Upstream Gold Deposits

Remember that before any mineral can be carried or concentrated by a stream it needs to enter the stream somewhere upstream from where it is then concentrated and there has to be enough for it to concentrate. The area that the gold comes from is called the original source and these sources usually consist of veins, mineralised zones in bedrock, as well as permanent placers or preserved placers that were formed in the past.

The original source can be at a distance from one or both sides of the stream and it can also consist of an exposed vein in the bedrock of a stream. The original source is in many cases a deposit that has a little amount of gold that is not convenient to waste time on. There are many cases in which the source has less than one milligram of gold per ton in it. However, when a long period of time goes by, natural weathering breaks up the rock and releases the gold, which is then carried to the stream.

Even though there are different methods in which this can occur, the most known of and most important is runoff, which is the occurrence that occurs when the soil becomes permeated with more water than it is able to bear and it starts to move across the top or surface.

There is also another type of runoff that is called ground runoff and this has to do with the water that gets to the stream through leakage. This seepage or leakage carries almost no sediment to the stream even though it sometimes moves some material through solution.

Gold can withstand travelling across the earth however the resistance will be equivalent eventually when the runoff gets to the flood stage and starts to erode the top of the earth. The speed in which this occurs is defined by the amount of runoff and the inclination of the slopes that is around the stream.

Due to the fact that the slopes of runoff are normally much more abrupt than the inclination of the stream, gravity has a big role in the movement and transporting of the gold. The progression of placers in these types of movement is residual to alluvial to stream.

After gold gets going on its journey of transportation on the surface of the earth it will not stop unless something obstructs or blocks it. As opposed to the bed load of a stream, the soil close to the banks of a stream are normally very hard right under the surface and do reject settling by heavier materials. The material is kept close to the surface and becomes easily eroded during heavy runoff and travels along the surface as well. Sooner or later it gets to the stream at the point of entry.  

The place where the gold goes into a stream is normally not the type of place a prospector is interested in looking into in order to placer gold. Normally there is simply not enough amount of gold worth recovering in this area. Due to the fact that the entry is usually always because of flooding conditions, and because the speed of the stream is faster than the of the sheet wash or gulley that carries the gold, the gold is very quickly moved down the stream to the place it is deposited.

The velocity of the stream is what will determine how far it moves down the stream. In some cases it only moves a short distance while in other occasions it moves long distances if cases where the stream is moving quickly. One thing that is for sure is that after the gold has been deposited, it has a tendency of remaining where it was deposited. Usually it does not go further down the stream.