Chasing The Wind

Another Lesson To Learn

Great advice for working bends in the creek. Check this out. 

 

Do Earthquakes Create Gold Deposits?

Montana "rocks and rolls" frequently with small tremors displacing dust and tilting the hanging on the cabin wall. Today was no exception. I am a wondering if it does impact gold movement. This insightful article, previous published is worth another read. 

Earthquakes Create Gold Deposits

Earthquakes make gold veins in an instant Pressure changes cause precious metal to deposit each time the crust moves. 

Expand Veins of gold, such as this one trapped in quartz and granite, may deposit when the high-pressure water in which they were dissolved suddenly vaporises during an earthquake. Scientists have long known that veins of gold are formed by mineral deposition from hot fluids flowing through cracks deep in Earth’s crust. But a study published today in Nature Geoscience1 has found that the process can occur almost instantaneously — possibly within a few tenths of a second. The process takes place along 'fault jogs' — sideways zigzag cracks that connect the main fault lines in rock, says first author Dion Weatherley, a seismologist at the University of Queensland in Brisbane, Australia.

When an earthquake hits, the sides of the main fault lines slip along the direction of the fault, rubbing against each other. But the fault jogs simply open up. Weatherley and his co-author, geochemist Richard Henley at the Australian National University in Canberra, wondered what happens to fluids circulating through these fault jogs at the time of the earthquake. What their calculations revealed was stunning: a rapid depressurization that sees the normal high-pressure conditions deep within Earth drop to pressures close to those we experience at the surface.

For example, a magnitude-4 earthquake at a depth of 11 kilometres would cause the pressure in a suddenly opening fault jog to drop from 290 megapascals (MPa) to 0.2 MPa. (By comparison, air pressure at sea level is 0.1 MPa.) “So you’re looking at a 1,000-fold reduction in pressure,” Weatherley says. Flash in the pan Related stories Gold-digging bacterium makes precious particles Subterranean worms from hell Fault maps could aid earthquake forecasts When mineral-laden water at around 390 °C is subjected to that kind of pressure drop, Weatherley says, the liquid rapidly vaporizes and the minerals in the now-supersaturated water crystallize almost instantly — a process that engineers call flash vaporization or flash deposition.

The effect, he says, “is sufficiently large that quartz and any of its associated minerals and metals will fall out of solution”. Eventually, more fluid percolates out of the surrounding rocks into the gap, restoring the initial pressure. But that doesn’t occur immediately, and so in the interim a single earthquake can produce an instant (albeit tiny) gold vein. Big earthquakes will produce bigger pressure drops, but for gold-vein formation, that seems to be overkill. More interesting, Weatherley and Henley found, is that even small earthquakes produce surprisingly big pressure drops along fault jogs. “We went all the way to magnitude –2,” Weatherley says — an earthquake so small, he adds, that it involves a slip of only about 130 micrometres along a mere 90 centimetres of the fault zone. “You still get a pressure drop of 50%,” he notes. That, Weatherley adds, might be one of the reasons that the rocks in gold-bearing quartz deposits are often marbled with a spider web of tiny gold veins. “You [can] have thousands to hundreds of thousands of small earthquakes per year in a single fault system,” he says. “Over the course of hundreds of thousands of years, you have the potential to precipitate very large quantities of gold.

Small bits add up.” Weatherley says that prospectors might be able to use remote sensing techniques to find new gold deposits in deeply buried rocks in which fault jogs are common. “Fault systems with lots of jogs can be places where gold can be distributed,” he explains. But Taka’aki Taira, a seismologist at the University of California, Berkeley, thinks that the finding might have even more scientific value. That’s because, in addition to showing how quartz deposits might form in fault jogs, the study reveals how fluid pressure in the jogs rebounds to its original level — something that could affect how much the ground moves after the initial earthquake. “As far as I know, we do not yet incorporate fluid-pressure variations into estimates of aftershock probabilities,” Taira says. “Integrating this could improve earthquake forecasting.”

Richard A. Lovett ~ 17 March 2013

Nature doi:10.1038/nature.2013.12615

How Are Fossils Formed?

 

 

For fossil formation to take place a series of fortunate events must occur. If any part of the series is missing, we will never see the fossil! In fact, fossilization is a rare occurrence. Nature tends toward recycling. That includes just about everything from plants and animals to rocks and minerals. Let’s narrow it down to just animals for a minute. Animals, dead or alive, are food for other animals. From insects to dinosaurs, an animal could be someone’s lunch! Any part of the animal’s body that isn’t consumed is usually scattered about; leftovers! Just like those leftovers in your fridge, these leftovers make great food for bacteria. In addition, these leftovers are exposed to the elements: sun, rain, and even the soil itself all help to breakdown and decompose the sturdiest of bones, shells and wood. So, if we are ever going to see a fossil, some very specialized events must intervene to ward off the natural process of decomposition. The following is the most common scenario for fossil formation:

How Are Fossils Formed? 

Death Is The First Step
To start with, an animal or plant must die in water or near enough to fall in shortly after death. The water insulates the remains from many of the elements that contribute to decomposition. An example may be helpful. Let’s say that a trilobite has died of old age on the bottom of the sea. Bacteria consume the soft body parts but leave the hard exoskeleton intact.

How are fossils formed? 

Step two is Sedimentation
As time passes, sediments bury the exoskeleton. The faster this happens the more likely fossilization will occur. Land and mudslides definitely help. River deltas are also good for quick accumulation of sediments. This further insulates our trilobite from decomposition.

The sediments themselves have a huge influence on how well our trilobite fossil turns out. Very fine-grained particles, like clays, allow more detail in the future fossil. Course sediments, like sand, allow less detail to show. The chemical make up of the sediments also contributes to the future fossil. If iron is present, it may give the rock a reddish color. Phosphates may darken the rock to gray or black. The possibilities are truly endless.

Permineralization
As the sediments continue to pile on, the lower layers become compacted by the weight of the layers on top. Over time, this pressure turns the sediments into rock. If mineral-rich water percolates down through the sediments, the fossilization process has an even better chance of preserving our ancient animal. Some of the minerals stick to the particles of sediment, effectively gluing them together into a solid mass. These minerals make an impact on our original trilobite as well. Over the course of millions of years, they dissolve away the outer shell, sometimes replacing the molecules of exoskeleton with molecules of calcite or other minerals. In time, the entire shell is replaced leaving rock in the exact shape of the trilobite.

Uplift
As the continental plates move around the earth, crashing into each other, mountains are formed. Former sea floors are lifted up and become dry land. This is exactly what has happened to our trilobite. Now a fully formed fossil, our trilobite is buried under hundreds or even thousands of feet of rock! Thanks to the movement of the plates, our trilobite will come closer to the surface and nearer to discovery by some fortunate fossil hunter. Luckily, nothing stays the same.

Erosion at work
Rain, wind, earthquakes, freeze and thaw all work toward erosion. The mountains that were built up are worn away over time. Our fossil trilobite once again sees the light of day! With a little wisdom about where to look and some luck, you may be the first one to find him!

This is the fossilization process known as Permineralization. It is not the only answer to the question: "How Are Fossils Formed?" There are many other ways that fossils can be formed. You can read about them using the links below.

About the author - Claudia Mann is a teacher, and a contributor to fossils-facts-and-finds.com where you can find more answers to the question.

Courtesy: FossilHQ