Placer Gold Deposit

There are a number of things that happens to conserve a placer deposit. Due to the fact that streams are always changing their positions, remains of their deposits are left secluded such as in the case of the terraces and beaches that are left at different periods when a stream is cutting into a channel that is deeper. The deposits that remain will sooner or later be worn away unless something is protecting them. One way that a placer is conserved is when it is buried. Most of the time this occurs when a stream has been covered by mud flows, lava, ash falls and so forth. Other ways this could occur are when:

• When there is a covering with gravel when the stream is obstructed.

• When there is a covering with lake deposits.

• When there is a covering with gravel.

• When there is a covering by the material of a landslide.

• When there is a covering with gravel when the course of the stream goes down under the normal base level of wearing down.

• When there is a covering of an older stream course with alluvial fan matter as conditions that favor the stream to exist do not succeed.

• When there is covering with glacial till.

• When there is a covering of beach placers with sediments from the sea as the coast is flooded and elevated.

The stony content of a placer might become firmly cemented when it is permeated with by mineral material like silica, lime and iron carbonate. This is more likely to occur as the placer gets older.

It is sometimes very difficult to break down these older cemented gravels and this is the reason why some of the tailings in the old mines are advantageous to work in. The gravels that are cemented were at times never broken down as they travel through the sluice boxes, and the gold was placed back into the existing stream bed.

The gold that can be seen in placers comes originally from veins and other mineralised areas in bedrock when the gold was set free from its rock by weathering and disintegration. Often times the source of gold in a placer was not in a deposit that could be mined successfully but the richer deposits normally occur when there is a second concentration from older gravel that bares gold. In most cases the original source of gold is not far from the place it was first stuck after having been carried by the water.

The minerals that are very heavy and resistant to chemical and mechanical destruction can be found with the gold in placer deposits. This is more commonly known as black sand. Black sand is on the most part magnetite, however some of the other minerals that can be found in sluice boxes are tungsten minerals, cinnabar, platinum, chromite, pyrite (you may have head of Fools Gold, well that’s pyrite), hemitite, zircon, and garnet.

There are additionally a number of other things that can be found such as amalgam, metallic copper, quicksilver, nails, and many other things. When the cross section of a river has gone through down faulting on the upstream side it creates a pocket that entraps gold, gravel, silt and sand as well as titanium minerals, and occasionally diamonds have been found.

Gold has a high gravity and is around six or seven times higher than quartz and increases up to nine times in the water and this is what causes the gold to work its way to the bedrock or travel until it becomes entrapped. Once it is caught in the bedrock it is difficult for the stream to lift it again. The specific gravity of gold is of nineteen and this means that it is nineteen times as much as an equal amount of water to its mass.