Residual Gold Placers

Residual placers take place when the gold is free from its initial place and the material that covers it breaks down. This comes about when there is repeated surface weathering. Breakdown takes place when there are steady and strong geologic conditions that cause the mechanical break down of the rock and the chemical decay of the minerals. The top of the ore that bears gold is increased while the rock falls apart, due to the fact that some of the softer and more soluble parts of the rocks get taken and carried away as a result of wearing away. 

Subsequent to the gold becoming freed from the bedrock encasement and rock decay as a result of the weather, it begins to journey down the hillside and from time to time washed down to the rivulets and gullies and afterwards into the stream beds. Even as it is traveling down the gold every so often concentrates itself in an amount that merits mining. These types of deposits are what are known as elovial Deposits.

There are some prospectors that believe that the forming of some placer deposit is due to the action of glaciers and this is in reality not the case. Although it is true that glaciers rub off loose soil and debris, they do not have the ability sort it and ice is not efficient in the concentration of metals. The streams that come from ice that has melted might now and then be effective enough in sorting to cause deposit to be formed though.

Bajada is a word for slope in Spanish and it is used to categorize a confluent alluvial fan down the base of a mountain range. The quantity of gold that is formed from bajada placers is not much in comparison to other placer workings because of the lack of efficient dry washing methods utilized in the past.

The structure of a bajada placer is pretty much the same as a stream placer except that it is conditioned by the climate and topography of the dry region it occurs in. The amount of the gold that has been released from its environment as it works down from the lode outcrop to the bajada is then placed on the slope close to the mountain range. The gold falls down the line, which is the contact of the mid fill with the bedrock.

Although the greatest amount of concentration of gold will be on the bedrock, bulk concentration does not take place the way it does in a stream deposit. Because of the fact that some amount of the gold is still imbedded in its matrix, it is probable that a smaller amount of gold will get to the bedrock and more of it may be spread all the way through the deposit than in the case of the stream gravels.