Money doesn't grow on trees, but gold can. An international team of scientists has found a way to grow and harvest gold from crops. A gold-mining technology called phytomining uses plants to extract particles of the precious metal from soil.
Some plants have a natural ability to absorb through root system and accumulate metals such as nickel, cadmium and zinc in leaves and shoots. For years, scientists have been looking for ways to use such plants, called supersinks, to remove pollutants from environment.
But nothing is known about superaccumulators of gold, since this metal is practically insoluble in water, and therefore plants do not natural way absorb its particles through the roots.
“Under some chemical conditions, gold solubility can be artificially increased,” says Chris Anderson, an environmental geochemistry and phytomining specialist at Massey University in New Zealand.
Getting gold
Fifteen years ago, Chris Anderson first demonstrated to the public that the mustard plant was capable of absorbing gold from chemically prepared soil containing particles of this metal.
The technology works something like this: find fast growing plant with a large volume of above-ground leafy matter, such as mustard, sunflower or tobacco. Plant the crop in soil containing gold. Nice place there may be waste heaps or dumps surrounding old gold mines. Conventional methods cannot ensure 100 percent extraction of gold from minerals, and therefore some volumes of the metal end up in waste. When the plant reaches maximum height, treat the soil with a chemical that dissolves the gold. The plant absorbs gold-containing water from the soil, during the process of “breathing” water emerges from tiny pores on the surface of the leaves, and the precious metal accumulates in the biomass. All that remains is to harvest.
However, putting the gold into the crop is the easy part of the job. Obtaining it from a plant turns out to be much more challenging task, explains Anderson.
"IN plant material gold behaves differently,” says the scientist. If a plant is burned, then some amount of metal will remain in the ashes, and some of it will disappear altogether. Ash treatment is also a major challenge and requires the use of large volumes of concentrated acids, which are dangerous to transport.
Gold, which can be found in plants, is in the form of nanoparticles and is therefore of great value to the chemical industry, which uses gold nanoparticles as a catalyst for chemical reactions.
Golden Harvest
Phytomining for gold will never replace traditional sources, the scientist says. “The value of this technology is the potential for revitalizing contaminated land in gold mining areas,” adds Chris.
The chemicals used to dissolve gold cause plants to absorb other contaminants from the soil, such as mercury, arsenic and copper, which are common elements found in mine waste and dangerous for people and the environment.
"If we can make a profit by extracting gold from crops while restoring soils, that would be a significant achievement," Anderson says. He is currently working with researchers in Indonesia to develop environmentally friendly technology for small firms using manual labor in gold mining, which will reduce mercury pollution as a result of the activity.
However, some scientists say the environmental risks associated with gold farming itself may be too great. Indeed, to dissolve gold particles in the soil, it is necessary to use cyanide and thiocyanate - the same dangerous chemical substances, used by mining companies to extract gold from stones. Independent agronomists are confident that the process itself can create environmental problems.
Money doesn't grow on trees - but gold might. An international team of researchers has found a way to grow and harvest gold from plants.
This technique uses plants to extract precious metal particles from the soil. Some plants have the natural ability to absorb metals such as nickel, cadmium and zinc through their roots and accumulate in their leaves and shoots. For years, scientists have been exploring the possibility of using these plants, called hyperaccumulators, to clean up chemical pollutants.
But there are no gold hyperaccumulators known to science, since gold does not dissolve in water, and plants do not have natural way extract its particles through its root system.
However, geochemist Chris Anderson from Massey University in New Zealand states: "Under certain chemical conditions, gold solubility can be enhanced."
15 years ago, Anderson first demonstrated that mustard plants were able to absorb gold from chemically treated soil containing metal particles.
The technology works something like this: You find a fast-growing plant with a large volume of above-ground foliage, like mustard, sunflower or tobacco. Plant it on soil containing gold. A good place is waste rock dumps near old gold mines. Traditional gold mining is unable to extract 100 percent of the gold from the surrounding rock, so some remains in waste. Once the crop is up, treat the soil with a chemical agent that makes the gold soluble. As moisture evaporates from the leaves of the plant, it will draw gold-rich water from the soil and concentrate it in its green mass. Then harvest.
As Anderson explains, putting the gold into the plant is the easiest part of the job. It is much more difficult to remove it back later.
“Gold behaves differently inside a plant,” he says. If the plant is burned, some of the gold will remain combined with the ashes, and some will simply disappear. Processing the remaining ashes is also difficult because it requires huge amounts of strong acid which may be dangerous to transport.
Extraction of precious metal using plants will never replace traditional methods gold mining According to Anderson, "The value of this technique lies in the restoration of sites contaminated by metal mining."
The chemicals that make gold soluble also cause plants to release other contaminants, such as mercury, arsenic and copper - substances that are common in mine waste sites and can pose a risk to people and the environment.
“If we can make a profit by extracting gold and at the same time restoring the soil, that would be a good thing,” says Anderson, who is currently working with a team of researchers in Indonesia to create a sustainable system whereby small-scale gold miners could reduce mercury pollution from their mines. operations.
However, some scientists point out that the environmental risk associated with growing gold-bearing plants is also not too low - the medicine in in this case not much better than the disease itself. The fact is that to dissolve gold particles in water, the same chemicals are used that mining companies use to extract gold from mineral rock - and these are cyanide and thiocyanate.
February 27th, 2015 , 10:37 am
After reading this post, you will learn: How to cheer yourself up early in the morning so that it is also good for your health? How to get around two hundred wives in one night if you have a harem. And what exactly is “liquid gold”?
In fact, the answer to this question is simple - it is chocolatl (or as it has been called for several centuries - cocoa). Linguists believe that the word "chocolate" is a combination of the terms "choco" ("foam") and "atl" ("water"). In ancient times, chocolate was only a drink. In the Mayan language there was a word "chacahuaa", which was used to describe a drink made from dried and ground cocoa beans. It reveals the later name of the Aztec drink “chocolatl”, which the leader Montezuma treated Cortez, who discovered cocoa for Europe. It is believed that the Spaniards found it difficult to pronounce this word and, taking the Aztec name for the cocoa tree “cacahuatl” as a basis, they began to call this drink cocoa.
However, the drink that the Aztecs treated the Spaniard Hernan Cortez was not much like modern hot chocolate. Chocolatl was prepared on hot stones from fermented and ground cocoa beans, thickly seasoned with hot pepper. Cortez's team dubbed this drink "bitter water", and, having tasted it only once (not a single member of the team decided to taste it again), the Spaniards were sincerely perplexed as to how the Indians could drink such a brew, and even consider chocolatl a gift from heaven. The Mayans, who first began cultivating cocoa in the 4th century AD, began adding pepper or, less commonly, wild honey to the drink.
And so, already in Europe there were several recipes for cocoa, some of which were even for a long time classified.
The basic recipe for the drink was:
- 700g cocoa,
- 750g white sugar,
- 56g cinnamon,
- 14g cloves,
- 14g pepper,
- 3 vanilla pods.
To taste, it was recommended to add a pinch of anise grains, nuts, musk or orange flowers to the resulting drink.
Other recipes:
Spain (XVII century)- Cocoa beans, water, honey, vanilla, cinnamon, nutmeg, honey (the drink began to be served hot).
Recipe for King Philip II, “increasing male strength” (XVI century)- Cocoa beans, water, vanilla pods, black pepper, honey.
Most interesting recipe (Francisco Hernandez, physician to the Spanish King Philip II) - mix together 50% roasted cocoa beans, 50% jujube beans and add crushed corn, the sacred ear-flower of the Aztecs, black pepper, honey and, if desired, chili pepper, allspice and Mexican magnolia flowers.
France (XVIII century)- Cocoa beans, vanilla, cinnamon, nutmeg, sugar, boiled milk (hot chocolate).
Recipe for Marie Antoinette (XVIII century)- In addition to the usual ingredients, orchid flower powder, orange flowers and almond milk were added to the drink.
By the way, Montezuma, the happy husband of two hundred wives, drank about fifty cups of a drink made from cocoa every day to fulfill his marital duty. There were rumors among his subjects that in one night Montezuma visited the chambers of all his wives, not depriving any of them of attention! The leader himself explained such an amazing tone only by the effect of cocoa, the use of which became his daily ritual from his youth.
This is now called “liquid gold” the blood of the earth, for which people are ready to shed their own. But for the Aztecs, everything was simpler; for them, a drink that increased potency was liquid gold. And cocoa beans themselves were essentially money; for example, for just 100 beans you could buy yourself a slave.
To be continued...
Photos were taken and interesting information received from the Criollo Museum of the History of Chocolate (Kirov, Spasskaya St., 15).
Where the bronze cliffs hung
Above the green mountain river,
A geologist in a checkered shirt stood up
And he swung his pickaxe at the rocks.
V. Soloukhin
Our planet is great and rich. In its depths are buried countless treasures - oil and coal, gold and diamonds, copper and rare metals. At the cost of enormous amounts of time and labor, humanity over the thousands of years of its existence has managed to extract only a small fraction of underground wealth from the earth. In all countries of the world, a large army of exploration geologists is examining, tapping, and feeling the Earth, trying to find new deposits of minerals. The experience of many generations and first-class technology, the erudition of great scientists and complex instruments - everything is put at the service of searching for earthly treasures. And yet these searches are rarely crowned with success. Nature jealously guards its secrets, yielding only to the most inquisitive and persistent.
Since ancient times, signs have been passed down from generation to generation indicating the emergence of gold-bearing veins and oil, copper ores and coal. The idea of using plants to search for minerals has long been conceived. In vintage folk beliefs it speaks of herbs and trees capable of detecting various deposits. For example, it was believed that rowan, buckthorn and hazel growing nearby hide gems, and the intertwined roots of pine, spruce and fir indicate gold placers beneath them. Of course, these legends remained a beautiful dream, and nothing more.
Geologists have resorted to the help of plants only in recent decades, when scientifically based connections were found between certain plants and deposits of certain minerals. Thus, in Australia and China, with the help of plants that select soils with a high copper content for growth, deposits of copper ore were discovered, and in America, deposits of silver were found using the same method.
Behind last years In our country, scientists have conducted thorough studies of the vegetation settling in areas where metal-bearing ores are located. The conclusions that scientists came to were truly amazing. The connection between the plant, the soil and the subsoil turned out to be so close that appearance or chemical composition For some plants, it was possible to judge what ores lie in the place where they grow. After all, the plant is not at all indifferent to what species is under the soil on which it grew. Groundwater gradually dissolves metals to one degree or another and, seeping upward into the soil, is absorbed by plants. Therefore, grass and trees growing above copper deposits will drink copper water, and above nickel deposits - nickel water. Whatever substances are hidden in the ground - beryllium or tantalum, lithium or niobium, thorium or molybdenum, water will dissolve their smallest particles and bring them to the surface of the earth; the plants will drink these waters, and microscopic amounts of beryllium or tantalum, lithium or niobium, thorium or molybdenum will be deposited in every blade of grass, in every leaf. Even if metals lie deep under the soil, at a depth of twenty or thirty meters, plants will sensitively respond to their presence by accumulating these substances in their organs. In order to determine how much and what metals a plant has accumulated, it is burned and the ash is studied. chemical methods. It happens that over large deposits of some ore, this metal accumulates in a plant a hundred times more than in the same plant growing in another area. Most metals are always accumulated by plants in very small quantities. The living organism of the plant needs them, and without them the plant gets sick. However, strong solutions of the same metals act as poison on many plants. Therefore, in areas of metal ore deposits, almost all vegetation dies. Only those trees and herbs remain that can withstand the accumulation of large quantities of any metal in their bodies. Thus, thickets appear in these areas certain plants, capable of drinking metallic water. They indicate the places where you need to look for minerals.
For example, large quantities Some plants from the legume family, such as Sophora and commonweed, are able to accumulate molybdenum in their bodies. Larch needles and wild rosemary leaves easily tolerate large amounts of manganese and niobium. Neither deposits of strontium or barium, willow and birch leaves accumulate these metals thirty to forty times more than normal. Thorium is deposited in the leaves of aspen, bird cherry and fir.
In the Altai Mountains, where copper ore has long been mined, you can often find a perennial herbaceous plant with narrow bluish leaves, above which rises an indistinct cloud of numerous pale pink flowers. This is downloading Patren. Sometimes kachim forms large thickets that stretch in wide stripes for several tens of kilometers. It turned out that in most cases copper ore lies just under the kachima thickets. Therefore, geologists, before starting underground work, draw up maps of the distribution of kachim and use the maps to determine the locations of supposed copper deposits. The powerful, woody, twisted cachima root goes deep into the ground. It penetrates through the soil and through cracks in the underlying rock reaches groundwater in which copper is dissolved. Copper water rises up to the bluish leaves and light flowers. From June to August, the kachima thickets appear from an airplane as a pink lace, draped by nature over the scorched steppe rocky slopes. On aerial photographs, this lace will be indicated by a clear stripe, indicating the places where copper ore occurs.
In the east of our country, dense thickets over deposits of rare metals that contain beryllium are formed by Stellera dwarf. Steller - very graceful plant with straight thin stems, densely dressed with bright green oval leaves pressed to the stem. The stem is crowned with a bright light crimson head, consisting of two dozen small tubular flowers; the outside of the tube is crimson, and the tip of the rim is white. Just like the kachim, this extremely elegant and tender plant developed underground powerful root, penetrating with its branches deep into cracks in solid rock and sucking up water with beryllium dissolved in it. 
Steller perfectly withstands the beryllium “menu”. Wide stripes of its continuous thickets indicate on aerial photographs the location of underground deposits of rare metals.
Everyone knows what enormous technical significance uranium has. Many countries around the world are searching for this radioactive element. And here plants help geologists. If the uranium content in the ash of burnt branches of bushes and trees is high, it means that uranium can be found in this area. Junipers are especially good at collecting uranium. Their powerful, long roots manage to penetrate to great depths during the two to three hundred years of life of each individual. Even if the uranium deposits are not rich, the juniper will accumulate quite a lot of uranium in its branches. Even better indicates the presence of uranium, the well-known berry bush blueberry. If this plant drinks uranium water, its oblong fruits acquire a wide variety of colors. irregular shape, and sometimes even turn from dark blue to white or greenish. Pink fireweed, growing on uranium deposits, can give the plant a range of colors - from white to bright purple. For example, fireweed flowers of eight different shades were collected near uranium mines in Alaska.
As a rule, uranium is accompanied by sulfur and selenium. Therefore, plants that accumulate these substances are also taken into account as an indicator of possible uranium deposits. If geologists know plants well, they will always distinguish selenium astragalus from all others. And where there is selenium, there may be uranium.
In some areas of the Karakum Desert, sulfur deposits appear close to the surface. The soil is so saturated with sulfur that, except for one type of lichen, nothing grows there. But lichens form large bald patches, clearly visible from an airplane.
Almost no vegetation grows in desert gold deposits. But wormwood and harelips feel excellent here. These plants accumulate such quantities of gold in their bodies that they can rightfully be called golden.
It is interesting that some plants living above ore deposits change their appearance in one way or another. Therefore, geologists in search of minerals must pay attention to the ugly shapes of trees and grasses. For example, where a large nickel deposit was discovered, nickel waters influenced herbaceous plants that “their own mother will not recognize them.” The well-known furry lumbago with large flower completely changed here. Above the nickel deposits, you can collect a bouquet of lumbago with flowers of the most varied colors - white, blue, and indigo. In addition, you can find here individuals whose petals seem to be torn into narrow ribbons or have none at all. Only bare, uncovered stamens stick out at the top of the stem.
The hairy breast has changed even more noticeably. This perennial resembles a small aster. Its small yellow baskets rise like a shield above a woolly white-felt stem framed by numerous oblong leaves. But nickel, which from the beginning of life penetrated into all her organs, did its dirty deed - the baby was unrecognizable. Smallest yellow flowers, which should have been collected into an inflorescence, scattered throughout the stem and hidden in the axils of the leaves. The leaves and stems also lost their shape and color. Every plant is a freak; one more unusual than the other. Ugly individuals of the hairy breast are so confined to deposits of nickel ores that, having encountered these forms somewhere in large quantities, geologists begin to carefully examine this area and almost always find nickel there.
It has also been noted that hollyhock flowers with abnormally dissected narrow petals may indicate deposits of copper or molybdenum.
Rocky slopes in Armenia blaze with tongues of fire in spring. The poppy is in bloom, coloring the foothills in festive red. The poppy petals with a large black spot at the base are wide, almost kidney-shaped. However, the poppy that grows in some areas is not similar to its relatives. Its petals are dissected into lobes in a way that is observed in most individuals growing in these areas. What's the matter? The fact is that deposits of lead and zinc are hidden in the ground here. These metals, constantly absorbed by the plant, changed the entire course of its development, and as a result, the shape of the petals also changed.
And the petals of poppies growing on copper-molybdenum deposits can be completely black, with a narrow red border - this is how they grow black spot. In other individuals, the spots on the petals become long and narrow, forming a kind of black cross in the center of the flower, or, conversely, move to the outer edge of the petal. In general, these poppies look so unusual that they immediately catch the eye of even an unobservant person. And for geologists they are a godsend!
Sometimes, with an increased content of metals in the soil, plants take on an unusual dwarf form. When cold wormwood grows over a lithium deposit, it appears undersized with its twisted stem and small, abnormally bluish leaves. Plants that absorb large amounts of boron also do not grow upward, but take on a form spread out on the ground, which differs sharply from the usual appearance of this plant. The gumweed that drinks lead water also grows small and stocky, and its leaves and stems become dark red, while its flowers become small and inconspicuous.
However, the opposite also happens. For example, in some areas of our country you can find giant aspens. The leaves of these tall, thick-trunked aspens are several times larger than usual. Can you imagine a thirty-centimeter aspen leaf? How the flags flutter giant leaves on the same giant petioles. Maybe these extraordinary trees do they drink “living” water? In a way, yes. They drink water saturated with thorium - here, under the soil, lies a deposit of rare metals.
Narrow rivers flow through the cold lands of Yakutia, among swampy swamps and open larch forests, flowing into deep rivers.
Summer is short and stormy in the Arctic. More ice floes, colliding, float along spring waters rivers, and already on their banks low thickets of rhododendrons are covered with a purple-pink foam of small flowers, blueberries are blooming tender leaves, wild rosemary smells intoxicating. Above all this spring splendor from dawn to dusk there is a tedious ringing of mosquitoes. Somewhere here, among the larches, under a dense lichen carpet, the richest diamond deposits lie deep in the ground. Diamonds are interspersed with small raisins in the rock containing coal. This type of rock with diamonds is called a kimberlite pipe. How to look for it, this kimberlite pipe, if it is hidden by nature under seven locks? Only occasional exposures of kimberlite to the surface help geologists discover diamond deposits. Either a powerful landslide will expose ancient layers of the earth, or a long-ago earthquake or volcanic eruption. True, in recent years, new smart devices have come to the aid of geologists, allowing them to “see” underground, but they cannot accurately indicate places natural storehouses jewelry. Is it possible to use vegetation as assistants, scientists wondered. It turned out it was possible. It was noticed that directly above the kimberlite pipes both trees and shrubs look much better than their counterparts growing on limestone. This is understandable. In rocks that include diamonds, in addition to coal, apatites containing phosphorus, mica containing potassium, and various rare metals necessary for the plant body were found. All these elements dissolve in greater or lesser quantities groundwater, then penetrating into the soil. Therefore, plants that are lucky enough to grow above diamond deposits feed much better than trees and shrubs growing on skinny limestone. That is why above the diamond deposits the larch is taller and thicker, the alder is curly, and the blueberry thickets are thicker. Where one hundred frail larches grew on limestone or a swamp, two hundred healthy ones grew on kimberlite pipes. If you rise above these places by plane, you can see denser and more lush thickets among the larch forests - just in those places where kimberlite pipes lie. But in such an important matter as the search for diamonds, the human eye is not trusted. Much more objective is the eye of the camera, dispassionately looking down at the ground. On the film, the camera carefully marks with dark spots on the gray background of light forests areas of denser and higher forest, and therefore, places where you need to look for diamonds.
No, it is not an easy task to search for minerals. And, of course, one cannot completely trust the testimony of trees and herbs alone. However, plants, like real scouts, have more than once helped geologists in search of underground treasures.
Primary gold deposits are associated with intrusive rocks: diorites, quartz diorites and granites. They are called intrusive or intruded because they were formed as a result of the solidification of magma that penetrated from the depths into the upper layers of the earth's crust, but did not reach the surface. Intrusive bodies formed by the solidification of magma that filled vertical or slightly inclined cracks in the earth's crust are called dikes.
The importance of intrusive rocks is enormous because they were formed from the same magma, which at the same time was a source of hot melts and solutions, during the solidification of which gold deposits appeared. In this sense, the presence of intrusive rocks serves as an indicator of the possible location of industrial ore bodies near them.
Gold is usually closely associated with sulfur compounds of non-ferrous metals and related minerals or with their oxidation products. These gold satellites are represented by chalcopyrite, pyrite, sphalerite, galena, arsenopyrite, stibnite, brown ironstone, etc.
Widespread satellite - chalcopyrite(copper pyrite) has a golden color with a metallic sheen and is very similar in appearance to gold in the rock. But even an inexperienced scout, without resorting to testing with acid, can easily recognize chalcopyrite by its higher hardness. Even harder than chalcopyrite, also similar to gold, its other companion is p i r i t(sulfur pyrite). They are valuable minerals: chalcopyrite-the main ore for copper, and pyrite used to produce sulfuric acid.
Sphalerite(zinc blende) has black, brown or Brown color, diamond shine. In quartz veins it is found mostly in the form of crystals, faceted with a system of regular planes. Scratched with a knife.
Galena(lead luster) is a silvery-white or gray mineral with a bright metallic luster, soft, heavy, almost twice as heavy as sphalerite. The cleavage is clearly expressed, and when struck with a hammer, the mineral crumbles along the cleavage cracks into regular cubes.
Arsenopyrite(arsenic pyrite) is a silver-white mineral with a metallic luster, hard to brittle. When hit with a hammer it will smell like garlic.
Antimonite(antimony luster) usually forms columnar and needle-shaped crystals or radial, often tangled clusters in quartz. The cyst is lead-gray, metallic luster. Soft and fragile.
Limonite(brown iron ore) - yellow-brown and dark brown in color. It is represented by a loose ocher mass or a lumpy sinter variety, often forming cubes along the pyrite. The most widely distributed mineral. Almost all quartz veins that come to the surface are mottled in color due to limonite. Often the ocher mass fills voids in quartz formed in place of decomposed pyrite and chalcopyrite. Large masses of brown iron ore are observed at the outcrops of quartz veins rich in pyrite, chalcopyrite and other sulfides or on sulfide ore bodies.
Accumulations of brown iron ores on sulfide bodies are called iron hats And. They are of interest because they themselves may contain large quantities of gold.
Quartz is the main mineral with which gold is associated. Therefore, gold can most often be found in quartz veins.
Quartz can be very diverse in color: white, gray, milky white, smoky, yellowish, etc. It also varies in structure: fine-grained, coarse-grained, confluent, banded, concentrically layered (typical of chalcedony), sometimes with voids on the walls which can be observed crystals (druze) of transparent rock crystal. Visible gold can often be found in yellow-brown quartz with ocher inclusions.
Primary (ore) gold deposits are the primary sources of numerous gold-bearing placers. The composition of gold placers is determined by the composition of the primary deposits as a result of the destruction of which they were formed.
Often in gold placers there are found in the form of impurities latina, osmic iridium, tin stone - cassiterite, wolframite, titanium ore - ilmenite, diamond, rubin. These minerals also have a high specific gravity (except for the last two), and they resist abrasion and other types of destruction when carried in a stream of water.
Most of the gold placers belong to alluvial, i.e., river ones, formed by the transfer and deposition of fragmentary material by channel flows and confined to the valleys of small and medium-sized mountain rivers.
There are placers where the bedrock ore bodies were not eroded after destruction and remained in the form of crushed stone, sand and clay at the site of their formation. Such placers are called eluvial: They usually occur on the wide, flat watersheds of modern rivers.
Placers are also found on mountain slopes, where gold-containing destroyed rocks accumulated, sliding down the slope from the bedrock deposit located above. Such placers are called deluvial: in terms of their industrial importance, they are much inferior to alluvial and even eluvial ones. It should also be noted coastal-sea and lake placers, common on the coasts of seas and large lakes.
Other types of placers are known in nature, but they are of secondary importance.
Alluvial gold placers have the greatest value for industry. Depending on the conditions and location of placers, they are divided into channel, spit, valley, terrace and spoon.
Channel placers lie in the beds of modern rivers. These placers are characterized by a relatively small thickness of gravel-pebble sands and often a complete absence peat- deposits in which gold is almost never found.
Spit placers lie on spits, islands and shallows of modern large rivers. There is no peat on most spits. On spits, a significant proportion of gold is represented by very thin “floating” particles. A slight increase in gold is observed in the head part of the spit.
Valley placers are characterized by a greater thickness of sand and the presence of peat compared to channel placers. The total thickness is 5-10, and sometimes more, meters. Placers of this type occur in the floodplain and mostly on the first terrace of the river valley.
Terrace placers lie on longitudinal terrace-like ledges of bedrock that make up the slopes of river valleys. These placers are usually located above river level. At the same time, “high terraces are poorly preserved and are represented by narrow fragments on the slopes of valleys.
Spoon placers They lie in the valleys of ravines and small springs and rivers with intermittent water flow. Along with gravel and pebbles, the bedrock composition contains crushed stone and boulders. Many spoon placers start directly from bedrock deposits. Placers of this type are characterized high concentration metal, which must be kept in mind when searching.
The sizes of placers are different. The largest number of them (about 60%) are no more than 3 km long; placers 3-10 km long account for 20-30%, and over 10 km - no more than 10%. Thus, the bulk of placers are usually located within the development of primary gold deposits or close to them in ravines, valleys or on terraces.
The age of placers varies greatly - from ancient to modern. The most ancient placers, as a rule, are composed of strong, firmly cemented rocks; deposits of young placers, the age of which does not exceed 60-70 million years, are usually represented by loose rocks.
For placers of all ages, the maximum concentration of gold is observed in the lowest layers of clastic (sand-pebble, often with boulders) deposits that lie directly on bedrock. In practice, the surface of bedrock underlying placers is called raft, and the gold-bearing layer is sands. Above the sands there is a practically non-gold-bearing layer called “peat”
The highest concentration of gold is observed at the very border of the sands and the raft. Particularly favorable places for the accumulation of gold are the uneven surfaces of the raft; protrusions of bedrock, cracks, depressions - pockets, funnels, etc. Along with gold, its satellites and other heavy minerals, such as magnetite, ilmenite, etc. accumulate here.
