gold growing

[Deleted]

some food for thought. Central otago has similar evidence of gold "growing" . Thanks go to PMAV for the article

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TRIANGLE GOLD (article)

Why is Victoria Nugget rich?
Conventional thinking insists that gold nuggets originate from quartz reefs where they were formed by the reaction of gold-bearing fluids with chemically reactive (usually carbon-rich) indicator beds adjacent to the reefs. Such thinking cannot explain why the Golden Triangle accounts for more than 90 percent of the nuggets exceeding 500 oz found in the world. Rocks very similar to the sandstones and slates which host the central Victorian gold deposits occur in many goldfields (e.g. Meguma, Canada) and hard-rock masses of gold larger than any reported in Victoria have been found in reefs in New South Wales (e.g. Holtermann Nugget, Hill End- 7,500 oz) and California. Why then are large near-surface nuggets such as occur in the Golden Triangle not found with the same abundance in other goldfields where large masses of gold occur in reefs?The only place in Victoria where a link between reef and near-surface nuggets can be argued with any credibility is Ballarat which produced three-quarters of the state's reef nuggets. The link remains tenuous, however, because the largest mass of gold found in a reef (Lady Don- 600 oz) was only about one-quarter the size of the largest "alluvial" nugget (Welcome- 2,200 oz). In addition, the reef nuggets invariably contained more than 4 percent silver whilst the "alluvial" ones were very pure (e.g. Welcome- 99.2 percent gold).



Nugget in situ Central Vic
If conventional thinking cannot explain the facts, old ideas must be abandoned and new hypotheses considered. The possibility that nuggets can grow in situ from groundwater solutions deserves serious consideration. There is ample evidence that gold can be transported in solution and deposited elsewhere under the low-temperature, low-pressure conditions which prevail at the Earth's surface. Such evidence includes a brass cartridge lying in mine water being completely replaced by gold (Tasmania), a $20 gold coin being recovered from a stream after several decades coated in gold crystals (Alaska), gold impregnations in coal and fossilised wood (Ballarat), gold inside a fossil shell (Croydon, Queensland) and iron concretions in a nugget identical to those in the surrounding soil (Coolgardie, W.A.).

What would be required to grow a large nugget in situ? The basic requirements appear to be:

1. a source of gold

2. a means of dissolving the gold and holding it in a stable form in the groundwater for transportation (probably over considerable distances)

3. steady delivery of dissolved gold to a precipitation site for a long time

4. some nucleating material and a precipitation mechanism.

How could these requirements have been met within the Golden Triangle? A source of gold is no problem given the number of reefs present. The most likely experimentally-proven reaction whereby gold in the reefs could have been dissolved involves chloride and hydrogen ions and oxygen: salt, acid and air in layperson's terms. Salt could have been concentrated in groundwater by evaporation when an arid climate prevailed. Acid could have been produced by the weathering of pyrite (iron sulphide) which is abundant in Victorian reefs. Air would have been present within the pores of the weathered rock above the watertable (the surface below which all the spaces in the rock are filled with water).

Steady delivery of gold to a precipitation site would require a very stable watertable (i.e. one not moving up and down very much). This would entail a low rainfall, a flat land surface and a lack of earth movements. The fact that within a particular area (e.g. Rheola) many nuggets occur at the same depth (and not always on the bottom) could reflect their growth at the same old watertable level. Agents which could cause gold to precipitate include copper, gold, organic matter (such as buried logs) and iron (in the ferrous state).

It can be argued that the Golden Triangle was unique in its ability to grow nuggets for the following reasons:

1. the reefs contained pyrite which weathered to form sulphuric acid

2. the acid was not neutralised because there was little carbonate present in either the reefs or their host rocks

3. at some stage during the Tertiary period (perhaps 5 million years ago) central Victoria had a climate sufficiently arid to generate saline groundwater (it is interesting to note that the distribution of nuggets within Victoria mirrors the distribution of saline groundwater even today)

4. at the same time central Victoria was very flat and free of significant earth movements (the Kosciusko Uplift had not begun) so that the watertable was very stable

5. the region contained iron-rich rocks (e.g. basalt at Ballarat, gabbro at Rheola) to aid precipitation of gold.

If nuggets did grow in situ at old watertables there is a possibility that predictive methods can be used in their location. It should be possible to plot old watertables on cross sections using reported nugget depths. Such surfaces are probably fairly regular (similar to the land surface at the time) but may have been tilted from the horizontal or disrupted by faulting during the Kosciusko Uplift. The trick is to find the intersection of an auriferous old watertable with the present surface in an area where nobody has taken a metal detector yet. The other advice for prospectors is to pay particular attention to areas where iron-rich rocks occur.





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[roscoe]

Hi, HS, Jim Straight, Reno Chris and I had a good discussion about growing gold on Doc`s Metal-detecting forum a few years back. Dunno if I still have the records but a few articles to get the pot boiling:
Biological Gold

RESEARCH SHOWS MICROBES MAY FORM GOLD NUGGETS - 30 January 2002
Gold nuggets may grow underground 'like potatoes', according to a dramatic scientific discovery by researchers in Australia's Co-operative Research Centre for Landscape Environments and Mineral Exploration (CRC LEME).
The prized pieces of bullion have long puzzled prospectors and geologists because they show up in places where there is no obvious local gold concentration from which a large piece of pure metal could have come.
An investigation by CRC LEME doctoral researcher Frank Reith has yielded evidence that the formation of gold nuggets may be the product of generations of soil microbes hard at work. This could lead to significant enhancements in gold discovery and exploitation in Australia.
Mr Reith was studying some microscopic "bubbly" formations on the surface of naturally-occurring flakes of alluvial gold, thought by researchers to be microfossils - the eons-old remnants of bacteria.
"I found some areas on gold flakes that were covered with apparent biofilms - traces of bacterial action. I stained for DNA, and got a positive result, which was suggestive, although this could have come from recent organisms," he explains.
But the test came when Frank tried to grow his own gold nuggets in the lab, and showed that certain tiny soil organisms - both fungi and bacteria - readily deposit gold, building it up in layers "like a miniature coral reef". They did this within a matter of days, piling up the gold atom by atom.
Researchers have long known certain microbes can dissolve gold out of rock. Mr Reith's work indicates they can also transport and precipitate it, or lay it down in a steadily-growing lump, which expands over a long period of time from a tiny flake to a prospector's delight.
The Chief Executive of CRC LEME, Dr Dennis Gee, says Mr Reith's work opens up a new way of thinking about Australian and other landscapes, and may lead to better ways to both find and extract gold and other minerals.
"The gold originated a few billion years ago, several kilometres down in the earth's crust. Over time erosion brought it to the surface and weathering distributed it across the landscape.
"Traditionally we tend to think of gold as a noble element, an inert metal that is mobilised mainly by chemical action. This research opens up the possibility that living organisms are involved in the whole process of mobilising, transporting and re-concentrating alluvial and elluvial (up-slope) gold."
The discovery of signs of bacterial action on gold flakes was made on material from the Tomakin Park gold mine in southeast NSW, and Palmer River in North Queensland but Dr Gee considers that a similar process may apply to all the main alluvial goldfields in Victoria, at Bathurst in NSW, in the Northern Territory and possibly at Coolgardie in WA.
"At Fly Flat, Coolgardie, the early prospectors saw gold nuggets lying on the surface, sparkling in the sun.
"We think these nuggets were formed metres down in the soil by microbial action, and were then gradually exposed by wind erosion and deflation (shrinking) of the surface sediments.
"Possibly these secondary nuggets grew like potatoes in the soil - although it may take millions of years to form a really large one.
"Frank has managed to reconstruct this biological process in the laboratory - making it a very strong probability that this is one way gold nuggets may be formed."
The discovery could have significant commercial implications for gold discovery and exploitation in Australia.
Dr Gee says that the new information may help guide gold exploration in future - by geologists searching for traces of the right microbes in soil.
Mr Reith considers it could also be used to develop an economic and environmentally-friendly biological method for gold extraction and concentration.
Dr Gee adds it could also help improve the "biox" process used to extract gold from the 'refractory' (hard to dissolve) ores, which make up a third of Australia's gold reserves, including some that cannot be economically exploited with present technology.
In this way, the research addresses two of four of Australia's National Research priorities - frontier technologies for industry and sustainability.
The discovery also illustrates how much we still have to learn about what lives in the continent of Australia - more than 99 per cent of our soil microbes remain undescribed by science, Dr Gee says.

[roscoe]

One of the most interesting articles I`ve come across covering chemical formation of nuggets. It`s by one of Australia`s leading experts (now passed away) Professor Allan Wilson

PART ONE

The Genesis of Noble Metal Nuggets

A.F.Wilson
Professor, Department of Geology and Mineralogy, University of Queensland.
A talk given at the 1980 Conference of the Gemmological Association of Australia.

Part One
There may be some who will raise their eyebrows and say ‘How can this be of interest to gemmologists?’ I suggest to you that it would be rather odd to have a fancy diamond wrapped up in a bit of barbed wire! Many of you who go looking for gemstones in creeks could come across nuggets and probably not even know it—and it is high time you knew something about their origin.
Looking at some of the historical information with respect to the gold rushes of the last 100 or so years, I find that there were some suspicions raised very early in the piece by eminent geologists such as Dunstan, and others, who were worried by the fact that sometimes quite large lumps, or nuggets, of gold appeared to have come from veins that were only an inch or so wide. They said ‘This is odd…how can they be due to a lump of gold just weathering out of a small vein and rolling down a hill?’ particularly when they noted the topography of the countryside where the nugget was found. There was no way you could have got a lump of gold rolling down a non-existent hill and have it ending up in a swamp! Also, it was noted that some—but not all, I want to qualify that-- nuggets were found in association with bogs where there was a high carbon content from rotting vegetation, etc.
Then a few astute observers noticed that in some of the mines in the United States, particularly in the Californian goldrush, wood in the mine areas was found to be impregnated with precious gold---pure gold—whereas the gold you get from veins normally has a high percentage of silver in it. That is, when it has formed from the relatively hotter fluid—at depth—you`ll get something like 5% silver—indeed some of the Queensland mines contain up to 30% silver in the gold---that is, the gold is not pure. Now, it turns out that many of the nuggets that were found in the alluvial deposits during the gold rush days (not only in this country, but in other countries as well) were almost pure gold. Mount Morgan is a case in point. That is probably the biggest mine in Australia—it has been operating for 100 years although it is now almost bankrupt. It started with the gold at the top and down the first few hundred feet being as pure as you can ever get and, at the time, this was the purest gold obtained from a mine. In my opinion, this was due to secondary enrichment. The silver and other impurities were leached out—the gold then remaining recrystallised forming new nuggets at higher levels. As you go down below the water table into the parent rock, that is where the silver and other components appear. Now the critics say ‘ Oh, this is nonsense. How can it be you could have gold moving in water and precipitating. Gold doesn`t dissolve.’ People will point out that gold doesn’t dissolve in hydrochloric acid, so this theory gives us a dichotomy. However, recent work has shown that there are ways in which you can make gold move.
Where you can get gold moving in relatively cold solutions, you have a mechanism for moving it and then, where you change the conditions that cause the solutions, the gold can be precipitated. The belief I`ve had for many years is that some nuggets have grown in the bogs and swampy areas; where the gold has come from tiny little veins… this material has come down as atoms or other complexes and there has then been precipitation around a nucleus in relatively cold water and thus the nuggets of new, or second generation gold have grown. I have been researching this for some time now and we have evidence to show this happens.
Let us look at some basic chemistry. Gold may have no electrical charge. It may exist as a solution or colloid (colloidal gold is very, very fine particles, it is used in this form in the treatment of gout by being injected into the body). Under certain conditions, where there is a high pO (this means a lot of oxygen) you can have gold in the form of a hydroxide with a single negative charge—this has been determined experimentally in the laboratory and we do find some of these exist in nature. Another complex is a type of sulphide of gold—these complexes are in solution—with a single charge. Again, gold can form a complex with hydrogen sulphide, also with a single charge, or even a sulphur complex with three charges. These tend to be in a neutral or alkaline situation. It has been found that some of the sodium-rich hot springs in volcanic areas have got gold in them. It has never been actively sought in these places, but traces of gold have been coming out of these springs—but only in this alkaline situation.
Again—in a different way—gold can also exist in an acid type situation where there is a high pO. For example—just near the surface of the ground—under the grass roots—provided acid is present due to—for example—the rotting of pyrites. This produces a different type of sulphur compound to the alkaline situation---the product is a sulphate rather than a sulphide.
Another one that has been known of for some years—though little use has been made of the knowledge—is a gold chloride with a single charge. This has been found in the presence of ferric, not ferrous, sulphate---again with a high pO. This is stable in acid chloride conditions. It was fairly common in Victoria where almost all gold mines in some areas had a lot of iron pyrites present.
Now—the iron pyrites rots, giving sulphur---very acid—and where this occurred near the surface (with high pO) iron sulphate was very common, and you had the ideal situation for gold, in the form of a chloride, to move. Once in the solution, it was then able to start to trickle down very, very slowly…and if you do your sums and look at where the nuggets have been found, most of them have been found in these lower areas. So—they come down in an acid environment, the surface flattens out, it gets into the bogs—where you have a lack of oxygen—the gold then precipitates as it can no longer be held in solution. This is where some of the big nuggets have been found (I would again point out that some big nuggets were released directly from the quartz vein where the rock had disintegrated. These nuggets usually have quite a bit of quartz in them). The nuggets found in the bog areas may have some quartz in them—it may safely be assumed this material was already present in the bog and was ‘gobbled up’ by the gold nugget as it grew.
We now turn to Brazil. In some—or most—tropical areas, humic acids are commonly present—this exists where there is dense vegetation, as in the jungle environment, resulting in perhaps one two or more feet deep rotting vegetation on the ground. It is known that, if oxygen is excluded—as would be the case with this thick layer—humic acid will attack gold very quickly, although this will not happen if carbonates are present. Sulphates, bi-sulphates or nitrates will also prevent the ‘dissolution’ of the gold. However, if there is no oxygen, and chloride is present—as in a salty area—with the gold and the humic acid, the process will take place and the gold will move. It will come down to where it meets carbonates (such as would be found in a river with hard water. Since the humate of gold cannot co-exist with the carbonate, precipitation of the gold takes place.
It has been found that this has actually occurred, and the following comparison will demonstrate.

[roscoe]

PART TWO


Part Two follows
In 1908, gravels were worked to obtain 8.5 grams per ton of placer gold. The specific gravity was 19.56. The same gravels were re-worked in 1926 (18 years later-Roscoe) and gave a yield of 5 grams per ton. Now—you may say this was left behind from the first working which was poorly carried out, however, let us look at this ‘new’ gold. Its surface was quite smooth showing no sign of the abrasions that would occur if it had been rolling around in the gravel. It has a specific gravity of 19.22. In other words, it was different to the gold that had been gathered earlier. This was green gold.
You may have heard of black gold---the Portugese words for this are Ouro Preto, and there is a place with this name in Minas Gerais. The black colour is due to humic encrustation---it is almost identical to greenish gold. The gold is quite pure but, because of its colour, for quite a while it was not recognized and was just thrown away.
Let us look at another difference between placer gold and this new gold. As you know, a usual method of separating gold is by using mercury which forms an amalgam. With placer gold, about 66% will be caught by the mercury, but only about 17-18% of the new gold will be caught by this method. That is, it is not easily picked up by this means because it has different properties with regard to amalgamation. However---using the cyanide method, about 45% of placer gold will be collected, but about 89% of the new gold can be picked up by the cyanide method.
The figures show the difference between detrital gold nuggets, which have obviously formed in a vein, were then weathered out and moved with rocks and gravel to their location, and those second generation nuggets which were formed by the means I have described.
Detrital gold nuggets, picked up and carried along after they had been released show obvious signs of wear with their rounded edges and scratched surfaces—some with quartz in them, have worn away between the quartz parts—obviously this will happenas the gold is comparatively soft. However, nuggets formed by the precipitation and growth method show angular corners, fairly sharp edges may be present as can octahedral crystal faces. These would plainly be worn away if the nugget had been carried along with other material from some other place or origin. Thin gold plates have been found in kaolin---obviously solutions have come down and then the gold has been precipitated. A specimen from California has pure gold crystals like filaments---these wouldn`t last five seconds of being tumbled around in gravels or conglomerates. Another nugget out of a so-called alluvial gold deposit was a gold and gold/silver alloy both with very sharp angles---this was found in a coarse conglomerate and if it had traveled in this material these angles would have been very quickly destroyed as some of the boulders were two to three feet across.
It is not only gold that grows in this manner. A nugget of platinum from the Urals had accretions (possibly from several nuclei which had grown together) rather like warts. Now if the nugget had moved after it had grown, These would have been rubbed down or away altogether, the smooth, shining surface of the specimen shows no evidence whatsoever of any abrasion, therefore it is clearly deducible that it grew in the environment where it was found.
Now, let us look at the platinoids, ruthenium, rhodium, platinum, osmiridium, palladium and osmium. Many a person panning for gold and gems has noticed what they call ‘lead shot’ in the pan and thrown it out---they are throwing out platinoid nuggets (these might look rather like the dental amalgam fillings from your teeth, so don`t think your fillings are falling out). If you have an eye for value, then look at this. At the time (some months ago) (this was in 1980—Roscoe), gold was bringing $350 an ounce, rhodium was $850 an ounce, platinum $510 and osmium $1200!
Incidentally, it is often forgotten (or not known) that platinum can be magnetic; ferro-platinum which has about 12% iron is quite magnetic and when material is being sorted by the use of a magnet to get rid of the iron, this platinum can be thrown out also.
It can be maintained that these platinoids could also move in solution in a similar manner to gold. Platinum is not soluble, but it will form a compound—and if potassium is added to this compound, a yellow powder will precipitate—K2Pt2Cl16—this is the ion—and given the right conditions in nature, the same thing will occur.
Any of the platinum compounds from whatever source in ultra basic rocks such as gabbro, dunite, serpentinite, etc. could disintegrate. For example, the arsenic in platinum arsenite could rot out leaving the ion platinum free to move down to the creeks or whatever situation—that is the sodium chloride platinum will dribble down into a situation where it will contact potassium from,say, a rotting pegmatite, and a yellow powder will precipitate. Incidentally, if these powders were found by someone who didn`t know what they were doing, the powder could easily---and no doubt has been--- be discounted as iron. However, these yellow powders are platiniferous. Under certain conditions, the ground water can affect the compound by releasing the sodium and chloride and thus the platinum nuggets will start to grow.
Gold and platinum nuggets have been found in the same diggings together with gemstones---many gemstone locations in eastern Australia have produced small nuggets and, if you ask around among the old-timers, you may find they have some of the ‘lead shot’ that came out of the dish when they were panning for gemstones or gold.
So, remember, when you are looking around, that while many of the nuggets in this State came from disintegrating veins, many of them formed into this ‘second generation’ gold by the liberating of gold atoms from rotting iron pyrites---these atoms either being carried out to sea or else settling down in a bog to grow into one of these new nuggets.

[RKC]

GOLD NUGGETS

www.abc.net.au/science/broadband/catalyst/ram/Ep10_Gold_Nuggets_hi.ram

Regards,
Rob (RKC)