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Earthquakes Deposit Gold In Fault Zones 55

Posted by samzenpus
from the shake-rattle-and-gold dept.
sciencehabit writes "Gold deposits may be created in a flash—literally. Along fault zones deep within Earth's crust, small cavities filled with fluids rich in dissolved substances such as gold and silicate minerals can expand suddenly to as much as 130,000 times their former size during a major earthquake, a new analysis suggests. In such circumstances, pressure drops accordingly, driving a process the scientists call flash evaporation. And when the pressure in the cavity suddenly drops, so does the solubility of minerals in the water there. Along with substantial quantities of quartz, large earthquakes could deposit as much as 0.1 milligrams of gold along each square meter of a fault zone's surface in just a fraction of a second Typical rates of seismicity along a fault, such as the San Andreas fault zone shown in the main image, could generate a 100-metric-ton deposit of gold in less than 100,000 years."
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Earthquakes Deposit Gold In Fault Zones

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  • by jfalcon (163956) on Monday March 18, 2013 @10:02AM (#43202621) Homepage Journal

    Much like a cross between Goldfinger and View to a Kill.

  • 1kg a year (Score:4, Informative)

    by RichMan (8097) on Monday March 18, 2013 @10:03AM (#43202631)

    100 metric tons/ 100,000 years
    1 metric tonne/1000 years
    1000kg /1000 years

    1kg/year

  • It is like a modern day Gold Rush.

  • by khallow (566160) on Monday March 18, 2013 @10:12AM (#43202711)
    There doesn't seem to be much point to the observation since the gold can dissolve again, perhaps even within a few minutes of the end of the earthquake (it is hot down there, especially after a big earthquake).
    • by Anonymous Coward

      A single event is economically irrelevant for other reasons (see above comment about the huge volume over which it is spread), but it won't become soluble again very easily unless fluid pressures and temperatures rise considerably, and the gold will be trapped in the quartz anyway (i.e. the new fractures created by the next pulse of high pressure fluid will break the quartz rather than dissolve it significantly before it cools again). Even If there is any re-dissolution, it will probably re-precipitate out

      • by khallow (566160)

        unless fluid pressures and temperatures rise considerably

        Let us recall, that was why the gold was there in the first place. It was originally dissolved in solution because of high fluid pressures and temperatures. I'm pretty sure temperature actually increases after an earthquake, so in order for precipitation to occur and stay, either the pressure has to drop and stay dropped, or gold becomes trapped as you claim.

        Even If there is any re-dissolution, it will probably re-precipitate out again shortly and nearby

        Why? Gold is no more likely to precipitate, if it's been in solution for a long time versus a short time. And why wouldn't have done so in the absence

    • by Anonymous Coward

      It might not be practically useful information but at least now we might know why exactly so much gold is found around California and Alaska and other fault lines. Has Iceland ever had a gold rush?

      • by MarkRose (820682)

        There is gold everywhere, but yes, fault lines are a great way to find certain kinds of gold deposits. If you want more information on why gold ends up where it does, I highly recommend a series of videos put out by the Sprott Group on ore deposists [youtube.com].

  • quick... send that nasaly-voiced old man to look for the glory hole!
  • Miners Know (Score:5, Interesting)

    by A10Mechanic (1056868) on Monday March 18, 2013 @11:50AM (#43203637)
    When I was younger, we'd explore the old 1800's silver mines at Alta, Utah. When the old miners hit a fault line (underground), they'd span out and mine that fault for all it was worth. It was pretty neat for us finding a rock face perfectly smooth and straight (the fault), that had been stoped out a hundred years ago, miles underground. It was like going back in time. In hindsight, it was probably dangerous... Ah, youth.
  • Sea water contains so much of salt of every metal there is. Thousands of tons of gold exists in the sea water. Just the cost of extraction far outweighs the value of the extracted metal.
    • Just the cost of extraction far outweighs the value of the extracted metal.

      Indeed. The concentration of gold in seawater is about 50 ppq (parts per quadrillion). That is less than two ounces for every cubic mile of water. It is implausible that it will ever be economical to extract gold from seawater.

      • by Anonymous Coward

        It's actually more like 92lbs/ mi^3. http://www.webelements.com/gold/ [webelements.com] quotes sea water values at 10 nanograms/Liter.

        • It's actually more like 92lbs/ mi^3. http://www.webelements.com/gold/ [webelements.com] quotes sea water values at 10 nanograms/Liter.

          No, the page you reference just pulls that number out of thin air, and even admits to doing so by saying that "perhaps" that is the concentration. Much more detailed information is here: Gold in Seawater [wikipedia.org], which quotes a figure about a thousand times less.

          This article [newscientist.com] states that people used to think seawater has much more gold than is estimated today, so that my explain your estimate.

          But if you want to extract gold (or anything else) from seawater, you would probably start with the effluent brine from a d

          • by istartedi (132515)

            ut if you want to extract gold (or anything else) from seawater, you would probably start with the effluent brine from a desalination plant. That way it is already partially concentrated, and may already be pumped up above sea level so you could use gravity to move it through your extraction mechanism.

            You could also find a natural salt flat left over from an ancient sea. These things exist of course, and they are mined... for salt. Even with all the water extracted, it's still not economical to separate

          • by cusco (717999)
            Sewage is a considerably better source.

            "http://pinktentacle.com/2009/01/gold-mined-from-sewage-sludge/"

            A sewage plant in Japan's Nagano prefecture has started mining gold from sludge, earning a cool 5 million yen ($56,000) in its first month of operation.
  • by Anonymous Coward

    The oceans contain about 20 million tons [noaa.gov] of gold, dissolved in the seawater and on the seabed, eclipsing the worlds current stock of mined gold by more than 100 times.

    Ironically, those promoting a gold standard for financial stability, would ensure that hyperinflation occurs in the future; as soon as innovations in nanotechnology, make the cost of extracting gold from seawater affordable/cheap, the value of gold itself will then plummet as its availability increases, causing inflation and eventually hyperin

  • by Diamonddavej (851495) on Monday March 18, 2013 @03:20PM (#43206315)

    Weatherley and Henley investigated a mesothermal gold deposit, the Revenge Mine in Australia (also known as orogenic gold deposits). These gold deposits form deep underground during mountain building events, generally 3 to 20 km deep, where greater hydrostatic pressures normally prevent fluids from boiling. Previously, geologists speculated that mesothermal gold ore was deposited when fluids cooled or interacted with other fluids with a different chemistry, not so it seems. Weatherley and Henley claim that, even at great depths and pressures, fluid pressure in a fault zone can momentarily approach zero during an earthquake, this is a great surprise. Also, the (normal) temperature and pressures during the formation of the Revenge Mine deposit was 1675 to 2075 bars and 425 to 525 C, this suggests the water was a Supercritical Fluid. I wonder if a phase change from supercritical fluid to a gas facilitated the precipitation of gold.

    Also, it should be pointed out that role of Earthquakes in the formation of gold and other mineral deposits has been acknowledged for decades (in particular the near surface epithermal fault hosted gold-silver veins). Epithermal deposits are formed near the surface (generally less than 1 km), the frequent occurrence of breccias, broken rock fragments and voids in the faults attests to vigorous fluid boiling. One famous example of earthquake provoked mineralisation is the San Andreas fault, where hot springs issuing from the fault zone emit more arsenic and mercury after an earthquake, gold is presumably deposited at depth as well e.g.

    Sibson, R.H. 1987. Earthquake rupturing as a mineralizing agent in hydrothermal systems. Geology 15(8), 701-704.

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