Older Gold Placers

Gold that can be found in older placers is usually finer than those that have their source close by and this is probably because of the alloy silver has been removed by the action of the water. When there is a good amount of gold in a placer deposit it is the result of very opportune circumstances. This occurs in places where there is an extensive amount of mineralization, quick rock decay, and properly developed stream patterns. When all these come together at the same time, large gold placers have the opportunity of being formed.

The process that occurs is simple; in places where the gold has been deposited, the power of the stream is strong enough to carry off the pieces of gold that had settled.

The richness of a deposit depends completely on the transporting power and if the bedrock is able to hold onto the gold that has deposited, and obviously how the gold sources does in the stream.

When a stream is wearing away at the materials, these materials are constantly being moved downstream. When this type of movement takes place, the water sorts it and this causes more of a concentration of the heavier elements.

Disposition then occurs in the stream when the speed goes down, which can occur due to changes in volume or grade. After this occurs, the gold rests with other sediments. In some cases the gold gets trapped inside the bedrock.

A bedrock is when the floor of a stream is actual rock. When the gravel gets covered with certain materials such as volcanic material, the stream will flow over this new floor or bed and makes deposits on what is known as false bedrock.

This is one of the reasons why there are certain areas that might have more than one layers of gravel with gold in it. One simple way of noticing how a stream lays down these various layers is to look at areas where road cuts have uncovered old stream deposits as well as in canyons where the benches can be noticed.

When there is hard and smooth bedrock it is not the best place for a placer deposit. The bedrocks that have the best formations are those that have cracks and crevices and those that are very decomposed, because these are the ones that are easily able to catch onto the gold.

The following are the different velocities in which a certain size of material can be carried down by a flowing stream. This was from a report that was done by the California Division of Mines and Geology:

• 3 in. per sec. = 0.170 mph will only start to work on fine clay.

• 6 in. per sec. = 0.340 mph will raise fine sand.

• 8 in per sec. = 0.4545 mph will lifts sand that is as course as linseed.

• 10 in per sec. = 0.5 mph will lift grave that has the size of a pea.

• 12 in per sec. = 0.6819 mph will carry along gravel the size of beans.

• 24. in per sec. = 1.3638 mph will roll along round pebbles that are 1 inch in diameter.

• 3 ft. per sec = 2.045 mph will sweep along slippery and pointed stones the size of hen eggs. 

When it comes to grade, a grade that ranges from thirty to around one hundred feet per mile will help the disposition of gold. Anywhere that the grade is higher than that, like in narrow canyons or mountain streams, it will not be an appropriate source of placer deposits.

After a streams goes out of a its mountain canyons and goes into a more level country or a stiller body of water, the material that was carried along by the stream is deposited or placed in the form of a fan. At the peak of this fan is where the fine gold will be deposited and it might never actually reach the bedrock. The action that happens in the rugged mountains during flooding season that allows the gold to reach the bedrock does not happen in the fan.

Just keep in mind that the gold is heavier then almost every other material in the stream bed and it will fall anywhere the flow or grade changes and will cause the stream to slow down or lose its power to carry it. This is the type of place you need to search out. Just remember that with every rainy season it will cause more gold to come down from the hillsides into the stream beds.

Something else you should be aware of is that in the past the early miners were working on deposits that had literally sat for thousands of years and had time to accumulate and develop. These days it is difficult to find that because there are practically no areas that have not been worked on. Your best option is to find the places that have not been worked on and try to get to the places that are difficult to get to, as they probably have not been worked on either.