Geology In

Measuring Devices for the World's Most Extreme Environment

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Norwegian research scientists are contributing to the development of the world's hottest geothermal well in a non-volcanic area. The goal is to exploit the inexhaustible supply of heat from the interior of the Earth, and this calls for equipment that can withstand the most extreme conditions.<br />
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The borehole is the world's hottest geothermal well in a non-volcanic area. Because terrestrial heat is encountered close to the surface in Italy, the country is rich in areas suitable for geothermal drilling – with searing temperatures reaching 500-600 degrees Celsius, resulting in supercritical water that the researchers are hoping to discover. And they have very good reasons. </div>
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If they can succeed in exploiting the energy in this water, they can drill geothermal wells that are ten times as effective as those currently in operation. This has the potential to reduce costs dramatically and pave the way for a fantastic energy future based on purely natural resources. However, in its supercritical phase, the liquid is corrosive and attacks any drilling equipment that encounters it.</div>
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<span style="font-family: "georgia" , "times new roman" , serif;">Supercritical energy bomb</span></h4>
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"We are faced with a lot of big challenges, but we've come a long way," says Magnus Hjelstuen, Research Manager at SINTEF Harsh Environment Instrumentation.<br />
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The measuring equipment SINTEF has developed as part of this project is a so-called "wireline logging tool" that can measure downhole temperatures and pressures. Such measurements are crucial in the search for the extremely energy-rich supercritical water. Temperature and pressure data indicate when the drill bit has entered a zone containing such water, and the well's geothermal properties (both the maximum temperature and temperature changes caused by drilling) will tell us how much energy the well can produce.<br />
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Since electrical cables do not function at temperatures over 350°C, SINTEF's measuring equipment is battery-powered. The temperature is logged deep in the borehole and is read off when the device returns to the surface.<br />
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In its supercritical phase, the liquid is corrosive and attacks any drilling equipment that encounters it.<br />
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This is no simple task. At two to three kilometres into the Earth's interior the temperature and pressure rise enormously. Something very special happens when the temperature reaches 374 degrees and the pressure is 218 times the air pressure at the surface. We encounter what we call supercritical water. This water is in a physical state that progresses from liquid into gas – and from there into a supercritical phase, in which it is neither.<br />
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It is this special form of water, as yet undiscovered, that the researchers are looking for. To reach the conditions that make it supercritical, the water must have a temperature of at least 374°C, under pressures of 200 bar.<br />
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"A water column at room temperature must be taken to a depth of 2.2 kilometres below the surface to reach a pressure of 220 bar," Hjelstuen explains.<br />
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But when the temperature of the water rises, its density falls. This means that we must go even deeper to pass 220 bar and attain supercritical conditions. If the water is contaminated with gases and minerals, which is always the case in a geothermal well, the temperature must be higher still for the water to become supercritical.</div>
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<span style="font-family: "georgia" , "times new roman" , serif;">Extreme equipment</span></h4>
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SINTEF uses electronics and sensors with extreme capabilities. Some of the components are in common use, while others are still at the prototype stage. The challenge for the Norwegian researchers has been to combine the sensors and electronics, and then develop computer software that enables the components to function together.<br />
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"Our challenge has been to find a combination of existing components which can perform optimally within our limitations in terms of instrument length, weight and diameter – not least in view of the environment the equipment will encounter in the well," says Hjelstuen.<br />
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The instrument is 2.6 metres long weighs 50 kilograms, but has a diameter of only 76 millimetres.<br />
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"For example, we use a micro-controller which functions at temperatures up to 300°C. This is only available as an early prototype (engineering sample). So we've been working closely with the manufacturer to get it to function the way we want it to," he adds.</div>
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<span style="font-family: "georgia" , "times new roman" , serif;">Intense pressure and temperature</span></h4>
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At present, the limiting temperature for electronics is around 250°C, and this means that the range of components available is very restricted. The number of suitable batteries is also not large. For example, the most robust batteries on the market work at temperatures of only 70 to 200°C and would explode if subjected to a temperature of 215 degrees. So making measuring equipment can be a challenging process.<br />
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"Since we begin drilling at normal surface conditions, the temperature on a winter's day may be as low as 0°C to start with, rising to over 400°C at the bottom of a well. Tackling such fluctuations makes enormous demands on the equipment. We've created a sort of "reverse Thermos flask" in which the inside temperature is kept below 210 degrees so as to reduce the strain on the equipment," says Hjelstuen.<br />
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The sensors are trialled and tested before being shipped to the field.<br />
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"At every stage an enormous amount of testing must be carried out in a way that as closely as possible simulates the environment our instruments will encounter in the well. Among other things we have used a furnace at Raufoss to test the technology at temperatures up to 450°C.</div>
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<span style="font-family: "georgia" , "times new roman" , serif;">Enormous potential</span></h4>
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In the process of harnessing the energy in the supercritical water, the researchers have made good use of the Norwegian petroleum industry's experience in drilling deep oil wells. The exploitation of geothermal heat has much in common with oil recovery. Petroleum technologists are therefore included in the team. However, whereas we have for many decades succeeded in exploiting the potential found in petroleum resources, nobody has yet managed to harness supercritical water.<br />
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"If we can succeed in exploiting geothermal heat there will be enough of it to supply the entire population of the planet with energy for many generations. There are nuclear power plants where water that meets the conditions for supercritical water is fed through turbines, so we know that we can succeed in exploiting the energy in such water once we have managed to extract it."<br />
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In the project's deepest descent into the Earth, the research team carried out measurements at a depth of 2810 metres. Here the temperature reached 443.6°C.</div>
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<u><i><span style="font-family: "trebuchet ms" , sans-serif;">The above story is based on <a href="https://www.sintef.no/en/latest-news/measuring-devices-for-the-worlds-most-extreme-environment/" rel="nofollow" target="_blank">materials</a> provided by <a href="https://www.sintef.no/en/" rel="nofollow" target="_blank">SINTEF</a>.</span></i></u></div>
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Measuring Devices for the World's Most Extreme Environment

Norwegian research scientists are contributing to the development of the world's hottest geothermal well in a non-volcanic are...

Study: East Bay Fault Is 'Tectonic Time Bomb,' More Dangerous Than San Andreas

1 San Andreas, Tectonic, USA 4:34 PM

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<span style="font-family: "georgia" , "times new roman" , serif;">Everyone knows that California’s San Andreas fault is a ticking time bomb ready to erupt – but a new study shows that another fault right under the East Bay is far more dangerous.</span><br />
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What will happen when the next big earthquake hits northern California? A team of researchers including CU Boulder Professor Keith Porter will explore that question at an event today marking the anniversary of the 1906 temblor that leveled much of San Francisco.<br />
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A modern earthquake could kill 800 people and cause more than $100 billion in economic losses from the shaking and subsequent fires, according to estimates come from the HayWired Scenario, a project spearheaded by the U.S.<br />
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Geological Survey (USGS), which is organizing the event on the campus of the University of California, Berkeley. The exercise looked at the potential outcomes of a magnitude 7.0 earthquake on California's Hayward Fault in the east San Francisco Bay Area.<br />
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Porter, a professor in CU Boulder's Department of Civil, Environmental and Architectural Engineering, said that the toll of such a disaster could be huge—on par with the impact of Hurricane Katrina on the southeastern United States in 2005.<br />
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"It's fairly likely that a person living in the Bay Area today will live to see a major Bay Area earthquake," Porter said. "The HayWired scenario reveals weak points in our designs for new buildings, our existing water infrastructure, not to mention problems with fires after earthquakes and with older elevators.<br />
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"California hasn't seen a major tremor since the rise of the Internet age—the last was 1994's Northridge earthquake in the Los Angeles area. The Hayward Fault itself last ruptured 150 years ago. Scientists estimate, however, that it or another Bay Area fault will likely produce a large earthquake in the next 30 years. The HayWired scenario seeks to help the region learn from the lessons of this when-not-if event without having to experience the costs.<br />
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"We tend to improve our building codes and other aspects of our infrastructure after a big disaster," Porter said. "We learn our lessons the hard way. But what the USGS's Science Application for Risk Reduction program has found is that simulated disasters can teach us the same lessons."<br />
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To drill down on those lessons, the project team drew from a wide range of information, including diverse computer simulations, industry data and surveys of California residents. The researchers will release their findings in three volumes. The first came out last year and USGS recently published the second online. CU Boulder is a coalition partner on the project. Porter coordinated the engineering analyses for this report and performed many of them himself.<br />
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Porter's expertise hones in on the long-lasting consequences for buildings and other infrastructure. He said that while California has adopted a stringent building code, these rules focus on getting people out of buildings alive, not necessarily on making them safe for people to go back into.<br />
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Under the current building code, an earthquake like the HayWired disaster could render one-quarter of buildings in the Bay Area unsafe for people to re-enter or otherwise limit their usability, he said. The earthquake could spark 450 large fires and cause 4,300 pipe breaks and leaks in the East Bay Municipal Utility District.<br />
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But, Porter added, that there's another impact of earthquakes that often gets ignored. Drawing on data from the elevator industry, Porter estimates that the hypothetical disaster could strand roughly 20,000 people in elevators across northern California.<br />
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"That's a big deal because electricity might not come back on in parts of the Bay Area for days or more after an earthquake," Porter said. "Imagine 20,000 people trapped in a metal box for days. That's pretty scary."<br />
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Still, Porter said that many of the scary numbers that he and his colleagues reported could be addressed with relatively small investments. For a 1 percent increase in construction costs, for example, new buildings could be made 50 percent stronger.<br />
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"Big earthquakes are inevitable in California," Porter said. "There will be some very serious losses in that kind of earthquake, but some of those losses can be avoided by thinking prudently in advance."<br />
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Porter's comments are timely as the California State Legislature is currently considering Assembly Bill 1857. This bill would establish a commission that would evaluate making the state's building code even tougher, potentially ensuring the survival of more buildings after a natural disaster.<br />
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<u><i><span style="font-family: "trebuchet ms" , sans-serif;">The above story is based on <a href="https://pubs.er.usgs.gov/publication/sir20175013v1" rel="nofollow" target="_blank">materials</a> provided by <a href="https://earthquake.usgs.gov/" rel="nofollow" target="_blank">USGS</a>.</span></i></u></div>

Study: East Bay Fault Is 'Tectonic Time Bomb,' More Dangerous Than San Andreas

Everyone knows that California’s San Andreas fault is a ticking time bomb ready to erupt – but a new study shows that another fault ri...

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Researchers Find Vast Reserve of Rare Earth Minerals

0 Geochemistry, Mining, Researches 8:18 PM

Researchers Find Vast Reserve of Rare Earth Minerals

Yttrium, sublimed-dendritic, high purity 99.99 % Y/TREM. Japanese researchers have mapped vast reserves of rare earth elements in dee...

New Type of 'Opal' Formed by Common Seaweed

0 Researches 6:28 PM

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<tr><td style="text-align: center;"><a href="https://2.bp.blogspot.com/-zP2FzMEw7v0/WtdjIfmPMxI/AAAAAAAAPr4/N7mNDp2XwjQ7Tq03qKbVGanPBXF_RU8ugCLcBGAs/s1600/New%2BType%2Bof%2B%2527Opal%2527%2BFormed%2Bby%2BCommon%2BSeaweed%2B%25281%2529.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img alt="New Type of 'Opal' Formed by Common Seaweed" border="0" data-original-height="582" data-original-width="1123" height="330" src="https://2.bp.blogspot.com/-zP2FzMEw7v0/WtdjIfmPMxI/AAAAAAAAPr4/N7mNDp2XwjQ7Tq03qKbVGanPBXF_RU8ugCLcBGAs/s640/New%2BType%2Bof%2B%2527Opal%2527%2BFormed%2Bby%2BCommon%2BSeaweed%2B%25281%2529.jpg" title="" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">This is the morphology and structural color of the brown algae seaweed known as Cystoseira tamariscifolia.<br /></td></tr>
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Scientists have discovered a completely new type of opal formed by a common seaweed which harnesses natural technology by self-assembling a nanostructure of oil droplets to control how light reflects from its cells to display a shimmering array of colours that until now, has only been seen in the gem stone.<br />
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The findings, published in Science Advances and led by Drs Heather Whitney and Ruth Oulton from the University of Bristol, show that the bright blue and green iridescent sheen from the brown algae seaweed, also known as "rainbow wrack" (Cystoseira Tamariscifolia) and commonly found throughout the European costal region including the UK, arises from a complex nanostructure that controls how light reflects from its cells containing chloroplasts.<br />
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Even more remarkable, is how these seaweeds can switch this self-assembly on and off, creating changing opals which react to the changing sunlight in tidal rockpools. Such structures arise from nanosized spheres packed tightly in a regular way and are known to optics experts to reflect different colours from incoming white light into different directions.<br />
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These types of structures are also seen naturally in gem stone opals, which comprise a nanostructure of tiny spheres of glass formed within hard stone deep below the earth's surface that naturally pack together in such a way that they diffract light into different directions giving the opal it's well-known opalescence.<br />
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Dr Ruth Oulton, Professor Martin Cryan and Dr Martin Lopez-Garcia (now at the International Iberian Nanotechnology Institute, Portugal), all experts in nano-optics in Bristol's School of Physics and Department of Electrical Engineering, discovered that these natural, "living" opals form not from glass but from tiny oil droplets made by the seaweed.<br />
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In a process unknown to present nanotechnology, the seaweed's chloroplasts-containing cells (which aid photosynthesis) self-assembles the oil droplets into a regular packing. Surprisingly, these seaweeds can switch this self-assembly on and off, creating changing opals which react to the changing sunlight in tidal rockpools. Even more remarkable is how the seaweed performs the dynamic self-assembly, over a timescale of just hours, is a true mystery to the research team.<br />
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Dr Martin Lopez-Garcia, said: "The formation of opals from oil droplets is a completely new discovery. If nanotechnologists were able to understand and mimic the dynamic properties of this seaweed opal, we may in the future have biodegradable, switchable display technology that may be used in packaging or very efficient, low cost solar cells."<br />
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Nathan Masters, a PhD student in the Schools of Physics and Biological Sciences at Bristol, discovered that by shining light onto the seaweed, the iridescence disappeared, but when kept in almost dark conditions, the blue-green sheen reappeared.<br />
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By imaging the seaweed at a sub-nanoscale level, the team discovered that the seaweed was switching on and off the self-assembly, going from a disordered, unreflective state to an ordered, opalescent one. But most surprising to the research team was that the opal is dynamic.<br />
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Why the seaweed does this remains to be proven, but Drs Heather Whitney and Heath O'Brien, who carried out the work while at Bristol's School of Biological Sciences, (now at Cardiff University), believe that because the opals sit in the same part of the cell as the chloroplasts -- the light energy harvesting bodies of the organism -- they are likely to be controlling the light levels, scattering the light evenly to all the available chloroplasts inside the cell. This may help the seaweed cope with different light levels during high and low tide.<br />
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Dr Ruth Oulton, Reader in Quantum Photonics in the School of Physics and Department of Electrical and Electronic Engineering, added: "In the past decade, nanotechnologists have been able to make artificial opals out of similar glass nanospheres.<br />
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But it seems that the humble seaweed is also able to make such artificial opals in its cells. So next time you're rock pooling in the UK during your summer holidays, see if you can find this amazing seaweed with its nano-manufacturing technology."<br />
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<i><u><span style="font-family: "trebuchet ms" , sans-serif;">The above story is based on <a href="http://www.bristol.ac.uk/news/2018/april/seaweed.html" rel="nofollow" target="_blank">Materials</a> provided by <a href="http://www.bristol.ac.uk/" rel="nofollow" target="_blank">University of Bristol</a>.</span></u></i></div>

New Type of 'Opal' Formed by Common Seaweed

This is the morphology and structural color of the brown algae seaweed known as Cystoseira tamariscifolia. Scientists hav...

Diamonds Buried Within Rare Meteorites Reveal Existence of "Lost Planet"

0 Diamonds, Meteorite, Researches 5:12 PM

Diamonds Buried Within Rare Meteorites Reveal Existence of "Lost Planet"

A different urelite meteorite, NWA 4231. Diamonds found in a meteorite that exploded over the Nubian desert in Sudan a decade ago wer...

Scientists Discover Clues to Recovery From Mass Extinction

1 Earth History, extinction, Researches 9:29 PM

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<span style="font-family: Georgia, "Times New Roman", serif;">About 252 million years ago, more than 90 percent of all animal life on Earth went extinct. This event, called the "Permian-Triassic mass extinction," represents the greatest catastrophe in the history of life on Earth. Ecosystems took nearly five million years to recover and many aspects of the event remain a mystery.</span><br />
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A research team, led by scientists from Arizona State University and funded by NASA and the National Science Foundation, is helping to understand why this extinction event happened and why it took life so long to recover. The study, published in Science Advances, was led by ASU School of Earth and Space Exploration graduate student Feifei Zhang, with direction from school faculty member Ariel Anbar.</div>
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<span style="font-family: "georgia" , "times new roman" , serif;">Mass extinction of marine ecosystems</span></h4>
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For this study, the research team focused on marine ecosystems, which were decimated during the Permian-Triassic mass extinction. Previous studies demonstrated that the loss of dissolved oxygen in Earth's oceans, an effect called "marine anoxia," played an important role in the mass extinction event. The team wanted to find out when the anoxia occurred, how widespread it was, and how long it persisted after the extinction event.<br />
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In particular, the team wanted to see if separate episodes of extinction that happened during the long period of recovery were driven by episodes of ocean anoxia and other environmental changes.</div>
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<span style="font-family: "georgia" , "times new roman" , serif;">Pioneering a new technique</span></h4>
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Typically, scientists determine ocean anoxia levels by looking at the abundance of pyrite, commonly known as "fool's gold," and other elements and minerals in ancient mud rocks. But mud rocks only provide clues to what may have happened at a single location. Scientists need to sample dozens of sites around the world to infer the big picture from mud rocks.<br />
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To overcome this, the team pioneered a new and more efficient approach. By studying the variations of uranium isotopes recorded in carbonates, the team was able to infer global anoxia occurring throughout the ocean using samples from a single outcrop. These sediments, collected in modern day Iran, were deposited 252-246 million years ago in a relatively shallow tropical ocean near the equator.<br />
<br />
The resulting variations of uranium isotopes gave the team the answers they were looking for. They were able to show that episodes of extinction coincided with pulses of ocean anoxia, driven by changes in ocean circulation and nutrient levels.<br />
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"This finding," says Zhang, "provides important insights into patterns of oceanic environmental change and their underlying causes, which were ultimately linked to intense climate warming during the Early Triassic."</div>
<h4 style="text-align: left;">
<span style="font-family: "georgia" , "times new roman" , serif;">Climate change - then and now</span></h4>
<div style="text-align: left;">
This team's discovery also calls attention to the possible effects of modern climate change, because global warming was the ultimate driver of marine anoxia in the Early Triassic period.<br />
<br />
"One of the most interesting and worrying things about the Permian-Triassic extinction is how similar those events are to what is happening today," says co-author Stephen Romaniello. "Similar to what happened during the Permian period, the Earth's modern oceans are facing rapid climate warming and enhanced nutrient fluxes."<br />
<br />
Point in fact, scientists have discovered more than 400 marine dead zones in the modern oceans. These are mostly linked to elevated nutrient fluxes in coastal areas, and global warming is likely to cause these zones to expand dramatically in the future.<br />
<br />
"Our work shows that if we continue on our present course, there is a good chance that oxygen depletion will exacerbate the challenges marine organisms are already facing," co-author Thomas Algeo added.</div>
<div style="text-align: left;">
<br /></div>
<div style="text-align: left;">
<u><i><span style="font-family: "trebuchet ms" , sans-serif;">The above story is based on <a href="https://asunow.asu.edu/20180416-studying-oxygen-earth%E2%80%99s-oceans-asu-scientists-discover-clues-recovery-mass-extinction" rel="nofollow" target="_blank">materials </a>provided by <a href="https://www.asu.edu/" rel="nofollow" target="_blank">Arizona State University.</a></span></i></u></div>
</div>

Scientists Discover Clues to Recovery From Mass Extinction

About 252 million years ago, more than 90 percent of all animal life on Earth went extinct. This event, called the "Permian-Trias...

Structures of Mineral Deposits

0 Geochemistry, Mining 7:47 PM

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<tr><td style="text-align: center;"><a href="https://4.bp.blogspot.com/-GDWspzkySew/WtYjmNSxBrI/AAAAAAAAPq4/jwetrFYyrTwuHcNDzGZ6sItn8JZq5XKsACLcBGAs/s1600/Structures%2Bof%2BMineral%2BDeposits.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img alt="Structures of Mineral Deposits" border="0" data-original-height="885" data-original-width="1280" height="442" src="https://4.bp.blogspot.com/-GDWspzkySew/WtYjmNSxBrI/AAAAAAAAPq4/jwetrFYyrTwuHcNDzGZ6sItn8JZq5XKsACLcBGAs/s640/Structures%2Bof%2BMineral%2BDeposits.jpg" title="" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Schematic diagram showing both major mineral deposit types formed in continental crust above SCLM,</td></tr>
</tbody></table>
<br />
<h4 style="text-align: left;">
<span style="font-weight: normal;"><span style="font-family: "georgia" , "times new roman" , serif;">Sedimentary Deposits</span></span></h4>
Mineral deposits formed as a consequence of sedimentary processes occur generally as lenses or beds which parallel enclosing sedimentary rocks, and may extend for thousands of feet or tens of miles, but are rarely more than a hundred feet thick. These deposits occur in sedimentary basins, along ancient slopes and stream channels, and in ancient lagoons. However, similar deposits may occur as a consequence of replacement of reactive beds of limestone or dolomite - usually at the base, or as impregnation of a permeable strata unit, giving the impression of initial deposition.<br />
<h4>
<span style="font-family: "georgia" , "times new roman" , serif;">Structural Deformation</span></h4>
Structural deformation may alter the form and attitude of some of these deposits. For example, salt domes along the coast of the Gulf of Mexico result from the squeezing of the salt from flat- lying beds, intruding upward along zones of weakness. Many limestone beds have been severely tilted and even overturned.<br />
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<h4 style="text-align: left;">
<span style="font-family: "georgia" , "times new roman" , serif;">Metamorphic Processes</span></h4>
Lenticular masses, veins, lodes and zones of disseminated mineralization result from metamorphic processes. These deposits may conform to the attitudes of the enclosing rocks or they may be cross -cutting (pegmatite veins).<br />
<h4 style="text-align: left;">
<span style="font-family: "georgia" , "times new roman" , serif;">Veins/Lodes</span></h4>
Veins and lodes consist of aggregates of minerals containing base and/or precious metals, uranium, etc. which have been deposited in fractures in the enclosing rock mass, or have replaced the rock immediately adjacent to the fracture. The  veins are roughly tabular, but usually thicken and thin at irregular intervals. Quartz, calcite and pyrite constitute the common gangue minerals in most metallic vein deposits. Lengths and widths of veins are usually in the order of hundreds to thousands of feet in length, less than a foot to a hundred feet in width, up to several thousand feet in depth. Veins formed in the deep volcanic environment generally have good depth continuity of values, while those formed in the epicrustal volcanic environment generally give out, or become uneconomic, <br />
at depths of 1000 to 1500 feet.<br />
<h4 style="text-align: left;">
<span style="font-weight: normal;"><span style="font-family: "georgia" , "times new roman" , serif;">Replacement Deposits</span></span></h4>
May be disseminated or massive. Bedded replacements, lead, zinc, silver, copper deposits in limestone, generally occur in more or less flat-lying (MANTOS) clusters having lateral dimensions of a hundred to several thousand feet, but are usually less than a hundred feet thick. The basal limestone bed in a sequence tends to be the favored horizon, particularly where it is adjacent to an intrusive, forming a<b> Contact Metamorphic </b>or <b>Pyrometasomatic</b> assemblage. These mineralized bodies are generally irregular in shapenand variable in size, but may border porphyry- type deposits and may be mined as a part of the adjacent deposit.<br />
<h4 style="text-align: left;">
<span style="font-family: "georgia" , "times new roman" , serif;"> Other host</span></h4>
Rocks containing carbonate as primary or alteration minerals, or organic material are favorable hosts for replacement by ore minerals as disseminations. Sizes and shapes are dependent upon the favored host.<br />
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<b>Porphyry-Related</b><br />
Deposits are formed in the epicrustal volcanic environment and constitute a principal source of copper-gold-molybdenum. Shallow porphyry intrusives, stockworks and breccia systems form large tonnage (up to several billion tons) low-grade deposits amenable to low-cost bulk mining and treatment. They are generally one to ten  miles in diameter and may extend to a mile in depth. Commonly thy are capped by a barren leached capping which is underlain by a zone of <b>SECONDARY ENRICHMENT</b> of values.<br />
<br />
<b>Weathering Concentration</b><br />
Deposits formed at the surface by <i>Weathering Concentration</i> (bauxite, iron and nickel laterites) have more or less tabular forms with large lateral dimensions (several <br />
 thousand feet to several miles, and thicknesses to a few hundred feet.<br />
<br />
<b>Stream Placer</b><br />
Deposits are usually not more than a few tens of feet thick, with valuable minerals (gold, platinum, tin, diamonds) occurring in relatively narrow and relatively long horizontal patterns. BEACH PLACERS tend to be roughly rectangular in outline and may have adjacent, related dune concentrations.<br />
<h3 style="text-align: left;">
<span style="font-family: "georgia" , "times new roman" , serif;">Recognition</span></h3>
<span style="font-family: "georgia" , "times new roman" , serif;">Recognition of the environment and existence of potentially economic mineral deposits may be based upon a variety of geological criteria:</span><br />
<b>a.</b>  <b>Association with specific types of igneous rocks</b> -- e.g., copper with quartz- monzonite porphyry, diamonds with kimberlite pipes, tin with granites, etc.<br />
<b>b.</b>  <b>Host rock association</b> -- e.g. lead and zinc with carbonate rocks.<br />
<b>c.</b>  <b>Wallrock alteration</b> -- e.g. a concentric pattern of feldspathization, sericitization and propylitization around porphyry copper deposits, and dolomitization around lead-zinc <br />
replacement deposits.<br />
<b>d.</b>  <b>Age of mineralization</b> -- e.g. banded iron formation deposits are characteristic of Precambrian age rocks.<br />
<b>e.</b>  <b>Gangue mineral association</b> -- e.g. gold associated with quartz-ankerite veins.<br />
<b>f. </b> Trace metal association -- e.g. gold associated with arsenic and mercury in trace amounts.<br />
<b>g.</b>  <b>Structural controls</b> -- e.g. laterite deposits associated with unconformities, replacement deposits associated with crests of anticlines.<br />
<b>h.</b> <b> Physiographic associations</b> -- e.g. silicified breccias often stand up as isolated hills; oxidized pyritic bodies in limestone generally form low covered areas.i.  Weathering effects- e.g. oxidation of pyrite leaves a residue of iron oxide gossan marking possible underlying deposits.<br />
<b>j.</b>  <b>Ore and gangue mineral in fresh or oxidized states in outcrop</b> of derived sediments may give surface evidence of underlying or adjacent deposits<br />
<br />
<br />
<b><span style="font-family: "georgia" , "times new roman" , serif;">See also: </span></b><br />
<span style="font-family: "georgia" , "times new roman" , serif;"><a href="http://www.geologyin.com/2014/05/tectonic-settings-of-metal-deposits.html" target="_blank">Tectonic Settings of Metal Deposits</a></span><br />
<span style="font-family: "georgia" , "times new roman" , serif;"><a href="http://www.geologyin.com/2014/11/veins-and-hydrothermal-deposits.html" target="_blank">Veins and Hydrothermal Deposits</a></span><br />
<span style="font-family: "georgia" , "times new roman" , serif;"><a href="http://www.geologyin.com/2014/11/methods-of-gold-mining.html" target="_blank">Methods of Gold Mining</a></span></div>

Structures of Mineral Deposits

Schematic diagram showing both major mineral deposit types formed in continental crust above SCLM, Sedimentary Deposits Mineral depo...

The Yellowstone Supervolcano Has Two Magma Chambers, Say Scientists

0 Tectonic, Yellowstone 5:06 PM

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<tr><td class="tr-caption" style="text-align: center;">Based on supercomputer modeling, about the location of a mid-crustal sill that separates magma under yellowstone.</td></tr>
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<br />
<br />
<span style="font-family: "georgia" , "times new roman" , serif;">Using supercomputer modeling, University of Oregon scientists have unveiled a new explanation for the geology underlying recent seismic imaging of magma bodies below Yellowstone National Park.</span><br />
<br />
Yellowstone, a supervolcano famous for explosive eruptions, large calderas and extensive lava flows, has for years attracted the attention of scientists trying to understand the location and size of magma chambers below it. The last caldera forming eruption occurred 630,000 years ago; the last large volume of lava surfaced 70,000 years ago.<br />
<br />
Crust below the park is heated and softened by continuous infusions of magma that rise from an anomaly called a mantle plume, similar to the source of the magma at Hawaii's Kilauea volcano. Huge amounts of water that fuel the dramatic geysers and hot springs at Yellowstone cool the crust and prevent it from becoming too hot.<br />
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With computer modeling, a team led by UO doctoral student Dylan P. Colón has shed light on what's going on below. At depths of 5-10 kilometers (3-6 miles) opposing forces counter each other, forming a transition zone where cold and rigid rocks of the upper crust give way to hot, ductile and even partially molten rock below, the team reports in a paper in Geophysical Research Letters.<br />
<br />
This transition traps rising magmas and causes them to accumulate and solidify in a large horizontal body called a sill, which can be up to 15 kilometers (9 miles) thick, according to the team's computer modeling.<br />
<br />
"The results of the modeling matches observations done by sending seismic waves through the area," said co-author Ilya Bindeman, a professor in the UO's Department of Earth Sciences. "This work appears to validate initial assumptions and gives us more information about Yellowstone's magma locations."<br />
<br />
This mid-crustal sill is comprised of mostly solidified gabbro, a rock formed from cooled magma. Above and below lay separate magma bodies. The upper one contains the sticky and gas-rich rhyolitic magma that occasionally erupts in explosions that dwarf the 1980 eruption of Mount St. Helens in Washington state.<br />
<br />
Similar structures may exist under super volcanoes around the world, Colón said. The geometry of the sill also may explain differing chemical signatures in eruptive materials, he said.<br />
<br />
Colón's project to model what's below the nation's first national park, which was sculpted 2 million years ago by volcanic activity, began soon after a 2014 paper in Geophysical Research Letters by a University of Utah-led team revealed evidence from seismic waves of a large magma body in the upper crust.<br />
<br />
Scientists had suspected, however, that huge amounts of carbon dioxide and helium escaping from the ground indicated that more magma is located farther down. That mystery was solved in May 2015, when a second University of Utah-led study, published in the journal Science, identified by way of seismic waves a second, larger body of magma at depths of 20 to 45 kilometers (12-27 miles).<br />
<br />
However, Colón said, the seismic-imaging studies could not identify the composition, state and amount of magma in these magma bodies, or how and why they formed there.<br />
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To understand the two structures, UO researchers wrote new codes for supercomputer modeling to understand where magma is likely to accumulate in the crust. The work was done in collaboration with researchers at the Swiss Federal Institute of Technology, also known as ETH Zurich.<br />
<br />
The researchers repeatedly got results indicating a large layer of cooled magma with a high melting point forms at the mid-crustal sill, separating two magma bodies with magma at a lower melting point, much of which is derived from melting of the crust.<br />
<br />
"We think that this structure is what causes the rhyolite-basalt volcanism throughout the Yellowstone hotspot, including supervolcanic eruptions," Bindeman said. "This is the nursery, a geological and petrological match with eruptive products. Our modeling helps to identify the geologic structure of where the rhyolitic material is located."<br />
<br />
The new research, for now, does not help to predict the timing of future eruptions. Instead, it provides a never-before-seen look that helps explain the structure of the magmatic plumbing system that fuels these eruptions, Colón said. It shows where the eruptible magma originates and accumulates, which could help with prediction efforts further down the line.<br />
<br />
"This research also helps to explain some of the chemical signatures that are seen in eruptive materials," Colón said. "We can also use it to explore how hot the mantle plume is by comparing models of different plumes to the actual situation at Yellowstone that we understand from the geologic record."<br />
<br />
Colón is now exploring what influences the chemical composition of magmas that erupt at volcanoes like Yellowstone.<br />
<br />
Studying the interaction of rising magmas with the crustal transition zone, and how this influences the properties of the magma bodies that form both above and below it, the scientists wrote, should boost scientific understanding of how mantle plumes influence the evolution and structure of continental crust.<br />
<br />
<br />
<u><i><span style="font-family: "trebuchet ms" , sans-serif;">The above story is based on <a href="http://dx.doi.org/10.1029/2018GL077090" rel="nofollow" target="_blank">Materials</a> provided by <a href="http://www.uoregon.edu/" rel="nofollow" target="_blank">University of Oregon</a>.</span></i></u></div>

The Yellowstone Supervolcano Has Two Magma Chambers, Say Scientists

Based on supercomputer modeling, about the location of a mid-crustal sill that separates magma under yellowstone. Using supercomputer...