Pocket and Bench Gold Placers
Pocket placers are usually re-reconcentrated material that can be found in a place that has most likely been overlooked for a number of years and these are the perfect types of places for amateur prospectors to go to. The bigger and more extensive placers were worked on many years ago and have now mostly disappeared. However, there are many areas that re-concentrate gold in these types of areas and the first re-reconcentration occurs in the form of a pocket deposit in a probable spot in the stream.
Bench placers are sometimes confused with gravel plain deposits due to the fact that they are left over concentrated material that was placed in a natural way when the stream was developing. Even though there are several different types, the best explanation is provided with the winding stream.
As a stream winds or meanders, changes its course, or produces oxbow lakes, it leaves a lot of the previous stream course with concentrated deposits at a distance from the new stream course. Later on the stream has a tendency of straightening out and in the course of a few thousand years, there might not be much evidence that the stream once meandered down the valley.
The first bed of the stream in its meandering turns into the soil on the bottom floor of the valley. In some cases the new stream cuts to a depth below the previous bed levels which will then be left up high and dry and these then turn into bench placers.
Another type of bench placer comes about when in its development the stream is a lot wider and places sand and gravel on both sides causing there to be a little bit of a levee. Sooner or later the levee becomes high enough to shoot the flood tide of the stream and as the stream becomes older, it wears the bed down deeper. Then again the material that had been previously deposited is left up high and dry and turns into a bench placer. Often times in the developing stage of the stream it formed one to two elevations of bench placers and one of them was usually much higher than the other one. These used to be called high and low benches by the early miners.
Geologically speaking a natural outcome made an area to allow a deposition to become permanent as the stream left the altitude. On the lower end, the situation was perfect for enduring retention of the deposit and this also turned into a placer deposit.
A great number of the placer deposits that were rich were found in the early history of western mining and were, because of the closeness of a stream and its continual supply of water, the first places underground mining occurred. Big and long flumes were built for water and the material was first sluiced.
After hydraulicking came to be, these very placers were the first to be mined by utilizing this method. Due to the fact that this kind of mining had all of the essentials for small time operations, a good number of the bench placers got worked on during the 1860’s to the 1870’s. These benches were then abandoned as they were worked out.
There were a great number of individuals who also worked on these placers during the Great Depression. The fact that this is the type of area that had a great amount of water in it, it was convenient for the amateur miners. Keep in mind that bench placers do not replenish themselves and were quite cleaned out during the Great Depression.