Eroding Streams

When a stream is eroding, the materials that are close to its activity are continuously being moved downwards. When this movement takes place, a continuous categorization is occurring, and this causes the heavier particles to become concentrated. Deposition than occurs in the stream when the speed of the stream has become reduced, whether that be to changes in the grade or the volume. When this takes place, the gold falls downwards along with other sediments. At times the placer gold can get trapped in irregularities in the bedrock, without a good amount of detrital material being trapped inside of it, however big placers are not formed by irregularities in the bedrock only. In cases where the bed of a stream is the genuine rock floor of the valley, it is real bedrock. However, when the gravels get covered with other material, such as volcanic material for example, the stream will flow on top of this “false” floor and it makes deposits on what we call false bedrock. Therefore an area can have a couple or more layers of gold bearing gravels. One simple way of studying areas to be able to see how a stream puts down these different layers is to study areas where road cuts show ancient stream deposits, as well as in canyons where one is able to see benches. Smoother and harder bedrock is not the best location for a good placer deposit to develop. The bedrock formations that are much decomposed, and that have crevices and cracks are perfect, and the ones of clayey or schistose nature and these are the best in their capability to trap gold.