing. Try chopping down that many trees now to provide the close timbering required in underground alluvial mines and see how you go (you'll be drawn and quartered)- there are alternatives to timber but not cheap because you are basically trying to keep wet sand and mud from burying you. And you will have to pump in most cases.....
3. Detecting is definitely the more fun way to go as a hobby and you can get gold shed from uplifted alluvials or from reefs being eroded away at surface (in the adjacent soil) as well
4. You can fairly easily prospect uplifted gravels shown on geological maps - not a lot to learn. The gravels containing the gold will usually be identified as Tertiary (particularly Older Tertiary) or Palaeogene. And they will usually be called fluvial or river gravels (many other gravel types lack gold). You need to prospect in the soil near what would have been the base of the gravels when they formed (where they lie on older bedrock). Not just everywhere where they lie on bedrock, but preferably the lowest former base, that would have been the active stream channel. Obviously old workings in the gravels that are shown on the maps are a clue to where to look. Needs a bit oif learning but not a lot. Uplifted gravels also have the advantage that the old-timers often lacked water (they would sometime stockpile for up to 3 years waiting for rain), so they could be very inefficient in getting all the gold in such cases. Mones weres till working such gravels in the 1980s (eg near Avoca in Victoria)

Hope that helps.

 

[Hawkear]

Good info in all these posts. One thing I could add is that some of the leads south of Ballarat have been suggested to be shore line deposits (Lake or Sea not specified) because of the nature of the sand and quartz pebbles in the leads. These deposits have now been covered by later lava flows and nowadays bleed out the side of current eroded hillsides.When I was detecting in the area, I had noted how smooth and rolled the quartz pebbles seem to be and consistent with being on a shoreline.
I am not sure whether there are any goldfields currently on our shores in Victoria but I have been told that there are at Wynyard in Tasmania.
Maybe someone may have some info about this.

 

[user 4386]

Good info in all these posts. One thing I could add is that some of the leads south of Ballarat have been suggested to be shore line deposits (Lake or Sea not specified) because of the nature of the sand and quartz pebbles in the leads. These deposits have now been covered by later lava flows and nowadays bleed out the side of current eroded hillsides.When I was detecting in the area, I had noted how smooth and rolled the quartz pebbles seem to be and consistent with being on a shoreline.
I am not sure whether there are any goldfields currently on our shores in Victoria but I have been told that there are at Wynyard in Tasmania.
Maybe someone may have some info about this.

The ones south of Ballarat are not really shoreline deposits - they have since been studied. Most Australian shoreline deposits are rather unimpressive - eg SE NSW and New England - there is a bit of shoreline gold at Waratah Bay and near Pt Conran. Even some of those are a bit suss (eg Bermagui). Alaska has large ones around Nome.

 

[Dave79]

The gold at Doctors Rocks near Wynyard was deposited there by a glacier that used to meet the sea there.

 

[user 4386]

The gold at Doctors Rocks near Wynyard was deposited there by a glacier that used to meet the sea there.

Do you have any info on that? I am a little confused, geologically-speaking because I don't think our last lot of glaciers reached the sea, and those before that pre-dated the existence of Bass Strait. I am doing some work on NW Tasmania coastal sediments so info would be appreciated (there is always somethiing new to be found).

 

[silver]

Do you have any info on that? I am a little confused, geologically-speaking because I don't think our last lot of glaciers reached the sea, and those before that pre-dated the existence of Bass Strait. I am doing some work on NW Tasmania coastal sediments so info would be appreciated (there is always somethiing new to be found).

Don't discount the weight of ice sheet holding the mantle lower than its free float position.... at the time.

 

[Moneybox]

Don't discount the weight of ice sheet holding the mantle lower than its free float position.... at the time.

Yes Silver, when I was young I had the ice at the top of my glass put me on the floor a couple of times

 

[Hawkear]

The ones south of Ballarat are not really shoreline deposits - they have since been studied. Most Australian shoreline deposits are rather unimpressive - eg SE NSW and New England - there is a bit of shoreline gold at Waratah Bay and near Pt Conran. Even some of those are a bit suss (eg Bermagui). Alaska has large ones around Nome.

I'll gather some of the quartz gravel from the Happy Valley area next time I am there and post a picture of it here as it is seems different to any other lead material I have seen in the rolled and smallish nature of the quartz pebbles. I will also try to locate the report which suggested that some of the leads were of lacustrine* nature. I think it was an early geologist's report and as said may well have been superseded by later geological studies.
* I looked that word up

 

[Dave79]

Do you have any info on that? I am a little confused, geologically-speaking because I don't think our last lot of glaciers reached the sea, and those before that pre-dated the existence of Bass Strait. I am doing some work on NW Tasmania coastal sediments so info would be appreciated (there is always somethiing new to be found).

Right you are, fluvioglacial it is. *I probably should have looked that word up!

 

[user 4386]

Right you are, fluvioglacial it is. *I probably should have looked that word up!

That makes sense - outwash from glaciers farther up the valleys.

 

[user 4386]

I'll gather some of the quartz gravel from the Happy Valley area next time I am there and post a picture of it here as it is seems different to any other lead material I have seen in the rolled and smallish nature of the quartz pebbles. I will also try to locate the report which suggested that some of the leads were of lacustrine* nature. I think it was an early geologist's report and as said may well have been superseded by later geological studies.
* I looked that word up

I have mapped that - incorrect mapping by the Geological Survey of Victoria (I published a paper correcting it). What actally occurred is that gold-bearing river gravels were later covered by the sea that deposited marine gravels on top of them. So the miners would sink through the marine gravels to get to the river gravels beneath, but they got no gold out of the overlying marine gravels (which form a continuous sheet over a huge area). A similar occurrence occurs west of Stawell near the airport. The marine gravels are characteristic - quite small but highly polished and very spherical compared with the quartz pebbles and cobbles of rounded but more irregular shape in the underlying river gravels.

 

[user 4386]

Don't discount the weight of ice sheet holding the mantle lower than its free float position.... at the time.

It was not an ice sheet during either glacial period at that locality - just valley glaciers only tens of metres thick.

 

[trekkie]

I have a question for you Goldierocks could you explain the area at beechworth as i went there for a few days panning and the amount of exposed bedrock and the sheer size of the boulders siting on top of ground in and around reedy creek all the way thru to eldorado. Have read a little imfo on area but doesn't explain much on geology.Any response would be helpful in researching gold deposits there.

 

[user 4386]

I have a question for you Goldierocks could you explain the area at beechworth as i went there for a few days panning and the amount of exposed bedrock and the sheer size of the boulders siting on top of ground in and around reedy creek all the way thru to eldorado. Have read a little imfo on area but doesn't explain much on geology.Any response would be helpful in researching gold deposits there.

Hi - Beechworth goldfield is a big area and much of the gold came from upstream of there, However in the area you mention the rock would be granite of Devonian age (the Mt Pilot batholith on the attached map). None of the gold is coming out of that granite (most of the tin is) - the gold is simply being washed downstream from Beechworth and from upstream of Beechworth from the gold-bearing quartz reefs in Palaeozoic metasedimentary rocks shown on the map.

 

[Hawkear]

I'll gather some of the quartz gravel from the Happy Valley area next time I am there and post a picture of it here as it is seems different to any other lead material I have seen in the rolled and smallish nature of the quartz pebbles. I will also try to locate the report which suggested that some of the leads were of lacustrine* nature. I think it was an early geologist's report and as said may well have been superseded by later geological studies.
* I looked that word up

A follow up on this post. Here is a picture of some of the quartz pebbles which are prolific on the hillsides around Happy Valley. In my experience those places offer some of the better detecting but alas not on this trip. Still looking for where I read about lake shore deposits in the area.

 

[trekkie]

Thanks Goldierocks great imfo explains why only flakes and specks were in my many pans. I did have an idea that it was coming from further up than woolshed falls so next time up there i will investigate.

 

[user 4386]

A follow up on this post. Here is a picture of some of the quartz pebbles which are prolific on the hillsides around Happy Valley. In my experience those places offer some of the better detecting but alas not on this trip. Still looking for where I read about lake shore deposits in the area.View attachment 1644

I have a paper somewhere that I wrote on those gravels.....

 

[user 4386]

I realise now that I may have misled people by using "Victorian" in the title - the principles and examples are not confined to Victoria, it just happens to be by far the largeast producer of alluvial gold.

It is not really Victoria specific - it applies at Tibooburra, around Mudgee, in the Eastern goldfields, western Tasmania (eg in the Tarkine) and in parts of Queensland (I have worked on palaeoplacers at each of these). Smaller ones that I have worked on around Narooma and slightly south. Many have been significant producers (eg St Ives and Jubilee near Kambalda and Kalgoorlie ) and some others are all or partly older paleoplacers (around Mudgee, Gulgong, Cudgegong, Sofala, Wattle flat, Bermagui, and Tibooburra). I am familiar with them all, and a number don't have ANY written record that they are palaeoplacers at all. I think part in South Australia (Barossa?) may be as well, but I am not very familiar with them.

I guess the point I was making is - that it is often not mentioned in reports on the areas that they were paleoplacers, and one can have poor success as a result. And it is particularly people who are "prospecting for gold in rivers and streams" (i.e. modern waterways) who would be having less success in palaeoplacer areas - bonanzas were limited in these modern streams.

Palaeoplacers commonly result from uplift of old placers, and the best ones are usually the oldest, resting directly on bedrock. It partly has to do with the prolonged deep weathering history that occurred on relatively flat plains in the past (Tertiary, ie Palaeogene)- the soil on these plains then only consisted of clay, vein quartz pebbles and gold (rock fragments had converted to clay), which were washed into the palaeoplacer streams, the clay washed away, and then the area was uplifted so that the palaeoplacer gravels were now mostly (not always by any means) higher than new streams that developed. However some were simply buried by new gravel brought in by the new streams that developed. or lavas that flowed down their valleys of the old streams obliterating them,. Once the area was uplifted, mostly freah rock was exposed in the new highlands but soils washed away as fast as it was produced on the new slopes, so there was no selective concentration of gold and vein quartz in the gravels - the newer and commonly less productive placers often had as much or more pebbles and cobbles consisting of unweathered bedrock, "diluting" the gold content compared with the earlier placers where all except the gold and quartz had broken down to clay (gold then being a larger proportion of the heavy material, and also more efficiently concentrated).

There is often some gold in young streams of palaeoplacer areas, but one needs to recognise the setting. Often the only gold is on gravels around the collars of old shafts where it has been brought up from below, because it only occurs at depth in the palaeoplacer (eg on the western fields at Ballarat, downstream along Bendigo Creek, Bealiba, SW of Avoca, west of Mudgee). Where the gravels are uplifted onto hillsides, they need to be exposed, especially where cut by younger streams, for them to give some decent gold in the younger (modern) streams nearby. Tibbooburra iis a good example where limited area of young (now dry) gullies near town have cut through very old palaeplacer gravels that are porrly exposed to the west and southwest.

But sometimes there are better places to be looking.....e,g steeper, young drainages draining directly off exposed gold-bearing reefs, not streams flwing over alluvium and old basalt flows on the plains that have buried the palaeoplacers..

 

[user 4386]

This cross-section shows two types of palaeoplacer and a modern river. One palaeoplacer is now deeply buried and covered by younger rocks including a baslt flow that has covered the paleoplacer valley. The only good alluvial gold you might get here would be on the shaft dump using a metal detector - definitely none of its gold would have got into the modern river. Another paleoplacer (probably even older) has been uplifted and its gravels are on a hilltop (called White Hills Gravel), You might get some good goldi n little gullies draining off it, or by detecting the hilltop gravels, but are unlikely to find that much of its gold has got into the modern river. that is far to the left.




Here is a publication that describes the basics for non-geologists. It is on pages 134-158 of the book cover shown.





I have posted this reference before - it describes some of these things in more detail for the Victorian situation - written for geologists but mostly understandable for non-geologists.

 

[user 4386]

I have a paper somewhere that I wrote on those gravels.....

The northern limit of those marine gravels shown by Hawkear is mostly the Mt Erip Reserve, Moonlight Creek, Pitfield and Dereel (on the ridge south from Misery Ck road). Because they sunk through them to get to the old river valleys with gold-bearing gravels beneath, I would suggest that nuggets would only be on mine dumps not in areas covered by extensive marine gravels. The marine gravels are mostly only a few million years old, the underlying river gravels 20-30 million years. Erosion south of some of these areas has stripped the marine gravels away, so you see the old river gravels exposed around Dereel itself, Rokewood, Cap Clear, Illabarook etc.

i.e. the marine sands are the unshaded area on this map that Dereel sits on the northern boundary of, and that Cape Clear sits between two of its areas.



https://researchonline.federation.edu.au/vital/access/services/Download/vital:1315/DS1?view=true