Part 3
What about the accusation that there in no way to design a dam so that it can withstand a large earthquake
How would engineers know how to build a tailing dam to withstand an earthquake
There are {mathematical methods} that take into account the cohesiveness of the soil, how it would act during an earthquake, and how stable a dam would be depending on the slope of the dam's walls.
The stability factor (SF) can be calculated depending on the shearing strength parameters of the soil and the dam.
SF = tg / tgß where, f is the inside friction angle of the embankment and the material that composes it, corresponding to the shearing strength, and ß is the gradient of the slope.
Other equations, such as those that take into account the balance of the vertical forces (? i X ) and of the horizontal forces (? i E ), would also be used in determining the design of the tailing dam.
There are other equations that engineers can use, and put together, it would allow engineers to design a tailing dam that would withstand an earthquake equal to the strongest possible earthquake that can occur at the Pebble site. The equations would also enable them to design the mine itself to withstand such an earthquake.
Taking into account, the density and viscosity of the slurry, and the forces that an earthquake of maximum determined magnitude will exert on the slurry, and the dam; engineer's will know the required shape that the dam should take so that it will retain its structural integrity.
This is a diagram of a tailing dam:
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Engineers can calculate the required shape of a dam, but constructing it within parameters has been difficult, and if it isn't constructed to specification, it would be vulnerable to failure of the dam's wall.
Taking {ground based measurements} has proven to be imprecise because the ground will usually be too wet on which to drive a surveillance vehicle, and may even be too moist to walk on. There will only be scattered areas suitable for taking measurements, which will result in obtaining only a very loose estimate of the incline, as well as the thickness of the dam's wall. Ground based measurements have huge margins of error, so you don't know if the dam is being built within the engineer's specifications.
Even though radar or laser measurements are now being used and are more precise, they can only be taken where the ground will support the laser, or radar, and therefore the measurements will also only be able to be taken from scattered vantage points, which is imprecise.
{Drone-surveying} solves these problems. Drones can be automated, with flight planning apps taking care of the piloting and flying. Once it has finished surveying the dam, the data is uploaded into a processing platform, like Propeller, which views and measures the tailing dam in 3D. This will include highlighting areas of the dam where too much material has been deposited, causing a bulge; or not enough material, which would produce an indention in the mine wall. Both problems, a bulge in the dam's wall, or an indention, would cause stresses to form in those areas, and thus produce weak spots in those areas.
An even more efficient and accurate tailings dam wall monitoring procedure is coming into use, which would be perfect for monitoring the construction of Pebble's tailing dam.
Photo-satellite surveying, {PhotoSat,} takes high resolution stereo photographs (3D) accurate to within inches, of hundreds of square kilometers in minutes. This gives a view of the entire mine site, which will be delivered in record time to the mine's engineers, and it will be in a format suitable for immediate use so that there will be no delays on any corrections to the angle or thickness of the dam's walls. Thus preventing the development of any weak spots in the dam.
As these methods come into use, tailing dams will be able to be built to the specifications of engineers who can design a tailing dam to withstand any designated potential earthquake.
Critics charge that even if a safe dam can be built, that won't fail during an earthquake, the tailing pond, which is confined by the tailing dam, will leak acid tinged, heavy metal toxic water into the groundwater below it.
The groundwater, in its travels, would then contaminate the streams, rivers, and lakes in the surrounding area
There is now a way to prevent leakage from the tailing pond into the groundwater
The Kittila mine located north of Finland, inside the Polar Circle, is located in an environment, and yearly temperature range, similar to the Pebble mine. The Finland Ministry of Environment, mandated that it's tailing pond have a water tight liner.
For the floor of the tailing pond, the company used locally obtained glacial till. It was crushed and compacted into a 40 inch layer which ended up with a water permeability of less than 5x10E-8 m/s.
Over that, the company used sheets of {bituminous geomebrane }
(BGM). The sheets of material are a composite, of which one component consists of the highest quality bitumen.
Bitumen is found world wide, but is best known as the tarry substance found in the La Brea Tar Pit in California. It is a sticky, black, and highly viscous liquid.
This is combined with butadiene styrene, a type of rubber with good abrasion resistance and good aging stability, it doesn't break down with age. The combination makes an elastic material that is also self sealing, the bituminous internal mass will flow and seal any punctures and penetrations.
These are combined with a sheet of glass fleece which is a dimensionally stable substance. Extremely high or low temperatures will not make it stretch or shrink. And even when physically stretched and stressed close to its point of rupture, it will return to its original size when the pressure is removed. It also has high strength with minimal weight. This makes the sheets of BGM light, but strong, and easier to maneuver and position so that they are correctly placed, and the glass fleece fabric prevents tearing of the composite sheet. It is also resistant to most acids.
Bituminous Geomembrane Liners stay flexible and do not stiffen, even at temperatures as low as -40°F. They lay flat, and in complete contact with the crushed glacial till floor of the tailing pond. Since they stay flexible, even at -40°F, they will mold themselves to any imperfections of the substrate over which they are being laid, even in deep sub zero temperatures, and will form a tight seal with the substrate. They also have a high friction coefficient and can be laid over even steeply angled dam walls.
The lowest temperature recorded at Pebble's site since 1947 is -31°F. Because temperatures at the Pebble site stay well above -40°F, even at the coldest times of the year, it would allow construction to be carried out year round at the Pebble site.
Based on the resulting composite's physical durability and resistance to punctures and tearing, and to most chemicals, the U.S. Navy Nuclear Safety Agency certifies BGM for a {1,000 year} life span.
BMG specifications call for it to be installed on a 2" compacted substrate, but in this case it was 40". The Pebble area has an abundance of glacial till available, so it could also lay down a thick compacted substrate, which in itself would be considered a water proof seal. The combination of BMG over compacted substrate is called a dual seal.
In addition to BGM being used on the floor of the tailing holding pond site, it would also be used on the inner wall of the tailing dam. This will ensure that there will be no leakage through the dam's wall.
In order to get to the ore in the deposit, an over burden of rock has to be removed. It is broken up, taken off site, and forms waste rock piles. These also contain iron pyrite, which is prevalent in the area. Because the pyrite is now open to air and rain water, it also generates sulfuric acid contaminated water, and Pebble critics say that it will seep down into the water table.
This is not a valid argument, because Northern Dynasty has stated that the waste rock will be stored in a lined, water proof, containment site. This would also be a dual seal. Critics also know this.
Critics say the tailing pond will have to be monitored indefinitely, and in the next hundreds of years, or even thousands of years, there is bound to be a leak, or spillage of the contents into the surrounding area, causing massive damage to the environment.
Therefore, no matter what, critics say that the Pebble mine is too dangerous to be built.
At present, {conventional methods} are not effective in decontaminating giant toxic tailing ponds.
{Solidification,} which involves adding cement to the slurry, has a basic flaw.
Although the toxic metals are physically bound in the cement matrix, they are not destroyed. Cement is porous and their leaching into the environment would only be reduced, not stopped.
Other methods, such as adding chemicals to precipitate the heavy metals, would not only take huge amounts of chemical reagents, they also tend to produce secondary pollution.
Scientists are now studying the use of {bioremediation} to clean up, or neutralize toxic tailing ponds.
Bioremediation refers to the process of using microorganisms to remove toxic compounds, such as heavy metals and arsenic, from tailing ponds, as well as break down, and eliminate, the sulfuric acid that would be produced by Pebble's sulfide ores, but at this time, it is a very slow process.
The Pebble deposit contains iron sulfide, but because it is uneconomic, it is discarded into the tailing pond. The tailing pond also contains some of the economic metals because the present methods of extracting them, are unable to extract all of the valuable metals.
For instance, the Pebble tailing pond slurry will contain copper sulfide, because only {85%} of the copper will be extracted from the ore, which means that there will still be a lot of copper in the discarded slurry.
The crushed ore contains crushed sulfur, and the crushed sulfur will readily react with the water in the slurry, and the oxygen in the air, to form sulfuric acid, HSO.
In addition to iron sulfide and economic metals, the Pebble deposit contains arsenic and also dangerous heavy metals, such as cadmium. Because they are not extracted as the ore slurry makes its way through the froth flotation tanks, they will be in the spent slurry that is discarded into the tailing pond.
Arsenic can dissolve in plain water, but is most soluble in sulfuric acid tinged water with a pH of 2.65. It wouldn't have time to dissolve while going through the water froth flotation tanks, but it would dissolve in the sulfuric acid laced tailing pond.
The sulfuric acid in the tailing pond would also dissolve the heavy metals present in the pond's slurry, as well as the residual copper that was not extracted in the froth flotation tanks. The metals would go into solution as ions with a positive charge, such as Cd².
Cadmium, even in small amounts, is a deadly compound that can cause severe health issues, such as kidney failure. Arsenic causes neurological, lung, and heart damage. Copper is not very dangerous to humans, but even in trace amounts, it is deadly to salmon.
Bioremediation is cleaner and safer for the environment than chemical processing. The drawback of microbial leaching is the slow rate at which microbes work. Still, bioremediation is considered to be the only viable method of decontaminating large tailing ponds, but it needs {improvement} in efficiency. Bioremediation systems in operation today are slow and rely on microorganisms native to contaminated sites. Thus, today's bioremediation systems are {limited} by the capabilities of native microbes.
Humans, and most microbes, use oxygen (O), for respiration, which through a series of oxidation steps, using {electron transport,}produces ATP, a high-energy molecule that the cell uses for performing its various functions, such as reproduction.
If a microbe lives in an area where there is no oxygen, such as in a slurry, it uses anaerobic respiration, respiration without oxygen. The process uses a respiratory electron transport chain that does not use oxygen.
An example would be a microbe that uses {Sulfate (SO4),} or one that uses the electrons of metal ions, such as Chromium (VI) [Cr], for the electron transport of respiration.
Anaerobic respiration is not respiration like we know it. We breath air into our lungs, in order to obtain oxygen, which, through a series of steps is turned into ATP. During the process, carbon dioxide (CO) is produced, and expelled by the lungs.
Microbes don't breath gas, they absorb, or transport, the needed molecules, in their soluble ion form, through their cell wall, and through a series of cellular transactions, convert it into adenosine triphosphate (ATP).
Microbes also release their respiratory end product into the environment.
Sulfate-reducing bacteria neutralize sulfuric acid, because when they 'breathe' the sulfate (SO) part of the sulfuric acid, HSO, it is changed into sulfide (S²), which is then released into its surroundings. In eliminating the sulfate part of any sulfuric acid, that the microbes use for their respiration, they also end up, in effect, destroying and removing that sulfuric acid from the slurry.
In addition to that, the sulfide that is produced, (S²) and released into the slurry, will react with several of the toxic heavy metals in the slurry, such as cadmium (Cd²), which will form insoluble cadmium sulfide, CdS. Because the sulfide forms such a strong bond with the cadmium, the bipolar water molecules can't pull it apart into its separate ion components, Cd² and S², and it precipitates out of solution.
Since the cadmium is no longer in solution in the slurry's water, if there was a tailing dam break, and the slurry spilled outside of the dam, the cadmium would stay put wherever it landed. It would no longer be considered a contaminate to the surrounding country side.
The same thing would be true for the other toxic metals in the Pebble tailing pond, that sulfide could precipitate out of solution.
{Pebble's metals:} (Related to toxic metals.)
Antimony (Sb), Arsenic (As), Cadmium (Cd), Chromium (Cr), Copper (Cu), Lead (Pb), Mercury (Hg), Selenium (Se), Uranium (Ur), Zinc (Zn)
Precipitated as sulfides:
Antimony, Arsenic, Cadmium, Copper, Lead, Selenium, Zinc
Leaves:
Chromium, Mercury, Uranium
Getting back to neutralizing the sulfuric acid in the tailing pond slurry, as well as the toxic heavy metals. The best bioremediation method is to use a {combination} of microorganisms.
Specific groups of sulfate-reducing bacteria are localized at different
{depths} of the slurry in the tailing pond.
The part of the slurry near the surface contains some oxygen, but turns more anoxic as the depth increases. This alone would cause the microbe composition to change according to the depth of the slurry, because some microbes function better if some oxygen is present, and others function better with out any oxygen. Different microbes would be dominate at different depths.
The types of ore, in the Pebble deposit, varies through out it, and as it is processed, and then discarded into the tailing pond, it will cause the tailing pond to have different combinations of metal in different parts of it. This will change the composition of the microbes in those areas. The varying metals will attract bacteria that use those specific metals for their respiration.
When microbes are first introduced into a contaminated site, they are {not very effective} in removing the contaminants. But, over time, each of the differing areas in the tailing pond will become populated with microbes best suited to that area. As they multiply in numbers, they will remove greater and greater amounts of sulfate and heavy metals at the sites, and the rate of remediation will increase.
By introducing a combination of microbes into the tailing pond, instead of only a few types, it will make it more likely that there will be microbes available that will be best suited for the different environments in the tailing pond.
Eventually, the rate of detoxifying the pond will increase more than having the most efficient microbes present at the differing sites can account for. This is because microbes have plasmids's.
A microbe's cytoplasm, in addition to having a large chromosome which directs the microbes functions, has multiple tiny circles of DNA, called plasmid's, floating in its cytoplasm, which work at protecting the microbe from outside dangers. These are how bacteria develop antibiotic resistance. It is also how microbes develop the ability to survive in toxic environments.
If a single bacteria developed resistance to an antibiotic, it wouldn't do much good for the other bacteria in the colony. The colony's of bacteria that could incorporate the protection developed by a bacteria in their colony, would thrive, compared to colony's that didn't have this ability. Over time, bacterial colonies that were able to transmit favorable genes to each other thrived, as their colonies were able to outperform competing colonies.
Now all bacteria have the ability to pass on beneficial traits to other bacteria.
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Even different strains of bacteria can transmit beneficial traits to each other. For example, resistance to cadmium and cobalt was transferred to the {completely different strains} of bacteria, E. coli to A. eutrophus. Some microbes are more efficient than others in removing heavy metals, and as these genes are transferred to other microbes in a slurry, the cleanup of the tailing pond increases in efficiency.
Different microbes use different methods of removing toxic metals. Some microbes {chelate} the metals. Chelate is Greek for claw. The microbe binds the metal in two places and forms an irreversible bond, which in effect, removes the metal from the slurry.
Other microbes produce {calcite} and bind metals such as lead and cadmium inside it, which isolates the metals from the slurry.
Others use metals as part of their {respiration,} such as using soluble chromium (VI) Cr, and in the process of respiration, changing it into insoluble Cr³, which precipitates out of solution.
Some microbes form a {coating} around themselves which contains pockets with negative cations which bind to the positively charged metal ions, and binds them in the coating. The coating, with its embedded metals, periodically sloughs off of the microbe, which leaves the metals embedded in the slurry, and no longer in solution.
In a test site, researchers added five different types of microbes, that used different means of neutralizing toxic metals. The efficiency of the microbial removal of toxic metals increased by a factor of 14.
Science has barely started to discover the microbes that can make heavy metals less toxic. Currently {less than 1%} of the microbes that can detoxify heavy metals, and arsenic, are known to science.
Over time, more will be discovered, and this will increase our ability to make tailing pond's safe.
Scientists are learning how to take genes from bacteria that use different methods of detoxifying heavy metals, and transcript them into plasmids, which they then insert into bacteria, and greatly enhance their ability to remove toxic metals from contaminated sites.
They were able to genetically engineer a microbe that was able remove {25 times} more cadmium and mercury than the microbes native to the site.
What about the toxic metals, Chromium, Mercury, and Uranium, that are not precipitated by sulfate reducing microbes?
{Uranium} is found throughout Alaska, although usually not in a large enough quantity to mine.
Sulfuric acid turns uranium into the very soluble U, which, even if it is not present in large amounts; since it is in solution, if there was a tailing dam breach, it could be carried long distances and present a danger to the area.
Microorganisms have been found in uranium tailing's that use soluble uranium (U) as an electron acceptor for their respiration, and end up changing it into insoluble U. These microorganisms could be used in the Pebble tailing pond, to precipitate any U that was present in the slurry.
Soluble chromium VI (Cr) is one of the most toxic heavy metals known.Insoluble {chromium III} (Cr³) has only one thousandth of the toxicity of Cr.
A {wide range } of microorganisms that use soluble Cr for respiration, and change it into insoluble Cr³, have been found in contaminated sites. So there is no shortage of microbes that can be used at the Pebble site.
In addition to that, heavy metal levels do not have to be brought down to Zero. The EPA has designated safe levels for each metal, and arsenic. The levels of the various contaminants will only have to be brought down to the levels listed as safe by the EPA. Future bioremediation will effectively accomplish that goal.
Mercury is in a deadly category by itself. Microbes get rid of any mercury that enters them by changing it to organic {methylmercury} which they are able to transport through their cell wall and into the surrounding environment.
If methylmercury enters a river, lake, or the ocean, which could happen if it escaped from a tailing pond, it would quickly be taken up by the aquatic wildlife, because methylmercury is readily absorbed in the intestine.
Because it is hard to break down methylmercury when it has been ingested, it works its way up the aquatic food chain, and is eventually consumed by humans. It is severely neurotoxic, especially to a pregnant woman's developing fetus. So it is a strongly banned substance, and authorities would not want there to be a chance of it getting into the ecosystem surrounding the Pebble tailing pond. If there was a way to eliminate it, there would be a greater chance that the Pebble mine would be approved.
Previously there was no reliable way to remove it from giant tailing ponds. However, a group of methylmercury dismantling bacteria have been found that take up methyolmercury, and {break it down} into harmless components. They would prevent the build up of any methylmercury that might be produced by microbes in the Pebble tailing pond.
Complementing that, a bacteria has been genetically engineered that contains mercury scavenging sites. The sites isolate and contain the mercury, which prevents it from harming the bacteria. These bacteria can survive an environment containing {24 times} the dose of mercury that would kill non-resistant bacteria. They remove the mercury from the area around them. In a test of such an environment, in just 5 days, they removed over 80% of the mercury present in the solution.
Adding them to the Pebble tailing pond, would bring down any methylmercury present in the slurry to such low levels, that very little would be produced. The methylmercury dismantling bacteria would then easily remove any methylmercury that might enter the slurry.
By the time Pebble is ready to build its mine, bioremediation will have advanced to the point where tailing ponds will no longer be considered a threat to the area
What are the chances that the Pebble mine will receive approval
Similar to Pebble, the Donlin Gold project is located in southwest Alaska, and is seeking approval to build a mine. It's 39 million ounce gold deposit has a high mercury content.
Environmental groups have been opposing it, and so have several Alaskan tribes. This April the U.S. Army Corps of Engineers issued its Environmental Impact Statement (EIS) {approval.} They concluded that the company's mine design would prevent the mercury from escaping the site. They also approved the 315 mile long natural gas pipeline that the company wanted to build.
The company will now have to get 100 permits approved before they can begin construction of a mine. The state and federal agencies that issue the permits, will use the EIS to {guide} their decisions.
The company received an EIS approval, even with their deposit having a high mercury content, and their planned mine is near the Kuskokwim River. The U. S. Army Corps of Engineers concluded that the the company's construction plans were so well thought out that they would protect the countryside from even the most severe adverse effect that could threaten the mine site.
Pebble has a thoroughly thought out and documented mine plan, and so it should also receive an EIS approval, although this is not a certainty.
Will the Pebble mine make a significant difference in the amount of America's holdings of strategic metals
The geology of how Pebble was formed shows how much ore could be in the Pebble deposit and the
surrounding area.
The Pebble deposit formed 90 million years ago. At that time the tectonic {Pacific Plate} that formed the ocean floor next to Alaska, was colliding with, and sliding under, the Alaskan continental plate. When it descend to a depth of {35 miles} the oceanic rocks started to melt. The heavier sections continued on downward, but the lighter, buoyant, melted sections, took on the aspects of a lava lamp, and all along the arc of the colliding plates, hot elastic sections of the oceanic plate began an ascent towards the underside of the continental plate. (This hot, melted rock is called magma. If it makes its way to the surface and erupts from a volcano, it's called lava.)
Melted oceanic rock contains small amounts of various metals spread throughout it, but in very low concentrations, such as 30 parts per million for {copper} and a few parts per billion for gold and silver. The total amount is large, but it is too diffuse to be economic.
Oceanic rock contains sulfur, which turns to hot liquid sulfur, when the rocks that form the floor of the ocean melt and turn into magma, as they descend to the 35 mile depth. Liquid sulfur droplets, circulating throughout the magma, scavenge transition metals, such as copper, gold and molybdenum, and concentrated them up to {100,000} times their normal levels.
As the plume of melted oceanic rock continued upward, it passed through a {layer} of metal enhanced molten rock, which further {enriched} the oceanic magma plume, with metals such as copper and gold. And this additional metal was also incorporated into the liquid sulfur.
The rocks that form the ocean floor have numerous open spaces, called pores, between the particles that made up the rock. Many of these open spaces are filled with salty ocean water (brine). At the depth where the oceanic plate melts, the pressure squeezes the atoms of the brine molecules so tightly, that, even though the magma is red hot, the brine can't turn into steam.
In the high temperature and pressure of the magma, the intensely hot brine becomes very reactive and the chlorine in it (NaCl) scavenges metals and concentrates them {1000 times higher} than their normal concentration in the magma.
Even normally inactive gold, forms soluble compounds in the circulating hot brine, such as {hydrogen gold chloride} (HAuCl2).
Mineralized porphyry deposits form over {durations} of a few hundred thousand years, to periods of several million years. {Giant} porphyry copper deposits require sufficiently long periods to accumulate large ore deposits. In addition to duration, magma that contains large amounts of copper, and associated metals, such as the magma associated with the Pebble deposit, will significantly increase the amount of ore that is formed.
The magma producing events that formed the Pebble ore deposit extended over a time scale of {3 to 4 million years,} which is {longer} than the duration of most porphyry producing episodes. Fresh, metal rich plumes of magma, repeatedly rose from a deep magma chamber, mixing in with the magma that was forming the Pebble deposit, and preventing it from cooling and solidifying, as well as replenishing it with additional quantities of metals. For millions of years, additional metal was repeatedly added to the Pebble deposit, eventually making it the largest ore deposit that has ever been discovered.
The hot molten magma that formed the Pebble deposit worked its way upward, cooling slightly as it rose, and becoming less molten, and thus thicker, until it could not work its way any higher, and ended up at a depth of {3.8 kilometers} (2.4 miles).
The metal enriched hot brine from the magma, then rose upward through cracks in the overhead rock. The hot brine, which is called hydrothermal fluid (hot water), can carry extraordinarily high concentrations of metals, such as {10% by weight} copper.
{Hot brine's} hold in solution greater concentrations of metal than cold brine's. As the brine from the magma moved toward the surface, it cooled, and by the time it reached Pebble's location, it cooled to the point where the metals started to precipitate into the open cracks and pores in the rock.
In addition to the water already present in the magma, surface water seeping through cracks in the rock, worked its way down to the magma chamber. Over the distances traveled, water picks up impurities, including salt.
As this salty (chloride containing) water entered, and circulated through the hot magma, it in turn, absorbed metals, plus the metal enriched sulfur, that had not been captured by the original brine that was in the magma.
This, now metal enriched water, that was circulating in the hot magma, in turn rose towards the surface, and added more metal to the evolving Pebble deposit. This continued for millions of years as fresh plumes of hot metal containing magma worked their way up into the magma chamber that was feeding the Pebble site.
How much ore are we talking about?
Pebble has been {drilled} to a depth of a little over a mile, 5,900 feet, which is 1.1 miles, and the drills were still encountering ore in quantity. In fact the grade of {molybdenum} was increasing with depth.
Molybdenum and copper and gold start precipitating out of hydrothermal solutions at a depth of {2.3 miles.} The magma chamber that produced the Pebble deposit is located below that, at a depth of 2.4 miles. This is far enough down, that the metals in the Pebble deposit, could have been deposited starting at a depth of 2.3 miles.
The Pebble deposit has been drilled to a depth of 1.1 miles. Mo, Cu, and Au most likely started precipitating out into the Pebble deposit at a depth of 2.3 miles. This means that Pebble's ore deposit could be more than double its present depth.
The Pebble deposit is open outward to the E, S, NW and SE. In those directions, the drills were still encountering full strength ore. This indicates that, in addition to the Pebble deposit being much deeper than presently delineated, it could be much wider. Therefore, the amount of ore in the Pebble deposit could be much greater than is presently listed.
Pebble's molybdenum ore, molybdenite, contains high concentrations of the critical metal, rhenium, whose high melting point of 5,725° F and, stable crystalline structure, that resists {creep_deformation,} makes it ideal for rocket and stealth {jet engine} turbine blades.
Molybdenum itself is a critical metal. When molybdenum is added to steel, it forms an ultra-high-strength steel that will maintain structural stability when placed under pressures reaching as high as 300,000 lbs/sq. inch.
Molybdenite (molybdenum + rhenium) increases with {depth,} and therefore the deeper the Pebble ore deposit is extended, the greater the proportion of molybdenum and rhenium it could contain.
And this could be just a tiny amount of what is actually there to be found
The Pebble property is surrounded by a 350 square mile {oval of solidified} magma that is located 6 miles underground. Ninety million years ago, this batholithic magma chamber was molten, and, in addition to forming the Pebble deposit, this giant 350 square mile magma chamber sent up multiple plumes of magma throughout the area. These could have produced additional ore deposits, which may be similar to the Pebble deposit, because they were produced from the same magma chamber that formed the Pebble deposit.
The United States Geological Survey states that the mineralized area around Pebble is the most {extensive} in the world and could host multiple deposits in the area.
Pebble is in an area that is poorly explored because of an extensive cover of glacial debris. A regional-scale airborne {aeromagnetic} survey was conducted to penetrate this cover and see what was under it.
Analysis of regional aeromagnetic data showed a 250 mile long magmatic arc in southwestern Alaska, extending to both the northeast and southwest of Pebble, that was similar in age to the Pebble deposit that was formed 90 million years ago. The people doing the aeromagnetic survey concluded that the Pebble district is "highly prospective for porphyry-style deposits similar to the giant Pebble porphyry Cu-Au-Mo deposit."
The journal {'Economic Geology'} reported on aeromagnetic survey's done in the area and stated that examination of southwestern Alaska has disclosed a number of large deep-seated anomalies in a setting similar to the porphyry environment of northern Chile and that this "suggests that southwestern Alaska is highly prospective for porphyry exploration."
A {U.S. Geological Survey} reports clustered groups of anomalies 15-25 miles long by 12-18 miles wide along the Alaska Lake Clark fault and that they are the same age as the near by Pebble deposit. The spacing of the clusters are similar to the giant porphyry copper-gold-molybdenum deposits of northern Chile, and favorably suggests similar discoveries in southwestern Alaska.
In Chile's Atacama desert there are multiple giant copper-gold-molybdenum-silver mines. These mines are located along a {375 mile} long belt. Like the Pebble deposit, they are also giant deposits, because they formed over a 3 million year period of magmatic hydrothermal episodic pulses, which in their case, started 38 million years ago.
Chile's mines have been in production for over 100 years, such as Chuquicamata, which has been in production since 1910, and is still one of the largest ore deposits in the world. A hundred years of continuous mining has barely touched it. And, like Escondida, another giant mine in the ore bearing belt, these mines are not composed of a single deposit, but a group of deposits located in the same general area.
Depiction of the multiple ore deposits (mines) in Chile's ore bearing belt.
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There are ways to determine if more deposits are in
the area surrounding the Pebble deposit
An aeromagnetic survey is done by a plane flying over an area while transmitting a current which varies in strength. According to Faraday's law of induction, this time varying field induces currents in conductive features, such as ore, in the ground. These currents produce an associated (secondary) magnetic field in the ore that can be detected by an electromagnetic receiver on the plane. There is no need for the transmitter or the receiver to touch the ground, so electromagnetic systems can be mounted on aircraft and be used to explore large areas quickly and efficiently.
What that means, is, if there is metal ore in the ground, the plane will induce currents and a magnetic field in the ore, which will be detected. Once the plane passes past the ore bearing structure, the signal will stop, and thus the width, as well as the location, of the deposit can be determined.
The electronic signal is traced on paper, and the site it maps is called an anomaly (if the scan indicates that an area is different from the normal rock background, it is an anomaly.)
However, the scans can't tell you if they are detecting gold or fools gold. Fools gold, also known as pyrite, is iron disulfide, and the iron would give a strong signal. So, even though scans can detect buried ore deposits, they can't tell you if the ore is of any value. But scans do two things. They show where an ore deposit is located, after which the site can be tested to determine what ore it contains. Plus the scan also gives a signature of the ore deposit.
Since Pebble has been drilled, its ore content is known. The scans of any anomalies in the area around Pebble, can be compared to Pebble's scan and any anomalies who's signatures are similar to Pebble's, could be a similar type of deposit.
But drilling is very expensive, and so, even if you find an anomaly with a signature similar to the Pebble site, you want to be sure, if possible, that you are drilling a site with valuable ore. You would also want to know what type of ore it contains. If it is just iron, you would skip it. If it contains valuable metals, such as gold &/or copper, then you would want to drill it.
It turns out that there is a way to know what type of ore a site contains. Because most sites in the area that would be discovered by an aeromagnetic survey, have a thick overburden of glacial till, you could not directly take samples to see if the site contained valuable ore.
But, over time, atoms, and isotopes, of any buried ore, migrate to the surface, being carried upward by ascending water, etc, and can be detected in parts per billion, or even parts per trillion, on the ground surface over the ore site. Testing the surface over an anomaly can detect ore buried as deep as 1,800 feet.
There were two companies that had claims adjacent to Northern Dynasty, and
after they did airborne scans over their property, they performed surface geochemical studies over the anomalies that they located. The geochemical tests of the anomalies would show if the site's contained valuable ore.
Northern Dynasty later bought their properties.
The results of those studies have not been reported by Northern Dynasty
So I researched the subject myself
Liberty Star Uranium & Metals (LBSR), had property in the same vicinity, one side of which, was adjacent to Northern Dynasty's Pebble property.
The company, Full Metals, also had property, with one side of it adjacent to a section of the Pebble property.
Liberty Star Uranium and Metals Corporation spent seven years, 2003-2010, doing an extensive work up of their property, including airborne scans and geochemical testing of the anomolies that the scans discovered.
McPhar Geophysics did an aeromagnetic survey over LBSR's property. Geotech Ltd. conducted a 6,000 foot deep ZTEM scan over LBSR's property. The scans showed several sites that had large, deep, anomalous areas.
To determine what types of metals were present in the deposits outlined by the scans under the layer of glacial till, LBSR took 11,000 geochemical soil samples, 4,274 vegetation samples, and 993 water samples.
How does testing the { ground surface} of an anomaly, tell if it can contain any valuable ore
Especially if the ore is buried a thousand feet underground
Soil samples
Even though an ore deposit may be deeply buried, it can be detected by sampling the surface area of the ground above the deposit, because minerals and isotopes that are unique to the ore in the deposit will make their way to the surface, although only in tiny amounts. It used to be difficult to detect them, but new {instruments} that can detect compounds in parts per billion, and even parts per {trillion,} can now, not only detect them, but give an accurate measurement of their concentration.
One ppt could be represented by detecting one yellow marble on 20,000 football fields (almost 39 square miles) covered with orange marbles.
Being able to accurately measure the metals is important because, if the instruments detect that the area has valuable metals, they can show up in the area away from a deposit, but in smaller amounts than what is present directly over the deposit. By being able to accurately tell the differences in the amounts of metal in the area, even if it is only a few parts per trillion difference, you can gauge where the center of the deposit is located, and the edges of the deposit. Using these instruments, it is now possible to detect ore deposits that are as deep as {1,800 feet.}
Testing ground samples
One method that is now being used, is testing for {resistate} porphyry indicator minerals, because they are more abundant than the valuable metals that are being sought, and so are easier to find, and at the same time, their presence indicates that the sought after valuable metals are also present. These are minerals that are resistant to erosion and destruction. The reason that they can indicate if there are valuable metals in the area with them, is because they are altered in hydrothermal environments that specifically produce the valuable metals. Even if they are deep underground, they make their way to the surface in trace amounts, and because they are resistant to destruction, weathering of the site won't destroy them. Their discovery will point to metal deposits hidden under the glacial till.
The word {isotope,} meaning at the same place, comes from the fact that isotopes are in the same place on the periodic table. Chemical elements, such as copper, can have different numbers of neutrons in their nucleus, but all its isotopes will have the same number of protons and electrons, and they will just be considered to be copper, with a different atomic weight. In addition to having a different atomic weight from the primary metal associated with them, they will have different chemical and physical properties. The isotopes will not only tell you which metals are present at the site, in certain cases, they will also
indicate their depth.
Because of their differing atomic weight, isotopes have different
{oxidation-reduction} reactions than the primary metal itself. Specific microbial communities that live underground use these isotopes for their metabolism. Some of these microbes, along with associated isotopes, are brought to the surface with ascending water. The metal isotopes will indicate what metals are present in the ore deposit, plus, since different microbes live at specific depths, the ones that were using the ore in the deposit, will reflect the deposit's depth.
{Vegitation} sampling
Trees with deep tap roots, such as the Alder trees that grow in the area, absorb geochemicals, such as gold ions, from a large volume of soil and groundwater.
{Experiments} have shown that it is possible to locate buried deposits by comparing the amount of gold over an anomaly, to the amount of gold away from the anomaly.
Gold is a toxic metal to Alder trees, and is transported to its extremities, its branches, bark, and leaves. One of the tests LBSR performed was taking samples of leaves from the Alder trees over an anomaly, as well as from Alder trees away from the anomaly. The samples from the Alder trees growing over the anomaly's had 20 times more gold than trees growing 650 feet away from the anomaly, indicating a buried deposit on the site.
Water samples
Copper {isotope ratios} in ponds and streams can provide insight into buried metal deposits. Surface waters proximal to the deposit, and which likely interacted with underlying concealed mineralization, have heavy d65Cu values which contrast with lighter values in waters distal from the deposit.
Ground water going through a deposit picks up trace amounts of the metal contained in the deposit. These can be detected in nearby streams, or ponds, that incorporate the ground water. Comparing the amounts against known background concentrations, will point out locations that have higher than normal amounts of metal, as well as what type of metal, such as gold, that may be located beneath a nearby downstream site.
In 2004/2005, Northern Dynasty allowed LBSR to conduct geochemical and geobiological sampling on the soil over their Pebble deposit
That way LBSR could compare the results with the anomalies that they were evaluating, and see if any of them were similar to Pebble's surface trace mineral signature. In return, LBSR shared their results with Northern Dynasty.
***
Tests of the soil over the area of what would become the {Pebble East Zone,} showed that there was a deposit containing gold, copper, and molybdenum under that area, EVEN THOUGH IT WAS UNDISCOVERED AT THAT TIME, and under 1,000 feet of glacial debris.
***
Northern Dynasty's planned step out drilling encountered the Pebble East zone exactly over LBSR's geochemical signature of the deposit, and the drilling showed that the metals it contained, were the same ones discovered in the geochemical surface testing.
This shows that the geochemical/geobiological surface testing of a site
WILL BE ABLE TO TELL YOU WHAT METALS, IF ANY, IT CONTAINS
In 2007 - 2010, a {geochemical evaluation} of the Pebble property was done by the U.S. Geological Department of the Interior. In addition to gold and rhenium etc., the samples detected arsenic and mercury, as well as trace amounts of uranium.
.................
LBSR's airborne scans outlined 7 large {anomalies,} that were 1.5 miles in diameter, plus 5 smaller anomalies.
Full Metals
Did an airborne survey that located 4 anomalies equal in size to the Pebble East and West deposits, (= to 2 Pebble deposits), plus 1 smaller anomaly. Geochemical sampling showed that all of them contained copper, gold, and molybdenum.
In July of 2010, Northern Dynasty formed a {joint venture} with LBSR, and LBSR's stock price went from $0.02 to $0.175
Having multiple deposits in nearby locations is not unusual.
Escondida's giant copper-gold deposit in Chile, is actually a group of related deposits. Seabridge Gold's giant KSM copper-gold mine is also not just one deposit, but a group of deposits, all located in the same general area.
Northern Dynasty has indicated that if any deposits similar to Pebble are found in the area, they will be included in the Pebble project.
How big could the Pebble project be
The Pebble deposit is most likely double its presently defined size, so that is the same as adding another Pebble deposit. Adding that to LBSR's plus Full metal's properties would give
10 deposits similar to the Pebble deposit in size, plus 6 smaller anomalies. Geochemical samples show that they all contain copper, gold, and molybdenum ore.
These figures only include the nearby LBSR and FULL METALS sites. Aeromagnetic surveys showed a 250 mile arc underlain by magma similar to which produced the Pebble deposit, and containing multiple anomalies. These could also be deposits similar to the Pebble deposit.
The future belongs to the optimist.
AI
