Downstream Gravity

In addition to its high specific gravity, as well as the perfect conditions for settling contained in its environment, there is another feature that speeds up the process of the settling of the gold.

This is the typical action of the bed load, which is the accumulation of debris that is held in the area between bedrock and the bottom of the stream. The gold that had been deposited by the stream load throughout the reduction of speed of the after flood stage is now dispersed somewhat regularly at varying depths.  

The bed load is additionally being carried down the stream and this means that the part of the bed between the rock and the floor of the stream is also being moved down the stream. This could be called sand flow or flow of sand and occurs very slowly. This movement is partly because of gravity and in part because of the force and the weight of the water in the stream.

This movement does not only have to do with the gravel and sand but with the big rocks that are not attached firmly to the bedrock. While the bed moves down the stream a great amount of activity is taking place.

The movement downwards to the level of the sea presses the grains of gravel and sand against each other and allows them to release pressure that then helps to improve the process of the gold going towards the bedrock. The minerals that are heavier also have a tendency of traveling down the stream and the journey to bedrock takes a curved course. 

Sooner or later after a long time, the gold gets to the bedrock and here is no longer able to sink anymore and so it starts moving down stream along with the bedrock. If in these journeys the gold happens to come across a crevice, it will usually gravitate to the bottom of the crevice where only very, very strong flood stages can remove it in order to be transported more.

Another interesting consequence that occurs in settling is the building up of pay streaks. While it travels downwards the velocity of the settling is slower and sands that are slower get further compressed and the lubrication of the water is reduced. In other words when some pieces start to slow down, other flakes of gold catch up to them and when they join they settle together. If the journey is a long one, and there is a large amount of flakes that are going to settle, a good amount of gold flakes can combine and settle together.

This accumulation or accumulations were the pay streaks the operators of old bucket dredges used to recover often times when these machines were in operation. There are a number of ways these pay streaks can be accumulated in placers. These can be become accumulated in a little and concentrated area, they can also accumulate over a big area, and they can accumulate on top of the whole layer of the placer.