How to find out if there is gold in the river?

From the editors. Russia has a huge number of placer gold deposits. For many years, our country has been ranked 1st in the world in the production of placer gold (about 80 tons per year). At the same time, in the production of ore gold, Russia noticeably lags behind China and Australia, where there is practically no placer gold mining. In Soviet times, conferences were held on the topic of predicting the primary sources of alluvial gold, entire teams worked, and mathematical methods for predicting the primary sources were even developed. However, then the work stopped (together with the USSR), and now, unfortunately, the topic is practically not being developed. To revive the topic, the editors publish an abbreviated translation of an article from a popular foreign magazine. Author: Chris Ralph Source: https://www.icmj.com/ Gold has to come from somewhere, right? Sometimes its source can be traced, sometimes it cannot. Although the precious metal always comes from a primary deposit, it can enter a river or stream from the sands that lie in the area of an ancient river bed. In other words, there are a great many ways to distribute gold, how can an ordinary miner know them all? How to track the source of a precious metal, and is it worth the effort? The root sources of many large placers, which have been mined for more than a century, are still unknown. In this article I will try to highlight the issue of the origin of gold and the indicators that can lead a miner to its source. I would also like to talk about situations when it is not possible to find a source. So, let’s imagine that you or your friend found a beautiful nugget, or better yet, a patch of nuggets. When the first inspiration wears off, you may wonder where they came from, where is the source? I know gold miners who managed to find a source, and the gold found compensated for all the effort spent on the search. I also know counter examples. My experience in searching for gold sources is both positive and negative. There is one place where, using a metal detector and a dry enrichment device, I was able to extract several ounces of gold at once. Previously, of course, there was much more precious metal there. I only got crumbs. This area is located in the upper reaches of one small tributary, along almost the entire length of which small mines are scattered. The gold deposits there were pointed and angular in shape, indicating the proximity of the source. The site appears to be ideal for mining. I spent several days studying it and searching for the source – without success. I was very upset, because it would seem that finding it would not be so difficult and, given the amount of gold mined earlier, it would be very profitable. For now, let’s remember the traditional method of tracking and sourcing alluvial gold. Previously, it was believed that the more irregular the shape of the gold, the closer its source should be. They looked for it with the help of trays and ingenuity. In dry areas, this approach did not work as well due to the lack of sufficient water. Sometimes samples had to be carried to the nearest stream. Of course, it is easier to work if it is possible to wash the material right on the spot. The modern prospector can use a metal detector to speed up the prospecting process and eliminate the need for gold panning. Methods for tracking a source are based on the fact that near it, the precious metal spreads in a fan-shaped plume down the slope. By taking samples from different areas, it is possible to determine whether the prospector has wandered too far from the plume. In this way, you gradually move up within the boundaries of the plume, gradually approaching the source. Theoretically, with such a spread of gold from the source, a kind of isosceles triangle is formed, expanding down the slope, but in practice this is not always the case. The steeper the slope, the sharper the tip of this triangle, and the gold concentrates closer to the source. As it descends, the precious metal gradually disperses, with nuggets mainly concentrated along the center line. If the gold in the area is large enough, you can use a metal detector, otherwise you will not be able to do without a tray and water. The main principle of searching for a source of gold is sampling along the river flow to determine the boundaries of the gold-bearing area. After this, several samples are taken about three meters up the slope to determine which side of the drain the precious metal is spreading from. If this happens on both sides, it is necessary to determine which side has more gold. If the difference is not great, there are probably several small sources through which you can get to the main one without much difficulty. If there is an order of magnitude more gold on one side than on the other, testing is carried out to determine the boundaries of its distribution up the slope. Typically, samples are taken along a line parallel to the drain. When working, you should remember the distribution pattern (fan-shaped). If a sufficient amount of gold is detected in several consecutive samples, you are on the right track and are within the boundaries of the distribution of the precious metal. The next group of samples is taken a little further up the slope (if you do everything correctly, they should also contain gold). As you approach the source (the top of the triangle), the content of the valuable component in the samples should gradually increase. The methods used by miners have not changed for centuries. Unfortunately, the method discussed here can only trace certain types of gold sources. The system is more effective if there are a pair of nests large enough to fan out the precious metal being searched for. There may simply not be enough gold in small sources to form a distinct distribution zone. The gold plume is also poorly manifested when many small sources are present, and this situation is quite typical. In this case, trying to find a single source is like hearing the voice of one person in a room full of noisy people. Before you start looking for a source, it is important to consider what type it might be. Studying the geology of the site can help with this. In some areas, gold-bearing veins run along faults or contact lines between different rocks. In other words, the source is indigenous, and it is a good idea to study the characteristics of the material containing the precious metal. It is more common in some breeds, less common in others. Geological information will allow you to concentrate your efforts on the most likely gold locations. To succeed, it is worth studying old reports and becoming familiar with the geological characteristics of the region. In addition to the most likely types of host rocks, one can try to determine the possible number of bedrock sources. Is he alone, or could there be several? In some breeds, nests are more common – that’s what you need. However, there are also less rich types of deposits from which placer gold can originate. In addition, the size of the precious metal may depend on the size of the deposit. Sometimes, to get to the source, you just need to walk along the quartz outcrops (unless, of course, there were very many people living on the site). In arid areas with little vegetation covering the surface, quartz also helps in the search. However, most often there are many quartz veins, and their excess only complicates the work. The source of the precious metal can be paleoplacers destroyed over time. They can be rich enough that you can trace the source, although it is more likely that you will encounter many small areas that will further confuse the search. So what is the best indicator to help you track the source of your gold? Nobody wants to waste time and energy. It is best to look for it on small tributaries, where the likelihood of the presence of an excessively large number of sources is lower. Another important indicator is when gold in a river suddenly cuts out and is no longer found after a certain boundary. This is a reliable indication that you should turn and focus your search up the slope. The gold itself partly speaks for itself. If it is rounded and smooth, then its source is most likely a paleoplacer. If the source is still indigenous, then the distance to it can be estimated based on the state of the gold particles. If the precious metal is uneven, angular, then its source must be somewhere nearby. However, it should be remembered that rounded gold can also come from a native source (the surface texture of naturally occurring rounded gold is different from water-rounded gold). A good indication of the presence of a nearby source is quartz. -7 + 13 Placer gold (placers) is found in sediments in the beds of ancient rivers and in the deposits of modern streams. Placers can be alluvial, terrace, or channel (bottom, spit). Terrace sediments are found on river banks, and bottom sediments are found under river water. Bedrock deposits are gold-filled cracks or crevices in bedrock or ore. Eluvial gold placers are formed on slopes in the remains of ore, which, under the influence of natural forces, have become detached from the ore deposit. They are usually located directly below the ore deposit from which they came off. Alluvial placers are deposits of part of the gold ore that have become detached from the ore deposit and have fallen into the action of water flow. The hill from which they were washed may no longer exist or even change its location.
During the Tertiary period, about 2 million years ago, the mountain ranges underwent major changes. Many water streams were formed, the channels of which do not exist today. Terraces of these streams located far from existing rivers are known as places containing rich placers. Often these deposits are dark blue in color. When exposed to light, the color of the deposits changes to dirty red. At the very bottom of the sediments of ancient streams, gold can be found, formed as a result of very strong rivers capable of creating deposits of high concentration. Look for layers that are painted in different colors, have different hardness and density. Some of these sediments, being quite hard, can resemble bedrock.
The principle of the “shortest path” also applies in this case with terraces. It is also necessary to check what is behind all the ledges in the sides of the valley, located far enough from the existing water level in the river. Where to dredge gold (part 1) The movement of gold, which is 19 times heavier than water, is quite predictable. In order to move gold from its place, a strong water pressure is needed, therefore, when it weakens for one reason or another, the gold settles in the place where the water pressure has dropped. Gold, especially its grains and nuggets, does not float but “crawls” along the bottom of the river, gravitational forces press them to the bottom. The bottom may be bedrock or layers of clay that are not washed away by the flow of water. As a rule, gold moves along the shortest path, tending to a straight line. Of course, when a river makes a bend and changes direction, the flow of water changes the position of the gold, but the gold is not carried by the water as easily as ordinary stones. Gold and sediment begin to move only when the water pressure is strong enough. So, when trying to determine where gold is concentrated in a river, you first need to know what the river looks like during a flood. This does not mean floods caused by heavy rainfall, but those that occur once a year with spring waters. If possible, thoroughly examine the river bed to see what the river bed might have looked like during one or the worst spring floods. Note the tops of the bends and the width of the channel during such a flood. After this, connect the midpoints of the floodplain with an imaginary line, taking into account the bends of the riverbed. It is most likely to find gold-bearing deposits along it. It is sometimes called the “gut of the river.” Gold always moves along this shortest path along the river bed. Figure 1
1 – border of the river bed; 2 – border of the river bed during flood; 3 – river core. The channel placer of gold, as a rule, begins at the end of the internal bend of the river bed and gradually narrows further along the “gut” of the stream. The closer you are to the turn of the modern river bed, the narrower and more powerful the placer stream will be; accordingly, the further you are from this turn, the wider and less powerful it will be. Figure 2
Placer jet shape. Another good indication of where a placer stream may be located are riffles containing large boulders along a line from one end of the inner bend of the river to the beginning of the other. Take a comfortable position at the end of a bend in the river, from which you can clearly see the beginning of the next bend down the river. Note the chain of boulders with riffles starting approximately where you are standing, and which extends in an almost straight line to the next bend. Typically, gold-bearing sands follow these boulders. In this case, a placer with gold may not be as wide as a riffle with a chain of boulders.
When dredging riverbed placers of gold, you must always clearly monitor whether you are moving to the right or left of its stream. Channel placer is only part of the alluvial sand deposits located in the modern river bed. Where to dredge gold (part 2) Taking into account the hydrology of each river bend, water flow moves faster along the outer bend of the river channel than along the inner bend of the river channel. Thus, the water pressure on the inner bend weakens, and on the outer bend it increases. Since gold moves downstream, the part of it that ends up at the outer bend is carried around the bend in the river. That part of the gold that is closer to the inner bend settles where the water moves more slowly at the beginning of the bend. This is also a good place to look for gold. Figure 3
1 – fast flow zone; 2 – slow flow zone;
3 – gold deposition line; 4 – place of gold deposition Under the influence of gravitational forces and other influences during a flood, gold is pressed to the bottom. The river bottom is bedrock. The bedrock may be shallow, with little sediment on top (or even completely clear), or it may be quite deep (9-12 meters below the sediment). Since the gold rests on bedrock, you need to reach it by dredging. Taking into account all of the above, you should look for a channel where the bedrock is shallow. This can be determined by examining the banks of the river above the water. The exposed rock on the banks indicates that it is shallow underwater. How shallow can only be determined by dredging. Sheer drops of bedrock on the banks may indicate a continuation of the steep slope further into the channel, meaning that the bottom may be quite deep. The gradual descent of bedrock on the banks means that the bedrock in the channel is shallow. Figure 4
1 – descent in bedrock; 2 – river bottom; 3 – sediments;
4 – placer gold; 5 – bottom of bedrock (raft) Keep in mind that the above rules do not work in all cases. If bedrock does not come to the surface on the banks themselves, examine the sides of the river valley. Note the ledges on both sides of the river valley close to each other, and then draw an imaginary line from the downstream ledge to the upstream ledge. In the place where the imaginary line crosses the river, the depth of the underlying rock is shallowest. Where to dredge gold (part 3) The bedrock at the bottom of a river is not the only place where gold can be found. If there are several layers of clay between the river bottom and the lower bedrock, and these layers of clay are dense, they can act as “false bedrock.” Thus, unless a flood is strong enough to erode and transport all the layers on the underlying bedrock, then it will only remove the material from the upper layers. Gold is heavier than the materials of the clay layers, but if they are motionless and not washed, then gold cannot penetrate through them. Therefore, gold can lie on a layer of clay and only slightly penetrate deep into the loose bottom sediments. Figure 5
1 – layers of clay; 2 – placer gold As a rule, gold occurs in the first, upper 15 cm of the clay layer. Clay layers differ from each other in terms of their thickness (thickness) from a few cm to meters. Therefore, it may take a long time to reach the next layer. When working in areas that have multiple layers of clay, you should work with each layer as if it were bedrock. Once you have reached the current layer, start moving left and right across the surface until you reach the edge of the clay layer. After finding the edges, you must decide whether to continue mining at that level or move deeper. However, remember that the presence of gold-bearing sands on a given layer of clay does not mean that another layer of sands will be strictly below it at the next level. It is possible that below, under this layer of clay, there is another one, but it may be located to the right or to the left, or may be completely absent. If you have already gone deeper, then it makes more sense for you to move on to the next layer or to the bedrock, whichever comes first. When mining sands on clay layers, gold of a fairly high size can be obtained, but the largest gold is mined from the underlying bedrock. Therefore, try to carry out work in places where you can quickly reach the underlying bedrock, or where there is no more than one or two layers of clay to it. Where to dredge gold (part 4) Gold moves only in those parts of the river where the water pressure is strong enough and makes it possible to wash away sediments heavier than water. Therefore, when the water pressure drops, gold sinks to the bottom and accumulates. Let’s look at some conditions that reduce the water pressure in a river during a flood – this will give us a rough list of places where gold can accumulate.
The inner bend of the river is a promising place for searching for gold. At the beginning of the internal turn of the river and at the location of the spit and rifts, there is a good concentration of gold. This is because the speed of the current at the inner bend of the river is less than the average speed of the current. We also know that the flow speed at the outer bend of the river is higher than the average flow speed. Therefore, as a rule, gold is never found at the outer turns of the riverbed, since the pressure of the water carries it away from there.
Consider the situation with a large boulder in the water. Water washes the boulder from all sides. If you take a closer look at how the water flows around the boulder, you will see that there are two places where the flow practically stops. This is the central part in the center in front of the boulder and just directly behind the boulder. There may be gold traps here, and it tends to be purer in the back pocket than in the top pocket. Boulders in the riverbed trap gold; if they are located on the “shortest path”, then the likelihood of finding gold behind them increases significantly. Figure 6
1 – boulders; 2 – gold
Likewise, any object at the bottom of a river that is washed by water will trap gold. For example, logs or pebble islands. Where to dredge gold – part 5 As long as the flow of water is strong enough to move the gold, it will continue to move. We have already talked to you about the turns of the riverbed and how they affect the water pressure. We have also already covered the situation with objects washed on all sides by water, such as boulders. We also mentioned that gold “crawls” along the bottom of the bedrock of the river (raft). The gold continues to move in this way as long as the water pressure is high enough. The following 2 circumstances can stop it:
– The raft at the bottom of the river can be quite uneven with ledges and obstacles behind which gold will accumulate.
– A river raft may have cracks and caverns where gold will fall.
The search must begin by studying the river bottom. Obstacles in the bedrock trap gold in different ways. If the top of the obstacle is inclined downstream, then gold is deposited behind the obstacle. In the case of an upstream slope, gold collects in front of the obstacle. The configuration of rock ledges located on the sides of the stream act in a similar way. Figure 7 Focus on cracks and caverns in the rock at the bottom of the stream. Once gold is found in one of these places, it will remain there until the underlying bedrock is altered by water pressure, an earthquake, or the movement of large boulders along the bottom. The smooth underlying rock at the bottom does not give the gold the opportunity to hide from the forces of water pressure, so it continues its movement down the river until it finds a secluded place. Figure 8
1 – cracks; 2 – protrusions; 3 – places of gold concentration; 4 – flat surface of the raft If you are dredging in a place and you reach the bedrock and it turns out to be level, then move to another place. It is possible that you will find a random nugget here too, but most likely you are wasting your time. Gold does not linger on smooth surfaces.
However, if there are cracks or cavities in the bedrock, be sure to have them checked. Gold usually settles in them. Any irregularities or protrusions on the surface of the underlying bedrock can act as a trap for gold. Gold is trapped in potholes in the bedrock, so search until you hit the edges of the potholes. The cracks in the rock may not be large. The smallest particles of gold will find their way into even the smallest cracks. Undoubtedly, it is worth familiarizing yourself with the contents of these cracks. It is better to clean them two or three times. To do this, use a powerful pump and crack cleaning tools. Very thin cracks must also be opened, as very large pockets of gold can accumulate in them. Sometimes a large amount of gold can be obtained from a trap that, at first glance, contains nothing. Therefore, do not pass by any cracks or caverns in the bedrock. Where to dredge gold part 6. Gold moves when the water pressure is strong enough to overcome the weight of the gold. The fourth case is where gold can concentrate, this is a place where the river widens or deepens and the flow of water slows down its speed.
Let’s consider the case of a certain volume of water flowing out. When water moves along a 7,62 m wide channel at a speed necessary for river sediments with gold to be dragged along the narrow river bed. If the same amount of water moves along a channel 30,48 m wide, then the flow speed slows down several times and the gold sinks to the bottom. This occurs when a river flows into a lake or another river. When it flows into standing water, the water pressure drops. Therefore, the area of the river bottom, at the beginning of the drop in water speed, will be the place where gold is deposited. It is possible that the gold will be spread in a thin layer over this entire area, so look for places where gold may be concentrated – overhangs, boulders, cracks, etc. Figure 9
1 – the channel widens and the flow slows down;
2 – fast current; 3 – gold precipitation. In a place where the bottom level changes sharply towards increasing depths, the water pressure drops and the flow speed slows down and the gold sinks to the bottom. In places where the channel changes from sloping to flat – the river flows out onto a plain with a lesser slope – a significant placer may be found. Waterfalls act in a similar way. Boulders at the base of the waterfall trap the gold, preventing the rushing water from washing it away. Sometimes gold is deposited right under the place where the water is bubbling. Figure 10
Using a topographic map, identify the locations of waterfalls, depressions and sudden changes in the landscape, check them. With the help of this article, a novice gold miner will be able to understand how to look for gold on the river and where to pan for gold. This article will teach you what to look for during the dredging process to achieve the best gold mining results.
Of course, despite strict adherence to all the rules listed below, you may not find anything. The first thing to do is make sure that you are looking for gold in a river that is known for its gold-bearing properties. Of course, your predecessors did not find all the gold, but if there was something in the river, then information about it should remain. Therefore, do not waste time on a river about which there is no such information. The search must begin by studying the river bottom. If nothing indicates the presence of gold, then most likely there is none in it.
Practice scouting river valleys to see where you would start dredging, even if you don’t intend to do so now. Like any skill, finding a place to dredge on a river comes with experience. Also consult with hydrologists, specialists who know the rivers well. You can buy a metal detector. This can save you a lot of time.
But if you don’t know anyone willing to share their secrets, then act according to the materials in this article.