Gold and Quartz geology

[Cappy Z.]

It is no secret that veins of white quartz have gold seams. When the quartz was liquid as was the gold it was deposited into cracks and became veins once cooled and hardened. My question is, how did the gold coagulate in these specific amounts? Were the gold molecules 'attracted' to each other and 'melted' together? Since the gold in quartz model is so prevalent does the quartz have some ability to attract gold when molten? Kind of like a magic wand attracting the iron filings in that kids game? It seems that when liquid at high temperatures the quartz becomes a readily available boat to carry the gold until its cooled. I suppose I am wondering if this could be repeated in a controlled scientific experiment?

 

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[mamabear]

am waiting to see what the answer is Cappy. It never ceases to amaze me how deposits occur. we have large seams of white clay that is perfect for firing, but how can it be so thick in one spot, & an inch away none. have you ever seen the books A Roadside Geology of - - - , WA, ID etc. they are great books. I found them quite informative, but just led to more questions. would love to be a professional student.

 

[Cappy Z.]

Thanks for posting Mamabear. The reason I ask the question about repeating mother natures activity in the science lab is because I think if we ever find a way to extract gold from sea water, the formula if you will, starts and ends with reverse engineering. It is a known fact that gold is added to glass to give it a red color. Glass of course is not dissimilar to volcanic magma particularly quartz. It seems to reason that during the volcanic processes whereby magma is pushed under great pressure into fractured crevasses and gold comes along for the ride, the gold must be coming from underground seawater. Maybe some chemical property in the white quartz 'attracts' the gold. Also maybe the white quartz facilitates the clumping of gold atoms as an amalgam would. Hence attempts at reverse engineering in the lab might offer the Philosophers Stone up for grabs.

 

[3xflyfisher]

Cappy,

The primary deposition of gold and gold bearing minerals are hydrothermal in nature. This means that the Au is carried in a solution associated with volcanic activity. As the solution and the surrounding host rock begin to to cool the Au then precipitates in the host rock. There are phase diagrams that have been developed that show silica minerals (quartz and others) and gold are deposited/precipitated at nearly the same temperatures (if I remember correctly quartz is slightly higher in temp), thus the association of Au with quartz. Other than the temperature relationship, quartz does not "attract" gold. Of course there are exceptions to this but generally this is how Au is deposited in volcanic host rocks. Many times other minerals are associated with the hydrothermal deposition of gold including sulfides, tellurides etc.
Another deposition process may be that a volcanic event occurs in existing rocks and forces gold bearing solutions into the cracks and fractures of the host rock creating vein structures in said host rock.
It is then the erosion of these deposition processes by wind, water, ice etc. that remove and free the gold from the host rock and when liberated the gold is then found in placer deposits (where dredging and panning would occur).
This is a very general explanation so hopefully someone else will chime in if you want a more in-depth answer. There are all sorts of geochemical/physics actions that complicate the gold deposition process.

Hope this helps.
3xflyfisher

 

[Cappy Z.]

Thanks 3xFlyfisher for posting. It seems that white quartz is the primary host rock for the gold when the temperature cools. I understand there are other rocks, but it seems white quartz has a greater claim on being found with gold. Also, I wonder how gold nuggets are formed in various sizes? Why one hears of 5 pound nuggets but most are pickers? I wonder what the geological processes were that allowed for a giant gold nugget to be formed. I sense there are clues here that would add to the understanding of how gold is formed and where it can be found. Recent articles I've read state on the ocean floors and continental shelves there are large concentrations of gold, not just dissolved in the water. Again, thanks for responding.

 

[Eu_citzen]

The thing with quartz and hydrothermal actions is they can pass through much rocks and dissolve minerals from the surrounding rocks.
As it then begins to cool it will deposit these minerals - which then occur in a more concentrated state then it did in the rocks it was dissolved from.
Most of the time!

As for the chemistry part, gold can occur as ions; Gold(I) and Gold(III) I think occur naturally. Not certain though.

Often (mostly?) they tend to go attract Chloride - Gold Chloride is water soluble.

As far has large nuggets are formed - that's still up for discussion I think.
Logically there has to be enough space, time and of course gold (chloride) present to make a large nugget.
That's my theory - A lot of gold has to crystallize out of solution and clump together.

 

[3xflyfisher]

I believe all nuggets are formed exclusively by the erosion of the original deposition of gold. Here in Colorado there have been many "nuggets" found that are are crystalline and very large (up to 8lbs if I remember correctly. These have been found more in alluvium or deposits that have not been transported, or transported far by water. Once the coarse gold is in a stream or river other erosional forces take over as the gold bounces and tumbles along the stream bed (think sand blasting but with water as the transport medium rather than compressed air), thus making coarse gold a nugget (rounded like landscaping river rock). Through this process a large crystalline nugget will break down into smaller pieces and become the pickers you mentioned and also the flour gold that many weekend prospectors recover. The closer to the source the coarser the gold is. Of course there are exceptions to this such as deposits in metamorphic rocks rather than volcanic rocks. In metamorphic situations while similar there are other forces/reactions taking place. I have a sample where the gold has precipitated onto various oxide and hydroxides of copper and while I am not sure, this may be a case of gold chloride precipitated the precious metal.

As far as size, depending on the conditions at the time of the original deposit any thing or size is possible. There a many many variables involved and also volumes of research discussing these variables thus this discussion could go on indefinitely. Eucitizen is right though that depending on the chemistry involved with a particular volcanic event, the gold chlorides can and do greatly contribute to the primary deposition of Au. Eu also is correct in that depending on the actual conditions involved in a particular deposition event there can be a cycle or multiple cycles of deposition/dissolving of the gold concentrating it through these cycles.

I think it appears that gold has an affinity for quartz since that is the type of specimens that most collectors prize, hence when found many are saved for the specimen value. In Nevada, many of the current large open pit mines operating show no or very little visible gold. It is microscopic and disseminated nearly equally through the host rock that is a nondescript tan/brown/gray (ugly!) rock, but can show high values of gold.

I am sure you have heard of the "black smokers" that have been discovered on the ocean floor. These can and do deposit precious metals that if on the surface would be economical to mine. Also associated with the smokers are silver, copper, lead, zinc and a myriad of other metals. But due to the depths of these it is not economical to recover these values.

Have a good'one,

3xflyfisher

 

[GoldDriller]

gold chloride can be extracted from quartz rocks through a process I have researched and developed called an " Obverse Process" . Basically a reverse engineering scientific technique of natures way of the centuries old process of the degrading process of the gold atom into its last stages of its existence . Reversing the death of a gold atom back into the metallic state. Being for the reason for the meaning of the term ,,,, " Obverse Process" ..

 

[DDancer]

Death of a gold atom? Really? Sorry don't buy that. Atoms don't die though materials in the trans-uranium series do change due to atomic decay. I don't consider that death and while the process can be reversed it requires a lot of effort. Gold does not lose its properties just because its locked into another matrix or chemical bond.

Bit lengthy....

Nitric,
The precipitation of gold from solution is pretty much the same whether its from and aqua regia solution or due to high temperature hydrothermal events. It involves and exchange of ionic carriers that gold can interact with to both allow gold to move into a solution and later be released as a solid.

Probably the most basic way to explain why gold and quartz are so strongly associated was hit apon by 3xfly and EU but not simplified. Both are correct and complement each other. In nature think of plain old water as a universal solvent. Put that solvent under high heat and pressure and it picks up other less solvent materials, ie silicon dioxide *quartz*, more solvent materials like chlorine and sulfur rich materials, ie salts and sulfides, and then interacts with a basically but not totally inert material like gold.
Bear in mind that the solvent has to pass thru a region where both the silica's and gold are present.

Due to the heat and pressure our quartz and gold move into this mobile solvent, water, and along the way push up thru the cracks and crevasses of less reactive rocks. At some point in time the solvent looses the properties, heat and or pressure, to maintain the dissolved materials its carrying. This allows the materials to resume their previous solid state. *just like normal salt does when the water evaporates another reference is to look up super saturated fluids*

Because of the point that these materials return to their solid state and leave the solvent, water, one forms before the other.... silica's will drop out of solution before chlorides or sulfides which carry gold.. and silica's being the most dominate material in the solution form your quartz veins. Now for the gold to drop out of solution one of two things will have to occur. Either the solution now contains other materials that will uncouple the gold from its solution form, other ionic materials, or the material the gold is attached to is so weakly bonded that it naturally drops out of solution. Now the process is not uniform. Some gold will be trapped in the forming quartz, whether in its crystal or in pockets, but most is forced to the boundary layer between the forming quartz and the host rock the solution has pushed up thru... ei the crack.
This boundary layer is what miners look for unless the gold is just all thru the quartz.

Gold in the crack well if the gold remains with its carrier~ chlorides or sulfides~ then there is little to no free gold in the ore or resulting placer deposits.
If the gold reacts with another material and precipitates out of solution often the gold will form seed crystals and grow just like any crystal. The same would occur if the gold is only weakly bonded to its carrier. Due to other materials in the solution gold generally will not form massive crystals unless its verrrryyy pure.

Gold nuggets. A gold nugget is just a large bit of gold found in a placer deposit. Lots of names describe them but its just a bit of metal. In rare cases crystalline. Gold found in its host rock is considered a specimen but that wont deter someone from removing the host rock on a large bit and calling it a nugget as well.

Thanks for reading. Not looking for total accuracy, just simplification. I do believe the experiments have been performed Cappy.

 

[huntsman53]

Quartz has a higher melting point (Quartz 1650 degrees Celsius) than Gold (1064 degrees Celsius) and will thus harden and cool quicker. I believe that the outer layers of Quartz as it cools, creates a vacuum effect similar to placing a candle or burning item in a jar, snuffing the flame or fire out and as the inside of the jar cools, it creates a vacuum. This is not unlike the atmospere where warm/hot = high pressure and cool/cold = low pressure and high pressure always flows towards low pressure (i.e. warm/hot flows to cool/cold). Therefore, Gold is not only forced into cracks in the Quartz due to volcanic activity and extreme squeeze pressure (weight of the earth over top of it), I believe it is also sucked into the cracks due to the process above.


Frank

 

[DDancer]

I'm not aware of a process that works as your describing it. All the gold in quartz specimens I've ever seen and taken apart indicate to me that the gold is trapped in the growing quartz matrix. As the matrix grows the crystals literally smash the gold in between them or trap bits of it inside cavities between crystals. I've recovered gold from very crystalline quartz outcrops and found bits of gold inside the samples that appear to be faceted, crystalline, but are in fact just faced due to contact with the surrounding crystals. The alternative method of the gold being between the crystals is that those happened to be the gaps available for it as it dropped out of solution.

Quartz formations are associated with hydrothermal events. They are water derived, not magma derived, formations. What I mean is that the silicates deposited in quartz formations are not a result of melting the quartz, or the gold for that mater, but from dissolving the base elements into high temperature, high pressure water. The resulting formations are created much as I laid out previously.