Detecting bigger gold in NSW...."Alluvial" vs "Eluvial"

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Pine Creek, Mount Todd, Cosmo are all quite a long way from Grove hill.
But yep, you are correct, no gold in the granite at all, but i also agree, that i have found some really good stuff within 1 km of the granite. I would also agree with moneybox, that sometimes Geos are wrong when it comes to alluvial gold. As for finding reefs and other deposits and just understanding how everything works, i wish i had 1 1/100th of the knowledge of you geos, and I tip my hat to your ability to learn. i wish i could understand geology a lot better than I do. Somme of the books you recommend, will find there way to me, and great for nightshift!
perhaps when the granite pushed up all that time ago, it just moved ground or released other host rocks that were near it, exposing it to the elements... I dunno.....but old Langley did have a few weird theorys, thaT DID LEAD HIM TO SOME GOOD FINDS.
Having said that, a thunderstorm lead me to a great patch....I literally pulled over to the side of the road to test a new detector, due to storm ahead of me. It just so happened that it turned into a 30 -40 odd oz patch that had never had a detector over it.
 
Pine Creek, Mount Todd, Cosmo are all quite a long way from Grove hill.
But yep, you are correct, no gold in the granite at all, but i also agree, that i have found some really good stuff within 1 km of the granite. I would also agree with moneybox, that sometimes Geos are wrong when it comes to alluvial gold. As for finding reefs and other deposits and just understanding how everything works, i wish i had 1 1/100th of the knowledge of you geos, and I tip my hat to your ability to learn. i wish i could understand geology a lot better than I do. Somme of the books you recommend, will find there way to me, and great for nightshift!
perhaps when the granite pushed up all that time ago, it just moved ground or released other host rocks that were near it, exposing it to the elements... I dunno.....but old Langley did have a few weird theorys, thaT DID LEAD HIM TO SOME GOOD FINDS.
Having said that, a thunderstorm lead me to a great patch....I literally pulled over to the side of the road to test a new detector, due to storm ahead of me. It just so happened that it turned into a 30 -40 odd oz patch that had never had a detector over it.
So that is how everything is made to be within a km - exclude things further than 1 km? 🤣

Seriously though, it is all one big gold belt extending NW for 200 km - to pick one tiny part of it seems to ignore the pattern (that gold is not closely related to granites in the belt, or more accurately, that the granites were already there for 65-75 million years before the gold deposits formed). Often, as probably in this case, if a lot of the rocks in a region are granites, a number of gold deposits will occur near granites. Opal jewellery stores and donut shops cluster around Melbourne town hall, but postdate the town hall by many decades - they just occur in the central Melbourne CBD (as with gold deposits occurring in the Pine Creek gold belt).

"geological evidence, used in conjunction with U-Pb age data obtained from SHRIMP in- situ analyses of hydrothermal gold-stage phosphates, demonstrates that the gold mineralisation is typically younger (c.1720-1710Ma) than the youngest phase of granitoid intrusion (c.1775Ma), and certainly post-dates the effects of peak contact-metamorphism".


1676539436811.png
 
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So that is how everything is made to be within a km - exclude things further than 1 km? 🤣

Seriously though, it is all one big gold belt extending NW for 200 km - to pick one tiny part of it seems to ignore the pattern (that gold is not closely related to granites in the belt, or more accurately, that the granites were already there for 65-75 million years before the gold deposits formed). Often, as probably in this case, if a lot of the rocks in a region are granites, a number of gold deposits will occur near granites. Opal jewellery stores and donut shops cluster around Melbourne town hall, but postdate the town hall by many decades - they just occur in the central Melbourne CBD (as with gold deposits occurring in the Pine Creek gold belt).

"geological evidence, used in conjunction with U-Pb age data obtained from SHRIMP in- situ analyses of hydrothermal gold-stage phosphates, demonstrates that the gold mineralisation is typically younger (c.1720-1710Ma) than the youngest phase of granitoid intrusion (c.1775Ma), and certainly post-dates the effects of peak contact-metamorphism".


View attachment 7987
I'm talking about detectable gold, 1 small part of that belt.
Of course there are other areas where detectable gold is , and there is no granite there at all. And I have found plenty not on that belt shown on your graphic.
I'm not questioning your knowledge. And I thank you for sharing it.
Yep, I have very little clues about geology, I don't pretend to know anything. But gold is where you find it. So.etimes it is where it shouldn't be.
 
If you look at the shafts you will see that there are three roughly parallel mineralized reef zones, each about 16 km in length, Ballarat West, Ballarat East and Little Bendigo. Something that is not obvious if you are just wandering around with no control. The GSV mineral localities layer can be separated by those with any GIS expertise into alluvial and hard-rock gold shafts (i.e. separate attributes) so that you can define source areas for all Victorian goldfields, not just Ballarat. You can then call up the stream layer and superimpose it on the hard-rock shafts, and sketch in the boundaries of the areas worth detecting.

In some cases there is also a lead layer, and some of the buried leads can have a vastly different course to modern streams and even be cut by them, Where such a layer exists it can also be superimposed, as these can become gold source areas for modern streams where cut by them. You can also call up rock type layers (avoid granite in most of central Victoria, avoid Tertiary basalt flow, avoid areas of young alluvium far from the edge of hills, focus on Devonian or older rocks in Victoria for gold). Superimpose them all as on this map.

The reason hard-rock shafts occur over a greater width in some areas is because in detail there are really two mineralized zones close together at Little Bendigo (Nerrina) and three at Ballarat West. So if you zero in to a larger scale on the areas you choose, you can see these zones start to separate into separate linear zones and focus your efforts even more.

New Project (3).gifgoldierocks I made a map of veins for a larger region of Victoria. Its incredible to see the parallel mineralized reef zones you were talking about in your post above delineated like this. Like you say, zoom in to separate linear zones and focus your search downhill and along the structural projection of the reefs.
 
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View attachment 7989goldierocks I made a map of veins for a larger region of Victoria. Its incredible to see the parallel mineralized reef zones you were talking about in your post above delineated like this. Like you say, zoom in to separate linear zones and focus your search downhill and along the structural projection of the reefs.
Yes - once you recognize the patterns it makes the search easier.

It is similar in the NT region (Pine Creek belt) once you add the minor occurrences not shown on my NT map above. The map only shows a small percentage of the gold occurrences (the big ones mined in the past). Many early woekers thought the Victorian gold was related to granite contacts but once you see the extent of linear zones it becomes obvious that in the main the pattern is unrelated to individual granites.

I would emphasize that that does not mean that gold is not related to granite elsewhere (eg North Queensland,, or central west NSW where both types occur). For example, Cadia and Browns Creek are granite-related, Hill End and Gundagai probably not. Young is in a fault-zone that cuts through granite (so it is spatially related to a granite older than it, but unrelated genetically to the granite - the granite was probably simply already there when the gold came in.

Here is a map around Cadia, Cowal etc - "Ordovician Magmatic Centre" means granite. Note how closely the gold is related spatially to the granites (mostly within them or within a few hundred metres of them).

1676586533829.png
Note that they are mostly on the contacts of the granite areas and just within the granites (give or take a couple of hundred metres at most). This is the big clue - they can still appear to form short, linear trends where the granites are elongated north-south (as some of these are).
I am over-simplifying slightly - "Ordovician volcanic centre" also includes lavas, but mostly with a composition similar to granite (essentially granite that has flowed out at surface).
 
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I recently saw a doco one on the McQuarie Arc in which the above goldfields are situated.
Gives some idea of how the rocks formed and the complicated tectonic history of the area.
There is a doco on You Tube about this area called "Islands of Gold in an Ocean of Land - The Macquarie Arc".
There are lots of other stuff on you tube if you can find them. Another interesting one is on the discovery of the Stavely Arc in Victoria.
Good viewing and explained well and well recommended for all prospectors to get some sense of geologic history.
 
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I recently saw a doco one on the McQuarie Arc in which the above goldfields are situated.
Gives some idea of how the rocks formed and the complicated tectonic history of the area.
There is a doco on You Tube about this area called "Islands of Gold in an Ocean of Land - The Macquarie Arc".
There are lots of other stuff on you tube if you can find them. Another interesting one is on the discovery of the Stavely Arc in Victoria.
Good viewing and explained well and well recommended for all prospectors to get some sense of geologic history.


Thanks Hawkear, That's a really good video. It explains geology in laymen's terms.
 
I'd love to learn more WalnLiz. I've heard a lot about you both and your adventures through a mutual friend. Keep well and hopefully see you in WA next year :)
regards
Jav
 
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10 Ounces of Alluvial & Eluvial Gold from the Bathurst Region of NSW

Firstly lets identify the difference...."Alluvial" gold is gold that has weathered from primary reefs and made its way to either ancient or modern water courses. Within these water courses it is moved by the stream or river and generally ends up on or near the bottom of these streams. Water action on these nuggets tends to erode the edges and as such are generally well rounded having few if any sharp edges.

"Eluvial" gold is gold that has weathered from a primary source and not made its way to a river or stream. It tends to be rough in nature with either sharp edges or a "prickly" formation, with in many cases the host rock still attached....we call these "species" and can quite often be large in size if they have only weathered a short distance from the parent reef. This is the gold that I most like to chase as many small stringer reefs were either missed or not substantial enough for the old timers to bother with. They were chasing the mother loads from large reefs and were extremely good at finding them to the point of very few were ever missed.

Successful detecting for these nuggets on a consistent basis is not a matter of luck and learning a few basics will greatly increase your chances of getting more rattles in your jar. Firstly, understanding how to read a geological map and by that I mean not just looking at rock structures in the areas you are searching. There are many more important things to look for such as "strike" and "dip", sheer or fault zones, uplifts and folding, direction of weathering, and the list goes on. It's worth taking the time to familiarize yourself with these as, when you overlay a topographic map to these areas you can soon establish which streams run through them and which direction they are travelling. These "geo" maps also show areas which have metamorphic zones and when they coincide with a fault zone in a gold bearing area you can very much narrow down where the best spots will be to start your research.

In NSW most of our gold fields tend to be at high elevation and as such make them very desirable for the detector operators who do their homework. Being high in elevation many of the smaller streams and creek beds have long bedrock sections and shallow overburden which makes them prime targets for the better PI machines and operators, as the gold is usually well within reach. Being able to isolate some tell tail signs like distinguishing greenstone from shalestone caused from metamorphic action by heat and pressure is also a good thing to know and learn, as being able to identify these areas will put you closer to the better gold.

Many of these high level gold deposits are also very rich in reef zones and shafts are common on almost every gold bearing area. This is where those who chase "Eluvial" gold can have some very rewarding finds if they can isolate some of the smaller stringer reefs that the old timers didn't bother about, and believe me when I say a very large number of these still exist to this very day. One small such stringer rewarded me with several ounces of rough gold from an area of less than 50 sq. metres from the primary source. They do exist and once you know what to look for, are not that uncommon to come across. My advice to the newcomers is keep well away from the larger shafts as when the old timers loamed their way up to them they didn't miss much. Also these deeper shafts saw a lot of action over considerable time, plus most of the miners camped on or near these shafts leaving huge amounts of accumulated rubbish strewn all over the place. Not fun when detecting. You will find that most of these shafts are in a line and follow fault zones. In my experience searching areas further up from these shafts are the most rewarding, remembering these hills/ mountains were hundreds of metres higher millions of years ago.

Successful detector operators are also the ones that take the time to become one with their machines. Coil selection also plays a big role. Not much benefit in running a large coil in a small stream/creek or a small coil for "eluvial" on the side of a mountain. Pretty obvious you might say but I have witnessed on many occasions wrong coil size has led to negative results in areas where they should have found a nugget. Pulse Induction or similar format machines are a must on our goldfields and will find more than 90% of the gold. VLF machines will find gold but with much less consistency coupled with a big headache from all the ground noise one has to contend with. If you want to be serious about getting good consistent gold, get a minimum of a GPX4500, 5000, 6000 Z7000 or SDC. As with any trade the better your tools the better your outcome.

There is a saying amongst fishermen that goes...10% of the fishermen catch 90% of the fish. The same goes for prospectors and that 10% get 90% of the gold. It is those who dedicate themselves to their craft and learn their trade who eventually become successful. One might say... but you still have to walk over that nugget so luck has some input. To that I say those who know "where" to walk, will walk over many more nuggets in the long run and make their own luck rather than rely on luck itself......may that big paddock be kind to you and may a large proportion of your targets be positive. Cheers Wal.

Below is a video of what type of creeks we tend to look for when chasing NSW alluvial gold.


Wow, I've been watching and subscribed to your Youtube channel for years.
 

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