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#1

Nirvanadirt
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From: Victoria
Joined: 07 January 2021
Posts: 41
Member
10 January 2021 10:16 pm

I'm new on the forum so inn gonna be asking all kinds of weird and sometimes silly questions in a feeble attempt to wrap my head around this whole gold geology subject (reckon it'll take a few more hours on the net, maybe a book or two, another half dozen questions on here and I'll be up to speed with it all and at least at a BD if not masters degree in geology standard of ????????) but as promised I stupidly digress,
So we all know of the giant nuggets through history like the welcome stranger, the one that the kid kicked on a walking track the size of a cricket ball, you know the ones - like the one I'll post in a few months! Well as I understand it these are all "squished" out of quartz reefs or other rock deposits that run in veins and are followed by folk like us after finding a gold vein in said rock. Does that mean that there are 400mm wide gold veins that are sitting in quartz somewhere in the ground waiting to be found or spat out by nature over time?
Do large scale mines follow giant veins underground? If not what is the average size (to simplify let's imagine the gold as a cylindrical vein) of a mid range producing commercial mine? The size of a coke can that narrows and widens as it goes? A roll of life savers?
How is it that we crush quartz to extract powder and little grains from a vein where as there might be a football nugget 20m away and a foot under the top soil? I know that this is a multi faceted question but it's one that I need to tick off for my masters degree ? Cheers guys n gals for any clarification on this phenomenon of big next to tiny (albeit very rarely)

1 user likes this post: aussiefarmer

#2

Ded Driver
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From: West of the Border, WA
Joined: 27 May 2018
Posts: 3,076
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11 January 2021 12:02 am

this thread might interest you Nirvanadirt
https://www.prospectingaustralia.com.au … 98#p438298
Hit the link to the ABC News article on post #18 by Rockhunter62
.. and this
https://www.perthnow.com.au/business/mi … 881204599z

Last edited by Ded Driver (11 January 2021 12:03 am)


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#3

goldierocks
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Joined: 10 January 2015
Posts: 3,100
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11 January 2021 08:39 am

The average size of gold deposits that are mined commercially are hundreds to thousands of metres long, many metres wide, and have around 5 to 9 grams of gold per tonne of rock (so you need 4 to 6 tonnes of rock to get one ounce). That is a big lump of rock (2.5 to 4 cubic metres). They usually consist of a network of small veins, and quartz is not always important but usually present, often with some sulphide minerals like pyrite and arsenopyrite. Low grade mines with ore bodies tens of metres wide can work down to about 1 gram per cubic metre (so you need 30 cubic metres for an ounce. more than a cube of sides 3 m).

Narrow (e.g. tens of cm), high grade (e.g. 1-3 oz/T) single quartz veins are mined in some mines - few mines of this type are large producers (for companies). Individuals and small companies and syndicates make money out of some of these, but most of them involve more than one vein of that type.

Last edited by goldierocks (11 January 2021 08:45 am)


Robert Benchley...
I have kleptomania, but when it gets bad, I take something for it.

#4

Nirvanadirt
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From: Victoria
Joined: 07 January 2021
Posts: 41
Member
11 January 2021 04:44 pm

So how do the large nuggets get created and then deposited or close to the surface Goldbearing areas? I mean did the welcome stranger start off as part of some freak vein of gold in a feed of some kind?

#5

goldierocks
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Joined: 10 January 2015
Posts: 3,100
Member
11 January 2021 05:28 pm

Nirvanadirt wrote:

So how do the large nuggets get created and then deposited or close to the surface Goldbearing areas? I mean did the welcome stranger start off as part of some freak vein of gold in a feed of some kind?

Go to "Where are the alluvial gold bonanzas" #31


Robert Benchley...
I have kleptomania, but when it gets bad, I take something for it.

1 user likes this post: Mackka

#6

UnderEmployedGeo
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Joined: 31 December 2020
Posts: 52
Member
11 January 2021 08:38 pm

It is true that some gold accumulations in some quartz veins is huge - like large enough to create huge nuggets if it were to fall out through weathering. There were old mines in places like southern cross and kambalda that regularly had to post armed guards at the operating faces to guard the gold in the walls - that's how rich it got when it went bonanza grade - you could have hooked out an ounce or two with your hands and chucked it in your pocket probably - nice little bonus!

There is also the theory that some of these nuggets found in elluvial situations - eg in Victoria on hillsides - actually form in the weathered profile through accumulation of gold particles (like hundreds of tiny nuggets coming together in a pool due to gravity) and also through chemical leaching. The dirty secret is that there is probably more than one way and trust me this stuff gets people animated at geological conferences. I have seen evidence of gold crystal formation in the soil profile in these reports - not all nuggets are just weathered crystals, some might have actually formed in place (which is a freaky idea really).


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