Gold and graphite

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Hi gang, I can't seem to upload an image of a piece of quartz with a layer of graphite attached to it. Usually graphite is an indicator, and where it meets with quartz you can find a heap of gold. I'll try to upload again.
....sorry nothing is happening
 
A reef near home has lots of quartz with a different rock attached and between the layers is where I've found some gold. But from the same mine there has been a lot of graphite removed and piled in the dump heaps. As you say, possibly a good indicator.

As a side note, graphite will display as non-ferrous on a VLF and give quite an alluring signal...which can be quite a pain in the a$$ when digging through piles of the stuff.
 
Ok. I'd heard of gold being associated with slate, not with graphite. I know a thin line of slate can be an indicator in source rock Quartz/gold mining. Cheers
 
Gold is where you find it. It could be anywhere. But I've always found my gold in association with quartz and ironstone. I'm not 100% sure if the stuff I've got is in fact graphite. Shale and slate are both metamorphic rocks and are relatively hard. This stuff feels smooth and it leaves a grey line on paper. It glows red when heated and heats up real quick. A graphite/carbon line is an indicator, probably pencil in thickness and run east west direction. Where it intersects a quartz reef, running north/south you get a mother lode of gold, usually a HUGE nugget. If you ever been to the tourist mine at Ballarat you would know what I mean.
As Northeast put it, there was a mine with heaps of graphite, I'll bet they found some really big stuff.
I'll try and upload the pic, if it doesn't come up can someone tell me what's gone wrong, I had no problems before...her goes. Bugger, maybe a moderator can tell me what I'm doing wrong.
 
Hi Heatho, I think I've got something wrong at my end. I can open all the boxes except the 6th one from the left. (the one to insert a pic) It stays on for a second then disappears. It's only after when I exit from the forum that it reappears, by then it sends the image to god knows where as I'm no longer on the site. Make sense?
I've been to the computer repair shop for other issues, maybe I've got a problem somewhere. Thanks for trying to help me......alex
 
Dig'n-it said:
Ok. I'd heard of gold being associated with slate, not with graphite. I know a thin line of slate can be an indicator in source rock Quartz/gold mining. Cheers
Gold is frequently associated with graphite, and black slate usually contains graphite
 
Gday all, from what I remember reading- when the hydrothermal fluids carrying the gold come into contact with reduced ground water it will cause the gold to come out of solution(chemical reaction) and be deposited. The ground water is reduced by the carbon content in the black slate or graphite or any other mineral containing carbon it travels through.
 
Hey Jeff
What do you mean by reduced ground water?
I understand the effects of huge crustal pressure, water that has seeped down from the surface, and heat causes hydrothermal fluids to be forced up through the weak cracks and faults in the earths crust and as the fluid rises and cools gold solidifies in the form of gold infused Quartz; And where the fluid is forced in to a flat make branch spur with intersecting fault containing other host rock like iron stone, slate or graphite (known as an indicator) a just right chemical reaction and drop in pressure at the intersecting fault causes nuggety gold to form. I hope I have this right, and happy to be corrected if not. Cheers
 
Reduced is the opposite of oxidised - it is water low in oxygen (chemists would say low oxygen fugacity, but don't worry about names). With certain types of gold deposit, the ore fluids are hot and reduced and neither acid or alkaline (intermediate pH - but don't worry re names)- in water of this probable metamorphic origin that rises from many km depth, significant hydrogen sulphide can be present. Hydrogen sulphide bonds with gold as gold bisulphide complex and in this way the water can carry a lot of dissolved gold (ordinary fresh water would not dissolve gold). This water rises to shallow depth where it hits ironstone or carbon and the gold bisulphide ion reacts with either of these to deposit metallic gold (e.g. if it reacts with iron the sulphur will form pyrite - iron sulphide - from the sulphur in solution as the gold drops out, so you will see pyrite and gold together with ironstone and carbon-rich slate). This ironstone is commonly magnetite because the iron minerals hematite and limonite do not cause the same effective reaction. So there is a good chemical reason why gold occurs associated with ironstone (eg Hill 50 at Mt Magnet) or carbon-rich slate (eg Bendigo).

This is not the only way that gold moves around. In the low-temperature zone of weathering close to surface, the pyrite in an already-formed gold ore body will oxidise (in contact with oxygen-rich rainwater) to form acid (low pH) water and if the water is very saline like in the outback, the gold will dissolve as a gold chloride complex (ie salty water contains sodium chloride, common salt). Ordinary dilute (non-acid, non-alkaline but neutral pH) rain water will not dissolve gold but highly saline and acid groundwater formed from rain and salt and oxidising pyrite will). This will trickle to greater depth with its contained gold (only tens of metres as a rule) and react with ironstone to deposit gold again. This is where you commonly see coarse gold associated with weathering ironstone (ferricrete), often in rock that is altered to white kaolin clay. A lot of the ironstone will be hematite and limonite in this case. Sometimes bauxite is also present (an extreme aluminium-rich product of weathering formed when even the silica gets dissolved out of clay to form aluminium minerals such as gibbsite and diaspore without silica). The upper levels of Boddington were of this type, and bauxite (aluminium ore) was produced as a by-product, but nowadays they mine the original primary ore at greater depth below the bauxite, clay and ironstone (ie in deeper in fresh rock).

I can understand how these two different processes can become confused in people's minds when they read different accounts, one discussing how the original high temperature gold deposit forms, the other discussing how the ore deposit is subsequently modified by weathering near surface. I hope I have made it clearer.

Of course some gold deposits can form by other means, but are less common (eg if you heat rock salt deposits buried in rocks at depth and dissolve them, gold can travel to shallow depths in these hot fluids, also as gold chloride complexes, and be reduced and deposit gold when they hit ironstone at shallower depth (eg gold around Cloncurry such as Ernest Henry, or perhaps Olympic Dam and Tennant Creek ore bodies).

Another method is in very hot chloride and hydrogen sulphide-rich fluids that are emitted from molten igneous intrusive bodies (eg Cadia).

And once any of these high temperature gold deposits form, they can also be later modified in the weathering zone as described above....

This is why gold is not simply "where you find it" - it forms in specific places following well-understood chemical processes. So a bit of knowledge increases your odds of success....
 
A drop in pressure can also form gold to form as stated above. The drop in pressure of a liquid containing bisulphide-complexed gold causes dissolved hydrogen sulphide to separate out of the liquid as a gas (and escape). Because there is less hydrogen sulphide remaining in the liquid, it can carry less gold, so some gold drops out as native gold.
 
Hey Dign it, ha what he said!

Loved your answer Goldierocks. Fascinating.
In line with the whole supergene topic- sometimes when Im out detecting and Im looking at a suspicious looking quartz reef, in a gold producing area, sometimes not even a couple of hundred metres from a known producing reef, the suspicious looking reef has obvious mineralisation, but Im getting no evidence of any gold, could it be that this process has removed all the gold to depth?
 
Jeff said:
Hey Dign it, ha what he said!

Loved your answer Goldierocks. Fascinating.
In line with the whole supergene topic- sometimes when Im out detecting and Im looking at a suspicious looking quartz reef, in a gold producing area, sometimes not even a couple of hundred metres from a known producing reef, the suspicious looking reef has obvious mineralisation, but Im getting no evidence of any gold, could it be that this process has removed all the gold to depth?

It depends where you are. For example, in places liken the Eastern Goldfields of WA there is deep weathering preserved from back in the Cenozoic (when it was wet and warm), it is quite likely that it can have been leached. But you would not be seeing fresh rock but your quartz veins would be in clay, or in soft weathered rock, probably with ironstone spread around. Sometimes we drill to 10 to 30 m (drill "refusal") before we see gold values.

In the highlands of Eastern Australia, the uplift has created topographic relief and the old Cenozoic weathering surface is partly to totally stripped, so fresh rock is exposed. Complete removal of gold is unlikely.

And of course, most quartz reefs never contained significant gold, and those that do only contain it in specific sections.
 
The main relevance to detecting is where to look in deeply weathered areas. Areas like where gullies cut through to the base of the weathering zone, or where later erosion has removed the upper part of the weathering zone (assuming you also have a gold-mineralised structure).
 
Ok thanks for the interesting reply Goldierocks. Im prospecting a field in the eastern highlands, most of the host rocks are Ordovician turbidites and only a foot or so below the more resilient quarts. So I guess not in this case.

Gday Tathradj your finding deeply weathered stuff around Nerrigundah?
That place is relatively close to me I was going to suss it out.
 

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